JP6223670B2 - Aluminum alloy sheet for automobile parts - Google Patents
Aluminum alloy sheet for automobile parts Download PDFInfo
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本発明は高強度な自動車部材用アルミニウム合金板に関するものである。 The present invention relates to a high-strength aluminum alloy plate for automobile members.
近年、地球環境などへの配慮から、自動車車体の軽量化の社会的要求はますます高まってきている。かかる要求に答えるべく、自動車車体のうち、パネル(フード、ドア、ルーフなどのアウタパネル、インナパネル)や、バンパリーンフォース(バンパーR/F)やドアビームなどの補強材などを、部分的に鋼板等の鉄鋼材料に代えて、アルミニウム合金材料を適用することが行われている。 In recent years, due to consideration for the global environment, social demands for reducing the weight of automobile bodies are increasing. In order to meet such demands, panels (outer panels such as hoods, doors, and roofs, inner panels), bumper force (bumper R / F), and reinforcing materials such as door beams, etc., are partly made of steel, etc. Instead of the steel material, an aluminum alloy material is applied.
ただ、自動車車体のより軽量化のためには、自動車部材のうちでも特に軽量化に寄与する、フレーム、ピラーなどの自動車構造部材にも、アルミニウム合金材料の適用を拡大することが必要となる。ただ、これら自動車構造部材は、要求される0.2%耐力が350MPa以上であるなど、前記自動車パネルに比べて高強度化が必要である。この点で、前記自動車パネルに使用されている、成形性や強度、耐食性、そして低合金組成でリサイクル性に優れた、JIS乃至AA6000系アルミニウム合金板では、組成や調質(溶体化処理および焼入れ処理、更には人工時効硬化処理)を制御しても、前記高強度化を達成するにはほど遠い。 However, in order to reduce the weight of the automobile body, it is necessary to expand the application of the aluminum alloy material to automobile structural members such as frames and pillars that contribute particularly to weight reduction among the automobile members. However, these automobile structural members need to have higher strength than the automobile panel, for example, the required 0.2% proof stress is 350 MPa or more. In this respect, the composition and tempering (solution treatment and quenching) of the JIS to AA6000 series aluminum alloy plates, which are used in the above-mentioned automobile panels, are excellent in formability, strength, corrosion resistance, low alloy composition and recyclability. Control of the treatment, and further, the artificial age hardening treatment, is far from achieving the high strength.
したがって、このような高強度な自動車構造部材には、同じような高強度が要求される前記補強材として使用されているJIS乃至AA 7000系アルミニウム合金板を用いる必要がある。しかし、Al−Zn−Mg系アルミニウム合金である、7000系アルミニウム合金は、Zn及びMgからなる析出物MgZn2を高密度に分布させることで高強度を達成する合金である。それゆえ、応力腐食割れ(以下、SCC)を起こす危険性があり、これを防止するため、やむを得ず過時効処理を行って、耐力300MPa程度で使用されているのが実情であり、高強度合金としての特徴が薄れている。 Therefore, it is necessary to use a JIS or AA 7000 series aluminum alloy plate used as the reinforcing material requiring the same high strength for such a high-strength automobile structural member. However, a 7000 series aluminum alloy, which is an Al—Zn—Mg series aluminum alloy, is an alloy that achieves high strength by distributing precipitates MgZn 2 composed of Zn and Mg at a high density. Therefore, there is a risk of causing stress corrosion cracking (hereinafter referred to as SCC), and in order to prevent this, it is unavoidable that it is over-aged and used at a proof stress of about 300 MPa. The characteristics of are fading.
このため、強度と耐SCC性の両方に優れた7000系アルミニウム合金の組成制御や、析出物などの組織制御が、従来から種々提案されている。 For this reason, various composition control of the 7000 series aluminum alloy excellent in both strength and SCC resistance and structure control of precipitates have been conventionally proposed.
組成制御の代表例として、例えば、特許文献1では、7000系アルミニウム合金押出材の、MgZn2を過不足なく形成するZn及びMg量(MgZn2の化学量論比)より過剰に添加されたMgが、高強度化に寄与することを利用し、MgをMgZn2の化学量論比より過剰に添加することにより、MgZn2量を抑えて、耐SCC性を低下させることなく、高強度化している。 As a typical example of composition control, for example, in Patent Document 1, Mg added in excess of Zn and Mg content (stoichiometry ratio of MgZn 2 ) of a 7000 series aluminum alloy extruded material that forms MgZn 2 without excess or deficiency. but by utilizing the fact that contributes to high strength by adding Mg to excess over stoichiometric ratio of MgZn 2, to suppress the MgZn 2 amount, without reducing the SCC resistance, and high strength Yes.
析出物などの組織制御の代表例として、例えば、特許文献2では、人工時効硬化処理後の7000系アルミニウム合金押出材の、結晶粒内における粒子径が1〜15nmの析出物を透過型電子顕微鏡(TEM)による観察結果で1000〜10000個/μm2の密度で存在させて、粒内と粒界との電位差を小さくして、耐SCC性を向上させている。 As a representative example of the structure control of precipitates and the like, for example, in Patent Document 2, a 7000-series aluminum alloy extruded material after artificial age hardening treatment is used for a precipitate having a particle diameter of 1 to 15 nm in crystal grains. As a result of observation by (TEM), it is made to exist at a density of 1000 to 10000 / μm 2 to reduce the potential difference between the inside of the grain and the grain boundary, thereby improving the SCC resistance.
この他にも、全ては例示できないが、7000系アルミニウム合金押出材の強度と耐SCC性の両方に優れさせる組成制御例や析出物などの組織制御例は、押出材での実用化の多さに比例して多数存在する。これに対して、7000系アルミニウム合金板における、従来の組成制御や析出物などの組織制御例は、板での実用化の少なさに応じて、きわめて少ない。 In addition to this, although not all can be exemplified, examples of composition control to improve both the strength and SCC resistance of 7000 series aluminum alloy extruded materials and examples of structure control such as precipitates are many practical applications in extruded materials. There are many in proportion to On the other hand, there are very few examples of conventional structure control such as composition control and precipitates in a 7000 series aluminum alloy plate according to the small practical use of the plate.
例えば、特許文献3には、7000系アルミニウム合金板同士が溶接接合されたクラッド板からなる構造材において、強度向上のために、人工時効硬化処理後の時効析出物の直径を50Å(オングストローム)以下の球状として一定量存在させることが提案されている。しかし、耐SCC性の性能については全く開示が無く、実施例に耐食性のデータも無い。
また、特許文献4には、人工時効硬化処理後の7000系アルミニウム合金板の結晶粒内における晶析出物について、400倍の光学顕微鏡での測定によって、大きさ(面積が等価な円相当径に換算)を3.0μm以下とし、平均面積分率を4.5%以下として、強度や伸びを向上させている。
For example, in Patent Document 3, in a structural material made of a clad plate in which 7000 series aluminum alloy plates are welded together, the diameter of an aging precipitate after artificial age hardening treatment is 50 mm (angstrom) or less in order to improve strength. It has been proposed that a certain amount exists as a spherical shape. However, there is no disclosure about the SCC resistance performance, and there is no corrosion resistance data in the examples.
Further, Patent Document 4 discloses that the crystal precipitates in the crystal grains of the 7000 series aluminum alloy plate after the artificial age hardening treatment are measured with a 400 times optical microscope to obtain a size (equivalent to an equivalent circle diameter in area). Conversion) is 3.0 μm or less, and the average area fraction is 4.5% or less to improve strength and elongation.
板の組織の制御に関しても若干ではあるが提案されている。例えば、特許文献5、6では、構造材用の7000系板の高強度化、高耐SCC性化を図るために、鋳塊を鍛造後に、温間加工域にて繰り返して圧延して、組織を細かくしている。これは、組織を細かくすることによって、耐SCC性低下の原因となる粒界と粒内との電位差の要因となる、方位差が20°以上の大傾角粒界を抑制して、3〜10°の小傾角粒界が25%以上である組織を得るためである。ただ、このような温間圧延の繰り返しは、常法の熱間圧延、冷間圧延の方式では、このような小傾角粒界が25%以上である組織を得ることができないために行われている。したがって、常法とは大きく工程が異なるために、板をつくるために実用的な方法とは言い難い。 There have been some proposals regarding the control of the plate structure. For example, in Patent Documents 5 and 6, in order to increase the strength and SCC resistance of a 7000 series plate for a structural material, the ingot is forged and rolled repeatedly in a warm working region after being forged. Is fine. This is because, by making the structure fine, a large tilt grain boundary having an orientation difference of 20 ° or more, which causes a potential difference between the grain boundary and the grain boundary, which causes a decrease in SCC resistance, is suppressed. This is to obtain a structure having a low-angle grain boundary of 25 ° or more. However, such warm rolling is repeated because the conventional hot rolling and cold rolling methods cannot obtain a structure in which such a low-angle grain boundary is 25% or more. Yes. Therefore, since the process is greatly different from the conventional method, it is difficult to say that it is a practical method for producing a plate.
この組織の制御に関して、7000系アルミニウム合金の板ではなく押出材ではあるが、特許文献7では、温間加工性に優れさせるために、亜結晶粒からなる繊維状組織で構成し、主方位がBrass方位であり、ODF(結晶方位分布関数)で表現されるBrass方位への集積度がランダム方位の10倍以上とした集合組織の提案もある。 Regarding the control of this structure, although it is an extruded material instead of a 7000 series aluminum alloy plate, in Patent Document 7, in order to improve the warm workability, it is composed of a fibrous structure composed of sub-crystal grains, and the main orientation is There is also a proposal of a texture in which the degree of integration in the Brass orientation, which is the Brass orientation and expressed by ODF (crystal orientation distribution function), is 10 times or more of the random orientation.
このように、強度と耐SCC性の両方に優れた7000系アルミニウム合金の組成制御や析出物、あるいは集合組織などの組織制御などの提案は、従来から押出材や前記温間圧延などの特殊な圧延分野については種々なされている。しかし、鋳塊を均熱処理後に熱間圧延および冷間圧延するような、常法によって製造される圧延板については、前記温間圧延を繰り返すような特殊な圧延以外には、あまり提案がないのが実状である。 As described above, proposals such as composition control of 7000 series aluminum alloy excellent in both strength and SCC resistance and structure control such as precipitates or textures have conventionally been made with special materials such as extruded materials and warm rolling. There are a variety of rolling fields. However, there are few proposals for rolled plates produced by conventional methods, such as hot rolling and cold rolling of the ingot after soaking, except for special rolling that repeats the warm rolling. Is real.
そして、押出材は、前記圧延板とは、その熱間加工工程などの製造過程が全く異なり、出来上がる結晶粒や析出物などの組織も、例えば結晶粒が押出方向に伸長した繊維状であるなど、結晶粒が基本的に等軸粒の圧延板とは大きく異なる。このため、前記押出材での組成制御や析出物などの組織制御などの提案が、7000系アルミニウム合金板にも、そして、この7000系アルミニウム合金板からなる自動車構造部材にも、そのまま適用でき、強度と耐SCC性の両方の向上に果たして有効であるかどうかは不明である。すなわち、実際に確認しない限りは、あくまで予想の域を出ない。 And, the extruded material is completely different from the rolled plate in its manufacturing process such as a hot working process, and the resulting structure of crystal grains and precipitates is, for example, a fibrous form in which the crystal grains are elongated in the extrusion direction. , The crystal grains are basically different from a rolled plate having equiaxed grains. For this reason, proposals such as composition control in the extruded material and structure control of precipitates can be applied to 7000 series aluminum alloy plates and also to automobile structural members made of this 7000 series aluminum alloy plates. It is unclear whether it is effective in improving both strength and SCC resistance. In other words, unless it is actually confirmed, it does not leave the expected range.
したがって、前記常法によって製造される7000系アルミニウム合金板の、強度と耐SCC性の両方に優れた組織制御技術については、未だ有効な手段がなく、不明な点が多く解明の余地があるというのが現状である。 Therefore, there is still no effective means for the structure control technology excellent in both strength and SCC resistance of the 7000 series aluminum alloy plate produced by the above-mentioned conventional method, and there are many unclear points and room for clarification. is the current situation.
以上述べた課題に鑑み、本発明の目的は、前記常法によって製造される、強度と耐SCC性の両方に優れた、自動車部材用の7000系アルミニウム合金板を提供することである。 In view of the above-described problems, an object of the present invention is to provide a 7000 series aluminum alloy plate for automobile members, which is manufactured by the conventional method and is excellent in both strength and SCC resistance.
この目的を達成するために、本発明自動車部材用アルミニウム合金板の要旨は、質量%で、Zn:3.8〜7.5%、Mg:0.7〜3.5%を含み、残部がAlおよび不可避的不純物からなる組成で、板厚が1〜3mmであるAl−Zn−Mg系アルミニウム合金板であって、平均結晶粒径が6.0〜14.5μmであるとともに、傾角5〜15°の小傾角粒界の〔(5−15°の結晶粒界の全長)/(2−180°の結晶粒界の全長)〕×100として計算した際の平均割合が16〜36%で、かつ傾角15°を超える大傾角粒界の〔(15°を超え180°以下の結晶粒界の全長)/(2−180°の結晶粒界の全長)〕×100として計算した際の平均割合が18〜37%である組織を有することである。 In order to achieve this object, the gist of the aluminum alloy sheet for automobile members of the present invention is, by mass, Zn: 3.8 to 7.5%, Mg: 0.7 to 3.5%, and the balance being An Al—Zn—Mg-based aluminum alloy plate having a composition of Al and inevitable impurities and having a plate thickness of 1 to 3 mm, an average crystal grain size of 6.0 to 14.5 μm, and an inclination of 5 to 5 mm. The average ratio when calculated as [(total length of 5-15 ° grain boundary) / (full length of 2-180 ° grain boundary)] × 100 of the low-angle grain boundary of 15 ° is 16 to 36%. , And an average when calculated as [(total length of crystal grain boundary of more than 15 ° and 180 ° or less) / (full length of crystal grain boundary of 2-180 °)] × 100 of the large tilt grain boundary exceeding the tilt angle of 15 °. The ratio is 18 to 37%.
本発明で言うアルミニウム合金板とは、鋳塊を均熱処理後に熱間圧延され、更に冷間圧延された冷延板であって、更に溶体化処理などの調質が施される、常法によって製造された7000系アルミニウム合金板のことを言う。言い換えると、前記特許文献5、6のような、鋳塊を鍛造した上で温間圧延を何回も繰り返すような特殊な圧延方法により製造される板を含まない。そして、このような素材アルミニウム合金板が自動車部材に加工される。 The aluminum alloy sheet referred to in the present invention is a cold-rolled sheet that is hot-rolled and then cold-rolled after soaking the ingot, and is further subjected to tempering such as solution treatment. This refers to the manufactured 7000 series aluminum alloy plate. In other words, it does not include a plate manufactured by a special rolling method such as Patent Documents 5 and 6 in which an ingot is forged and then warm rolling is repeated many times. And such a raw material aluminum alloy plate is processed into a motor vehicle member.
本発明では、このような常法によって製造された7000系アルミニウム合金板の組織を、通常の等軸な再結晶組織ではなく、前記押出材に類似した加工組織として、繊維状組織で構成する。そして、これを、平均結晶粒径が15μm以下であるとともに、傾角5〜15°の小傾角粒界の平均割合が15%以上で、かつ傾角15°を超える大傾角粒界の平均割合が15〜50%である組織と規定する。このような組織とすることによって、板に歪が入った場合に、局所的に集中せずに、均一に転位する組織とできる。これによって、常法によって製造された7000系アルミニウム合金板であっても0.2%耐力が350MPa以上であるような高強度とし、また、伸びも大きくして成形性を確保できる。また、このような高強度であるにも関わらず、耐SCC性の低下を抑制したものとすることができる。 In the present invention, the structure of the 7000 series aluminum alloy plate manufactured by such a conventional method is not a normal equiaxed recrystallized structure, but a fibrous structure as a processed structure similar to the extruded material. Then, the average grain size is 15 μm or less, the average ratio of small-angle grain boundaries with an inclination angle of 5 to 15 ° is 15% or more, and the average ratio of large-angle grain boundaries with an inclination angle of 15 ° or more is 15 It is defined as an organization that is ~ 50%. By setting it as such a structure | tissue, when distortion | strain enters into a board, it can be set as the structure | tissue which dislocation | distributes uniformly, without concentrating locally. As a result, even a 7000 series aluminum alloy plate manufactured by a conventional method has a high strength such that the 0.2% proof stress is 350 MPa or more, and the elongation is increased to ensure the formability. Moreover, although it is such high intensity | strength, it can be set as what suppressed the fall of SCC resistance.
以下に、本発明の実施の形態につき、要件ごとに具体的に説明する。 Hereinafter, embodiments of the present invention will be specifically described for each requirement.
アルミニウム合金組成:
先ず、本発明アルミニウム合金板の化学成分組成について、各元素の限定理由を含めて、以下に説明する。なお、各元素の含有量の%表示は全て質量%の意味である。
Aluminum alloy composition:
First, the chemical component composition of the aluminum alloy sheet of the present invention will be described below, including reasons for limiting each element. In addition,% display of content of each element means the mass% altogether.
本発明アルミニウム合金板の化学成分組成は、Al−Zn−Mg−Cu系の7000系アルミニウム合金として、本発明で意図する自動車部材の強度や耐SCC性などの特性を保証するために決定される。この観点から、本発明アルミニウム合金板の化学成分組成は、質量%で、Zn:4.0〜8.0%、Mg:0.5〜2.0%を含み、残部がAlおよび不可避的不純物からなるものとする。この組成に、更に、Cu:0.05〜0.6%、Ag:0.01〜0.15%の1種又は2種を選択的に含んでもよく、これに加えて、あるいはこれとは別に、Mn:0.05〜0.3%、Cr:0.03〜0.2%、Zr:0.03〜0.3%の1種又は2種以上を選択的に含んでも良い。 The chemical component composition of the aluminum alloy plate of the present invention is determined as an Al—Zn—Mg—Cu based 7000 series aluminum alloy in order to guarantee the characteristics of the automotive member intended for the present invention such as strength and SCC resistance. . From this viewpoint, the chemical composition of the aluminum alloy sheet of the present invention is, by mass%, Zn: 4.0-8.0%, Mg: 0.5-2.0%, with the balance being Al and inevitable impurities. It shall consist of This composition may further optionally include one or two of Cu: 0.05 to 0.6% and Ag: 0.01 to 0.15%, in addition to or in addition to this. Separately, one or more of Mn: 0.05 to 0.3%, Cr: 0.03 to 0.2%, and Zr: 0.03 to 0.3% may be selectively included.
Zn:3.0〜8.0%:
必須の合金元素であるZnは、Mgとともに、微細析出物を形成して強度を向上させる。Zn含有量が3.0質量%未満では強度が不足し、8.0質量%を超えると粒界析出物MgZn2が増えてSCC感受性が鋭くなる。従って、Zn含有量は3.0〜8.0%の範囲、好ましくは5.0〜7.0%の範囲とする。Zn含有量が高くなり、SCC感受性が鋭くなるのを抑えるために、後述するCuあるいはAgを添加することが望ましい。
Zn: 3.0-8.0%:
Zn, which is an essential alloying element, forms fine precipitates together with Mg to improve the strength. If the Zn content is less than 3.0% by mass, the strength is insufficient, and if it exceeds 8.0% by mass, the grain boundary precipitate MgZn 2 increases and the SCC sensitivity becomes sharp. Therefore, the Zn content is in the range of 3.0 to 8.0%, preferably in the range of 5.0 to 7.0%. In order to prevent the Zn content from increasing and the SCC sensitivity from becoming sharp, it is desirable to add Cu or Ag described later.
Mg:0.5〜4.0%
必須の合金元素であるMgは、Znとともに、微細析出物を形成して強度と伸びを向上させる。Mg含有量が0.5%未満では強度が不足し、4.0質量%を超えると、板の圧延性が低下し、SCC感受性も鋭くなる。従って、Mg含有量は0.5〜4.0%、好ましくは0.5〜1.5%の範囲とする。
Mg: 0.5-4.0%
Mg, which is an essential alloy element, forms fine precipitates together with Zn to improve strength and elongation. If the Mg content is less than 0.5%, the strength is insufficient, and if it exceeds 4.0% by mass, the rollability of the plate is lowered and the SCC sensitivity becomes sharp. Therefore, the Mg content is in the range of 0.5 to 4.0%, preferably 0.5 to 1.5%.
Cu:0.05〜0.6%、Ag:0.01〜0.15%の1種又は2種:
Cu及びAgはAl−Zn−Mg系合金の耐SCC性を向上させる作用がある。これらをいずれか一方又は両方含有する場合、Cu含有量が0.05%未満、及びAg含有量が0.01%未満では、耐SCC性向上効果が小さい。一方、Cu含有量が0.6%を超えると、圧延性及び溶接性などの諸特性を却って低下させる。またAg含有量は0.15%を超えて含有させてもその効果が飽和し、高価となる。従って、Cu含有量は0.05〜0.6%、好ましくは0.4%以下、Ag含有量は0.01〜0.15%とする。
One or two of Cu: 0.05 to 0.6% and Ag: 0.01 to 0.15%:
Cu and Ag have the effect of improving the SCC resistance of the Al—Zn—Mg alloy. When one or both of these are contained, the effect of improving SCC resistance is small when the Cu content is less than 0.05% and the Ag content is less than 0.01%. On the other hand, if the Cu content exceeds 0.6%, various properties such as rollability and weldability are reduced. Moreover, even if it contains Ag content exceeding 0.15%, the effect will be saturated and it will become expensive. Therefore, the Cu content is 0.05 to 0.6%, preferably 0.4% or less, and the Ag content is 0.01 to 0.15%.
Mn:0.05〜0.3%、Cr:0.03〜0.2%、Zr:0.03〜0.3%の1種又は2種以上:
Mn、Cr及びZrは、鋳塊の結晶粒を微細化して強度向上に寄与する。これらをいずれか1種、又は2種あるいは3種を含有する場合、Mn、Cr、Zrの含有量がいずれも下限未満では、含有量が不足して、再結晶が促進され、耐SCC性が低下する。一方、Mn、Cr、Zrの含有量がそれぞれの上限を超えた場合には、粗大晶出物を形成するため伸びが低下する。従って、Mn:0.05〜0.3%、Cr:0.03〜0.2%、Zr:0.03〜0.3%の各範囲とする。
One or more of Mn: 0.05 to 0.3%, Cr: 0.03 to 0.2%, Zr: 0.03 to 0.3%:
Mn, Cr and Zr contribute to strength improvement by refining the crystal grains of the ingot. When any one, two or three of these are contained, if the content of Mn, Cr, or Zr is less than the lower limit, the content is insufficient, recrystallization is promoted, and SCC resistance is improved. descend. On the other hand, when the contents of Mn, Cr, and Zr exceed the respective upper limits, a coarse crystallized product is formed and the elongation is lowered. Therefore, the ranges are Mn: 0.05 to 0.3%, Cr: 0.03 to 0.2%, and Zr: 0.03 to 0.3%.
Ti、B:
Ti、Bは、圧延板としては不純物であるが、アルミニウム合金鋳塊の結晶粒を微細化する効果があるので、7000系合金としてJIS規格で規定する範囲での各々の含有を許容する。Tiの上限は0.2%、好ましくは0.1%、Bの上限は0.05%以下、好ましくは0.03%とする。
Ti, B:
Ti and B are impurities in the rolled plate, but have the effect of refining the crystal grains of the aluminum alloy ingot, so that each content in the range specified by the JIS standard is allowed as a 7000 series alloy. The upper limit of Ti is 0.2%, preferably 0.1%, and the upper limit of B is 0.05% or less, preferably 0.03%.
その他の元素:
また、これら記載した以外の、Fe、Siなどのその他の元素は不可避的な不純物である。溶解原料として、純アルミニウム地金以外に、アルミニウム合金スクラップの使用による、これら不純物元素の混入なども想定(許容)して、7000系合金のJIS規格で規定する範囲での各々の含有を許容する。例えば、Fe:0.5%以下、Si:0.5%以下であれば、本発明に係るアルミニウム合金圧延板の特性に影響せず、含有が許容される。
Other elements:
In addition to these elements, other elements such as Fe and Si are inevitable impurities. As a melting raw material, in addition to pure aluminum ingots, the inclusion of these impurity elements due to the use of aluminum alloy scrap is assumed (allowed), and each content within the range specified by the JIS standard of 7000 series alloys is allowed. . For example, if Fe: 0.5% or less and Si: 0.5% or less, inclusion is permitted without affecting the characteristics of the aluminum alloy rolled sheet according to the present invention.
組織:
本発明の7000系アルミニウム合金板組織においては、その前提として、通常の7000系アルミニウム合金板と同様に、前記組成および前記常法による製造方法からして、微細なナノレベルのサイズの析出物が、結晶粒内に多数存在して、強度や耐SCC性などの基本特性を達成している。この析出物とは、結晶粒内に生成する、前記MgとZnとの金属間化合物(組成はMgZn2など)であり、これに前記組成に応じて更にCu、Zrなどの含有元素が含まれる微細分散相である。
Organization:
In the 7000 series aluminum alloy sheet structure of the present invention, as a premise, as in the case of a normal 7000 series aluminum alloy sheet, a fine nano-level size precipitate is formed from the composition and the production method according to the conventional method. Many exist in the crystal grains to achieve basic properties such as strength and SCC resistance. This precipitate is an intermetallic compound of Mg and Zn (composition is MgZn 2 or the like) that is generated in crystal grains, and further contains contained elements such as Cu and Zr according to the composition. It is a finely dispersed phase.
平均結晶粒径と結晶粒界割合:
その上で、本発明の7000系アルミニウム合金板組織は、更なる高強度化や耐SCC性などの特性の向上のために、平均結晶粒径を15μm以下とした繊維状の微細加工組織とする。また、この繊維状の微細加工組織は、傾角5〜15°の小傾角粒界の平均割合が15%以上で、かつ傾角15°を超える大傾角粒界の平均割合が15〜50%となる組織である。
Average grain size and grain boundary ratio:
In addition, the 7000 series aluminum alloy sheet structure of the present invention is a fibrous microfabricated structure with an average crystal grain size of 15 μm or less in order to further enhance the properties such as higher strength and SCC resistance. . Further, in this fibrous finely processed structure, the average ratio of small-angle grain boundaries having an inclination of 5 to 15 ° is 15% or more, and the average ratio of large-angle grain boundaries exceeding 15 ° is 15 to 50%. It is an organization.
このように、小傾角粒界が一定割合以上存在するとともに、一定割合の大傾角粒界と混在するような、繊維状の微細加工組織とすることによって、常法によって製造された7000系アルミニウム合金板であっても、板に歪が入った場合に、局所的に歪が集中せずに、均一に変形する組織とできる。これによって、局所的な破断を防止でき、0.2%耐力が350MPa以上であるような高強度とし、伸びも大きくして成形性を確保できる。また、このような高強度であるにも関わらず、耐SCC性の低下を抑制したものとすることができる。 As described above, a 7000 series aluminum alloy manufactured by a conventional method is obtained by forming a fibrous microfabricated structure in which a low-angle grain boundary exists at a certain ratio or more and is mixed with a large-angle grain boundary at a certain ratio. Even in the case of a plate, when the plate is distorted, the strain can be uniformly deformed without locally concentrating the strain. As a result, local breakage can be prevented, high strength such that 0.2% proof stress is 350 MPa or more, and elongation can be increased to ensure moldability. Moreover, although it is such high intensity | strength, it can be set as what suppressed the fall of SCC resistance.
一方、これらの要件を欠いて、平均結晶粒径が15μmを超えるか、小傾角粒界の平均割合が15%未満となるか、あるいは大傾角粒界の平均割合が15%未満となると、前記高強度化が達成できず、伸びも低下して成形性が低下する。 On the other hand, when these requirements are lacking, when the average crystal grain size exceeds 15 μm, the average proportion of the low-angle grain boundaries is less than 15%, or the average proportion of the large-angle grain boundaries is less than 15%, Higher strength cannot be achieved, elongation is lowered, and moldability is lowered.
本発明で言う小傾角粒界とは、後述するSEM/EBSP法により測定した結晶方位の内、結晶方位の相違(傾角)が5〜15°と小さい結晶粒の間の粒界である。また、本発明で言う大傾角粒界とは、この結晶方位の相違(傾角)が15°を超え、180°以下の結晶粒の間の粒界である。ここで、方位差が2〜5°未満の結晶粒界は、高強度化への効果や影響がごく小さいので、本発明においては考慮せず、規定しない。 The small-angle grain boundary referred to in the present invention is a grain boundary between crystal grains having a small crystal orientation difference (tilt angle) of 5 to 15 ° among crystal orientations measured by the SEM / EBSP method described later. The large tilt grain boundary referred to in the present invention is a grain boundary between crystal grains having a difference in crystal orientation (tilt angle) of more than 15 ° and 180 ° or less. Here, crystal grain boundaries having an orientation difference of less than 2 to 5 ° are not considered and are not defined in the present invention because the effects and influences on increasing the strength are very small.
この小傾角粒界の平均割合として、本発明では、測定した小傾角粒界の結晶粒界の全長(測定された全小傾角粒の結晶粒界の合計の長さ)の、同じく測定した、結晶方位の相違が2〜180°の結晶粒界の全長(測定された全結晶粒の結晶粒界の合計の長さ)に対する割合を、傾角5〜15°の小傾角粒界の割合と規定している。すなわち、規定する傾角5〜15°の小傾角粒界の割合(%)は、〔(5−15°の結晶粒界の全長)/(2−180°の結晶粒界の全長)〕×100として計算でき、この値の平均を15%以上とする。なお、製造の限界から、5〜15°の小傾角粒界の割合の上限は60%程度である。 As an average ratio of the low-angle grain boundaries, in the present invention, the total length of the grain boundaries of the measured small-angle grain boundaries (the total length of the grain boundaries of all the small-angle grains measured) was also measured. The ratio of the crystal orientation difference with respect to the total length of the crystal grain boundary of 2 to 180 ° (the total length of the measured crystal grain boundaries of all crystal grains) is defined as the ratio of the small tilt grain boundary with the tilt angle of 5 to 15 °. doing. That is, the ratio (%) of the specified low-angle grain boundaries with an inclination angle of 5 to 15 ° is [(total length of 5-15 ° crystal grain boundaries) / (total length of 2-180 ° crystal grain boundaries)] × 100. The average of these values is 15% or more. From the production limit, the upper limit of the proportion of the low-angle grain boundaries of 5 to 15 ° is about 60%.
一方、大傾角粒界の平均割合は、同じく、測定した大傾角粒界の結晶粒界の全長(測定された全小傾角粒の結晶粒界の合計の長さ)の、同じく測定した、結晶方位の相違が2〜180°の結晶粒界の全長(測定された全結晶粒の結晶粒界の合計の長さ)に対する割合を、傾角15°を超える大傾角粒界の割合と規定する。すなわち、規定する大傾角粒界の割合(%)は、〔(15°を超え180°以下の結晶粒界の全長)/(2−180°の結晶粒界の全長)〕×100として計算でき、この値の平均を15〜50%の範囲とする。 On the other hand, the average ratio of the large tilt grain boundary is also the same as the total crystal grain boundary of the measured large tilt grain boundary (the total length of the measured grain boundaries of all the small tilt grain). The ratio of the orientation difference to the total length of the crystal grain boundary having a difference of 2 to 180 ° (the total length of the measured crystal grain boundaries of all crystal grains) is defined as the ratio of the large tilt grain boundary exceeding the tilt angle of 15 °. That is, the ratio (%) of the specified large tilt grain boundary can be calculated as [(total length of crystal grain boundary of more than 15 ° and 180 ° or less) / (full length of crystal grain boundary of 2-180 °)] × 100. The average of these values is in the range of 15 to 50%.
結晶粒径と結晶粒界割合の測定:
これら本発明で規定する平均結晶粒径や結晶粒界(小傾角粒界および大傾角粒界)の各平均割合は、いずれもSEM/EBSP法によって測定する。この場合の板の組織の測定部位は、通常のこの種組織の測定部位と同じく、この板の幅方向断面とする。そして、この板の幅方向断面の任意の箇所から採取した5個の測定試験片(5箇所の測定箇所)の各測定値を平均化したものを、本発明で規定する平均結晶粒径や、小傾角粒界および大傾角粒界(結晶粒界)の平均割合とする。
Measurement of grain size and grain boundary ratio:
Each of these average crystal grain sizes and crystal grain boundaries (small-angle grain boundaries and large-angle grain boundaries) defined in the present invention are all measured by the SEM / EBSP method. The measurement site | part of the structure | tissue of the board in this case is taken as the cross section of this board in the width direction similarly to the measurement part of this normal structure | tissue. And what averaged each measured value of five measurement specimens (5 measurement locations) taken from any location of the cross section in the width direction of this plate, the average crystal grain size defined in the present invention, The average ratio of the low-angle grain boundary and the large-angle grain boundary (crystal grain boundary).
前記SEM/EBSP法は、集合組織の測定方法として汎用され、電界放出型走査電子顕微鏡(Field Emission Scanning Electron Microscope:FESEM)に、後方散乱電子回折像[EBSP: Electron Back Scattering (Scattered) Pattern] システムを搭載した結晶方位解析法である。この測定方法は、他の集合組織の測定方法に比して、高分解能ゆえに高測定精度である。そして、この方法によって、板の同じ測定部位の平均結晶粒径と結晶粒界の平均割合を同時に高精度に測定できる利点がある。アルミニウム合金板の結晶粒界の平均割合や平均結晶粒径の測定を、このSEM/EBSP法により行うことは、従来から、例えば特開2009−173972号、あるいは前記特許文献5、特許文献6などの公報で公知であり、本発明でも、この公知の方法で行う。 The SEM / EBSP method is widely used as a texture measurement method, and is applied to a field emission scanning electron microscope (FESEM) in a backscattered electron diffraction image (EBSP: Electron Back Scattering (Scattered) Pattern) system. Is a crystal orientation analysis method. This measurement method has high measurement accuracy because of its high resolution as compared with other texture measurement methods. This method has an advantage that the average crystal grain size and the average ratio of crystal grain boundaries at the same measurement site of the plate can be simultaneously measured with high accuracy. Measurement of the average ratio of crystal grain boundaries and average crystal grain size of an aluminum alloy plate by this SEM / EBSP method has been conventionally performed, for example, in Japanese Patent Application Laid-Open No. 2009-173972, Patent Document 5, Patent Document 6, and the like. In the present invention, this method is also used.
これら開示されたSEM/EBSP法は、前記FESEM(FE−SEM)の鏡筒内にセットしたAl合金板の試料に、電子線を照射してスクリーン上にEBSPを投影する。これを高感度カメラで撮影して、コンピュータに画像として取り込む。コンピュータでは、この画像を解析して、既知の結晶系を用いたシミュレーションによるパターンとの比較によって、結晶の方位が決定される。算出された結晶の各方位は3次元オイラー角として、位置座標(x、y)などとともに記録される。このプロセスが全測定点に対して自動的に行なわれるので、測定終了時には数万〜数十万点の結晶方位データが得られる。 In these disclosed SEM / EBSP methods, an EBSP is projected onto a screen by irradiating an electron beam onto a sample of an Al alloy plate set in a lens barrel of the FESEM (FE-SEM). This is taken with a high-sensitivity camera and captured as an image on a computer. In the computer, the orientation of the crystal is determined by analyzing this image and comparing it with a pattern obtained by simulation using a known crystal system. Each calculated orientation of the crystal is recorded as a three-dimensional Euler angle together with position coordinates (x, y) and the like. Since this process is automatically performed for all measurement points, tens of thousands to hundreds of thousands of crystal orientation data can be obtained at the end of measurement.
このように、SEM/EBSP法には、透過電子顕微鏡を用いた電子線回折法よりも、観察視野が広く、数百個以上の多数の結晶粒に対する、平均結晶粒径、平均結晶粒径の標準偏差、あるいは方位解析の情報を、数時間以内で得られる利点がある。また、結晶粒毎の測定ではなく、指定した領域を任意の一定間隔で走査して測定するために、測定領域全体を網羅した上記多数の測定ポイントに関する、上記各情報を得ることができる利点もある。これらFESEMにEBSPシステムを搭載した結晶方位解析法の詳細は、神戸製鋼技報/Vol.52 No.2(Sep.2002)P66-70などに詳細に記載されている。 Thus, the SEM / EBSP method has a wider field of view than the electron diffraction method using a transmission electron microscope, and has an average crystal grain size and an average crystal grain size of hundreds of crystal grains. There is an advantage that information on standard deviation or orientation analysis can be obtained within a few hours. In addition, since the measurement is performed by scanning a specified region at an arbitrary fixed interval instead of measurement for each crystal grain, there is also an advantage that each of the above-described information on the numerous measurement points covering the entire measurement region can be obtained. is there. Details of the crystal orientation analysis method in which the EBSP system is mounted on these FESEMs are described in detail in Kobe Steel Engineering Reports / Vol.52 No.2 (Sep.2002) P66-70 and the like.
ここで、アルミニウム合金板の場合、通常は、以下に示す如きCube方位、Goss方位、Brass方位(以下、B方位ともいう)、Cu方位(以下、Copper方位ともいう)、S方位等と呼ばれる多くの方位因子(これら各方位を有する結晶粒)からなる集合組織を形成し、それらに応じた結晶面が存在する。これらの事実は、例えば、長島晋一編著、「集合組織」(丸善株式会社刊)や軽金属学会「軽金属」解説Vol.43、1993、P285-293などに記載されている。 Here, in the case of an aluminum alloy plate, it is usually called Cube orientation, Goss orientation, Brass orientation (hereinafter also referred to as B orientation), Cu orientation (hereinafter also referred to as Copper orientation), S orientation, etc. A texture composed of the orientation factors (crystal grains having these orientations) is formed, and there is a crystal plane corresponding to them. These facts are described in, for example, “Cross Texture” (published by Maruzen Co., Ltd.) edited by Shinichi Nagashima, “Light Metal”, Vol. 43, 1993, P285-293, etc.
これらの集合組織の形成は同じ結晶系の場合でも加工、熱処理方法によって異なる。圧延による板材の集合組織の場合は、圧延面と圧延方向で表されており、圧延面は{ABC}で表現され、圧延方向は<DEF>で表現される(ABCDEFは整数を示す)。かかる表現に基づき、各方位は下記の如く表現される。
Cube方位 {001}<100>
Goss方位 {011}<100>
Rotated−Goss方位{011}<011>
Brass方位(B方位) {011}<211>
Cu方位(Copper方位){112}<111>
(若しくはD方位{4411}<11118>
S方位 {123}<634>
B/G方位 {011}<511>
B/S方位 {168}<211>
P方位 {011}<111>
The formation of these textures differs depending on the processing and heat treatment methods even in the case of the same crystal system. In the case of a texture of a plate material by rolling, it is expressed by a rolling surface and a rolling direction, the rolling surface is expressed by {ABC}, and the rolling direction is expressed by <DEF> (ABCDEF indicates an integer). Based on this expression, each direction is expressed as follows.
Cube orientation {001} <100>
Goss orientation {011} <100>
Rotated-Goss orientation {011} <011>
Brass orientation (B orientation) {011} <211>
Cu orientation (Copper orientation) {112} <111>
(Or D direction {4411} <11118>
S orientation {123} <634>
B / G direction {011} <511>
B / S orientation {168} <211>
P direction {011} <111>
その上で、平均結晶粒径を以下の式により算出した。平均結晶粒径=(Σx)/n(ここで、nは測定した結晶粒の数、xはそれぞれの結晶粒径を示す)。 Then, the average crystal grain size was calculated by the following formula. Average crystal grain size = (Σx) / n (where n is the number of crystal grains measured and x is the respective crystal grain size).
これらの測定に際しては、対象となる溶体化処理後の冷延板の幅方向断面を機械研磨し、更に、バフ研磨に次いで電解研磨して、表面を調製した試料を用意した。その後、FESEMを用いて、EBSPによる結晶方位測定並びに結晶粒径測定を行った。EBSP測定・解析システムは、EBSP:TSL社製(OIM)を用いた。 In these measurements, a sample having a surface prepared by mechanically polishing the cross-section in the width direction of the cold-rolled sheet after the solution treatment, and then electrolytically polishing following buffing was prepared. Thereafter, the crystal orientation measurement and the crystal grain size measurement by EBSP were performed using FESEM. As the EBSP measurement / analysis system, EBSP: manufactured by TSL (OIM) was used.
(製造方法)
本発明における7000系アルミニウム合金圧延板の製造方法について、以下に具体的に説明する。
(Production method)
The manufacturing method of the 7000 series aluminum alloy rolled sheet in the present invention will be specifically described below.
本発明では、7000系アルミニウム合金圧延板の通常の製造工程による製造方法で製造可能である。即ち、鋳造(DC鋳造法や連続鋳造法)、均質化熱処理、熱間圧延の通常の各製造工程を経て製造され、板厚が1.5〜5.0mmであるアルミニウム合金熱延板とされる。この段階で製品板としても良く、また冷間圧延前もしくは冷間圧延の中途において1回または2回以上の中間焼鈍を選択的に行ないつつ、更に冷延して、板厚が3mm以下の冷延板の製品板としても良い。 In this invention, it can manufacture with the manufacturing method by the normal manufacturing process of a 7000 series aluminum alloy rolled sheet. That is, an aluminum alloy hot-rolled sheet having a thickness of 1.5 to 5.0 mm is manufactured through normal manufacturing processes such as casting (DC casting or continuous casting), homogenization heat treatment, and hot rolling. The At this stage, a product plate may be used. Further, it is further cold-rolled while selectively performing intermediate annealing once or twice before cold rolling or in the middle of cold rolling to obtain a cold plate having a thickness of 3 mm or less. It is good also as a product board of a rolled sheet.
(溶解、鋳造冷却速度)
先ず、溶解、鋳造工程では、上記7000系成分組成範囲内に溶解調整されたアルミニウム合金溶湯を、連続鋳造法、半連続鋳造法(DC鋳造法)等の通常の溶解鋳造法を適宜選択して鋳造する。
(Dissolution, casting cooling rate)
First, in the melting and casting process, an ordinary molten casting method such as a continuous casting method or a semi-continuous casting method (DC casting method) is appropriately selected for the aluminum alloy melt adjusted within the above-mentioned 7000-based component composition range. Cast.
(均質化熱処理)
次いで、前記鋳造されたアルミニウム合金鋳塊に、熱間圧延に先立って、均質化熱処理を施す。この均質化熱処理(均熱処理)は、組織の均質化、すなわち、鋳塊組織中の結晶粒内の偏析をなくすことを目的とする。均質化熱処理条件は、好ましくは400〜550℃程度の温度で、2時間以上の均質化時間の範囲から適宜選択される。
(Homogenization heat treatment)
Next, the cast aluminum alloy ingot is subjected to a homogenization heat treatment prior to hot rolling. The purpose of this homogenization heat treatment (soaking) is to homogenize the structure, that is, eliminate segregation in crystal grains in the ingot structure. The homogenization heat treatment conditions are suitably selected from a range of homogenization time of 2 hours or more, preferably at a temperature of about 400 to 550 ° C.
(熱間圧延)
熱間圧延は、熱延開始温度が固相線温度を超える条件では、バーニングが起こるため熱延自体が困難となる。また、熱延開始温度が350℃未満では熱延時の荷重が高くなりすぎ、熱延自体が困難となる。したがって、熱延開始温度は350℃〜固相線温度の範囲から選択して熱間圧延し、2〜7mm程度の板厚の熱延板とする。この熱延板の冷間圧延前の焼鈍 (荒鈍) は必ずしも必要ではないが実施しても良い。
(Hot rolling)
In the hot rolling, the hot rolling itself becomes difficult because burning occurs under conditions where the hot rolling start temperature exceeds the solidus temperature. On the other hand, when the hot rolling start temperature is less than 350 ° C., the load during hot rolling becomes too high, and the hot rolling itself becomes difficult. Therefore, the hot rolling start temperature is selected from the range of 350 ° C. to the solidus temperature and hot rolled to obtain a hot rolled sheet having a thickness of about 2 to 7 mm. Annealing (roughening) of the hot-rolled sheet before cold rolling is not necessarily required, but may be performed.
(冷間圧延)
冷間圧延では、上記熱延板を圧延して、1〜3mm程度の所望の最終板厚の冷延板 (コイルも含む) に製作する。冷間圧延パス間で中間焼鈍を行っても良い。
(Cold rolling)
In cold rolling, the hot rolled sheet is rolled to produce a cold rolled sheet (including a coil) having a desired final thickness of about 1 to 3 mm. Intermediate annealing may be performed between cold rolling passes.
(溶体化処理)
冷間圧延後は調質として溶体化処理を行う。この溶体化処理については、通常の連続熱処理ラインによる加熱,冷却でよく、特に限定はされない。ただ、各元素の十分な固溶量を得ることや結晶粒の微細化のためには、450〜550℃の溶体化処理温度とすることが望ましい。
(Solution treatment)
After cold rolling, solution treatment is performed as a tempering. The solution treatment is not particularly limited and may be heating and cooling using a normal continuous heat treatment line. However, in order to obtain a sufficient solid solution amount of each element or to refine crystal grains, it is desirable to set a solution treatment temperature of 450 to 550 ° C.
溶体化処理時の加熱(昇温)速度は平均で0.01℃/s以上、100℃/s以下の範囲とすることが望ましい。平均加熱速度が0.01℃/s未満と小さすぎては、粗大な結晶粒が生じて、溶体化処理後の組織を、平均結晶粒径が15μm以下である繊維状の微細組織とできない。また、傾角15°を超える大傾角粒界の平均割合が15〜50%で、傾角5〜15°の小傾角粒界の平均割合が15%以上である組織とできない。この結果、強度や耐SCC性が低下する。一方、溶体化処理炉の設備能力の限界から、平均加熱速度は100℃/sを超えて大きくはできない。 The heating (temperature increase) rate during the solution treatment is desirably 0.01 ° C./s or more and 100 ° C./s or less on average. If the average heating rate is too small as less than 0.01 ° C./s, coarse crystal grains are formed, and the structure after the solution treatment cannot be made into a fibrous fine structure having an average crystal grain size of 15 μm or less. In addition, it is impossible to obtain a structure in which the average ratio of large tilt grain boundaries exceeding 15 ° is 15 to 50% and the average ratio of small tilt grain boundaries having a tilt angle of 5 to 15 ° is 15% or more. As a result, strength and SCC resistance are reduced. On the other hand, the average heating rate cannot exceed 100 ° C./s due to the limit of the equipment capacity of the solution treatment furnace.
また、溶体化処理後の平均冷却(降温)速度は1℃/s以上、500℃/s以下とすることが望ましい。平均冷却速度が1℃/s未満と小さすぎては、粗大な再結晶が生じて、溶体化処理後の組織を、平均結晶粒径が15μm以下である繊維状の微細組織とできない。また、傾角15°を超える大傾角粒界の平均割合が15〜50%で、傾角5〜15°の小傾角粒界の平均割合が15%以上である組織とできない。そして、強度や成形性を低下させる粗大な粒界析出物も形成される。この結果、強度や耐SCC性が低下する。 The average cooling (temperature decrease) rate after the solution treatment is desirably 1 ° C./s or more and 500 ° C./s or less. If the average cooling rate is too low, less than 1 ° C./s, coarse recrystallization occurs, and the structure after the solution treatment cannot be made into a fibrous fine structure having an average crystal grain size of 15 μm or less. In addition, it is impossible to obtain a structure in which the average ratio of large tilt grain boundaries exceeding 15 ° is 15 to 50% and the average ratio of small tilt grain boundaries having a tilt angle of 5 to 15 ° is 15% or more. And the coarse grain boundary precipitate which reduces intensity | strength and a moldability is also formed. As a result, strength and SCC resistance are reduced.
一方、溶体化処理炉の設備能力の限界から、平均冷却速度は500℃/sを超えて大きくはできない。この冷却速度を確保するために、溶体化処理後の冷却は、ファンなどの空冷、ミスト、スプレー、浸漬等の水冷手段など、強制的な冷却手段や条件を各々選択して用いる。ちなみに、溶体化処理は基本的に1回のみであるが、室温時効が長時間化して材料の強度が高くなった場合などには、成形性の確保のため、溶体化処理を前記好ましい条件にて再度施して、この進みすぎた室温時効硬化を一旦キャンセルしても良い。 On the other hand, the average cooling rate cannot exceed 500 ° C./s because of the limit of the equipment capacity of the solution treatment furnace. In order to ensure this cooling rate, for cooling after the solution treatment, forced cooling means and conditions such as air cooling such as a fan, water cooling means such as mist, spray, and immersion are selected and used. Incidentally, the solution treatment is basically only once, but when the room temperature aging is prolonged and the strength of the material is increased, the solution treatment is performed under the above-mentioned preferable conditions in order to ensure formability. It may be applied again, and this excessive room temperature age hardening may be canceled once.
そして、本発明のアルミニウム合金板は、素材として、自動車部材に成形加工され、自動車部材として組み立てられる。また、自動車部材に成形加工された後で、別途人工時効硬化処理されて、自動車部材あるいは自動車車体とされる。 And the aluminum alloy plate of this invention is shape-processed into a motor vehicle member as a raw material, and is assembled as a motor vehicle member. Further, after being molded into an automobile member, it is subjected to a separate artificial age hardening treatment to obtain an automobile member or an automobile body.
人工時効硬化処理:
本発明の7000系アルミニウム合金板は、前記人工時効硬化処理によって自動車部材としての所望の強度とされる。この人工時効硬化処理を行うのは、素材7000系アルミニウム合金板の自動車部材への成形加工後が好ましい。人工時効硬化処理後の7000系アルミニウム合金板は、強度は高くなるものの、成形性は低下しており、自動車部材の形状の複雑化によっては成形できない場合も生じるからである。
Artificial age hardening treatment:
The 7000 series aluminum alloy plate of the present invention has a desired strength as an automobile member by the artificial age hardening treatment. The artificial age hardening treatment is preferably performed after forming the material 7000 series aluminum alloy plate into an automobile member. This is because the 7000 series aluminum alloy plate after the artificial age hardening treatment has high strength but has low formability, and may not be formed depending on the complexity of the shape of the automobile member.
この人工時効硬化処理の温度や時間の条件は、所望の強度や素材の7000系アルミニウム合金板の強度、あるいは室温時効の進行程度などから自由に決定される。ちなみに、人工時効硬化処理の条件を例示すると、1段の時効処理であれば、100〜150℃での時効処理を12〜36時間(過時効領域を含む)行う。また、2段の工程においては、1段目の熱処理温度が70〜100℃の範囲で2時間以上、2段目の熱処理温度が100〜170℃の範囲で5時間以上の範囲(過時効領域を含む)から選択する。 The temperature and time conditions of this artificial age hardening treatment are freely determined from the desired strength, the strength of the 7000 series aluminum alloy plate of the material, the progress of room temperature aging, and the like. By the way, exemplifying the conditions of artificial age hardening treatment, an aging treatment at 100 to 150 ° C. is performed for 12 to 36 hours (including an overaging region) in the case of one-stage aging treatment. In the two-stage process, the first-stage heat treatment temperature is in the range of 70 to 100 ° C. for 2 hours or longer, and the second-stage heat treatment temperature is in the range of 100 to 170 ° C. for five hours or longer (over-aged region). Select from).
下記表1に示す各成分組成の7000系アルミニウム合金の冷延板の組織を種々変えたものについて、強度などの機械的な特性と耐SCC性との関係を評価した。これらの結果を下記表2に示す。 The relationship between the mechanical properties such as strength and the SCC resistance was evaluated for various 7000 series aluminum alloy cold-rolled steel structures having the composition shown in Table 1 below. These results are shown in Table 2 below.
冷延板の組織は、主として、表2に示す、溶体化処理時の平均加熱速度と平均冷却速度とを制御した。具体的には、各例とも共通して、下記表1に示す各成分組成の7000系アルミニウム合金溶湯をDC鋳造し、45mm厚み×220mm幅×145mm長さの鋳塊を得た。この鋳塊を470℃×4時間の均質化熱処理後に、この温度を開始温度として熱間圧延を行い、板厚5.0mmの熱延板を製造した。この熱延板を、荒鈍(焼鈍)することなしに、またパス間での中間焼鈍なしに冷間圧延して、共通して板厚2.0mmの冷延板とした。 The structure of the cold rolled sheet mainly controlled the average heating rate and the average cooling rate during the solution treatment shown in Table 2. Specifically, in common with each example, a 7000 series aluminum alloy molten metal having each component composition shown in Table 1 below was DC cast to obtain an ingot of 45 mm thickness × 220 mm width × 145 mm length. The ingot was subjected to homogenization heat treatment at 470 ° C. for 4 hours, and then hot-rolled using this temperature as a starting temperature to produce a hot-rolled sheet having a thickness of 5.0 mm. This hot-rolled sheet was cold-rolled without being roughened (annealed) and without intermediate annealing between passes to obtain a cold-rolled sheet having a thickness of 2.0 mm in common.
この冷延板を、各例とも共通して500℃×30秒の溶体化処理を施したが、この溶体化処理温度への平均加熱(昇温)速度と、この温度からの平均冷却(降温)速度とは、表2に示すように種々調節した。この溶体化処理後のアルミニウム合金板から試験片を採取して組織を以下のようにして調査した。この結果を各々表2に示す。 This cold-rolled sheet was subjected to a solution treatment of 500 ° C. × 30 seconds in common with each example, but the average heating (temperature increase) rate to this solution treatment temperature and the average cooling (temperature decrease) from this temperature ) The speed was variously adjusted as shown in Table 2. Test pieces were collected from the aluminum alloy plate after the solution treatment, and the structure was examined as follows. The results are shown in Table 2.
(結晶粒界の平均割合、平均結晶粒径)
前記溶体化処理後の試験片の平均結晶粒径と結晶粒界の平均割合の測定は、板の幅方向断面の組織を前記した測定方法により行った。
(Average ratio of grain boundaries, average grain size)
The measurement of the average crystal grain size and the average ratio of crystal grain boundaries of the test piece after the solution treatment was performed by the measurement method described above for the structure of the cross section in the width direction of the plate.
そして、TSL社製EBSP測定・解析システム(OIM)を搭載した、日本電子社製SEM(JEOL JSM 6500F)を用い、この組織における粒界の割合(%)と平均結晶粒径(μm)の測定を行った。各例とも、この測定を、前記した通り、板の幅方向断面の任意の箇所から採取した試験片5個について各々行い、これらの測定値を各々平均化した。各試験片の測定領域は共通して圧延方向に平行な断面の圧延方向400μm×最表層から板厚方向100μmの領域とし、測定ステップ間隔も共通して0.4μmとした。 And using JEM SEM (JEOL JSM 6500F) equipped with TSL EBSP measurement / analysis system (OIM), measurement of grain boundary ratio (%) and average grain size (μm) in this structure Went. In each example, as described above, this measurement was performed on each of five test pieces taken from arbitrary positions on the cross section in the width direction of the plate, and these measured values were averaged. The measurement area of each test piece is commonly an area of 400 μm in the rolling direction of the cross section parallel to the rolling direction × 100 μm in the plate thickness direction from the outermost layer, and the measurement step interval is also 0.4 μm in common.
また、自動車部材への成形加工後の人工時効硬化処理を模擬して、この溶体化処理後のアルミニウム合金板を、120℃×24時間の共通する条件で、人工時効硬化処理を行った。こうして得られたアルミニウム合金板の任意の箇所から試験片を採取して、機械的特性や耐食性を以下のようにして調査した。これらの結果も各々表2に示す。 In addition, the artificial age hardening treatment after forming the automobile member was simulated, and the aluminum alloy plate after the solution treatment was subjected to an artificial age hardening treatment under the common conditions of 120 ° C. × 24 hours. Test specimens were collected from arbitrary locations on the aluminum alloy plate thus obtained, and the mechanical properties and corrosion resistance were investigated as follows. These results are also shown in Table 2.
(機械的特性)
各例とも前記人工時効硬化処理後に圧延直角方向の室温引張試験を行い、引張強度(MPa)、0.2%耐力(MPa)、全伸び(%)を測定した。室温引張り試験はJIS2241(1980)に基づき、室温20℃で試験を行った。引張り速度は5mm/分で、試験片が破断するまで一定の速度で行った。
(Mechanical properties)
In each example, a room temperature tensile test in the direction perpendicular to the rolling was performed after the artificial age hardening treatment, and tensile strength (MPa), 0.2% proof stress (MPa), and total elongation (%) were measured. The room temperature tensile test was performed at a room temperature of 20 ° C. based on JIS2241 (1980). The tensile speed was 5 mm / min, and the test was performed at a constant speed until the test piece broke.
(微細析出物)
各例とも、参考として、倍率300000倍の透過型電子顕微鏡で観察し、結晶粒内の2.0〜20nmのサイズの析出物の平均数密度(個/μm2)を測定した。この観察を試験片5個について行い、結晶粒内の2.0〜20nmのサイズの析出物の数密度を各々求めて、平均化(平均数密度と)したところ、各発明例ともに、2.0〜20nmのサイズの析出物の数密度は平均で2〜9×104個/μm3の範囲であった。ここで、析出物のサイズは、面積が等価な円の直径に換算して測定した。
(Fine precipitate)
In each example, as a reference, it was observed with a transmission electron microscope having a magnification of 300000 times, and the average number density (pieces / μm 2 ) of precipitates having a size of 2.0 to 20 nm in the crystal grains was measured. This observation was performed on five test pieces, and the number density of precipitates having a size of 2.0 to 20 nm in the crystal grains was obtained and averaged (average number density). The number density of precipitates having a size of 20 nm was in the range of 2 to 9 × 10 4 pieces / μm 3 on average. Here, the size of the precipitate was measured in terms of the diameter of a circle having an equivalent area.
(耐SCC性)
前記人工時効硬化処理後の試験片の耐SCC性を評価するために、クロム酸促進法による耐応力腐食割れ試験を行った。圧延直角方向に4%のひずみの負荷を試験片にかけ、120℃×24時間の時効硬化処理を行った後、90℃の試験溶液に最大10時間まで浸漬し、SCCを目視で観察した。なお、応力負荷はジグのボルト・ナットを締めることにより試験片の外表面に引張応力を発生させ、負荷ひずみはこの外表面に接着した歪みゲージによって測定した。また、試験溶液は蒸留水に酸化クロム36g、2クロム酸カリウム30g及び塩化ナトリウム3g(1リットル当たり)を加えて作製した。SCCが発生しなかったものを○、10時間までにSCCが発生したものを×と評価した。
(SCC resistance)
In order to evaluate the SCC resistance of the test piece after the artificial age hardening treatment, a stress corrosion cracking test by a chromic acid acceleration method was performed. A 4% strain load was applied to the test piece in the direction perpendicular to the rolling, and after age-hardening treatment at 120 ° C. for 24 hours, the specimen was immersed in a test solution at 90 ° C. for a maximum of 10 hours, and SCC was visually observed. The stress load was determined by generating a tensile stress on the outer surface of the test piece by tightening the bolts and nuts of the jig, and the load strain was measured with a strain gauge adhered to the outer surface. A test solution was prepared by adding 36 g of chromium oxide, 30 g of potassium dichromate and 3 g of sodium chloride (per liter) to distilled water. The case where no SCC occurred was evaluated as ◯, and the case where SCC occurred within 10 hours was evaluated as x.
表1、2から明らかなように、各発明例は、本発明アルミニウム合金組成範囲内であり、冷延率および溶体化処理時の平均加熱速度と平均冷却速度とが前記した好ましい範囲内で製造されている。この結果、溶体化処理後の組織として、平均結晶粒径が15μm以下であるとともに、傾角5〜15°の小傾角粒界の平均割合が15%以上で、かつ傾角15°を超える大傾角粒界の平均割合が15〜50%である組織を有している。この結果、前記人工時効処理後の0.2%耐力が350MPa以上、好ましくは400MPa以上であり、耐SCC性にも優れている。ここで、全伸びは自動車部材用として13.0%以上が好ましい。 As is clear from Tables 1 and 2, each invention example is within the composition range of the aluminum alloy of the present invention, and the cold rolling rate and the average heating rate and the average cooling rate during the solution treatment are produced within the above-described preferable ranges. Has been. As a result, as a structure after the solution treatment, a large-angle particle having an average crystal grain size of 15 μm or less and an average ratio of small-angle grain boundaries with an inclination angle of 5 to 15 ° of 15% or more and an inclination angle of more than 15 °. It has a structure in which the average ratio of the boundaries is 15 to 50%. As a result, the 0.2% yield strength after the artificial aging treatment is 350 MPa or more, preferably 400 MPa or more, and the SCC resistance is also excellent. Here, the total elongation is preferably 13.0% or more for automobile members.
これに対して、各比較例は、合金組成が表1の通り、本発明範囲から外れる。比較例7はZnが下限に外れる。比較例8はMgが下限に外れる。比較例9はCuが上限を超えているため、熱延中に大幅な割れが発生して製造を中断した。比較例10はZrが上限に外れる。 On the other hand, each comparative example is outside the scope of the present invention as shown in Table 1. In Comparative Example 7, Zn falls outside the lower limit. In Comparative Example 8, Mg deviates from the lower limit. In Comparative Example 9, since Cu exceeds the upper limit, a large crack occurred during hot rolling, and the production was interrupted. Comparative Example 10 Zr is Ru out to the upper limit.
また、比較例11、12は、合金組成は表1の通り本発明範囲内であるものの、溶体化処理時の平均加熱速度と平均冷却速度とが小さすぎるなど、適切ではなく、溶体化処理後の組織が、本発明で規定する範囲から外れて、通常の等軸な再結晶組織となっている。すなわち、平均結晶粒径が15μmを超え、傾角5〜15°の小傾角粒界の平均割合が15%未満で、かつ傾角15°を超える大傾角粒界の平均割合が15%未満である。このため、前記人工時効処理後でも高強度化されていない。 In Comparative Examples 11 and 12, although the alloy composition is within the scope of the present invention as shown in Table 1, the average heating rate and the average cooling rate during the solution treatment are not appropriate, such as after the solution treatment. This structure deviates from the range defined in the present invention and is a normal equiaxed recrystallized structure. That is, the average crystal grain size exceeds 15 μm, the average ratio of small-angle grain boundaries with an inclination angle of 5 to 15 ° is less than 15%, and the average ratio of large-angle grain boundaries with an inclination angle of more than 15 ° is less than 15%. For this reason, the strength is not increased even after the artificial aging treatment.
以上の結果から、本発明アルミニウム合金板が高強度と高延性そして耐SCC性を兼備するための本発明各要件の臨界的な意義が裏付けられる。 The above results support the critical significance of the requirements of the present invention for the aluminum alloy sheet of the present invention to have both high strength, high ductility and SCC resistance.
以上説明したように、本発明は、強度と耐応力腐食割れ性とを兼備した自動車部材用7000系アルミニウム合金板を提供できる。したがって、本発明は車体軽量化に寄与する、フレーム、ピラーなどの自動車構造部材や、これ以外の他の自動車部材にも好適である。 As described above, the present invention can provide a 7000 series aluminum alloy plate for automobile members having both strength and stress corrosion cracking resistance. Therefore, the present invention is also suitable for automobile structural members such as frames and pillars that contribute to weight reduction of the vehicle body, and other automobile members.
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US14/420,974 US20150218677A1 (en) | 2012-09-20 | 2013-09-13 | Aluminum alloy sheet for automobile part |
EP13839895.3A EP2899287B1 (en) | 2012-09-20 | 2013-09-13 | Aluminum alloy plate for automobile part |
MX2015003449A MX2015003449A (en) | 2012-09-20 | 2013-09-13 | Aluminum alloy plate for automobile part. |
AU2013319131A AU2013319131B2 (en) | 2012-09-20 | 2013-09-13 | Aluminum alloy plate for automobile part |
CN201380047549.XA CN104619873B (en) | 2012-09-20 | 2013-09-13 | Automobile component aluminium alloy plate |
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PCT/JP2013/074863 WO2014046047A1 (en) | 2012-09-20 | 2013-09-13 | Aluminum alloy plate for automobile part |
US16/025,056 US20180305794A1 (en) | 2012-09-20 | 2018-07-02 | Aluminum alloy sheet for automobile part |
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