JP2012062528A - Method for pretreatment of plating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for pretreatment of plating, which reduces the number of processes of the pretreatment of plating for an aluminum alloy.SOLUTION: In the method for pretreatment of plating, a mixed solution of an acidic ammonium fluoride (NHFHF) with the concentration of 50-100 g/L and a ferric chloride (FeCl) with the concentration of 10-300 g/L is used as a treatment liquid for removing an alteration layer and aluminum alloy component, thereby removing the alteration layer and an aluminum alloy in one step.

Description

  The present invention relates to a pretreatment method for plating a surface of an aluminum alloy member such as a cylinder block.

Ni-SiC plating is applied to the piston sliding surface of the aluminum alloy cylinder block. As this pretreatment for plating, a zinc undercoat is generally formed. In order to form this zinc undercoat, as shown in FIG. 2, the oil film adhering to the cylinder block surface is removed by degreasing, and then the Al oxide film, processed fluidized layer or oil-containing phase on the cylinder block surface is removed. Etch the denatured layer with an alkaline solution and remove the alloy components remaining on the cylinder block surface by pickling. Then, form a rough zinc film and dissolve this zinc film with nitric acid. There is known a double zinc replacement method in which a passive film containing zinc is used, and this passive film is replaced with a dense base film made of Zn—O—Al.
The above methods are not efficient because alkali etching, pickling, zinc film replacement, acid treatment, zinc film replacement and many processes are added, and a water washing process is added between the processes.

  In Patent Document 1, as the processing solution used for the above etching and pickling, an acidic etching solution in which nitric acid, sulfuric acid, and ammonium ammonium fluoride (acidic ammonium fluoride) are mixed can be used in two steps in one step. Proposals have been made.

  Patent Document 2 proposes a treatment liquid containing a fluorine compound such as copper ion, nitric acid and acidic ammonium fluoride as a treatment liquid for simultaneously etching a metal film made of silver or a silver alloy and a transparent conductive film such as ITO. Has been.

Japanese Patent Laid-Open No. 11-193481 JP 2009-206462 A

The acidic etching solution disclosed in Patent Document 1 is a mixture of nitric acid and sulfuric acid, and even when acidic ammonium fluoride is contained, the oxidizing power is excessively strong and a passive film is formed on the surface of the aluminum alloy and etching proceeds. It becomes difficult to do.

  The etching solution disclosed in Patent Document 2 contains nitric acid and acidic ammonium fluoride, but forms a passive film on the surface of the aluminum alloy as described above.

In order to solve the above problems, the present invention provides a plating pretreatment method in which after degreasing the surface of an aluminum alloy, the altered layer on the surface is removed and the aluminum alloy component is removed, and then a zinc undercoat is formed on the surface. As a treatment liquid for removing the deteriorated layer and removing the aluminum alloy component, acidic ammonium fluoride (NH ₄ F) having a concentration of 50 g / l (liter) to 100 g / l and a concentration of 10 g / l to 300 g are used. By using a mixed solution with ferric chloride (FeCl ₃ ) of / l or less, the deteriorated layer and the aluminum alloy are removed in one step.

The mixing ratio (vol%) of the acidic ammonium fluoride solution and the ferric chloride solution constituting the mixed solution is preferably 50 to 200 parts of the ferric chloride solution added to 100 parts of the acidic ammonium fluoride solution. .

According to the present invention, the removal of the deteriorated layer and the removal of the aluminum alloy component by the alkali etching solution are conventionally performed in two steps, but this can be performed in one step. As a result, the cycle time of the plating pretreatment is shortened and the efficiency is greatly improved. In addition, investment in dedicated and general-purpose facilities can be reduced with the reduction in the number of processes.

Schematic of plating pretreatment process according to the present invention Schematic diagram of conventional plating pretreatment process Illustration explaining the adhesion test method

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, in this embodiment, the removal of the deteriorated layer and the removal of the aluminum alloy component (including dissolution of the smut) are performed in one step, and the formation of the zinc undercoat is also performed in one step. ing.

In this embodiment, the formation of the zinc undercoat is performed by electrolysis in the same solution, that is, by anodic electrolysis of a rough zinc coat, and by the active oxygen generated by the electrolysis, a dense Zn-O-Al film is formed. To form.

As a treatment liquid that removes the altered layer and the aluminum alloy component in one step, we focused on ferric chloride (iron chloride [III]) and ammonium acid fluoride, and combined them to verify a suitable range. .

The determination as to whether or not it was suitable was made based on the adhesion of the Ni—SiC plating film. Moreover, verification was performed by JIS-H8504-11 (extrusion test method) shown in FIG.
For the extrusion test method, a flat bottom hole with a diameter of φ6.5 mm was left from the back side with respect to the plated surface, and then a sample was placed on a cradle with a hole with a diameter of φ25 mm, and a pin with a diameter of φ6.3 mm Is inserted into the hole in the flat bottom and punched out.
A change in the state of plating on the punched piece part was examined, and adhesion ◎ ○ × was determined.
◎ indicates that no peeling of the plating is observed, ○ indicates that peeling of the plating is partially observed, and × indicates that peeling of the plating is observed on the entire circumference.
The following table shows the results of verification.

  As apparent from the above (Table 1) to (Table 5), when using a mixed solution of acidic ammonium fluoride and ferric chloride, the concentration of acidic ammonium fluoride is set to 50 to 100 g / l, The ferric chloride concentration is preferably 10 to 300 g / l, and the ferric chloride concentration is more preferably 50 to 200 g / l.

However, the mixing ratio with which the above range could be verified is a range in which 50 to 200 parts of ferric chloride solution was mixed with 100 parts of acidic ammonium fluoride solution.
In the verification, the liquid temperature was set to 70 ° C. and the processing time was set to 60 seconds. However, the same result was obtained even when the liquid temperature was reduced to 50 ° C. and the processing time was reduced to 30.

The plating pretreatment process according to the present invention can be used as a pretreatment for plating applied to an aluminum alloy member such as an engine cylinder block.

Claims (1)

After degreasing the surface of the aluminum alloy, removal of the deteriorated layer on the surface and removal of the aluminum alloy component are performed, and thereafter, the removal of the deteriorated layer and the aluminum alloy are performed in the pretreatment method for forming a zinc undercoat on the surface. As a treatment liquid for removing components, acidic ammonium fluoride (NH ₄ F · HF) having a concentration of 50 g / l (liter) to 100 g / l and ferric chloride having a concentration of 10 g / l to 300 g / l A plating pretreatment method characterized in that the deteriorated layer and the aluminum alloy are removed in one step by using a mixed solution with (FeCl ₃ ).

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