JPH07207491A - Chrome plating treatment on surface of aluminum or aluminum alloy - Google Patents

Abstract

PURPOSE:To easily improve the adhesive strength of a chrome plating film by forming a projecting and recessing part of specific roughness on the surface of aluminum and giving chrome plating to the projecting and recessing part. CONSTITUTION:A projecting and recessing part of maximum roughness of 10-20mum measured by a tracer type roughness meter is formed on the surface of aluminum or aluminum alloy. Then, chrome plating is given to the projecting and recessing part. In this way, the projecting and recessing part formed by the pretreatment shows the anchor effect, and the adhesive strength of the chrome plating film is improved without a complex process, such as zinc plating substitution being required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for plating chromium on aluminum and aluminum alloy surfaces.

[0002]

2. Description of the Related Art Aluminum or aluminum alloy (hereinafter abbreviated as Al) easily forms an oxide film on its surface. When plating is applied, this oxide film is a factor that hinders the adhesion of the plating and the deposition of the plating. Therefore, the zinc displacement plating method is generally used as a pretreatment for the intended plating. Specifically, the zinc displacement plating method is degreasing → washing with water → alkaline etching → washing with water →
The target plating treatment is performed through the steps of acid activity → washing → first zinc displacement plating → washing → acid treatment → second zinc displacement plating → water washing. Thus, the workability is poor due to the extremely long pretreatment process, and the cost is increased as compared with plating on steels.

[0003]

In the prior art, as described above, the pretreatment process is long and complicated, and the productivity is unavoidable. It is difficult to perform plating directly on the Al surface, and as mentioned above, use zinc that has relatively good adhesion to general plating metal and change (replace) the Al surface layer to zinc.
After that, the target plating is applied to secure the adhesion with the plated metal. When chromium plating is performed without pretreatment on the surface of Al, the chromium plating film is deposited, but the adhesion to the base material is extremely poor, and it is in a situation where it is peeled off and dropped off with a small impact.

In view of the above-mentioned state of the art, the present invention is to provide a method capable of performing chromium plating on the Al surface by a simple pretreatment.

[0005]

The present invention is characterized in that an uneven surface having a maximum surface roughness of 10 to 20 μm is formed on an aluminum or aluminum alloy surface, and chromium plating is applied to the uneven surface. Is a method of chromium plating on the surface of aluminum or aluminum alloy.

[0006]

In the present invention, any means such as shot blasting, etching, knurling, laser irradiation, and honing can be adopted as means for forming the uneven surface on the Al surface. It was confirmed by many experiments that the optimum roughness of the uneven surface was in the range of 10 to 20 μm as measured by a stylus type roughness meter. When chromium plating is applied to the Al surface on which the uneven surface is formed, the chromium plating layer is formed so as to dig into the uneven surface, and a kind of anchor effect ensures the adhesion between the base material Al and the chromium plating film. To do.

[0007]

EXAMPLE The main components most used for aluminum die casting are Si: 10.8% and Cu: 1.9.
%, Fe: 0.9%, Al: balance ADC12 material was used as a target base material for the test. Die cast AD
The surface is machined using C12 material (70 × 150 × 3t), and the surface roughness is 6 μm or less (VV
V) Finished and shot blasted on the processed surface. The shot blasting conditions are 180 alumina particles with an average particle size of 88 μm and an air pressure of 5 kgf / c.
m ² and treatment was performed for 6 minutes per 1 dm ² . The shot is dry. At this time, the maximum surface roughness of the shot blasting surface is 10 to 20 μm, and the center line average surface roughness is 1 to 2 μm. As the next step, it was attached to a plating jig and degreased by immersing only the object to be treated in a degreasing liquid containing alkali as a main component. After that, it is rinsed with water to start the chrome plating process. Chromic plating conditions are as follows: Chromic acid: 250 g / liter, sulfuric acid: 2.5 g / liter, current density: 30 A / d
m ² , the time was 2 hours, and the bath temperature was 50 ° C. As a result of applying chromium plating under these conditions, a good chromium plating film was formed.

FIG. 1 shows a photomicrograph (magnification: 400 times) of the metal structure of the cross section of the ADC12 material plated with the chromium plating layer obtained in the above example. In FIG. 1, 1 is an ADC12 material (Al base material), 2 is its shot blasting surface, and 3 is a chromium plating film.

When the chromium plating was applied under the conditions shown in this example, the chromium plating did not rise at all. As a test of adhesion, the Brinell hardness meter was used to observe the deformed and indented part, and as a result, good adhesion was obtained without chrome plating peeling. The result of the indentation test was also good, and there was no difference compared with the case where the normal zinc displacement plating was pretreated, and almost the same adhesion was obtained. Although shot blasting was used for the unevenness processing of the Al surface in the above-mentioned examples, similar results were obtained by using etching, knurling, laser irradiation, honing, or the like instead.

[0010]

According to the present invention, it is possible to improve the adhesion of the chrome plating film by forming an uneven surface on the Al surface and reducing the adhesion of the plating due to the oxide film formed on the Al surface and by the anchor effect. It is possible to omit the zinc plating substitution which requires complicated process,
The industrial effect is extremely remarkable.

[Brief description of drawings]

FIG. 1 is a micrograph showing a metal structure of a cross section of an Al base material on which a chromium plating film is formed, which is obtained according to an embodiment of the present invention.

Claims (1)

[Claims] 1. An aluminum or aluminum alloy surface, characterized in that an uneven surface having a maximum surface roughness of 10 to 20 μm is formed on an aluminum or aluminum alloy surface, and chromium plating is applied to the uneven surface. Chrome plating method on top.