The Improvement Of Aluminum Alloy Electroplating Pretreatment Process

After electroplating various metals on the surface of aluminum and aluminum alloy, the physical or chemical properties of the surface can be significantly improved. When aluminum and aluminum alloy are used as conductors, electroplating silver on the surface can improve the conductivity of the surface or electrical contact part; In order to make aluminum easy to weld, copper, nickel or tin are electroplated on its surface; In order to improve its wear resistance, thick chrome is electroplated on its surface. In terms of decoration, most of them are actually electroplated. Electroplating on the surface of aluminum and aluminum alloy has been tried for a long time and has been used in practical production.

However, there are oxides between aluminum and aluminum alloy and the coating. The thermal expansion coefficients of aluminum and aluminum alloy and metal coating are different. The coating has pinholes and residual electroplating solution, resulting in poor coating adhesion. It will peel off after long-term use, even immediately after plating. In the field of surface treatment, the electroplating process of aluminum and aluminum alloy is still in the exploratory stage. There has been no substantive breakthrough for a long time, and a perfect and mature process has not been formed so far. The poor adhesion of coating is the bottleneck of aluminum and aluminum alloy electroplating quality and product qualification rate.

Traditional Aluminum And Aluminum Alloy Electroplating

Aluminum and aluminum alloy can form coating by electrolysis in electrolyte, but the coating has weak adhesion and is easy to peel off. Therefore, aluminum can be deposited in an aqueous solution containing zinc oxide compound before electroplating. This method is zinc replacement method or deposition method. The surface of aluminum and aluminum alloy can also be treated first, and a thin porous oxide film can be obtained through anodizing power supply for electroplating.

2.1 Process Flow Of Conventional Aluminum And Aluminum Alloy Electroplating

The electroplating process of aluminum and aluminum alloy consists of pretreatment, electroplating and post-treatment. Pre plating treatment is the most critical process related to the quality of electroplating products. Its main purpose is to remove the grease on the surface of aluminum and aluminum alloy and naturally form oxide film and other dirt. The conventional general process flow is: degreasing – water washing – corrosion reduction – water washing – Pickling – water washing – activation – water washing – primary zinc dipping – water washing – dezincification – water washing – secondary zinc dipping – water washing – neutral nickel plating – water washing – subsequent electroplating. There are also subsequent electroplating after using wave anodic oxide film to replace zinc dipping process.

2.2 Shortcomings Of Traditional Pretreatment Process

1. Long process flow and many processes.
2. The process is complex and the operation range is narrow. All process parameters must be strictly controlled.
3. The application scope of the process is not wide, and the pretreatment processes of aluminum alloys with different brands cannot be the same. The pretreatment process must be adjusted according to the brand of aluminum alloy.
4. On the premise of strictly controlling the pretreatment process, the qualified rate of electroplating products is very low. The qualified rate of ordinary decorative electroplating is 85% ~ 90%, and that of functional electroplating is 60% ~ 70%.
5. The applicable life of each process solution is short and the treatment cycle is short.Because of the above shortcomings in the traditional pretreatment of aluminum and aluminum alloy, it must be improved.

The Improved Pretreatment Process Of General Aluminum And Aluminum Alloy Electroplating

Degreasing and alkaline etching in one – water washing – Pickling – water washing – ash removal – water washing – alkaline activation – zinc dipping – water washing – neutral nickel plating – water washing – subsequent electroplating.

Practice Summary

The new process aims at the actual defects of current aluminum alloy electroplating, combined with the special physical and chemical properties of aluminum alloy, and improves on the basis of the original process. The specific advantages are as follows:

1. The process flow is short. The purity of the aluminum alloy surface is improved by selectively dissolving other metals in the aluminum alloy surface layer, which is the improvement of the adhesion of the coating.
2. Firstly, the alkaline activation process is used to replace the acidic activation process to completely remove the residual silicon and silica gel on the surface of the alloy in the pretreatment process, so as to effectively improve the adhesion of the coating.
3. Direct zinc immersion without water washing after alkaline activation can avoid the formation of oxide layer exposed in the air during secondary zinc immersion after water washing after acidic activation.
4. Only one simple zinc dip is needed, and the adhesion of the coating is obviously better than that of the secondary zinc dip and the complex multicomponent cyanide zinc dip process.
5. The process has wide universality and is used for pretreatment of aluminum alloy electroplating of almost all brands.
6. The one-time qualified rate of product electroplating is significantly higher than that of traditional process. If only the adhesion of the coating is evaluated, the qualified rate of the product is close to 100%.
7. The process operation in actual production is simple and convenient.
8. The actual production of large-scale gantry automatic production line for a long time has proved that the improved new aluminum alloy electroplating pretreatment is very stable.
9. It is convenient to improve the process based on the traditional aluminum alloy electroplating process.
10. The use of Haocheng aluminum oxidation power supply can quickly improve the film application speed, shorten the film application time, save resources and save costs.