ã€China Aluminum Industry Net】 I. INTRODUCTION After plating all kinds of metals on the surface of aluminum and aluminum alloys, the physical or chemical properties of the surface can be significantly improved. When aluminum and aluminum alloys are used as conductors, silver plating on the surface can increase surface or electricity. The conductivity of the contact area; in order to facilitate the welding of aluminum, the surface of the plating of copper, nickel or tin; In order to improve its wear resistance, the surface of the plating thickness. In terms of decorativeness, electroplating enamel is mostly used.
The electroplating of aluminum and aluminum alloy surfaces has been tried and used for practical production long ago. However, there are oxides between aluminum and aluminum alloy and the coating. The thermal expansion coefficient of aluminum and aluminum alloy and metal coating are different. The coating has pinholes and residual plating solution and other factors, resulting in poor adhesion of the coating. When used for a long time, it will peel off or even be plated. Immediately after peeling off, in the field of surface treatment, the electroplating process of aluminum and aluminum alloys is still in the exploratory stage. There has been no substantial breakthrough for a long time, and there has been no perfect and mature process. The incompatibility of plating is the quality of aluminum and aluminum alloy plating and product qualification rate is still an industry bottleneck.
Second, the traditional aluminum and aluminum alloy electroplating Aluminum and aluminum alloy electrolysis in the electrolyte can form a coating, but the coating binding force is not strong, easy to peel. Therefore, aluminum can be first deposited in the aqueous solution containing zinc oxide compounds and then electroplating, this method is either zinc displacement or deposition. It is also possible to first obtain a thin porous oxide film on the surface of aluminum and aluminum alloys by anodizing the power supply to perform electroplating.
2.1 General aluminum and aluminum alloy plating process The aluminum and aluminum alloy plating process consists of three parts: pre-plating, electroplating, and post-plating. Pre-plating treatment is a relatively key process related to the quality of electroplated products. Its main purpose is to remove the grease on the surface of aluminum and aluminum alloys, naturally forming oxide films and other contaminants.
The conventional general process flow is: degreasing-washing-demineralization-washing-pickling-washing-activation-washing-primary zincation-washing-removal-zinc-washing-secondary zincation-washing-neutral nickel-plating-washing- Subsequent plating.
There is also a wave of anodized film instead of zinc immersion process in the subsequent plating.
2.2 Inadequacies in the traditional pre-treatment process 1. Long process flow and many processes.
2. The process is complex, the operating range is narrow, and the process parameters must be strictly controlled.
3. The scope of application of the process is not wide. Different grades of aluminum pretreatment can not be identical, and the pretreatment process must be adjusted according to the grade of aluminum alloy.
4. Under the premise of strictly controlling the pretreatment process, the qualification rate of electroplating products is very low, the pass rate of general decorative electroplating is 85% to 90%, and the pass rate of functional electroplating is 60% to 70%.
5. Each process solution has a short service life and a short processing cycle.
As the traditional pre-treatment of aluminum and aluminum alloys agrees with the above deficiencies, they must be improved.
3. Improved general-purpose aluminum and aluminum alloy electroplating pretreatment process Degreasing and caustic combo in one - Washing - Pickling - Washing - Deashing - Washing - Alkaline activation - Zinc-leaching - Washing - Neutral nickel plating - Washing - Subsequent electroplating .
4. Practice Summary The new process is based on the actual defects of the current aluminum alloy electroplating, combined with the special physical and chemical properties of the aluminum alloy itself, to improve on the basis of the original process, as follows:
1. The process flow is short. By selectively dissolving other metals on the surface layer of the aluminum alloy, the purity of the aluminum alloy surface is improved, and the adhesion of the plating layer is improved.
2. Alkaline activation was used instead of the acid activation process to completely remove the residual silicon and silica gel on the surface of the rate alloy during the pre-plating process, effectively increasing the plating adhesion.
3. After alkaline activation without direct washing and direct zinc immersion, it can avoid the formation of an oxide layer by exposure to air in the acidic activation after the second zinc immersion.
4. Just a simple zinc immersion can be, the bond strength of the coating is significantly better than the secondary zinc leaching and complex multi-component cyanogen leaching zinc process.
5. The versatility of the process is almost used for all types of aluminum alloy plating pretreatment.
6. The one-time pass rate of product electroplating is obviously higher than the traditional one. If the evaluation of the bond strength of a simple coating is good, the product's pass rate is close to 100%.
7. The actual production process is simple and convenient.
8. The actual production of a large-scale automatic production line for a long time has proved that the improved pretreatment of the new aluminum alloy plating is very stable.
9. Facilitate the process improvement based on the traditional aluminum alloy plating process.
10. The use of Haocheng aluminum oxidation power supply can achieve rapid increase in the film speed, shorten the film on time, save resources, to achieve cost-effectiveness.
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