Improvement of pretreatment process for aluminum and aluminum alloy electroplating

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 electrical conductivity of the surface or electrical contact parts.To make aluminum easy to weld, electroplate its surface with copper, nickel, or tin;In order to improve its abrasion resistance, thick plating was applied on its surface.On the decorative side, it's actually mostly electroplating.

Aluminum and aluminum alloy surface plating, has long been tried and has been used in practical production.But between aluminium and aluminium alloy and coating oxide, aluminium and aluminium alloy with different thermal expansion coefficient of metal coating, coating with factors such as pinhole and remnants of plating solution, causing poor bonding strength, long time use will flake peeling off immediately after plating, even in the field of surface treatment, aluminium and aluminium alloy electroplating technology is still in the exploratory stage, no substantive breakthrough for quite a long time, has not been formed complete, mature technology.Weak coating adhesion is the plating quality of aluminum and aluminum alloy and product qualification rate is still the bottleneck of the industry.

Traditional aluminum and aluminum alloy electroplating

Aluminum and aluminum alloy in the electrolyte electrolysis can form a coating, but the coating binding force is not strong, easy to peel.Therefore, aluminum can be deposited in an aqueous solution containing zinc oxides before electroplating.In addition, a thin layer of porous oxide film can be obtained by anodizing the surface of aluminum and aluminum alloy before electroplating.

2.1 process flow of conventional aluminum and aluminum alloy electroplating

Aluminum and aluminum alloy plating process has three parts: pretreatment, plating, post-treatment.Pretreatment is a key process that affects 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 general process flow is as follows: degreasing - washing - erosion reduction - washing - pickling - washing - activation - washing - zinc dipping - washing - zinc removal - washing - zinc dipping - washing - neutral nickel plating - washing - subsequent electroplating.

There is also a wave of anodic oxidation film instead of zinc dip process after the subsequent plating.

2.2 deficiencies in traditional pretreatment processes

1. Long process and multiple working procedures.

2. The process is complex and the operating range is narrow, so the process parameters must be strictly controlled.

3. The scope of application of the process is not wide, and the pretreatment process of aluminum alloy of different brands cannot be the same, so the pretreatment process must be adjusted according to the brand of aluminum alloy.

4. Under 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 the qualified rate of functional electroplating is 60%-70%.

5. Solution of each process has short applicable life and treatment cycle.

The above deficiencies are common in conventional pretreatment of aluminum and its alloys, so improvements must be made.

Improved universal aluminum and aluminum alloy electroplating pretreatment process

Two in one - degreasing alkali etching - washing - pickling - washing - ash removal - washing - alkaline activation - zinc dipping - washing - neutral nickel plating - washing - subsequent electroplating.

Four. Practice summary

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

1. Short process, through the selective dissolution of aluminum alloy surface layer of other metals to improve the purity of aluminum alloy surface, is to improve the coating adhesion.

2. Replace acid activation process with alkaline activation process to thoroughly remove the residual silicon and silica gel on the surface of the alloy in the pretreatment process of plating, so as to effectively improve the coating adhesion.

3. Direct zinc leaching without water after alkaline activation can avoid the formation of oxide layer after acid activation by water and then zinc leaching in air exposure.

4. Only one simple zinc dip can be, coating adhesion is significantly better than the secondary zinc dip and complex multiple cyanide zinc dip process.

5. Due to the wide universality of the process, it can be used for almost all brands of aluminum alloy before electroplating.

6. The one-time qualification rate of electroplating products is significantly higher than that of traditional processes.If the adhesion of pure coating is evaluated, the qualified rate of the product is close to 100%.

7. The actual production process is simple and convenient.

8. The actual production of the long-time large-scale gantry automatic production line proves that the new improved aluminum alloy electroplating pretreatment is very stable.

9. It is convenient to improve the process based on the traditional aluminum alloy electroplating process.