Analysis of Common Surface Treatment Processes for Aluminum Alloy Die Castings

Analysis of Common Surface Treatment Processes for Aluminum Alloy Die Castings

Aluminum alloy die castings are widely used in automotive, electronics, home appliance and other fields due to their advantages of light weight and high strength. However, after die casting, the surface is prone to problems such as pores and oxide layers, so surface treatment is required to improve performance and appearance. The following are five mainstream surface treatment processes:

The anodic oxidation process is one of the most widely used processes. It forms an oxide film by placing the die casting in an electrolyte solution as the anode and passing a direct current. The thickness of this oxide film can reach 5-20μm. It not only endows products with various colors such as silver white and bronze, but also significantly improves corrosion resistance and wear resistance. It is commonly used in products with high requirements for appearance and durability, such as mobile phone middle frames and household hardware.

The electroplating process deposits a metal coating on the surface of die castings through electrolysis. Common coatings include chromium, nickel, zinc, etc. The electroplating layer is uniform and dense, which can enhance the decoration and electrical conductivity of products. For example, chrome plating is often used for automobile door handles, which not only improves the glossiness but also resists external corrosion; electronic components usually achieve good electrical conductivity through zinc plating. However, the electroplating process has strict requirements for pre-treatment. It is necessary to remove surface oil stains and oxide layers first to ensure the adhesion of the coating.

The spraying process is divided into powder spraying and liquid spraying. It forms a film by uniformly spraying paint on the surface of die castings and curing it. Powder spraying has no solvent pollution, and the coating thickness is uniform (usually 60-120μm) with strong impact resistance, which is suitable for products such as outdoor lamps and home appliance casings; liquid spraying can achieve a more delicate surface effect and can be formulated into various textures such as matte and high gloss to meet different design needs.

The chemical conversion coating process does not require electricity. It forms a protective film through the reaction between the die casting and a chemical solution. Common ones include chromate conversion coatings and chromium-free conversion coatings. This process is simple to operate and low in cost. The coating is thin and does not affect the dimensional accuracy of the product. It is mainly used to improve the adhesion of subsequent coatings or as a temporary protective layer, and is suitable for mass-produced small parts.

The polishing process improves the surface roughness of die castings through mechanical grinding or chemical action, and is divided into mechanical polishing, chemical polishing and electrolytic polishing. Mechanical polishing can quickly remove surface defects and achieve a mirror effect; chemical polishing does not require complex equipment and is suitable for parts with complex shapes; electrolytic polishing can further improve the surface finish and corrosion resistance, and is often used in fields with extremely high surface precision requirements such as medical devices and precision instruments.

Different surface treatment processes have their own advantages. In practical applications, comprehensive selection should be made based on the product's application scenario, performance requirements and cost budget to achieve the dual improvement of the function and appearance of aluminum alloy die castings.