The surface treatment process of aluminum alloy castings for ice boxes is designed around anti oxidation, anti corrosion, improving durability, and adapting to usage scenarios. The core processes include anodizing, spraying, passivation, electrophoretic coating, and chemical conversion coating. Each process optimizes surface performance through different principles to meet the needs of ice boxes in low-temperature storage, humid environments, and possible food contact scenarios.
Anodizing is a widely used core process that forms a dense oxide film (mainly composed of Al ₂ O3) on the surface of aluminum alloy through electrolysis. The thickness of ordinary anodic oxide film is usually 5-20 μ m, and the surface hardness can reach 200-300HV, which can effectively resist collisions and scratches, and avoid surface damage during ice box use. The thickness of the hard anodized film can be increased to 20-50 μ m, and the hardness can reach 400-600HV, making it suitable for ice box components with high wear resistance requirements. This process can achieve various appearance effects such as natural color and dyeing. Natural color oxidation maintains the metallic texture, while dyeing oxidation can match different design requirements. The surface of the ice box treated with anodizing is not easily discolored due to contact with ice cubes or water stains, and its performance is stable within the temperature range of -20 ℃ to 60 ℃. The film layer will not peel off, and some anodizing processes that meet food contact standards can be directly used on the surface of ice boxes that come into contact with food ingredients.
The spraying process is divided into powder spraying and liquid spraying, focusing on improving weather resistance and decorative properties. Powder spraying evenly adheres powder coating to the surface of castings through electrostatic adsorption, and solidifies at high temperatures of 180-220 ℃ to form a paint film with a thickness of 20-60 μ m. The adhesion is strong, and the scratch test can reach level 1 or above. It can resist UV and humid environment erosion, and has a wide range of color options that can be customized according to needs. Liquid spraying uses solvent based or water-based coatings, which are flexible in application and suitable for complex shaped ice box castings. The paint film is smooth and delicate, and the decorative effect is outstanding. The spraying process can completely isolate air and moisture, prevent aluminum alloy corrosion, and the paint film has a certain degree of flexibility, which can buffer the impact caused by slight collisions. It is suitable for outdoor use or ice boxes with high appearance requirements. Water based coatings are more in line with environmental protection requirements and do not release volatile harmful substances.
Passivation treatment is a basic anti-corrosion process that forms a thin and dense passivation film (chromate or chromium free passivation film) on the surface of aluminum alloy through chemical immersion, with a film thickness of only 0.5-2 μ m. This process is simple to operate and cost-effective. The passivation film can slow down the oxidation rate of aluminum alloy, prevent the appearance of white rust on the surface, and provide a good foundation for subsequent coatings. The chromium free passivation process avoids heavy metal pollution and is more suitable for environmental protection and food contact requirements. It is often used as a pre-treatment step for spraying and electrophoresis to improve the adhesion of subsequent coatings and extend the overall protection life. For ice boxes that only require basic anti-corrosion and have low appearance requirements, or for scenarios that require cost control in mass production, passivation treatment is an economical and practical choice.
Electrophoretic coating deposits coating particles on the surface of aluminum alloy through the action of an electric field, forming a uniform paint film with a thickness of 10-30 μ m. The advantage of this process is that the paint film has good density and excellent corrosion resistance. The neutral salt spray test can withstand corrosion for more than 500 hours, and the paint film color is uniform and consistent without defects such as sagging or pinholes. It is suitable for complex shaped ice box castings and can ensure uniform protection in every corner. The electrophoretic paint film has a smooth surface, is easy to clean, and is not easily stained. It is suitable for ice boxes with high corrosion resistance requirements, such as long-term storage of damp items or frequent outdoor use. Its protective effect is long-lasting and stable, which can effectively extend the service life of the ice box.
The chemical conversion coating process is mainly used as an auxiliary treatment to form a conversion film on the surface of aluminum alloy through chemical immersion, with a film thickness of 0.1-1 μ m. Although it has weak corrosion resistance, it can significantly improve the adhesion between the subsequent coating and the substrate, and prevent coating detachment. This process is divided into phosphate chromate type, chromium free type, etc. Chromium free type is more environmentally friendly and suitable for production scenarios with strict environmental requirements. In the production of ice boxes, chemical conversion coatings are often used in conjunction with spraying and electrophoresis processes as a pre-treatment step to make the paint film more firmly bonded to the surface of the casting, avoiding paint film peeling due to low temperature environments or collisions, and ensuring the durability of the overall protective effect.
The selection of different processes should be based on actual needs. Anodizing is suitable for wear-resistant and food contact scenarios, spraying focuses on appearance and weather resistance, passivation is suitable for basic anti-corrosion or base treatment, electrophoretic coating balances protection and decoration, and chemical conversion film serves as an auxiliary process to enhance coating adhesion. Multiple processes can be combined to achieve a balance between protective performance and practical needs, meeting the requirements of different ice box product usage scenarios.
