Reasons for anodic oxidation of aluminum alloy die castings
Aluminum alloys are not recommended for anodizing and electroplating. Why is this? Because the surface of aluminum alloy die castings is easy to produce gas streaks, cold separation, sand holes and other defects. The general anodes should be changed to aluminum extruded materials, electroplated to zinc aluminum alloys or zinc alloys.
The so-called anodic oxidation of aluminum is an electrolytic oxidation process in which the surface of aluminum and aluminum alloys is usually converted into an oxide film, which has protective, decorative and some other functional characteristics. Anodizing of aluminium from this definition involves only part of the process of forming an anodic oxide film.
Using metal or alloy parts as anode, electrolysis is used to form oxide film on the surface. Metal oxide films change the surface state and properties, such as surface coloring, improving corrosion resistance, enhancing wear resistance and hardness, protecting metal surface, etc. For example, aluminum anodization, aluminum and its alloys in the corresponding electrolyte (such as sulfuric acid, chromic acid, oxalic acid, etc.) as an anode, under specific conditions and applied current, electrolysis. Anodic aluminum or its alloys are oxidized to form a thin layer of alumina with a thickness of 5-30 microns and a hard anodic oxide film of 25-150 microns. The hardness and wear resistance of anodized aluminium or its alloys are improved, up to 250-500 kg/square millimeter, good heat resistance, melting point of hard anodic oxide film as high as 2320 K, excellent insulation, breakdown voltage as high as 2000V, and corrosion resistance is enhanced. It does not corrode in_=0.03NaCl salt spray for thousands of hours. The thin layer of oxide film has a large number of micro-pores, which can absorb various lubricants, and is suitable for making engine cylinders or other wear-resistant parts. Nonferrous metals or their alloys (such as aluminum, magnesium and their alloys) can be anodized. This method is widely used in mechanical parts, aircraft and automotive parts, precision instruments and radio equipment, daily necessities and building decoration.
Anodizing of aluminum alloys in the existing process is still a difficult problem. Electroplating can be done by some manufacturers, usually plating a layer of zinc, then copper plating bottom, and then electroplating. The cost is too high and the yield is low.
A general term for aluminum based alloys. The main alloying elements are copper, silicon, magnesium, zinc, manganese, and the minor alloying elements are nickel, iron, titanium, chromium, lithium and so on. Aluminum alloy is one of the most widely used non-ferrous metal structural materials in industry. It has been widely used in aviation, aerospace, automobile, machinery manufacturing, shipping and chemical industry.
