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Aluminum alloy surface treatment - hard anodizing of 7 series aluminum

August 17, 2023
1. Process overview
The full name of hard oxidation is hard anodizing treatment, which takes the corresponding electrolyte of the alloy (such as sulfuric acid, chromic acid, oxalic acid, etc.) as the anode, and electrolytes under certain conditions and impressed current. Hard anodized film thickness of 25-150um, film thickness of less than 25um hard anodized film, mostly used in tooth keys and spiral parts, most of the hard anodized film thickness requirements of 50-80um, wear or insulation anodized film thickness of about 50um. Under some special process conditions, it is also required to produce a hard anodized film with a thickness of more than 125um, but it must be noted that the thicker the anodized film, the lower the microhardness of its outer layer and the increased roughness of the film surface.
Second, process characteristics
1. The surface hardness of aluminum alloy after hard oxidation can be up to about HV500;
2. Oxide film thickness: 25-150 microns;
3. Strong adhesion, according to the oxidation characteristics generated by hard oxidation: the generated oxygen film has 50% penetration in the aluminum alloy, 50% attached to the aluminum alloy surface (two-way growth);
4. Good insulation: breakdown voltage up to 2000V;
5. Good wear resistance: for aluminum alloy with copper content not exceeding 2%, the maximum wear index is 3.5mg/ 1000 RPM. All other alloys wear index should not exceed 1.5mg/ 1000 cycles.
6. Non-toxic, harmless to human body. The electrochemical process of anodized film treatment for production is harmless, so many industrial machining in order to environmental protection requirements, some products use hard anodized aluminum alloy instead of stainless steel, instead of traditional spraying, electroplating hard chromium and other processes.
3. Application fields
Hard oxidation is mainly suitable for areas requiring high wear resistance, heat resistance, and good insulation properties of aluminum and aluminum alloy parts. Such as various cylinder blocks, pistons, valves, cylinder linings, bearings, aircraft cargo holds, tilting rods and guides, hydraulic equipment, steam impels, comfortable flatters, gears and buffers. The traditional electroplating of hard chromium has the characteristics of low cost, but the defect of this film is that the thickness of the film is large, which affects the measurement of mechanical fatigue strength of aluminum and aluminum alloys.
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