Long Lasting Durability and Corrosion Protection
Hard sulfuric acid anodize is commonly referred to as hard-coat or hard sulfuric anodizing. This Type III anodize as designated by the Mil-A-8625 standard, results in superior hardness, abrasion and corrosion resistance as compared to other types of anodize.
Hard sulfuric anodizing is also covered in the AMS 2469 and ASTM B580 specifications. Hard anodize is processed in a refrigerated tank at higher voltages than other anodized coatings. The natural color will vary from a tan or dark gray to almost black depending on the alloy of aluminum and thickness of the coating and can be dyed to a variety of colors. Hard anodize coatings are usually thick, greater than .001, and will change the dimensions of a part by 50% of the total thickness of the deposit. (50%- penetration and 50%-buildup). After sulfuric anodizing hard anodize solutions may be sealed in hot water, sodium dichromate, nickel acetate, dewatering oil, wax or PTFE solutions.