Improvement of Hard Anodizing Process for Low Surface Roughness ZL105A Sand-Cast Aluminum Parts

By analyzing the reasons for the increase of surface roughness of ZL105A sand-cast aluminum after hard anodic oxidation and grinding, and optimizing the hard anodic oxidation solution, a hard anodic oxidation solution containing oxalic acid, sulfuric acid and passivator was developed. The results showed that macro holes appearred on the surface of ZL105A sand-cast aluminum parts after traditional hard anodizing and grinding, which was the root cause of unqualified surface roughness. The passivation agent in the developed hard anodizing solution could inhibit the growth of micropores. After treatment with the oxidation solution, a hard anodizing film with a surface roughness of 0.2-0.4 μm and a hardness higher than 300 HV was obtained.