Study on Process of Mixed-acid Electrolytic Coloring for A390 Aluminum Alloy as Vehicle Casting Material

摘要

A390 aluminum alloy with high Si content was used as vehicle casting material and adopted to cast the stepped-type castings in this study. The castings were electrolytic coloring anodized in the mixed-acid of H_2SO_4, CuSO_4 and FeSO_4. The parameters studied include casting thickness, current density and electrolytic coloring anodizing time. The effects of these parameters on the oxide film will be evaluated to establish the optimal process conditions in this kind of surface treatment for the A390 aluminum alloy vehicle castings. The oxide film thickness of stepped-type casting increases with the increase of anodizing time, but, its microhardness decreases conversely. The condition to acquire maximum thickness of oxide film is 3.9 A/dm~2 for the current density and 65 minutes for the anodizing time, while the condition to attain to maximum microhardness of oxide film is 1.3 A/dm~2 and 15 minutes. The optimal conditions for thick section of stepped-type casting to produce bright yellowish color on oxide film is 2.6 A/dm~2 and 27.5 minutes, but for thin and medium sections, the optimal conditions to obtain the same color is 2.6 A/dm~2 and 15 minutes.