Effect of Surface Treatment on Glossiness of Al-Mg-Zn Alloy Casting

In this study, the effects of various surface treatments on the glossiness of AC4CH-T6 casting and newly developed bright aluminum alloy casting were examined. With the AC4CH-T6 casting, it was difficult to obtain a bright surface by buffing, because of the surface irregularity between the hard eutectic silicon and the aluminum matrix. On the other hand, with the developed silicon-free alloy casting, it was possible to produce a bright surface by buffing, and this glossiness was superior to that of the AC4CH-T6 casting covered with the decorative chrome electroplating. The glossiness of the developed casting decreased sharply after chemical polishing, depending on the generation of local dissolution close to the intermetallic compound and pin-hole. However, electropolishing under an optimum conditions helped realize a smooth and bright surface. As with the anodization from sulphuric acid solution, glossiness of the developed alloy casting decreased because of the prior dissolution of the intermetallic compound. However, anodization from the developed solution suppressed this dissolution, forming a uniform oxide film. As a result, bright surface could be produced for the developed alloy casting by anodization.