Analysis of the Formation of Light Spots on the Surface of Die-cast Magnesium Alloy Components

After chemical conversion treatment of magnesium die-cast components,light spots often appear on their surfaces.The reason for such a problem was analyzed.It shows hot spots formed on the die surface during casting process decrease the solidification velocity of molten magnesium and big primary α phase is formed on the surface of casting.The different corrosion resistance of primary α phase and eutectic microstructure(α+β) makes the composion of chemical conversion coating different, so that the surface with primary α phase is discolored and light spots appear.