Zn alloy casting industry using green sand molding is increasingly becoming to very competitive circumstance, due to the various casting methods such as die cast, sand mould and so on with the recent coming of the lightening demand in automotive and decorative industry. So, this project is to produce tertiary alloy of Zinc-Aluminium-Magnesium (Zn-3Al-2Mg) with different composition of bentonite and silica sand in the green sand mould. However, Zn alloy casting using green sand still now plays an important role in the foundry society, because it allows us to manufacture at low cost and also sand can be recycled. Furthermore, it is appropriate method for multi kind and small quantity production. The mentioned method of mold is differing in composition of bentonite with 5%-17%. Differ in the composition of bentonite and silica sand give differ in result. Sample with 13% of bentonite is the best surface properties while sample of 5% and 17% of bentonite gave dull surface properties. The morphologies give not much difference from each other. Sample of 13% of bentonite have the most amount of grain boundaries and the grain boundaries size is much bigger than the others.
