Calcium is the primary agent used to enhance the apparent viscosity of molten aluminium, in order to stabilize the foam structure in liquid metal foaming process. It is also known as an effective silicon modifier in Al-Si alloys. Behind the favourable operations of the calcium, its negative effects on the oxidation behaviour of aluminium alloys threat the application of Ca-doped aluminium materials. In this study, the effects of calcium addition on the short time oxidation behaviour of the molten aluminium were investigated. The formation mechanism and consequence of several oxide particles as well as their chemical composition were indicated via several microscopy and analysis techniques. Results showed that calcium addition initially can lead to the formation of several nano-calcium aluminate particles. Such particles tend to form in regions of the aluminium oxide layer which can be affected by the mechanical tensions. Increasing the amount of calcium in the alloy will change the oxidation behaviour, and promotes the formation of compound oxide layers which can be characterized based on their brittle nature and relatively large thickness
