Interfacial characterisation of overcasting a cast Al-Si-Mg (A356) alloy on a wrought Al-Mg-Si (AA6060) alloy

The microstructure and tensile properties of hybrid Al-Si-Mg (A356) and Al-Mg-Si (AA6060) materials were investigated through overcasting. The solid bonding at AA6060/A356 interface was obtained under as-cast condition and T7 heat-treated condition. The oxide film on the surface of the AA6060 inserts was successfully removed by properly designed casting structure and optimised overcasting process. Fine equiaxed primary α-Al grains could be formed at the bonding interface, during which the primary α-Al grains in the A356 alloy were grown up on the primary α-Al grains in the solid inserts of AA6060 alloy. EBSD results revealed that these two types of primary α-Al grains exhibited the same orientation, indicating the cast A356 alloy and the wrought AA6060 alloy shared one primary α-Al grain at the interface. The interfacial bonding strength was measured at a level of 180 MPa. Heat-affected zone was not significant in the overcast structure because the decrease of the ultimate tensile strength of overcast arts was only 3-5% in comparison with the properties of the original AA6060 alloys under aged condition.