Effect of insert materials on microstructure and mechanical properties of Al/Mg bimetal produced by a novel solid-liquid compound process

A novel lost foam casting solid-liquid compound method was developed for the preparation of the A356 aluminum alloy/AZ91D magnesium alloy bimetal (Al/Mg bimetal), and the effect of insert materials on microstructure and mechanical properties of the Al/Mg bimetal was studied in this paper. Obtained results indicated that the insert materials played a great role in the bonding of the Al/Mg bimetal. The Al/Mg bimetal with a defect-free and uniform metallurgical interface was achieved by use of the A356 aluminum alloy solid insert. With an optimized parameter in the condition of the AZ91D magnesium alloy solid insert, the Al/Mg bimetal also obtained a metallurgical bonding. Nevertheless, the crack defects were always found in the interfaces of the bimetallic samples produced with the AZ91D solid insert. The formation mechanism of the crack were proposed by stress distribution, thermodynamics and intermetallic compounds (IMCs) analyses. The microstructures exhibited that the interfaces of the bimetallic samples prepared with different insert materials were constituted by Al3Mg2+Mg2Si layer, Al12Mg17+Mg2Si layer as well as Al12Mg17+delta-Mg eutectic layer. The Al/Mg bimetal produced with the A356 solid insert possessed a much higher bonding strength compared to the bimetal obtained with the AZ91D solid insert, whereas their hardnesses were basically same. The fractured samples produced with different insert materials showed brittle fracture morphologies, and the fractures primarily occurred between the Al3Mg2+Mg2Si layer and Al12Mg17+delta-Mg eutectic layer.