Investigation on the Interface Characteristics of Al/Mg Bimetallic Castings Processed by Lost Foam Casting

The lost foam casting (LFC) process was used to prepare the A356 aluminum and AZ91D magnesium bimetallic castings, and the interface characteristics of the reaction layer between aluminum and magnesium obtained by the LFC process were investigated in the present work. The results indicate that a uniform and compact interface between the aluminum and magnesium was formed. The reaction layer of the interface with an average thickness of approximately 1000 μm was mainly composed of Al₃Mg₂ and Al₁₂Mg₁₇ intermetallic compounds, including the Al₃Mg₂ layer adjacent to the aluminum insert, the Al₁₂Mg₁₇ middle layer, and the Al₁₂Mg₁₇ + δ eutectic layer adjacent to the magnesium base. Meanwhile, the Mg₂Si intermetallic compound was also detected in the reaction layer. An oxide film mainly containing C, O, and Mg elements generated at the interface between the aluminum and magnesium, due to the decomposed residue of the foam pattern, the oxidations of magnesium and aluminum alloys as well as the reaction between the magnesium melt and the aluminum insert. The microhardness tests show that the microhardnesses at the interface were obviously higher than those of the magnesium and aluminum base metals, and the Al₃Mg₂ layer at the interface had a high microhardness compared with the Al₁₂Mg₁₇ and Al₁₂Mg₁₇ + δ eutectic layers, especially the eutectic layer.