The role of vacuum degree in the bonding of Al/Mg bimetal prepared by a compound casting process

Abstract

Lost foam casting (LFC) solid-liquid compound process has been regarded as an attractive method for preparing the Al/Mg bimetal, and the vacuum degree is an extremely important factor during the LFC process. In this work, the effects of the vacuum degree on the interfacial microstructures, mechanical properties as well as fracture behavior of the Al/Mg bimetal were systematically studied. The results show that the vacuum degree had a significant effect on the defect fraction and interface layer fraction of the Al/Mg bimetal, while the phase compositions of the interface layer were almost invariant. The defect fraction initially reduced with increasing vacuum degree and then increased when the vacuum degree exceeded 0.03 MPa, and the change rule of the interface layer fraction was opposite to that of the defect fraction. The phase distribution in the interface layer was heterogeneous, and the interface layer was divided into three regions: Al12Mg17+δ(Mg) eutectic, Al12Mg17+Mg2Si and Al3Mg2+Mg2Si. The microhardnesses of the interface layers of the Al/Mg bimetal obtained with different vacuum degrees were much higher than those of the Mg and Al matrixes. An optimal bonding was obtained with a vacuum degree of 0.03 MPa. The fracture of the Al/Mg bimetal mainly occurred in the junction zone of the Al12Mg17+Mg2Si region and the Al3Mg2+Mg2Si region, exhibiting a brittle fracture mode.