Effect of beryllium addition and heat treatment on the microstructure and mechanical properties of the 15%Mg2Si/Al-8Si composite

Abstract

In the present work, the effect of beryllium (Be) addition (0, 0.3, 0.6, 1.0, 1.5 and 2.0 wt%) on the microstructure and mechanical properties of the 15%Mg2Si/Al-8Si composite has been investigated. With the addition of Be, the morphology of the primary Mg2Si particles changed from dendritic to regular, the eutectic Si phase was refined remarkably, and the size of the Mg2Si phase was decreased evidently. With addition of 1.5%Be, the mean grain size of α-Al decreased from ~24 μm to ~13 μm and the finest eutectic Si phase were obtained, in the meantime, the Mg2Si particles were present in fully modified square to spherical. In addition, it was proposed that the according to the microstructure analysis, the BeO phases might be responsible for the modification of Mg2Si phases. With addition of 1.5%Be, the maximum improvement of the mechanical properties was achieved, and the corresponding Be-modified alloys in T6 heat treated condition obtained the best tensile properties compared with other experimental alloys, with the corresponding yield strength(YS), ultimate tensile strength(UTS) and elongation(EL) values being 178.2 MPa, 282.0 MPa and 5.1%, respectively. Meanwhile, the shear properties of 1.5% Be-modified and T6 heat treated is improved compared with the un-modified alloy, with the corresponding shear stress (SS) and deformation rate(DR) being 161.0 MPa and 36.3%. Furthermore, the 1.5% Be-modified and T6 heat treated is improved compared with the un-modified alloy, the wear amount and friction coefficient decrease to 0.55mm3 and 0.5, suggesting it can be a good candidate for the commercial applications.