Effect of Heat Treatment on Mechanical Properties and High Temperature Properties of Extruded MgSnSiSr Alloy

In order to give a suitable heat treatment technique for as-ext ruded Mg-5Sn-2Si-2Sr alloy, the microstructure and mechanical properties of the as-extruded alloy after T4, T5, T6 heat treatm ent were investigated by means of hardness tester, the X-ray diffraction, the tensile tester and the optical microscopy. The results show that the T5 treatment is appropriate for the as-ex truded Mg-5Sn-2Si-2Sr alloy because a large amount of precipitated phases are observed on the grain boundary. The yield and tensile strengths for the alloy treated by T5 tech nique are 210.9 MPa and 257.0 MPa, respectivel y, which is higher than the alloy treated by other technique. The mechanical property is decreased after T4 treatment because the effect of softening annealing is much stronger than solid solution strengthening. The mechanical proper ties can not be improved after T6 treatment due to the increase of the second phase size and the grain growth.