Effect of homogenization treatment on microstructure and mechanical properties of Mg-13Gd-3.5Y-2Zn-0.5Zr magnesium alloy

Abstract

Homogenization heat treatment on the as-cast Mg-13Gd-3.5Y-2Zn-0.5Zr magnesium alloy was carried out with the temperature range of 505-525℃ and the time range of 4-24h. Optical microscope(OM), scanning electron microscope(SEM), X-ray diffractometer(XRD) and universal material experiment machine were used to analysize the changes of microstructure evolution and mechanical property before and after homogenization. The results show that the reticular eutectic compounds in initial grain structure are transformed into discontinuous bulk-shaped LPSO (long-period stacking ordered) phases at the grain boundary and the discrete distribution of the square-shaped rich rare-earth phases dissolved. The mechanical properties test results show that the ultimate tensile strength and the elongation of the cast magnesium alloy are 172.9MPa and 1.8%, respectively. The mechanical properties of the alloy are improved after homogenization, the ultimate tensile strength of room temperature is 212.3MPa and the elongation is 3.1% under the homogenization of 515℃/16h. At the same time, the ultimate tensile strength of high temperature at 200℃ reaches the highest 237.2MPa and the elongation is 9.7%. The fracture microstructure of as-cast alloy indicates that the fracture is cleavage brittle fracture dominated by tearing edges and cleavage steps, small and shallow dimples occur in the alloy after homogenization treatment, but is still quasi-cleavage fracture dominated by cleavege steps, and limited plasticity is improved. Meanwhile, LPSO phase can be the crack initiation source.

Keywords

• Mg-13Gd-3.5Y-2Zn-0.5Zr magnesium alloy
• homogenization
• microstructure
• mechanical property