Effect of heat treatment on microstructure and mechanical properties of Mg97.5Gd1.9Zn0.6 alloy
ZHEN Rui1,2, FANG Xin-xian1,2, PI Jin-hong1,2, XU Heng-yuan1, WU Zhen1
1. School of Materials Science and Engineering, Nanjing Institute of Technology, Nanjing 211167, China;
2. Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, Nanjing 211167, China
Abstract：A ternary alloy strengthened by the phase with long period stacking ordered (LPSO) structure with composition of Mg97.5Gd1.9Zn0.6 (atom fraction/%) was prepared by conventional permanent mold casting. The microstructure evolution and mechanical properties in as-cast, as-annealed, as-extruded and extruded-T5 alloy were systematically investigated by OM,SEM,TEM and electronic universal testing machine. The results show that the as-cast microstructure of the alloy consists of the α-Mg matrix, (Mg,Zn)3Gd eutectic and lamellar 14H-LPSO phase. Annealing at 510℃ results in the transformation of (Mg,Zn)3Gd into the block-shaped 14H-LPSO phase. According to the distribution and morphology of the 14H-LPSO phase observed in the microstructure after annealing, the peritectoid transformation (Mg,Zn)3Gd +α-Mg→14H-LPSO possibly occurs during annealing. The lamellar 14H-LPSO and β' p precipitates have also been observed in the alloy during extruded-T5 treatment. Under the combined action of 14H-LPSO toughening and precipitation strengthening, the aged sample shows the best tensile properties at room temperature:ultimate tensile strength of 361 MPa, yield strength of 216 MPa and elongation of 6.9%.
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