Solidification Structure And Mechanical Properties Of Mg-13Zn-17Y Alloy Under High Pressure

Alloy Mg-13Zn-17 Y is the research object in this paper. OM, SEM, TEM, XRD and EDS are used to analyze the microstructure and phase of the alloy. Then based on the analysis, the influence of pressure(atmospheric pressure, 1GPa, 2GPa, 3GPa) on the solidification structure, phase and mechanical properties of the alloy is studied in the paper.As the results shows, after as-cast homogeneous, the microstructure of the alloy is composed of α-Mg, 14 H and Mg24Y5. α-Mg solid solution grow in the dendritic crystal form, but the 14 H is lath-shaped in this case. The Mg-13Zn-17 Y alloy that made in atmospheric solid solution is composed in α-Mg and 14 H phase. α-Mg solid solution is also growth in the dendritic crystal form and the 14 H has been lath-shaped. With the growth of the solid solution time, the dendrite arm length of α-Mg decreases and the wide strip of 14 H phase becomes thin.After high-pressure solid solution, the alloy is composed of α-Mg, 14 H and S phase. With the increase of the solid solution pressure, the dendrite arm length of α-Mg increases and the wide strip of 14 H phase becomes thin, S phase is from fine flake into fine needle shape. In this situation, the content of Zn atoms in α-Mg solid solution increases from 1.43at% in 1GPa to 2.25at% in 3GPa, however, the content of Y decreases from 3.11at% in 1GPa to 2.64at% in 3GPa.The Mg-13Zn-17 Y alloy that formed in low superheat and 1 or 2GPa pressure is composed of α-Mg and S phase. α-Mg phase grow in the dendritic crystal form and its first dendritic arms and secondary dendrite arms are short. S and α-Mg phase form eutectic layer microstructures which are mutual crisscross and connected into a net. When the pressure is 3GPa, the alloy microstructure is composed of α-Mg, 14 H and S phase. With the increase of pressure, the volume fraction of S phase in the alloy increases gradually.The Mg-13Zn-17 Y alloy that formed in high superheat and 1 or 2GPa pressure is also composed of α-Mg and S phase. The α-Mg and S phase are growth in eutectic layer shape. When the pressure is 3GPa, the alloy microstructure is composed of α-Mg, 14 H and S phase, meanwhile, a small amount of 14 H generated around the S phase. With the increase of the solidification pressure, the tensile strength of the alloy shows a trend of increase and reaches the maximum at 2GPa. Meanwhile, the elastic modulus and microhardness of the alloy increase gradually, and the fracture mode of the alloy tends to change from cleavage fracture to quasi cleavage fracture gradually.