Microstructure and mechanical properties of Mg97Zn1Y2 alloy reinforced with LPSO structure produced by semisolid squeeze casting

Effects of semisolid squeeze casting (SSC) process on microstructures and mechanical properties of the LPSO structure reinforced Mg₉₇Zn₁Y₂ alloy were studied by optical microscopy, SEM equipped with EDS, TEM, XRD and Nanoscale indentation for the first time. The LPSO structure and α-Mg grains in the Mg₉₇Zn₁Y₂ alloy can be refined significantly by SSC. The gran size of α-Mg was decreased from 170 µm to 109 µm, and the LPSO structure could be distributed uniformly in the alloy under the combined action of ultrasonic vibration (UV, preparation for semisolid slurry) and squeeze casting (SC). The type of LPSO structure was remained as the initial 18R-type structure after SSC, but a strip YZn₃ phase precipitated out inner the block LPSO structure, which has never been found in the LPSO-containing Mg₉₇Zn₁Y₂ alloy. With the increase of squeeze pressure, the amount of YZn₃ phase was increased and the tensile strength and elongation of the alloy were increased at first and then maintained nearly constant. When the pressure was 100 MPa, the optimum mechanical properties were obtained. The yield strength, ultimate tensile strength and elongation were 141 MPa, 234 MPa and 11.6%, which were enhanced by 28.2%, 11.1% and 45.1%, respectively, compared with those of the alloy without SSC.