Influence of high pressure during solidification on the microstructure and strength of Mg-Zn-Y alloys

The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction (XRD) and Vickers-hardness testing. Under atmospheric-pressure solidification, Mg-6Zn-1Y consisted of α-Mg, Mg7Zn3 and Mg3YZn6; whilst Mg-6Zn-3Y consisted of α-Mg, Mg3Y2Zn3 and Mg3YZn6. Under 6 GPa high-pressure solidification, both alloy consisted of α-Mg, MgZn and Mg12YZn. The shape of the main second phase changed from a lamellar structure formed for atmospheric-pressure solidification to small particles formed for solidification at 6 GPa pressure. The dendrite microstructure was refined and was more regular, and the length of the primary dendrite arm increased under 6 GPa high-pressure solidification, which was attributed to increasing thermal undercooling, compositional undercooling and kinetics undercooling. After solidification at 6 GPa pressure, the solid solubility of Y in the second phase and the Vickers-hardness increased from 15 wt.% and 69 MPa for Mg-6Zn-1Y to 49 wt.% and 97 MPa; and from 19 wt.% and 71 MPa for Mg-6Zn-3Y alloy to 20 wt.% and 92 MPa, respectively.

Graphical AbstractXRD patterns after atmospheric-pressure (A.P.) solidification, and high-pressure (6 GPa) solidification for Mg-6Zn-1Y (a) and the Mg-6Zn-3Y (b)Figure optionsDownload as PowerPoint slide