Droplet-based processing of magnesium alloys for the production of high-performance bulk materials
Permanent URL:
http://hdl.handle.net/2047/d20000640
Wong, Peter (Committee member)
Jung, Yung Joon (Committee member)
Three Mg-Zn-Y alloys, Mg97Zn1Y2, Mg88Zn10Y2 and Mg76.5Zn20Y3.5, were chosen for this research to investigate the potentials for the droplet-based processing of high-performance alloys by the UDS process. Spray deposits produced with uniform (mono-size) droplets 700-1000 μm in diameter were characterized by full density and fine equiaxed grains, in contrast to the coarse dendritic structure of the original cast ingot. While the primary equiaxed grains were the HCP Mg-rich solid solution in the deposits of all three compositions, the Mg97Zn1Y2 deposits also had X-phase, and the Mg88Zn10Y2 and Mg76.5Zn20Y3.5 deposits had the I- and W-phases in the intergranular regions. The primary grains in the Mg97Zn1Y2 deposits exhibited striations indicative of X-phase precipitation on basal planes. The occurrence of I-phase in the Mg88Zn10Y2 and Mg76.5Zn20Y3.5 alloys is in line with previous reports on the existence of a pseudo-binary system between Mg and I-phase.
Subsequent thermomechanical processing of the spray deposits by rolling resulted in further microstructural refinement and improved room- and elevated- temperature strength, especially in the case of Mg97Zn1Y2 which had a room-temperature tensile strength of 340 MPa and an elevated-temperature (473K) tensile strength of 271 MPa. The other two alloys, Mg88Zn10Y2 and Mg76.5Zn20Y3.5, respectively, had 305 MPa and 271 MPa at room temperature, and 237 MPa and 216 MPa at 473 K. These strength values significantly exceed those of commercial wrought Mg alloys, which typically range 200 MPa to 300 MPa at room temperature and 150 MPa to 200 MPa at 473 K. Although the process parameters still need to be further optimized, UDS processing, combined with thermomechanical processing, enables safe and effective processing of high-performance magnesium alloys.
Mg-Zn-Y
UDS
W-Phase
X-Phase
Engineering
Mechanical Engineering
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