Influences of Al and high shearing dispersion technique on the microstructure and creep resistance of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn alloy

Abstract

Effects of 0.25% Al addition and the high shearing dispersion technique (HSDT) on the microstructure and creep resistance of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (Elektron21, El21) alloy were investigated. Compressive creep testes were performed at 240 °C over a stress range between 80 and 140 MPa. The results indicate that the creep resistance of El21 was significantly improved by about one order of magnitude with the addition of 0.25% Al and HSDT than that of El21 without Al and HSDT. Microstructural characterizations show that the grains were coarsened from 80.1 ± 5.0 to 167.0 ± 5.7 μm due to the loss of grain refiner Zr by the chemical reaction of Al with Zr. With the addition of 0.25% Al to El21, the grain morphology was changed from equiaxed to typical dendrite. The morphology of intermetallic Mg3RE was modified from network to a pronounced dendritic structure. Owing to the employment of HSDT, the dendrite arm spacing of primary α-Mg was refined from 74.0 ± 6.4 to 56.2 ± 1.6 μm in Al-containing El21 alloy, the dominant Al–Zr compound changed from Al2Zr3 to Al2Zr phase. A small amount of Al2Nd phase was formed. Creep data analysis indicates that the dominant controlling mechanism for H-El21A alloy is dislocation climb during creep deformation. Its superior creep resistance was mainly attributed to the pronounced and dense dendritic structure of Mg3RE intermetallic in the α-Mg hindering the grain boundary sliding and dislocation movement. In addition, the relative homogeneous dispersion of Al2Zr phase and Al2Nd phase with a high melting point can also act as efficient reinforcements to inhibit the dislocation movement and benefit the creep properties.