Effects of Static Magnetic Field on Compression Properties of Mg-Al-Gd Alloys Containing Gd-Rich Ferromagnetic Phase

The Mg–0.6Al–20.8Gd (wt.%) alloys were homogenized at 620 °C for 20 min under 0 T and 1 T, followed by furnace cooling, quenching, and air cooling, respectively. The effects of the magnetic field on the phase constituent, microstructure, secondary phase precipitation, and mechanical properties of the Mg–Al–Gd alloys were investigated. The Mg–Al–Gd alloys contained α-Mg, Mg(5)Gd, Al(2)Gd, and GdH(2) phases, and the phase constituents were hardly influenced by the applied magnetic field. However, the precipitation of the paramagnetic Mg(5)Gd upon cooling was accelerated by the magnetic field, and that of the ferromagnetic Al(2)Gd phases was inhibited. In addition, the Al(2)Gd phase was significantly refined and driven to segregate at the grain boundaries by the magnetic field, and the resultant pinning effect led to the microstructure change from dendritic α-Mg grains to rosette-like ones. When the magnetic field was only applied to the homogenization stage, the content of the Mg(5)Gd phase remained unchanged in the quenched alloy, whereas the Mg(5)Gd laths were significantly refined. By contrast, the contents of the Al(2)Gd and GdH(2) phases were increased, while the precipitation sites were still within the α-Mg grains. The Mg(5)Gd laths were incapable of providing precipitation strengthening, while the Al(2)Gd and GdH(2) particles brought positive effects on the enhancement of the mechanical properties. In the quenching condition, the hardness, compression strength, and ductility can be improved by the magnetic treatment, whereas these mechanical properties can be suppressed in the furnace cooled condition by the magnetic treatment.