Abstract
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, Mg5Gd, Al2Gd, and GdH2 phases, and the phase constituents were hardly influenced by the applied magnetic field. However, the precipitation of the paramagnetic Mg5Gd upon cooling was accelerated by the magnetic field, and that of the ferromagnetic Al2Gd phases was inhibited. In addition, the Al2Gd 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 Mg5Gd phase remained unchanged in the quenched alloy, whereas the Mg5Gd laths were significantly refined. By contrast, the contents of the Al2Gd and GdH2 phases were increased, while the precipitation sites were still within the α-Mg grains. The Mg5Gd laths were incapable of providing precipitation strengthening, while the Al2Gd and GdH2 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.
Highlights
Magnesium alloys with low density have been the focus of worldwide attention due primarily to their potential for applications in the automotive industry
SEM observations (Figure 2), the as-cast Mg–Al–Gd alloy was composed of rosette-like α-Mg, The α‐Mg+Mg5Gd eutectic structure was distributed among the α‐Mg grains, and the Al2Gd eutectic Mg5 Gd, and polygonal Al2 Gd phases, while no long period stacking-ordered (LPSO) phase was generated
Conclusions and the ferromagnetic Al2 Gd phases were investigated in the Mg–0.6Al–20.8Gd alloys, as well as the effectsofofthe the magnetic field on the content and morphology of the paramagnetic α‐
Summary
Magnesium alloys with low density have been the focus of worldwide attention due primarily to their potential for applications in the automotive industry. To overcome the problem of poor corrosion resistance for pure magnesium, rare earth (RE) elements were commonly added to the magnesium alloys, and the strength and thermal stability were significantly improved [3,4,5,6]. Researchers still put the efforts on enhancing the mechanical properties of the Mg–RE alloys, with the purpose of expanding their application fields, e.g., Materials 2020, 13, 4957; doi:10.3390/ma13214957 www.mdpi.com/journal/materials. The improvement of the mechanical properties has relied mainly on grain refinement and precipitation strengthening in Mg alloys. Zhang et al found that the Al2 RE phase hindered the dislocation climbing and grain boundary sliding for the enhanced strength of the Mg-4Al-RE alloys [9]
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