Precipitation and Excess Solid Solubility in Mg-Al-Zr and Mg-Zn-Zr Processed bySpray Atomization and Deposition

摘要

The microstructures of two magnesium alloys (Mg-5.6wt.%Zn-0.3wt.%Zr and Mg-8.4wt.%Al-0.2wt.%Zr) processed by spray atomization and deposition were examined and subsequently correlated with the processing history. The microstructural characterization was accomplished utilizing semi-quantitative energy-dispersive X-ray analysis (EDAX), scanning electron microscopy and X ray diffraction analysis. The microstructure of the as-spray-deposited Mg-Zn-Zr alloy consisted of relatively coarse 950-100 microns) equiaxed cells. Lattice parameter measurements using X ray diffraction revealed a super-saturated solid solution of zinc in the magnesium matrix. The presence of the Mg7Zn3 phase at the cell boundaries of the Mg-Zn-Zr alloy was confirmed through semiquantitative EDAX analysis. The microstructure of the Mg-Al-Zr alloy in the as-deposited condition consisted of relatively coarse cells of magnesium surrounded by an intergranular eutectic microconstituent which was identified as (Mg)+Mg17Al12; X-ray diffraction results also revealed a supersaturated solid solution of aluminum in the magnesium matrix. The aforementioned microstructural features were related to the solidification conditions of the droplets at the moment of impact with the substrate; these conditions were computed from previously developed numerical models. Furthermore, the effect of the magnitude of K sub m on the computed fraction solidified as a function of flight distance is discussed.