Abstract:Foil powders of Al-5.0-Cr-4.0-Y-1.5-Zr (%) were prepared by using a multi-stage atomization-rapid solidification powder-making device. The obtained powders were exposed thermally at various temperatures. Variation of microstructures and properties of the alloy powders was investigated by micro-hardness measurement, X-ray diffraction, differential thermal-analysis, and transmission electron microscopy with energy disperse X-ray analyses. The results show that cubic Al₂₀Cr₂Y (a=1.437nm) and metastable Ll₂ Al₃Zr (FCC, a=0.4051nm) or equilibrium DO₂₃ Al₃Zr (tetragonal structure, a=0.4091nm, b=1.730nm) are main second phases precipitated from supersaturated solid solution of the rapidly solidified foil powders during thermal exposure. The cubic dispersion precipitates prior to the two other Al₃Zr type intermetallic phases in the course of the decomposition. Precipitation of incoherent Al₂₀Cr₂Y results in softening of foil powder, and coherent Ll₂ Al₃Zr has intensive precipitation strengthening effect. The Al₂₀Cr₂Y phase is structurally stable, but it is prone to coarsen and polygonize above 450℃. Both Al₃Zr type intermetallic phases have much smaller coarsening rate than Al₂₀Cr₂Y at temperature higher than 450℃. These two phases are able to keep their fine spherical morphologies up to 550℃, but Al₃Zr transforms into DO₂₃ structure from Ll₂ structure during thermal exposure above 550℃. 

Key words: rapid solidification; heat-resistant Al alloy; decomposition behavior; precipitation hardening effect