Influence of atomized powder size on microstructures and mechanical properties of rapidly solidified Al–Cr–Y–Zr aluminum alloys

Rapidly solidified powders of Al–5.0Cr–4.0Y– 1.5Zr (wt%) were prepared by using a multi-stage atomization- rapid solidification powder-making device. The atomized powders were sieved into four shares with various nominal diameter level and were fabricated into hotextruded bars after cold-isostatically pressing and vaccum degassing process. Influence of atomized powder size on microstructures and mechanical properties of the hot-extruded bars was investigated by optical microscopy, X-ray diffraction, transmission electronic microscopy with EPSX and scanning electron microscopy. The results show that the fine atomized powders of rapidly solidified Al–5.0Cr– 4.0Y–1.5Zr aluminum alloy attains supersaturated solid solution state under the exist condition of multi-stage rapid solidification. With the powder size increasing, there are Al20Cr2Y (cubic, a = 1.437 nm) and Ll2 Al3Zr (FCC, a = 0.407 nm) phase forming in the powders, and even lumpish particles of Al20Cr2Y appearing in the coarse atomized powders, as can be found in the as-cast master alloy. Typical microstructures of the extruded bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy can be characterized by fine grain FCC a-Al matrix with ultra-fine spherical particles of Al20Cr2Y and Al3Zr. But a small quantity of Al20Cr2Y coarse lumpish particles with micro-twin structures can be found, originating from lumpish particles of the coarse powders. The extruded bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy by using the fine powders eliminated out too coarse powders have good tensile properties of r0.2 = 403 MPa, rb = 442 MPa and d = 9.4% at room temperature, and r0.2 = 153 MPa, rb = 164 MPa and d = 8.1% at high temperature of 350 C.