Al-20Sn-1 Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa.The characteristics of the powders are determined by means of dry sieving,scanning electron microscopy (SEM),optical microscopy (OM),and X-ray diffractometry (XRD).The results show that the powders exhibit a bimodal size distribution and a higher gas pressure results in a broad size distribution.All particles in both cases are spherical or nearly spherical and satellites form on the surface of coarse particles.Dendritic and cellular structures coexist in the particle.With decreasing particle diameter,the secondary dendrite arm spacing (SDAS) decreases and the cooling rate increases.The particles processed under high gas atomization pressure (1.6 MPa) exhibit a lower SDAS value and a higher cooling rate than those of the same size under low gas atomization pressure (1.1 MPa).The XRD results show that the Sn content increases with decreasing particle size.
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