Quench-solidifed Al-Si alloy powder which contains more than 12 wt % Si is preformed, and the preforming is compression-molded into an aluminum alloy part. The aluminum alloy part is repeatedly subjected to a heating-and-cooling cycle of heating the aluminum alloy part to a temperature between 440.degree. C. and 500.degree. C. and cooling it to a temperature not higher than 380.degree. C.