An aluminum alloy is prepared from an aluminum alloy powder having a composition of:lubricating componentPb: 3 to 15 Wt %;hardening componentSi: 1 to 12 Wt %;rainforcement componentone or more selected among Cu, Cr, Mg, Mn, NiZn, Fe and: 0.2 to 5.0 Wt %;and remainder of aluminum as principal material or matrix.To the aluminum alloy powder set forth above, powder state Pb in 3 to 12 Wt % is added. With the mixture of the aluminium alloy powder and Pb powder, a billet is formed. For the billet, extrustion process is performed in a extrusion ratio greater than or equal to 40. In the extruded block, Si particle dispersed in the aluminum matrix is in a grain size smaller than or equal to 12 .mu.m. Furthermore, at least of half of added Pb power particle is dispersed to have greater than or equal to 0.74 of circularity coefficient.