Al-si alloys and method of casting

Abstract

A cast hypereutectic Al-Si alloy having 12% to 15% Si, and a method of producing such alloy. The alloy and a melt used in the method has at least one element of a first group of elements and at least one element of a second group of elements and further comprises Cu 1.5 to 5.5%; Ni 1.0 to 3.0%; Mg 0.1 to 1.0%; Fe 0.1 to 1.0%; Mn 0.1 to 0.8%; Zr 0.01 to 0.1; Zn 0 to 3.0%; Sn 0 to 0.2%; Pb 0 to 0.2%; Cr 0 to 0.1; Si modifier (Na, Sr) 0.001 to 0.1%; B (elemental) 0.05% maximum; Ca 0.03% maximum; P 0.05% maximum; and others 0.05% maximum each, the balance, apart from incidental impurities being Al. The element of the first group provides stable nucleant particles in the melt. The element of the second groups forms an intermetallic phase such that crystals of the phase form in advance of and nucleate primary Si to provide complex particles which promote nucleation of Al-Si eutectic on cooling of the melt below the eutectic solidification temperature. The level of each of the elements of the first and second groups is such that, on solidification of the melt, the casting has a microstructure in which any primary Si present is substantially uniformly dispersed, and in which the microstructure predominantly comprises a eutectic matrix. The element of the first group is not solely Ti where the element of the second group is solely Sr.