Processing of Hypereutectic AlSiCuFe Alloys in the Semi-Solid State

Abstract

Hypereutectic Al-Si based alloys are expected to be more wear resistant than the AlSi8Cu3Fe alloy, currently used in compressor connecting rods in die cast grades. Die casting of such alloys, however, is not straightforward. Semi-solid processing was thus considered to overcome the problems encountered in casting hypereutectic Al-Si alloys. Two experimental hypereutectic AlSiCuFe alloys were obtained by adding 8 to 12 wt% Si to the AlSi8Cu3Fe alloy. The ingots of these alloys were melted and cooled to very near their liquidus points, 625°C and 675°C respectively, before they were poured into a permanent mould in order to produce nondendritic feedstock for thixoforming. This low superheat casting process largely replaced α-Al dendrites with relatively smaller α-Al rosettes. The slugs machined from the ingots thus obtained were thixoformed after they were heated in situ in the semi-solid range for 5 minutes in a laboratory press. Several thixoformed parts were heat treated to the T6 temper with an accompanying increase in hardness from 91-96 HB to 130-131 HB.