Wear properties of thixoformed AlSiCuFe alloys

Abstract

High-performance compressors which use low-viscosity lubricants face heavier wear problems and thus require a material more resistant to wear than the current high pressure die cast AlSi8Cu3Fe alloy in connecting rod applications. While hypereutectic versions of this alloy are expected to offer superior wear resistance, their processing via die casting is not straightforward. Semisolid processing of hypereutectic AlSiCuFe alloys offers to overcome the problems encountered in casting hypereutectic Al-Si alloys. A series of experimental AlSiCuFe alloys obtained by adding elemental silicon to the parent AlSi8Cu3Fe alloy were melted and were cooled to within 5 to 15°C of their liquidus points before they were poured into a permanent mould in order to produce non-dendritic feedstock for thixoforming in the present work. The slugs machined from the ingots thus obtained were thixoformed after they were heated in situ in the semisolid range for 5 minutes in a laboratory press. The hardness of the thixoformed and heat treated parts were 84–96 HB and 121–131 HB, respectively. A modified Falex Block on Ring equipment was employed to investigate the wear properties of these alloys under service conditions which prevail in connecting rod applications in compressors. The wear resistance of the thixoformed near-eutectic AlSiCuFe alloy was found to be the highest. In spite of a notable increase in the hardness of the wear test samples, the T6 heat treatment did not appear to have an impact on the wear resistance.