Papers by Author: Robert Mackay

Abstract: The main aim of the metallurgical investigation was to enhance our understanding of the role Cu and Si have on the development of shrinkage porosity in the as-cast structure, which in turn can affect high cycle fatigue (HCF) properties of Al-9Si-1Cu (W328) and Al- 7Si-4Cu (W319) alloys. In order to achieve this objective a novel approach using thermal analysis and calculated fraction solid techniques was developed to assess mushy zone kinetics, the state between the liquidus and solidus where a solid skeletal α-Al phase and the Al-Si eutectic phase grow at the expense of an inter-dendritic liquid. Specifically, the cooling curve and calculated fraction solid curve were partitioned into segments, which reflect different stages of feeding through the entire solidification event of the alloy. Each partitioned segment corresponds to a stage of feeding, which in turn signifies a relative degree of pore growth susceptibility. Two thermal analysis techniques, both using calibrated thermocouples, were used to precisely understand the solidification path for both the W319 alloy and the W328 alloy.

Abstract: The potential use of an Al-9Si-1Cu alloy (W328 alloy) as a replacement for W319 alloy in engine blocks was investigated.. The ambient mechanical properties (tensile, hardness and fatigue) of sand and permanent mould cast test bars along with bars machined from a sand cast automotive component were studied. The tensile properties were evaluated in as-cast and T6 heat-treated conditions. The effects of Fe and Mn on properties were also investigated. The castings in W328 alloy exhibit lower porosity than W319 alloy, which is attributed to the smaller solidification range and feeding distance and larger volume fraction of the eutectic phase. Higher iron levels increased the level of intermetallics and reduced properties. The addition of Mn did not offset the effect of higher iron levels. The W328 alloy offers some advantages over the 319 alloy and is a potential candidate for production of automotive components such as engine blocks and cylinder heads.