EFFECT OF PROCESS VARIABLES ON STRUCTURE AND PROPERTIES OF ALUMINUM-SILICON PISTON ALLOY

The majority of automotive pistons are cast in one of the groups of lo w expansion AI-SI eutectic alloys. The structure and mechanical proper ties of these alloys are highly dependent upon cooling rate, compositi on, modification and the heat-treatment operations. The effect of thes e variables were investigated in this study, using locally available a utomotive 'scrap pistons' as basic raw materials. Strontium master all oy was used as the source of the modifier and a natural-gas-fired cruc ible furnace was used for melting purposes. The microstructures of the alloy, both in the modified and unmodified conditions, were studied i n this investigation. Properties such as the ultimate tensile strength (UTS), percentage elongation, hardness and percentage porosity for bo th rates of cooling have been determined, both with and without the ad dition of strontium. Significant changes in structures were observed t o occur, especially in the primary and eutectic silicon phases. Full h eat treatment has also shown a great influence on the structure and pr operties of the aluminium-silicon piston alloy. The residual stress in the modified alloy is fully relieved due to thermal treatment. Finall y, attempts were made to correlate the observed structures and propert ies obtained during the experiment. (C) 1998 Elsevier Science S.A. All rights reserved.