On the development of next generation heat-resistant aluminum alloys for cylinder head and piston applications

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To compete successfully on the global scale, automotive manufacturers must develop superior processes to deliver parts cost-effectively, with the requisite properties. Casting is the most feasible near net shape manufacturing process in this context. The choice of alloy, process and heat treatment in the case of critical components requires knowledge of their service conditions. The added stipulation of achieving lighter weight automobiles that comply with fuel economic standards without sacrificing power or performance must also be factored in. Thus, refinements continue to be investigated in both the alloys used and the casting process itself. Classic aluminum alloys, such as 356 and 319, used in engine components have a working temperature range of 100-150oC max. On the other hand, improvements in engine performance have raised the temperatures in Al cylinderheads beyond 200-300oC. One of the ways of extending the temperature capability of these alloys is by means of dispersion strengthening, where the presence of stable Al3X dispersoids homogeneously distributed in the Al matrix provides the required strengthening at elevated temperatures. These nano-sized precipitates with a cubic L12 structure and low lattice parameter mismatch with the matrix act as effective barriers to dislocations at high temperatures, thereby maintaining the alloy strength. While Sc and Zr additions to commercial wrought Al alloys have been reported to increase the tensile strength, few studies report on the use of this technique in Al-Si based alloys. The goal, therefore, is to make these alloys retain their strength within the 260-400oC range that may be encountered under service conditions. This project will aim to develop heat-resistant Al alloys for automotive cylinder heads and pistons, capable of sustained high temperature performance. Investigations will focus on alloy development, process development (evaluating different testing concepts), selecting alloys with high thermal fatigue resistance, and controlling the residual stresses in such components, currently areas of concern in the automotive industry. Working closely with scientific personnel from industry, the findings will directly benefit this important sector and the Canadian economy.