Optimization of the solution heat treatment process to improve mechanical properties of 319 Al alloy engine blocks using the billet casting method

The use of Al engine blocks has increased significantly to improve vehicle fuel efficiency. However, the large tensile residual stress along the cylinder bores necessitates the optimization of mechanical properties in this region to prevent premature engine failure. This study, utilizing billet castings which replicate the microstructure along the engine cylinder bores, observed the influence of varying solution heat treatment parameters on microstructure and mechanical properties. Microstructural analysis was carried out on the billet castings using optical microscopy, SEM and EDX, while mechanical properties were assessed using tensile testing. The results suggest that the optimal solution heat treatment parameters, resulting in the most effective Al2Cu dissolution and largest increase in tensile properties for all the replicating billet castings, were at 500 °C for 2 h. In addition, solutionizing at 515 and 530 °C, although more effective in dissolving Al2Cu, resulted in incipient melting of Al2Cu and Al5Mg8Cu2Si6, which deteriorated the tensile properties. The results from this study will assist in the development and implementation of an optimized heat treatment schedule, preventing in-service engine failure and improving process efficiency.