Energy Efficient Heat Treatment for Linerless Hypereutectic Al-Si Engine Blocks Made Using Vacuum HPDC Process

Heat treatment standards developed by the aluminum industry over the last several decades are often not well optimized when applied to components cast by high cooling rate processes such as High Pressure Die Casting (HPDC), Low Pressure Permanent Mold (LPPM), Squeeze Casting, etc. The inherently finer as-cast structures should not require long solution times for the effective dissolution of intermetallic phases and the adequate thermal modification of structural constituents. Hence, long and expensive T6 and T7 treatments should not be required. Heat treatment studies involving as-cast laboratory samples with SDAS = 13.6 μm (equivalent to a thick-section HPDC casting) were conducted. Traditional and modified solution and aging treatments were compared. These studies suggest that a reduction of up to 92% in thermal processing time is possible while maintaining and/or improving the cast component’s metallurgical characteristics including hardness (≥75 HRB), dissolution of secondary phases, and spheroidization of the eutectic Si as well as overall homogeneity. Vacuum HPDC of an actual hypereutectic Al-20%Si motorcycle engine block confirmed the potential for significantly reduced heat treatment times, energy consumption, and overall costs.