Consequences of Inappropriate Temperatures of the Solution Heat Treatment in Al-Si-Cu Cast Alloys

Abstract

Al-Si-Cu alloy systems have a great importance in the casting industry due to their excellent castability, good mechanical properties and wear resistance. Addition of alloying elements, such as Mg and Cu, makes these alloys heat treatable. Improving of their mechanical properties allows their using in new, more demanding applications (e.g. engines, cylinder heads etc.). The most applied heat treatment for this alloy is a T6 (age hardening). Such a heat treatment is required for precipitation of the Al2Cu hardening dispersed phase that increases the mechanical properties of Al alloys. Therefore, the consequences of different solution heat treatment temperatures 505, 515 and 525 °C for AlSi9Cu3 and 515, 525 and 545 °C for AlSi12Cu1Fe cast alloys, with holding times 2, 4, 8, 16 and 32 hours, were investigated in this study. The effect of solution treatment was evaluated based on changes in microstructure (optical microscopy) and mechanical properties (hardness, impact energy and ultimate tensile strength). The study confirms the strengthening of the experimental alloys caused by application of optimum conditions of T6 and melting of the Cu-rich phases with application of inappropriate solution temperature, as well as distortion and changes of the testing bars.