RESPONSE OF VARYING LEVELS OF SILICON AND TRANSITION ELEMENTS ON ROOM- AND ELEVATED-TEMPERATURE TENSILE PROPERTIES IN AN Al-Cu ALLOY

The research involved here was accomplished through a study of the tensile properties in both the as-cast and heat-treated conditions, where the effects of different heat treatments, i.e., T5, T6, T62 and T7, commonly applied to aluminum casting alloys were evaluated at ambient temperature and at high temperature (250 degrees C) using different holding or stabilization times at testing temperature. The tensile data showed that the ultimate tensile strength (UTS) and percentage elongation values of the six alloys increased in the one-step solution heat-treated condition compared to the as-cast case. The multi-step solution heat treatment displayed higher tensile properties than those achieved with the one-step solution treatment. The use of the T62 treatment (multi-step solution treatment followed by artificial aging) allows for maximum dissolution of the copper phases in the multiple stages of solution treatment, resulting in the greatest improvement in both UTS and yield strength (YS). At ambient temperature, T6 and T62 treatments provide the best improvements in both UTS and YS values of all alloys. The T62-tempered alloy showed maximum improvement with a UTS value of similar to 401.55 MPa. Likewise, in the Al-2%Cu-8%Si series the T62-tempered alloy displayed the highest UTS with a value of similar to 293.5 MPa. The YS values improved overall after solution treatment. The YS values followed the same trend as the UTS at both ambient and high-temperature testing. At high-temperature testing at 250 degrees C after one hour of stabilization, the UTS of the alloys increased with the T6 and T62 heat treatment conditions, but remained the same after T5 heat treatment; the highest UTS value was exhibited by the T62-tempered alloy with similar to 195 MPa.