Optimization of Artificial Ageing Time and Temperature on Evaluation of Hardness and Resistivity of Al-Si-Mg (Cu or/& Ni) Alloys

The factors necessary to obtain an optimal heat treatment that influence the hardness and resistivity of Al-6Si-0.5Mg casting alloys with Cu or/and Ni additions were investigated. The alloys were homogenised (24hr at 500C), solutionized (2hr at 540C) and artificially ageing at various times and temperatures. The alloys were aged isochronally for 60 minutes at temperatures up to 400C and isothermally at 150, 175, 200, 225, 250 & 300C for different periods in the range 15 to 360 minutes. The hardness and electrical resistivity of the alloys were measured for various artificial ageing times and temperatures. From the isochronal ageing treatment, hardness found maximum ageing at 225C. And from the isothermal ageing treatment, hardness found maximum for 60 minutes at 225C. So the optimal heat treatment consists of 60 minutes ageing at 225C. Keywords—Ageing, Al-Si-Mg alloy, hardness, resistivity.