Aging behavior of 359-type Al–9%Si–0.5%Mg casting alloys

The present study investigated the influences of aging temperature and time on the tensile properties and quality indices of 359-type Al–9%Si–0.5%Mg casting alloys. These alloys are still not widely used by most foundrymen in spite of the fact that they are extremely promising for several fields of engineering applications because of their superior strength. For the purposes of validating their use in industrial applications, a solid data base was created, based on the present study, correlating the tensile properties and the quality indices of these alloys with the aging parameters. Quality charts were used as an evaluation tool for selecting the optimum aging conditions for developing high strength and optimum quality in 359 casting alloy. Aging at a low temperature was observed to produce the greatest strength and optimum quality in the 359-type castings compared to aging at higher temperatures. The peak-strength for 359 alloy was observed to be attained after shorter aging times on condition that the aging temperature is increased. The aging times required for reaching peak-strength in 359 alloys are 32, 24, 1 h, 30, and 10 min when applying aging temperatures of 155, 170, 195, 220, and 245 °C, respectively. Aging treatment at higher temperatures is accompanied by a reduction in the tensile properties and quality index values of the castings; however, it also introduces the possibility of a significant economical strategy for minimizing the time and the cost of this treatment. Depending on the required level of tensile properties and based on the quality charts developed, it is possible to make a rigorous selection as to the most suitable aging parameters to be applied to the 359 alloy so as to obtain the best possible cost-effective compromise between alloy strength and quality.