EFFECT OF NI, MN, SC, AND ZR ADDITION ON THE TENSILE PROPERTIES OF 354-TYPE ALLOYS AT AMBIENT TEMPERATURE

The present study was carried out to investigate the effects of Ni (high and low), Mn, Zr, and Sc additions, individually or in combination with other additives, on the microstructure and tensile properties of 354 casting alloy (Al-9 wt% Si-1.8 wt% Cu-0.5 wt% Mg) at ambient temperature following aging in the temperature range 155-300 degrees C for different aging times. Solution heat treatment of the studied alloys improves the tensile properties and alloy quality of all alloys. The presence of Ni and Zr (with no Cu), and Sc and Zr provides improvement as these alloys show the best YS values. Multiple aging peaks are observed in the age-hardening curves of all studied alloys, related to the precipitation sequence which occurs in each alloy. The best combination of properties is achieved after aging at 190 degrees C/2 h for all alloys studied, with the exception of the alloy containing 2 % Ni + 0.25 % Zr that showed the best combination at 190 degrees C/4 h. These conditions may therefore be considered as the appropriate T6 heat treatment parameters for these alloys. Under the experimental conditions of the present study, aging at 190 degrees C (for 2 or 4 h) introduces a technologically useful strategy for this particular alloy system as it provides a significant economic benefit in the form of a noticeable reduction in the aging time required to reach peak strength.