EFFECT OF NI, MN, SC, AND ZR ADDITION ON THE TENSILE PROPERTIES OF 354-TYPE ALLOYS AT AMBIENT TEMPERATURE G. H. Garza-Elizondo, A. M. Samuel, and F. H. Samuel Universite ´ du Que ´bec a Chicoutimi, Chicoutimi, QC, Canada S. Valtierra Nemak, S.A., Garza Garcia, N.L., Mexico Copyright Ó 2016 American Foundry Society DOI 10.1007/s40962-016-0072-0 Abstract 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 microstruc- ture and tensile properties of 354 casting alloy (Al–9 wt% Si–1.8 wt% Cu–0.5 wt% Mg) at ambient temperature fol- lowing aging in the temperature range 155–300 °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 pre- cipitation sequence which occurs in each alloy. The best combination of properties is achieved after aging at 190 °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 °C/4 h. These conditions may therefore be considered as the appropriate T6 heat treatment parameters for these alloys. Under the experimental con- ditions of the present study, aging at 190 °C (for 2 or 4 h) introduces a technologically useful strategy for this par- ticular 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. Keywords: aluminum alloys, additives, tensile properties, Sigma plots, microstructure Introduction In recent years, the development of diesel and direct fuel injection gasoline engines with high specific powers have resulted in a marked performance impact on piston mate- rials due to increased combustion pressure and piston temperatures. 1 Improved strength has been a continuing goal in aluminum alloy development for more than three decades. 2,3 While the applications in Al–Si casting alloys should generally be carried out at temperatures of no more than 230 °C, for certain applications such as those required by the automotive industry, these alloys may operate over a wide range of conditions where temperatures are liable to rise much higher than 230 °C. 4 The addition of transition elements such as Ni and Cu are considered to be an effective way to improve the strength of Al–Si alloys in the as-cast and solution-treated condi- tions by forming stable aluminides. 5,6 At temperatures over 190 °C, however, these strengthening phases—which include the h 0 (Al 2 Cu) and S 0 (Al 2 CuMg) phases—tend to become unstable, coarsen rapidly, and then dissolve, pro- ducing an alloy with an undesirable microstructure for high-temperature applications. Apart from these phases, there are other microstructural features which contribute to strength, ductility, and durability; these include secondary dendrite arm spacing, grain size, and the size and mor- phology of interdendritic eutectic Si particles. 4,7,8 The principal aim of this research study was to investigate the effects of Ni (low and high contents), Mn, Zr and Sc additions on the strength of cast aluminum alloy 354 (Al– 9 wt% Si–1.8 wt% Cu–0.5 wt% Mg) at room temperature, for different aging temperatures and times. The research was divided into two parts: This paper reports on the first part dealing with the tensile properties of the alloys at ambient temperature, while the second part focuses on the high-temperature performance following stabilization at International Journal of Metalcasting