Effect of Fe Concentration and Superheating on the Microstructure and Tensile Properties of High Mg 413.0-Type Alloys: Role of Sr, Be, P, and La.

The present work was undertaken to explore the multiple alloys and process steps that have been suggested to mitigate the harmful effects of high iron content in cast Al-Si alloys. The base alloy used was ommercial 413.0 alloy containing 0.35%Mg. Iron was added at three Fe levels up to 1.8%. The addition of Sr, 1.0%Zn, 0.2%Ti were made to the alloys so prepared, which were melted and maintained at a superheat of 750 °C or 950 °C. The melts were poured in different molds that produced three solidification rates. In total, 40 castings were prepared: half of the castings were used for metallographic examinations in the as-cast condition, while the other half were set aside for tensile testing following T6 treatment. The results show that at a solidification rate of 50 °C/s, 1.8%Fe could be dissolved in the aluminum matrix regardless of other melt treatments. With regard to the other solidification rates, superheating at 950 °C, coupled with Sr addition or Sr + Be, reduces the average β-platelets length by 80% (0.8 °C/s) or 95% (8 °C/s). The addition of P causes a marked drop in the alloy tensile strength due to the precipitation of primary Si, AlSiSr, and β-AlFeSi hard-phase particles. Therefore, reducing the iron content in the castings may be considered a major objective to be recommended for developing alloys with higher strength and optimum quality values. More than 1000 tensile bars were tested in this study.