Effect of Si and Fe on thermal modification behavior of Al-4.5Cu-xSi-yFe

This study was undertaken to improve the tensile properties of Al-4.5Cu-xSi-yFe alloy through thermal modification (T6 heat treatment). To this end, different amounts of Si (0.1-2.5 wt.%) and Fe (0.05-2.5 wt.%) were added to the alloy composition in order to investigate the effect of Fe/Si ratio on the alloy tensile properties and quality index in as-cast and heat treated conditions. According to the results, adding Si up to 2.5 wt.% improved the base (Fe-free) alloy fluidity. However, the maximum fluidity in Fe-bearing alloys obtained at 1.5 wt.% Si. The optimum Si content for maximum tensile strength and fracture strain in low-Fe alloys was determined as 1.5 and 0.5 wt.%, respectively. However, in Fe-containing alloys the optimum Si was determined based on the Fe/Si ratio. At the Fe/Si≤1 the compacted α-FeMn compound is the dominant Fe-phase which is not detrimental to the tensile properties. At the Fe/Si>1 the fraction of detrimental β-platelets is increased at the expense of α-FeMn. In as-cast condition, the maximum tensile strength and ductility are obtained in 1.5 wt.% Si containing alloy at the Fe/ Si ratio of unity and 0.3, respectively. Applying heat treatment encouraged the precipitation hardening as well as dissolution/ fragmentation of hard eutectic Si and Fe-rich platelets. Under this circumstance, the maximum tensile strength belongs to the sample containing 2.5 wt.% Si and Fe/Si ratio of unity where its tensile strength is higher than that of the as-cast and heat treated base alloy by 40 and 15%, respectively.