Mechanical Performance of Zr-Containing 354-Type Al-Si-Cu-Mg Cast Alloy: Role of Additions and Heat Treatment

Abstract

In this article, the volume fraction of intermetallic compounds in Zr-containing 354-type Al-Si-Cu-Mg alloys, characteristics of eutectic Si particles, and tensile, hardness, and impact properties have been evaluated with varying Ni and Mn contents and combination. The results revealed that additions of Ni and Mn in different amounts and combinations increased the volume fraction of intermetallic compounds in the tailored alloys, compared to the base alloy (cf. 12.21% for 4% Ni-containing alloy with 2.5% for base alloy), producing a significant effect on the mechanical performance. The proposed additions enhanced the mechanical performance of the alloys, namely, the ambient- and elevated-temperature tensile properties, hardness values, and impact properties. For the Mn-containing alloys, the improvement in properties was attributed to the formation of sludge particles in the form of blocky α-Al15(Fe,Mn)3Si2 alongside the script-like α-iron phase that resisted crack propagation. The precipitation of Ni-bearing phases such as Al9FeNi, Al3CuNi, and Al3Ni in the Ni-containing alloys improved the mechanical properties through hindering cracks propagation. Interestingly, addition of 0.75 wt.% Mn to the base alloy proved to be competitive in strength values to the addition of 2 and 4 wt.% Ni, and better in terms of ductility values. The investigations showed that the variations in hardness and impact values follow the same trend as variations in the percentage volume fraction of intermetallic compounds, i.e., maximum property value is associated to the alloy with highest volume fraction of intermetallic compounds. Furthermore, the impact properties showed higher dependency on Al2Cu phase particles rather than the eutectic Si particles.