Determination of microstructure and mechanical and thermophysical properties of Al–Si–Mg-XCr alloy

Abstract

The study added different proportions of Cr to the Al–Si–Mg eutectic alloy and applied heat treatment to the quaternary alloy. So, the Al–Si–Mg eutectic alloy's microstructure and morphology were looked at after Cr was added and it was heated. In addition, the hardness, tensile strength, fracture surface analysis, and thermoelectric properties of newly produced Al-12.95 % Si-4.96 % Mg-X%Cr alloys were also determined. In the newly formed alloy, along with the expected Si and Mg2Si phases in the Al matrix phase, a randomly distributed CrSi2 binary intermetallic phase in a white hexagonal structure was observed with the effect of Cr addition. Additionally, a magnesium-rich Al9FeMg3Si5 intermetallic phase was observed, which we think was formed by the effect of Fe impurity atoms. Hardness and tensile strength values, which are the mechanical properties of the alloy, increased significantly after heat treatment. The hardness value of the 0.5 % Cr-added sample increased by approximately 77 % and reached 107.95 ± 6.0 kg/mm2. At the same time, the hardness value of the intermetallic CrSi2 phase in the quaternary Al-12.95 wt%Si-4.96 wt%Mg-1.0%Cr alloy was found to be 794.3 ± 30 kg/mm2. Similarly, the maximum tensile strength value of the 0.5 % Cr-added sample after heat treatment increased by approximately 105 % and reached 160.53 MPa. Melting temperatures (Tm) (K), fusion enthalpy (ΔH) (J/g), and specific heat Cpl (J/gK) were determined for non-heat-treated materials. The 0.5, 1.0, and 1.5 Cr-added samples had Tm of 563.38 °C, 558.44 °C and 572.61 °C, respectively. The ΔH value of samples with 0.5 %, 1.0 % and 1.5 % Cr addition is 605.70 (J/g), 579.92 (J/g) and 552.24 (J/g), respectively. Cpl was 0.724 J/g.K, 0.698 J/g.K and 0.653 J/g.K for 0.5 %, 1.0 %, and 1.5 % Cr-added samples. In both heat-treated and non-heat-treated samples, Cr enhanced electrical resistance.