The effect of thermal ageing on microstructure and mechanical properties of Al-Si-Fe/Mg alloys

In this paper the microstructure and ageing behavior of Al-Si-Fe/Mg alloys produced through sand-casting route is presented. 4.0-6.0 wt% Mg was added to Al-Si-Fe alloy. Standard mechanical properties test samples were prepared from the sand cast 25 mm diameter by 45 mm rods. Thermal ageing was done for 6 h at 200 °C. The ageing characteristics of these alloys were evaluated using tensile properties, hardness values, impact energy and microstructure as criteria. The thermal aged samples exhibited higher yield strength, tensile strength and hardness values as the weight percent of magnesium increased up to 5 wt% in the Al-Si-Fe/Mg alloys as compared to as-cast samples. The optimum values were obtained at 5 wt%Mg. Lower percent elongation, reduction in area and impact energy values were obtained for age-hardened Al-Si-Fe/Mg alloy samples as compared to as-cast samples. The increases in hardness values and strength during ageing are attributed to the formation of coherent and uniform precipitation in the metal lattice. It was found that the age-hardened showed acceleration in ageing compared to the as-cast alloy. However, the 5 wt%Mg addition to the alloy showed more acceleration to thermal ageing treatment. These results show that better mechanical properties are achievable by subjecting the as-cast Al-Si-Fe/Mg alloys to thermal ageing treatment.