Heat Treatment of Al–Mg–Si–Mn Alloys with Varying Mg/Si Ratio

The current study investigated the heat treatment response of Al–Mg–Si–Mn alloys with varying Mg/Si ratio. In this regard, Al–5Mg–2Si–0.6Mn–0.15Ti (AMS52) and Al–2Mg–2Si–0.1Mn–0.15Ti (AMS22) alloys were studied. It is found that lower Mg content in AMS22 alloy has caused the formation of ternary eutectic Al–Mg2Si–Si phases. The modification of binary eutectic Al–Mg2Si phases upon heat treatment is intangible in AMS52 alloy. However, there was a significant modification of the eutectic Al–Mg2Si binary phases in AMS22 alloy. The aging treatment has caused a major improvement in the yield strength of both alloys. Moreover, the AMS22 alloy exhibited a remarkable increase in yield strength (269 MPa) as compared to AMS52 alloy (184 MPa). However, the improved strength in these alloys is achieved at the expense of elongation. TEM results revealed the presence of β′ and β phases in both alloys. The number density of β phases in the AMS52 was much higher than the AMS22 alloy, while the size of β phase is smaller in the former alloy than in the latter alloy. Fractography of tested tensile specimens revealed that the crack is initiated by the fracturing of iron-bearing phases which advances through the debonding of remnant eutectic Mg2Si phases from the Al-matrix.