Investigation into the correlation between composition, microstructure, and mechanical properties of Al-xFe-(6-x)Mn alloys

Abstract

The Al-Fe-Mn alloy system exhibits excellent thermal stability, making it a promising candidate for heat-resistant aluminum alloys. Nevertheless, systematic investigations into the influence of Fe/Mn ratio and cooling rate on the microstructural evolution and mechanical properties of Al-Fe-Mn alloys remain insufficient. In this work, Al-xFe-(6-x)Mn alloys prepared at two cooling rates were studied by tensile test, nanoindentation, TEM, etc. The results show that the co-addition of Mn and Fe can promote the transformation of coarse Al₁₃Fe₄ or lamellar Al₆Mn phase to Al₆(Fe, Mn) fibers. In addition, when the Fe/Mn ratio is 1, the matrix stacking fault energy is the lowest, and the Al/Al₆(Fe, Mn) is coherent: (3 1 1)_{Al6(Fe, Mn)}//(0 0 2)_Al, (2 -2 1)_{Al6(Fe, Mn)}//(-1 1 1)_Al. The coherent interface generally enhances the thermal stability of the reinforcement phase due to the minimized interfacial energy. Nanoindentation results show that the hardness of the matrix and Al₆(Fe, Mn) is the lowest when Fe/Mn is 1, among which the low hardness of the matrix is a reflection of the low stacking fault energy, while the hardness of Al₆(Fe, Mn) is inversely proportional to the entropy value. High cooling rate can promote the transformation of skeleton-like Al₆(Fe, Mn) into fibers of about 100 nm, greatly improving the mechanical properties of the alloy. The hardness of the chilled Al-4Fe-2Mn alloy is significantly higher than that of other alloys, reaching 115 HV. This work can provide important reference for improving the mechanical properties and heat resistance of heat-resistant alloys.