Effects of Sn and Mn Addition on the Microstructure and Mechanical Properties of As-Extruded Mg–2Al–1Zn Alloys

The effects of low Sn (1.0 wt%) and Mn (0.5 wt%) content on the microstructures and mechanical properties of as-extruded Mg–2Al–1Zn (AZ21) alloys were systematically investigated. The combined addition of Sn and Mn significantly refined the grains of the AZ21 alloy, reducing the average grain size from 25.77 to 2.17 μm. The volume fraction of the dynamically recrystallized (DRXed) grains decreased from 78.49 to 43.81% with Sn (1.0 wt%) and Mn (0.5 wt%) addition. The Al₈Mn₅, Al₁₁Mn₄, and Al₉Mn₄ phases were formed in Mg–2Al–1Zn–1Sn–0.5Mn (AZTM2110) alloy, and the Mg₁₇Al₁₂ phase disappeared. The orientation relationship between Al₉Mn₄ and Al₁₁Mn₄ was (002)_Al11Mn4//(\(\bar{3}\)02)_Al9Mn4, [\(\bar{1}\)00]_Al11Mn4//[223]_Al9Mn4, and the orientation relationship between Al₈Mn₅ and α-Mg was (\(\bar{2}\)52)_Al8Mn5//(\(\bar{1}\)2\(\bar{1}\)3)_α−Mg. The Al₉Mn₄ and Al₁₁Mn₄ phases grew in the same direction. The intensity of basal fiber texture of AZTM2110 alloy decreased by 21.7%. The ultimate tensile strength, yield strength, and elongation of the AZ21 alloy increased by 29.03%, 65.05%, and 61.02%, respectively. Grain-refinement strengthening was the main mechanism underlying the improvement in AZTM2110 alloy strength. Grain refinement and the weakened basal fiber texture improved the plasticity of the AZTM2110 alloy.