| Summary: | The effect of Mn content on the microstructure evolution and mechanical properties of Al–Cu–Mg–<i>x</i> Mn alloys at ambient temperature was investigated. The findings show that in the Mn-containing alloys at the as-cast state, the blocky primary T(Al<sub>20</sub>Cu<sub>2</sub>Mn<sub>3</sub>) phase coexisting with the Al<sub>2</sub>Cu phase appeared. With the increase in Mn content, the majority of the Al<sub>2</sub>Cu phase dissolved, nd a minor amount of the T phase remained at the grain boundary after solution treatment. The rod-like T<sub>Mn</sub> (Al<sub>20</sub>Cu<sub>2</sub>Mn<sub>3</sub>) nanoprecipitate was simultaneously distributed at grain boundaries and the interiors, while a high density of needle-like θ″ (Al<sub>3</sub>Cu) nanoprecipitate was also observed in the T6 state. Further increases in Mn content promoted the dispersion of the T<sub>Mn</sub> phase and inhibited the growth and transformation of the θ″ phase. Tensile test results show that 0.7 wt.% Mn alloy had excellent mechanical properties at ambient temperature with ultimate tensile strength, yield strength, and fracture elongation of 498.7 MPa, 346.2 MPa, and 19.2%, respectively. The subsequent calculation of strengthening mechanisms elucidates that precipitation strengthening is the main reason for the increase in yield strength of Mn-containing alloys.
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