| Summary: | The effects of Mn addition on the room temperature tensile strength and deformation mechanisms of as-cast Mg-8Al-1Nd-1.5Gd-<i>x</i>Mn alloys (<i>x</i> = 0, 0.3, 0.5, 1.0 wt.%) are investigated in this paper. The results indicate that the addition of Mn contributes to the precipitation of Al-Mn-RE intermetallics and the refinement of <i>α</i>-Mg matrices, thereby improving the tensile strength of the 1.0 Mn alloy at 190 MPa. The fracture mechanism of Mn-containing alloys transforms from a cleavage fracture to a ductile fracture as the Mn content increases from 0.3 to 1.0 wt.%. The presence of intermetallic particles in the dimples confirms the hindrance effect of Al<sub>10</sub>Mn<sub>2</sub> (Nd,Gd) on dislocation slips. The novel technology of in-grain misorientation axes (IGMAs) is used to identify activated slip modes and deformation twins. It can be concluded that the activated pyramidal <i><a></i> slip during tensile deformation significantly promotes the ductility of the 1.0 Mn alloy with an elongation rate of 9.8%. It is worth noting that reducing the coarse <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mfenced open="{" close="}" separators="|"><mrow><mn>10</mn><mover accent="true"><mrow><mn>1</mn></mrow><mo>¯</mo></mover><mn>2</mn></mrow></mfenced></mrow></semantics></math></inline-formula> tensile twins and enhancing the proportion of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mfenced open="{" close="}" separators="|"><mrow><mn>10</mn><mover accent="true"><mrow><mn>1</mn></mrow><mo>¯</mo></mover><mn>1</mn></mrow></mfenced></mrow></semantics></math></inline-formula> compressive twins and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mfenced open="{" close="}" separators="|"><mrow><mn>10</mn><mover accent="true"><mrow><mn>1</mn></mrow><mo>¯</mo></mover><mn>1</mn></mrow></mfenced></mrow></semantics></math></inline-formula>-<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mfenced open="{" close="}" separators="|"><mrow><mn>10</mn><mover accent="true"><mrow><mn>1</mn></mrow><mo>¯</mo></mover><mn>2</mn></mrow></mfenced></mrow></semantics></math></inline-formula> double twins contributes to maintaining the continuous plastic deformation of Mg alloy.
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