Origin of non-uniform plasticity in a high-strength Al-Mn-Sc based alloy produced by laser powder bed fusion

•The origin of non-uniform plasticity of the Al-Mn-Sc based alloy produced by laser powder bed fusion has been clarified.•The non-uniform plasticity of the alloy originates from those microstructural areas containing fine and equiaxed grains.•The absence of work hardening in fine-grain areas is attributed to the lack of mobile dislocations and grain boundary particles.•Quantitative strength contributions from solutes, grain boundaries and secondary precipitates in bimodal grain microstructure have been identified.