New strategy to solve the ambient strength-ductility dilemma in precipitation-strengthened Mg-Gd alloys via Li addition

• Li addition overcomes the strength-ductility trade-off of precipitation-strengthened Mg-Gd alloy. • Li addition into Mg-Gd alloy reduces its density and increases its specific yield strength. • Li addition change the dominant phase from β ′ to β H − I I ′ in the peak-aged Mg-Gd-Li alloy. • β , β 1 R , β H − I I ′ phases and Li clusters offer better combined strengthening effect than β ′ phase. • Li addition enhances the activity of non-basl dislocations to accommodate the strain. The ambient strength-ductility trade-off has been a long-standing dilemma in metallic alloys, in particular Mg alloys. Here we report a new strategy to solve such a strength-ductility dilemma in precipitation-strengthened Mg-Gd alloys via Li addition. Different from the strengthening of traditional β ′ phase in Mg-7Gd (wt%) alloy, 1 wt% Li addition to this alloy not only boosts the precipitation of different sized β , β 1 R , β H − I I ′ phases and Li clusters to offer better combined strengthening effect, but also enhances the activity of dislocations to accommodate the strains during plastic deformation. Consequently, both the ambient tensile yield strength and ductility are simultaneously improved as compared to Mg-7Gd (wt%) alloy. Moreover, Li addition brings a reduction in density, in turn increasing the specific yield strength. The present strategy with Li addition offers a new insight into the development of Mg alloys with high strength-ductility synergy and with high specific yield strength.