Microstructure and impact behavior of Mg-4Al-5RE-xGd cast magnesium alloys

•Gd addition to the Mg-4Al-5RE alloys produced by various casting methods can refine the grains and modify the morphology of the acicular Al11RE3 phase to the short rod-like.•Gd addition increases the impact toughness due to the lower tendency of the modified second phases toward crack initiation.•The fine-grained HPDC alloys have an inconsistent strain rate sensitivity during the impact event.•The fine-grained HPDC alloys have excellent impact toughness but show an insufficient plastic deformation capacity.