Effects of rare earth Er additions on microstructure development and mechanical properties of die-cast ADC12 aluminum alloy

► The α-Al dendrite and the eutectic Si were significantly refined by adding Er. ► The Hv of alloys first increased with increasing Er content, then decreases. ► The UTS of alloys increased with addition of Er, but the EL decreased. The effects of rare earth erbium (Er) additions (0, 0.3, 0.6 and 0.9wt.%) on the microstructure development and tensile properties of die-cast ADC12 aluminum alloy have been investigated in the present work. The microstructures and fracture surfaces of die-cast samples were examined by optical microscopy and scanning electron microscopy (SEM). It was found that the secondary dendrite arm spacing (SDAS) will decrease with increasing Er content, as the Er content increases to 0.6%, the lowest SDAS was obtained. In addition, the Er modified the eutectic silicon from a coarse plate-like and acicular structure to a fine branched and fibrous one. The microhardness of die-casted alloys were measured, the microhardness corresponding to the die-casted samples with 0, 0.3, 0.6 and 0.9wt.% Er additions are 100.6, 107.1, 113.6 and 108.5Hv, respectively. The tensile properties were improved by the addition of Er, and a good ultimate tensile strength (269MPa) but poor elongation (2%) were obtained when the Er addition was 0.6wt.%. Furthermore, fractographic examinations revealed that refined pore and spheroidized α-Al dendrite were responsible for the high ultimate tensile strength.