Microstructure and mechanical properties of dissimilar spot friction stir welded Zr55Cu30Al10Ni5 bulk metallic glass to pure copper

A Zr55Cu30Al10Ni5 bulk metallic glass (BMG) plate with thickness of 2 mm was successfully spot friction stir welded to a commercial pure Cu plate. Microstructural characterization revealed that some serrations formed at the edge of the BMG plate and some nano-sized nucleuses were dispersed in the BMG side along the Cu/BMG joint interface. In the upper Cu side close to the keyhole, some blocky and strip-like BMG fragments were embedded in the Cu matrix. As a result, significantly elongated Cu grains with width of about 200 nm were formed between the strip-like BMG fragments. Shear tensile tests showed that the Cu/BMG spot joints fractured at a maximum load of about 2300 N through the stir zone pullout fracture mode.