Ultrasonic-assisted soldering W90 Tungsten heavy alloy to AZ31B Mg alloy using Sn-xAl alloy

A double-layered W/Mg structure is expected to be a new generation of nuclear radiation shielding material. The tungsten heavy alloy (W90) and AZ31B Mg alloy were firstly bonded by ultrasonic-assisted soldering using pure Sn and Sn-Al filler metal in an atmospheric environment. The influence of ultrasonication time on the microstructure and mechanical properties of the joint was investigated. The typical microstructure of the W90/Sn/Mg joint was W90/Mg₂Sn + Sn/Mg₂Sn layer/Mg. As the ultrasonication time increased from 2 s to 10 s, the joint width reduced and the thickness of the Mg₂Sn layer increased. The shear strength of the joint firstly increased, then flattened, and finally decreased. The joint strength reached the maximum value of 10.5 MPa. The fracture position of the joint changed from the W90/filler metal interface to the Mg₂Sn layer. The addition of Al in Sn resulted in the formation of the Al₄W phase at the W/Sn-1Al interface. The W/filler metal interface changed from the semi-coherent interface to the coherent interface and the joint strength increased. As the ultrasonication time was 6 s, the shear strength W90/Sn-1Al/Mg joint reached the maximum value of 24.6 MPa and the joint fractured at two positions: W90/filler metal interface and filler metal. With the further increase of ultrasonication time, the joint strength decreased and the joint fractured in the Mg₂Sn layer.