Transient Liquid Phase Bonding of Magnesium Alloy AZ31B and 304 Stainless Steel

Transient liquid-phase bonding of magnesium alloy (AZ31B) to stainless steel (304) was performed using a copper interlayer. The microstructure and bonding strength of the bonded joint were studied. The results show that when the welding condition is 510 degrees C/30 min or 530 degrees C/10 min, no eutectic phase is observed in the welded joint and the metallurgical bond is weak. When the welding condition is 520 degrees C/30 min or 530 degrees C/20 min, the joint interface forms Mg-Cu eutectic. The weld width increases significantly and interfacial bonding strength improves. At 530 degrees C/30 min, a laminar diffusion region with a width of about 350 mu m forms at the magnesium side in the welded joint. Microstructures are Mg-Cu eutectic layer, followed by Mg-rich solid solution layer, Mg-17(Cu,Al)(12) dispersed in magnesium alloy matrix and permeability zones of Mg-Cu-Al ternary compounds distributed in grain boundaries of magnesium alloy. The shear strength of the joint reaches the highest value of 52 MPa. Under the welding condition of 540 degrees C/30 min or 530 degrees C/40 min, isothermal solidification occurs in eutectic liquid on the interfacial diffusion zone and the joint shear strength decreases, which is attributed to continuous network distribution of Mg-Cu-Al compound along the magnesium grain boundary. Recrystallization happens and grains grow in the AZ31B matrix.