Effect of bonding time on microstructure and mechanical properties of transient liquid phase bonded magnesium AZ31 alloy

The transient liquid phase (TLP) bonding of a magnesium alloy AZ31 was undertaken using pure nickel interlayers. The formation of a eutectic between the magnesium and nickel was obtained by bonding at 515 °C and the microstructural developments across the joint region were examined as a function of hold time from 5 to 120 min. Reaction zones were identified within the joint and the changes of width of the reaction zones were examined with respect to changes in the joint shear strength and hardness. The results showed that as the bonding time was increased to 60 min, the width of the eutectic zone was completely removed and the joint solidified isothermally. Under these conditions a maximum hardness value of 179 VHN was recorded and the highest joint shear strength of 36 MPa was obtained. However, when the bonding time was increased to 120 min, the shear strength of the interface decreased and this was attributed to the formation and segregation of brittle Mg–Ni intermetallics within the joint.