The transient liquid phase (TLP) bonding was used to fabricate autogenous joints in a magnesium alloy AZ31 with the aid of a pure Ni interlayer. A $13{mu}m$ thick pure Ni foil was used in order to form a Mg-Ni eutectic liquid at the joint interface. The interface of reaction and composition profiles were investigated as a function of bonding time using a pressure of 0.16 MPa and a bonding temperature of $515^{circ}C$. The quality of the joints produced was examined by metallurgical characterization and the joint microstructure developed across the diffusion bonds was related to changes in mechanical properties as a function of the bonding time.