Interface behaviour of brazing seam of contact-reaction brazing an AZ31 magnesium with amorphous filler metal

In order to achieve brazing of magnesium alloy without brazing flux, a new AlSiCu amorphous alloy was designed as an intermediate layer. The contact reaction brazing method was used to brazing AZ31 magnesium alloy with AlSiCu amorphous alloy as an intermediate layer. The SEM and OM methods were used to analyze the structure of the brazing seam, and it was found that there were block, granular, and dendritic alloy phases in the brazing seam. The composition of the alloy phases in the brazing seam was measured by EDS analysis, and the intermetallic compounds of MgAl were found. Unfixed micro-holes were found in the brazing seam held at 450 °C for 15 min, and these micro-holes disappeared and a complete interface connection was formed in the brazing seam when the holding time increased to 20 min. With the increase of brazing time, the brazing seam became wider and the dendrite in the brazing seam began to spread towards the base metal and gradually decreased after holding for 25 min. After holding for 30 min, the dendrite disappeared and the second phase appeared as granular and short rod distribution, and the number decreased significantly. The joint strength increases significantly with the increase of holding time, and the tensile shear strength of the lap joint is 110 MPa. The average hardness of the brazing seam is 94.2 HV, the hardness values of the matrix phase and the second phase are different greatly. The probe was used to analyze the microstructure and morphology of the shear fracture, and it was found that cleavage patterns and dimples existed on the fracture surface at the same time.