Microstructure and properties of MgAlCd filler metal scraped brazing AZ31 magnesium alloy joint

In order to simplify the brazing process of magnesium alloy and make the liquid filler metal rapidly wet the base metal, the phase diagram method was used to design the series of Cd22.8Mg9.2Al and Cd26.3Mg15.3Al series filler metal. The brazing of AZ31 magnesium alloy was realized by scraping brazing under the condition of flame heating. The microstructure and phase of the filler metal and brazing seam were analyzed by XRD, SEM, and EDS. The results show that the microstructure of filler metal is composed of CdMg matrix, granular Al12Mg17, and massive (Al) solid solution. The amount of Al12Mg17 and (Al) solid solutions in filler metal increases with the increase of Al content, and the hardness of filler metal also increases. The Al content increases from 9.2 to 15.3%, and Vickers hardness increases from 183.6HV to 252HV. DSC results show that the melting point of filler metal is between 396.1 °C and 401.5 °C. The analysis results of the brazing seam show that the microstructure of the brazing seam is composed of CdMg3 and Al12Mg17. With the increase of Al content in filler metal, the fracture morphology changes from a river like pattern to rock sugar shape, the fracture mode changes from trans-granular fracture to intergranular fracture and the shear strength of joint decreases from 71 MPa to 53 MPa. The main reason for this phenomenon is the increase in the amount and size of the Al12Mg17 phase.