Study On The Vacuum Brazing AZ31B Magnesium Alloy By Aluminum And Zinc Based Filler Metal

Metal magnesium and its alloys are the lightest engineering structures. With the development of various high performance magnesium alloys, more and more magnesium alloy structure is applied in every field. Brazing has the advantages of low welding temperature, small distortion, high accuracy of welding parts, and has a unique advantage in the connection of complex structure parts and thin-walled structure parts. Because the variety of magnesium based filler metal is less than that of magnesium alloy, it is easy to oxidize, and the cost is high, which limits the application of magnesium alloy brazing structure. In this experiment,Al based solder Al86Si10 Cu and zinc based filler metal ZnAl15, AZ31 B magnesium alloy and AZ31B/LY12 Al alloy metal alloy by vacuum brazing process, to study the temperature and time of the brazed joint microstructure and microhardness were investigated to explore feasibility magnesium based brazing magnesium alloy homogeneous metal and magnesium alloy / aluminum alloy dissimilar metals, to further develop AZ31 B brazed research to lay a solid foundation. The results show that:（1） With the ZnAl15 and Al86Si10 Cu as the solder, the interface can be obtained by the interface of the AZ31 B homogeneous metal vacuum brazing joint with the appropriate technology, Brazed joint by brazing seam zone and matrix grain boundary penetration zone and joint formation includes three stages: wetting and spreading, reactive spreading and Mg matrix grain boundary penetration.（2） The microstructure of the AZ31 B brazing joint was composed of Al86Si10 Cu solder at 540℃ and 15 min, and the eutectic structure, Mg₂ Cu and Al3Mg₂ of the three elements(α-Mg+ Mg₁₇Al₁₂+Mg₂Si) were obtained. The width of the joint zone increases with the increase of temperature and time, and the width of the eutectic zone is more obvious. The microhardness of the joints showed high in the middle, low at both ends and the distribution of brazing seam zone and matrix grain boundary osmotic the hardness increased with the increase of brazing temperature and holding time.（3） The AZ31B solder joints of ZnAl15 were brazed at 470 ℃,20 min, and the microstructure of the joint was composed of α-Mg,（Mg Zn+α-Mg） eutectic structure and Al2 Mg and Mg₂Zn₁₁. Compared with the Al86Si10 Cu, the eutectic microstructure of the ZnAl15 solder joints of the AZ31 B solder is larger and the microstructure is finer, and the grain boundary permeability region is obviously characterized by the mesh organization. With the increase of holding time, the width of the grain boundary permeability increased, and the microstructure of the grain boundary was more obvious.（4） For 480℃,15 min under the conditions of the AZ31B/ZnAl15/LY12 brazed joint and 520℃,15 min conditions AZ31B/ Al86Si10Cu/LY12 of brazed joints brazing seam zone and AZ31 B matrix with good interface bonding, brazing seam zone and LY12 substrate interface with poor brazing seam regional organization is compact. For 500℃、510℃,15 min under the conditions of the AZ31B/Al86Si10Cu/LY12 brazed joints, the brazing seam area and AZ31 B matrix and LY12 substrate interface with poor brazing seam district organization is compact.