Study On The Diffusion Brazing Of AZ31B Magnesium Alloy And Copper Of Property And Microstructure Of The Joint

Magnesium and magnesium alloys have the proportion of small, specific strength andspecific stiffness, conductivity and thermal conductivity, good damping properties of a seriesof advantages, copper and copper alloy not only have excellent thermal conductivity, goodductility and corrosion sex, hot and cold processing performance, but also have a highresistance to oxidation and corrosion resistance, high strength. Magnesium and copper whichmake them excellent performance have been widely used in engineering, such as aerospace,defense and automotive, computer and other fields. In this paper, with Al foil ang Zn foil asinterlayer, by means of SEM、EDS、XRD、testermicrohardness testing methods、electronicuniversal tensile，microstructure and properties of interfacial microstructure of the joint wereresearched, and the optimum technological parameters were identified with Al foil, Zn foil asinterlayer for diffusion brazing of AZ31B/Cu.For the first time use the Al foil and Zn foil as intermediate layer, realizes the AZ31B/Cudissimilar metal metallurgical bonding by diffusion brazing method, which reduces theAZ31B/Cu direct diffusion brazing temperature. The temperature were decreased by100℃,150℃.The diffusion brazing of AZ31B/Cu used Al foil as interlayer, the diffusion zone widthof joint widen as the holding time increases. When soldering temperature reaches420℃,holding time is120min, the pressure is2.5MPa, the diffusion width of the joint reached about400m. The phase structure on the AZ31B side are-Mg、(-Mg+Mg12Al17) eutecticzone、Mg12Al17intermetallic compound, and the phase structure on the copper side are Al-Cusolid solution、Al-Cu intermetallic compound. The microhardness of the welded jointshowing a gradient distribution. The maximum hardness reaches185HV. The shear strengthof welded joints shows the law of first increases and then decreases with holding timeincreasing. When soldering temperature is450℃, pressure is2.5MPa, the holding time is90min,the maximum shear strength of the joint reaches65MPa,which reaches approximately 40%AZ31B magnesium alloy. Welded joint fracture occurs in the middle region of thediffusion layer. Fracture of the joint showing mixed fracture of cleavage fracture along grainboundaries.The diffusion brazing of AZ31B/Cu used Zn foil as interlayer, when the temperaturereaches410℃，holding time is50min, a pressure is2.5MPa，the diffusion width of the jointreached about200m, and the composition of the diffusion layer is not uniform.Microstructure phase structure are mainly-Mg, rose-like （-Mg+MgZn+Mg2Zn11）eutectic phase and Mg2Zn11intermetallic compound, the metal compound of Cu5Zn8,Cu solidsolution. Microhardness of diffusion zone presents the law that is high in the middle, thelower close to the base material. When the temperature is410℃, holding time is40min,themaximum hardness of the joint reaches350HV. Shear strength of welded joints withtemperature and holding time increasing, which shows the law of first increases and thendecreased. When the temperature is410℃, holding time is40min, pressure is2.5MPa, themaximum shear strength of the joint reaches45MPa,which reaches approximately26%AZ31B magnesium alloy. Welded joints fracture is in Cu substrate side, and showed brittle-ductile mixed fracture.The formation process of diffusion brazed joint is broadly divided into three phases, thefirst is solid phase diffusion stage, the second is generating and spreading of the eutecticliquid phase, the third that is phase solidify to form the joint.