Microstructure And Element Diffusion In Welding Interface Of AZ31B/Cu Dissimilar Materials

Magnesium has some excellent perfommances such as lower density, higher specificstrength, higher specific modulus, while copper have the properties of good thermalconductivity, electrical conductivity, corrosion resistance and outstanding cool and hotprocessability and so on. Mg-Cu bimetals have been extended from navigation and militaryfields to civil products of high additional value such as automobile, computerandcommunication equipment.In orde to lose weight and multiplicity propose, it is necessary toweld this two materials.The dissimilar metals of AZ31B Magnesium and copper were weldedby means of the diffusion brazing and TIG welded. By means of SEM、EPMA、XRD、microhardness tester and other analytical testing methods, the microstructure and diffusionbehavior were to corresponding study during the diffusion process.In the diffusion brazing bonding between AZ31B and Cu, a better wettability of theMg-Cu eutectic liquid is relative Cu side, while the a poor wettability is relative Mg side. Theformer produce the wetting spreading, the later produce the reaction and wetting spreading.The joint include the grain boundaries layer、the low-melting eutectic layer and Mg-Cuintermetallic compound layer. The microstructure of interface zone of AZ31B/Cu compositefrom Mg alloy to copper includes the grain boundary penetration layer composed of α-Mg andMg17(Cu, Al)12which was precipitated along the grain boundary of α-Mg solid solution,eutectic of α-Mg and Mg2Cu,intermetallic compoundCu2Mg, eutectic of α-Mg and Mg2Cu,and Cu(Mg) solid solution, respectively. The microhardness of the welded joint showing agradient distribution.With the heating temperature and holding time increase, the width of the diffusion regionis significantly increased, the shear strength of the welded AZ31B/Cu joint showed ascendand then declines, the strength reaches maximum of61MPa at500℃,40min,2.5MPaconditions approximately44%of the base metal. The fracture was showing quasi-cleavagefracture characteristics. The fusion zone of Mg/Cu TIG welded joint was composed of fusion zone and brazingzone.The fusion zone include non-crystal and column dendrite structure which consisted ofCu2Mg、Mg2Cu phase, and little oxide phase. The joint of TIG weld fracture occurred fusionzone close to the Mg side, the fracture plastic morphology is in Cu side, the typical brittlefracture morphology is in Mg side.With Mg/Cu diffusion under different process conditions study Mg/Cu diffusion growthmechanism of the reaction layer and element diffusion theory, According to the method ofBoltzmann-Matano established Mg element, Cu element diffusion concentration distributionequation in the interface region, Combined with the error function solution and diffusioncoefficient set up the diffusion equation of interfacial transition zone response elements.Simulation of Mg and Cu elements in the Mg2Cu and Cu2Mg Intermetallic compoundsconcentration diffusion, and with the EPMA experimentally measured results were close to.