Study On Diffusion Bonding Of Mg Alloy And Al Ally By Using Silver As Interlayers

Magnesium alloys are widely used in many fields, especially in the fields of aerospace, automobile and electronic industries due to their unique performances, such as low density, high strength, excellent processing performance, high impact resistance performance. Bonding of Mg and Al can not only combine their excellent performance, but also expand the applications in the high-tech fields. So it is meaningful to combine Mg and Al together.In this paper, diffusion-bonding of Mgl and1060A1with silver interlayer has been investigated. Effects of the welding process parameters (bonding temperature, holding time) on the microstructure and mechanical properties of the joints have been studied. The microstructure and elemental distributions at joint interface were characterized by SEM, EPMA and EDS. Shear strength and microhardness were used to evaluate the mechanical performance of the joints. The fracture surfaces of the joint after shear strength test were measured by XRD and SEM. The formation and the elemental diffusion law of Mg/Ag foil/Al joints were analyzed based on Fick’s second law and Boltzmann-Matano method.The addition of silver foils has successfully eliminated the formation of brittle Mg-Al intermetallic compounds with high hardness by impeding the inter-diffusion of Mg and Al. The strength of the joints has been improved. The typical microstructure of Mg/Ag foil/Al joint is Mg3Ag-MgAg-Ag-Ag2Al multilayer structure. The thicknesses of Mg3Ag, MgAg and Ag2Al increased with the rising bonding temperature and longer holding time. The shear strength of the joints increased with the rising bonding temperature, which was opposite to holding time. The maximum strength (11.8MPa) of the joint was obtained at470℃for30min. The brittle failure of Mg/Ag foil/Al joints occurred between Ag2Al and Al base.The addition of silver films has reduced the difficulties of bonding Mg and Al. The strength of the joints has been improved further by decreasing the amount of micro-crack at the interface. Strong Mg/Ag film/Al joints were prepared by diffusion bonding. Mg3Ag and MgAg were formed at the interface of Mg/Ag film/Al joints, rather than Mg-Al intermetallic compounds. The thicknesses of Mg3Ag and MgAg increased with the rising bonding temperature and longer holding time. The shear strength of the joints increased first and then decreased with the increase of bonding temperature and holding time. The maximum strength (14.5MPa) of the joint was obtained at390℃for30min. Fracture failure in Mg/Ag film/Al joint occurred between Mg3Ag layer and MgAg layer. Transgranular fracture, intergranular fracture and plastic deformation were observed on fracture surfaces of Mg/Ag foil/Al joint.The diffusion coefficient of Mg, Ag and Al at the interfaces of Mg/Ag and Ag/Al were calculated according to Fick’s second law and Boltzmann-Matano method. The diffusion coefficient of Mg, Ag and Al increased with the rising bonding temperature. Reaction-diffusion equations of Mg, Ag and Al at the interfaces of Mg/Ag and Ag/Al were obtained and optimized based on the calculated diffusion coefficients and error function. The relations between the thickness of each compound layer at the interface and bonding temperature T, holding time were achieved by the empirical formula of diffusion rate and Mg, Ag, Al diffusion distance. The difficulty of the growth of the three different compound layers at the Mg/Ag foil/Al interface was MgAg>Mg3Ag>Ag2Al.