The interfacial structure and mechanical properties of Al/Mg joints with and without Zn interlayer by friction stir-induced brazing bond have been investigated. The results revealed that the formation of brittle Al-Mg intermetallics could be effectively suppressed by the addition of Zn interlayer and using appropriate welding parameters, which were replaced by α(Mg)+Mg-Zn and Al-Mg-Zn intermetallic. When rotation speed was further increased, Al-Mg intermetallics were formed again at the interface. The shear strength of Al/Mg joints with Zn interlayer was improved by up to ∼ 25% in comparison with those of the joints without Zn interlayer. A mixture of ductility and cleavage fracture occurred on fracture surfaces of Zn-added joints which was different from the cleavage fracture feature of the direct joints.
We explored the growth kinetics of intermetallic compound (IMC) layers at the joint interface of the friction stir lap welded Mg alloy to Al alloy joint during post-weld annealing treatment. The intermetallic layer formed between the Al alloy and Mg alloy was composed of continuous β phase and γ phase; the β phase layer grows faster than the γ phase layer. A quantitative analysis of the IMC layer thickness as a function of aging time and temperature was performed. The diffusion coefficients were calculated from the parabolic relationship between the migration of the interface and the annealing time. The activation energies for IMC growth were determined as 113.5 and 69.3 kJ mol−1 for the γ and β phases, respectively.
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