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.
In this paper, the interface characterization and materials flow pattern of overlap joints of dissimilar alloys of 6061-T6 aluminum alloy and AZ31B magnesium alloy welded by friction stir overlap welding with a reverse conical pin tool were investigated. The results shown that: when AZ31B magnesium alloy sheet was placed over 6061-T6 aluminum alloy sheet, and AZ31B magnesium alloy sheet was settled at advancing side while 6061-T6 aluminum alloy sheet was at retreating side, it could eliminate the influence of migration interface on the strength of the lap joints. What is more, the intermetallic compound Mg17Al12 were formed at advancing side of magnesium alloy sheet and retreating side of initial interface between magnesium alloy sheet and aluminum alloy sheet. According to the distribution of intermetallic compound and the characteristics of migration interface, the plastic flowing pattern of metal in welding process was also evaluated.
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