Microstructural and mechanical properties of Al-Mg-Si-Cu joint fabricated by rotary friction welding

The correlation between the microstructural evolution and mechanical properties in different regions of Al-Mg-Si-Cu joint fabricated by rotary friction welding (RFW) has undergone a rigorous quantitative investigation using Vickers hardness evaluation, uniaxial tensile tests, electron backscatterred diffraction, X-ray diffractometry and transmission electron microscopy. The results of the investigation indicate that premature yielding and localized stress concentration inevitably occurred at the weakest heat affected zone (HAZ) region, remarkably compromising the mechanical properties of the joint. TEM observations revealed the presence of the rod-like Q ' phase and lath-like C phase within the BM and the pre-beta '' phase in the weld zone, while no precipitate was identified in the HAZ on either sides. Although partial dynamic recrystallization occurred in HAZ reduced the grain size, extensive dislocation recovery and precipitate dissolving were two factors to be responsible for the lowest strength of the HAZ. On the contrary, fully recrystallization, severe plastic deformation and reprecipitation synthetically contributed to the strength recovery in the weld zone. Eventually, a model based on microstructural evolution that can quantitatively describe the observed strength difference in different regions is developed, suggesting that the major strength contributor is the dislocations strengthening, then the precipitation strengthening.