The Heterogeneity in Microstructure and Property of the Welded Joints between 6N01 and 7N01 Aluminum Alloys
6N01 alloy and 7N01 alloy are two important lightweight structural materials for the application of high-speed railway body. The microstructure, hardness distribution and corrosion characteristics in a typical T-joint between T5-treated 6N01 alloy and T5-treated 7N01 alloy dissimilarly welded by metal-inert gas welding (MIG) was investigated by electron back-scattering diffraction (EBSD),optical microscopy, Vickers hardness test and accelerated corrosion test. The results showed that there were significant differences in the grain structures between the weld seam, fusion zone and heat-affected zones. The weld seam had an equiaxed grain structure and the fusion zone consisted of equiaxed grains and columnar grains. In the region near the weld seam, abnormal grain growth was observed in the 6N01 part, while in the 7N01 part only recovery and partial recrystallization happened. In the heat-affected zones of the 6N01 part, there was a hardness groove, namely softening zone, the hardness of which was lower than that of the weld seam. The softening zone is attributed to obvious coarsening of precipitates affected by the heat input during welding. An obvious decrease in hardness occurred only in the weld seam after corrosion. In addition, the corrosion attacks mainly happened in the weld seam and heat-affected zones.
Keywords: welding, aluminum alloy, grain, hardness, corrosion
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