Temperature evolution in fatigue test of 2024 aluminum alloy weld fabricated by friction stir welding

The weld joints were fabricated by friction stir welding (FSW) on 8 mm thick 2024-O aluminum alloy with a rotating speed of 300 r/min and a welding speed of 60 mm/min. The microstructure and mechanical properties of parent material and weld joints were investigated. The fatigue tests were conducted on both parent metal and weld joint, during which the surface temperatures were recorded by an infrared thermal imager. The results show that the welds exhibit high gradient inhomogeneity in microstructure, and have good fatigue properties. The thermal mechanical affected zone (TMAZ) in advancing side is the weak area as examined by the tensile tests. The temperature change of the specimen surface of the parent material meets the characteristic of “three stages”. Surface temperature variation tendency of the FSW welds is the same with that of the parent material in the first stage and the third stage, but has a downward trend in the second stage. The grains of the weld nugget zone and TMAZ accumulate lots of elastic and plastic strain energy through cyclic softening in the second stage that depress the conversion rate of mechanical energy to thermal energy.