Microstructural comparison of friction-stir-welded aluminum alloy 7449 starting from different tempers

Since friction stir welding (FSW) does not create defects that are normally associated with fusion welds, it has become the preferred method for joining aluminum 7XXX series alloys. This work analyzes and compares friction stir welds of two different tempers in aluminum alloy 7449. A thorough analysis was done to characterize the two as-received alloys. Weld parameters were kept identical for the two different starting tempers. Thermocouples were used in the heat-affected zone at three different depths to obtain experimental thermal profiles. Hardness traverses and differential scanning calorimetry were used to analyze the strength of the welds and to analyze precipitate evolution. Simulated thermal profiles were generated via finite element analysis for the weld centerline. Our analysis confirms that preexisting precipitates in the as-received material have an effect on the final microstructure of the welds. A highly overaged aluminum 7449 alloy responds better to FSW as compared to a slightly overaged aluminum 7449 alloy.