Numerical prediction and experimental investigation of aerospace-grade dissimilar aluminium alloy by friction stir welding

In a global scenario, the high strength lightweight dissimilar aluminium alloy 7075 and 2014 joining delivers a new opportunity to reduce weight in aerospace vehicles. The dissimilar aluminium alloy joining faces a technical challenge during fusion welding, due to the difference in thermo-mechanical properties. In this present work, the temperature distribution and grain size effects on dissimilar friction stir welded aerospace-grade aluminium alloy 7075 and 2014 was studied numerically and verified experimentally. The 3D integrated multiphysics model, coupled with a moving coordinate system, was simulated with the frictional effects of tool shoulder, pin to the workpiece and stick-slip mechanism. The dissimilar numerical model predicts the temperature and grain size changes across the weld zone. To verify the numerical model, two experiments T9 and T11 welded with a specimen size of 200 x 100 x 3 mm by the FSW-3T-CNC machine. The high-temperature computerized compact DAQ (R) 9212 and Lab VIEW(C) software interfaced with K-type thermocouple to measure the temperature. The measured temperature and grain size across the weld are in good agreement with simulated values. Optical microstructure and SEM micrographs illustrate T9 and T11 dissimilar joint with a clear onion pattern in the stir zone, which ensures the proper mixing of material with dynamically recrystallized fine equiaxed grains. The variation in hardness value observed from stir zone to base metal region and the average hardness in stir zone as 139 HV and 133 HV for T9 and T11 specimen, respectively.