Experimental and numerical investigations into the failure mechanisms of friction stir welded AA7075-T6 thin sheets

The formability of AA7075-T6 friction stir (FS) welded tailor-made blanks was investigated through the hemispherical-punch stretching method, experimentally and numerically. The effect of welding process and deformation temperature on formability and failure mechanisms are studied. The results show that formability of the material increases where forming occurs at a higher temperature (180 °C) and reduces after FS welding. At higher temperature (180 °C which has no effect on previous T6 heat treatment) the failure mechanism converts from shear fracture to localize necking. The latter can be concluded by increasing the m-value at the higher temperature. Also, forming limit diagrams (FLDs) were plotted experimentally and numerically for all the conditions. Three different localized necking models were applied through the numerical simulations in order to predict the onset of failure. The results revealed that Tresca criterion is reliable for predicting FLDs of base and FS welded at different temperatures.