Influence of base metal temper conditions on AA6082 and AA7050 dissimilar friction stir weld properties

In this work, the effect of base metal temper conditions was studied on joint properties of various dissimilar AA6082/AA7050 weld combinations: (i) 6082-T6/7050-T7, (ii) 6082-T6/7050-O, (iii) 6082-O/7050-T7, and (iv) 6082-O/7050-O. The weld macrostructure showed high susceptibility to onion ring formation when either side base metal was in O-temper condition. Heterogeneity in weld nugget microstructure was found to be minimum for dissimilar joints produced with different tempered base metals having the largest strength difference. The weld nugget average hardness was highest (120.86 HV) for the hardest base metals combination and lowest (97.57 HV) for the softest base metals combination dissimilar joints. The highest joint tensile strength was 218.5 MPa for weld fabricated from base metals having the smallest difference in tensile strength. In contrast, the lowest joint tensile strength was 120.4 MPa for weld produced from the combination of base metals having the greatest difference in tensile strength. All welded joints were fractured from the advancing side and exhibited ductile fracture behavior.