Flat plates of AA 6061 alloy were welded by using friction-stir welding technique. The plates were placed in direct contact to the bench of the tool holder machine and mechanically fixed, with the bench functioning as a cooling substrate. For the friction-stir welding tool, the optimal values of spindle speed and feed rate were 1045 rpm and 18.6 mm/min, respectively. The welded plates were mechanically characterized in terms of Vickers microhardness (HV), ultimate tension strength (UTS), yield point (YP) and elongation to failure (EF). The weld bead showed a decrease in hardness of 33 % approximately. Tension test results of the welded plates showed UTS, YP and EF were reduced to 66, 60 and 33 % in relation to those of the base metal. X-ray diffraction analysis revealed the presence of q (Al2Cu), Q' (Al3Cu2Mg9Si7), β² (Mg5Si6), β¢ (Mg9Si5), aAl and Al phases inside the weld bead, while the base metal showed to contain β² and β¢ precipitates inside the Al-rich matrix. Heat treatment of solid solution and ageing at 433 K by 18 hours increased the weld bead hardness to 110 HV in the welded plates.
Hinojosa-Torres et al. (Tue,) studied this question.