Effect of friction stir welding on microstructure and corrosion behavior of LF6 aluminum alloy

The LF6 aluminum alloy plates were joined by friction stir welding method. The tool rotational (1180 rpm) and transverse speed (0.56 mm s(-1)) were kept constant during welding of 4 mm thick plates. The microstructural features, hardness and tensile properties of the welded samples were determined to evaluate the structural integrity in comparison with the base metal. The electrochemical behavior of base metal (BM), thermo-mechanically affected zone (TMAZ) and weld nugget zone (WNZ) was also investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution. The microstructural study revealed significant grain refinement and agglomeration of beta (Mg2Al3) intermetallic precipitates in the WNZ. The relatively higher hardness and a decrease in the ductility (3%) also assured the formation of precipitates beta precipitates in the WNZ welded samples. The fracture surface of welded sample also revealed the existence of beta precipitates within the elongated dimples which may be considered as the crack initiation sites. The relatively lower corrosion rate (23.68 mpy) and higher charge transfer resistance (403 Omega cm(2)) of BM compared to WNZ could be associated with the galvanic dissolution of Al-matrix through competitive charge transfer and relaxation (adsorption/desorption of intermediate species) processes specifically at the vicinity of the beta precipitates.