Electrochemical and Microstructural Investigations of AA6063 Friction Stir Welded Joint

In the present study, the influence of the pin rotating speed on corrosion behavior and mechanical properties of the friction stir welded (FSW) 6063 aluminum alloy joints was investigated. The welding process was performed at rotating speeds of 800, 1000, and 1200 rpm and a constant traverse speed of 50 mm/min. The joints were analyzed via optical microscopy, scanning electron microscopy, and microhardness test. A cyclic polarization test and electrochemical impedance spectroscopy (EIS) were performed so as to study the effect of the pin rotating speed on corrosion behavior of joints in the solution of sodium chloride (3.5%). Microhardness results showed that the maximum amount of hardness is related to the sample with 1000 rpm rotating speed because of optimized input heat, which caused an increase in the grain refinement and dynamic recrystallization. The cyclic polarization test demonstrated that the corrosion rate in the heat affected zone (HAZ) was higher than that of the base and weld metals; this is due to grain coarsening and an increase of secondary phase particles, which causes intensification of galvanic corrosion. It was found that the higher the pin rotating speed, the higher the corrosion rate. The growth of secondary phase particles was identified due to an input heat increase. Also, EIS results indicated that increasing the pin rotating speed at FSW reduces the polarization resistance (RP) amount at the Nyquist diagram, followed by a decrease of corrosion resistance. A lower amount of RP and corrosion resistance verified in the HAZ was compared to those of the weld metal.