Effect of microstructure and intermetallic precipitates on the electrochemical behavior of dissimilar AA6061-T6/ER5183/AA5086-H32 aluminum TIG weld

In the present work, dissimilar tungsten inert gas welding of AA6061-T6 to AA5086-H32 has been conducted using pulsed and alternating welding current. Microstructure examination revealed that the extent of the heat-affected zone in pulsed weld joint is narrower than the one obtained by alternating current. Energy-dispersive spectroscopy analysis showed that, regardless the welding process, both alloys contained Fe-rich intermetallic precipitates in base metal and heat-affected zone. Besides, only β-phase is detected in 6061, while Al 3 Mg 2 was found in 5086 alloy. The electrochemical behavior of each zone of the weldments is evaluated in ASTMG69 media according to two setups where the open circuit potential is affected; a second setup is used to check the results. The polarization curves of base metal and heat-affected zone of both alloys overlap each other, and the entire curves exhibit a cathodic plateau with constant current density, while the lowest resistance polarization was obtained in weld zone of both assemblies. Atomic force microscopy and scanning electron microscopy micrographs of the exposed surface suggest that all welding regions suffer from localized corrosion where the intermetallic precipitates act as nucleation sites for corrosion.