Microstructural and Mechanical Behavior of Friction-Stir-Welded AA6061-T6 and AZ31 Alloys with Improved Electrochemical Corrosion

The effect of tool travel speed on the mechanical, microstructure and corrosion behavior of friction-stir-welded dissimilar AA6061-T6/AZ31 alloys has been characterized. Two different electrochemical techniques were studied in detail, i.e., potentiodynamic polarization test and electrochemical impedance spectroscopy at various pH values (i.e., pH = 2, pH = 7 and pH = 12) for all set of welded samples. Microstructural investigations were performed with the help of optical, SEM and EBSD microscopy techniques. The maximum corrosion rate (C-r) (29 mm/yr) at pH = 2 was obtained for sample A1 and minimum C-r (26 mm/yr) corresponding to sample A3, whereas, at pH = 12, maximum Cr (21 mm/yr) was obtained for sample A2 and minimum (19 mm/yr) was corresponding to sample A3. The cryo-Charpy impact test demonstrates the drop in values in all the cases with respect to room temperatures (25 degrees C), i.e., 16, 24 and 47% for sample A1, 19, 24 and 57% for sample A2, and 12, 33 and 36% for sample A3 at 0, - 20 and - 40 degrees C, respectively. The intermetallic compounds (IMCs) like Al12Mg17 and Al3Mg2 (before corrosion) and Mg(OH)(2) and Al(OH)(3) (after corrosion) were formed in the stir zone (SZ). The joint efficiency was 65, 84 and 91%, at different levels of welding speed, i.e., 16, 20 and 25 mm/min, respectively. The fracture analysis of tensile and cryo-Charpy impact toughness test was shown in both ductile and brittle fracture behavior.