The AA7075 is one of the strongest aluminium alloys that have superior mechanical properties such as high strength-to-weight ratio, toughness, tensile strength etc. AA7075 finds application in the aerospace and automobile industries because of its natural ageing property. Also, aluminium alloys find wide applications in shipbuilding, marine structures etc. because of their lower corrosion rate [1]. When FSW and TIG welding processes are compared for AA6061-T6, the FSW joint shows higher strength compared to the TIG joint. The inferior mechanical properties in the case of TIG or metal inert gas welded (MIG) joint is due to the higher temperature generated during the process as compared to the FSW [2–8]. The mechanical properties of welded joints can be increased by using the FSW process rather than MIG. The heat-affected zone (HAZ) of the FSW joint is confined than the MIG process. In the FSW joint, electrical conductivity and hardness have a reciprocal effect [9]. In the case of FSW, hardness is lowest in HAZ, while in TIG and MIG welds hardness is lower in HAZ and weld centre [10]. When the corrosion behaviour of AA6061 alloy joined by FSW and TIG was compared, it was observed that in the case of FSW, the fine grain structure of the weld nugget zone caused corrosion. In the case of TIG, the corrosion is higher than both the parent material and FSW. This is because TIG weld contains plenty of silicon and aluminium eutectic precipitates at the dendrites of metal and inhomogeneous distribution of iron particles at these precipitates [11]. Joint made with TIG is sensitive to intergranular and exfoliation corrosion as compared to joints made with FSW and base metal AA5083-H321 [12]. In the case of AA6063-T6 joints, tensile strength is similar in both TIG and FSW joints before natural ageing [13]. AA2014 FSW has a lower corrosion rate as compared to welds made with TIG as the TIG weld zone consists of coarse grains [14]. Corrosion rate increases in the lower hardness region in the case of both TIG and FSW [14].
TIG welds with AA 4043 filler material showed higher hardness and corrosion resistance as compared to filler material AA4047 [18]. The appropriate value of current to perform TIG welding is 130 amperes [20]. The base metal AA5086-H116 showed a lower corrosion rate than samples with TIG and FSW welds. FSW joint showed better corrosion resistance to exfoliation, but FSW joint is susceptible to pitting corrosion in a contrast to TIG welds [21]. The lower thermal expansion coefficient of the Silicon and aluminium oxide layer causes discontinuity of the Al matrix which reduces the electron movement [23]. Friction stir vibration welding results in finer grains than FSW and TIG as a result of improved recrystallization [25].
Although many researchers compared FSW and TIG processes, investigation on the comparison of FSW with TIG in terms of the corrosion behaviour and electrical conductivity of AA7075 is lacking. Thus, the aim of the current study is to compare the microstructure, mechanical, corrosion behaviour, and electrical conductivity properties of FSW and TIG welded AA7075 aluminium alloy. The results are compared in terms of microstructure, hardness, tensile properties, corrosion and electrical conductivity.