Enhancing corrosion resistance and mechanical properties of dissimilar friction stir welded 5083-6061 aluminium alloys using external cooling environment

Abstract

Dissimilar friction stir welding of AA5083-AA6061 alloys in different cooling environments (air, liquid nitrogen, and water) was successfully employed as an alternative method to enhance corrosion resistance and mechanical properties. The evolution of microstructure, corrosion behavior, and mechanical properties of friction stir welded joints were studied using optical microscopy (OM), electron backscattered diffraction, scanning electron microscope, electrochemical workstation, and universal testing machine. The results indicated that the width of the stir zone and grain size of heat-affected zones were reduced by the use of external cooling media. Electron backscattered diffraction results showed that the grain size in air-cooled friction stir welding, nitrogen-cooled friction stir welding and water-cooled friction stir welding were 7.6 µm, 4.5 µm, and 3.2 µm, respectively, and water-cooled friction stir welding joint developed a larger fraction of high-angle grain boundaries at stir zone. The intermetallics formed in the joints using cooling media were finer compared to that of the air-cooled samples. The corrosion behavior of the stir zone was impacted by the cooling environment while potentiodynamic polarization results revealed that the water-cooled friction stir welding joint showed excellent corrosion resistance due to the finer size of intermetallics. The minimum hardness values shifted to the stir zone in the case of nitrogen-cooled friction stir welding and water-cooled friction stir welding from the heat-affected zone location as in the air-cooled friction stir welding joint. For the joint made with water-cooled friction stir welding, maximum yield strength was obtained with a joint efficiency of 96% relative to AA5083 base material.

Influence of brass interlayer and water cooling on microstructure, mechanical and corrosion behaviour of friction stir welded AA6061-T6 alloy

“…WCFSW with and without interlayer joints fractured in SZ due to improved hardness in HAZ. The shifting of water-cooled weld fracture location towards weld centre, that is, SZ was also observed by Sinhmar et al 41 and Kumar et al 44…”

“…WCFSW with and without interlayer joints fractured in SZ due to improved hardness in HAZ. The shifting of water-cooled weld fracture location towards weld centre, that is, SZ was also observed by Sinhmar et al 41 and Kumar et al 44 Generally, in metals, dimples indicate a ductile fracture, and these are formed when dislocations interact. Dislocations can easily slide, climb, and cross-slip during the initial stages of deformation.…”

“…The elongated grains in TMAZ (Figure 4(e) and (g)) were due to the frictional heating and slight mechanical deformation containing slightly refined and elongated grains. Kumar et al 44 stated that following the application of water coolant, the cooling rate increases, resulting in shorter period to maintain the peak temperature after the weld. Consequently, the grain size decreased in HAZ and TMAZ (Figure 4(b), (d), (f) and (h)) of the WCFSW with and without interlayer.…”

Friction stir welding of dissimilar alloy combinations—A Review

“…14 However, FSW process would be a better alternative for conventional processes when it is joining dissimilar materials. As an evidence sound welds for dissimilar Al-Al, 15 Mg-Mg, 16 Cu-Cu, 17 steel-steel 18 alloys and the combination of Al/Mg, 19 Al/Cu, 20 Al/steel, 21 Al/Ti, 22 Mg/steel, 23 Ti/steel, 24 Cu/steel 25 and stainless steel/superalloy 26 were reported.…”

Microstructure, mechanical and electrochemical studies of dissimilar friction stir welded aluminium alloys

“…They also found that galvanic coupling caused high corrosion density at the nugget zone. Out of all samples, less corrosion resistance was obtained for the sample welded at high rotation speed due to the formation of defects and insufficient material mixing [30][31][32].…”