Effect of tool geometry and welding speed on mechanical properties of dissimilar AA2198–AA2024 FSWed joint

Abstract

Keywords:Friction stir welding FSW tool design Al-Li alloys Welding speed 2024 aluminum alloy Tensile properties DIC A B S T R A C T Different tool geometries were used to investigate the joining of aluminum alloys (AA2198 to AA2024) by friction stir welding (FSW). Three shoulder profiles (flat, raised spiral, and raised fan) and five different pin profiles (cone, half threaded cylindrical, straight cylindrical, tapered cylindrical and square) were selected. Preliminary investigations were conducted by moving the tool into a seamless sheet made of the AA2024-T3 in order to select the tools that produce defect-free joints. Preliminary investigations showed the raised fan shoulder profile helps the material flow from the edge of shoulder to the pin creating a smooth surface finish with no flash in comparison with flat and raised spiral shoulder profiles. Pins with a minimum diameter equal to half the plate thickness produced lack of penetration (LOP) defects, while increasing minimum pin diameter to the plate thickness eliminates the LOP defects. Half threaded cylindrical pin produced tunneling defect, whereas defect free joint made by straight cylindrical, tapered cylindrical and cubic pin profiles. So they were selected for joining AA2024 to AA2198. Fracture locations of different joint variants were observed the vicinity of the thermomechanical affected zone (TMAZ) of AA2198-T3 alloy, and in the nugget on the AA2198-T3 side which have the minimum hardness and highest strain localization as confirmed by hardness maps and digital image coronation (DIC). Higher measured temperature than dissolution temperature of AA2198 main strengthening precipitates could be the reason of low hardness and fracture in TMAZ and center of nugget. Furthermore a raised fan shoulder with a tapered cylindrical pin produced highest elongation and yield strength and it was selected as the best candidate for optimization of the welding parameters. It was found that higher rotational and traverse speeds enhance the formation of tunneling and kissing bond defects, suggesting that longer pins have to be used for higher traverse speeds. Welding speed 750 rpm with 450 mm min −1 could create joint with highest yield strength.

Effect of rolling process on fatigue performance of stir zone of AA6061‐T6 doube‐side friction stir welding joint

“…The weakening of AS interface has been widely investigated. Texier et al 45 observed higher strain between SZ and TMAZ of AS of the AA2024‐AA2198 dissimilar FSW joint. They indicated that the local macroscopic strain localization leading to necking and failure was closely related to local crystallographic orientation heterogeneities.…”

Main Issues in Quality of Friction Stir Welding Joints of Aluminum Alloy and Steel Sheets

“…This is because the larger shoulder (i.e., larger taper angle being the tool tip diameter always 4 mm for all the pins) of tool T1 increases friction between tool and sheets, thus generating high temperatures in weld and the consequent formation of thick IMCs. Khalilabad et al [51] investigated the effects of tool geometry on FSW joint quality. They found that conical and threaded cylindrical pins had the tendency to result in defective joints with kissing bond, tunnel, and flash, as compared to cubical, cylindrical, and tapered cylindrical pins.…”

“…In both cases, limited capability of metal intermixing led to the occurrence of welding defects. Khalilabad et al [51] investigated the effects of tool geometry on FSW joint quality. They found that conical and threaded cylindrical pins had the tendency to result in defective joints with kissing bond, tunnel, and flash, as compared to cubical, cylindrical, and tapered cylindrical pins.…”

Analysis of AA2XXX/AA7XXX friction stir welds

“…Giraud et al (2016) noticed the influence of the process parameters on material mixing, weld integrity, and mechanical behavior. Masoumi Khalilabad et al (2018) observed that increasing the traverse speed of the tool increases the global hardness of the joint, but also creates defects like a kissing bond, in the case of an AA2198/AA2024 FSWed joint.…”