Achievement of high-quality joints and regulation of intermetallic compounds in ultrasonic vibration enhanced friction stir lap welding of aluminum/steel

Improved Interface Morphology and Failure Load of Ultrasonic-Assisted Friction Stir Lap Welding Joint of 2024 Aluminum Alloy to 304 Stainless Steel

“…As is known, for the butt joint by FSW, the steel plate is always put at the advancing side (AS) based on the difference in the thermal flow behaviors of these two materials [24][25][26]. For the lap joint, the aluminum alloy plate is often served as the upper plate in order to greatly decrease and even avoid the tool wear, and can be placed at the AS [30,33] or the retreating side (RS) [16,19]. In this study, the upper aluminum plate was placed at the AS, as displayed in Figure 1a.…”

“…In recent years, to heighten the loading capacity of Al/steel FSW joints, the assisted welding process has gradually become a research hotspot in addition to the optimization of process parameters such as welding speed, rotating velocity, and so on [21][22][23]. The ultrasonic-assisted process has been successfully used in friction stir butt welding [24][25][26] and friction stir spot welding [27][28][29], and some researchers have also used ultrasonicassisted FSLW (UAFSLW) to join aluminum to steel [5,[29][30][31]. Hong et al [29] studied the UAFSLW joint of 6061 aluminum alloy and 301L steel and showed that the excessive growth of the Al-Fe IMC layer in the weld core region of the joint was suppressed by the stirring action of the welding tool and the ultrasonic vibration; the average thickness of the IMCs was reduced from 10 µm in the FSLW joint to 6 µm in the UAFSLW joint, and the 16.5 kN tensile load of UAFSLW joint was 27.9% higher than the traditional FSLW joint.…”

“…Hong et al [29] studied the UAFSLW joint of 6061 aluminum alloy and 301L steel and showed that the excessive growth of the Al-Fe IMC layer in the weld core region of the joint was suppressed by the stirring action of the welding tool and the ultrasonic vibration; the average thickness of the IMCs was reduced from 10 µm in the FSLW joint to 6 µm in the UAFSLW joint, and the 16.5 kN tensile load of UAFSLW joint was 27.9% higher than the traditional FSLW joint. Liu et al [30] used UAFSLW and traditional FSLW to weld 6061 aluminum alloy and Q235 steel. Their results showed that the assistance of ultrasound improved the mechanical interlocking capacity of the interface center, changed the IMC type from highly brittle FeAl 3 to highly ductile FeAl, reduced the thickness of the IMC layer from 5.01 µm to 0.71 µm, and then fabricated the joint with the failure load 21% larger than the traditional FSLW joint.…”

“…Their results showed that the assistance of ultrasound improved the mechanical interlocking capacity of the interface center, changed the IMC type from highly brittle FeAl 3 to highly ductile FeAl, reduced the thickness of the IMC layer from 5.01 µm to 0.71 µm, and then fabricated the joint with the failure load 21% larger than the traditional FSLW joint. In fact, similar to the UAFSLW process, ultrasonic-assisted FSW (UAFSW) of Al/steel butt joints has an enhanced joint loading capacity [5,[24][25][26]30]. Wu et al [5] reported that the addition of ultrasound during FSW improved the micro and macro mechanical interlocking structures which were positive on the joint loading capacity.…”

“…In summary, the addition of ultrasound vibration to the FSLW process can improve the tensile properties of the Al/Steel joint. However, some current studies only focus on UAFSLW of 6000 series aluminum alloys and steels [29,30]. 2024 aluminum alloy and 304 steel are two kinds of metals that are widely used in the field of aerospace, so research on the joining of these two metals by the FSW process is necessary.…”