Friction stir weld assisted diffusion bonding of 5754 aluminum alloy to coated high strength steels

• Successful lap joints of Al 5754 sheet to coated DP600 and 22MnB5 steels.
• Negligible effect of welding speed on mechanical properties of Al 5754/22MnB5 joints.
• Lower strength of Al 5754/22MnB5 joints compared with Al 5754/DP600 joints.

In the present paper friction stir-induced diffusion bonding is used for joining sheets of 5754 aluminum alloy to coated high strength steels (DP600 and 22MnB5) by promoting diffusion bonding in an overlap configuration. Mechanical performance and microstructures of joints were analyzed by overlap shear testing, metallography, and X-ray diffraction. Our results show that the strength of joint is dependent upon tool travel speed and the depth of the tool pin relative to the steel surface. The thickness and types of intermetallic compounds formed at the interface play a significant role in achieving a joint with optimum performance. That is, the formation of high aluminum composition intermetallic compounds (i.e. Al5Fe2) at the interface of the friction stir lap joint appeared to have a more negative effect on joint strength compared to the presence of high iron composition intermetallic phases (i.e. FeAl). This is in agreement with previously reported findings that FeAl intermetallic can improve the fracture toughness and interface strength in Al/St joints.