ICME-W Ultrasonic plus resistance spot welding for joining aluminum to steel

Professor Zhang and his colleagues made a breakthrough in cost-effective dissimilar metal joining for fuel-efficient vehicles. Press hardened boron steels with ultrahigh strength (above 1500 MPa) are widely used in crash-sensitive safety components. Joining such steels to aluminum alloys is challenging due to various factors including the steel’s tenacious Al-Si coating. Prof. Zhang's team successfully applied ultrasonic plus resistance spot welding (abbreviated as U+RSW) to join 1.2-mm-thick AA6022-T4 to 1.4-mm-thick Al-Si coated press hardened boron steel, Usibor®-AS 1500. The joint had a high lap shear strength of 5 kN with a button pull-out fracture from the AA6022 sheet. The results of that study are published in Metallurgical and Materials Transactions A.

The U+RSW process was developed initially on joining aluminum alloy to uncoated low carbon steels. In their papers published in Materials & Design and Welding Journal, U+RSW was used to join 1-mm-thick AA6061-T6 to 0.9-mm-thick AISI 1008 steel with 0.4-mm-thick AA6061-T6 or 0.3-mm-thick AA3003 as the insert. The thickness of intermetallic layer formed at the Al insert/steel interface was less than 1.5 µm, resulting in a sound joint strength of 3.2 kN and a nugget pull-out failure mode.

In collaboration with Prof. Carolin Fink, they further studied the application of U+RSW to join 1.2-mm-thick AA6022-T4 to 1-mm-thick Zn-coated (galvannealed) Dual Phase steel DP980. In tensile (or lap) shear testing, the peak strength was 3.7 kN with a button pull-out fracture from the AA6022 sheet. The results are published in Science and Technology of Welding and Joining (access courtesy of Taylor & Francis Online).