Peculiar roles of nickel diffusion in intermetallic compound formation at the dissimilar metal interface of magnesium to steel spot welds

• Published in: Materials & design Vol. 230; p. 111980
• Main Authors: Walker, Luke, Fink, Carolin, Hilla, Colleen, Lu, Ying, Zhang, Wei
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2023; Elsevier
• Subjects: Computational thermodynamics; Dissimilar metal joining; High strength steel; Intermetallics; Magnesium alloy; Resistance spot welding; Intermetallics; Computational thermodynamics; Dissimilar metal joining; Magnesium alloy; High strength steel; Resistance spot welding
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2023.111980

[Display omitted] •Two largely immiscible metals, magnesium and steel, were spot welded together with a stainless steel or nickel interlayer.•The nickel interlayer formed various Mg-Ni and Al-Ni intermetallics which degraded joint strength and ductility.•Although containing a high amount of Ni, the stainless steel interlayer formed a thin layer of Al-Fe intermetallics.•Joint efficiency with stainless steel interlayer reached 71%, much higher than the literature efficiency values of 16–50%.•Thermodynamic and diffusion kinetics calculations revealed a peculiar difference in nickel dissolution for the interlayers. There is an increased need to join magnesium alloys to high-strength steels to create multi-material lightweight body structures for fuel-efficient vehicles. Direct joining of these two metals is difficult, primarily because pure Mg and pure Fe are immiscible. Although a variety of interlayer materials have been used to facilitate the dissimilar joining in the literature, it is not well understood how the interlayer material affects the joint properties. In this study, a newly developed process, ultrasonic interlayered resistance spot welding (Ulti-RSW), was used to join an Mg alloy to a dual phase high-strength steel with two different interlayer materials: austenitic stainless steel and pure nickel. The IMCs formed with the two interlayers were drastically different, and computational thermodynamics and diffusion simulations revealed that such different IMCs resulted from the peculiar difference in nickel dissolution governed by local chemical potential gradients and diffusion kinetics. The joint with austenitic stainless steel interlayer had an under one micron thick Al-Fe IMC layer and a joint efficiency superior than that with the nickel interlayer as well as other joining processes in the literature.