PSI - Issue 17

Available online at www.sciencedirect.com Structural Int grity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect

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Procedia Structural Integrity 17 (2019) 355–362

ICSI 2019 The 3rd International Conference on Structural Integrity Determination of Fracture Modes in Novel Aluminum-Steel Dissimilar Resistance Spot Welds Liting Shi a,b , Jidong Kang a , Xu Chen b , ICSI 2019 The 3rd International Conference on Structural Integrity Determination of Fracture Modes in Novel Aluminum-Steel Dissimilar Resistance Spot Welds Liting Shi a,b , Jidong Kang a , Xu Chen b ,

Amberlee S. Haselhuhn c , David R. Sigler c , Blair E. Carlson c a CanmetMATERIALS, 183 Longwood Road South, Hamilton, Ontario, L9P 0A5, Canada b School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China cGeneral Motors Global R&D Center, 30470 Harley Earl Blvd, Warren, MI 48092, U.S.A. Amberlee S. Haselhuhn c , David R. Sigler c , Blair E. Carlson c a CanmetMATERIALS, 183 Longwood Road South, Hamilton, On ario, L9P 0A5, Canada b S hool of Chemical Engineering a d Technology, Tianjin Uni ersity, Tianjin, 30 072, China cGeneral Motors Global R&D Center, 30470 Harley Earl Blvd, Warren, MI 48092, U.S.A.

Abstract Abstract

With increasing demands to improve vehicle fuel economy, multi-material body structures are increasingly utilized in the automotive industry for structural lightweighting purposes. These multi-material structures pose challenges in dissimilar material joining, particularly aluminum to steel. General Motors (GM) developed a new resistance spot welding technique using a multi ring domed electrode and multiple solidification weld schedules to address these challenges. In aluminum-steel resistance spot welds (RSWs), an iron-aluminum intermetallic compound (IMC) layer is formed at the interface and its strength affects tensile shear specimen fracture modes, i.e. interfacial versus pull out fracture. Based upon the experimental heat affected zone (HAZ) and IMC shear strengths using a new mini-shear test specimen, it was observed that it was not suitable to use the critical weld nugget diameter of 4√ recommended by the American Welding Society (AWS) to determine the fracture modes of these unique aluminum-steel spot welds. In the present study, a new formula considering the shear strength of intermetallic layer in aluminum to steel RSWs is derived to calculate a critical aluminum-steel weld nugget diameter based upon experimental results. The calculated critical weld nugget diameters were then compared with experimental results to predict fracture modes for aluminum steel stack-ups with different sheet thicknesses. With incr asing demands to improve vehicle fuel economy, multi-material body structures are incr asi gly utilized in the automotive industr for structural lightweighting purposes. These multi-material structures pose challeng s i dissimilar material joining, particularly aluminum to steel. General Motors (GM) developed a new r sistance spot welding technique using a multi ring domed electrode and ultiple solidification weld schedules to address these challenges. In aluminum-steel resistanc spot welds (RSWs), an iron-aluminum intermetallic compound (IMC) layer is formed at the interface and its strength affects tensile shear specimen fracture modes, i.e. i terfacial versus pull out fracture. Based upon the experimental heat affected zone (HAZ) and IMC shear strengths using a new mini-shear test specimen, it was observed that it was not suitable to use the critical weld nugget dia eter of 4√ recommended by th American Welding Society (AWS) to d termine t e fracture modes of these unique aluminum-steel spot welds. In the present study, a new for ula considering the shear strength of intermetallic layer in aluminum to steel RSWs is d rived to calculat a critical aluminum-steel weld nugget diameter bas upon experimental res lts. The calculated critical weld nugget diameters were then compared with experimental results to predict fracture modes for aluminum steel stack-ups with different sheet thicknesses.

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers.

Keywords: resistance spot welds; intermetallic compound layer; critical weld nugget diameter; predict fracture modes Keywords: resistance spot welds; intermetallic compound layer; critical weld nugget diameter; predict fracture modes

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers.

2452-3216  2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ICSI 2019 organizers. 10.1016/j.prostr.2019.08.047