Abstract
Liquid metal embrittlement (LME) in Zn-coated steels is a serious issue in automotive design. The risk of rising LME surface cracks in resistance spot welding (RSW) of Zn-coated high strength steels has triggered significant research activities across the globe. This paper presents a state-of-the-art review of the various phenomena and issues related to LME during RSW. Various aspects of LME surface cracks have been described in this review, focusing on the macro- and microscopic features of LME, spot weld cracks, the sensitivity of the LME cracks towards surface locations, welding conditions, and susceptibility to high strength and galvanized steels. We also focus on the effects of various processing factors, such as temperature, stress, microstructure, and the nature of the galvanized layer, related to studies with actual spot welds LME cracks. Finally, we summarize the possible mechanisms of embrittlement and the remedies for minimizing LME cracks, with suitable guidelines to suppress surface cracks during RSW.
Highlights
Steels with yield strength higher than 550 MPa are classified as advanced high strength steels (AHSSs) [2,3]
transformation-induced plasticity (TRIP) steel is composed of a multiphase microstructure composed of ferrite, bainite, and retained austenite which is similar to DP steel
We focused on an overview of liquid metal embrittlement of the galvanized TRIP
Summary
There are several types in advanced high strength steels (AHSSs), such as dual-phase (DP), transformation-induced plasticity (TRIP), twinning-induced plasticity (TWIP), complex phase (CP), martensitic (MART or MS), interstitials free (IF) steels, and so on [1]. AHSSs have unique microstructures, such as a combination of retained austenite, bainite, and/or ferrite multiphases, that are transformed or twinned during elongation. Steels with yield strength higher than 550 MPa are classified as AHSSs [2,3]. Steel is an important raw material for various industries. The global AHSSs market share was $13,147 million in 2016. We will only discuss the important steels used in automotive structures. Anoverview overviewof ofimportant important advanced advanced high high strength strength steels steels (AHSSs)
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