LME susceptibility of a medium-Mn advanced high-strength steel with galvanizing coating

Abstract Zn-induced liquid metal embrittlement (LME) cracks tend to be formed in hot-dip galvanizing (GI) medium-Mn advanced high-strength steel (AHSS) in the process of resistance spot welding (RSW). In the present study, the LME susceptibility of the medium-Mn AHSS with GI coating was systematically evaluated in accordance with the criterion of “Auto/Steel Partnership (A/SP)”. The samples were welded at 16 groups of distinct welding current levels from 7.0 kA to 14.5 kA in 0.5 kA increments. Some severe LME cracks were evident in the cross sections of the RSW joints even below expulsion, and more pronounced and serious LME cracks appeared at or above expulsion. It was discovered that the tendency for LME crack formation tended to worsen as the welding current increased. The maximum LME crack lengths of Type A, B, C, and D among all groups were approximately 1,285.0 μm, 980.5 μm, 1,397.0 μm, and 131.9 μm, respectively. Results revealed that the medium-Mn AHSS with GI coating displayed high LME susceptibility, which consequently failed to satisfy the necessary criterion for RSW application in the automotive industry. Moreover, the elevated Mn content was deemed as a critical factor leading to the high LME susceptibility of medium-Mn AHSS with GI coating.