12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

Third generation advanced high strength steels (AHSS) were developed as automotive structural materials capable of enhancing vehicle fuel efficiency and crashworthiness. The use of zinc (Zn) coated AHSS is limited by Zn-assisted liquid metal embrittlement (LME) that leads to surface cracking during high temperature processing. It has been reported that AHSSs are generally more sensitive to Zn-assisted LME compared to conventional mild and high strength low alloy (HSLA) steels; the factors controlling the LME sensitivity of AHSSs are not precisely established. AHSS grades have tailored multi-phase microstructures and relatively rich alloy compositions; microstructural and alloying variations may influence LME susceptibility. In this work, the influence of starting microstructure variations on Zn-LME sensitivity is studied using a 0.25C-2.7Mn-1.45Si steel alloy, continuous annealed to generate different AHSS microstructures: martensitic, quench and partitioned (Q&P;), dual-phase (DP), and transformation-induced plasticity (TRIP)-assisted bainitic ferrite (TBF). High temperature tensile tests were conducted on electrogalvanized (EG) sheets of different starting microstructure variants to compare Zn penetration characteristics, and the critical temperatures and stresses required for inducing LME. The results are interpreted in the context of the specific influence of starting microstructure on LME behavior during resistance spot welding of Zn-coated AHSS sheets.