Supercritical area and critical nugget diameter for liquid metal embrittlement of Zn-coated twining induced plasticity steels

Liquid metal embrittlement induced cracking of zinc-coated twining induced plasticity steels was investigated during their resistance spot welding. Crack resistance of steel was investigated in relation to liquid metal embrittlement phenomenon. It was found that there are supercritical area and critical nugget diameter for cracking the welds. This suggests that crack-free welds are obtained only if the maximum nugget diameter being formed at expulsion current maintains below the critical nugget diameter of liquid metal embrittlement. Moreover, different Zn-coated (galvanized, galvannealed and electrogalvanized) twining induced plasticity steels are embrittled by liquid zinc but their cracking resistances are depended on chemical composition and process conditions of coating materials. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.