Description
P 1336 – Influence of surface coatings on liquid metal embrittlement during resistance spot welding of advanced high strength steel sheets
The coating of high-strength steel sheet influences the occurrence of liquid metal induced cracking (LME). Therefore, in this work, coatings commonly used in industry with the same base material were characterised with regard to their structure and chemical composition and investigated with regard to their susceptibility to LME. From this comparative investigation, potentials for resistance to LME were identified. These potentials are tested experimentally by using a method developed by the research centre. In addition to uncoated samples, the investigations covered zinc coatings commonly used in industry, such as electrolytically galvanised, hot-dip galvanised, galvannealed and zinc-magnesium coatings.
The LME susceptibility of these different coatings is investigated with a welding under tensile load test set-up. The resulting susceptibility is derived from the crack lengths and the probability of occurrence of LME in the individual tests. A LME susceptibility ranking for the zinc coatings could be determined. Zinc-magnesium coatings were found to be most susceptible to LME, followed by hot-dip galvanised and galvannealed. The greatest LME resistance was found in electrolytically galvanised samples.
Recommendations for action to increase processing safety and weld spot quality are derived from the results.
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Published in:
September 2022
Authors:
M.Sc, B. El-Sari, Dr.-Ing. M. Biegler, Prof. Dr.-Ing. M. Rethmeier
