Challenges in Resistance Welding of Ultra High Strength Steels
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Increasing the use of Ultra High Strength Steels (UHSS) in vehicle bodystructures is important for reducing weight and cutting CO2 emissions. This thesis investigates challenges in resistance welding that can be a barrier to implementing UHSS as a replacement for low strength steels in vehicle structures. Empirical research has been performed to offer new approaches for improved joint strength and to increase knowledge on cracking mechanisms in resistance projection welding and resistance spot welding of UHSS. By optimising the current build-up phase and peak current during the first milliseconds of weld time, it was shown that the strength could be improved by up to two-fold for projection welded joints. An approach to improve the ductility and strength of resistance spotwelds in UHSS using reduced cooling time was unsuccessful. The reduced cooling rate after weld metal solidification did not fully create the desired softened microstructure. The study on the surface cracking mechanism in resistance spot welded dual-phase UHSS showed that cracking is linked to the galvanization method. It is proposed that formation of aluminium oxide layers on the electrode tips increases the surface temperature and thereby increases the probability for liquid metal embrittlement and surface cracking.
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xvii, 59 p.
TRITA-IIP, ISSN 1650-1888 ; 15:02
Resistance welding, spot welding, surface cracks, nut welding, UHSS, projection welding
Manufacturing, Surface and Joining Technology
Research subject Materials Science and Engineering
IdentifiersURN: urn:nbn:se:kth:diva-167985ISBN: 978-91-7595-577-3OAI: oai:DiVA.org:kth-167985DiVA: diva2:813651
2015-06-03, M311, Brinellvägen 68, KTH, Stockholm, 10:00 (Swedish)
Barsoum, Zuheir, Docent
Melander, Arne, Professor
FunderXPRES - Initiative for excellence in production research
QC 201505262015-05-262015-05-252015-05-26Bibliographically approved
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