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Surface breaking cracks in resistance spot welds ofdual-phase steels with electro and hot dip zinc coating
KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Welding Technology.
KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Welding Technology.
KTH, School of Industrial Engineering and Management (ITM), Production Engineering.ORCID iD: 0000-0002-6061-662X
2013 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 18, no 1, 25-31 p.Article in journal (Refereed) Published
Abstract [en]

In normal production of resistance spot welded galvanised structures, it is difficult to completely avoid surface breaking cracks. Known key factors to cause cracking are zinc coating, electrode wear during subsequent welding and insufficient electrode cooling. In this report, an embrittlement mechanism was investigated that could be coupled to the galvanisation method for dual phase steels. With identical bulk material and weld parameters, the first 50 spot welds were crack free with electrogalvanised coating, while only 10 out of 50 were crack free with hot dip galvanised coating. Energy dispersive X-ray spectroscopy analysis of the worn electrode surfaces used for welding of the hot dip galvanised coating revealed areas of aluminium oxide. Since aluminium oxide is a very strong isolator, the electrical resistance will increase, which in turn is suggested to increase the surface temperature of the spot weld and thereby increase the probability for liquid metal embrittlement and surface cracks.

Place, publisher, year, edition, pages
2013. Vol. 18, no 1, 25-31 p.
Keyword [en]
Resistance spot welding, Liquid metal embrittlement, Surface cracking, Advanced high strength steel
National Category
Engineering and Technology
Research subject
SRA - Production
Identifiers
URN: urn:nbn:se:kth:diva-105376DOI: 10.1179/1362171812Y.0000000068ISI: 000312215500004Scopus ID: 2-s2.0-84871349725OAI: oai:DiVA.org:kth-105376DiVA: diva2:570652
Funder
XPRES - Initiative for excellence in production research
Note

QC 20130220

Available from: 2012-11-20 Created: 2012-11-20 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Challenges in Resistance Welding of Ultra High Strength Steels
Open this publication in new window or tab >>Challenges in Resistance Welding of Ultra High Strength Steels
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.
Series
TRITA-IIP, ISSN 1650-1888 ; 15:02
Keyword
Resistance welding, spot welding, surface cracks, nut welding, UHSS, projection welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-167985 (URN)978-91-7595-577-3 (ISBN)
Presentation
2015-06-03, M311, Brinellvägen 68, KTH, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Funder
XPRES - Initiative for excellence in production research
Note

QC 20150526

Available from: 2015-05-26 Created: 2015-05-25 Last updated: 2015-05-26Bibliographically approved

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Melander, Arne

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