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Joining in Car Body Engineering is a major annual conference for automotive welding experts. ArcelorMittal’s Global Research & Development team is very active in this field and regularly contributes to the conference program. This year, ArcelorMittal R&D experts are going to present two topics to conference delegates:
Many OEMs are now deploying a weight reduction strategy for their vehicles which sees them make increasing use of advanced high strength steels (AHSS). OEMs also use thickness reduction to reduce the weight of large panels made from mild steels. As a result, very complex three-sheet stack-ups often need to be welded.
However, when welding two AHSS with a very thin outer panel, we frequently observe that the molten zone does not develop completely up to the thin sheet. This paper will demonstrate that, despite there being no fusion of the interface, diffusion welding will link thin sheets of steel in the stack-up and provides good robustness and mechanical properties.
The paper was authored by:
Laurent Cretteur, Joining Team Leader for Automotive Joining Technologies and Properties (AUJTP) at ArcelorMittal Global R&D.
Yohan Merdji, Research Engineer in Joining Techniques at ArcelorMittal Global R&D.
An example of a thin steel sheet diffusion welded to thicker steel sheets
During spot welding, some zinc-coated high strength steels are prone to liquid metal embrittlement (LME). The zinc present on the surface of the steel is likely to melt at temperatures above 420°C. Under certain conditions (temperature, stress…), the liquid zinc rapidly penetrates grain boundaries and causes embrittlement. That results in cracks appearing on the surface of spot welds. The LME phenomenon strongly depends on the welding conditions and combination (stack-ups).
One solution is to avoid sensitive stack-ups. As there are only a few stack-ups which induce LME cracking, design rules can be implemented to avoid sensitive combinations. This paper defines those design rules and demonstrates that ArcelorMittal’s Fortiform® products can be widely used in the body-in-white (BIW) without inducing LME.
The study was authored by:
Yacine Benlatreche, Research Engineer in Joining Techniques at ArcelorMittal Global R&D.
Thomas Dupuy, Joining Team Leader at ArcelorMittal Global R&D.
Example of small LME cracks observed on a spot weld
Joining in Car Body Engineering
9-11 April 2019
Bad Nauheim, Germany
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