C. H. J. Gerritsen, ArcelorMittal Research Industry Gent, OCAS NV, Zelzate, Belgium; C. A. W. Olea, GKSS-Forschungszentrum Geesthacht GmbH, Geesthacht, Germany
Friction Stir Welding is already used industrially for many so-called light alloys (e.g. aluminium alloys). FSW of other materials is also of increasing interest, with steel a prime example. However, FSW of steel is not so straightforward, because of the high forces and temperatures experienced, which make tool wear and breakage a problem in particular. Although no serious contender, therefore, to replace conventional fusion welding processes for most steel applications any time soon, there may nonetheless be specific cases where FSW can bring added benefits. One such example is the use of the fact that the FSW process is a solid-state process to overcome possible incompatibility issues between a substrate and coating. For example, in some cases enrichment of steel weld metal with Al from the coating can lead to the formation of brittle intermetallics or excessive grain growth. In this paper, an evaluative study is presented into FSW of butt welds in Usibor1500P steel sheet coated with AlSi. The idea is that the stirring during the FSW process breaks up the coating and disperses it through the weld metal and that no brittle structures form since there is no melting taking place. The work presented includes welding procedure development on 1.5 mm thickness sheets and extensive joint evaluation through radiography, cross-sectioning, metallography, SEM and EPMA evaluation, as well as mechanical testing after heat treatment appropriate to Usibor1500P.
Summary: In this paper, Friction Stir Welding of an Al-Si-coated steel is discussed. Fusion welding of this steel can result in the formation of brittle Fe-Al intermetallics as the weld pool is enriched with Al from the coating. FSW was therefore investigated, since this is a solid-state process that may overcome these issues.
