Table of Contents
Texture, Stress, and Microstructure
Volume 2008 (2008), Article ID 360617, 8 pages
http://dx.doi.org/10.1155/2008/360617
Research Article

Mechanical Behaviour and Microstructure of Aluminum-Steel Sheets Joined by FSSW

1Univ Paris-Sud, UMR8182, ICMMO, Laboratoire de Physico-Chimie de l'Etat Solide, Orsay 91405, France
2CNRS, Orsay 91405, France
3Institut de Soudure, Zone d'Activité Aéroport de Metz, 2-4 rue Pîlatre de Rozier, Goin 57420, France

Received 3 July 2007; Accepted 12 December 2007

Academic Editor: Claude Esling

Copyright © 2008 S. Bozzi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

At the prospect of a lightening of the automobile structures, welded spots have been realized on a stacking of two sheets (a 6008 aluminum alloy on steel) Friction Stir Spot welding (FSSW). Different process parameters have been tested, but only the influence of the dwell time will be described in the present paper. The dwell time corresponds to the time during which the probe stays in rotation at its bottom location before extracting. A study of the microstructures and textures associated to mechanical tests (tensile shear tests) allowed determining the best set of welding parameters. The recrystallized area around the welding spot has been characterized by electron back-scattered diffraction (EBSD). A mechanism of continuous dynamic recrystallization has been identified since the misorientation of subboundaries increases close to the weld, and this is for all the dwell times tested. Elsewhere, the increase of the dwell time induced a larger recrystallized zone. It has also been found that a long dwell time induced a larger welded area but also a higher quantity of intermetallic compounds (especially FeAl, Fe2Al7, and FeAl2) with high-microhardness values (up to 800 Hv). Thus, the dwell time must not exceed a certain value, otherwise it can weaken the weld.