Residual Stress Investigation of Dissimilar Overlap-friction Stir Welds Made from Al and Steel

One of the main research topics at the GKSS Research Centre is the investigation and further development of friction stir welding techniques. In this context dissimilar overlap joints of sheets made from aluminum and steel were produced by friction stir welding at GKSS. A set of four different specimens was produced with different welding and tool speeds. Aluminum alloy AA5754-H22 and dual phase steel alloy DP600 were used. The aluminum and steel sheets were 1.5 mm thick and the stirring zone was 12 mm wide. The residual stress distribution in these specimens was investigated at the high energy materials science synchrotron beamline HARWI II operated by GKSS at the HASYLAB / DESY, Germany. A beam with a photon energy of 100 keV and a size of 2 x 0.2 mm2, with the larger beam dimension being parallel to the weld, was used in transmission geometry. A Mar345 detector system was employed to monitor complete Debye-Scherrer rings. The diffraction peak shifts of the Al {311} and Fe {211} lattice planes were used to determine the residual stress in the respective material. Peak positions were determined relatively to the Cu {220} peak of a Cu-powder directly attached to each specimen. This allowed the correction for peak shifts induced by the distortion of the specimens and the resulting change of the sample-to-detector distance. The results for the weld zone show that the stresses in weld direction are close to the yield strength for the steel and about 70% of the yield strength for Al. Furthermore, high welding and tool rotation speeds result in steeper stress gradients in steel and almost symmetric stress profiles in both materials, whereas low welding and tool rotation speeds result in a broader stress profile in steel and asymmetry of the profiles in both materials.

MARTINS Rene;  SHEIKHI Shahram;  DOS SANTOS Jorge;  SCHREYER Andreas; 

2009-04-28

BLACKWELL PUBLISHING

JRC51045

0108-7673,