title: Spatially resolved positron annihilation spectroscopy on friction stir weld induced defects.
abstract: A friction stir welded (FSW) Al alloy sample was investigated by Doppler broadening spectroscopy (DBS) of the positron annihilation line. The spatially resolved defect distribution showed that the material in the joint zone becomes completely annealed during the welding process at the shoulder of the FSW tool, whereas at the tip, annealing is prevailed by the deterioration of the material due to the tool movement. This might be responsible for the increased probability of cracking in the heat affected zone of friction stir welds. Examination of a material pairing of steel S235 and the Al alloy Silafont36 by coincident Doppler broadening spectroscopy (CDBS) indicates the formation of annealed steel clusters in the Al alloy component of the sample. The clear visibility of Fe in the CDB spectra is explained by the very efficient trapping at the interface between steel cluster and bulk.
authors.affiliation: Physik-Department E 21 and FRM II, Technische Universität München, 85747 Garching, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Hain
authors.affiliation: Physik-Department E 21 and FRM II, Technische Universität München, 85747 Garching, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Hugenschmidt
authors.affiliation: Physik-Department E 21 and FRM II, Technische Universität München, 85747 Garching, Germany.
authors.forename: Philip
authors.initials: P
authors.lastname: Pikart
authors.affiliation: Physik-Department E 21 and FRM II, Technische Universität München, 85747 Garching, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Böni
keywords: (coincident) Doppler broadening spectroscopy ((C)DBS); defect mapping; friction stir welding (FSW); positron annihilation spectroscopy