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Fatigue performance of friction stir welded AlMgSi-alloy 6082
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.ORCID iD: 0000-0002-8494-3983
2001 (English)In: Aluminium, ISSN 0002-6689, Vol. 77, no 7-8, 572-575 p.Article in journal (Other academic) Published
Abstract [en]

Friction stir welding is a relatively new solid-state welding method, ideal to join large, thin-walled aluminium profiles. In this paper results from tensile and fatigue testing of friction stir welds of the hardenable Al-Mg-Si alloy AA6082 is presented. For temper T4, post weld age treated (PWAT), the fatigue strength was found to be lower than for temper T6, and with a steeper slope of the stress-life curve. The lower fatigue strength for the statically stronger T4 + PWAT material was unexpected. Fracture in T6 initiated and propagated in the vicinity of the weak weld/HAZ border, directly outside the stirred up edge on the advancing (or shear-) side of the weld. For T4 + PWAT many fractures occurred in the weld, often initiated on the advancing side.

Place, publisher, year, edition, pages
2001. Vol. 77, no 7-8, 572-575 p.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-25117OAI: oai:DiVA.org:kth-25117DiVA: diva2:355880
Note
QC 20101008Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Fatigue Strength of Friction Stir Welded Joints in Aluminium
Open this publication in new window or tab >>Fatigue Strength of Friction Stir Welded Joints in Aluminium
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid state Friction stir welding (FSW) is of major interest in the welding of aluminium since it improves the joint properties. Many applications where Al-alloys are used are subject to varying load conditions, making fatigue failure a critical issue. In the scope of this thesis, the fatigue performance of friction stir welded AlMgSi-alloy 6082 has been investigated. Static and dynamic properties of different joint configurations and welds produced with varying process parameters have been determined. Microstructures of fractured surfaces have been studied to evaluate the effect of weld discontinuities on fatigue. The mechanical strength of the friction stir welds was set in relation to that of conventional fusion welds, and that of other FS welded Al-alloys.

The friction stir process produced aluminium butt welds with high and consistent fatigue strengths, which exceeded the strengths of similar fusion welded samples. A smooth weld geometry showed to be of great importance for the fatigue performance, favouring the friction stir welds. Welding speed in a tested range of 0.35-1.4 m/min had only a modest influence on the properties of the friction stir welds; properties were not deteriorating at the highest speed. The softening of the alloy around the weldline was modelled. A fair description of the hardness profiles across the weld was obtained. At a low and high welding speed a full and partial softening respectively was predicted, indicating that full softening is not required to obtain a flawless weld.

In case of friction stir overlap welds, tool design is even more important than in butt welding to secure weld quality. A broad tool shoulder with a concave pin end gave the best performance. In particular, the minimal influence on the sheet interface when welding with such a tool was beneficial for the fatigue strength. The stress distribution in overlap and T-type test specimens has been modelled. The stress intensity factors were determined. The corresponding crack propagation rates were in fair accordance with the experimental results. It was found that a simplified approach, developed to estimate ∆K for overlap spot welds, could be used also for friction stir overlap joints.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 68 p.
Keyword
Materials science, Applied Materials Technology, friction stir welding, fatigue, mechanical properties, welding speed, softening, Materialvetenskap
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-160 (URN)91-7178-001-7 (ISBN)
Public defence
2005-04-13, Kollegiesalen, Valhallavägen 79, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101008Available from: 2005-04-06 Created: 2005-04-06 Last updated: 2010-10-08Bibliographically approved

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Sandström, Rolf

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