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Influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.ORCID iD: 0000-0002-8494-3983
2003 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 25, no 12, 1379-1387 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this investigation was to determine whether the fatigue strength of friction stir (FS) welds is influenced by the welding speed, and also to compare the fatigue results with results for conventional arc-welding methods: MIG-pulse and TIG. The Al-Mg-Si alloy 6082 was FS welded in the T6 and T4 temper conditions, and MIG-pulse and TIG welded in T6. The T4-welded material was subjected to a post-weld ageing treatment. According to the results, welding speed in the tested range, representing low and high commercial welding speed, has no major influence on the mechanical and fatigue properties of the FS welds. At a significantly lower welding speed, however, the fatigue performance was improved possibly due to the increased amount of heat supplied to the weld per unit length. The MIG-pulse and TIG welds showed lower static and dynamic strength than the FS welds. This is in accordance with previous comparative examinations in the literature on the fatigue strength of fusion (MIG) and FS welds. The TIG welds had better fatigue performance than the MIGpulse welds. The softening, of the alloy around the weldline has been modelled. Using a model without adjustable parameters, a fair description of the hardness profiles across the weld as a function of welding speed was obtained. The softening in front of the Friction Stir Welding tool was also estimated. At the low and high welding speeds a full and partial softening is predicted, respectively.

Place, publisher, year, edition, pages
2003. Vol. 25, no 12, 1379-1387 p.
Keyword [en]
friction stir welding, aluminium alloy, welding speed, fatigue, tensile properties, microstructure, MIG-pulse and TIG welding
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-22992DOI: 10.1016/s0142-1123(03)00059-8ISI: 000186843200007OAI: oai:DiVA.org:kth-22992DiVA: diva2:341690
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-10-08Bibliographically 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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