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Flow modelling of friction stir welding using brass markers in copper
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-8494-3983
(English)In: Science and technology of welding and joining, ISSN 1362-1718Article in journal (Other academic) Submitted
Abstract [en]

This paper describes the behaviour of the material flow in 50 mm thick friction stir welded phosphorous-alloyed copper with both experiments and modelling work. In Sweden the friction stir welding is going to be used for sealing copper canisters for storage of nuclear waste from fuel elements. An understanding of the material flow during the process is essential in order to predict the weld quality and thereby the maintenance of the weld. A marker technique is used which involves inserting dissimilar material into the weld zone before joining. The material flow can then be examined. In these experiments Ø 9 brass rods are used. After welding, the copper was sliced, etched and examined by optical microscopy. The results show that the weld tool pushes the brass as far as 37 mm backwards from the inserted location, which is little more than one pin diameter. This brass is first seen on the advancing side. Most brass is found behind its inserted location, on both sides of the centre line. The material movement underneath the pin in the weld root is insignificant. The pin area has a nugget with a fine grain structure, but also a part near the shoulder with coarser grains. A finite element model is developed in order to describe the temperature and material flow. The model and the examined welds were compared showing a satisfactory agreement for most features.

Keyword [en]
friction stir welding, viscous flow, marker, finite element method
URN: urn:nbn:se:kth:diva-12016OAI: diva2:294199
QS 20120328Available from: 2010-02-16 Created: 2010-02-16 Last updated: 2012-03-28Bibliographically approved
In thesis
1. Investigation and modelling of friction stir welded copper canisters
Open this publication in new window or tab >>Investigation and modelling of friction stir welded copper canisters
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work has been focused on characterisation of FSW joints, and modelling of the process, both analytically and numerically. The Swedish model for final deposit of nuclear fuel waste is based on copper canisters as a corrosion barrier with an inner pressure holding insert of cast iron. Friction Stir Welding (FSW) is the method to seal the copper canister, a technique invented by The Welding Institute (TWI).

The first simulations were based on Rosenthal’s analytical medium plate model. The model is simple to use, but has limitations. Finite element models (FEM) were developed, initially with a two-dimensional geometry. Due to the requirements of describing both the heat flow and the tool movement, three-dimensional models were developed. These models take into account heat transfer, material flow, and continuum mechanics. The geometries of the models are based on the simulation experiments carried out at TWI and at Swedish Nuclear Fuel Waste and Management Co (SKB). Temperature distribution, material flow and their effects on the thermal expansion were predicted for a full-scale canister and lid. The steady state solutions have been compared with temperature measurements, showing good agreement.

In order to understand the material flow during welding a marker technique is used, which involves inserting dissimilar material into the weld zone before joining. Different materials are tested showing that brass rods are the most suitable material in these welds. After welding, the weld line is sliced, etched and examined by optical microscope. To understand the material flow further, and in the future predict the flow, a FEM is developed. This model and the etched samples are compared showing similar features. Furthermore, by using this model the area that is recrystallised can be predicted. The predicted area and the grain size and hardness profile agree well.

Microstructure and hardness profiles have been investigated by optical microscopy, Scanning Electron Microscopy (SEM), Electron Back Scatter Diffraction (EBSD) and Rockwell hardness measurements. EBSD visualisation has been used to determine the grain size distribution and the appearance of twins and misorientation within grains. The orientation maps show a fine uniform equiaxed grain structure. The root of the weld exhibits the smallest grains and many annealing twins. The appearance of the nugget and the grain size depends on the position of the weld. A large difference can be seen both in hardness and grain size between the start of the weld and when the steady state is reached.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 62 p.
Friction Stir Welding (FSW), Copper, Welding, Finite Element Method (FEM), SKB, Material flow
National Category
Materials Engineering
urn:nbn:se:kth:diva-11999 (URN)978-91-7415-568-6 (ISBN)
Public defence
2010-03-04, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
QC20100719Available from: 2010-02-15 Created: 2010-02-12 Last updated: 2010-07-19Bibliographically approved

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