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Influence of tool geometry on the material flow during friction stir welding of 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: Journal of Materials Processing Technology, ISSN 0924-0136Article in journal (Other academic) Submitted
Abstract [en]

The understanding of the material flow during friction stir welding of thick sections of copper is of great interest. Sweden plans to use this method to seal 50 mm thick copper canisters which will contain spent nuclear fuel. In this study two different weld tools are investigated. The first experiment uses a pin length of 52 mm and the second a pin length of 30 mm. The shoulder diameter, process parameters and materials are the same for both experiments. Experiments as well as FEM modelling work are reported. The experimental part includes a marker inserting technique using brass rod, which allows the material flow to be examined. After welding, the weld line is sliced, etched and examined by optical microscope. The experiments show more brass in the weld with shorter pin length and the nugget zone has different appearances in the two cases. A finite element model is applied to describe the temperature, material flow, dynamic viscosity, strain rate and shear stress in the welds. The outcome of the model and the feature of the experimental welds are compared showing a satisfactory result. The size of the thermomechanically affected zone is predicted by this model.

Keyword [en]
friction stir welding, copper, marker, viscosity, FEM simulation
URN: urn:nbn:se:kth:diva-12017OAI: diva2:294215
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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