Modelling residual stresses in friction stir welding of Al alloys-a review of possibilities and future trends

Residual stresses are very important in any joining process of materials since they act as pre-stresses in the loading situation of the joint, thereby affecting the final mechanical performance of the component. This is also the case for friction stir welding (FSW) which is a complex solid-state joining process characterized by a pronounced multiphysical behaviour involving phenomena such as change of temperature, material flow, change of microstructures and formation of residual stresses. Thus, models of FSW are typically divided into thermal models, flow models, residual stress models and microstructural models where the classification of the model normally originates from its purpose rather than from the modelling discipline applied. In the present paper, the focus is on presenting and classifying the most important residual stress models for FSW of aluminium alloys in terms of their background, numerical framework and application as well as putting them into proper context with respect to some of the new trends in the field, e.g. coupling with subsequent load analyses of the in-service situation or applying residual stress models of FSW in numerical optimization.