A review of microstructural changes occurring during FSW in aluminium alloys and their modelling

Friction stir welding (FSW) process is currently considered as a promising alternative to join aluminium alloys. Indeed, this solid-state welding technique is particularly recommended for the assembly of these materials. Since parts are not heated above their melting temperature, FSW process may prevent solidification defects encountered in joining aluminium alloys and known as limitations to the dissemination of these materials in industries. During the past years, large literature has been devoted to the modelling of microstructural evolution in aluminium alloys during FSW processes and mainly dedicated to the analysis of precipitate evolutions and grain recrystallization mechanisms. Precipitate size distribution models have aroused widespread interest in recent years demonstrating their relevance to follow precipitation process in multicomponent alloys and multiphase systems. Efficient recrystallization models are also available and based on various grain growth mechanisms. In addition, multi-scale coupling strategies have recently emerged considering thermal, mechanical and metallurgical solutions. Consequently, the effect of FSW process parameters on weld properties is now investigated to determine optimized welding strategies regarding microstructure evolution. This research is based on reliable models reported in the literature enhancing the estimation of final weld state and associated properties as an answer to industrial needs. Validations of proposed modelling strategies have been reported based on in-depth analyses of experimental observations. This present work proposes a review of recent models dedicated to microstructural evolutions in aluminium alloys during FSW process. The interest and efficiency of current approaches will be discussed to highlight their limitations. Guidelines will propose new routes toward enhanced modelling strategies for future developments.