A review of microstructural changes occurring during FSW in aluminium alloys and their modelling Dimitri Jacquin, Gildas Guillemot To cite this version: Dimitri Jacquin, Gildas Guillemot. A review of microstructural changes occurring during FSW in aluminium alloys and their modelling. Journal of Materials Processing Technology, Elsevier, 2021, 288, pp.116706. 10.1016/j.jmatprotec.2020.116706. hal-02911059 HAL Id: hal-02911059 https://hal.archives-ouvertes.fr/hal-02911059 Submitted on 3 Aug 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. A review of microstructural changes occurring during FSW in aluminium alloys and their modelling Dimitri Jacquin a) Gildas Guillemot b) a) University of Bordeaux, I2M CNRS, Site IUT, 15, rue Naudet - CS 10207, 33175 Gradignan Cedex, France b) MINES ParisTech, PSL Research University, CEMEF UMR CNRS 7635, CS10207, 06904 Sophia Antipolis, France Abstract: 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. Keywords: Friction Stir Welding; Aluminium alloys; Microstructure modelling; Precipitation process; Recrystallization mechanism; Guidelines 1 Contents I. Introduction ........................................................................................................................ 3 I.1. Advantages and disadvantages ................................................................................... 3 I.2. Current applications ................................................................................................... 5 I.3. Problems raised by FSW processes ............................................................................ 8 II. Overview – Complex material and heat flows ................................................................. 10 II.1. Material flow ............................................................................................................ 11 II.2. Thermal aspects ........................................................................................................ 13 II.3. Mechanical aspects ................................................................................................... 16 II.4. Physical phenomena ................................................................................................. 17 II.4.a. Microstructures ................................................................................................... 17 II.4.b. Precipitation ....................................................................................................... 19 II.4.c. Grain evolution ................................................................................................... 21 III. Modelling and simulation ............................................................................................. 23 III.1. Molecular dynamics ................................................................................................. 24 III.2. Precipitation modelling ............................................................................................ 27 III.2.a. Semi-analytical model .................................................................................... 29 III.2.b. Precipitate size distribution models ................................................................ 36 III.3. Grain evolution modelling ....................................................................................... 48 III.3.a. DDRX modelling ............................................................................................ 53 Derby and Ashby recrystallization approach ......................................................... 53 Zener-Hollomon approach ..................................................................................... 55 Avrami model approach ......................................................................................... 57 III.3.b. GDRX modelling ............................................................................................ 60 III.3.c. CDRX modelling ............................................................................................ 63 Empirical model ..................................................................................................... 63 Physical model ....................................................................................................... 68 III.3.d. Monte-Carlo - Potts models ............................................................................ 74 IV. Recommendations ........................................................................................................ 81 IV.1. Precipitation modelling ............................................................................................ 81 IV.2. Grain evolution modelling ....................................................................................... 87 Conclusion ................................................................................................................................ 96 References ................................................................................................................................ 98 2 I. Introduction Since its discovery in 1991 by Thomas (1991) at The Welding Institute (TWI, 2019), Friction stir welding (FSW) process has become a technique of choice in the joining of aluminium components. Wang et al. (2008) have demonstrated that this process is able to produce thick assemblies with both high mechanical properties and large fatigue performances. Microstructures observations show fine grains and restricted Heat Affected Zone limiting cracks development. Sahu and Pal (2017) obtained similar results when considering welding of aluminium alloys with dissimilar thickness and various joining configurations. Tensile and yield strength measured after joining processes were found close to the base material properties. Mechanical performances are usually better in FSW processes than those obtained by conventional joining processes as fusion welding also considering lower level of residual stresses. This process is developed in order to increase local temperature by plastic deformation to achieve stirring domain. A rigid cylindrical tool consisting of a threaded pin and a shoulder rotates and slowly plunges into the junction line between two parts placed end to end. Friction and stirring generate heat and soften the material, allowing local plastic deformation and material mixing. Process control prevents melting of parts during joining process thus restricting material transformations to solid state. In a process of lightening aeronautical structures, welding of aluminium alloys offers an alternative to traditional bolting or riveting processes, allowing to overcome the major drawbacks of these techniques: heterogeneous junction, mass contribution by added metal, stress concentration close to the holes decreasing fatigue resistance. Consequently FSW process results in a weight saving as well as a reduction in the manufacturing costs. These advantages are clearly attractive to answer current industrial needs. Consequently, the use of FSW processes in industries is a major economic and technical challenge for the aircraft, shipbuilding or even automotive industries where first applications have recently emerged.