In the present investigation, a numerical three-dimensional (3-D) heat flow model for friction stir welding (FSW) has been developed, based on the method of finite differences. The algorithm, which is implemented in MATLAB 5.2, is provided with a separate module for calculation of the microstructure evolution and the resulting hardness distribution. The process model is validated by comparison with in-situ thermocouple measurements and experimental hardness profiles measured at specific time intervals after welding to unravel the strength recovery during natural aging. Furthermore, the grain structure within the plastically deformed region of the as-welded materials has been characterized by means of the electron backscattered diffraction (EBSD) technique in the scanning electron microscope (SEM). Some practical applications of the process model are described toward the end of the article.

A process model for friction stir welding of age hardening aluminum alloys

Microstructural evolution in the friction stir welded 6061 aluminum alloy (T6-temper condition) to copper

Friction welding is now well established as a means of joining many different types of materials, because it has proved itself to be a reliable and economical way of producing high quality welds. The present paper introduces different friction welding processes, their advantages and shortcomings. The history of friction welding and typical applications are also reviewed. In the context of friction welding, a number of subjects, such as frictional behaviour, joining mechanism, interface temperature and heat generation, still exist, where different concepts for explanation of the physical mechanisms have been proposed by different investigators. To clarify some inconsistencies in the interpretation of the friction welding process, a thorough review and critical assessment of the literature associated with this process is attempted.

Friction welding – critical assessment of literature

Mechanical and thermal modelling of Friction Stir Welding

https://hal.archives-ouvertes.fr/hal-00664802/document

Integrated modeling of friction stir welding of 6xxx series Al alloys: Process, microstructure and properties

The present investigation is concerned with the development of an overall process model for the microstructure and strength evolution during continuous drive friction welding of AlMgSi alloys and AlSiC metal matrix composites. In Part I the different components of the model are outlined and analytical solutions presented which provide quantitative information about the HAZ temperature distribution for a wide range of operational conditions. Moreover, a general procedure for modelling the HAZ strain rate distribution has been developed by introducing a series of kinematically admissible velocity equations which describe the material flow fields in the radial, the rotational, and the axial direction, respectively. Calculations performed for both types of materials show that the effective strain rate may exceed 1000 s −1 in positions close to the contact section due to the high rotational velocities involved. Application of the model for evaluation of the response of AlMgSi alloys and AlSiC metal matrix composites to the imposed heating and plastic deformation is described in an accompanying paper (Part II).

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—I. Haz temperature and strain rate distribution

In the present investigation, attempts have been made to bridge the various analytical heat flow models (i.e. the thick plate, the medium thick plate, and the thin plate solutions) by establishing dimensionless maps for a general outline of the quasi-stationary temperature distribution pertaining to a moving heat source on plates of different thickness and thermal properties. The accuracy of the maps has been tested against extensive experimental data, as obtained from in situ thermocouple measurements and numerical analysis of a large number of stringer bead welds. It is shown that the thermal programme within the HAZ (heat affected zone) of such weldments can be adequately predicted from the medium thick plate solution for a wide range in operational conditions (including aluminium and steel welding).

Dimensionless maps for heat flow analyses in fusion welding

The present investigation is concerned with the development of an overall process model for the microstructure and strength evolution during continuous drive friction welding of AlMgSi alloys and AlSiC metal matrix composites. In Part II the heat and material flow models presented in the first paper (Part I) are utilized for prediction of the HAZ subgrain structure and strength evolution following welding and subsequent natural ageing. The modelling is done on the basis of well established principles from thermodynamics, kinetic theory and simple dislocation mechanics. The models are validated by comparison with experimental data, and are illustrated by means of novel mechanism maps. These show the competition between the different process variables that contribute to microstructural changes and strength losses during friction welding of AlMgSi alloys and AlSiC metal matrix composites.

Oe. Grong

Papers

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—I. Haz temperature and strain rate distribution

Dimensionless maps for heat flow analyses in fusion welding

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—II. Haz microstructure and strength evolution