B. de Meester

Effect of boundary conditions and heat source distribution on temperature distribution in friction stir welding

Abstract Welding experiments on Al-6005A have been carried out using a fully instrumented milling machine. The power input was calculated from the measured torque and forces. The thermal cycles were measured at various locations close to the weld centreline. A finite element pseudo-steady-state uncoupled thermal model was developed, taking into account the influence of the welding parameters on the power input. The distribution of the total power input between surface and volume heat sources was also studied. The measured and predicted thermal cycles are in good agreement when proper contact conditions between the workpiece and the backing plate are introduced.

Effect of rotational material flow on temperature distribution in friction stir welds

Abstract A finite element pseudosteady state thermal model takes the mechanical power as input data while distributing the total power input between surface and volume heat sources. A simple model for the material flow around the tool has been developed in order to take heat convection into account based on the shape of the thermomechanically affected zone. The model is assessed for a large number of different welding parameters. Special attention is given to the type of contact at the tool/workpiece interface, i.e. sliding, sticking or both and at the workpiece backing plate interface. The rotational material flow creates asymmetry in the temperature distribution between the two sides of the weld.

Deformation kinetics of the Ti--6Al--4V alloy at low temperatures

The deformation kinetics of theα + β titanium alloy Ti-6 A1-4V were investigated over the temperature range of 4.2 to 760 K. It was found that the Gibbs free energy of activation AG at 0 K and zero effective stress is ∼ 1.3 eV (∼ 1.25 × 105 J/mole) (∼0.17 μob3), the maximum force for the dislocation-obstacle interaction is ∼ 80 × 10-6 dyne (∼ 80 × 10-11N) (∼ 0.19 μob2) and the activation distance x0* at which the force first rises rapidly ∼ 1.5b. These quantities, and others, are the same as those for unalloyed titanium, where it was established that interstitial solutes are the obstacles controlling the dislocation motion. The results for the Ti-6A1-4V alloy are in slightly better accord with ρG being independent of temperature than proportional to the shear modulus, but the evidence is not conclusive.

Finite Element Modelling of Friction Stir Welding of Aluminium alloy Plates - Inverse Analysis using a Genetic Algorithm

This paper presents finite element simulation results of instrumented FSW experiments on aluminium alloys 6005A-T6 and 2024-T3. The SAMCEF™ finite element code is used to perform the simulations. The FE model involves a sequential thermal-mechanical analysis and includes contact between the meshed tool, workpiece and backing plate. The model takes into account the pressure applied by the tool on the weld as well as the heat input. The heat transfers such as convection in air and contact conductance with the backing plate are modelled. For each experiment, the temperature time-histories were recorded at several locations in the workpiece. The heat input in the finite element model is identified by minimising the objective function of a constrained problem using a genetic optimisation algorithm. The objective function is the square of the difference between the experimental measurements and the numerical prediction of temperature. Finally, levels of residual stress predicted by simulation are presented.

Development of base materials for welding

Abstract The various aspects of weldability, seen as a material property, are introduced. These are illustrated by considering examples, in particular the recent advances in structural C–Mn and microalloyed steels. Important issues for the further development of the weldability of these materials are outlined. In concluding, the growing importance of mathematical modelling as a tool for the design of new weldable materials is emphasised.The various aspects of weldability, seen as a material property, are introduced. These are illustrated by considering examples, in particular the recent advances in structural C-Mn and microalloyed steels. Important issues for the further development of the weldability of these materials are outlined. In concluding, the growing importance of mathematical modelling as a tool for the design of new weldable materials is emphasised

Friction stir welding and hybrid laser welding applied to 6056 alloy

Innovative welding processes are continuously gaining industrial interest. Both friction stir welding (FSW) and hybrid laser welding (HLW) are automated welding processes which allow achieving high quality joints in aluminium alloys, in combination with a high productivity. The EN AW-6056-T4 alloy is a relatively recent high strength weldable AlMgSiCu alloy, which is used in aviation. This alloy was subjected to FSW and HLW. The optimisation procedures which were used for FSW and HLW to assess the most appropriate welding parameters are discussed. A comparison is made between the mechanical properties in the as-welded and in the T78 post-weld heat treated (PWHT) temper. Concerning the friction stir welds, the PWHT only caused a decrease of the elongation after fracture; the thermal treatment had no effect on the minimal hardness zones of the weld, hence the tensile strength did not change. The hybrid laser welds however showed a significantly higher tensile strength after PWHT, but this was also accompanied by a ductility loss. Fatigue testing was performed on the PWHT welds. Friction stir welds clearly possessed better fatigue properties than hybrid laser welds.

Friction Stir Welding of Aluminium High Pressure Die Castings: Parameter Optimisation and Gap Bridgeability

It is well established that friction stir welding (FSW) allows joining of aluminium alloys which can hardly be fusion welded. A well-known limitation of weldability in aluminium alloys is high hot crack sensitivity, such as encountered in Al-Cu and Al-ZnMgCu alloys. The weldability of cast alloys containing a significant amount of gases with MIG, TIG or laser welding is however also significantly compromised due to the occurrence of porosity, blowholes and cracks in the fused metal. In this study, the high pressure die cast aluminium alloy EN AC-46000-F, which belongs to the latter category of alloys with strongly reduced weldability, is successfully joined with the FSW technique. The selection of optimum welding conditions is discussed as function of the tensile properties and salient microstructural features. Moreover, the gap bridging ability of the FSW process is highlighted, by demonstrating the influence of weld gap on joint strength and the occurrence of weld flaws.

Welding in the World—50 years

This year, Welding in the World celebrates its 50 anniversary as the leading technical publication of the International Institute of Welding. In 1963, there were 4 issues with 17 total papers. This year, we will publish over 80 papers in 6 issues. The original editor (1963–1966) was Guy Parsloe. He was succeeded in 1968 by Philip Boyd who held this position until 1991 and was followed by John Hicks (1991–1995). From 1996 through 2009, the International Institute of Welding CEO served as the editor of Welding in the World and included Michel Bramat, Daniel Beaufils, Andre Charbonnier, and Cecile Mayer. In 2009, Bruno de Meester, Thomas Bollinghaus, and John Lippold were appointed as coeditors. The original publication coordinator at the Secretariat was Andre Leroy (1963–1974). He was succeeded in 1975 by Henri Granjon, who held this post until 1986, followed by Michel Bramat (1986–2000), Noelle Fauriol (2001–2004), and Veronique Souville (2004–2012). The current coordinator is Pierre Tran.