(local) Alloying and cladding of advanced Al-alloys employing friction stir welding
Start / End:
September 2009 to September 2013
This project is a collaborative research project between the Materials Innovation Institute (M2i), the University of Twente and the National Aerospace Laboratory (NLR).
Friction stir welding (FSW) is a relatively new solid-state joining technology for metals, see Figure 1. It shows no solidification-related joint imperfections which makes it suitable for hard-to-weld highly alloyed aerospace aluminum grades, like AA 2xxx and 7xxx.
Fig 1. Schematic representation of the friction stir welding process
The aim of this project is to add material to the weld region during FSW. This technology has the following potential advantages:
•Protective coating against wear and corrosion.
•Increase of the weld strength.
•Welding of geometries which require additional material.
•Filling of end-hole.
A prototype of the modified friction stir welding tool is produced and is continuously being developed with help of experiments and numerical simulations.
The weld properties strongly depend on the welding conditions. Important process parameters are the welding speed, the tool rotation rate and the applied down force. Also the type of tool and material grade play an important role. A thorough understanding of the material flow around the pin of the rotating tool moving through the work piece is required to improve the weld quality and speed up the welding process. Various approaches exist to accurately simulate the material flow around the tool pin.
Two numerical methods are used for the development of a material flow model of the new modified friction stir welding tool, i.e. the Arbitray Lagrangian Eulerian (ALE) method and the meshfree method. Both methods are programmed in an in-house simulation program which provides many opportunities for the implementation of new features.
Two problems are being tested for both methods. At first the cladding problem of the plate is shown in figures 2 and 3. Secondly, the rotation of the probe in a 2D plate is being tested and is shown in figure 4.
Fig 2. Schematic representation of the cladding in 2D (ALE method)
Fig 3. Schematic representation of the cladding in 2D (meshfree method)
Fig 4. Schematic representation of a 2D rotating probe in a plate
An advanced numerical model with the ALE or meshfree method will be generated. The numerical results should provide more insight of the material behavior flowing out of the tool. This knowledge might be used to modify the tool for optimizing the properties of the cladding layer.