ICME Analysis for Al 2219-T87 in Friction Stir Welding

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ICME Analysis for Al 2219-T87 in Friction Stir Welding

Research Background

Figure 1. Al-Cu Phase Diagram.

Friction stir welding (FSW) is a solid-state joining process, it works by mechanically intermixing two pieces of metal that allows the metal to be fused by a rotating tool. This research is focused on FSWing aluminum 2XXX series, specifically aluminum 2219-T87. The aluminum base alloy is strengthened by the copper precipitants, which is gained by a specific heat treatment. During the FWS process high strain rates, temperature gradients, and plastic deformation affect the microstructure. Due to the elevated temperatures in the FSW process the strengthening precipitates will undergo coarsening and eventually lose their strengthening effectiveness[1]. Experimentation has been done on this material at constant process parameters, but at different RPMs (100, 200 and 300 RPM) to view the change in the microstructure. At 100 and 200 RPM the weld material hardness and tensile strength decreased from the parent material, but at 300 RPM the strength increased.

At the 300 RPM the weld tool must have elevated the temperature high enough to transform the copper particles. In Figure 1 you can see that above 548°C material is right above the solidus line and is in the L + α region. From the literature it is believed that there is a
Figure 2. Multiscale modeling diagram example for Friction Stir Welding .

correlation of the temperature at the workpiece/weld tool interface with the process parameters[2][3]. Multiscale modeling can be on this material to produce the correct process parameters that will create the welded material microstructure to be stronger than the base material microstructure.

Problem

At relatively lower strain rates the copper particles in Al 2219 coarsen and at relatively high RPM the welded material flash out and cause several defects.

Solution

Use multiscale modeling to discover the optimized parameters that will give a high enough strain rate and temperature for the correct microstructure.

Electronic Scale

Down scaling- energies and elastic modulus needed between AL-Cu. Up scaling- using electrons DFT simulation to get the energies and elastic moduli of Al-Cu.

Molecular Scale

Down scaling- Dislocation mobility and stacking fault energy needed between AL-Cu. Up scaling- Using DD simulation to get dislocation mobility and stacking fault energy.

Macroscale

Internal state variable continuum to model the strain rate/temperature relationship. With all the information passed up from the lower length scales a material model can be created with the correct material properties and tool parameters.

References

  1. Schneider, J. Processing effects on the friction stir weld stir zone. 2012
  2. Mishra R, Ma Z. Friction stir welding and processing. Materials Science and Engineering R: Reports. 2005;50(1-2):1-78.
  3. Mendez PF, Tello KE, Lienert TJ. Scaling of coupled heat transfer and plastic deformation around the pin in friction stir welding.Acta Materialia. 2010;58(18):6012-6026.
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