Thermal and Thermo-Mechanical Modeling of Friction Stir Welding of Aluminum Alloys

In this project, we modeled the FSW process using our own FEM code, which includes both a heat transfer analysis for the temperature development during the FSW process and a thermo-mechanical analysis for post-weld residual stress and distortion determination.
A moving heat source with a heat distribution simulating the heat generated from the friction between the tool shoulder and the workpiece was used in the heat transfer analysis. Using a trail-and-error procedure, the total heat input to the workpiece and the heat convection coefficients of the bottom surface are determined by fitting the measured temperature data with the analytical model. Once these process parameters are determined for this particular FSW arrangement, the complete temperature history in the entire workpiece was then calculated by the finite element numerical procedures. This temperature history was then used as the input for the thermo-mechanical analysis for the determination of residual stress after the FSW process. As in the fusion welding, the residual stress and strain were developed as the temperature of the workpiece cools down. Finally we modeled the release of the fixture, which was used to clamp down the workpiece during the FSW process. The release of the fixture changes the distribution of the residual stress and the distortion of the workpiece. Comparison of the temperature distribution with the experimental data was made. Residual stress distributions in the weld and the distortion of the workpiece after releasing the fixture are predicted.

Temperature analysis of the tool

Tool temperature contour at steady state: normal speed

Tool temperature contour at steady state: cold (fast) weld

Temperature Distribution (Tool)

Modeling of Al alloy plate: mesh division

Yield strength v.s. temperature in different zones was used in the analysis

Temperature in the AA 2195 plate Fitting with the thermocouple data

An Example showing the temperature contour

Peak temperature contour at a cross-section

Residual stress along (X,Y,Z)=(225,Y,1.5mm)

Residual distortion along (X,Y,Z)=(225,Y,1.5mm)

Student: Xinhai Qi
Advisor: Dr. Bill Yuh-Jin Chao