A methodology for controlling grain size in friction stir processes

Abstract

Microstructural modification via dynamic recrystallization (DRX) is the main mechanism involved in grain refinement associated with friction stir processing. Introduced in this work is a methodology for controlling grain size through the manipulation of process parameters in friction stir processes. A robust 3D FE model was used to simulate a selective test matrix whose resulting state variables were used to relate the desired output, the average grain size in this case, to the controlled process parameters. The Zener-Hollomon parameter, which is namely the temperature compensated strain rate, was used in calculating the predicted grain size from the state variables of the FEM simulations. The methodology was validated by comparing experimental test cases whose target grain size was found to compare favorably with the resulting microstructure. Evidence of grain size refinement and homogeneity was observed in the friction stir processed samples of Magnesium alloy AZ31B.