Development of fresh and fully recrystallized microstructures through friction stir processing of a rare earth bearing magnesium alloy

Abstract

In the present study the friction stir processing (FSP), as an effective thermomechanical processing routine, has been conducted under the different rotational speeds on a solution treated rare earth bearing magnesium alloy. The various processing conditions result in a wide range of Zener-Holloman parameters to elaborate the desired microstructure in respect of the grain size. The obtained results indicate that applying the process on the primary solution treated material leads to the development of fully recrystallized microstructures, where the capability of refinement is directly affected through controlling the strain rate and temperature. In this regard, the resulting microstructures have been classified into "fresh and recrystallized" and "recrystallized and deformed" regions. The grain orientation speared (GOS) maps have also been employed to separate the recrystallized grains and deformed ones. Interestingly, the "recrystallized and deformed" microstructure holds a specified recrystallization texture, and exhibits unexpected hardenability during subsequent room temperature deformation. This is supported by Schmid factor analysis and fractography examinations revealing activation of basal slip and twinning systems in "recrystallized and deformed" microstructure.