| Title |
Prediction of Grain Size in Friction Stir Welded Metallic Materials |
| Authors |
김현(Hyun Kim) ; 최효남(Hyo-Nam Choi) ; 이승준(Seung-Joon Lee) |
| DOI |
https://doi.org/10.3365/KJMM.2026.64.7.605 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
Friction stir welding (FSW); Zener-Hollomon parameter; Dynamic recrystallization; Grain size; Hardness |
| Abstract |
In current study, the microstructural evolution and mechanical properties were investigated for friction stir welded (FSW) metallic materials such as aluminum alloys (e.g., AA7075, AA7068) and medium Mn steel through the Zener-Hollomon parameter (Z). For three materials, an increase in the welding speed led to a decrease in the peak temperature within the stir zone (SZ) during FSW, which consequently resulted in higher Z values. The average grain size (D) in the SZ exhibited a clear power-law relationship with the Z parameter, showing pronounced grain refinement at higher Z values. For example, the derived equations on a logarithmic scale were log D = 2.73 - 0.20 log Z for AA7075, log D = 7.57 - 0.34 log Z for AA7068, and log D = 2.79 - 0.18 log Z for the medium Mn steel. The reasons why the difference in the relationship between Z and D values are strongly dependent on stacking-fault energy and dynamic recrystallization mechanism of metallic materials during FSW. However, the hardness trends differed significantly among the materials. For the aluminum alloys, the relationship between hardness and Z parameter was hardly observed in SZ, because of the suppression of precipitation hardening during FSW despite the presence of grain refinement and accumulated dislocations. Regarding the prediction of hardness for the medium Mn steel, the hardness in SZ was reduced with increasing Z parameter, due to the strain-induced martensitic transformation after FSW. Overall, these findings suggest that the D in SZ can be consistently predicted using the Z parameter, while their mechanical properties should be interpreted based on the intrinsic microstructural changes. |