Investigating the Effects of Friction Stir Processing (FSP) an‎d Pre-Process Heat Treatment on the Microstructure an‎d Mechanical Properties of Mg-6Y-2.2Nd-1.2Gd Alloy

10/5/2026 12:00:00 AM

This study is devoted to investigating the effects of friction stir processing (FSP) an‎d prior heat treatment on the microstructure an‎d mechanical properties of a Mg-6Y-2.2Nd-1.2Gd alloy. Magnesium alloys, owing to their high strength-to-weight ratio an‎d favorable mechanical characteristics, have attracted considerable attention, particularly in the automotive an‎d aerospace industries. The addition of alloying elements such as yttrium, neodymium, an‎d gadolinium to magnesium promotes solid-solution strengthening, the formation of thermally stable grain-boundary phases, an‎d an overall enhancement of mechanical properties, thereby improving both strength an‎d thermal stability. Nevertheless, the as-cast microstructure of these alloys is typically characterized by coarse grains an‎d an inhomogeneous distribution of secondary phases, which severely limits their mechanical performance. To improve the initial microstructure, the optimum homogenization conditions were determined using differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, an‎d phase diagram eva‎luations. The results demonstrated that homogenization at 540 °C for 4 h leads to a more uniform distribution of alloying elements an‎d a reduction in structural discontinuities, resulting in increases of approximately 71% in yield strength an‎d 60% in ultimate tensile strength compared with the as-cast condition, while the elongation was also improved by about 65%. Subsequently, FSP was applied in one to four consecutive passes. The results revealed that increasing the number of passes significantly enhances grain refinement due to the activation of dynamic recrystallization mechanisms, with the optimum mechanical performance achieved after three FSP passes. Under this condition, the yield strength, ultimate tensile strength, an‎d elongation increased by approximately 15%, 18%, an‎d 64%, respectively, relative to the homogenized state. The application of a fourth pass led to a slight degradation in mechanical properties as a result of excessive heat accumulation. Fractographic analysis using scanning electron microscopy (SEM) showed that the fracture mechanism evolves from predominantly brittle fracture in the initial conditions to a fully ductile, dimple-dominated fracture after FSP. Overall, the findings of this study demonstrate that the combination of optimized homogenization treatment an‎d three-pass friction stir processing provides an effective route to achieving a favorable balance between strength an‎d ductility in the Mg-6Y-2.2Nd-1.2Gd alloy.

آلياژ منيزيم , عناصر كمياب خاكي , خواص مكانيكي , فرايند هم‌زدن اصطكاكي

Magnesium alloy , Rare earth elements , Mechanical properties , Friction stir processing

Parnia parsayan

Dr. Ali Reza Eivani