Effects of Rotation Rates on Microstructure, Mechanical Properties, and Fracture Behavior of Friction Stir-Welded (FSW) AZ31 Magnesium Alloy

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 44; no. 1; pp. 517 - 530
• Main Authors: Yang, J., Wang, D., Xiao, B. L., Ni, D. R., Ma, Z. Y.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-01-2013; Springer; Springer Nature B.V
• Subjects: Alloys; Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Exact sciences and technology; Fractures; Joining, thermal cutting: metallurgical aspects; Magnesium; Materials Science; Mechanical properties; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metallic Materials; Metals. Metallurgy; Microstructure; Nanotechnology; Structural Materials; Surfaces and Interfaces; Thin Films; Welding; Rotation Rate; Basal Plane; Friction Stir Weld; Misorientation Angle; Ultimate Tensile Strength; Magnesium base alloys; Welded joint; Friction; Rupture; Mechanical properties; Friction welding; Microstructure
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-012-1373-4

Three rotation rates were selected for friction stir welded (FSW) rolled AZ31 plates, at a constant welding speed of 100 mm/minutes. As the rotation rate was increased from 800 and 2000 to 3500 rpm, the nugget shape varied from a basin- or ellipse-shaped homogeneous structure to a two-layer structure. The grain characteristic was similar in the nugget zones (NZs) at 800 and 2000 rpm, with the column-rotated basal plane. However, at 3500 rpm, the equiaxed fine grains and column-rotated basal plane were found in the lower zone of the two-layer structure, while elongated coarse grains and the basal plane with little inclination comparable to that in the parent material (PM) were detected in the upper zone. Tensile tests indicated that the fracture behaviors of the FSW AZ31 joints at 800 and 2000 rpm were similar with the weak zones being located at the NZ middle and along the boundary between the NZ and the thermo-mechanically affected zone, while contrasting fracture features were found at 3500 rpm. The ultimate tensile strength (UTS) of the joints increased as the rotation rate increased, with the highest UTS being about 95 pct of the PM at 3500 rpm. The variations in the strength and fracture behavior of the joints with the rotation rate were accounted for by the variation in the texture.