Abstract
In this study, the stain accumulation processes of pure Mg material during FSW processes with different rotation speeds are measured and calculated and the microstructure is characterized. Copper foil is inserted as a marker to reveal the flow of pure Mg. The results indicate that the strain accumulation process can be divided into three stages, acceleration stage, high velocity flow stage and decelerate & constant velocity flow stage, respectively. The speed of strain accumulation is relatively low in acceleration stage and high velocity flow stage, while it becomes really high in decelerate & constant velocity flow stage. The higher the speed of rotation, the more severe plastic deformation occurs within the material. The accumulated strain of pure Mg are 12.8 and 14.5 at the rotation speed of 1000rpm and 1500rpm, respectively. Relatively believable equations are established by calculation and derivation. It can be seen from the microstructure that pure Mg material has experienced an obviously grain growth process follows by significantly refinement during the FSW deformation. High temperature field caused by friction is the main reason which leads to the grain growth.
Highlights
As one of structural metallic materials with the lowest density in engineering applications, magnesium (Mg) and its alloys have the following advantages such as high specific strength and high specific stiffness, high damping and electromagnetic shielding performance, and the excellent properties of casting and machining (Mordike and Ebert, 2001)
The high thermal conductivity rate always results in the widening of heat affected zone, overheating and the Strain Evolution of FSWed Magnesium microstructural coarsening
As one of the severe plastic deformation (SPD) technologies, friction stir welding (FSW) process can result in the fine microstructure with excellent mechanical properties (Nikulin et al, 2012; Zhou et al, 2020)
Summary
As one of structural metallic materials with the lowest density in engineering applications, magnesium (Mg) and its alloys have the following advantages such as high specific strength and high specific stiffness, high damping and electromagnetic shielding performance, and the excellent properties of casting and machining (Mordike and Ebert, 2001). As one of the severe plastic deformation (SPD) technologies, FSW process can result in the fine microstructure with excellent mechanical properties (Nikulin et al, 2012; Zhou et al, 2020). Studies on the variation of strain and/or strain rate of pure Mg during FSW processes are still limited. A computational fluid dynamics based- 3D thermo-mechanical model built by Albakri et al (2013) was used to study the effect of FSW parameters on FIGURE 1 | The initial microstructure of the base metal. Temperature field, material flow and strain rate of AZ31 Mg alloy. Liu et al (2019a; 2019b) developed an experimental method by inserting the marker to approximately determine the strain and strain rate during FSW process of pure copper. Electron back-scattered diffraction was conducted on the samples which were final polished with Argon ion polishing to reveal the detailed microstructural features
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