Microstructure And Mechanical Properties Of Friction Stir Processed Mg-Gd-Y-Nd-Zr Alloy

This study mainly aims to investigate the microstructural and textural evolutions of Mg-Gd-Y-Nd-Zr alloy during the FSP as well as its effect on the mechanical properties of FSP alloy. In this study, characterization techniques such as electron backscatter diffraction(EBSD), x-ray diffraction(XRD) and optical microscope(OM) were employed. By the analysis the microstructure and texture, the mechanisms of grain refinement and textural evolution were further analysed to reveal the effects of rare elements on the FSP Mg-RE alloys. The conclusions were as follows:① The FSP could be successfully used in Mg-Gd-Y-Nd-Zr alloy to modify the microstructure and texture with rotation rate of 800 rpm and traverse speed of 100 mm/min.② The microstructure is uniform and forms the fine equiaxed in SZ of SS-FSP alloy, while the some fine grain bands were formed in entire SZ of AG-FSP alloy, indicating that the existing forms of rare elements which dissolves in solid solution BM and precipitates from aging BM have significant influence on microstructure during FSP.③ The texture of SZ in FSP Mg-Gd-Y-Nd-Zr alloy was weak and complicated, while the type of texture is similar with the FSW/FSP of traditional Mg alloys. Due to the influence of tool pin and tool shoulder, the type of texture in CZ is different from the FSW/FSP of traditional Mg alloys. The similar textural evolution in SZ of SS-FSP alloy and AG-FSP alloy confirms that the existing forms of rare elements in two kinds of alloys have rarely effect on textural evolution during FSP.④ The microstructure of SZ is fully dynamic recrystrallization during FSP. The dominant mechanism of grain refinement during FSP was continuous DRX. The discontinuous DRX was existed but weakened due to the Gd and Y element.⑤ The second phases and grain refinement was attributed to the change of hardness of SS-FSP alloy and AG-FSP alloy, andthe second phases hada more important effect than grain size on the hardness in the FSP alloy. For the SS+AG-FSP alloy and AG+AG-FSP alloy, the grain refinement is the main factor to control hardness.⑥Themechanical properties of Mg-Gd-Y-Nd-Zr alloycould be improved by FSP due to the grain refinement and solution hardening. After ageing, the YS and UTS of the aged FSP alloys were improved and the EI was decrease.