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| 1 | Effect of Yttrium Addition on Microstructural Characteristics and Superplastic Behavior of Friction Stir Processed ZK60 Alloy显示文摘As-extruded ZK60 and ZK60-Y magnesium alloy plates were successfully processed via friction stir processing(FSP) at a tool rotation rate of 1600 r/min and a traverse speed of 200 mm/min. FSP resulted in the formation of equiaxed recrystallized microstructures with the average grain sizes of w8.5 and w4.7 mm in the ZK60 and ZK60-Y alloys, respectively. Moreover, FSP broke and dispersed the MgZn2 and W-phase(Mg3 Zn3 Y2) particles and dissolved MgZn2 phase in the FSP ZK60 alloy. With the addition of rare earth element yttrium(Y) into the ZK60 alloy, the ratio of the high angle grain boundaries(HAGBs) in the FSP alloys increased from 64% to 90%, and a certain amount of twins appeared in the FSP ZK60-Y alloy. The maximum elongation of 1200% and optimum strain rate of 3 103s1achieved at 450 C in the FSP ZK60-Y alloy were substantially higher than those of the FSP ZK60 alloy. This is attributed to the fine grains with high ratio of HAGBs and the distribution of a large number of dispersed second phase particles with high thermal stability in the FSP ZK60-Y alloy. Grain boundary sliding was identified as the primary deformation mechanism in the FSP ZK60 and ZK60-Y alloys from the superplastic data analyses and surficial morphology observations. | Z.A.Luo G.M.Xie Z.Y.Ma G.L.Wang G.D.Wang | 2013 | Journal of Materials Science & Technology2013，29，12： | 9 |
| 2 | Effect of Rotation Rate on Microstructure and Mechanical Properties of Friction Stir Spot Welded DP780 Steel显示文摘DP780 steel sheets consisting of ferrite and martensite were successfully friction stir spot welded(FSSW)at the rotation rates of 500 to 1500 r/min using a W-Re alloy tool.The effect of rotation rate on microstructure and mechanical properties of the FSSW DP780 was investigated.The peak temperatures in the welds at various rotation rates were identified to be above A3temperature.FSSW caused the dynamic recrystallization in the stir zone(SZ),thereby producing the fine equiaxed grain structures.At the higher rotation rates of≥1000 r/min,a full martensitic structure was observed throughout the SZs,whereas at the lower rotation rate of 500 r/min,the SZ consisted of a fine dual phase structure of ferrite and martensite due to the action of deformation induced ferrite transformation.The maximum average failure load as high as 18.2 k N was obtained at the rotation rate of 1000 r/min and the fracture occurred at the thinned upper sheet. | G.M.Xie H.B.Cui Z.A.Luo W.Yu J.Ma G.D.Wang | 2016 | Journal of Materials Science & Technology2016，32，4： | 2 |
| 3 | Microstructural refinement mechanism and its effect on toughness in the nugget zone of high-strength pipeline steel by friction stir welding显示文摘High-strength pipeline steel was subjected to friction stir welding(FSW)at rotation rates of 400-700 rpm,and the grain refinement mechanism of the nugget zone(NZ)was determined.The thermomechanical process during FSW in the NZ was simulated by multi-pass thermal compression,thereby achieving the austenitic non-recrystallization temperature(T_(nr)).The austenitic non-recrystallization in the NZ at the lowest rotation rate of 400 rpm caused a significant grain refinement.Furthermore,the reduced rotation rate also resulted in the formation of a high ratio of island-like martensite-austenite(M-A)constituent.The toughness of the NZs was enhanced as the rotation rate decreased,which is attributed to the fine effective grains and homogeneously distributed fine M-A constituents dramatically inhibiting crack initiation and propagation. | R.H.Duan G.M.Xie P.Xue Z.Y.Ma Z.A.Luo C.Wang R.D.K.Misra | 2021 | Journal of Materials Science & Technology2021，，34： | 1 |
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