Effect of pin rotational speed on microstructure and properties of SSFSW weld for thick-plate magnesium alloy
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摘要: 对9 mm厚板AZ31B镁合金进行静止轴肩搅拌摩擦焊(stationary shoulder friction stir welding，SSFSW)工艺试验，探讨搅拌针转速(500 ~ 1000 r/min)对焊缝组织及力学性能的影响规律. 结果表明，在给定焊接速度80 mm/min下，搅拌针转速在600 ~ 800 r/min范围可获得表面光滑、无内部缺陷的对接焊缝，当转速为1 000 r/min时焊缝表面出现不连续凹坑但内部仍无缺陷. 随着转速增加，晶粒尺寸由(11.11 ± 1.68) μm增加到(18.95 ± 1.83) μm；在700 r/min时焊核区晶粒尺寸沿板厚差异最小. 焊缝中间硬度分布具有不均匀性且随转速增加而减小，最大差异为10.97 HV，最低硬度47 HV位于前进侧的热力影响区与焊核区界面处. 在700 r/min下接头力学性能最佳，强度系数为90.2%、对应断后伸长率为母材69.3%. 随着转速增加，断裂模式由韧-脆混合断裂转变为剪切-韧性混合断裂.
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关键词:
- AZ31B镁合金厚板 /
- 静止轴肩搅拌摩擦焊 /
- 搅拌针转速 /
- 组织特征 /
- 力学性能
Abstract: The thick-plates of AZ31B magnesium alloy with 9 mm thickness were joined successfully by stationary shoulder friction stir welding (SSFSW) to explore the influence of stirring needle speed (500 – 1000 r/min) on the microstructure and mechanical properties of weld. The results show that the butt weld with smooth surface and no internal defects can be obtained at the rotation speed of 600 − 800 r/min under the given welding speed of 80 mm/min. When the rotation speed is 1000 r/min, discontinuous pits appear on the surface but there are still no defects in the weld. With the increase of rotating speed, the grain size increase from (11.11 ± 1.68) μm to (18.95 ± 1.83) μm. At 700 r/min, the grain size difference in the nugget zone is the smallest along the plate thickness. The inhomogeneity of hardness distribution in the WNZ decreases with the increase of rotational speed. The maximum difference of hardness in the middle of the plate thickness is 10.97 HV, and the minimum hardness is 47 HV at the interface between the heat affected zone and the nugget zone of the advancing side. The joint has the best mechanical properties at 700 r/min, the strength coefficient is 90.2% and the corresponding elongation is 69.3% of the BM. With the increase of rotational speed, the fracture mode changes from ductile-brittle mixed fracture to shear-ductile mixed fracture. -
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图 2 SSFSW工艺示意图及试样切割位置
Figure 2. Schematic diagram of SSFSW process and cutting positions of specimens
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图 3 焊缝表面和接头截面宏观形貌
Figure 3. Weld surface and Macroscopic of cross-sections of SSFSW joints. (a) 500 r/min; (b) 600 r/min; (c) 700 r/min; (d) 800 r/min; (e) 1 000 r/min
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图 5 SSFSW接头典型宏观形貌以及不同区域的显微组织
Figure 5. Typical macrostructure of SSFSW joint and microstructure of different areas. (a) Typical macrostructure; (b) BM; (c) top of WNZ; (d) middle of WNZ; (e) bottom of WNZ; (f) AS-TMAZ; (g) RS-TMAZ; (h) AS-HAZ; (i) RS-HAZ.
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图 6 顶部晶粒尺寸
Figure 6. The grain size of the top WNZ. (a) 500 r/min; (b) 600 r/min; (c) 700 r/min; (d) 800 r/min; (e) 1 000 r/min
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图 7 中部晶粒尺寸
Figure 7. The grain size of the middle WNZ. (a) 500 r/min; (b) 600 r/min; (c) 700 r/min; (d) 800 r/min; (e) 1 000 r/min
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图 8 底部晶粒尺寸
Figure 8. The grain size of the bottom WNZ. (a) 500 r/min; (b) 600 r/min; (c) 700 r/min; (d) 800 r/min; (e) 1 000 r/min
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图 11 700 r/min接头截面显微硬度分布
Figure 11. Cross-sectional hardness profiles of joints at 700 r/min
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图 12 不同转速下WNZ硬度值分布
Figure 12. Microhardness distributions in WNZ at different rotational speed. (a) Microhardness distributions of the top WNZ; (b) Microhardness distributions of the middle WNZ; (c) Microhardness distributions of the bottom WNZ; (d) Microhardness distributions along WNZ thickness direction
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图 14 BM和SSFSW接头的拉伸性能
Figure 14. Tensile properties of BM and SSFSW joints. (a) True stress-strain curve; (b) Tensile properties of BM and SSFSW joints
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图 18 断口不同区域SEM图像
Figure 18. SEM images of different areas of fracture. (a) 600 r/min; (b) 700 r/min; (c) 800 r/min; (d) 1000 r/min
表 1 AZ31B化学成分(质量分数，%)
Table 1 The chemical compositions of AZ31B
Al Zn Mn Si Fe Cu Ni Ca Mg 3.1 0.99 0.38 <0.08 <0.003 <0.01 <0.001 <0.04 余量 
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表 2 AZ31B物理性能
Table 2 Physical properties of AZ31B
抗拉强度Rm/MPa 屈服强度Rel/MPa 断后伸长率A50(%) 熔点T/℃ 热导率λ/W·(m−1·K−1) 硬度H/HV 256 156 14 650 155 52 ~ 59
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表 3 不同转速下WNZ硬度值的平均值和方差
Table 3 Mean and variance of Microhardness distributions in WNZ at different rotational speed
转速w/(r·min−1) WNZ顶部 WNZ中部 WNZ底部 沿WNZ厚度方向 硬度平均值H/HV 方差 硬度平均值H/HV 方差 硬度平均值H/HV 方差 硬度平均值H/HV 方差 600 56.38 10.90 54.22 6.30 52.41 5.28 57.71 4.07 700 54.07 2.53 54.65 10.97 52.93 5.24 60.83 3.28 800 56.02 6.90 55.11 9.82 53.65 3.84 56.70 4.08 1 000 56.68 2.39 59.23 9.02 54.65 3.00 59.63 5.40
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表 4 SSFSW接头和BM的拉伸性能
Table 4 Tensile properties of SSFSW joint and BM
转速w/(r·min−1) 抗拉强度Rm/MPa 屈服强度Rel/MPa 断后伸长率A(%) 强度系数B(%) 600 205 88 5.5 80.1 700 231 96 9.7 90.2 800 227 94 9.3 88.7 1000 227 93 8.9 88.7
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期刊类型引用(1)
1. 王鹏，吴璇，张喆，钱志杰，高吉成. 搅拌摩擦焊在镁合金焊接中的应用与进展. 兵器材料科学与工程. 2025(01): 155-164 . 
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