Multi-zone fatigue crack growth behavior of friction stir welding of 2A12-T4 aluminum alloy
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摘要: 疲劳裂纹扩展速率是材料内在组织性能的宏观外在表现，显微组织和残余应力对宏观疲劳裂纹的扩展有显著的影响. 文中研究了2A12-T4铝合金搅拌摩擦焊不同区域的疲劳裂纹扩展速率. 结果表明，在焊缝区域，由于搅拌针强烈的机械和焊接热作用，材料组织发生变化，并伴有残余应力的产生，导致不同区域裂纹的扩展速率存在明显差异. 在低应力强度因子范围(ΔK)时，热影响区和垂直于焊缝方向的疲劳裂纹扩展速率基本相同，并且都高于沿焊缝方向裂纹的扩展速率；在高应力强度因子范围(ΔK)时，垂直于焊缝方向的扩展速率逐渐高于热影响区速率，此时这两个区域的裂纹扩展速率仍然高于沿焊缝方向裂纹的扩展速率.Abstract: Fatigue crack growth rate is the macroscopic and external performance of the internal structure of the material. Microstructure and residual stress have a significant effect on the growth of macroscopic fatigue cracks.In this paper, the fatigue crack growth rate of different areas of 2A12-T4 aluminum alloy friction stir welding is studied.The results show that: in the weld area, due to the strong mechanical and welding heat action of the stirring pin, the material structure changes, accompanied by the generation of residual stress, resulting in significant differences in the growth rate of cracks in different areas.At low ΔK, the heat-affected zone and the fatigue crack growth rate perpendicular to the weld are basically the same, and both are higher than the crack growth rate along the weld.At high ΔK, the growth rate perpendicular to the weld seam direction is gradually higher than the heat-affected zone rate. At this time, the crack growth rate in these two regions is still higher than the crack growth rate along the weld seam direction.
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Keywords:
- friction stir welding /
- 2A12 aluminum alloy /
- residual stress /
- microstructure
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图 1 预制裂纹于不同区域的裂纹扩展试样(mm)
Figure 1. Crack propagation samples of prefabricated cracks in different regions. (a) in NZ; (b) in HAZ; (c) in PWZ
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图 3 裂纹预制于不同区域的裂纹扩展速率曲线
Figure 3. Crack growth rate curves of cracks prefabricated in different regions
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图 4 焊缝微观组织
Figure 4. Microstructure of welding joint. (a) macroscopic optical micrograph; (b) EBSD images near the heat affected zone; (c) EBSD images near the weld nugget
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图 5 2A12-T4搅拌摩擦焊缝横向残余应力分布
Figure 5. 2A12-T4 Friction stir welding lateral residual stress distribution
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图 6 裂纹低速扩展阶段断口SEM组织形貌
Figure 6. SEM microstructure of fracture at low-speed crack propagation stage. (a) NZ; (b) HAZ; (c) PWZ
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图 7 裂纹中速扩展阶段断口SEM组织形貌
Figure 7. SEM microstructure of fracture at the stage of medium-speed crack growth. (a) NZ; (b) HAZ; (c) PWZ
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图 8 裂纹高速扩展阶段断口SEM组织形貌
Figure 8. SEM microstructure of fracture at high-speed crack growth stage. (a) NZ; (b) HAZ; (c) PWZ
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图 9 疲劳断口瞬断区SEM组织形貌
Figure 9. Microstructure of SEM in the transient fracture zone of fatigue fracture. (a) NZ; (b) HAZ; (c) PWZ
表 1 2A12-T4合金的化学成分(质量分数，%)
Table 1 2A12-T4 alloy chemical composition
Si Fe Cu Mg Zn Ti Mn 其它元素 Al 0.5 0.5 3.8 ~ 4.9 1.2 ~ 1.8 0.3 0.15 0.3 ~ 0.9 Ni:0.1, (Fe + Ni):0.5 余量 
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