Microstructure evolution of 2195 Al-Li alloy friction stir welded joint and enhancing performance by laser shock peening
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摘要:
为了研究2195铝锂合金搅拌摩擦焊接头的组织与性能特点并试图加以改善，采用不同参数焊接了6.5 mm厚的2195-T8铝锂合金试板，使用OM，EBSD和TEM等技术观察并分析了搅拌摩擦焊接头各区域的组织变化，通过显微硬度分析、拉伸试验和数字图像相关技术(digital image correlation，DIC)等方法测试并讨论了接头的性能特点. 结果表明，2195-T8铝锂合金的搅拌摩擦焊在试验参数范围内能稳定获得成形良好的接头，强度系数达到70%、断后伸长率达到7%. 搅拌摩擦焊接头内各区域发生了强化相的损失，焊核区的T1相和θ'相完全溶解，形成β'/δ'相. 焊核区和轴肩影响区在拉伸试验中发生应变集中. 对焊缝进行双面激光冲击强化(laser shock peening，LSP)处理后，接头屈服强度提升51 MPa，且断裂路径从焊核区变为热力影响区外侧，改变后断裂位置对应于硬度测试中的最低硬度区域.
Abstract:To investigate the microstructure and mechanical properties of friction stir welding (FSW) joints of 2195 aluminum-lithium alloy and attempt to improve them, 6.5 mm thick 2195-T8 aluminum-lithium alloy test plates were welded using different parameters. The microstructure evolution of different zones of the joints was investigated using OM, EBSD, TEM and other analytical techniques. The mechanical properties including microhardness and tensile properties of the joints were tested and digital image correlation (DIC) was applied. The results indicate that FSW of 2195-T8 aluminum-lithium alloy can reliably produce well-formed joints within the tested parameter range, with a strength coefficient of 70% and a fracture elongation of 7%. T1 and θ' completely dissolved in the weld nugget zone while β'/δ' was formed. Strain concentration occurred in the weld nugget and shoulder affected zones during tensile testing. After double-sided laser shock peening (LSP), the yield strength of the joint increased by 51 MPa, and the fracture path shifted from the weld nugget zone to the outer side of the thermal-mechanical affected zone. The new fracture location corresponded to the region of lowest hardness as determined by hardness testing.
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图 2 接头各区域EBSD形貌
Figure 2. EBSD maps of different areas of the joint. (a) HAZ；(B) TMAZ； (c) NZ
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图 3 热力影响区与焊核区的TEM图
Figure 3. TEM pictures of TMAZ and NZ. (a) bright field (BF) image of TMAZ；(b) selected area electron diffraction image (SAED) of TMAZ；(c) BF image of NZ
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图 4 2195-T8铝锂合金FSW接头横截面显微硬度分布
Figure 4. Microhardness distribution curves of 2195-T8 Al-Li alloy FSW joint cross sections. (a) hardness at different thickness positions of the joint；(b) the hardness of joints with different parameters is similar
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图 5 2195-T8铝锂合金FSW接头的拉伸性能
Figure 5. Tensile properties of 2195-T8 Al-Li alloy FSW joints
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图 7 2195-T8铝锂合金FSW接头应变分布
Figure 7. Strain distribution of 2195-T8 Al-Li alloy FSW joint
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图 8 LSP前后显微硬度硬度对比
Figure 8. Comparison of microhardness before and after LSP. (a) comparison of hardness in thickness direction; (b) top hardness comparison; (c) bottom hardness comparison
表 1 不同处理条件下接头的拉伸性能
Table 1 Tensile properties of joints under different treatment conditions
处理条件 抗拉强度
Rm/MPa屈服强度
ReL/MPa断后伸长率
A(%)原始接头 427 273 7.6 仅铣去上层0.6 mm 444 297 7.1 铣去上层0.6 mm +
双面LSP448 348 6.1 
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