目的 探究1.8 mm厚2198-T8铝锂合金材料在无针搅拌摩擦点焊（Pinless Friction Stir Spot Welding, PFSSW）工艺下的高周疲劳性能,分析不同旋转速度与焊接时间组合对焊接接头疲劳寿命的影响,揭示疲劳裂纹的萌生与扩展机制,为优化焊接工艺参数提供理论依据。方法 采用无针搅拌摩擦点焊技术,分别在950 r/min-6 s、950 r/min-9 s和1 180 r/min-6 s 3种组合（旋转速度-焊接时间）下对2198-T8铝锂合金进行焊接。通过高周疲劳试验,建立接头的应力幅（S）-疲劳寿命（N）曲线,评估其疲劳寿命。利用扫描电子显微镜（SEM）观察疲劳断口的裂纹源及瞬断区形貌,分析裂纹萌生位置及扩展路径,确定接头的断裂模式。结果 3种焊接工艺参数下的S-N曲线表达式分别为：950 r/min-6 s（lg S=9.113-1.208lg N）、950 r/min-9 s（lg S=4.172-0.208lg N）和1 180 r/min-6 s（lg S=4.386-0.253lg N）。当焊接时间从6 s增加到9 s,或旋转速度从950 r/min增加到1 180 r/min时,接头S-N曲线的斜率显著增大,表明疲劳性能对载荷的敏感性增强。在相同应力幅下,950 r/min-6 s接头的疲劳性能最优,但其对疲劳载荷的敏感性也最高。疲劳裂纹主要萌生于Hook缺陷处,瞬断区的断口形貌呈现韧窝、准解理和解理特征,表明接头断裂模式为混合断裂。结论 无针搅拌摩擦点焊工艺参数对2198-T8铝锂合金焊接接头的疲劳性能具有显著影响。在相同应力幅下,950 r/min-6 s组合表现出最优的疲劳性能,但其对疲劳载荷的敏感性较高。延长焊接时间或增加旋转速度会导致接头疲劳性能对载荷的敏感性增强。疲劳裂纹主要萌生于Hook缺陷处,断口形貌分析结果表明,接头断裂模式为混合断裂。
Abstract
The work aims to investigate the high-cycle fatigue performance of 1.8 mm thick 2198-T8 Al-Li alloy joints fabricated by probeless friction stir spot welding (PFSSW), analyze the effects of different rotational speed and welding time combinations on the fatigue life of the welded joints, and reveal the mechanisms of fatigue crack initiation and propagation, thereby providing a theoretical basis for optimizing welding process parameters. The PFSSW technique was employed to weld 2198-T8 Al-Li alloy under three rotational speed/welding time combinations of 950 r/min-6 s, 950 r/min-9 s, and 1 180 r/min-6 s. High-cycle fatigue tests were conducted to establish the S-N curves of the joints and evaluate their fatigue life. The fatigue fracture surfaces were observed through scanning electron microscopy (SEM) to analyze the crack initiation sites and transient fracture zones, and to determine the fracture modes of the joints. The S-N (stress amplitude vs. fatigue life) curve expressions for the three welding parameter combinations were as follows: 950 r/min-6 s (lg S=9.113-1.208lg N), 950 r/min-9 s (lg S=4.172- 0.208lg N), and 1 180 r/min-6 s (lg S=4.386-0.253lg N). When the welding time increased from 6 s to 9 s or the rotational speed increased from 950 r/min to 1 180 r/min, the slope of the S-N curves significantly increased, indicating enhanced sensitivity of fatigue performance to loading. Under the same stress amplitude, the 950 r/min-6 s joint exhibited the best fatigue performance but was also the most sensitive to fatigue loading. Fatigue cracks primarily initiated at Hook defects, and the transient fracture zones exhibited dimples, quasi-cleavage, and cleavage features, indicating a mixed fracture mode. In conclusion, the PFSSW process parameters significantly affect the fatigue performance of 2198-T8 Al-Li alloy welded joints. The 950 r/min-6 s combination shows the best fatigue performance under the same stress amplitude but is highly sensitive to fatigue loading. Increasing welding time or rotational speed enhances the sensitivity of joint fatigue performance to loading. Fatigue cracks mainly initiates at Hook defects, and fracture surface analysis reveals a mixed fracture mode. The findings provide important references for optimizing the PFSSW process parameters for 2198-T8 Al-Li alloy.
关键词
铝锂合金 /
无针搅拌摩擦点焊 /
疲劳性能 /
断裂模式
Key words
Al-Li alloy /
probeless friction stir spot welding /
fatigue performance /
fracture mode
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基金
中煤科工西安研究院（集团）有限公司科技创新基金（2024XAQN02）; 国家自然科学基金（42302355）
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