焊接缺陷对异种铝合金TIG对接接头疲劳行为的影响

以5A06-O/7A05-T6异种铝合金钨极氩弧焊（TIG）对接接头为对象，通过疲劳试验数据和断口形貌分析，研究了气孔缺陷和未熔合缺陷对焊接接头疲劳性能的影响规律及机理。结果表明:气孔缺陷和未熔合缺陷对5A06-O/7A05-T6对接接头的疲劳性能均产生不利影响，且缺陷的大小、位置与载荷的交互作用是影响疲劳裂纹提前萌生的主要因素，同一应力水平下，疲劳裂纹更易萌生于尺寸较大且位置更接近于材料表面的焊接缺陷处，而随着应力水平的降低，焊接缺陷对焊接接头疲劳性能的不利影响更为显著；与气孔缺陷相比，未熔合缺陷边缘的应力集中效应更明显，更易导致疲劳裂纹萌生，且焊接接头组织相较于焊接母材组织更脆，疲劳裂纹以穿晶和沿晶形式交替扩展，使疲劳寿命进一步缩短。 

Influence of welding defects on fatigue behavior of dissimilar aluminum alloy TIG butt joint

Fatigue tests and fracture morphology analyses were performed to determine the influence law and mechanism of pore defect and incomplete fusion defect on the fatigue performance of 5A06-O/7A05-T6 dissimilar aluminum alloy TIG butt joint. The results show that both pore defect and incomplete fusion defect have adverse effects on the fatigue properties of 5A06-O/7A05-T6 butt joint, and the interaction between the size and location of defects and the load is the main factor affecting the early initiation of fatigue cracks. Fatigue cracks are more likely to initiate at the welding defects with larger size and closer to the material surface under the same stress level, and the interaction between welding defects and fatigue loading increases with the decrease of stress level, and ultimately decreases the fatigue strength. Compared with pore defect, the effect of stress concentration at the edge of incomplete fusion defect is more significant, which is more likely to cause fatigue crack initiation, the microstructure of welded joint is more brittle than that of welding base metal, and the fatigue crack propagates alternately in the transgranular and intergranular form, which further shortens the fatigue life.