The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental result...The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental results show that most specimens mainly failed at the 7075 side weld toes even though the base material tensile strength of 7075 is higher than that of 6061.The maximum stress-strain concentration in the two finite element models is located at the 7075 side weld toe,which is basically consistent with the actual fracture location.The weld zone on the 7075 side experiences severe material softening,with a large gradient.However,the Vickers hardness value on the 6061 side negligibly changes and fluctuates around 70 HV.No obvious defects are found on the fatigue fracture,but a large number of secondary cracks appear.Cracks germinate from the weld toe and propagate in the direction of the plate thickness.Weld reinforcement has a serious impact on fatigue life.Fatigue life will decrease exponentially as the weld reinforcement increases under low stress.It is found that the notch stress method can give a better fatigue life prediction for TIG weldments,and the errors of the predicted results are within the range of two factors,while the prediction accuracy decreases under low stress.The equivalent structural stress method can also be used for fatigue life prediction of TIG weldments,but the errors of prediction results are within the range of three factors,and the accuracy decreases under high stress.展开更多
基金Partially funded by the National Natural Science Foundation of China(No.51065012)。
文摘The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study,and the weld seam cross-section hardness was measured.The experimental results show that most specimens mainly failed at the 7075 side weld toes even though the base material tensile strength of 7075 is higher than that of 6061.The maximum stress-strain concentration in the two finite element models is located at the 7075 side weld toe,which is basically consistent with the actual fracture location.The weld zone on the 7075 side experiences severe material softening,with a large gradient.However,the Vickers hardness value on the 6061 side negligibly changes and fluctuates around 70 HV.No obvious defects are found on the fatigue fracture,but a large number of secondary cracks appear.Cracks germinate from the weld toe and propagate in the direction of the plate thickness.Weld reinforcement has a serious impact on fatigue life.Fatigue life will decrease exponentially as the weld reinforcement increases under low stress.It is found that the notch stress method can give a better fatigue life prediction for TIG weldments,and the errors of the predicted results are within the range of two factors,while the prediction accuracy decreases under low stress.The equivalent structural stress method can also be used for fatigue life prediction of TIG weldments,but the errors of prediction results are within the range of three factors,and the accuracy decreases under high stress.
文摘双钨极热丝TIG堆焊技术热输入量可控、沉积效率高和稀释率低,在管道内壁堆焊时无刚性固定约束亦能有效保障管道直线度,是一种很有前途的堆焊技术.文中采用双钨极热丝TIG堆焊技术在输油管道高强钢内壁制备两层Inconel 625镍基合金堆焊层,用金相显微镜和扫描电镜对镍/钢堆焊复合板进行微观组织分析,对镍/钢复合板进行硬度测试,并分别在距离镍/钢界面0.5、1.0、1.5 mm处的镍基合金堆焊层取样,进行耐晶间腐蚀性能测试.结果表明:堆焊层的微观结构表现出细胞枝晶结构,沿沉积方向外延生长,枝晶间存在二次相(如Laves相和碳化物);镍/钢堆焊复合板焊态下镍合金堆焊层硬度大于高强钢基板大于钢侧热影响区;试验得出通过钨极热丝TIG堆焊技术得到的堆焊层晶间腐蚀敏感度(degree of sensitization,DOS)值小于1,具有优异的耐晶间腐蚀抗性;随着堆焊层的位置靠近钢侧距离的增加,堆焊层中Fe含量减少,镍基合金堆焊层耐腐蚀性能增加.
