CNTs/Al复合材料搅拌摩擦加工质量的超声衰减评价

Ultrasonic Attenuation Evaluation for Friction Stir Processing Quality of Carbon-nanotubes Reinforced Aluminum Matrix Composites

针对搅拌摩擦加工法制备的碳纳米管增强铝基复合材料的主要碳纳米管团聚缺陷,提出超声波衰减法对加工质量进行无损评价,通过改变搅拌摩擦加工次数得到不同团聚程度的碳纳米管增强铝基复合材料;根据超声衰减理论分别测量各个试样的衰减系数,从宏观上对团聚缺陷进行评价,最大和最小衰减系数相差50倍,通过超声特征扫描成像检测法验证了评价结果的有效性;同时测量了搅拌摩擦加工次数为3次和6次的纯铝试样的衰减系数分别是0.032、0.029 dB/mm,基本排除了在搅拌摩擦加工后纯铝晶粒变化对试验结果带来的影响;最后又采用超声衰减法从微观角度对团聚缺陷进行评价,随着搅拌次数增加,衰减系数从0.178 dB/mm变化到0.025 dB/mm,每搅拌1次衰减系数降低约1倍,可以得出团聚程度越严重,衰减系数越高。

For the main defect named carbon-nanotubes（CNTs） reunion of carbon-nanotubes reinforced aluminum matrix（CNTs/Al） composites which was processed by friction stir method,ultrasonic attenuation method is proposed for nondestructive evaluation.By changing the times of friction stir processing,the different CNTs/Al composites in which the severity of CNTs reunite is different could be obtained.And then the CNTs reunion defects could be evaluated by measuring attenuation coefficient of the different CNTs / Al composites from the macro perspective,and it has 50 times difference between maximum and minimum attenuation coefficients,and the results had been validated by ultrasonic feature scan imaging testing method.At the same time,the attenuation coefficient from pure aluminum specimens which were processed three times and six times respectively were measured as 0.032 dB/mm and 0.029 dB/mm,by which the influence from the changes of the pure aluminum grain can be excluded after friction stir processing on the result of experiment.Finally the CNTs reunion defects is evaluated from the micro perspective as well,and attenuation coefficient changes from 0.178 d B/mm to 0.025 d B/mm and is reduced about 1 times after each stirring with the increase of stirring times,and so the same result shows that the severity of CNTs reunion is aggravating,the attenuation coefficient increasing.