The Inspection And Repair Of Discrepancy Bonded Joints Of Cf/PA6 Composite And AA6061 Based On Ultrasonic Welding Technology

Adhesive bonding technology is widely used in the fabrication of auto parts.However,some adhesion discrepancies caused by workpieces warping et al in the process of adhesivial bonding of workpieces will reduce the mechanical properties of bonded workpieces.Although some present adhesive inspection methods can detect the discrepancies to a certain extent,it only detect the discrepancies in cured bonded discrepant joints and it is very difficult to repair the discrepancies.For solving above issues,as a part of the united fund program of General Motors Corporation(GM)-Zhengzhou University,“Joint Quality Inspection and Repair in Adhesive-Bonding of Polymeric Composites”,this study focuses on the explore of online inspection and repair methods of bond discrepancies of uncured bonded 30%Cf/PA6 composite and AA6061 aluminum alloy.Two inspection method,i.e.,continuous and step by step two point ultrasonic inspection methods and one online repair method were proposed based on the ultrasonic welding technology.The mechanisms of inspection and repair of bond discrepancies were analyzed.The following results are obtained.A decrease in adhesive coverage led to a decrease in strength for the discrepant joints.Especially,a reduction of adhesive coverage of more than 50% resulted in the joint strength decreased by 59.0% compared to sound joints.Hence,it is necessary to develop a method to identify and repair the discrepant joints with lack of adhesive coverage.Because of uncured adhesive has higher absorbility to ultrasonic energy than Cf/PA6 composite and AA6061 Al,the adhesive coverage beneath the horn influenced the absorbation to ultrasonic energy and temperature of adhesive,which will affect the horn displacement during inspection.Hence,the bond discrepancies of lack of adhesive coverage would cause the decrease in horn displacement and the slop of horn displacement-time curve can be used as an index to judge the bond discrepancies.It is feasible to continuously inspect the bond discrepancies of uncured joints of Cf/PA6 composite and AA6061 Al using ultrasonic welding mechine with the optimal inspection parameters of 40 mm inspection distancement,0.075 MPa inspection pressure and 10mm/s inspection rate.However,the continuous absorbation of adhesive and upper workpieces to ultrasonic energy raised quickly their temperature and even melt the surface of upper workpieces.It is difficult for long time inspection and thus had an influence on the inspection efficiency.To overcome above problems in continuous inspection method,Stepwise quasi-static two-point inspection method was developed.The distances between two inspection points,(15mm,16 mm and 13mm)were determined for the adhesive-bonded joints of Cf/PA6-Cf/PA6,AA6061-Cf/PA6 and AA6061-AA6061 based on the results of adhesive spread.Using ?10 horn and the inspection parameters of 0.075 MPa inspection pressure and 0.5s inspection time,stepwise quasi-static two-point inspection method successfully detected the bond discrepancies in uncured bonded joints of Cf/PA6-Cf/PA6,AA6061-Cf/PA6 and AA6061-AA6061 at the inspection rate of 35mm/s.The threshold horn displacements of the discrepant joints were determined,which is 0.11 mm,0.20 mm and 0.18 mm for the bonded joints of Cf/PA6-Cf/PA6?AA6061-Cf/PA6 and AA6061-AA6061 based on the experimental results respectively.Once the horn displacement was lower than above threshold horn displacements,there was some bond discrepancies in the bonded joints.The experimental results showed that uncured Cf/PA6-Cf/PA6 joints had similar mechanism of the stepwise quasi-static two-point inspection to that of continuous inspection method while that of AA6061-Cf/PA6 and AA6061-AA6061 was affected by the resistance effect of adhesive to desformation of AA6061 Al prior to ultrasonic oscillation.The more the adhesive between the upper and lower the prominence the resistance effect of adhesive is,and the large the horn displacement.It is able to repair the bond discrepancies in 30 wt.%Cf/PA6 joints with ultrasonic welding technology.The strength of the discrepant bonded joint was restored to above 73% of that of sound joints after ultrasonic repaired with the repairing parameters of 0.14 MPa horn pressure and 1.5s welding time.The discrepant joints with 25% and 50% adhesive coverages had better repairing outcome than that of discrepant joints with 75% adhesive coverage.Microstructure analysis showed that the main repair mechanism of diacrepant joints is the formation of weld at discrepancies sites during ultrasonic welding.However,due to the adhesive has large support effect to upper workpieces and more ultrasonic energy was absorbed by adhesive for discrepant joints with 75% adhesive coverage,there exist some unmelt zone in fusion zone at discrepancies sites.Hence,the discrepant joints with 75% adhesive coverage had unsatisfactory ultrasonic repairing effect.