A Study On Silane Treatment And Adhesive Technology Of C_f/PA6 Composites And AA6061-T4 Aluminum Alloys

As a part of the united fund progrem,“Adhesive Bonding of Similar and Dissimilar Materials”,which carried out by General Motors Corporation(GM)and Zhengzhou University,this study was focused on the challenging technical problems in adhesive-bonding of carbon fiber reinforced nylon composites based on the C_f/PA6 composites.The KH550 and KH560 silane surface pretreatment processes and adhesive-bonding technology of the similar and dissimilar materials of C_f/PA6 and AA6061-T4 materials were developed.The chemical composition and microstructure of silane coating were analyzed using scanning electron microscope(SEM)and X-ray Photoelectron Spectroscopy(XPS).The strength of the bonded-coated C_f/PA6-C_f/PA6 and C_f/PA6-AA6061-T4 workpieces at ambient and elevated temperature(82oC)was measured using tensile-shear strength of single-lapping samples.The influence of silane coating on the strength of the bonded-coated C_f/PA6-C_f/PA6 and C_f/PA6-AA6061-T4 workpieces at ambient and elevated temperature(82oC)and their durability on the environmental conditions of thermal cycles of 82 oC to ambient temperature and hot-humid exposure in 54 oC water were evaluated using the degradation of strength of adhesive-bonding joints at ambient or elevated temperature.The results showed that :The electric resistance of 6% KH550 and KH560 silane solutions decreased and stabilized with prolonging the hydrolytic time.The higher the hydrolytictemperature,the lower of electric resistance of silane solutions for the same hydrolytic time.The optimal hydrolytic temperature and time were 70 oC and above 6min for both KH550 and KH560 silane.However,the optimal pH value is 5 and 6 for KH550 and KH560 silan,respectively.The pretreatment of KH550 and KH560 silane resulted in the compact and homogeneous silane coating on the surface of C_f/PA6 and AA6061-T4 workpieces,which caused a decreased in the roughness and surface energy of coated workpieces.The optimal silane coating time is 2 min for AA6061-T4 workpieces and 10 min for C_f/PA6 workpieces respectively.The analysis of XPS showed that there exist Si-O-Si and Si-N covalent bonds on the surface of C_f/PA6 and Si-O-Si and Al-O-Si covalent bonds on the surface of AA6061-T4 workpieces.Abrasion of adherends prior to silane pretreatment increased the number of N atom and Si-N covalent bonds.Although the pretreatment of both KH550 and KH560 silane increased the strength of bonded C_f/PA6-C_f/PA6 and C_f/PA6-AA6061-T4 workpieces,the pretreatment of KH560 silane had more effective improvement on the adhesive-bonding than that of KH550 silane.Compared to the strength of bonded bare workpieces,the strength of bonded C_f/PA6-C_f/PA6 and C_f/PA6-AA6061-T4 workpieces increased by 23% and 21% respectively after pretreatment of KH560 silane.The reason is that the formation of Si-O-Si and Si-N covalent bonds on the surface of C_f/PA6 and Si-O-Si and Al-O-Si covalent bonds on the surface of AA6061-T4 workpieces enhanced the bond adhesion between the silane coating and adhesive,silane coating and and adherends respectively.All of them is in favor to improve the adhesive-bonding performance of C_f/PA6-C_f/PA6 and C_f/PA6-AA6061-T4 workpieces.Abrasion of adherends prior to silane pretreatment enhanced the improvement effect of KH560 silane on the adhesive-bonding performance of C_f/PA6 workpieces.The single abrasion pretreatment increased the strength of bonded C_f/PA6-C_f/PA6 to the similar joint strength of non-abrasion-silane coated workpieces(about 7.6MPa).Abrasion of adherends prior to silane pretreatment increased the strength to 9.32 MPa for bonded C_f/PA6-C_f/PA6 and 12.6MPa for C_f/PA6-AA6061-T4 workpieces.The strength of both joints increased by 48% and 34% compared with that of bare workpieces.The reason is that abrasion of adherends prior to silane pretreatment increased the number of N atom and Si-N covalent bonds,which enhanced the bond adhesion between the silane coating and C_f/PA6 adherents.Although the strength of all adhesive-bonding joints decreased by 23-29%,30% and 50% at elevated temperature(82oC),after thermal cycles of 82 oC to ambient temperature and hot-humid exposure for one week in 54 oC water respectively,Silane pretreatment improved the elevated performance of adhesive-bonded workpieces,especially for the process of abrasion prior to silane pretreatment.Compared with the adhesive-bonding joints fabricated with bare workpieces,the bonding strength at 82℃increased by 22-24% and 21%,the room strength increased by 47% and 41% after thermal cycle from 82℃/30 min to room temperature,and increased by 25% and 19% after immersed in water at 54 oC for one week for the abrasion-silane coated C_f/PA6-C_f/PA6 and C_f/PA6-AA6061-T4 workpieces respectively.