Low pressure plasma treatment for improving the strength and durability of adhesively bonded aluminium joints

The effectiveness of radio frequency plasmas of oxygen, air and argon in removing the organic layer from the deliberately contaminated surface of AA6016T6 alloy has been assessed. Plasma treatment of the alloy surface has been characterised using wettability (water contact angle) and surface chemical analysis (X-ray photoelectron spectroscopy, XPS). The performance of bonded single lap shear joints has been characterised before and after immersion in water for 2 weeks at 60 °C. Oxygen plasma treatment had the most marked effect on joint performance; resulting in a 40% increase in initial joint failure stress and a 38% increase of aged joint failure stress compared with the contaminated alloy. This improvement is correlated with low carbonaceous over layer thickness and carbon concentration, determined by XPS, and increased surface energy, as indicated by low water contact angle.