The evaluation of non-tank surface treatments for aluminium bonding repairs

Abstract

Adhesive bonding has been adopted as the field repair method for aircraft structures damaged during manufacture or in service. To obtain strong and durable bonds, proper surface treatment of the adherends is very important. In this paper, various non-tank methods for the surface treatment of aluminium in the field have been investigated. These methods–abrasion, gelled FPL treatment, phosphoric acid non-tank anodize, PasaJell 105 and HF/Alodine 1200—were evaluated in terms of single lap-shear strength, durability as determined using the Boeing wedge test, and residual strength following long-term immersion in water, hydraulic fluid and JP-4 fuel. In addition, surface morphologies were observed with scanning electron microscopy and chemical analysis of the surfaces was carried out using Fourier transform infra-red spectroscopy and X-ray photoelectron spectroscopy. The initial bond strengths of the fifferent treatments were comparable. However, wedge test results revealed that surfaces prepared by abrasion and HF/Alodine 1200 had poor durability. In addition, the long-term immersion tests showed that the PasaJell 105 treatment generated good surface stability, with bond strength and durability as effective as the well-known phosphoric acid non-tank anodize ( PANTA) process. Being much easier to apply than the PANTA procedure, PasaJell 105 treatment should be the first candidate for the field repair of aircraft structures.