Durability of bonds formed between epoxy adhesive and aluminium alloy treated with phosphonate inhibitors

A traditional organosilane coupling agent, gamma-glycidoxypropyl trimethoxysilane (gamma-GPS), was compared with a series of phosphonate hydration inhibitors in the role as metal pretreatments for adhesive bonding. The bond durability of epoxy adhesive-bonded double cantilever beam specimens in hydrothermal environments was assessed where the aluminium adherend had been pretreated with either class of compound. The performance of the compounds is related to the structure of the adsorbed film on the metal substrate and its subsequent interaction with the epoxy adhesive in the bonded system. These assessments were conducted using XPS and Fourier transform infrared spectroscopy (FTIR) analysis of the deposited films and XPS analysis of failed bond specimens to determine the zone of fracture. The bond failure mechanisms are discussed in terms of a simple bond degradation model.