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The development of a durable adhesive bonding technology for joining of aluminium automotive structures requires a full understanding of the importance of the environment on the chemistry of the adhesively bonded system. This paper describes the accelerated testing procedures used by Alcan to provide information on the significance of environmental factors on adherend surface, the bonding interface and adhesive and so establish the best combination of adhesive and surface pretreatment for good long term durability. The stress/humidity test provides information on adhesive and interface performance, while the neutral salt spray test illustrates durability and corrosion resistance of the pretreatment. Outdoor exposure testing provides the means of comparing the accelerated tests with real life durability.

The proposed manufacturing scheme imposes various process constraints on the uncured adhesive, while the cured adhesive joints must also be durable under load in warm, wet environments. These requirements are together satisfied by only one class of adhesives, namely the single part epoxies, and are only satisfied by careful matching of adhesive and metal surface pretreatment. The stiffness of the cured adhesive is a less quantifiable requirement; it determines both the impact strength at low temperature and the creep limit in shear at high temperature. These properties must be balanced to give the bonded vehicle structure long-term integrity.