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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.

Weld bonding of aluminium autobody structures offers automotive vehicle manufacturers the opportunity of achieving significant weight reduction, compared to equivalent steel structures. Further, this is achievable using volume production manufacturing methods. This paper considers all key aspects of the weld bonding process, in particular the equipment requirements and the factors that are important in reliably achieving satisfactory structures. Methods of minimising damage to the adhesive bondline and assessment of spot weld quality are discussed. Using experience gained from extensive weld bonding trials, suitable parameters for robust weld bonding are recommended.

The paper summarises work which has been carried out to establish the sensitivity of the Alcan AVT weld-bonding system to manufacturing process variability. The robustness of the joint-line to factors such as panel fit-up, bondline thickness, adhesive fillet size and missing adhesive is discussed and their effects demonstrated. Manufacturing factors, such as pretreatment damage during part forming and the cure-cycle window for the adhesive, are considered and their effects on performance are indicated. Finally the effect of a series of manufacturing shortfalls and environmental factors have been put together in one experiment and the resulting strength and fatigue performance of bonded joints has been established.

A proven design and manufacturing system for building automotive structural frames and unibody structures in adhesively bonded sheet aluminum is described. The system, which was developed to be compatible with established procedures and facilities for building spot-welded steel vehicles, allows the weight of such vehicle body structures to be reduced by almost half, yet provides structures of similar rigidity, excellent resistance to fatigue and corrosion attack and has been proven through evaluation tests carried out on replicas of production cars built using the technology. While developed for manufacturing automobile structures from adhesively bonded stamped sheet, adaptation of this technology to the construction of adhesively bonded perimeter and tubular structural frames is also described.

Experiments have been carried out on the collapse behavior, the energy absorption and the flexural stiffness of adhesively bonded, spot-welded and weld-bonded aluminum box structural assemblies and the results compared with those for equivalent spot-welded mild steel structures. It has been found that weld-bonded aluminum box beams can exhibit specific energy absorptions that are three times greater than those for the mild steel beams and, hence, show that aluminum vehicle structures which typically can be built at about half the weight of steel structures, should nevertheless have more than adequate impact resistance. In flexural testing, the results suggest that the overall stiffness improvements of bonded structures may be a combination of improved beam stiffness, and superior connections between structural elements.

In order to prove that the aluminum structured vehicle technology (ASVT), that was jointly developed by Alcan International and Gaydon Technology, could be used to produce satisfactory automobiles, a fleet of replica vehicles was built using the technology and was subjected to a comprehensive series of test track and road evaluation programs. This paper describes the novel way in which six Austin Rover Metro replicas were built using the ASV technology. It then goes on to describe the tests that were performed on the vehicles and the results obtained. The tests included static torsion, 1000 mile pave (Belgian block), pothole braking, accelerated corrosion and 30 mph barrier impact.

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.