Microstructure,tensile properties and fracture behaviour of aluminium alloy 7150

A study has been made to understand the microstructure, tensile properties and fracture characteristics of aluminium alloy 7150. Detailed optical and transmission electron microscopical observations were used to analyse the intrinsic microstructural features of the alloy in the T77 condition. The alloy was deformed to failure over a range of strain rates in environments of 3.5% sodium chloride solution and laboratory air. The environment was found to have little influence on strength of the alloy. The strength only marginally increased with an increase in strain rate. However, for all strain rates, the ductility of the alloy degraded in the aggressive environment. The ratio of strain to failure in sodium chloride solution to that in laboratory air indicates that the alloy is only mildly susceptible to stress corrosion cracking. The fracture behaviour was different in the two environments. However, in a given environment the fracture behaviour was essentially the same. In the aggressive environment fracture was predominantly intergranular while fracture revealed a ductile transgranular failure in laboratory air. An attempt is made to discuss the kinetics of the fracture process in terms of competing mechanistic effects involving intrinsic microstructural features, matrix deformation characteristics, environment and strain rate.