The influence of microstructure on the formability and fracture of an aluminum-copper alloy (2036)

The effect of aging on strain hardening and fracture in an aluminum copper alloy (2036) in sheet form was investigated. Two distinct types of strain hardening behaviour were identified. In the peak-aged and over-aged conditions, a high initial hardening rate was observed that was dependent upon the distribution of precipitates. The initial period was followed, after about 10 pct extension, by a low hardening rate similar to that of cold worked commercial purity aluminum. In the asquenched and in the naturally aged conditions, the initial rate was lower but strain hardening was maintained at a higher level at high strains. Observations of both forming limit data and fracture maps were interpreted on the basis both of measured strain hardening and of microstructure. Three different samples of the alloy in the naturally aged condition having known press shop performance were also studied. It was shown that the sample with poorest performance had a significant amount of grain boundary precipitaion. Re-heat treatment of these samples showed that reduction in the amount of grain boundary precipitation significantly improved the performance in small radius bend tests. It is suggested that variations in press shop performance may be related to changes in fracture behaviour and that the role of fracture events and their dependence on microstructure is an important one informing operations.