Behaviour of aluminium at elevated strain-rates and temperatures

Abstract

The purpose of this thesis is to look at the effects of increased strain-rates and temperatures on the aluminium alloy AA6060. To do this, more than 50 experiments conducted in three different machines have been performed, and the results have been analyzed. To describe the behaviour of the aluminium alloy at different strain-rates and temperatures, the results from the experiments have been used in finding appropriate parameters for a material model. The material model used is the Zener-Hollomon equation,which predicts flow stress with strain-rate and temperature as variables.

The results confirm that the importance of strain-rate first becomes significant when the absolute temperature is increased to a level of 50 % of the melting point. For AA6060 this means a temperature above approximately 200 °C. Increasing the temperature above this point will further increase the effect of elevated strain-rates.

With increasing temperatures, metals will see an increase in ductility. This applies to the material AA6060 as well, but not without exceptions. When the temperature increases rapidly beyond about 470 °C, the materialwill behave brittle. This is because the Mg2Si enclosed in the aluminium is not allowed to diffuse into the grains evenly, thus making the material porous.