The influence of ageing conditions and liquid nitrogen cooling of extrusion dies on nanoindentation creep in 6060 aluminium alloy

Abstract In the present research, the effect of ageing conditions such as time and temperature as well as the use of liquid nitrogen as a cooling agent on creep behaviour and relevant creep parameters such as steady creep strain rate was investigated by nanoindentation tests. Also, the creep behaviour of the material during the nanoindentation tests has been studied with the aid of measurements that have been collected during the holding stage of the experiment. The results indicate that ageing conditions influence the hardness of the material. Specifically, when using liquid nitrogen as a cooling agent during the extrusion process at ageing temperatures of 160 °C and 180 °C, a decrease in material hardness has been observed. Also, the results revealed that creep displacement is strongly affected by the ageing conditions. Additionally, no important change was found regarding the creep strain rate over the creep time both for the ageing conditions and the use of liquid nitrogen as a cooling agent. Finally, the creep stress exponent ( n ) increases for the ageing temperature of 160 °C, 180 °C and 200 °C, with increasing the ageing time.