Cryogenic Temperature and Strain Rate Dependence of Mechanical Properties for Extruded AA6060 Alloys

Tensile properties and fracture behavior of an AA6060 alloy were investigated at room temperature (295K) and cryogenic temperature (77K). It was found that both ultimate tensile strength and elongation increased with decreasing temperature. In particular, the latter increased with increasing strain rate at 77K. The changes in mechanical properties were thought to be due to a higher working hardening rate at low temperature, while the effect of strain rate on strain hardening was obscure at both temperatures. The hardness after tensile testing at 77K increased due to an increased accumulated dislocation density. Fracture occurred in a semi-ductile transgranular manner at 295K, while a mixture of intergranular and transgranular mode with less slip localization occurred at 77K. Moreover, a decreased testing temperature led to a decreased size of dimples. The rotation of grain orientations can lead to increased Schmid factors and change of the latter was strongly dependent on the deformation temperature, which was clarified by compression tests.