Fatigue crack growth resistance of 7075 Al alloy after equal channel angular pressing

摘要

This work presents experimental results on effects of severe plastic deformation (SPD) and subsequent natural ageing on tensile mechanical properties and fatigue crack growth resistance of fine-grained 7075 Al alloy. The alloy was subjected to equal channel angular pressing (ECAP) after solution treatment. Fatigue crack propagation tests were conducted in room condition, at load ratio R = 0.1 and different load ranges on small disk shaped compact tension specimens. Fatigue fracture surface is also investigated using scanning electron microscopy observations and showed more ductile fatigue crack growth in the unECAPed specimen. Despite the increased tensile strength after ECAP, the ductility that controls low-cycle fatigue behaviour has decreased. It is found that ECAP has resulted in a remarkable change in Paris regime parameters and a significant increase in fatigue crack growth rate. The decrease in fatigue crack growth resistance and ΔK_c after ECAP can be attributed to the decrease in alloy's ductility.