A B S T R A C T 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.Keywords 7075 Al alloy; ageing; ECAP; fatigue crack growth.
N O M E N C L A T U R Ea = Crack length B = Specimen thickness C = Paris law parameter E T = Total energy expended for fatigue crack growth E d = Energy expended for plastic deformation at the crack tip E s = Energy expended for formation of free surfaces E r = Energy expended for relaxation m = Paris law parameter N = Number of cycles R = Cyclic load ratio W = Specimen width ΔK = Stress intensity factor range ΔK c = Stress intensity factor range for catastrophic failure ΔP = Applied load range
I N T R O D U C T I O NAluminium alloys are widely used in engineering applications. There is, nevertheless, much significance to improve mechanical properties of the alloys using engineering processes. Although mechanical properties of all crystalline materials are determined by several factors, the average grain size plays a very significant and often a dominant role. In order to decrease the grain size of a material using metal-working procedures, it is necessary to impose an exceptionally high strain in order to introduce a high density of dislocations subsequently rearranged to form an array of grain boundaries. In practice, because of the limitations of Correspondence: A. Fallahi.