Influence of Plastic-Cold Deformation on Mechanical Properties and Fatigue Crack Growth Behaviour of Annealed Al6061 Alloy

Abstract

Improving the strength of annealed Al6061 without compromising formability remains a key challenge. This study investigates plastic-cold deformation (PCD) using nominal compressive stresses of 10 MPa (PCD10) and 18 MPa (PCD18) as a simple approach to strengthen the alloy. Although the applied stress was lower, PCD10 produced a more concentrated near-surface hardened layer than PCD18, accompanied by higher tensile strength and better fatigue crack growth (FCG) resistance. PCD10 sustained approximately 55% more fatigue cycles to failure, with more pronounced crack-growth retardation at low stress intensity factor range (DK), a lower Paris exponent (m = 3.16 vs 3.57), and a higher maximum stress intensity factor at failure (K_max = 24.01 vs 19.36 MPa·m^1/2). Fractographic and energy-dispersive X-ray spectroscopy (EDS) analyses showed that Fe-rich intermetallic particles were associated with local microvoid nucleation and crack-path deviation in both conditions. The more contained fracture morphology observed for PCD10 was consistent with its lower fatigue crack-growth rate. Overall, the results show that the spatial distribution of near-surface plastic deformation has a greater influence on the mechanical and fatigue behaviour of gripping-induced PCD than nominal compressive stress alone. Localised contact deformation therefore provides a simple and energy-efficient route for improving the structural performance of annealed Al6061.