Influence of retrogression and re-ageing heat treatment on the fatigue crack growth behavior of 7010 aluminum alloy

Abstract

Aluminum alloys are widely used in aircraft structural components where light weight, high strength and good corrosion resistance are the primary requirements. These alloys are generally used in peak-aged (T6) condition in which they are susceptible for stress corrosion cracking. In the recent years, retrogression and re-ageing (RRA) treatment on aluminum alloy is carried out to enhance their corrosion resistance maintaining the ultimate tensile strength. The aim of this work was to study the influence of RRA treatment on the fatigue crack growth rate (FCGR) behavior. The 7010 aluminum alloy was heat treated to two different conditions i.e., T6 and RRA. The microstructures of these alloys were characterized by using TEM. Standard compact tension (CT) specimens were prepared and FCGR tests were carried out by using a 100 kN servo-hydraulic test machine as per ASTM E647-15e1. The constant amplitude FCGR tests were carried out at a stress ratio, R = 0.5 using sine wave loading pattern at 10 Hz. Crack length was monitored by following compliance technique. Microstructural studies show that RRA treated alloy contain fine and densely populated precipitates in the matrix along with coarse and discontinuous precipitates in the grain boundary. The fatigue crack growth rate was observed to reduce along with an increase in the threshold stress intensity factor range (?Kth) for RRA treated alloy compared to the T6 alloy. The mechanisms for reduction in fatigue crack growth rate of RRA treated alloy is attributed to the microstructural modifications. The increased resistance is expected to enhance the damage tolerance capability of the alloy. � 2019 The Authors. Published by Elsevier B.V.