Abstract
The influence of loading rate on the environment-assisted cracking (EAC) behavior of AA7075-T651 immersed in 0.6 and 1.0 M NaCl solution was assessed at applied potentials ranging from −800 to −1200 mVSCE via a slow-rising stress intensity (K) testing methodology. Measured crack growth rates under rising K loading are compared to those obtained using a fixed K protocol, which revealed that rising K-based testing consistently yields increased crack growth rates relative to static K approaches across all tested conditions. However, relative to other alloy systems, EAC in AA7075-T651 is only modestly loading rate-dependent, as demonstrated by testing conducted at fixed dK/dt ranging from 0.25 to 2.0 MPa√m/h. The implications of the observed results are considered in the context of current EAC testing specifications, with specific focus on the conservatism and efficiency of rising K-based approaches.
Highlights
It is well-established that 7xxx-series Al alloys are susceptible to environment-assisted cracking (EAC) when immersed in halide-containing solutions [1,2,3,4,5,6,7], with the degree of susceptibility strongly depending on alloy composition and heat treatment [8,9,10,11]
The objective of this study is to assess the influence of the applied loading rate on the EAC susceptibility of AA7075-T651 immersed in aqueous NaCl solution at applied potentials ranging from −800 to −1200 mVSCE
Comparison of Rising vs. Static K Testing for AA7075-T651 Immersed in 0.6 M NaCl as a Function of Applied Potential
Summary
It is well-established that 7xxx-series Al alloys are susceptible to environment-assisted cracking (EAC) when immersed in halide-containing solutions [1,2,3,4,5,6,7], with the degree of susceptibility strongly depending on alloy composition and heat treatment [8,9,10,11]. Fracture mechanics-based methods for evaluating EAC, such as those codified in ASTM G168 [38], ASTM E1681 [39], ASTM F1624 [40], and ISO 7539-9 [41], enable the direct extension of laboratory-generated data to the design and lifting of inservice components [42,43,44] via the similitude principle [44,45,46] This distinct advantage has led to the use of such methods to quantify EAC susceptibility in 7xxx-series Al alloys in a wide range of environments and heat treatment conditions [7,8,9,47,48,49,50,51,52,53,54], with the primary goal being the quantification of the threshold stress intensity (KTH ) and the relationship between the applied stress intensity (K) and crack growth rate.
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