Pre-exposure embrittlement of an Al-Cu-Mg alloy, AA2024-T351

Abstract

When Al-Cu-Mg (AA2024-T351) alloy plate is immersed in 0.53 m NaCl solution, intergranular corrosion occurs, which initially takes the form of narrow fissures at the surface. Although growth of these fissures is initially rapid, it soon slows and the penetration depth is limited. However, these intergranular fissures can give rise to intergranular subcritical crack growth and eventual catastrophic fracture if specimens are strained slowly in laboratory air after pre-exposure to the NaCl solution. In our experiments, tensile specimens of the alloy were strained at strain rates in the range 10-7–10-4/s, and the cracking propensity was found to increase with pre-exposure times up to around 300 h. However, cracking was much reduced with longer pre-exposure times and became negligible after 500 h. This rather unexpected result can be explained by the observation that the intergranular corrosion fissure becomes increasingly broad and un-crack-like with extended pre-exposure times, failing to meet the prerequisite initiation conditions required for intergranular stress corrosion cracking. A further unexpected result was that straining specimens in the same 0.53 m NaCl solution after pre-exposure produced no intergranular crack growth. To investigate this further, tensile tests were conducted under electrochemical control, and this showed that the free corrosion potential in the test solution was too low in 0.53 m NaCl to allow cracking to proceed.

Stress Corrosion Cracking of Friction Stir-Welded AA-2024 T3 Alloy

“…The combined action of applied stress and corrosive environment can also promote stress corrosion cracking (SCC) in susceptible alloys [19][20][21][22] and the effect of the microstructural modification induced by FSW on the intrinsic susceptibility of such alloys is yet far to be completely understood. The higher number of works are on the SCC of alloy 7XXX but, in the knowledge of the authors, only few papers reported the SCC behavior of FSW joints in AA-2024.…”

Initiation and short crack growth behaviour of environmentally induced cracks in AA5083 H131 investigated across time and length scales

“…of the material with respect to their IGC and IGSCC behaviour. Nevertheless a mechanistic understanding of crack initiation, propagation, and final failure is still incomplete (Holroyd and Scamans, 2016) (WEARMOUTH et al, 1973) (Holroyd et al, 2015) (Jones and Danielson, 2003) (Jones, 2003). One reason for this is that only recently have the tools become available to observe these phenomenon at relevant time and length scales.…”