Effect of Air Storage on Stress Corrosion Cracking of ZK60 Alloy Induced by Preliminary Immersion in NaCl-Based Corrosion Solution

Abstract

The preliminary exposure of Mg alloys to corrosion solutions can cause their embrittlement. The phenomenon is referred to as pre-exposure stress corrosion cracking (PESCC). It has been reported that relatively long storage in air after pre-exposure to the corrosion solution is capable of eliminating PESCC. This effect was attributed to the egress of diffusible hydrogen that accumulated in the metal during pre-exposure. However, recent findings challenged this viewpoint and suggested that the corrosion solution retained within the side surface layer of corrosion products could be responsible for PESCC. The present study is aimed at the clarification of the role of hydrogen and the corrosion solution sealed within the corrosion products in the “healing” effect caused by post-exposure storage in air. Using the slow strain rate tensile (SSRT) testing in air and detailed fractographic analysis of the ZK60 specimens subjected to the liquid corrosion followed by storage in air, we found that PESCC was gradually reduced and finally suppressed with the increasing time and temperature of air storage. The complete elimination of PESCC accompanied by recovery of elongation to failure from 20% to 38% was achieved after 24 h of air storage at 150–200 °C. It is established that the characteristic PESCC zone on the fracture surface is composed of two regions, of which the first is always covered by the crust of corrosion products, whereas the second one is free of corrosion products and is characterised by quasi-brittle morphology. It is argued that the corrosion solution and hydrogen stored within the corrosion product layer are responsible for the formation of these two zones, respectively.

Corrosion and Mechanical Behavior of the As-Cast and Solid-Solution-Treated AM50 Magnesium Alloy in Different Media

“…H separated by the corrosion process is also affected by Al. Existence of the β-Mg 17 Al 12 phase aids in the storage of hydrogen in Mg alloys [ 12 , 24 , 25 ]. Thus, after solution treatment, as the content of the β-Mg 17 Al 12 phase decreases, the hydrogen-storage ability decreases and the effect of hydrogen embrittlement decreases.…”

Improving Corrosion and Stress Corrosion Cracking Performance of Machined Biodegradable Alloy ZX20 by HF-Treatment

“…However, controversial observations have been reported on this issue so far, challenging the importance and exact role of hydrogen in the SCC mechanism in Mg. The details of this aspect can be found elsewhere [49,53,[65][66][67].…”

“…However, this reduction was notably lower for the HF-treated specimens. Notice that tensile testing was conducted in air after preliminary immersion in SBF; thus, the phenomenon referred to as pre-exposure SCC (PESCC) [49][50][51][52][53] was investigated. However, to the best of our knowledge, no papers exist reporting the effect of HF-treatment on true SCC, which is commonly assessed through the mechanical properties of biodegradable Mg alloys upon slow-strain rate tensile (SSRT) testing directly in SBF.…”

Corrosion and Mechanical Behavior of Metal Materials

“…Crucial attention was paid to the effect of severe plastic deformation on the corrosion behavior of a tantalum-tungsten alloy [24]; the severely deformed crystallographic orientations in the tantalum-tungsten alloy could be greatly weakened by an electrochemical process and could reduce the corrosion rate. The pre-exposure SCC (PESCC) of a ZK60 alloy induced by preliminary immersion in a NaCl-containing solution was systematically studied in one paper [25], and it was argued that the hydrogen stored within the corrosion product layer and the corrosion solution was responsible for the formation of these two zones. Meanwhile, the corrosion resistance of dilute Fe-Al alloys could be improved by preheating a nanoscale Al 2 O 3 protective layer in a H 2 atmosphere [26].…”