Effect of Gd on microstructure and stress corrosion cracking of the AZ91‐extruded magnesium alloy

Abstract

AZ91 and AZ91-xGd (x = 0.5, 1.0, 1.5 wt%) magnesium alloys are extruded into plates. The addition of Gd promotes the formation of Al 2 Gd, effectively reducing the volume fraction of the β-Mg 17 Al 12 phase and making the banded structures of the extruded magnesium alloys thinner. The corrosion weight loss tests and electrochemistry analyses demonstrate that Gd significantly improves the pitting resistance of the AZ91 in 3.5-wt% NaCl solution saturated with Mg(OH) 2 . Slow strain rate tensile tests show that in a corrosive environment, compared with AZ91, the elongation to failure of the AZ91-1.0Gd alloy is increased by 47%, and the alloy exhibits excellent stress corrosion resistance in this study. The fracture mode of AZ91 is changed from typical intergranular fracture to a mixture of transgranular and intergranular fracture in the corrosion solution by adding Gd. The mechanism of Gd to improve the stress corrosion resistance of the AZ91 magnesium alloy is that Gd increases the corrosion resistance, especially the pitting of AZ91.

Enhanced corrosion resistance of the as-cast AZ91 magnesium alloy by micro-addition of the strontium and rare earth elements

“…However, the cast RE1 alloy (containing 1 wt-% RE) exhibited a remarkably better corrosion resistance than the RE0 alloy (containing 1 wt-% Sr) owing to the better effect of RE elements on the modification of β phase and also lower Volta-potential values of the Al 11 RE 3 particles compared to that of the Al 4 Sr phase. Furthermore, previous studies showed that the RE elements could assist the formation of a more compact RE-containing corrosion layer, resulting in the improvement of the corrosion resistance of AZ91 alloy [20,24,25]. Thus, for another reason, the RE-containing alloys showed better corrosion resistance than the Srcontaining alloys.…”

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

“…Several authors suggested that the partial elimination of PESCC of Mg and its alloys caused by air storage in a desiccator at room temperature or by vacuum annealing at elevated temperatures can be attributed to the removal of diffusible hydrogen, which had been accumulated in the bulk metal during pre-exposure [ 5 , 7 , 10 ]. However, the concentration of diffusible hydrogen in the matrix of the pre-exposed specimens is negligible, as has been shown in the present and previous studies [ 16 , 19 , 20 ].…”

“…Nevertheless, understanding the mechanisms governing PESCC is of great importance because it sheds light on the nature of SCC, which is still under debate. For example, the widespread belief that hydrogen plays a key role in the mechanism of SCC [ 9 , 10 , 11 , 12 ] is primarily based on the observed similarity between the features of PESCC and hydrogen embrittlement (HE) in other metallic materials [ 13 ]. It was established that the degree of PESCC in many Mg alloys increases with decreasing strain rate [ 6 , 14 ] and increasing time of pre-exposure in various corrosion solutions [ 7 , 8 , 15 , 16 , 17 , 18 , 19 , 20 ].…”

Attaining High Functional Performance in Biodegradable Mg-Alloys: An Overview of Challenges and Prospects for the Mg-Zn-Ca System

“…Mg alloys are known to be extremely prone to SCC in various corrosive environments, including distilled water [ 202 , 203 , 204 ], saline solutions [ 205 , 206 ], and all simulated body fluids (SBF) [ 163 , 202 ] commonly used for the examination of the corrosion properties of biomedical Mg alloys. The susceptibility of the alloys to SCC can be characterized by a number of characteristics, including the ultimate tensile stress and elongation to failure in a corrosive medium, the threshold stress (σ SCC ) and threshold stress intensity factor (K 1SCC ), below which SCC does not occur, as well as by a few variations in the SCC susceptibility indexes (I SCC ), which are equal to the loss of the ductility or strength (or both) of an alloy in a corrosive environment with respect to the alloy tested in air.…”