The article shows that the use of quantitative fracture description may lead to significant progress in research on the phenomenon of stress corrosion cracking of the WE43 magnesium alloy. Tests were carried out on samples in air, and after hydrogenation in 0.1 M Na 2 SO 4 with cathodic polarization. Fracture surfaces were analyzed after different variants of the Slow Strain Rate Test. It was demonstrated that the parameters for quantitative evaluation of fracture surface microcracks can be closely linked with the susceptibility of the WE43 magnesium alloy operating under complex state of the mechanical load in corrosive environments. The final result of the study was the determination of the quantitative relationship between Slow Strain Rate Test parameters, the mechanical properties, and the parameters of the quantitative evaluation of fracture surface (microcracks).
In this work an assessment of the susceptibility of the AE44 magnesium alloy to stress corrosion cracking in a 0.1M Na2SO4 environment is presented. The basic assumed criterion for assessing the alloy behavior under complex mechanical and corrosive loads is deterioration in mechanical properties (elongation, reduction in area, tensile strength and time to failure). The AE44 magnesium alloy was subjected to the slow strain rate test (SSR) in air and in a corrosive environment under open circuit potential (OCP) conditions. In each variant, the content of hydrogen in the alloy was determined. The obtained fractures were subjected to a quantitative evaluation by original fractography methods. It was found that under stress corrosion cracking (SCC) conditions and in the presence of hydrogen the mechanical properties of AE44 deteriorated. The change in the mechanical properties under SCC conditions in a corrosive environment was accompanied by the presence of numerous cracks, both on fracture surfaces and in the alloy microstructure. The developed method for the quantitative evaluation of cracks on the fracture surface turned out to be a more sensitive method, enabling the assessment of the susceptibility of AE44 under complex mechanical and corrosive loads in comparison with deterioration in mechanical properties. Mechanical tests showed a decrease in properties after SSRT tests in corrosive environments (UTS ≈ 153 MPa, ε = 11.2%, Z = 4.0%) compared to the properties after air tests (UTS ≈ 166 MPa, ε = 11.9%, Z = 7.8%) but it was not as visible as the results of quantitative assessment of cracks at fractures (number of cracks, length of cracks): after tests in corrosive environment (900; 21.3 μm), after tests in air (141; 34.5 μm). These results indicate that the proposed new proprietary test methodology can be used to quantify the SSC phenomenon in cases of slight changes in mechanical properties after SSRT tests in a corrosive environment in relation to the test results in air.
This article presents an assessment of the susceptibility of the WE54 magnesium-based alloy to stress corrosion cracking in an 0.1 M Na 2 SO 4 environment. In this work, the basis criterion for assessing the alloyÕs behavior under complex mechanical and corrosive loads is the deterioration in its mechanical properties (elongation-e, %, reduction in area-Z, %, tensile strength-R m, MPa) along with a fractographic analysis of fracture surfaces. The WE54 magnesium-based alloy was subjected to the slow strain rate test (SSRT) under mechanical loads in corrosive environment (0.1 M Na 2 SO 4 solution). The test was carried out in four variants: (a) SSRT in air, (b) cathodic hydrogen charging for 24 h at a current density of 50 mA/cm 2 followed by SSRT in air, (c) SSRT in a corrosive environment under open-circuit potential conditions, and (d) SSRT in a corrosive environment under cathodic polarization at a current density of 50 mA/cm 2. In each variant, the content of hydrogen in the alloy was determined. It was demonstrated that under SCC conditions, in the presence of hydrogen, the plastic properties of WE54 decreased significantly, whereas the alloyÕs strength properties changed to a smaller degree. The change in the mechanical properties under SCC conditions in a corrosive environment was accompanied by a change in the fracture surface morphology and by the presence of numerous cracks, both on fracture surfaces and in the alloyÕs microstructure.
Modern magnesium alloys containing rare earth (RE) elements from the Mg-Y-RE-Zr and Mg-Al-RE systems are characterized by low density and good mechanical properties. Therefore, these alloys are used in the automotive and aerospace industries. However, magnesium alloys offer insufficient corrosion resistance in environments containing electrolyte solutions. Hydrogen is themain corrosive factor appearing during chemical reactions between magnesium and water in anelectrolyte solution. The results showed that when samples were immersed in 0.1M sodium sulfate solution, some cracks were observed inside the Al11RE3 and Al8CeMn4 intermetallic phases. Phase identification was performed by electron backscatter diffraction (EBSD) analysis. The microstructure of the alloys before and after corrosion was observed using a scanning electron microscope (SEM).
The paper organises the current state of knowledge concerning the effect of hydrogen on stress corrosion of magnesium alloys. This review describes phenomena and mechanisms connected with stress-corrosion cracking (SCC) in commonly used magnesium alloys from Mg-Al-Zn system. In addition, some information about SCC in alloys from Mg-Y-RE-Zr and Mg-Al-RE systems is described. It seems that microstructural factors (e.g., matrix α-Mg and intermetallic phases) related to the presence of Y, Zr and rare earth elements (RE) plays an essential role in hydrogen-induced cracking (HIC).
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