Magnesium and Magnesium Alloys

Ghali, Edward

doi:10.1002/9780470872864.ch58

Cited by 66 publications

(28 citation statements)

References 29 publications

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“…A higher number of grain boundaries leads to more active sites for oxidation and, consequently, more extensive surface film formation. Additionally, the grain refinement increases the overall grain boundary area, thereby optimizing the size of any detrimental cathodic precipitates [61]. Table 4 and Figure 4 show that Al-7 wt.% Co displays the lowest corrosion current density and the lowest passivation current density (i p ), though still of the same order of magnitude.…”

Section: Polarization Behavior Of Cp-almentioning

confidence: 87%

Al-Co Alloys Prepared by Vacuum Arc Melting: Correlating Microstructure Evolution and Aqueous Corrosion Behavior with Co Content

Lekatou

Sfikas

Petsa

et al. 2016

Metals

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Hypereutectic Al-Co alloys of various Co contents (7-20 weight % (wt.%) Co) were prepared by vacuum arc melting, aiming at investigating the influence of the cobalt content on the microstructure and corrosion behavior. Quite uniform and directional microstructures were attained. The obtained microstructures depended on the Co content, ranging from fully eutectic growth (7 wt.% and 10 wt.% Co) to coarse primary Al 9 Co 2 predominance (20 wt.% Co). Co dissolution in Al far exceeded the negligible equilibrium solubility of Co in Al; however, it was hardly uniform. By increasing the cobalt content, the fraction and coarseness of Al 9 Co 2 , the content of Co dissolved in the Al matrix, and the hardness and porosity of the alloy increased. All alloys exhibited similar corrosion behavior in 3.5 wt.% NaCl with high resistance to localized corrosion. Al-7 wt.% Co showed slightly superior corrosion resistance than the other compositions in terms of relatively low corrosion rate, relatively low passivation current density and scarcity of stress corrosion cracking indications. All Al-Co compositions demonstrated substantially higher resistance to localized corrosion than commercially pure Al produced by casting, cold rolling and arc melting. A corrosion mechanism was formulated. Surface films were identified.

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Section: Polarization Behavior Of Cp-almentioning

confidence: 87%

Al-Co Alloys Prepared by Vacuum Arc Melting: Correlating Microstructure Evolution and Aqueous Corrosion Behavior with Co Content

Lekatou

Sfikas

Petsa

et al. 2016

Metals

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“…1,7,17 Similarly, the so called Al-Mn-Fe IMPs, such as Al 8 (Mn,Fe) 5 function as highly potent cathodic sites in Mg, although the Mn has been shown to prevent some of the detrimental galvanic effects of Fe impurities by incorporating the Fe into the Al-Mn IMPs. 1,6,16 Furthermore, Mg-Zn IMPs have approximately the same open circuit potential (OCP) as many Mg alloys. However, the cathodic kinetics of this IMP are more rapid than Mg, 16 attributed to the presence of Zn.…”

mentioning

confidence: 99%

“…For example, in the Mg-Al alloys which contain Mn (such as AZ31, AZ91 and AM50), Al-Mn IMPs that are rich in Al such as Al 4 Mn, Al 6 Mn, display relatively low rates of cathodic kinetics in comparison to other IMPs that are rich in Mn such as Al 8 Mn 5 ; the latter displaying relatively rapid cathodic kinetics. 1,7,17 Similarly, the so called Al-Mn-Fe IMPs, such as Al 8 (Mn,Fe) 5 function as highly potent cathodic sites in Mg, although the Mn has been shown to prevent some of the detrimental galvanic effects of Fe impurities by incorporating the Fe into the Al-Mn IMPs. 1,6,16 Furthermore, Mg-Zn IMPs have approximately the same open circuit potential (OCP) as many Mg alloys.…”

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confidence: 99%

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Exploring the Effects of Intermetallic Particle Size and Spacing on the Corrosion of Mg-Al Alloys Using Model Electrodes

Bland

Birbilis

Scully

2016

J. Electrochem. Soc.

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The effect of the area fraction, size and distribution of model cathodic, intermetallic particles (IMPs) in an anodic Mg matrix on corrosion was investigated. Model Mg-Al electrodes were developed to study IMP effects in isolation from other metallurgical effects, with particles simulated by Al electrodes embedded in a Mg matrix. Arrays of model Mg-Al electrodes were constructed using high purity Al as a surrogate for Al-rich IMPs and flush mounted in commercial purity Mg. The area fraction, size and spacing of these electrodes each altered the corrosion rate and cathodic reaction kinetics assessed after a 24 and 48 hour immersion period at the open circuit potential. Corrosion rate increased with increasing area fraction of Al electrodes but decreased with increasing electrode spacing given a fixed area fraction. The affected zone around electrodes and at the Al/Mg interface was explored to ascertain its impact on the resultant global corrosion rate and kinetics. The effect of local pH at the Al electrode on the prospects for Al corrosion and chemical redeposition were also explored. Magnesium (Mg) alloys continue to be of growing interest due to their good balance of specific properties (i.e. properties relative to weight).1-3 However, due to the inherently negative electrochemical potential of Mg and its alloys, 4,5 Mg-alloys are highly reactive compared to other engineering metals. Mg-alloys are susceptible to several forms of localized corrosion, whilst also highly prone to macro-as well as micro-galvanic corrosion. Due to the low solid solubility of most alloying elements in Mg 6 and particularly low solubility limits for most transition elements; secondary phases readily form during most types of material processing, including casting 7,8 and welding, 9-15 which can adversely alter the corrosion performance.There are many secondary phases, or intermetallic particles (IMPs), which are particularly common in Mg alloys. Each IMP 16 has its own unique dissolution or reduction kinetics, dependent on its composition, size and dispersion within the material. For example, in the Mg-Al alloys which contain Mn (such as AZ31, AZ91 and AM50), Al-Mn IMPs that are rich in Al such as Al 4 Mn, Al 6 Mn, display relatively low rates of cathodic kinetics in comparison to other IMPs that are rich in Mn such as Al 8 Mn 5 ; the latter displaying relatively rapid cathodic kinetics. 1,7,17 Similarly, the so called Al-Mn-Fe IMPs, such as Al 8 (Mn,Fe) 5 function as highly potent cathodic sites in Mg, although the Mn has been shown to prevent some of the detrimental galvanic effects of Fe impurities by incorporating the Fe into the Al-Mn IMPs. 1,6,16 Furthermore, Mg-Zn IMPs have approximately the same open circuit potential (OCP) as many Mg alloys. However, the cathodic kinetics of this IMP are more rapid than Mg, 16 attributed to the presence of Zn. Mg-Zn IMPs are cathodic to the α-Mg and, therefore, tend to cause localized corrosion through micro-galvanic coupling which is often manifest at the Mg matrix/IMP interface. Some ...

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“…At present, light alloys such as aluminum alloys [1] and magnesium alloys [2][3][4] have got more and more extensive attention for the purpose of weight reduction in the automobile industry. It was reported that the tensile strength of the magnesium alloy was sensitively dependent on its microstructure and casting defects [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Study on the effect of corrosion on the tensile behavior of an AZ91 alloy

Wang

Liu

Zhang

et al. 2010

Materials & Corrosion

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The effect of corrosion on the tensile behavior of an as-cast AZ91 alloy was investigated via systematical experiments. The corrosion residual strength of the AZ91 magnesium alloy is approximately negative linear dependent on the extreme depth of corrosion pit, which was quantitatively obtained by the corrosion morphology analysis and the statistic analysis. Experimental results reveal that the corrosion residual strength of the AZ91 magnesium alloy dropped quickly in the first 40 h due to the initiation and development of the corrosion pit and subsequently decreased slowly as a result of the development of the corrosion pit encountered the b phase. The b phase at the grain boundary of the primary a phase acts as an effective barrier to prevent the development of the corrosion pit into the alloy matrix and thus remarkably prevents the drop of the corrosion residual strength. In general, the variation of the corrosion residual strength exhibits an exponential decay regulation within the testing time. Consequently, the empirical prediction of the corrosion residual strength was given with regard to the variation of the corrosion residual strength varied with the immersion time.

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Magnesium and Magnesium Alloys

Cited by 66 publications

References 29 publications

Al-Co Alloys Prepared by Vacuum Arc Melting: Correlating Microstructure Evolution and Aqueous Corrosion Behavior with Co Content

Al-Co Alloys Prepared by Vacuum Arc Melting: Correlating Microstructure Evolution and Aqueous Corrosion Behavior with Co Content

Exploring the Effects of Intermetallic Particle Size and Spacing on the Corrosion of Mg-Al Alloys Using Model Electrodes

Study on the effect of corrosion on the tensile behavior of an AZ91 alloy

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