Special Issue "Effect of Rare Earth Additions on the Microstructure, Mechanical Properties and Corrosion of Magnesium Alloys"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: 20 July 2020.

Special Issue Editor

Dr. Pablo Pérez Zubiaur
Website
Guest Editor
Centro Nacional de Investigaciones Metalúrgicas (CENIM). Consejo Superior de Investigaciones Científicas (CSIC). Avda. Gregorio del Amo 8, 28040 Madrid, Spain
Interests: magnesium alloys; material processing; microstructure; powdermetallurgy; high temperature oxidation

Special Issue Information

Dear Colleagues,

The low density of magnesium makes alloys based on this element potential candidates for many components in which “weight saving” constitutes a significant part of design. Nevertheless, the extended use of magnesium alloys has been limited by their low strength and poor corrosion resistance. Considerable attempts have been devoted to improving mechanical and corrosion properties of magnesium alloys through the proper choice of the alloying additions and/or thermomechanical processing. Numerous benefits have been reported from the use of rare earth additions (yttrium included); strengthening induced by the formation of hard second phases, lessening the inherent basal texture of wrought magnesium alloys, refining grain size because they assist recrystallization of the magnesium matrix or lowering less noble the corrosion potential of many second phases. In spite of these advantages, some issues need to be considered in future development of magnesium alloys containing rare earth elements. Firstly, there is a gradual trend in increasing the price of rare earth elements because of their higher consumption that cannot be totally sustained by exploited natural resources. Because of the low solubility of most of rare earth elements, small additions of these elements result in higher volume fractions of Mg-RE compounds which accelerating corrosion phenomena in magnesium alloys through the establishment of intense galvanic cells. Taken into account the preceding points, this Special Issue is dedicated to the effect of rare earth elements on the microstructure of magnesium alloys containing rare earth elements (commercial or new alloys) as a way for maximizing mechanical properties/corrosion resistance, attempting to reduce the total content of rare earth additions.

Dr. Pablo Pérez Zubiaur
Guest Editor

Manuscript Submission Information

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Keywords

  • Magnesium alloys
  • Rare earth additions
  • Microstructure
  • Mechanical properties
  • Corrosion resistance
  • Processing route

Published Papers (5 papers)

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Research

Open AccessFeature PaperArticle
Corrosion Behaviour of Mg98.5Nd1Zn0.5 (at. %) Alloy in Phosphate Buffered Saline Solution
Metals 2020, 10(1), 148; https://doi.org/10.3390/met10010148 - 19 Jan 2020
Abstract
The corrosion behaviour of Mg98.5-Nd1-Zn0.5 (at. %) alloy was studied in phosphate buffered saline (PBS) solution to evaluate its degradation performance as a potential candidate for biomedical applications. The alloy, produced by casting and hot extrusion, consists of a fine-grained magnesium matrix with [...] Read more.
The corrosion behaviour of Mg98.5-Nd1-Zn0.5 (at. %) alloy was studied in phosphate buffered saline (PBS) solution to evaluate its degradation performance as a potential candidate for biomedical applications. The alloy, produced by casting and hot extrusion, consists of a fine-grained magnesium matrix with an average grain size of 3.8 μm embedding a high volume fraction of (Mg, Zn)12Nd precipitates. Hydrogen release tests revealed a stable low corrosion rate of 0.6 mm/year after 24 h of immersion. Electrochemical testing data proved good correlation with the data from hydrogen evolution, with the corrosion rate stabilizing below 1 mm/year. Full article
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Open AccessArticle
The Influence of Holding Time on the Microstructure Evolution of Mg–10Zn–6.8Gd–4Y Alloy during Semi-Solid Isothermal Heat Treatment
Metals 2019, 9(4), 420; https://doi.org/10.3390/met9040420 - 08 Apr 2019
Cited by 1
Abstract
A semi-solid microstructure of Mg–10Zn–6.8Gd–4Y alloys is acquired via an isothermal heat treatment process, and the effects of the holding time on the microstructure evolution of Mg–10Zn–6.8Gd–4Y alloys are investigated. The results show that the microstructure of the cast alloy is composed of [...] Read more.
A semi-solid microstructure of Mg–10Zn–6.8Gd–4Y alloys is acquired via an isothermal heat treatment process, and the effects of the holding time on the microstructure evolution of Mg–10Zn–6.8Gd–4Y alloys are investigated. The results show that the microstructure of the cast alloy is composed of primary α-Mg dendritic grains with a eutectic structure (W-phase and eutectic Mg) distributed at the grain boundaries. The primary α-Mg dendritic grains grow in size with increasing holding time, and they tend to grow into more globular structures in the initial stage; they then become a bit more dendritic, as small branches grow from the grain boundaries after holding the sample at 580 °C for 10 min. Meanwhile, the interdiffusion of magnesium atoms within the eutectic region, and between the primary α-Mg and eutectic structure, leads to the formation of fine and relatively globular eutectic Mg grains in the eutectic structure after holding for 10 min. The eutectic Mg grains begin to grow, coarsen, coalesce, or be swallowed by the surrounding primary grains, causing fluctuations of the general grain size. Over the whole isothermal heat treatment process, two mechanisms—coalescence and Ostwald ripening—dominate the grain coarsening. Full article
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Open AccessArticle
Application of an Evolving Non-Associative Anisotropic-Asymmetric Plasticity Model for a Rare-Earth Magnesium Alloy
Metals 2018, 8(12), 1013; https://doi.org/10.3390/met8121013 - 02 Dec 2018
Cited by 7
Abstract
Magnesium sheet metal alloys have a hexagonal close packed (hcp) crystal structure that leads to severe evolving anisotropy and tension-compression asymmetry as a result of the activation of different deformation mechanisms (slip and twinning) that are extremely challenging to model numerically. The low [...] Read more.
Magnesium sheet metal alloys have a hexagonal close packed (hcp) crystal structure that leads to severe evolving anisotropy and tension-compression asymmetry as a result of the activation of different deformation mechanisms (slip and twinning) that are extremely challenging to model numerically. The low density of magnesium alloys and their high specific strength relative to steel and aluminum alloys make them promising candidates for automotive light-weighting but standard phenomenological plasticity models cannot adequately capture the complex plastic response of these materials. In this study, the constitutive plastic behavior of a rare-earth magnesium alloy sheet, ZEK100 (O-temper), was considered at room temperature, under quasi-static conditions. The CPB06 yield criterion for hcp materials was employed along with a non-associative flow rule in which the yield function and plastic potential were calibrated for a range of plastic deformation levels to account for evolving anisotropy under proportional loading. The non-associative flow rule has not previously been applied to magnesium alloys which require the use of flexible constitutive models to capture the severe anisotropy and its evolution with plastic deformation. The non-associative flow rule can provide the required flexibility by decoupling the yield function and plastic potential. For the associative flow rule, such flexibility can only be achieved by multiple linear transformations of the stress tensor resulting in expensive models for calibration and simulations. The constitutive model was implemented as a user material subroutine (UMAT) within the commercial finite element software, LS-DYNA, for general 3-D stress states along with an interpolation technique to consider the evolution of anisotropy based upon the plastic work. To evaluate the accuracy of the implemented model, predictions of a single-element model were compared with the experimental results in terms of flow stresses and plastic flow directions under various proportional loading conditions and along different test directions. Finally, to assess the predictive capabilities of the model, full-scale simulations of coupon-level formability experiments were performed and compared with experimental results in terms of far-field load-displacement and local strain paths. Using these experiments, the constitutive model was evaluated across the full range of representative stress states for sheet metal forming operations. It was shown that the predictions of the model were in very good agreement with experimental data. Full article
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Open AccessArticle
Effects of Ag, Nd, and Yb on the Microstructures and Mechanical Properties of Mg‒Zn‒Ca Metallic Glasses
Metals 2018, 8(10), 856; https://doi.org/10.3390/met8100856 - 20 Oct 2018
Cited by 1
Abstract
Mg‒Zn‒Ca metallic glasses are regarded as promising biodegradable materials. Previous studies on this alloy system have mostly focused on the composition regions with a large critical size (Dc) for the formation of metallic glasses, while this paper investigates the composition regions [...] Read more.
Mg‒Zn‒Ca metallic glasses are regarded as promising biodegradable materials. Previous studies on this alloy system have mostly focused on the composition regions with a large critical size (Dc) for the formation of metallic glasses, while this paper investigates the composition regions with a small Dc, which has been overlooked by researchers for a long time. The effects of the addition of Ag, Nd, and Yb elements on the microstructure and mechanical properties of Mg‒Zn‒Ca metallic glasses were studied. It was found that the Mg‒Zn‒Ca metallic glass exhibits a single and uniform amorphous structure with a compressive strength of 590 MPa. After the addition of a small amount of Ag into the alloy, the amorphous matrix is retained and new precipitate phases that lead to the decrease of the compressive strength are formed. The addition of the rare earth elements Nd and Yb changes the microstructure from a single amorphous matrix to a large number of quasicrystal phases, which results in an increase in compressive strength. The compressive strength of the Mg‒Zn‒Ca‒Yb alloy increases to 606.2 MPa due to the formation of multi-layered swirling solidified structure and a large number of small quasicrystals with high microhardness. Moreover, this study can be considered as a useful supplement to the existing studies on the Mg‒Zn‒Ca alloy system; it also provides new ideas for designing the microstructure and spatial structure of quasicrystal containing alloys with high performances. Full article
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Open AccessArticle
Effects of Gd, Y Content on the Microstructure and Mechanical Properties of Mg-Gd-Y-Nd-Zr Alloy
Metals 2018, 8(10), 790; https://doi.org/10.3390/met8100790 - 03 Oct 2018
Cited by 4
Abstract
The effects of Gd, Y content on the microstructure and mechanical properties of Mg-Gd-Y-Nd-Zr alloy were investigated using hardness measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and uniaxial tensile testing. The results indicate that the alloys in as-cast [...] Read more.
The effects of Gd, Y content on the microstructure and mechanical properties of Mg-Gd-Y-Nd-Zr alloy were investigated using hardness measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and uniaxial tensile testing. The results indicate that the alloys in as-cast condition mainly consist of α-Mg matrix and non-equilibrium eutectic Mg5.05RE (RE = Gd, Y, Nd). After solution treatment, the non-equilibrium eutectics dissolved into the matrix but some block shaped RE-rich particles were left at the grain boundaries and within grains. These particles are especially Y-rich and deteriorate the mechanical properties of the alloys. Both the compositions of the eutectic and the block shaped particle were independent of the total Gd, Y content of the alloys, but the number of the particles increases as the total Gd, Y content increases. The ultimate tensile strength increases as the total Gd, Y content decreases. A Mg-5.56Gd-3.38Y-1.11Nd-0.48Zr alloy with the highest ultimate tensile strength of 280 MPa and an elongation of 1.3% was fabricated. The high strength is attributed to the age hardening behavior and the decrease in block shaped particles. Full article
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