Special Issue "Microstructure and Mechanical Properties of Magnesium Alloys and Composites"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (30 April 2020).

Special Issue Editors

Prof. Andrzej Kiełbus
Website
Guest Editor
Institute of Materials Engineering, Silesian University of Technology, Gliwice, Poland
Interests: magnesium alloys, casting, structure, heat treatment, casting aluminium alloys, mechanical properties
Prof. Tomasz Rzychoń
Website
Guest Editor
Institute of Materials Engineering, Silesian University of Technology, Gliwice, Poland
Interests: magnesium alloys, die casting, creep resistance, X-ray diffraction analysis, microstructure, mechanical properties, magnesium composite

Special Issue Information

Dear Colleagues,

The progress that is being made in the aerospace and automotive industry is closely related to the development of construction materials characterized by higher strength, lower density, and better creep resistance and corrosion resistance compared to the materials used so far. Attractive materials for the transportation industry are undoubtedly magnesium alloys and composites based on magnesium alloys, which are characterized by promising mechanical properties (specific strength, specific stiffness), high recyclability, and low primary material cost. In the past three decades, such properties of magnesium alloys as creep resistance, ductility, strength, and corrosion resistance have significantly improved. The improvement of properties of magnesium alloys results from the implementation of various alloying elements, in particular, rare-earth metals, the optimization of chemical composition, the improvement of existing and the use of new manufacturing technologies, and the use of advanced research to determine the relationship between the microstructure and the properties of magnesium alloys. Magnesium alloys, as well as composites based on magnesium alloys, still have great potential for improving mechanical and physical properties. An example is age-hardened magnesium alloys, in which the strength level is still lower that that obtained in aluminum alloys. Further improvement of strength properties is possible through a better understanding of the effect of structural factors (shape, orientation, and size and growth of precipitates) on the strengthening. The creep resistance is also a wide field for improvement. Better mechanical properties at elevated temperatures can be achieved by formation of thermally stable phases or a continuous intermetallic phases skeleton. Especially, the development of the technology for the production of magnesium composites offers great opportunities to improve creep resistance, and it should be noted that literature data is still insufficient in this field. In magnesium alloys, the production of parts by high pressure die casting technology is still the predominant technology. The mechanical properties of magnesium castings are lower compared to alloys produced by plastic forming techniques. New processing techniques allow one to obtain fine grain size and a combination of excellent strength and ductility. An important issue is also the reduction of production costs of magnesium alloys. Thus, in recent years, studies of magnesium alloys that do not contain expensive rare earth metals have been of great importance, despite the excellent strength properties of alloys with rare earth metals.

This Special Issue is dedicated to presenting the current status of knowledge on the mechanical properties of magnesium alloys and their composites, and the relationship between the microstructure and mechanical properties of alloys and composites produced in different technologies.

Prof. Andrzej Kiełbus
Prof. Tomasz Rzychoń
Guest Editors

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Keywords

  • Magnesium alloys
  • Structure
  • Mechanical properties
  • Magnesium composites
  • Creep resistance
  • Heat treatment
  • Casting
  • Forming

Published Papers (7 papers)

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Research

Open AccessArticle
Effect of Modification on Microstructure and Properties of AZ91 Magnesium Alloy
Crystals 2020, 10(6), 536; https://doi.org/10.3390/cryst10060536 - 24 Jun 2020
Abstract
Refinement of α-Mg solid solution grains has a significant influence on the improvement of mechanical properties of cast magnesium alloys. In the article, the effects of three modifiers on microstructure and properties of AZ91 magnesium alloy casted to a sand mould were described. [...] Read more.
Refinement of α-Mg solid solution grains has a significant influence on the improvement of mechanical properties of cast magnesium alloys. In the article, the effects of three modifiers on microstructure and properties of AZ91 magnesium alloy casted to a sand mould were described. Overheating, hexachloroethane and wax-CaF2-carbon powder were applied. The research procedure comprised microstructure analysis by means of light microscopy, scanning electron microscopy and quantitative analysis with AnalySIS Pro® software and mechanical properties’ investigation. The microstructure of AZ91 alloy in the as-cast condition consists of α-Mg solid solution with precipitates of Mg17Al12, Mg2Si and Al8Mn5 phases. It was reported that all applied modifiers cause refinement of α-Mg solid solution grains and a decrease of the volume fraction of α-Mg+Mg17Al12 compound discontinuous precipitates. The best results were obtained in the case of wax-CaF2-carbon powder. Full article
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Open AccessArticle
Microstructure and Texture Evolution during Twin-Roll Casting and Annealing of a Mg–6.8Y2.5Zn–0.4Zr Alloy (WZ73)
Crystals 2020, 10(6), 513; https://doi.org/10.3390/cryst10060513 - 16 Jun 2020
Abstract
In the present work, the microstructure and texture of a Mg–6.8Y–2.5Zn–0.4Zr sheet manufactured by twin-roll casting were investigated. The twin-roll cast state consisted of two apparent phases: the α-Mg matrix, which was made up of dobulites with an average grain size of approximately [...] Read more.
In the present work, the microstructure and texture of a Mg–6.8Y–2.5Zn–0.4Zr sheet manufactured by twin-roll casting were investigated. The twin-roll cast state consisted of two apparent phases: the α-Mg matrix, which was made up of dobulites with an average grain size of approximately 50 µm and the LPSO (long-period stacking ordered) phase, which formed network-like precipitates along the grain boundaries. After twin-roll casting, annealing was carried out under conditions of different temperatures ranging from 450 °C to 525 °C and holding times between 2 h and 24 h. It was found that heat treatment led to the formation of a microstructure in which grains were apparent. Furthermore, it could be observed that high temperatures > 500 °C led to changes in the morphology of the LPSO structures. On one hand, the network-like structure dissolved while, on the other hand, both rodlike and blocky LPSO phases precipitated predominantly at the grain boundaries of the α-Mg matrix. This process was fostered by high temperatures and long holding times. Full article
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Open AccessArticle
Stabilisation of a Segment of Autologous Vascularised Stomach as a Patch for Myocardial Reconstruction with Degradable Magnesium Alloy Scaffolds in a Swine Model
Crystals 2020, 10(6), 438; https://doi.org/10.3390/cryst10060438 - 29 May 2020
Abstract
In patients with severe heart failure, the surgical reconstruction of the damaged myocardium with regenerative biological grafts is an innovative therapeutic option. However, natural patch materials are often too delicate for a full wall repair of the left ventricle. A degradable magnesium scaffold [...] Read more.
In patients with severe heart failure, the surgical reconstruction of the damaged myocardium with regenerative biological grafts is an innovative therapeutic option. However, natural patch materials are often too delicate for a full wall repair of the left ventricle. A degradable magnesium scaffold could provide temporary mechanical stability until the sufficient physiological remodeling of such grafts. An autologous vascularised gastric patch was employed for the reconstruction of the left ventricular myocardium in a porcine model. Magnesium alloy (LA63) scaffolds were fixed over the biological patch. The function of the implant was assessed via magnetic resonance imaging. Angiography was carried out to detect a connection between the gastric and coronary vasculature. The explants were examined via µ-computer tomography and light microscopy. All the test animals survived. The prostheses integrated biologically and functionally into the myocardium. No rupture of the prostheses occurred. An anastomosis of the gastric and coronary vasculature had developed. The magnesium scaffolds degraded, on average, to 30.9% of their original volume. This novel technique responds to the increasing demand for regenerative myocardial grafts. The magnesium scaffolds’ biocompatibility and degradation kinetics, as well as their stabilizing effects, indicate their applicability in the surgical treatment of terminal heart failure. Full article
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Open AccessArticle
Enhanced Mechanical Properties of Surface Treated AZ31 Reinforced Polymer Composites
Crystals 2020, 10(5), 381; https://doi.org/10.3390/cryst10050381 - 08 May 2020
Abstract
To enhance the potential application of naturally biodegradable polylactic acid (PLA)-based composites reinforced with magnesium alloy, anodized coatings between Mg and PLA were fabricated on AZ31 magnesium alloy rods. After anodizing (AO) at four different treatment times, the surface demonstrated a typical porous [...] Read more.
To enhance the potential application of naturally biodegradable polylactic acid (PLA)-based composites reinforced with magnesium alloy, anodized coatings between Mg and PLA were fabricated on AZ31 magnesium alloy rods. After anodizing (AO) at four different treatment times, the surface demonstrated a typical porous MgO ceramics morphology, which greatly improved the mechanical properties of composite rods compared to untreated pure Mg. This was attributed to the micro-anchoring effect, which increases interfacial binding forces significantly between the Mg rod and PLA. Additionally, the AO layer can also substantially improve the degradability of composite rods in Hank’s solution, due to good corrosion resistance and stronger bonding between PLA and Mg. With a prolonged immersion time of up to 30 days, the porous MgO coating was eventually found to be degraded, evolving to a comparatively smooth surface resulting in a decline in mechanical properties due to a decrease in interfacial bonding strength. According to the current findings, the PLA-clad surface treated Mg composite rod may hold promise for use as a bioresorbable implant material for orthopedic inner fixation. Full article
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Open AccessArticle
Effect of Necklace-Type Distribution of SiC Particles on Dry Sliding Wear Behavior of As-Cast AZ91D/SiCp Composites
Crystals 2020, 10(4), 296; https://doi.org/10.3390/cryst10040296 - 13 Apr 2020
Abstract
In this study, the dry sliding wear behaviors of SiC particle reinforced AZ91D matrix composites fabricated by stirring casting method were systematically investigated. The SiC particles in as-cast composites exhibited typical necklace-type distribution, which caused the weak interface bonding between SiC particles and [...] Read more.
In this study, the dry sliding wear behaviors of SiC particle reinforced AZ91D matrix composites fabricated by stirring casting method were systematically investigated. The SiC particles in as-cast composites exhibited typical necklace-type distribution, which caused the weak interface bonding between SiC particles and matrix in particle-segregated zones. During dry sliding at higher applied loads, SiC particles were easy to debond from the matrix, which accelerated the wear rates of the composites. While at the lower load of 10 N, the presence of SiC particles improved the wear resistance. Moreover, the necklace-type distribution became more evident with the decrease of particle sizes and the increase of SiC volume fractions. Larger particles had better interface bonding with the matrix, which could delay the transition of wear mechanism from oxidation to delamination. Therefore, composites reinforced by larger SiC particles exhibited higher wear resistance. Similarly, owing to more weak interfaces in the composites with high content of SiC particles, more severe delamination occurred and the wear resistance of the composites was impaired. Full article
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Open AccessArticle
First Principles Study on the Thermodynamic and Elastic Mechanical Stability of Mg2X (X = Si,Ge) Intermetallics with (anti) Vacancy Point Defects
Crystals 2020, 10(3), 234; https://doi.org/10.3390/cryst10030234 - 23 Mar 2020
Abstract
In this paper, based on the density functional theory, through thermodynamic and mechanical stability criteria, the crystal cell model of intermetallic compounds with vacancy and anti-site point defects is constructed and the lattice constant, formation heat, binding energy, elastic constant, and elastic modulus [...] Read more.
In this paper, based on the density functional theory, through thermodynamic and mechanical stability criteria, the crystal cell model of intermetallic compounds with vacancy and anti-site point defects is constructed and the lattice constant, formation heat, binding energy, elastic constant, and elastic modulus of Mg2X (X = Si, Ge) intermetallics with or without point defects are calculated. The results show that the difference in the atomic radius leads to the instability and distortion of crystal cells with point defects; Mg2X are easier to form vacancy defects than anti-site defects on the X (X = Si, Ge) lattice site, and form anti-site defects on the Mg lattice site. Generally, the point defect is more likely to appear at the Mg position than at the Si or Ge position. Among the four kinds of point defects, the anti-site defect x M g is the easiest to form. The structure of intermetallics without defects is more stable than that with defects, and the structure of the intermetallics with point defects at the Mg position is more stable than that at the Si/Ge position. The anti-site and vacancy defects will reduce the material’s resistance to volume deformation shear strain, and positive elastic deformation, and increase the mechanical instability of the elastic deformation of the material. Compared with the anti-site point defect, the void point defect can lead to the mechanical instability of the transverse deformation of the material and improve the plasticity of the material. The research in this paper is helpful for the analysis of the mechanical stability of the elastic deformation of Mg2X (X = Si, Ge) intermetallics under the service condition that it is easy to produce vacancy and anti-site defects. Full article
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Open AccessArticle
Rheological Solidification Behavior and Mechanical Properties of AZ91-Sn Alloys
Crystals 2019, 9(12), 641; https://doi.org/10.3390/cryst9120641 - 03 Dec 2019
Cited by 1
Abstract
The solidification and tensile deformation behaviors of rheo-cast AZ91-Sn alloys were revealed to study the effects of Sn alloying on improvement of AZ91 alloy’s mechanical properties. Two kinds of Mg17Al12 phases precipitated from the supersaturated magnesium matrix during rheo-solidification were [...] Read more.
The solidification and tensile deformation behaviors of rheo-cast AZ91-Sn alloys were revealed to study the effects of Sn alloying on improvement of AZ91 alloy’s mechanical properties. Two kinds of Mg17Al12 phases precipitated from the supersaturated magnesium matrix during rheo-solidification were observed: coarse discontinuous precipitates (DP) at grain boundaries and small-sized continuous precipitates (CP) inside grains. With increasing Sn content, the amount of Mg17Al12 phases was increased whilst the amount of Al atoms in the matrix was decreased. Due to the higher melting point of Mg2Sn than Mg17Al12, Mg2Sn precipitated earlier from the melt, and therefore provided heterogeneous nuclei for Mg17Al12 during the eutectic reaction. Due to grain refinement and solid solution strengthening, AZ91-2.4Sn (mass%) gained 52% increase in tensile strength and 93% increase in elongation compared with pure AZ91 alloy. The higher-density twins and microcracks induced by Sn alloying relaxed stress concentration during plastic deformation, so the fracture mode was transformed from cleavage fracture of pure AZ91 alloy to ductile fracture of AZ91-Sn alloys. Full article
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