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As one of the lightest metallic materials, magnesium is considered as a promising replacement for aluminum, titanium, and steel. However, lightweight energy-saving magnesium and magnesium alloys suffer from poor ductility (5%–8%) due to their hexagonal closed packed crystalline structure and a limited number of easily activated independent slip systems at room temperature. This creates some challenges for magnesium and its alloys for various industrial applications. One technique to improve both strength and ductility, without any tangible weight penalty, of magnesium and its alloys is to add nanosize (less than 100 nm) reinforcements (e.g. nanoparticles) to the matrix as creat so-called magnesium nanocomposites. Various nano-reinforcing materials including oxides (Al2O3, TiO2, Y2O3, ZnO, ZrO2), carbides (SiC, B4C, TiC), nitrides (BN, AlN, TiN), borides (TiB2, SiB6, ZrB2), and carbonaceous materials (carbon nanotube and carbon nanoplatelets). The volume fraction of these nano-size reinforcing structures are normally less than 3 vol% to avoid the clustering (agglomeration) of the nano-reinforcements which can adversely affect strength and ductility. That is, depending on the matrix (magnesium and magnesium alloys) and the nanosize reinforcement, there is an optimum volume fraction beyond which the properties (strength and ductility) would decrease. Though various aspects of the microstructure/mechanical property/manufacturing process of the magnesium nanocomposites have been studied so far, the failure and, in particular, fracture of these materials have not been yet classified properly. Investigating the fracture of magnesium nanocomposites, including the type of fracture, fracture mechanism, the effect of the nano-reinforcements on the fracture of Mg nanocomposites, enables the researchers to assess the role of nanosized reinforcement on the modes of failure and mechanical properties. This paper aims at providing a review of the fractography of compressive and tensile tests of nanocomposites Mg, classifying fractography by all kinds of reinforcement and working conditions of the Mg nanocomposite. Also, the effect of test temperature, cyclic loading, and heat treatment on the fracture of magnesium -matrix nanocomposite is discussed thoroughly. Among various nanoparticles and according to the review of the available literature, Al, Y2O3, and NiTi can significantly improve the tensile strength of the Mg matrix while ZnO and Sm2O3 reinforced nanocomposites show higher compressive yield stress.

Lightweight energy-saving magnesium (Mg) nanocomposites could be titled materials of future. Remarkable specific strength along with acceptable ductility is two key features of these materials which have made them a unique class of emerging materials. However, magnesium nanocomposites are at the initial stages of development and therefore systematic research is required to establish microstructure/property relationships at different potential conditions (i.e. temperatures and strain rates). In this paper, a recently introduced magnesium-samarium oxide (Mg–Sm2O3) nanocomposite, with different volume fractions of nanosize Sm2O3 particles as reinforcement, is employed to study ambient temperature rate-dependent plastic response of the material. To study the rate-dependent response of the materials, a depth-sensing nanoindentation measurement technique was used which is considered a non-destructive, robust, and convenient method to assess the controlling mechanisms of creep phenomenon in small scales. Tests were performed on both nanocomposites and pure Mg for the purpose of comparison. Microstructural observations and nanoindentation data indicate that the creep resistance of the materials is directly associated with the volume fraction of the nanoparticles. The results of this study would provide the required reference lines for the forthcoming elevated temperature creep assessment of the materials.

Magnesium (Mg), as the lightest metallic material, is 33% lighter than aluminum which makes it, potentially, a great replacement for aluminum and its alloys. However, Mg in pure and alloyed conditions is brittle at ambient temperature which largely limits their applications. One key solution to enhance the strength and ductility of Mg and its alloys is to embed thermally-stable nano-size reinforcements within the Mg matrix to produce so-called “Mg nanocomposites”. The Mg nanocomposites are considering revolutionizing energy-saving lightweight materials of the future with enhanced strength and ductility properties. Mg nanocomposites are, however, at the initial degrees of improvement and consequently, systematic research is required to set up microstructure/property relationships at distinct potential conditions (i.e. temperatures and strain rates). In the present study, a nanoindentation testing approach is adopted to assess ambient-temperature small scale mechanical properties of a group of Mg nanocomposites reinforced with rare-earth element nanoparticles (NPs), i.e. Sm2O3. This paper tried to assess various nanoindentation-driven properties of the Mg-Sm2O3 nanocomposites and compare them with the pure Mg as the baseline.

Effects of nanofiber SiC (0.5 and 1 vol%) addition on microstructure, mechanical properties and creep behaviour of cold chamber high pressure die casting AZ91-1Sr alloy have been investigated. Experimental results indicate that the AZ91-1Sr alloy contains of α-Mg, β-Mg17Al12 and Al4Sr intermetallic phases. With addition of nanofiber SiC, the Al4C3 and SiC peaks were detected. Also, the mechanical properties of the matrix alloy were improved. The AZ91-1Sr-1%SiC nanocomposite displays the best yield strength and hardness increment. Furthermore, the creep resistance of the matrix alloy was increased with increasing nanofiber SiC and the best creep resistance was obtained in the AZ91-1Sr-1SiC nanocomposite. The values of stress exponents and the activation energies for experimental specimen were found between 3.17–5.54 and 103.5–155.3 kJ/mol., respectively. When considered the results obtained from the values of stress exponents, the activation energies and SEM micrographs, it was thought that the dominant creep mechanism for the matrix alloy and nanocomposites is dislocation climb controlled. Both of the nano-composites exhibited superior creep resistance compared to the matrix alloy under all the creep test conditions. [ABSTRACT FROM AUTHOR]

Magnesium (Mg), as the lightest metallic material, is 33% lighter than aluminum which makes it, potentially, a great replacement for aluminum and its alloys. However, Mg in pure and alloyed conditions is brittle at ambient temperature which largely limits their applications. One key solution to enhance the strength and ductility of Mg and its alloys is to embed thermally-stable nano-size reinforcements within the Mg matrix to produce so-called "Mg nanocomposites". The Mg nanocomposites are considering revolutionizing energy-saving lightweight materials of the future with enhanced strength and ductility properties. Mg nanocomposites are, however, at the initial degrees of improvement and consequently, systematic research is required to set up microstructure/property relationships at distinct potential conditions (i.e. temperatures and strain rates). In the present study, a nanoindentation testing approach is adopted to assess ambient-temperature small scale mechanical properties of a group of Mg nanocomposites reinforced with rare-earth element nanoparticles (NPs), i.e. Sm2O3. This paper tried to assess various nanoindentation-driven properties of the Mg-Sm2O3 nanocomposites and compare them with the pure Mg as the baseline. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) nanocomposites are created when nano-size particles are embedded into the Mg (or Mg alloy) matrix. The Mg nanocomposites, cited as high-strength energy-saving materials of future, are a group of emerging materials with excellent combination of strength and ductility and superior specific strength property (strength-to-weight ratio). Having said this, Mg nanocomposites are considered as promising replacement for other structural alloys (i.e. aluminum and titanium) wherever low density and high strength are required, i.e. transportation, aerospace, defense, etc. To be able to apply this group of materials for real components, different failure mechanisms at ambient and elevated temperatures under static and dynamic loading condition must be well documented. Compared with other metals and alloys, rate-dependent plastic deformation (creep), at ambient and elevated temperatures, of these novel materials is not yet well studied which seems a tangible lack of knowledge. This is required since the materials in service are often exposed to medium and elevated temperatures and/or static loads for long duration of time and this encourages creep failure on them. To this end, the information and the controlling mechanisms on time/temperature-dependent response of the material need to be developed to be able to predict the response of the Mg nanocomposites where the materials are under creep conditions. This paper aims at providing an overview on (i) creep-resistant Mg alloys (as matrix) and their chemical compositions, and (ii) responses of the Mg nanocomposites at different creep conditions (time and temperature). The controlling mechanisms contributing to the strength and ductility of the Mg nanocomposites due to the presence of the nanoparticles have been reviewed briefly in the present article. In this paper both traditional (uniaxial) and depth-sensing indentation creep of Mg nanocomposites are reviewed. Also, some fundamental questions and possible explanations have been raised on the creep characteristics of Mg nanocomposites and the contribution of microstructural features (i.e. grain boundaries, twins, precipitates, nanoparticles). This overview article provides a comprehensive summary to understand one of the failure modes (creep) at ambient and elevated temperature in the energy saving Mg nanocomposites that would be of interest for those in academia who explore novel nanocomposites. [ABSTRACT FROM AUTHOR]