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There has been a spurt in the quest for ignition resistant Mg materials that can be employed in the aerospace sector, consequent to the recent lifting of the ban on magnesium based materials by Federal Aviation Administration (FAA). Literature studies show some advances in the field of development of ignition proof Mg materials. This article aims at capturing the currently available data on the ignition properties of Mg based materials. One of the objectives of this article is to reduce the ambiguity between ignitability and flammability of Mg materials and bridge the gap in understanding by clearly demarcating the tests and standards available for the two. Further, most importantly, the factors affecting the ignition temperatures of Mg materials and their mechanisms are emphasized such that an informed approach can be undertaken while designing the Mg based alloys for the aerospace applications. This article also demonstrates and emphasizes that the studies on the ignitability can be stretched to new classes of materials like LPSO (Long Period Stacking Order) alloys and nanocomposites in order to attain a maximized benefit in the existing domain of materials of Mg base. Keywords: Magnesium, Ignition, Geometrical, test and metallurgical factors, Mechanisms, New magnesium alloys and magnesium based nanocomposites

In the present study, new quaternary MgY1.65Zn0.74Al0.53 and MgY3.72Zn1.96Al0.45 alloys (wt.%) were synthesized employing the Disintegrated Melt Deposition (DMD) casting technique followed by hot extrusion. Microstructural characterization revealed the presence of 14H long-period stacking ordered structure (LPSO) and Mg4Y2ZnAl3 phases aligned along the direction of extrusion in both alloys. Refined grains (⩽5 μm) due to the effect of dynamic recrystallization (DRX) were also observed to co-exist with larger worked grains (⩾20 μm) in the extruded microstructures. Compared to monolithic Mg, significant increase in the microhardness (∼67–88%), tensile yield strength (∼245–290%) and ultimate tensile strength (∼113–144%) were observed in the Mg–Y–Zn–Al alloys. Despite the significant increase in strength of materials, failure strains of both Mg–Y–Zn–Al alloys were comparable to monolithic Mg. Ignition temperatures of both Mg–Y–Zn–Al alloys were found to outperform commercially available AZ31, AZ80 and WE43 (high-temperature) Mg alloys, and the highest ignition temperature of 770 °C was achieved in the MgY3.72Zn1.96Al0.45 alloy. Keywords: Mg–Y–Zn, LPSO, DMD, Mechanical properties, Magnesium alloys

In this work, boron rich nanoparticles (B4C, SiB6 and ZrB2) were added to bulk melt processed Mg–Al, Mg–Zn and Mg–RE (Rare Earth) series contemporary magnesium alloys, respectively. The most obvious positive effect when adding B4C nanoparticles to the Mg–Al alloy was the significant increase in tensile ductility (to about 25%). Here, there was no significant change in grain size or crystallographic texture due to nanoparticle addition. However, it was observed that stacking faults formed more easily in the magnesium matrix due to nanoparticle addition. Also, it was observed that coarser nanoparticles broke down high strain zones (HSZs) during tensile deformation. The addition of SiB6 to Mg–Zn alloy also resulted in similar significant increase in tensile ductility (to about 23%). Tensile deformation induced alignment of more rounded and spherical nanoparticles was observed. Stacking faults forming more easily in the alloy matrix was also observed. However, the formation of nanograins (nanoscale recrystallization) during room temperature tensile deformation was observed in this system. This implied that nanograin rotation during deformation was also responsible for the observed enhanced tensile ductility. When ZrB2 was added to Mg–RE alloy, the tensile strength was significantly enhanced (yield strength >400 MPa) after thermal ageing. Here, the ZrB2 nanoparticles induced the formation of thermal ageing resistant long period stacking/ordered (LPSO) nanograins and nanolayers in the Mg–RE alloy matrix. Regarding the Mg–Al and Mg–Zn nanocomposites having high tensile ductility (>20%), it was also hypothesized that a further 5–10% cold working could significantly increase the tensile strength while maintaining the ductility above 10%. This simple hypothesis could greatly increase the suitability of bulk melt processed magnesium alloy nanocomposites (originally having high ductility) towards multiple structural (including transport) applications beneficial (yet lucrative) to mankind.

This study highlights the use of a metallic coating of nanoscale thickness on carbon nanotube to enhance the interfacial characteristics in carbon nanotube reinforced magnesium (Mg) composites. Comparisons between two reinforcements were targeted: (a) pristine carbon nanotubes (CNTs) and (b) nickel-coated carbon nanotubes (Ni–CNTs). It is demonstrated that clustering adversely affects the bonding of pristine CNTs with Mg particles. However, the presence of nickel coating on the CNT results in the formation of Mg 2 Ni intermetallics at the interface which improved the adhesion between Mg/Ni–CNT particulates. The presence of grain size refinement and improved dispersion of the Ni–CNT reinforcements in the Mg matrix were also observed. These result in simultaneous enhancements of the micro-hardness, ultimate tensile strength and 0.2% yield strength by 41%, 39% and 64% respectively for the Mg/Ni–CNT composites in comparison with that of the monolithic Mg.

The main objective of the present work is to investigate the dry sliding wear behaviour of a magnesium matrix composite reinforced with zinc oxide nano-particles. Magnesium matrix composites have many applications, especially in the automotive and aerospace industries, due to their superior specific properties. A magnesium matrix composite with 0.5. vol.% ZnO nano-reinforcement was prepared using powder metallurgy and was hot extruded to eliminate pores. The wear behaviour of the Mg/ZnO nano-composite was investigated by conducting dry sliding tests as a function of wear with an oil-hardened non-shrinking (OHNS) steel disc as the counterpart on a pin-on-disc apparatus. Wear tests were conducted for normal loads of 5, 7.5 and 10. N at sliding velocities of 0.6, 0.9 and 1.2. m/s at room temperature. The variations of the friction coefficient and wear rate with the sliding distances (500. m, 1000. m and 1600. m) for different normal loads and sliding velocities were plotted and analysed. To study the dominant sliding wear mechanism for various test conditions, the worn surfaces were analysed using scanning electron microscopy. The wear rate was found to increase with the load and sliding velocity. � 2014 Elsevier Ltd.

Development of amorphous alloy/glassy particle reinforced light metal composites is an emerging research field. In this investigation, we have synthesized and characterized Ni 60 Nb 40 amorphous alloy particle reinforced Mg-composites with varying volume fractions. Microwave-assisted two-directional rapid sintering technique followed by hot extrusion was used to produce these pure Mg-based composites. The structural and mechanical properties of the developed composites were investigated, and are discussed using structure–property relationship. Structural analysis indicated the retention of amorphous structure of the reinforcement in all the composites. It was found that the distribution of the reinforcement was strongly dependent on the volume fraction ( V f ). The addition of Ni 60 Nb 40 amorphous alloy particles modified the preferred crystal orientation of Mg, as was observed from X-ray diffraction (XRD) analysis. The composites showed significant improvement in hardness (increment up to 120%) and compressive strength (∼85% increase at 5% V f ). Comparison of mechanical properties of the developed composites with those of conventional Mg-composites having ceramic/metallic reinforcements, highlight the effectiveness of using amorphous particles as promising reinforcement materials.

Several challenges are involved in employing fusion-based additive manufacturing (AM) technologies for magnesium (Mg) alloys. In this study, a novel 3D printing (3DP) technique was used to additively manufacture a green component made of Mg-5.9Zn-0.13Zr powder at ambient temperature that can be densified during subsequent liquid phase sintering, obtaining a functional part with zero process contaminants. Density measurement, microstructural, and mechanical investigations of the green components sintered for 5 h at different temperatures ranging from 535 °C to 610 °C indicated an improvement in properties with an increase in sintering temperature. Swelling during sintering was observed at temperatures ≥ 580 °C. Sintering at 573 °C with an extended holding time up to 60 h resulted in comparable density, compressive properties, and elastic modulus similar to that of human cortical bone. Furthermore, mercury porosimetry analysis revealed that additively manufactured Mg components could provide pores characteristics matching with those found in human bone. Keywords: 3D printing, Binder jetting, Magnesium alloys, Liquid phase sintering, Inkjet technology

In the present study, new AZ51/Al2O3–2Ca magnesium nanocomposite was successfully synthesized by simultaneously adding 2wt.% aluminum, 2wt.% Ca and 1.5vol.% nanosized Al2O3 (50nm) into AZ31 matrix using a disintegrated melt deposition (DMD) technique. AZ51/Al2O3 nanocomposite was developed following the same processing route except adding Ca. Composite samples were then subsequently hot extruded at 400°C and characterized. Microstructural characterization studies revealed equiaxed grain size, reasonably uniform distribution of intermetallics and nanoparticulates in the matrix and minimal porosity. Results also showed that the addition of Ca into AZ51/Al2O3 nanocomposite helped to reduce the average grain size and introduced (Mg,Al)2Ca second phase. Physical properties characterization revealed that addition of Ca reduced the coefficient of thermal expansion (CTE) when compared to Ca free nanocomposite. Ca addition also assisted in improving overall mechanical properties including microhardness, 0.2% yield strength, ultimate tensile strength, and work of fracture while the ductility was compromised. NPRP 08-424-2-171 from the Qatar National Research Fund (QNRF), Qatar

Novel Mg nano-composites reinforced with either Bi 2 O 3 nano-particles or hybrid Al–Bi 2 O 3 particles (Bi 2 O 3 nano-particles hybridized with Al using ball milling) have been synthesized, in this work, through powder metallurgy route using microwave assisted rapid sintering technique followed by hot extrusion. Compared to monolithic Mg, the Mg/ x Bi 2 O 3 ( x (vol.%) = 0.22, 0.66 and 1.11) nano-composites displayed higher strength while failure strain was compromised. Midst the diverse nano-composites formulations, the Mg/0.22Bi 2 O 3 nano-composite revealed the best overall enhancement in tensile yield strength (0.2% YS), compressive yield strength (0.2% CYS), ultimate tensile strength (UTS) and ultimate compressive strength (UCS) (up to +24%, +9.0%, +28%, and +39%, respectively) compared to pure Mg while both tensile and compressive failure strain (FS t , FS c ) remained statistically the same. To improve the mechanical response of Mg/ x Bi 2 O 3 nano-composites further, the Bi 2 O 3 nano-particles were hybridized with Al to outcome hybrid Al–Bi 2 O 3 particles. Hybridizing Bi 2 O 3 nano-particles with Al (Al–Bi 2 O 3 ) and getting embedded in Mg matrix discovered a remarkable mechanical response enhancement in the case of hierarchical Mg/0.92Al– x Bi 2 O 3 configurations compared to their Mg/ x Bi 2 O 3 nano-composites equivalents. Selectively, an enhancement of +27% (0.2%YS), +39% (0.2%CYS), +21% (UTS), +31% (UCS) and +33% (FS t ) was witnessed in the case of hierarchical Mg/0.92Al–0.22Bi 2 O 3 configuration compared to its Mg/0.22Bi 2 O 3 nano-composite equivalent whereas FS c remained statistically the same. Here, some of the strengthening mechanisms that might be accountable for the notable mechanical response enhancement of Mg nano-composites owing to presence of Bi 2 O 3 nano-particles, either solely or as the hybridized form, have been classified. The effect of both as received Bi 2 O 3 nano-particles and hybrid Al–Bi 2 O 3 particles on textural evolution of Mg nano-composites is also scrutinized in this work.

The hot deformation behavior and microstructural evolution of cast-extruded AZ31B magnesium alloy and nanocomposite have been studied using processing-maps. Compression tests were conducted in the temperature range of 250–400 °C and strain rate range of 0.01–1.0 s−1. The three-dimensional (3D) processing maps developed in this work, describe the variations of the efficiency of power dissipation and flow instability domains in the strain rate ( e ) and temperature (T) space. The deformation mechanisms namely dynamic recrystallization (DRX), dynamic recovery (DRY) and instability regions were identified using processing maps. The deformation mechanisms were also correlated with transmission electron microscopy (TEM) and optical microscopy (OM). The optimal region for hot working has been observed at a strain rate ( e ) of 0.01 s−1 and the temperature (T) of 400 °C for both magnesium alloy and nanocomposite. Few instability regimes have been identified in this study at higher strain rate ( e ) and temperature (T). The stability domains have been identified in the lower strain rate regimes.

This study is aimed at understanding the ductility enhancing function of carbon nanotube (CNT) nanoparticles in a concentrated magnesium alloy (AZ81) nanocomposite. CNT nanoparticles were selected for reinforcement purposes due to the well known lack of affinity between magnesium and carbon. The nanocomposite exhibited similar grain size and hardness to the monolithic alloy, reasonable nanoparticle distribution and non-dominant (0 0 0 2) texture in the longitudinal direction. Compared to the monolithic alloy in tension, the nanocomposite exhibited higher failure strain (+73%) without significant compromise in strength, and higher energy absorbed until fracture (EA) (+79%). Compared to the monolithic alloy in compression, the nanocomposite exhibited slightly lower failure strain (−6%) with significant compromise in strength, and slightly lower EA (−7%). The beneficial effects of CNT nanoparticle addition on tensile ductility enhancement (with occasional drastic increase in strength) of AZ81 alloy is discussed in this paper.

In this study, the effects of the addition of individual micro- and nano-sized metallic elements (micron-Ti and nano-Cu) and their combination on the microstructure and mechanical properties of pure Mg were investigated. The materials were produced by rapid microwave sintering assisted powder metallurgy technique followed by hot extrusion. From the microstructural characterization and mechanical property evaluation, it was identified that the solid solubility, size and the method of addition of elements significantly influenced the properties. While the insoluble micron-Ti enhanced the strength and reduced the ductility due to weak interface, the addition of nano-Cu with relative solid solubility enhanced the strength due to the formation of Mg2Cu intermetallics and retained the ductility. The positive effect of their combined addition was found to be more pronounced when they were pre-processed, rather than their direct addition. The change in particle morphology, Ti3Cu intermetallic formation and good interfacial bonding with the matrix achieved due to pre-processing contributed towards its superior strength and ductility.

The present study investigates the feasibility of joining AZ31B magnesium nanocomposites by rotational friction welding. The AZ31B magnesium metal matrix composite, which was reinforced with alumina (Al2O3, average particle size of 50 nm) and calcium (Ca), was produced by a hybrid casting process and hot extruded at 350 °C. Joining processes were done by varying the friction welding parameters. The integrity of the joints was investigated by optical microscopy. The mechanical properties of the joints were examined by tension tests and micro hardness tests. The efficiencies of the joints were analysed using statistical analysis. The fracture mode was studied using a scanning electron microscope. It was observed that as the friction pressure and forging pressure increased, the joint efficiency increased. Also, as the friction time increased, the efficiency of the joint decreased.

An experimental analysis was performed to predict flow curves, dynamic recrystallisation behaviour of AZ91magnesium/titanium metal matrix composite based on result from hot compression test. The compression tests were carried out in a temperature range of 300–500 °C and at a strain rate range of 0.001–1 s −1 and the flow curves were obtained. The processing map of the studied material was obtained by following the dynamic material model. Microstructural characterization studies conducted on the compressed composite samples using optical and scanning electron microscopy, revealed dynamic recrystallization, debonding of Ti Particles, particle breakage, and flow localization. The observations were performed in order to describe the behavior of the material under hot forming operation in terms of material damage and micro structural modification.

In the present study, a non-heat-treatable aluminum alloy was reinforced with silicon and silicon carbide, respectively, using disintegrated melt deposition technique. The results of the chemical composition analysis following processing revealed that more silicon in comparison to silicon carbide was incorporated irrespective of starting with the same weight percentages of each element. The results of the microstructural characterization following thermomechanical processing revealed, in common, completely recrystallized matrix, minimal presence of porosity, uniform distribution of Si and SiC in the matrix and identical Si–Al and SiC–Al interfacial characteristics for both the Al/Si and Al/SiC materials. Furthermore, the results of tensile testing revealed an improved combination of tensile strength, ductility and matrix microhardness in the case of aluminum alloy containing silicon when compared to the aluminum alloy reinforced with silicon carbide. The results of mechanical properties characterization were finally correlated with constitutional and microstructural aspects of metallic matrix.

During the sliding of aluminium alloys dispersed with graphite particulates, a layer of graphite is usually present at the sliding interface. This tribo-layer significantly reduces the amount of direct metal-to-metal contact, giving rise to low friction and a low rate of wear, making these composites useful candidate materials for anti-friction applications. Such self-lubricating composites are commonly fabricated via the squeeze casting, slurry casting or powder metallurgy route. These processes are expensive while the less-expensive conventional casting route is limited by the agglomeration of graphite particles in the composites, giving rise to poor mechanical properties. In this work, graphite particulate-reinforced Al–4.5 wt.% Cu composites with two effective graphite contents (Al–4.5 Cu/4.2 wt.% C and Al–4.5 Cu/6.8 wt.% C) were synthesized through an innovative partial liquid phase casting (rheocasting) technique, which is a modification of the conventional casting process. Unlubricated (without the use of conventional liquid lubrication) friction and wear performance of these composites as well as the un-reinforced aluminium alloy was determined using a pin-on-disk tester. The results revealed that the graphite-reinforced composites have a higher wear rate than the un-reinforced matrix alloy while their frictional characteristics are very similar within the range of testing conditions. Combining these with the information gathered from worn-surface examinations and wear-debris analysis, it is suggested that there exists a certain threshold for the amount and size of graphite particulates in these composites to enable them to have improved tribological properties.

In the present study an aluminium-based metallic matrix (Al-2wt%Cu) was reinforced with SiC particulates using conventional casting and partial liquid phase casting (rheocasting) techniques. Microstructural characterization studies conducted on the rheocast samples revealed a more uniform distribution of SiC particulates and good interfacial integrity between SiC particulates and metallic matrix when compared to the conventionally cast composite samples. Results of ambient temperature mechanical tests demonstrate an increase in 0.2% YS, UTS and ductility in case of rheocast samples when compared to the unreinforced and conventionally cast composite samples. The results of microstructural characterization and mechanical testing were finally rationalized in terms of the nature of processing technique employed to reinforce Al-2wt%Cu metallic matrix with SiC particulates.