Aluminium matrix composites (AMCs) reinforced with micro and nano-sized Al2O3 particles are widely used for high performance applications because of their improved physical and mechanical properties. ...To improve the wettability and distribution of reinforcement particles within the matrix, a novel three step mixing method was used. The process included heat treatment of micro and nano Al2O3 particles, injection of heat-treated particles within the molten A356 aluminium alloy by inert argon gas and stirring the melt at different speeds. The influence of various processing parameters such as the heat treatment of particles, injection process, stirring speed, reinforcement particle size and weight percentage of reinforcement particles on the microstructure and mechanical properties of composites was investigated. The matrix grain size, morphology and distribution of Al2O3 nanoparticles were analysed by SEM, optical microscopy equipped with image analyser, EDS and XRD. The hardness and compression strength of samples were also investigated. The results showed the poor incorporation of nanoparticles in the aluminium melt prepared by the usual method. However, the use of heat-treated particles, injection of particles and the stirring system improved the wettability and distribution of the nanoparticles within the aluminium melt. In addition, the hardness, compressive strength and porosity increased as the weight percentage of nano Al2O3 particles increased.
Mg-Zn-Ca-Mn alloys have been developed due to their great potential as new generation of biomaterials while thermo-mechanical processes can promote its mechanical and corrosion properties. In this ...study, effect of hot deformation parameters such as temperature and strain rate on mechanical behavior and corrosion properties of Mg-4Zn-0.5Ca-0.75Mn alloy was investigated. Therefore, hot extrusion process at 450 °C with ratio of 12:1 and hot deformation tests at various conditions (300–450 °C and 0.001–1 s−1) were carried out to refine the grain size and improve both mechanical and corrosion properties of Mg-Zn-Ca-Mn alloy. Electrochemical tests were carried out in simulated body fluid (SBF) solution at room temperature using Ivium-n-Stat. The microstructural results and flow curves showed the fine grain microstructure and twinning-free grains as well as fully recrystallized grains achieved at 350 °C and 400 °C at lower strain rates. Also, polarization curves indicated that the corrosion potential shifts toward more noble potential by increasing the temperature parameter. The corrosion rate decreased from 0.31 to 0.12 mm/year at 400 °C and 0.001 s−1 due to the fine grain microstructure. Indeed, the protective passive film covered the grain boundaries surface which decreases the corrosion rate and retards the breakdown of passive film and pitting corrosion. Fine grain and fully recrystallized microstructure through hot compression test at 400 °C of Mg-Zn-Ca-Mn alloy provided a great potential for biomedical application owing to the combination of both improved mechanical properties and enhanced corrosion resistance. Finally, the lowest corrosion rate of the Mg-Zn-Ca-Mn alloy was obtained at 400 °C which is nearly similar with the coated samples and Mg alloys reinforced with hydroxyapatite.
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•Corrosion behavior of Mg-Zn-Ca-Mn alloy as a biomaterial was investigated in this study.•Thermomechanical process led to microstructure evaluation by DRX and second phase distribution.•Corrosion rate decreased from 0.31 to 0.12 (mm/year) due to the microstructure evaluation.•Fine grain and fully recrystallized microstructure led to high corrosion resistance at 400 °C.•Uniform distribution of grain size and second phase resulted high corrosion resistance at 400 °C.
In general, graphene nanoplatelets (GNPs) did not entirely imparted their extraordinary properties to the particulate magnesium matrix composites (PMgMCs) due to the poor wettability between GNPs and ...Mg matrix alloys as well as presence of agglomerated GNPs. Therefore, in this study, microstructure and mechanical characterizations were used to investigate effect of GNPs content on the microstructural and mechanical properties of AZ80 magnesium alloy. Current study explored the potential and mechanism of GNPs in improvement of mechanical properties of PMgMCs with insight of microstructure. Therefore, AZ80 reinforced by low contents of GNPs (0.1 and 0.6 wt%) were fabricated by rheo casting followed by hot extrusion. Simultaneously enhancement of tensile properties, the strengthening and the fracture strain efficiencies were achieved in AZ80/0.1GNPs composite by cost effectiveness and simple adaptability of manufacture method which results fairly uniform distribution of GNPs. The addition of 0.1 wt% GNPs led to grain refinement (~10%), dynamic recrystallization, stronger basal texture (~750%), more dissolution of β-eutectic phase (~66%) which results more dynamic precipitates (~70%) and reduction of yield asymmetry (~23%). Compared to the AZ80 alloy, the tensile and compressive yield strengths of AZ80/0.1GNPs composite were enhanced by 40% and 15%, respectively. In both tensile and compressive testes, the effective load transfer was the most important strengthening mechanism. Also, the tensile and compressive failure strains of AZ80/0.1GNPs nanocomposite were enhanced by 50% and 37%, respectively. The uniform dispersion of GNPs, increase of non-basal slip, grain refinement, lower eutectic content and smaller discontinuous intergranular precipitates increased failure strain.
Metal-matrix composites (MMCs), as light and strong materials, are very attractive for application in industries such as automotive, military, aerospace and electrical. Nano and micro-composites ...(A356/Al2O3) with different wt% of particles were fabricated by stir-casting and compo-casting. Optical microscopy and SEM were used to characterise the microstructure, and tensile, hardness and compression tests were used to identify the mechanical properties. The microstructural study revealed uniform distribution, grain refinement and low porosity in micro and nano-composite specimens. The addition of micro and nano alumina led to improved yield strength, ultimate tensile strength, compression strength and hardness. The fabrication process type and particle size were the effective factors influencing the mechanical properties. Decreasing alumina particle size and using compo-casting process obtained the best mechanical properties.
This paper investigates the effect of dwell time and heat treatment on the modified friction stir clinched (MFSC) joint of AA2024-T3/AA6061-T6 Al alloys. The precipitation-hardening heat treatment ...method involves the combination of solution heat treatment (at 520 °C for 1 h) and aging (at 165 °C for 18 h) processes. The microstructure, failure load, hardness, and fracture behavior of the as-welded and heat-treated MFSC joints were investigated. TEM images show that re-precipitation of strengthening Al2CuMg and MgZn2 phases, dislocation density, and tangles are more pronounced in the heat-treated MFSC joint. A rise in dwell time increases the average grain sizes (1.39–6.65 μm), tensile-shear strength (101–133 MPa), and cross tension strength (59–88 MPa) of the MFSC welded 2024-T3/6061-T6 joints due to an upsurge in the in-process exposure time-induced heat input and inter-material flow. An increase in dwell time beyond 15 s is undesirable. It induces the formation of nugget cracks and micro-voids in the joints and an impaired joint failure load consequently ensues. Heat treatment processing further causes grain coarsening (2.48–9.15 μm) and improves the hardness (at the weld center), tensile-shear (146 MPa), and cross tension (102 MPa) failure strengths of the MFSC joints due to the re-precipitated strengthening phases.
In general, individual carbonaceous reinforcements did not entirely impart their excellent mechanical properties to the Mg matrix alloy, which is mainly due to the aggregation of them. The present ...work explores the potential and mechanism of developed mechanical properties by adding GNPs + CNTs in the AZ80 matrix composite based on the texture and microstructural evolutions. In this work, carbonaceous hybrid reinforcement is selected to significantly improve mechanical properties by more homogeneous dispersion of them in the AZ80 alloy via simple semi-powder metallurgy and rheo casting followed by extrusion (430 °C). The results show that network structure of hybrid reinforcement has a significant effect on reduction of grain size of extruded AZ80 alloy (25%), compared to 1D and 2D carbonaceous reinforcements. In the composites, the strongest and weakest basal textures (4.7 and 3.1 multiples of random distribution, respectively) are observed in AZ80/CNT and AZ80/GNP + CNT composites, respectively. In comparison with the AZ80 alloy, the AZ80/GNP + CNT composite shows 112%, 28%, 148% and 278% improvement in TYS, UTS, TFS and toughness, respectively. The maximum improvement of CYS (15%), UCS (23%) and CFS (37%) is attained in the AZ80/GNP composite.
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•Synergetic effect of GNPs + CNTs on the AZ80 alloy was investigated in this study.•Synergetic effect of GNPs + CNTs was observed on the grain and eutectic morphology.•Synergetic effect of GNPs + CNTs on the tensile properties was indicated in this study.•GNPs + CNTs enhanced simultaneously yield strength and toughness of AZ80 matrix alloy.•Homogenous dispersion and bridging the CNTs promoted fracture strain and toughness.
Hot deformation behavior of 6061 aluminum alloy was investigated by performing compression test in the temperature range of 350–500°C. Equivalent strain rates were selected in the range of ...0.0005–0.5s−1 in order to obtain processing and stability maps of the studied material using a Dynamic Material Model. Microstructure of the samples after deformation was analyzed by light and electron microscopy and the differences were compared together. The stresses obtained from the flow curves were related to strain rate (ε̇) and temperature (T) by a constitutive equation in hyperbolic sine function with hot deformation activation energy of 274kJ/mol, and were described by the Zener–Hollomon equation. Microstructure results showed that with decreasing Z value, the elongated grains coarsened and the tendency of dynamic recrystallization enhanced. Correspondingly, the subgrain size increased and the dislocation density decreased. Moreover, the main softening mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization. XRD results showed that the (200) texture has an important role in development of dynamic recystallization at high temperature.
The role of twin boundaries (TBs) in the dynamic recrystallization (DRX) of Ni-30Cu (Monel400) was investigated through hot compression tests in the temperature interval of 750–1150 °C and strain ...rate of 0.01 s−1. Electron Back Scattered Diffraction (EBSD) analysis showed that DRX at 750 and 950 °C was limited to bulging and sparse nucleation on random high angle grain boundaries (HAGBs) while the primary coherent twin boundaries (TBs), with a length density of 55% in the starting microstructure, did not take part in the bulging process before conversion into HAGBs. The sluggish DRX was therefore attributed to the necessary conversion of primary TBs into HAGBs. The investigation also revealed that a new variant of TBs formed behind the protruding grain boundaries separated the bulges from the parent grains, indicating that unlike primary TBs, the newly formed TBs contributed to the occurrence of DRX. The formation of the new TBs was related to the dissociation of well-developed subgrains and the migration of random HAGBs. A mechanism for the occurrence of DRX in hot deformed Monel 400 is proposed that takes into account the contribution from the new TBs.
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For the ultra-fine grained hybrid carbonaceous (graphene nano-plates (GNPs) + carbon nano-tubes (CNTs)) reinforced high entropy alloys (HEAs), there is a lack in understanding of the structure ...evaluations, mechanical and wear behaviors. In this work, the CrCoFeMnNi HEA and CrCoFeMnNi-X(GNP+CNT) (X = 0.2 and 0.8 wt%) composites were successfully fabricated via mechanical alloying (MA) following by spark plasma sintering (SPS). The effect of various contents of GNPs+CNTs on the phase and microstructure evaluations, the micro-hardness, shear deformation and wear behavior were investigated. The results demonstrated that the major FCC phase was obtained after 50 h milling for CrCoFeMnNi HEA powders, where a two-phase structure was obtained by incorporation of GNPs+CNTs. The Cr7C3 carbide and spinel oxide phases in the SPS processed CrCoFeMnNi-X(GNP+CNT) composites showed higher and lower intensities compared to those of the CrCoFeMnNi HEA, respectively. The considerably effect of GNPs+CNTs to hinder crystal growth was reflected via 31% lower coarsening of crystal size (CS) in the CrCoFeMnNi-0.2 wt% (GNP+CNT) composite than the CrCoFeMnNi HEA. The micro-hardness was improved with increasing the hybrid carbonaceous reinforcement concentration, where the surface roughness showed lessening trend. Ultimate shear stress (USS) of CrCoFeMnNi-0.2 wt% (GNP+CNT) composite (591 MPa) was the highest in comparison with CrCoFeMnNi HEA and CrCoFeMnNi-0.8 wt% (GNP+CNT) composite. The worn surface of the CrCoFeMnNi-0.8 wt% (GNP+CNT) composite presented small debris, some black adhesion and micro cracks where the worn track was the most prominent and oxidation wear resistance was significantly improved. The considerable reduction in the friction coefficient (FC) values about 16% and 43% and improvement in the wear resistance (WR) values by 81% and 91% were achieved with incorporation of 0.2 wt% and 0.8 wt% GNPs+CNTs, respectively. These indicated that hybrid carbonaceous reinforcement obviously developed self-lubricating ability, however, the efficiency of WR was affected by agglomeration of reinforcement phase.
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•Fairly uniform dispersion of hybrid carbonaceous reinforcement was achieved.•Incorporation of GNPs+CNTs increased the dissolution of carbon atoms (higher LS and LP).•Incorporation of GNPs+CNTs promoted formation of carbide phases in the FCC matrix.•USS was the highest in CrCoFeMnNi-0.2 wt% (GNP+CNT) composite.•The roughness values considerably decreased about 200% with adding GNPs+CNTs.
