Aitao Tang

Development of magnesium-graphene nanoplatelets composite

In recent years, graphene has attracted a great research interest in all fields of sciences due to its unique properties. Its excellent mechanical properties lead it to be used in nanocomposites for strength enhancement. In current work, a new magnesium-graphene nanoplatelets composite is fabricated for the first time using semi-powder metallurgy method. The effect of graphene nanoplatelets addition on the mechanical behaviour of pure magnesium under both tension and hardness is investigated. The results demonstrate that graphene nanoplatelets are distributed homogeneously in the magnesium matrix, therefore act as an effective reinforcing filler to prevent the deformation. Compared to monolithic magnesium, the magnesium/0.3 wt% graphene nanoplatelets composite exhibited improved elastic modulus, yield strength, ultimate tensile strength and Vickers hardness. The improvement in elastic modulus, yield strength (0.2%), ultimate tensile strength and Vickers hardness for magnesium/0.3 wt% graphene nanoplatelets composite relative to pure magnesium are up to +10.6%, +5%, +8% and +19.3%, respectively. In addition to tensile and hardness tests for the analysis of mechanical properties of as synthesized composite, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction are used to investigate the surface morphology, elemental percentage composition and phase analysis, respectively.

Effect of mole ratio of Y to Zn on phase constituent of Mg-Zn-Zr-Y alloys

The phase constituent evolution of Mg-Zn-Y-Zr alloys with the mole ratio of Y to Zn both in the as-cast and as-annealed states at the Mg-rich corner was investigated by XRD and SEM/EDS analysis and was further explained from the ternary phase diagram calculation. The results show that the formation of the secondary phases in Mg-Zn-Y-Zr alloys firmly depends on the mole ratio of Y to Zn, and X (Mg12YZn)-phase, W (Mg3Y2Zn3)-phase and I (Mg3YZn6)-phase come out in sequence as the ratio of Y to Zn decreases. The mole ratios of Y to Zn with the corresponding phase constituent are suggested quantitatively as follows: the phase constituent is α-Mg+I when the mole ratio of Y to Zn is about 0.164; α-Mg+I+W when the mole ratio of Y to Zn is in the range of 0.164~0.33; α-Mg+W when the mole ratio of Y to Zn is about 0.33; α-Mg+W+X when the mole ratio of Y to Zn is in the range of 0.33-1.32; and α-Mg+X when the mole ratio of Y to Zn is about 1.32. The results also offer a guideline for alloy selection and alloy design in Mg-Zn-Y-Zr system.

Influence of stacking fault energy on formation of long period stacking ordered structures in Mg–Zn–Y–Zr alloys

The influence of alloying elements on the stacking fault energy (SFE) of Mg−Y−Zn−Zr alloys was calculated by using first-principles, and the microstructure of as-cast Mg-1.05Y-0.79Zn-0.07Zr (mole fraction, %) alloy prepared by conventional casting was investigated by SEM, TEM and HRTEM. The block-like long period stacking ordered (LPSO) phase, the lamellar LPSO phase and stacking faults were observed simultaneously and the lamellar LPSO structure and stacking faults were both formed on (0001)α-Mg habit plane and grown or extended along Mg - ) 0 1 01 ( α direction. The calculation results by the first-principles showed that the addition of Y can sharply decrease the stacking fault energy of the Mg−Zn−Y−Zr alloy, while Zn slightly increases the stacking fault energy of the alloy. The influence of stacking fault energy on the formation of LPSO was discussed. It shows that LPSO may nucleate directly through stacking faults and the lower stacking fault energy was in favor of formation of LPSO.

Effects of Yttrium Addition on Microstructure and Mechanical Properties of as-extruded AZ31 Magnesium Alloys

The effects of yttrium addition on microstructure and mechanical properties of as-extruded AZ31 magnesium alloys were investigated by OM, XRD and SEM. The results show that the addition of yttrium results in the formation of a new phase, Al2Y. When the addition of yttrium is higher than 1.48%-2.91% (mass fraction), another new phase, Al3Y5Mn7, forms, and the amount of β-Mg17Al12 phase in the AZ31 alloy decreases sharply. The tensile test at room temperature indicates that the yield strength of as-extruded AZ31 alloys improves with the addition of yttrium, but the elongation decreases, which is possibly related to the formation of coarse blocky compounds containing yttrium and the grain coarsening in the alloys.

Microstructure, mechanical properties, bio-corrosion properties and cytotoxicity of as-extruded Mg-Sr alloys.

In this study, as-extruded Mg-Sr alloys were studied for orthopedic application, and the microstructure, mechanical properties, bio-corrosion properties and cytotoxicity of as-extruded Mg-Sr alloys were investigated by optical microscopy, scanning electron microscopy with an energy dispersive X-ray spectroscopy, X-ray diffraction, tensile and compressive tests, immersion test, electrochemical test and cytotoxicity test. The results showed that as-extruded Mg-Sr alloys were composed of α-Mg and Mg17Sr2 phases, and the content of Mg17Sr2 phases increased with increasing Sr content. As-extruded Mg-Sr alloy with 0.5wt.% Sr was equiaxed grains, while the one with a higher Sr content was long elongated grains and the grain size of the long elongated grains decreased with increasing Sr content. Tensile and compressive tests showed an increase of both tensile and compressive strength and a decrease of elongation with increasing Sr content. Immersion and electrochemical tests showed that as-extruded Mg-0.5Sr alloy exhibited the best anti-corrosion property, and the anti-corrosion property of as-extruded Mg-Sr alloys deteriorated with increasing Sr content, which was greatly associated with galvanic couple effect. The cytotoxicity test revealed that as-extruded Mg-0.5Sr alloy did not induce toxicity to cells. These results indicated that as-extruded Mg-0.5Sr alloy with suitable mechanical properties, corrosion resistance and good cytocompatibility was potential as a biodegradable implant for orthopedic application.

Microstructure, corrosion behavior and cytotoxicity of biodegradable Mg-Sn implant alloys prepared by sub-rapid solidification.

In this study, biodegradable Mg-Sn alloys were fabricated by sub-rapid solidification, and their microstructure, corrosion behavior and cytotoxicity were investigated by using optical microscopy, scanning electron microscopy equipped with an energy dispersive X-ray spectroscopy, X-ray diffraction, immersion test, potentiodynamic polarization test and cytotoxicity test. The results showed that the microstructure of Mg-1Sn alloy was almost equiaxed grain, while the Mg-Sn alloys with higher Sn content (Sn≥3 wt.%) displayed α-Mg dendrites, and the secondary dendrite arm spacing of the primary α-Mg decreased significantly with increasing Sn content. The Mg-Sn alloys consisted of primary α-Mg matrix, Sn-rich segregation and Mg2Sn phase, and the amount of Mg2Sn phases increased with increasing Sn content. Potentiodynamic polarization and immersion tests revealed that the corrosion rates of Mg-Sn alloys increased with increasing Sn content. Cytotoxicity test showed that Mg-1Sn and Mg-3Sn alloys were harmless to MG63 cells. These results of the present study indicated that Mg-1Sn and Mg-3Sn alloys were promising to be used as biodegradable implants.

Effects of Al-10Sr master alloys on grain refinement of AZ31 magnesium alloy

Abstract The effects of Al-10Sr master alloys on grain refinement of AZ31 magnesium alloy were investigated, and the refinement efficiency of different Al-10Sr master alloys (commercial, solubilized, rolled and remelted+rapidly cooled) was compared and analyzed. The results indicate that the morphology and size of Al 4 Sr phases in the microstructures of different Al-10Sr master alloys, are of great difference. For the commercial Al-10Sr master alloy, the Al 4 Sr phases evolve from coarse block shape to relatively fine block shape after being dissolved at 500 °C for 4 h and followed by water quenching; but after being rolled at 300 °C for 50% reduction or remelted and followed by rapid cooling, the Al 4 Sr phases mainly exhibit fine granule and fibre shapes. In addition, the different Al-10Sr master alloys can effectively reduce the grain size of AZ31 magnesium alloy, but their refinement efficiency is different. The refinement efficiency of the Al-10Sr master alloy obtained by remelting and rapid cooling is the best, then the rolled, solubilized and commercial Al-10Sr master alloys are in turn. The difference of refinement efficiency for different Al-10Sr master alloys may be related to the dissolution rates of Al 4 Sr phases with different morphologies and sizes in the melt of AZ31 magnesium alloy.

Phase transformation refinement of coarse primary carbides in M2 high speed steel

Abstract The decomposition of the coarse primary M 2 C carbide in M2 high speed steel was investigated by using optical microscope, scanning electron microscope, energy dispersive spectrometer and X-ray diffraction analysis. It is indicated that the SEM observation using deeply etched samples can clearly reveal the details of the decomposition products of primary M 2 C eutectic carbides. The MC is granular and M 6 C is peanut-shaped in the decomposition products, and the decomposition products are found to be very small in the size. With the increase of annealing temperature and duration, part of the peanut-shaped M 6 C carbides change to simple skeleton-shaped ones. The phase transformation refinement of primary M 2 C carbides in M2 steel by the decomposition of metastable M 2 C carbides at high temperature can be obtained if suitable annealing parameters are applied. The complete decomposition of M 2 C to M 6 C and MC will occur when (1 100 °C, 4 h) or (1 150 °C, 2 h) annealing treatment is employed in M2 high speed steel.

Effects of heat treatment on microstructure and mechanical properties of ZK60 Mg alloy

The microstructure and mechanical properties of ZK60 Mg alloy were investigated under different solution treatments and artificial aging conditions. When as-cast ZK60 alloy was solution treated at 400℃ for 10 h and artificially aged at 150℃, the volume fraction of precipitates increased with the aging time up to 30 h. When the as-cast ZK60 alloy was solution treated at 400℃ for 10 h and artificially aged at 200℃ for 15-20 h, the volume fraction of precipitates reached a peak value. Tensile test at room temperature showed that a high density of the second phase precipitates was beneficial to improving the strength and elongation. Solution treatment at 400℃ for 10 h and artificial aging at 150℃ for 30 h is considered the optimum heat treatment condition to obtain a good combination of strength and ductility.

Microstructure and mechanical properties of asextruded Mg–xAl–5Sn–0·3Mn alloys (x = 1, 3, 6 and 9)

Abstract Properties of Mg–xAl–5Sn–0·3Mn alloys (x = 1, 3, 6 and 9) prepared by hot extrusion are reported. The orientation relationship between Mg2Sn precipitate and Mg matrix in Mg–9Al–5Sn–0·3Mn alloy was determined. The yield strength of the as extruded alloys initially decreased with increasing Al content, then increased for Al contents >6 wt-%. These changes are interpreted in terms of the effect of texture, grain size and second phase on the yield strength of the alloys.