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Li Z.,Nanchang University | Li Z.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City | Yan H.,Nanchang University | Yan H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City
Journal of Rare Earths | Year: 2015

The study systematically investigated the effects of master alloy addition containing rare earth elements La and Yb on the microstructures characteristic and tensile properties of AlSi10Cu3 alloy. It was studied by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy diffraction spectrum and differential thermal analyzer. The results showed that the addition of (La+Yb) obviously reduced the sizes of the primary α-Al phase and eutectic Si particles as well as β-Al5FeSi phase and improved the morphology of the primary α-Al phase and eutectic Si particles. The optimum addition of (La+Yb) addition was 0.6 wt.%. Comparing the 0.6 wt.% (La+Yb) modified AlSi10Cu3 alloy with the unmodified alloy, it was found that the mean diameter, mean area and SADS of primary α-Al phase were decreased by 50.80%, 75.74% and 50.83% respectively; the aspect ratio, size (length) and mean area of eutectic Si particles were decreased by 66.30%, 81.78% and 78.99%, respectively, and the average size of the β-Al5FeSi phase was 16.4 μm. In addition, the addition of (La+Yb) greatly improved the tensile properties of AlSi10Cu3 alloy, especially in the ultimate tensile strength and elongation as a result of the significant improvement in microstructure. © 2015 The Chinese Society of Rare Earths.


Chen X.-H.,Nanchang University | Chen X.-H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City | Yan H.,Nanchang University | Yan H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City
Journal of Materials Research | Year: 2015

Nanosized Al2O3 (Al2O3np) reinforced Al7075 composites were fabricated by specially made Al2O3np containing Mg powder and subtype multifrequency ultrasonic vibration. Compared to traditional techniques, Al2O3np was effectively dispersed in the matrix by the novel method. Microstructural studies showed that the addition of Al2O3np caused the grain refinement and that the resultant microstructures of composites depended on the dominant size and degree of Al2O3np clustering. The grain refinement could be mainly attributed to particle pushing mechanisms. Compared to the matrix alloy, the ultimate tensile and compressive strength of the as-cast composite with 1.5 wt% Al2O3np fabricated at 800 °C were increased by 59.6% and 42.6%, respectively. Transmission electron microscope analysis showed that high density dislocations and clear interfaces between particles and matrix were present in the grains, suggesting that the superior improvement of mechanical properties can be attributed to dislocation-type strengthening of matrix alloy and load transfer from matrix to hard nanoparticles. Copyright © Materials Research Society 2015.


Yan H.,Nanchang University | Yan H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City | Wang Z.,Nanchang University | Wang Z.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City
Journal of Rare Earths | Year: 2016

The influence of heat treatment (T6) on the ambient temperature dry sliding wear behavior of the extruded AZ91 alloy treated with Y using a pin-on-disc apparatus was investigated. Wear rates and friction coefficients were measured within a load range of 5-70 N at a sliding speed of 0.188 m/s over a constant sliding distance of 226.195 m. Worn surfaces and debris were examined using a scanning electron microscope equipped with an energy dispersive spectrometer. The experimental results revealed that, as applied load was increased, the alloy wear rates increased, but the friction coefficients decreased. Four chief operating wear mechanisms were observed, i.e., abrasion, oxidation, delamination and plastic deformation. The extruded AZ91 alloy treated with Y exhibited better wear resistance by adopting T6, which was mainly due to large amounts of fine Mg17Al12 distributed in the grains and the resulting modified strength and micro-hardness. © 2016 The Chinese Society of Rare Earths.


Huang B.-H.,Nanchang University | Huang B.-H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City | Yan H.,Nanchang University | Yan H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City
Chinese Rare Earths | Year: 2015

The effects of heat treatment on microstructure and mechanical properties of extruded AZ61-x% La magnesium alloy were investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD)as well as tensile testing. The results showed that, after the T6 treatment, the β-Mg17Al12 phases dispersed around the grain boundary suffered completely dissolved re-precipitated and re-distributed around the grain boundaries; the morphology of β-Mg17Al12 phase changed from network to blocky. In addition, some fine block B phases were also observed in the region of grain. Rare earth phase could refine grains and significantly improve the hardness of the alloy. However, after T6 treatment, hardness was decreased even though the tensile strength, yield strength and elongation of alloy has increased. Meanwhile, T5 treatment has less effect on the mechanical properties of the alloy. ©, 2015, Editorial Office of Chinese Rare Earths. All right reserved.


Chen X.-H.,Nanchang University | Chen X.-H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City | Yan H.,Nanchang University | Yan H.,Key Laboratory of Light Alloy Preparation and Processing in Nanchang City
Materials and Design | Year: 2016

Interactions between the solidification front and the remaining suspended particles take place during solidification of particles reinforced composites. The particles are either engulfed by the solidification front or pushed by the solid-liquid interface. In this study, the relation of distribution and clustering degree of nano-Al2O3 in Al7075 with the microstructure of alloy was investigated by conducting casting experiment. A hydrodynamic model for calculating the critical interface velocity required to push nano-particles by the interface was proposed. In addition, the influence of the nano-particles present ahead of solidification front on interface shape was discussed. Microstructural studies showed that the resulting microstructures of composites depended on the size and degree of nano-Al2O3 clustering. Based on the model, it was found that for particles below approximately 36% of the critical radius, r < 0.36 r* = 0.9973 μm, the critical interface velocities were four orders of magnitude lower than those obtained by micron particles, suggesting that smaller particles are easily engulfed by the interface rather than pushed. The experimental results were validated by the prediction of the model. Result showed that the constitutional super-cooling of local melts and the accumulation of solute behind the particle caused formation of a cellular interface. © 2016 Elsevier Ltd.

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