Hansong Xue

Microstructural characteristics and properties in centrifugal casting of SiCp/Zl104 composite

The microstructural characteristics and Brinell hardness of a cylinder produced by centrifugal casting were investigated using 20% (volume fraction) SiC(p)/Zl104 composites. Macrostructure and XRD analysis show that most of SiC particles segregate to the external circumference of the cylinder, the other SiC particles maintain in the inner circumference of the cylinder, and a free particle zone is left in the middle circumference of the cylinder. Microstructural characteristics and quantitative assessment of SiC particles show that most of congregated SiC particles in 20%SiC(p)/Zl104 composites are dispersed by centrifugal force, and the other congregated SiC particles and most of alumina oxide are segregated to the inner circumference of the cylinder. The SiC particles in aluminum melt can promote the refinement of primary alpha(Al) during solidification, and fine primary alpha(Al) grains can also promote the uniform distribution of SiC particles. Brinell hardness of SiC(p)/Zl104 composites is connected with not only the volume fraction of SiC particles, but also the distribution of SiC particles in matrix alloy.

Effects of Ultrasonic Treatment on Microstructure and Mechanical Properties of Mg-5Zn-2Er Alloy

The effects of the ultrasonic treatment on the microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy were investigated. The results show that the ultrasonic treatment has significant effect on the microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy. The phases in Mg-6Zn-0.5Y-2Sn alloy are α-Mg, MgZn2, MgSnY, Mg2Sn, and a small amount of I-phase. With the application of ultrasonic treatment, I-phase nearly disappears, and with increasing the ultrasonic treatment power, the coarse dendrites gradually change into roundish equiaxed grains. The second phases at the α-Mg boundaries transform from coarse, semicontinuous and non-uniform to fine, discontinuous, uniform and dispersive. When the ultrasonic treatment power is 700 W, the best comprehensive mechanical properties of Mg-6Zn-0.5Y-2Sn alloy are obtained. Compared with the untreated alloy, the 0.2% tensile yield strength, ultimate tensile strength and elongation are improved by 28%, 30% and 67%, respectively.

Effects of temperature on fracture behavior of Al-based in-situ composites reinforced with Mg2Si and Si particles fabricated by centrifugal casting

Abstract An aluminum-based in-situ composites reinforced with Mg 2 Si and Si particles were produced by centrifugal casting Al–20Si–5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg 2 Si particles in the composites is as high as 38%, and ultimate tensile strengths (UTS) of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.

A facile green synthesis of Sm2O3 nanoparticles via microwave-assisted urea precipitation route and their optical properties

Samarium oxide (Sm2O3) nanoparticles with a narrow size distribution were successfully synthesized by microwave-assisted using urea as precipitant without surfactant or template. The Sm2O3 particles were characterized using X-ray diffraction analysis, field-emission scanning electron microscopy, field-emission transmission electron microscopy and ultraviolet-visible-near-infrared spectrophotometer. The results showed that the samples prepared with different concentration of urea had different particle sizes. When the concentration of urea was 1.2 mol/L, the sample had the smallest particle size. A possible mechanism for the formation of the nanoparticles was proposed. Optical properties of Sm2O3 nanoparticles showed that the nanoparticles had a strong absorption property in the deep ultraviolet region between 200 nm and 270 nm.

Effects of Mg content on primary Mg2Si phase in hypereutectic Al–Si alloys

Abstract Hypereutectic Al–Si alloy with variant Mg contents were fabricated by casting, and the effects of Mg content on the microstructure of primary Mg2Si particles in hypereutectic Al–Si alloys were investigated. The results show that the volume fraction of primary Mg2Si particles increases linearly with raising the Mg content, but the average size of Mg2Si particles does not exhibit a corresponding change. When the Mg content is 3%, directions have the fastest growth velocity, so that Mg2Si particles are likely to form octahedron shape. When gradually increasing the Mg content, the distributions of Mg and Si atoms on the solid–liquid interface become inhomogeneous, which results in the formation of irregular octahedron structures. Finally, when the Mg content is about 10%, the morphology of primary Mg2Si particles changes from the octahedron shape into various complex structures with a large size.

Effect of Bi on Microstructure and Mechanical Properties of Extruded AZ80-2Sn Magnesium Alloy

Abstract The effects of Bi on the microstructure and mechanical properties of AZ80-2Sn alloy were investigated. The results show that the addition of Bi within the as-cast AZ80-2Sn alloy promotes the formation of Mg3Bi2 phase, which can refine the grains and make the eutectic phases discontinuous. The addition of 0.5 % Bi within the as-extruded AZ80-2Sn alloy, the average grain size decreases to 12 μm and the fine granular Mg17Al12 and Mg3Bi2 phases are dispersed in the α-Mg matrix. With an increase in Bi content, the Mg17Al12 and Mg3Bi2 phases become coarsened and the grain size increases. The as-extruded AZ80-2Sn-0.5 %Bi alloy has the optimal properties, and the ultimate tensile strength, yield strength and elongation are 379.6 MPa, 247.1 MPa and 14.8 %, respectively.

Mechanical and thermal expansion properties of SiCp/ZAlSi9Mg composites produced by centrifugal casting

Centrifugal casting was applied to produce cylindrical castings using SiCp/Al composite slurry, which contained 20% SiC particles. The castings comprised a particle free zone and a particle rich zone. The amount of SiC particles had a dramatic transformation from the particle rich zone to the particle free zone, and the maximum content of SiC particles in the particle rich zone reached up to 40 vol%. The ultimate tensile strength (UTS) of the as-cast SiCp / Al composites in the particle rich zone was 143 MPa, and the fracture was caused by the desorption of SiC particles from matrix alloy. The coefficient of thermal expansion (CTE) of the SiCp / Al composites in the range of 20 and 100 °C was determined as 16.67×10-6 s-1, and the experimental CTE was lower than the predicted data based on the Kerner’s model. The results show that the decrease in CTE in the case of the composites at high temperature stage can be attributed to the solute concentration of Si in Al and the plastic deformation of the matrix alloy in the composites with void architecture.

Effects of Yttrium Addition on Microstructure and Mechanical Properties of AZ80–2Sn Magnesium Alloys

Abstract The effects of Y on microstructure and mechanical properties of as-cast AZ80–2Sn magnesium alloys were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. Y addition not only changes the as-cast microstructure but also influences the mechanical properties of AZ80–2Sn alloy. Unmodified AZ80–2Sn alloys under casting state show that Mg17Al12 eutectic phase is semicontinuous and reticulated shape and distributes mainly at grain boundaries. Moreover, there are numerous Mg2Sn precipitate particles dispersing in Mg17Al12 eutectic phases. Y addition to as-cast AZ80–2Sn alloys has an important influence on the precipitation phase. But there has no obvious effect on grain refinement with Y addition. The results show that the AZ80–2Sn alloys with variable Y contents all contain Al2Y phase. By adding Y, the amount of Mg17Al12 is decreased and the dimension of that is reduced. Mg17Al12 eutectic phase turns to discontinuous, and the more disperse phases occur with the increase of Y content. The tensile tests indicate that a minor addition of Y can contribute to the formation of the dispersed small polygonal Al2Y particles and the improvement in the room-temperature strength. However, excessive Y addition leads to the coarsening of Al2Y phases, and thus results in the decline of strength and ductility.