Hao Ran Geng

Influence of Y and Ba on Microstructure and Mechanical Properties of AZ91 Magnesium Alloys

The influences and mechanism of combined addition of Ba and Y on the structure and mechanical properties were studied in this paper. The test results showed that the moderate amount of Y refines the microstructure obviously and improves mechanical properties efficiently. The Al2Y phase improves the elevated temperature mechanical properties. The Ba addition raises the ignition temperature of AZ91 magnesium alloy obviously, a little amount of Ba addition can refine the structure and increase the mechanical properties of AZ91 magnesium alloy in the room and elevated temperature. This paper also studies the raising mechanism of ignition temperature and the strengthening and refining mechanism of Ba and Y to alloys.

Effect of Si3N4 on Properties of Aluminum Borate Whisker/Aluminum Phosphates Ceramic

Aluminum Borate Whisker/Aluminum Phosphates composites (ABW/AP) added Si3N4 were prepared with pressure sintering technique. The influence of Si3N4 on the mechanical properties and dielectric properties were investigated. After sintered at 1050°C for 1h, the results showed that the flexural strength of the composites with 5wt% Si3N4 addition reach 167.29MPa,the dielectric constant (ε) and loss tangent (tanδ) of the composites are 2.99 and 0.0089 at 10GHz. The testing results was discussed.

Study on Mechanical Properties and Physical Properties of Copper Based Electrical Contact Materials Reinforced by CNT

A new method of carbon nanotube with electroless plating of nickel is proposed. It is shown that in a certain condition, the compacted and well-distributed coating of nickel is obtained without the process of sensitization and activation. Upon the surface treatment of the carbon nanotube, the CNT-consolidated composites for copper-based electrical contact have been made in the way of powder metallurgy. Some important mechanical properties and physical properties, including sliding wear property, electrical conductivity and fusion resistance, were investigated. The experiment results showed that Carbon nanotube inside the composite was uniformly distributed and a proper addition of CNT effectively improves the comprehensive property of the composites. When the carbon nanotube takes up 4vol. % in the material, it is highly effective in improving its sliding wear property and fusion resistance; though its electrical conductivity drops. Its overall properties meet the requirements of electrical contact materials

Effects of Heat Treatment on Microstructure and Properties of AZ91D Magnesium Alloy

The microstructure, hardness and corrosion resistance of AZ91D alloy were investigated under different solution treatments and artificial aging conditions.When ascast AZ91D alloy was heat treated at 415°C by solution treatmentfor 12 h and artificially aged at 200°C, the volume fraction of precipitates increased with the aging time up to 10 h.When ascast AZ91D alloy was treated at 430°C by solution treatment for 12 h and artificially aged at 200°C for 10h, the volume fraction of precipitates reached a peak value.The results of the corrosion test showed that a high corrosion resisting of the second phase precipitates was beneficial to improving the strength and hardness. Solution treatment at 445°C temperature for 12 h destroied the consecutiveness of β-Mg17Al12 phases.

Grain Refinement of Zn-50Al Alloy through the Addition of Zn-Al-Ti-C Master Alloy

In this paper, two types of Zn-Al-Ti-C master alloy with different Ti/C ratios were produced throug a two-step method, characterized by XRD and SEM, and their refinement behaviors and mechanism in Zn-50Al alloy were studied. Both of the master alloys remarkably reduced the size of α-Al grains, impeded the dendritic growth and promote the equiaxed growth of α-Al grains in Zn-50wt.%Al alloy. The master alloy containing both TiC and dditional Ti in the Zn-Al matrix was found to have higher refinement ability than that containg only TiC. The refinement effect of both master alloys was greatly enhanced as the solidification temperature of Zn-50Al melt decreases. TiC particles were observed to be located at the center of α-Al grains and act as the nucleating substrate for α-Al. The decrease of melt solidification temperature and the presence of additional Ti atoms in the Zn-50Al melt cause higher melt supercooling, which further elevate the nucleating rate of α-Al grains on TiC particles and promote the equiaxed growth of α-Al grains.

Fabrication and Characterization of Nanoscale Porous Copper Film

Cu-38Zn thin film (wt %) was deposited on the unheated microscope glass at the nanometer scale by DC magnetron sputtering. Subsequently, the nanocrystalline films were dealloyed in H2SO4 aqueous solution etching of zinc component, resulting in the formation of nanoscale porous copper film with average porous diameter of approximately 94 nm. The films microstructure and element composition were characterized by X-ray diffraction and scanning electron microscopy. The experimental results show that Cu-38Zn films are quasi-amorphous structure, porous copper film with different porous sizes is prepared by selective dissolution of zinc atoms from a nanocrystalline dual-phase film under free corrosion conditions, the grain size of the Cu-Zn films has an important effect on the dealloying process and the microstructures of the nanoscale copper films.

Preparation of the Multiple Rare Earth Conversion Membrane Based on the Magnesium Alloy AZ91 and their Corrosion Resistance Performance

Chemical membrane coating method was adopted for AZ91 magnesium alloy surface to explore the preparation method for cerium (Ce) conversion membrane, lanthanum (La) conversion membrane and double rare earth conversion membrane. The methods such as Scanning Electron Microscope (SEM), Energy Spectrometer (EDS) and X-ray Crystallography (XRD) were introduced for the detection of conversion membrane. The experiment results revealed that the corrosion resistance of double rare earth conversion membrane would get strengthened firstly, and degraded later along with the prolongation of conversion time. The corrosion resistance from low to high of conversion membrane is cerium (Ce) conversion membrane < lanthanum (La) conversion membrane < double rare earth conversion membrane. Therefore, double rare earth conversion membrane is more effective to improve the corrosion resistance for magnesium alloy and its corrosion resistance is better than that of single rare earth conversion membrane.

Anomalous Change of the Electrical Resistivity and the Structure of Sn Melt with Temperature

On the basis of measuring the electrical resistivity of Sn melt and referring to analysis of high temperature XRD, the change of electrical resistivity and structure for Sn melt with temperature was carried out. The results show that there is discontinuous change of electrical resistivity for Sn melt with the temperature in the metrical temperature range. There is a correlation between the electrical resistivity change and the structure change of Sn melt. The correlation radius and the fluid cluster size of Sn melt decrease with the increasing of temperature, so that the electrical resistivity of Sn melt increases. But there is an anomalous change in the vicinity 673K, it results in a discontinuous change in electrical resistivity of Sn melt.

Microstructure and Mechanical Behaviors of AZ91 Magnesium Alloy with Thermal Rate Treatment Technique

Microstructure and mechanical behaviors of AZ91 cast magnesium alloys with melt superheating and thermal rate treatment technique were studied. Alloy grains thicken at 820°C and refine at 870°C when they contains Mn element and the crucible had no coating on the internal surface. Moreover, the strengthening γ phase is more dispersive and uniform at 870°C. Thermal rate treatment significantly improved the microstructure, mechanical behaviors and casting quality of AZ91 alloy as microstructure of AZ91 alloy reserves some characteristics of the high temperature melt.

Abnormal Changes of the Rheological Property of Sn Melt Induced by Temperature

Rheological behaviors of Sn melt were systematically studied using a comprehensive measurement instrument designed in our lab. Structure of the Sn melt was analyzed by a liquid XRD technology. The result indicates that in the vicinity of 400°C, 800°C and 1200°C, the melt is a non-Newtonian fluid, while it is a Newtonian fluid within the temperature ranges of 400—800°C, 800—1200°C and over 1200°C. It is evidenced that the rheological property of the Sn melt is correlated to the changes in the melt structure. When the temperature is raised, the correlation radius rc, the coordination number Ns decreases, while in the vicinity of 400°C and 800°C, the correlation radius rc and the coordination number Ns of the Sn melt all show discontinuous changes.