Bo Gao

Effect of erbium on properties and microstructure of Al-Si eutectic alloy

Eutectic Al-12.6 wt.%Si alloys with various contents of the rare earth element Er were prepared by the conventional casting technique. The effect of Er on the microstructure and properties of the eutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as the friction and wear tests. It was found that the addition of Er obviously improved the anti-wear properties, and reduced the friction coefficient of the alloys. The appropriate addition of Er would change the size and shape of the eutectic silicon, and thereby refine the microstructure of the Al-Si alloys. The refinement mechanism was also discussed.

Effect of neodymium on primary silicon and mechanical properties of hypereutectic Al-15%Si alloy

Abstract The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase. So, optical microscopy (OM) and X-ray diffraction (XRD) were adopted to study affection of Nd on primary silicon of hypereutectic Al-15%Si alloy in this paper. The results of OM showed that pure Nd could effectively refine primary silicon of hypereutectic Al-15%Si alloy. When Nd addition was 0.3%, the average size of primary silicon reduced from 20-40 μm of initial sample to 10-20 μm of modified sample. XRD pattern showed that no new phase was formed after Nd modification. The results of mechanical properties test showed that whole properties of modified samples were significantly improved. Tensile strength increased about 32.6% from 147 MPa to 195 MPa. Elongation was increased about 160% from 1.0% to 2.6%. The improvement of mechanical properties should attribute to primary silicon refinement after modification.

Study on nanostructures induced by high-current pulsed electron beam

Four techniques using high-current pulsed electron beam (HCPEB) were proposed to obtain surface nanostructure of metal and alloys. The first method involves the distribution of several fine Mg nanoparticles on the top surface of treated samples by evaporation of pure Mg with low boiling point. The second technique uses superfast heating, melting, and cooling induced by HCPEB irradiation to refine the primary phase or the second phase in alloys to nanosized uniform distributed phases in the matrix, such as the quasicrystal phase Mg30Zn60Y10 in the quasicrystal alloy Mg67Zn30Y3. The third technique involves the refinement of eutectic silicon phase in hypereutectic Al-15Si alloys to fine particles with the size of several nanometers through solid solution and precipitation refinement. Finally, in the deformation zone induced by HCPEB irradiation, the grain size can be refined to several hundred nanometers, such as the grain size of the hypereutectic Al-15Si alloys in the deformation zone, which can reach ∼400nm after HCPEB treatment for 25 pulses. Therefore, HCPEB technology is an efficient way to obtain surface nanostructure.

Effect of CaO on Fluorine in the Decomposition of REFCO3

Abstract Influence of CaO on thermal decomposition of REFCO 3 was studied. The results showed that CaO did not affect significantly the decomposition ratio of REFCO 3 . The XRD experiment showed that there was a great deal of CaF 2 in the roasting production, the gas chromatographic analysis on the gas of REFCO 3 decomposed, and the 70% content of fluorine in the gas of REFCO 3 added 15% CaO was reduced. CaO could absorb the fluorine from the decomposition of REFCO 3 , and the environmental pollution of the fluorine was greatly alleviated.

Influence of High Current Pulsed Electron Beam (HCPEB) Treatment on Wear Resistance of Hypereutectic Al-17.5Si and Al-20Si Alloys

The paper reports an analysis of the effect of high current pulsed electron beam(HCPEB) on microstructure transformations and wear resistance of hypereutectic Al-Si alloys. HCPEB treatment with 2.5 J /cm2 energy density leads to the formation of “halo” centered on primary Si, composition homogeneity, the formation of supersaturated solid solution of Al and grain refinement of top melted surface layer. The wear resistance of 15 pulse-treated Al-17.5Si and Al-20Si alloys is drastically improved by a factor of 6.5 and 2, respectively. The increase of hardness in modified surface layer has a positive effect on wear of hypereutectic Al-Si alloys.

Study on the Corrosion Mechanism of Zn-5Al-0.5Mg-0.08Si Coating

A new type of hot-dip Zn-5Al-0.5Mg-0.08Si and Zn-5Al alloy coatings was performed on the cold rolled common steel. The hot-dip process was executed by self-made hot-dip galvanising simulator. SEM and EDS test results demonstrated that Mg was mainly distributed in crystal boundaries. XRD test results showed that the corrosion product of Zn-5Al-0.5Mg-0.08Si alloy coating was almost Zn5(OH)8C12⋅H2O. The features of Zn5(OH)8C12⋅H2O are low electric conductivity, insolubility and good adhesion.The corrosion resistance of alloy-coated steels was detected by neutral salt spray test. The microstructural characterization of the coating surface after neutral salt spray test and removing the corrosion products revealed that the corrosion process of Zn-5Al-0.5Mg-0.08Si coating was uniform and the coating surface was almost flat. As a result, the corrosion resistance of Zn-5Al-0.5Mg-0.08Si coating has a remarkable improvement with a factor of 9.2 compared with that of Zn-5Al coating.

The Corrosion Mechanism of Zn-5%Al-0.3%Mg Coating

A new hot dip Zn-5%Al-0.3%Mg alloy coating was performed on cold rolled common steel. The hot-dip process was executed by self-made hot dip galvanising simulator (China patent, No.201010160353). The corrosion resistance of alloy-coated steels was detected by neutral salt spray test . SEM and EDS test results demonstrate that Mg is mainly distributed in the crystal boundary. XRD test results shows corrosion product of Zn-5%Al-0.3%Mg alloy coating is mainly Zn5(OH)8Cl2•H2O. The characteristic of Zn5 (OH)8Cl2•H2O is dense and insoluble, so it is protective. In order to study the anticorrosion mechanism, all the tests of the Zn-5%Al-0.3%Mg alloy were carried out with Zn-5%Al coating together.

The Effects of RE and Si on the Thickness and Cross Section Morphology of Zn-6Al-3Mg Alloy Coating

Hot-dip galvanized steels are widely used in modern industry. The corrosion resistance and formability of them are closely related to the thickness and cross section microstructure of the hot-dip coating. In this paper, the effects of Si and RE on the thickness of Zn-6Al-3Mg alloy coating (ZAM) were investigated. Steel sheets were coated by using an experimental hot-dip galvanizing simulator. The thickness and cross section microstructure of ZAM coating alloyed with different content of Si and RE were characterized by using optical microscope and SEM, and element distribution was study by EDS. The results demonstrated that the reaction between Al from the bath and Fe form the steel sheets was suppressed by the addition of 0.1 wt. % Si to the Zn-6Al-3Mg bath, and the addition of RE effectively decreased the thickness of coating by means of improving the flowing property of the zinc alloy bath. Under the combined effects of Si and RE, the thickness of Zn-6Al-3Mg alloy coating went down from 33 μm to 10.1 μm.

Effect of Nd on Structure and Properties of Hypereutectic Al-Si Alloys

The influence of Nd on structure and properties of hypereutectic Al-Si alloys (Al-17.5%Si, Al-25%Si) was investigated in this paper. For Al-17.5%Si alloy, there is no obvious variation in morphology of primary Si before and after Nd modification, but the average size of primary Si is decreased from 34.73µm to 23.39µm after 0.3%Nd modification. Compared with initial sample, the tensile strength and yield strength of 0.3%Nd-modified sample are increased by 11.6% and 1.5%, and wear resistance of Al-17.5%Si alloy is enhanced to a factor of 2.1 after 0.3%Nd modification. However, for Al-25%Si alloy, the tensile strength and yield strength of 0.3%Nd-modified sample are respectively improved by 22.1% and 9.5% as compared to initial sample. Meanwhile, wear resistance of modified sample is improved to a factor of 3 relative to initial sample. The property improvement of two alloys can be attributed to the change in morphology and size of primary Si after Nd modification.

Research on Mechanism of Polymer Inhibiting Secondary Reaction in Clinker Leaching Process

In this paper, the mechanism of polymer inhibiting secondary reaction in clinker leaching process was studied by IR spectrum of leaching residue obtained from the reaction of dicalcium silicate with sodium aluminate solution and the adsorption law of polymer AY and PEG on the surface of dicalcium silicate. The results indicated that the main adsorption mode of polymer AY and PEG were chemisorptions and physical adsorption respectively. The mechanism of decreasing the occurrence of secondary reaction is encapsulating surface of dicalcium silicate by AY and PEG. The adsorption mode of polymer AY on dicalcium silicate particles was single molecule adsorption and its adsorption isotherm was the typical “L” type. It accorded with Langmuin equation, and the adsorption free energy EAY was 57.89kJ.mol-1. The adsorption mode of polymer PEG on dicalcium silicate particles was multimolecular adsorption and its adsorption isotherm was the typical “S” type. It accorded with Freundlich equation and the adsorption free energy EPEG was 1.63kJ.mol-1.