Papers by Author: Ai Qin Wang

Abstract: In this paper ,the WC and high-Cr Cast Iron layer were obtained on the surface of ZG30Cr steel by casting-penetrating process, the organization and wear properties of penetrating layer were studied.The results show that the layer is dense, without pores, slag and other defects, the penetrating layer and substrate are metallurgical bonding. When 30 %WC and 70 % Cr-Fe with 100～120 mesh are added to permeability agent ,the penetrating layer has the best wear resistance, is 6.8 times the matrix materials. Keywords: The layer structure; Particle size; Wear resistance

Abstract: The laser welding of particle reinforced SiCp/ZC71 magnesium matrix composite was carried out using a Nd:YAG laser welding experimental system. The mechanical properties of welded joint was studied by tensile test and the morphology of tensile fracture, microstructure as well ingredient of welded joint were observed by SEM. The results show that welding technology for composites is harsher. SiC particles distributed uniformly and the white magnesium intermetallic compound dots disappeared in the laser welded seam because the precipitation of the magnesium intermetallic compounds was prohibited owing to the rapid solidification and cooling of the laser-welded seam.. There is no evident heat affect zone in the weld seams；The mechanical properties of welded joint are worse than those of matrix metal. The weld zone is the weakest part in welded joint. The much lower tensile strength of the seam compared to the tensile strength of the ZC71/SiCp substrate attributed to the surface roughness of the seams and some solidification micron-sized pores (especially between SiC particles and magnesium alloy matrix)，The fracture morphology of welded joint indicated a brittle cleavage fracture.

Abstract: This work aims to eliminate contamination of the surface of crucible with silicon carbide during fusion preparation sample of the X-ray fluorescence analysis used in relation to electroless Ni–P plating process on the surface of SiC crucible in the alkaline bath. The structure, morphology and component of the coated layers were clarified by means of XRD, SEM and EDAX. Also, the electrochemical measurements was carried out to characterize the reduction mechanism of Ni deposition. The bath compositions were nickel sulfate 20 g/L, sodium hypophosphite 30 g/L, sodium citrate 10 g/L，ammonium chloride 20 g/L, containing a mixed additives of thiourea, sodium lauryl sulfate and coumarin. The thickness of coating was 3.47 μm after plating for 15 min from this bath at 318 K. The coating is relatively dense and smooth and has a nodular surface morphology. The uniform Ni–P film is a mixture of microcrystalline of Ni₅P₄ and crystalline phases of Ni in the alkaline bath, with the components of 4.74%P and 95.26%Ni. The nickel deposition reaction occurs at -1.07 V appropriately with the peak current density of 32 mA/cm² and the electrochemical deposition of nickel is mainly controlled by the electrochemical process.

Abstract: Mn18Cr2 steel is one of austenitic deformation strengthening steel. The existing form of TiN and its influence on the austenitic structure in the steel by adding small amounts of TiN nanoparticles are discussed in this study, which may provide some advices to explore new way to strengthen high manganese steel. The microstructures of Mn18Cr2 steel added small amounts of TiN nanoparticles are observed by Transmission Electron Microscopy (TEM). The results show that TiN nanoparticles exist in austenite and there have a very good match interface between the two phases, the crystal face relationship are {220}_γ//{220}_N, {422}_γ//{422}_N, (111)_γ //(200)_N , orientation relationship are <110>_γ// <110>_N, <211>_γ//<211>_N, [112]_γ // [011]_N, moreover, the relationship of (111)_γ and (200)_N is not only parallel but also coherent. Meanwhile, there are many high density dislocations, a small amount of stacking faults, twins and ε-martensite in the austenite due to the role of TiN nanoparticles.

Abstract: The WC and high-Cr cast iron layer were obtained on the surface of ZG30 steel by infiltration casting process, so the surface alloying of ZG30 steel was realized. The microstructures and phase structures of penetrating layer were studied by SEM, TEM, XRD, the hardness of the test material was measured by the hardness tester, and the wear resistance was tested by wear test machine. The mechanism of alloyed layer forming was analyzed. The effects of WC contents on the wear resistance of alloyed layer were studied. The results show that the layer is dense, without pores, slag and other defects, the thickness of the alloyed layer is about 6-7mm, and the penetrating layer and matrix are metallurgical bonding. The maximum hardness of the alloyed layer surface is 820Hv. When the content of WC is 15%, the penetrating layer has the highest wear resistance which is 18.8 times as high as the matrix.

Abstract: The elastic-plastic finite element mechanical model of hypereutectic Al-Si alloy was established based on ANSYS software. When the Si particles were circle, trapezium, rectangle or triangle, the microstress of Al-Si alloy under the external load were simulated. When the size of Si particles changed from 25μm to 45μm, the stress of Si particles and matrix interface was calculated. The effects of morphology and size of Si particles and loads on micro-mechanics characteristic of alloy were analyzed. The results showed that: under the same load, triangle or wedge angle Si particles make the biggest stress in the matrix, trapezoidal particles make the second and the spherical particles make the smallest. With the increase of the load, the stress and the stress concentration of Si particles in the matrix was increased, the stress of wedge angle particle increases remarkably, but the stress of spherical particles increases slowly. With the increase of the size of Si particles, the stress and the stress concentration of Si particles in matrix are increased.

Abstract: In the present work, rapidly solidified Al-21Si-0.8Mg-1.5Cu-0.5Mn alloys strips was prepared by melt-spinning method. The microstructures, phase and morphology characteristics of the experimental alloy were characterized by means of scanning electron microscopy, transmission electric microscopy. The results show that the microstructures are changed obviously compared with conventional condition. The nucleation and growth of primary silicon are suppressed and primary silicon can not deposited, meanwhile, α-Al phase is nucleated which prior to eutectic. The microstructures of the rapidly solidified alloys are composed of primary micro-nanostructure α phase and feather-needles-like (α+Si) eutectic which set in the α phase. The mechanism of formation for microstructures of melt-spinning Al-Si alloy have also been discussed.

Abstract: A rapid-solidified hypereutectic Al-21Si-0.8Mg-1.5Cu-0.5Mn alloys strips has been prepared by single roller melt-spinning. The effects of solution technology on the microstructures and properties of the strips have been investigated by SEM, TEM. The results showed that the nucleation and growth of primary silicon are suppressed and α-Al is nucleated which prior to eutectic. The Cu, Mg and Mn are all supersaturated solution in α-Al. The major part of Si solution in α-Al, and the rest are precipitated by the micro-nanocrystals eutectic silicon. The metastable microstructures of micro-nanocrystals hypoeutectic are formed. And in the solution process, Si are precipitated from the matrix and gradually aggregate up to form small particles distributing in the matrix with the heating time. At 480°C for 100 minutes followed by quenching in water and a natural aging for 96h, the finer and more roundness of silicon particle and the maximum Vickers hardness are formed.

Abstract: Rapidly solidified hypereutectic Al-21Si was prepared by the single roller melt-spinning technique. The microstructure morphology characteristics and phase structures of the alloy were characterized using SEM, TEM and XRD technique. The results showed that the grains were refined and the micro-nano composite structures were formed under rapid solidification. The microstructure of the Al-21Si alloy was composed of micro-nanostructured α-Al phase and feather-needle-like eutectic α-Al+β-Si phase. The α-Al phase was the leading phase in the eutectic α+Si phase. The nucleation and growth of primary silicon are suppressed and primary silicon could not be precipitated. The hypereutectic Al-21Si alloy showed the hypoeutectic solidification microstructure. Wear resistance was improved obviously when the rapidly solidified and was five times higher than that of the traditional casting alloys.

Abstract: The wear resistance, corrosion resistance, high temperature resistance layers were prepared on the surface of ductile iron via laser alloying process, using the mixed ponder of sub-micron carbides power as starting materials. The microstructures of the different laser alloying layers were characterized by XRD, SEM, EDS, TEM. The microhardness and wear resisitance of the laser alloying layers were examined. The results reveal that the flat alloyed coating combines metallurgically with the substrate. the laser area was composed by alloyed zone ,heat-affected zone and matrix zone. The alloyed zone was composed mainly by ledeburite and carbide, while martensite and retained austenite were contained in the heat affected zone, there is no significant change in the Matrix zone. Under conditions that the laser power, spot diameter remain unchanged, with in 400 ~ 1000 mm/min scanning speed, the hardness of alloyed coating increases with increasing scanning speed. The weightlessness of the alloyed samples under the dry sliding friction is one-sixteenth of ductile iron. The wear resisitance of the alloyed coating has improved significantly.