Papers by Author: Jian Peng

Abstract: In this paper, the microstructure and mechanical property of the Al-Zn-Mg-Cu aluminum matrix composite reinforced by SiC particles with the contents of 2.5, 4.5, and 6.5wt% through vacuum casting are studied. The homogenization treatment was conducted at 465°C heat insulation for 24h. The purpose of this study is to analyze hot extrusion influence on the microstructure and hardness of the Al-Zn-Mg-Cu aluminum matrix composite. SiCp under pre-processing possesses good wetability with the analysis of Laser Particle Sizer and XRD. Metallurgical microscope, XRD, SEM and EDS is applied to analyze the microstructure of the Al-Zn-Mg-Cu aluminum matrix composite. It has proved that the hot extrusion can effectively improve the homogenization of SiCp and dissolve the second rough phases to reinforce the dispersal of CuAl₂ and MgZn₂ phase. The hardness of Al/SiCp composite rises as the increase of the SiCp content. It is shown that when the SiCp content is above 5%, its hardness obviously reinforced as well as that of the Al/SiCp composite.

Abstract: The influence of melt superheating treatment on microstructure of as cast AZ61 magnesium alloy was investigated at the melt superheating temperatures of 750°C, 800°C, 850°C, 900°C and 950°C respectively. The characteristics of dendrite spacing were analyzed and the component uniformity of the alloy was evaluated. The results showed that the melt superheating treatment could significantly refine the microstructure of the alloy. With the increase of the superheating temperature, the dendrite spacing gradually decreased. When the superheating temperature was 900°C, the primary dendrite spacing of 228.8μm and the secondary dendrite arm spacing of 11.2μm could be obtained. The concentrations of Al and Zn elements increased with the position change from the center of a dendrite to its primary dendrite spacing. With the increase of the superheating temperature, the distribution of Zn and Al in the alloy was more uniform under 850°C. The optimized superheating temperature of AZ61 alloy was 850-900°C.

Abstract: Titanium dioxide (TiO2) and silicon dioxide (SiO2) coating deposition were respectively performed by the dip coating technique on magnesium AZ31 alloy with extrusion surface finishes. The anticorrosive effect of different sol-gel coating was compared by measuring the weight loss when the samples were immerged in atmosphere, acetic acid aqueous solution with pH 5.0, distilled water with pH 6.4, aqueous 5% sodium chloride solution with pH 7.0. Morphological and structural characteristics of the coatings were analyzed by scanning electron microscopy (SEM), and semi quantitative analyses of the composition were performed by energy dispersive X-ray analysis (EDX) line scans. The results show that the anticorrosion properties of magnesium alloy with SiO2 or TiO2 are magnificently impactful in atmosphere. The anticorrosion effect of TiO2 coating is much preferable in a relatively strong acid environment.

Abstract: The mechanical properties and microstructure of the as-extruded ZM21 magnesium alloy and its modified alloy ZME210 with addition of 0.35wt% cerium were investigated with different extrusion ratios from 14 to 182 by using mechanical property test, microscopic structure quantitative analysis, SEM observation and energy spectrum analysis. The results showed that both ZM21 and ZME210 had an extrusion ratio limit for grain refining, and the grains were found to be finer with higher extrusion ratio when the ratio was not higher than the limit value. The extrusion ratio limit for the best effect for grain refining of ZME210 is lower than that of ZM21. It was found that the Ce can refine the grains effectively after hot extrusion with different extrusion ratios. The effects of Ce on the microstructure and mechanical properties were analyzed.

Abstract: The flow stress-strain curves and other information during hot compression testing of AZ61B magnesium alloy was investigated by simulated test on Gleeble-1500D thermal-mechanical simulator. The relations between Z and other characteristic value, including peak stress, peak strain and grain size, was calculated by regression analysis. The mathematical model of flow stress was introduced to predict the flow stress. The predicting values is close to the experimental values with not more than 10% error.

Abstract: With different heat treatment, the microstructure and mechanical properties of ZK60 magnesium alloy were investigated. It can be concluded that heat treatment has great effect on mechanical properties of ZK60. With artificial aging after extruding, the precipitation of the second phase from the supersaturated solid solution significantly improved mechanical properties. It can greatly increase yield strength of ZK60 alloy, while the tensile strength has little change. For the combination of solid solution strengthening and age hardening, two opposite factors must be considered. On one hand, the solid solution strengthening and the later precipitation strengthening is good for alloy’s strength; on the other hand, the properties decrease as the grains grew under high temperature for a long time during solution heating.

Abstract: The microstructures and mechanical properties of Mg-Zn-Zr-Y alloy extruded bar with different heat treatment processes were investigated, including solution treatments of 400 oC, 450 oC and 500 oC for 3 hours followed by 170 oC×24h aging treatment, and solely aging treatments of 160 oC, 180 oC for 24hours without solution after extruding. By comparing the grain size, strength and elongation of the samples, the heat treatment processes for extruded products with high strength and with medium strength were recommended.

Abstract: The hot compression deformation behavior of AZ61B magnesium alloy has been investigated by using a Gleeble-1500D thermal simulator. The samples were compressed to a reduction of 50% at two temperatures (623 and 673K) with different strain rates (0.01, 0.1 and 1s-1). The relationships between flow stress and deformation temperature were analyzed, and the deformation activation energy and stress exponent were calculated based on the experimental results. With aid of the optical microscopy, scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD) techniques, the microstructure and micro-texture of the deformed samples were characterized. The effects of the temperature and strain rates on the hot compression behavior of the AZ61B magnesium alloy have been investigated by detail analyses of the flow stress and microstructural characteristics of the deformed samples. For the 50% compressed samples, dynamic recrystallization occurred during the hot compression. The orientations of the dynamic recrystallized grains with equiaxed shape were investigated by EBSD technique. The relationships among the flow stress, dynamic recovery and recrystallization have been discussed by considering both the temperature and strain rate effects.

Abstract: The effects of homogenization on the formability for hot deformation of ZM21 wrought magnesium alloys was investigated. The alloys were produced by semi-continuous casting. Experiments including homogenizing annealing, micro-hardness testing and hot compress testing on Gleeble 1500D thermal simulator were carried out. The suggested homogenization parameters from the experimental results for ZM21 alloy is 400
C×12h.

Abstract: The properties and microstructures after different annealing processes of an as-extruded ME magnesium alloy were investigated. The results showed the better properties with the tensile strength of 205 MPa and the elongation of 19.8%, respectively, could be obtained after annealing at 623 K for 4h and air-cooled, meaning that elongation value increased 40% than that of as-extruded sheets while the strength remained almost same. The annealing hold time corresponding with the higher elongation would shorten with the increase of annealing temperature. There is legible necking on broken tensile specimen. The behavior of fracture showed obvious characteristic of ductile rupture, with many tearing edges and cavities.