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Peng J.,Chongqing University | Tao J.,No 59 Institute Of China Ordnance Industry | Tong X.,Chongqing University | Pan F.,Chongqing University
China Foundry | Year: 2014

For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile properties. In the present research, an heavy AZ61 alloy ingot with a diameter of 500 mm was made by semi-continuous casting. The microstructure and mechanical properties at different positions along the radial direction of the large ingot were investigated by using an optical microscope (OM), a scanning electron microscope (SEM), an energy dispersive spectroscope (EDS), and a micro-hardness tester. The results indicate that the microstructure of the AZ61 ingot is non-uniform in different locations. It changes from equiaxed to columnar grains from the center to the edge; the average grain size gradually reduces from 1,005 μm to 763 μm, the secondary dendrite arm spacing reduces from 78 μm to 50 μm, and the Mg17(Al,Zn)12 phase is also refined. The micro-hardness value increases from 55.4 HV at the center to 72.5 HV at the edge of the ingot due to the microstructure differences, and the distribution of micro-hardness at the edge of the ingot is more uniform than that in the center. The tensile properties at room temperature show little difference from the center to the edge of the ingot except that the elongation at the edge is only 3.5%, much lower than that at other areas. The fracture mechanism is ductile fracture at the center and cleavage fracture at the edge of the ingot, and at the 1/2 radius of the ingot, a mixture of ductile and cleavage fracture is present. Source

Yu X.,Chongqing University | Jiang B.,Chongqing University | Jiang B.,Chongqing Academy of Science and Technology | Yang H.,Chongqing University | And 5 more authors.
Applied Surface Science | Year: 2015

Oxidation properties of Mg-Y-Sn, Mg-Y and Mg-Sn alloys at 500 °C and corrosion behavior of the oxidized alloys were investigated. The results showed that Mg-Y-Sn and Mg-Y alloys exhibit better oxidation resistance compared with pure Mg and AZ31. Y-enriched oxide films were formed on the surfaces of Mg-Y-Sn and Mg-Y alloys after being oxidized at 500 °C for 6 h and the films are mainly composed of Y2O3 and MgO according to X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The compact surface oxide film can effectively protect the matrix from oxidizing. Simultaneously, the electrochemical corrosion and immersion tests showed that corrosion resistance of the oxidized Mg-Y-Sn and Mg-Y alloys has been enhanced compared with the initial unoxidized alloys. Y plays a decisive role in improving the protective property of the oxide film. © 2015 Elsevier B.V. All rights reserved. Source

Liang X.,Chongqing Vocational Institute of Electronic Engineering | Peng S.,No 59 Institute Of China Ordnance Industry
Jixie Gongcheng Xuebao/Journal of Mechanical Engineering | Year: 2013

The structure characteristics of one shaft part with several oversized section change steps apply to starting motor of new energy vehicles, and its technological difficulties of cold extrusion technology are analyzed, also the design main points of its cold extrusion technology on technological process, forming blank and cold extruding die are elaborated. The compound cold extrusion dies of preforming, upsetting and cold extruding are designed. The compound cold extrusion process are simulated and analyzed by using the Three-dimensional plastic finite element and the numerical simulation analysis software. The structures, sizes and parameters of forming dies are optimized and improved, the forming problems are solved by this. The purposes of reducing the cost of production and processing greatly, and energy conservation and environmental protection are attained, and a strong foundation is laid for the mass industrialization in future. © 2013 Journal of Mechanical Engineering. Source

Xie H.,Chongqing University | Xie H.,Yangtze Normal University | Jiang B.,Chongqing University | Jiang B.,Chongqing Academy of Science and Technology | And 4 more authors.
Tribology International | Year: 2016

The effects of the base lubricant with and without nanoparticles on the tribological behavior of magnesium alloy/steel contacts were investigated using a reciprocating sliding ball-on-flat tribometer. Three sets of contact conditions were used to evaluate the effect of concentration, the capacity of carrying load and the stability of the lubrication film, respectively. The results showed that the tribological properties of the base lubricant have been improved by adding the nanoparticles. As compared with the SiO2 nanolubricants, the positive effect of the MoS2 nanolubricants is more pronounced in terms of the load carrying capacity and the lubrication film stability. Mechanisms by which the nanolubricants improve tribological behaviors are discussed. © 2015 Elsevier Ltd. Source

Dai J.,Chongqing University | Jiang B.,Chongqing University | Jiang B.,Chongqing Academy of Science and Technology | Li X.,Chongqing University | And 6 more authors.
Journal of Alloys and Compounds | Year: 2014

The formation of Al-Ce intermetallic compounds (IMCs) during interdiffusion of Mg-Al/Mg-Ce diffusion couples prepared by solid-liquid contact method was investigated at 623 K, 648 K and 673 K for 24 h, 48 h and 72 h, respectively. During the whole diffusion process, Al was the dominant diffusing species, and it substituted for Mg of the Mg-Ce substrate. Five Al-Ce IMCs of Al4Ce, Al11Ce3, Al3Ce, Al2Ce and AlCe were formed via the reaction of Al and Ce. The formation of Al4Ce as the first kind of IMC was rationalized on the basis of an effective Gibbs free energy model. The activation energy for the growth of the total diffusion reaction layer was 36.6 kJ/mol. © 2014 Published by Elsevier B.V. Source

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