Papers by Author: Ren Guo Guan

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Authors: Zhan Yong Zhao, Fu Rong Cao, Ren Guo Guan
Abstract: AZ31 magnesium alloy profiles were prepared by continuous rheo-extrusion process, and effects of solution and aging treatments on the microstructures and mechanical properties was investigated by OLYMPUS optical microscope, scanning electron microscope, energy dispersive spectroscopy device and tensile machine. The results reveal that saturated solid solution was formed in the profile at a solution temperature of 415 °C and 16 hours. During aging treatment of saturated solid solution, β-Mg17Al12 phase nucleates firstly at grain boundaries and takes on globular growth, which is mainly due to the lower interfacial energy in coherent or semi-coherent interface between β-Mg17Al12 phase and matrix phase. Lower interfacial energy is favorable to the nucleation and growth of β-Mg17Al12 phase at grain boundary. With the increase of aging time or the rise of aging temperature, β-Mg17Al12 phase precipitates out gradually from grain interior and starts to grow in globular shape. After β-Mg17Al12 phase grows to a certain extent, it grows in lamellar shape along the orientation of lower mismatch between β-Mg17Al12 phase and matrix phase. After solution at 415°C and 16h and aging at 180°C and 8h, the ultimate tensile strength and elongation to failure of the profile are 305MPa and 13%, respectively.
Authors: Ren Guo Guan, Zhan Yong Zhao, Fu Rong Cao, Hong Qian Huang, Chun Guang Dai, Qiu Sheng Zhang
Abstract: AZ31 magnesium alloy profiles were prepared by continuous rheo-extrusion, and effects of annealing temperature and time on recrystallization of AZ31 magnesium alloy were investigated. The results reveal that when the profile is annealed in the temperature range from 200°C to 300°C, the moving velocity of grain interface with different dislocation densities on both sides increases with increasing annealing temperature, which is favorable to the formation of crystallized nucleus in the region in which interface sweeps over. As a result, the time required by the accomplishment of recrystallization becomes short. After recrystallization finishes, continuous temperature rise or prolonged holding time result in grain growth. When the profile is annealed at elevated temperature, with the prolongation of holding time, the grain growth rate accelerates obviously, and hence recrystallized microstructure becomes coarse. When the profile is annealed at lower temperature, the grain growth rate becomes small, and the time required by the accomplishment of recrystallization is long, but recrystallized microstructure is fine and homogeneous. When the profile is annealed at 250°C for 4h, average recrystallized grain size is 15μm.
Authors: Zhan Yong Zhao, Ren Guo Guan, Fu Rong Cao, Li Qing Chen
Abstract: The influence of the interfacial friction on the continuous rheo-forming microstructures of magnesium alloy. The effects of interfacial friction on the microstructure evolution in magnesium alloy were investigated. It was shown that strong shear stress and internal friction occur inside the melt under the interfacial friction. In roller-shoe chamber, the growth direction of dendrites growing along the normal direction of the roller near the roller-shoe is changed under shear stress and melt resistance force. when the degree between dendrite and normal direction of roller is about 45 degree, the dendrites can be stablized and grow easily along this direction. Under an appropriate pouring temperature, with the increase of pouring temperature, there is enough room for the grains near the roller-shoe to grow, the grains are not easy to collide mutually, so the dendrites form. In roller-shoe chamber, coarse dendrites near the roller become gradually refined when they grow into the mushy region. Moreover, because dynamic friction force and shear stress of roller are stronger at the exit of the chamber, dendrites fracture and fracture layer or cracks appears. The microstructures consist of mainly rosette and spherical grains on the central position.
Authors: Ren Guo Guan, Zhan Yong Zhao, Chao Lian, Run Ze Chao, Chun Ming Liu
Abstract: In this paper, effects of the parameters of sloping plate process on microstructures of A2017 alloy were investigated, and semisolid ingot of A2017 alloy was prepared. The grain size of the ingot prepared by the wavelike sloping plate is much smaller than that prepared by the flat sloping plate. The primary grain becomes rounder and smaller with the increment of the sloping plate length. High preheating temperature of the plate reduces the nucleation rate of the melt and leads to coarse microstructure. When the casting temperature is 720°C, the sloping angle is 45°, and the wavelike plate length is between 400mm and 500mm, semisolid ingot of A2017 alloy with fine and homogeneous microstructures can be obtained. The reheated microstructure of semisolid ingot is mainly composed of spherical solid grains and the melted liquids and is suitable for semisolid forming.
Authors: Ren Guo Guan, Zhan Yong Zhao, Fu Rong Cao, Xiao Ping Sun, Qi Sheng Zhang
Abstract: Based on continuous casting and extrusion (CAXTEX) process, a semisolid metal forming process, continuous rheo-extrusion of magnesium alloy, was proposed. Effect of casting temperature on semisolid region distribution, microstructure formation and stability of forming process, as well as microstructure and mechanical properties of the AZ31 alloy fabricated by the process were investigated. Microstructure evolution from dendrite to rosette or spherical grains was observed with the application of large shearing force provided by the roll. The results indicate that semisolid region in the roll-shoe gap moves downward gradually with the increase of casting temperature, and proper casting temperature range of 730~750°C is suggested. Under the suggested casting temperature, 10×15mm sectional bar of AZ31 alloy with smooth surface and homogeneous striped microstructure has been obtained. As the product was aged for 14h at 180°C after 16h solution at 415°C, the ultimate tensile strength and elongation could reach 305MPa and 11.5%, respectively.
Authors: Ren Guo Guan, Zhan Yong Zhao, Chao Lian, Run Ze Chao, Chun Ming Liu
Abstract: AZ31 magnesium alloy sheets with a cross section of 5mm×50mm were prepared by semisolid metallic rheo-rolling device self-designed, and microstructure formation mechanism of AZ31 magnesium alloy during rheo-rolling was investigated. The results reveal that during the preparation of semisolid slurry, melt firstly nucleates heterogeneously on the surface of sloping plate. Under the vibration and shear of sloping plate, a relatively homogenous temperature field and composition filed are formed around some grains and are favorable for the direct growths of globular grains; meantime, dendrites formed under the vibration and shear are broken up and rounded gradually and better semisolid slurry is formed. During rheo-rolling, under the action of roll interfacial friction and rolling force, laminar flow shear inside the alloy is enhanced, and grains are further broken up and elongated. When the pouring temperature is 670°C, excellent AZ31 magnesium alloy sheet with good microstructure can be obtained.
Authors: Ren Guo Guan, Tong Zhao, Lin Lin Wang, Tong Cui
Abstract: New magnesium alloys with optimized chemical compositions with good biocompatibility were designed. Experimental results show that MZ alloy mainly consists of Ca2Mg5Zn5+α (Mg) and MgZn+MgZn2+Mg2Ca+Zn-Zr compounds. Ca has a strong capability for grain refinement in such alloy. Zr can refine magnesium alloy. Zn addition does not refine the solidification microstructure but plays significant strengthening role during aging treatment. The main strengthening phases of Mg-Zn-Zr alloy are γ(MgZn) and δ(Mg2Zn3). The tensile strength of MZ alloy plate aged at 170°C for 12h is 320MPa, and the elongation-to-failure is 18.4%, the alloy has a potential application of implantation biomaterial.
Authors: Hong Qian Huang, Ren Guo Guan, Tong Zhao, Zhan Yong Zhao, Fu Rong Cao
Abstract: Magnesium and magnesium alloys, as biomaterials, possess many properties that are superior to those of other metals. However, magnesium and magnesium alloys have strong chemical activity and porous and brittle surface oxide film, as degradable implantation materials, their degradation rates are too fast. Hydroxyapatite (HA) has good biocompatibility and biological activity and has become one of the replacement materials of biomedical stiff hemopoietic tissue, but the application of HA biomaterial is hindered because HA is brittle and has low strength. Integrating good mechanical properties of metallic materials with excellent biological performance of HA, the composite obtained by coating HA to the surface of metallic matrix is ideal rehabilitation material of bone tissue. In the present study, a new Mg-4.0Zn-1.0Ca-0.6Zr (wt%) was designed according to the requirements of biocompatibility. The microstructures and the mechanical properties of the new alloy were investigated by experiment. The excellent mechanical properties fully meet the service requirements of human bone tissue for mechanical property. Flat and dense hydroxyapatite coating was prepared on the surface of magnesium alloy matrix by preceding alkali heat treatment, electrodeposition and post alkali heat treatment. The Structure and constituent of HA coating and the biodegradation behavior of HA-coated Mg-4.0Zn-1.0Ca-0.6Zr (wt%) alloy were evaluated. Resuls showed that the degradation rate of HA-coated Mg-4.0Zn-1.0Ca-0.6Zr (wt%) alloy in SBF biomimetic solution decreased obviously and tended to be stable after 10 days. As degradable implantation materials, HA-coated Mg-4.0Zn-1.0Ca-0.6Zr (wt%) alloy fully meets the service requirements of human bone tissue.
Authors: Ren Guo Guan, Zhen Huan Xing, Lu Shi, Chao Wang, Yi Wang
Abstract: By using self-made vibrating wavelike sloping plate setup, semisolid billets with fine spherical or rosette grains have be prepared by semi-continuous casting, and the solidified shell on the sloping plate surface can be effectively avoided. Burst nucleation in the whole melt and dendrite fracture causes the formation of fine spherical microstructures. Under the current experimental conditions, proper casting temperature ranges of 660°C~680°C and the amplitude value of under 2mm proper are suggested. When the reheating temperature is 575°C and the holding time is 60min for AZ91D alloy, 597°C and 90min for Al-6Si-2Mg (wt-%) alloy, semisolid forging process can be successfully implemented. Thixo-forming products of two alloys are fine with smooth appearance, good microstructures and properties.
Authors: Tong Cui, Ren Guo Guan, Hai Ming Qin, Fu Lin Song
Abstract: In vitro degradation behaviour and biological properties of Mg-4.0Zn-2.0Sr alloy sheet had been studied. The results indicate that a novel biodegradable Mg-4.0Zn-2.0Sr (wt. %) alloy sheet was successfully produced using a series of metallurgical processes. The corrosion of Mg-4.0Zn-2.0Sr (wt. %) alloy sheet immersed in SBF occurred as a cyclic process: pitting corrosion →extending of pitting corrosion along grain boundary→ localized corrosion → pitting corrosion again at the new exposed surfaces and the corrosion products were found that contain HA, CaCO3 and MgOH. The change of corrosion rate of Mg-4.0Zn-2.0Sr alloy sheets immersed in SBF is unstable until the 17th day and the average corrosion rate of the alloy sheets was 1.244 g/(m2 • h) after 17 days immersing, which is slightly higher than that of Mg-4.0Zn-1.0Sr alloy sheet 1.163 g/(m2 • h). The corrosion resistance property in SBF of Mg-4.0Zn-2.0Sr alloy is slightly lower than that of Mg-4.0Zn-1.0Sr alloy, which is proved by electrochemical measurements.
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