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Research on semi-solid thixoforming process of az91d magnesium alloy brackets for generators in JH70-type motorbikes

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Rare Metals 2005年第4期24卷 381-391页

作者： WANG Kai LIU Changming HAN Zhaotang CAO Jianyong ZHANG Zonghe College of Mechanical Engineering Chongqing University Chongqing 400044 China Chongqing magnesium Industry Ltd. Co. Chongqing 401326 China

The investment on semi-solid die casting processes of az91d magnesium alloy brackets for generators in JH70-type motorbikes is introduced. The processes of low super-heat and cooling slope for the preparation of billets with non-dendritic microstructure, the remelting of billets for thixoforming and the parameters in the process of semi-sohd thixoforming have been researched. The results show that primary billets with non-dendritical structures can be prepared by forming great amount of nuclei in melt via the process of low super heat. By optimizing the remelting process through adjusting the current of the induced equipment, semi-solid billets with a structure of spherical grains were obtained from the primary billets with non-dendritical structure. The range of 580℃ to 583℃ is the proper remelting temperatures by which the billets have an expected thixotropy and can be transferred to a die-casting machine. The optimized parameters of semi-solid forming in a die-casting machine are as follows： the area of the ingate in the die is 383.5 mm^2, the speed of the pierce of the machine 5 m/s, the shot pressure of the pierce 75 MPa, and the maintenance pressure of the pierce 350 MPa. The castings of brackets for supporting generators in JH70 type motorbikes were formed by adopting the optimized processes and parameters mentioned above.

关键词： semi-solid thixoforming az91d magnesium alloy bracket motorbike

Cerium-Based Sealing Treatment of Mg–Al Hydrotalcite Film on az91d magnesium alloy

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Acta Metallurgica Sinica(English Letters) 2016年第11期29卷 993-1000页

作者： Qiang-Sheng dong Zhi-Xin Ba Zhang-Zhong Wang Juan Kuang Zheng-Yang Cai Chen Yuan School of Materials Science and Engineering Nanjing　Institute of Technology Nanjing 211167 China Jiangsu Key Laboratory of Advanced Structural Materialsand Application Technology Nanjing 211167 China

An environment-friendly cerium-based sealing treatment was developed to improve the surface integrity and corrosion resistance of Mg–Al hydrotalcite film on az91d magnesium alloy. The cerium dioxide was generated through three stages namely nucleation, growth and dissolution, modifying the surface of az91d Mg alloy, and the hydrotalcite film became integral after being treated for 30 min. The results of polarization curves showed that the anti-corrosive performance of the hydrotalcite film was enhanced by the sealing treatment. Moreover, the immersion tests and electrochemical impedance spectrum measurements also demonstrated that the sealed hydrotalcite film provided a longer-term protection of magnesium alloy from corrosion as compared to the unsealed one.

关键词： az91d magnesium alloy Mg-Al hydrotalcite film Sealing treatment Ce-containing solution Corrosion resistance

Hot deformation behavior and microstructure evolution of as-cast az91d magnesium alloy without pre-homogenization treatment

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Rare Metals 2013年第4期32卷 338-346页

作者： Yan Xu Lian-Xi Hu Yu Sun School of Materials Science and Engineering Harbin Institute of Technology School of Mechanical Engineering Beihua University

The deformation behavior and the microstruc-ture evolution of as-cast az91d magnesium alloy without pre-homogenization treatment were systematically inves-tigated. The flow stress behavior was studied by com-pression tests in strain rate range of 0.001-1.000 s^-1 and deformation temperature range of 220-380 ℃ with a maximum deformation strain of 60 %. The dependence of flow stress on deformation temperature and strain rate was described by hyperbolic sine constitutive equation. Through regression analysis, the average apparent activa- tion energy and coefficient of strain rate sensitivity were estimated to be 181.98 ***^-1 and 0.14, respectively. The results also reveal that the variation of peak stress depends on strain rate and deformation temperature. Microstructure observation shows that, at temperatures higher than 300 ℃ and strain rates lower than 0.01 s^-1, dRX developed extensively at the grain boundaries and in the core of coarse grains, resulting in a more homogeneous microstructure. Furthermore, the effects of strain, defor-mation temperature, strain rate, and eutectic β phase on the microstructure evolution of as-cast az91d magnesium alloy were discussed.

关键词： az91d magnesium alloy Isothermalcompression Constitutive equation Peak stress Microstructure evolution

Rheo-diecasting of az91d magnesium alloy by taper barrel rheomoulding process

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Transactions of Nonferrous Metals Society of China 2010年第6期20卷 966-972页

作者：杨柳青康永林张帆丁瑞华李炯 School of Materials Science and Engineering University of Science and Technology Beijing State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing School of Materials Science and Engineering University of Science and Technology Beijing Beijing Guangling Jinghua Science and Technology Co. Ltd.

A self-developed taper barrel rheomoulding(TBR)machine was introduced,and the rheo-diecasting process was implemented by combining TBR machine with the high pressure die casting(HPdC)*** characteristics of the rheo-diecasting components were investigated at different rotation *** characteristics and microstructural evolution of the semi-solid slurry during the rheo-diecasting process were analyzed and the mechanical properties of the rheo-diecasting components were *** experimental results show that the process is able to obtain such components in which the primaryα-Mg particles are fine,nearly spherical and uniformly distributed in the *** the rotation speed of internal taper barrel is 700 r/min,the primaryα-Mg particles get a mean diameter of about 45μm and a shape factor of about *** magnesium alloy melt has complex stirring-fixed flow characteristics when flowing in TBR *** with conventional die-casing process,the rheo-diecasting process can improve the mechanical properties of components;especially,the elongation is improved by 80%.

关键词： az91d magnesium alloy rheo-diecasting microstructure flow characteristics mechanical properties

Effect of extrusion ratio on microstructure and mechanical properties of az91d magnesium alloy recycled from scraps by hot extrusion

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Transactions of Nonferrous Metals Society of China 2010年第6期20卷 987-991页

作者：胡茂良吉泽升陈晓瑜 College of Materials Science and Engineering Harbin University of Science and Technology

A method for recycling az91d magnesium alloy scraps directly by hot extrusion was *** microstructural analyses were performed using the techniques of optical microscopy,scanning electron microscopy(SEM)and energy dispersive spectroscopy(EdS).Microstructural observations revealed that all the recycled specimens consisted of fine grains due to the dynamic *** main strengthening mechanism of the recycled specimen was grain refinement strengthening and homogeneous distribution of oxide *** interfaces of individual scraps of extruded materials were not identified when the scraps were extruded with the extrusion ratio of *** layers of the scraps were broken into pieces by high compressive and shear forces under the extrusion ratio of *** ultimate tensile strength and elongation to failure increased with increasing the extrusion *** specimens with the extrusion ratio of 40:1 showed higher ultimate tensile strength of 342.61 MPa and higher elongation to failure of 11.32%,compared with those of the cast specimen.

关键词： extrusion ratio az91d magnesium alloy scraps mechanical property microstructure

Organic-magnesium complex conversion coating on az91d magnesium alloy

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Transactions of Nonferrous Metals Society of China 2010年第B7期20卷 643-647页

作者：陈晓明李光玉连建设 Key Laboratory of Automobile Materials Ministry of EducationJilin University College of Materials Science and Engineering Jilin University

An organic-magnesium complex conversion(OMCC)coating on az91d magnesium alloy was obtained by treating in a solution containing organic ***,FESEM and XPS were used to examine the surface morphology,thickness and structure of the conversion *** results show that the continuous and uniform conversion coating is deposited on az91d alloy and the main component of the coatings is organic compound containing benzene ring,which forms a chemical bond with *** polarization measurement and salt spray test show that the corrosion resistance of the conversion coating is much higher than that of traditional chromate conversion coating.

关键词： chromium-free conversion coating organic compound corrosion XPS az91d magnesium alloy

Compressive deformation of Semi-Solid az91d magnesium alloy

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Journal of Materials Science & Technology 2005年第4期21卷 505-509页

作者： Weimin MAO Aimei YIN Xueyou ZHONG Foundry Institute School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083China

The compression tests of semi-solid az91d Mg alloy have been conducted on a parallel-plate viscometer. The results are as follows. With increasing the compression temperature, the deformation rate or the strain rate of the specimens rises, but the compressive stress continuously decreases; the deformation strain is obviously linear with the compressive stress and independent on compression temperature under a given compression load. In the wake of the compression load being added, the compressive strain increases but the compressive stress decreases clearly; the deformation strain is obviously linear with the compressive stress under different compression load. The mathematical apparent viscosity model about the semi-solid compressed az91d Mg alloy has been established, i.e ηapp =2004.2exp（15.61 fs）γ^***^-1.3511

关键词： Semi-solid az91d magnesium alloy Compressive deformation

Effect of Holding Time on Thixotropic Fluidity of Semi-solid az91d magnesium alloy

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Journal of Materials Science & Technology 2007年第2期23卷 247-252页

作者： Zesheng JI Maoliang HU Xiaoping ZHENG College of Material Science and Engineering Harbin University of Science and Technology Harbin 150040 China

To investigate the thixotropic fluidities, microstructures and mechanical properties of semi-solid az91d magnesium alloy during reheating, a self-made die set with channels of different sizes were used. The results show that critical forming forces and maximal forming forces could be obtained and related to the holding times in the semi-solid forming process. In the holding time of 0-2700 s, with increasing the holding time, maximal forming force decreased sharply and critical forming force decreased slowly. In the whole thixotropic flowing process, the filling-in was steady and the surface fineness was good. The forming force increased when the slurry changed the flowing direction or flowed from the big-diameter chamber to the small-diameter one. The tensile strength and elongation to failure of the sample after holding time for 2700 s, compared to as-cast sample, are increased by approximately 42.7% and 180%, respectively, and the fractured surfaces presented dimple-like pattern.

关键词： az91d magnesium alloy Semi-solid Thixotropic fluidity Microstructure

Effect of RE on the ignition-proof, microstructure and properties of az91d magnesium alloy

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Journal of University of Science and Technology Beijing 2005年第6期12卷 540-544页

作者： Zhihong Chen Xueping Ren Ya Zhang Materials Science and Engineering School University of Science and Technology Beijing Beijing 100083 China

The magnesium alloy is prone to burn during die-casting, which limits its applications severely, so the effect of adding rare earth （RE） on the ignition-proof of az91d Mg alloy is studied. The results indicate that the addition of mischmetal RE elements has a remarkable influence on the ignition-proof property of the magnesium alloy. It is found that the ignition temperature of the magnesium alloy can be greatly raised by adding a proper amount of RE. When the amount is 0.1wt%, the ignition temperature reaches 877℃ which is 206℃ higher than that of az91d without RE and the mechanical properties of the alloy are also improved, However, the amount of RE must be properly controlled because too much RE would induce grain coarsening and reduce the mechanical properties.

关键词： az91d magnesium alloy ignition-proof RE mechanical properties microstructure