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Precipitation and responding damping behavior of heat-treated AZ31 magnesium alloy

Diqing WAN , Jincheng WANG , Gaifang WANG , Lin LIN , Zhigang FENG

金属学报(英文版) doi:10.1016/S1006-7191(08)60063-0

Microstructure observation and dynamic mechanical analysis were carried out to investigate the precipitation and responding damping behaviors of AZ31 magnesium alloy. All the strain amplitude-dependent damping curves of the aged alloys are located between the curves of solutionized and as-cast alloys, although they have different critical strain amplitudes. The G-L theory is employed to explain the damping mechanism involving the interaction between the dislocation and the precipitated phase. In addition, a damping peak is observed at temperatures close to 330 ℃ for AZ31 magnesium alloy, which is related to the β-Mg17Al12 phase dissolution.

关键词: Magnesium alloys , null , null , null , null

Influence of Grain Size and Texture on the Yield Asymmetry of Mg-3Al-1Zn Alloy

S.M. Yin C.H. Wang Y.D. Diao S.D. Wu S.X. Li

材料科学技术(英文)

The yield asymmetry between compression and tension of magnesium alloy Mg-3Al-1Zn (AZ31) with different grain sizes and textures has been studied by tensile and compressive testing of as-cast, as-extruded and equal channel angular pressed (ECAPed) specimens. The significant yield asymmetry (the ratio of yield strength between compression and tension σycyt is~0.44) was found in as-extruded specimens and the corresponding microstructure evolution during deformation revealed that {1012} tensile twinning is the underlying reason for the large yield asymmetry. Strong texture and grain size are influential factors for large yield asymmetry. The separate contributions of grain size and texture on yield asymmetry were investigated.

关键词: Magnesium alloys

Surface Modification on Biodegradable Magnesium Alloys as Orthopedic Implant Materials to Improve the Bio-adaptability: A Review

Wan Peng , Tan Lili , Yang Ke

材料科学技术(英文) doi:10.1016/j.jmst.2016.05.003

Magnesium (Mg) and its alloys as a novel kind of biodegradable material have attracted much fundamental research and valuable exploration to develop its clinical application. Mg alloys degrade too fast at the early stage after implantation, thus commonly leading to some problems such as osteolysis, early fast mechanical loss, hydric bubble aggregation, gap formation between the implants and the tissue. Surface modification is one of the effective methods to control the degradation property of Mg alloys to adapt to the need of organism. Some coatings with bioactive elements have been developed, especially for the micro-arc oxidation coating, which has high adhesion strength and can be added with Ca, P, and Sr elements. Chemical deposition coating including bio-mimetic deposition coating, electro-deposition coating and chemical conversion coating can provide good anticorrosion property as well as better bioactivity with higher Ca and P content in the coating. From the biodegradation study, it can be seen that surface coating protected the Mg alloys at the early stage providing the Mg alloy substrate with lower degradation rate. The biocompatibility study showed that the surface modification could provide the cell and tissue stable and weak alkaline surface micro-environment adapting to the cell adhesion and tissue growth. The surface modification also decreased the mechanical loss at the early stage adapting to the load-bearing requirement at this stage. From the interface strength between Mg alloys implants and the surrounding tissue study, it can be seen that the surface modification improved the bio-adhesion of Mg alloys with the surrounding tissue, which is believed to be contributed to the tissue adaptability of the surface modification. Therefore, the surface modification adapts the biodegradable magnesium alloys to the need of biodegradation, biocompatibility and mechanical loss property. For the different clinical application, different surface modification methods can be provided to adapt to the clinical requirements for the Mg alloy implants.

关键词: Bio-adaptability , Coating , Biodegradable , Magnesium alloys , Orthopedic implants

Influence of Al Content on the Atmospheric Corrosion Behaviour of Magnesium-Aluminum Alloys

Ruiling Jia

材料科学技术(英文)

The influence of Al content on the Mg-Al alloys corrosion performance during sodium chloride induced atmospheric corrosion has been studied. It was found that the corrosion rate of three Mg-Al alloys was accelerated with increasing Al content. The poor corrosion resistance was attributed to the galvanic coupling between the α  phase and eutectic phase or ® phase and the formation of porous corrosion products.

关键词: Magnesium alloys

Review On Research And Development Of Magnesium Alloys

Z. Yang , J.P. Li , J.X. Zhang , G.W.Lorimer , J. Robson , null , null , null , null

金属学报(英文版)

The current research and development of magnesium alloys is summarized. Several aspects of magnesium alloys are described: cast Mg alloy, wrought Mg alloy, and novel processing. The subjects are discussed individually and recommendations for further study are listed in the final section.

关键词: Magnesium alloys , null , null

A Phase-field Model to Simulate Recrystallization in an AZ31 Mg Alloy in Comparison of Experimental Data

Mingtao WANG , B.Y.Zong , Gang WANG

材料科学技术(英文)

A model has been established to simulate the realistic spatio-temporal microstructure evolution in recrystallization of a magnesium alloy using the phase field approach. A set of rules have been proposed to decide the real physical value of all parameters in the model. The thermodynamic software THERMOCALC is applied to determine the local chemical free energy and strain energy, which is added to the free energy density of grains before recrystallization. The Arrhenius formula is used to describe boundary mobility and the activity energy is suggested with a value of zinc segregation energy at the boundary. However, the mobility constant in the formula was found out by fitting to a group of grain size measurements during recrystallization of the alloy. The boundary range is suggested to decide the gradient parameters in addition of fitting to the experimental boundary energy value. These parameter values can be regarded as a database for other similar simulations and the fitting rules can also be applied to build up databases for any other alloy systems. The simulated results show a good agreement with reported experimental measurement of the alloy at the temperatures from 300 to 400℃ for up to 100 min but not at 250℃. This implies a mechanism variation in activity energy of the boundary mobility in the alloy at low temperature.

关键词: Static recrystallization , null , null , null

Effect of the width on AZ31 sheet rolling

Qingwei DAI

金属学报(英文版)

A pyramid sheet has been used in experiments and three-dimensional finite element simulation to study the edge cracks and effects of width on AZ31 sheet under rolling. Results show that the edge cracks of Mg sheet comply with the Normalized Crockroft & Latham theory. It can be predicted by D=-0.124+0.09X-0.008X2, if D≥0, the edge cracks occur. The sheet shearing deformation at the edge brings about cracks. The strain rate changes periodically with different X. With initial width increases, the recrystallized grain size decreases. The finite element model has been validated by the experiment results.

关键词: Finite elements method , 镁合金 , 轧制 , 边裂

Application of Edge-to-edge Matching Model to Grain Refinement in Mg-Al Based Alloys

M.-X.Zhang , P.M.Kelly , M.Qian , J.A.Taylor

材料科学技术(英文)

An edge-to-edge matching model has been used to analyze the crystallographic features between Mg matrix and three commonly accepted heterogeneous nucleants for Mg grains, Al4C3, Al2CO and Al8(Mn, Fe)5. The model has predicted that Al2CO is the most effective nucleant of the three compounds assessed for Mg grains and that Al4C3 can be a nucleant for Mg grains, but it is not as effective as Al2CO. This prediction is consistent with most recent experimental results. The Al8(Mn, Fe)5 intermetallic compound is predicted to have the lowest efficiency as a grain refiner. The model may be used to provide theoretical guidance for selection of new and potent grain refiners for Mg-Al based alloys.

关键词: Crystallography , null , null , null , null

Effect of thermomechanical treatment on microstructure and hardness behavior of AZ63 magnesium alloy

H. Jafari

金属学报(英文版) doi:10.1016/S1006-7191(08)60115-5

Due to their high specifc strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two diferent thermomechanical treatments (TMTs). For the first TMT, after solution treated at the temperature of 380 ℃ for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. In the second TMT, the specimens were solution treated at the temperature of 380 ℃ for 20 h, underwent 2% cold worked and quenched in water of 0 ℃. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of the Beta-phase (Mg17Al12) in the alloy matrix. The results also reveal that, the best hardness from the first TMT was produced by specimen that was pre-aged at 150 ℃ whereas, in the second TMT, aging at 250 ℃ exhibited the best hardness values.

关键词: Thermomechanical treatment , Magnesium , Cold work , Aging , AZ63

Rheological Behavior of Semi-Solid AZ91D Alloy

Weimin MAO , Zisheng ZHEN , Shijian YAN , Xueyou ZHONG

材料科学技术(英文)

The rheological behavior and microstructure of semi-solid AZ91D was studied using a Couette type viscometer. The results show that the apparent viscosity of semi-solid AZ91D increases with the cooling rate increasing when it is continuously cooled and mechanically stirred and the empiric relation of the apparent viscosity with the cooling rate and solid fraction at shearing rate 93.7 s-1 is expressed as η=[0.66-0.63e(-ε3.01)]e (fs/0.14), and with the shearing rate and solid fraction at cooling rate 4ºC/min is shown as η=0.55e(fs/0.11- /87.59), as well as the cooling rate and shearing rate have an important effect on the microstructure of the semi-solid AZ91D alloy slurry, and decreasing the cooling rate and increasing the shearing rate are favorable to the nondendritic evolution of the primary grains.

关键词: Rheological behavior , null , null

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