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Intensive melt shearing was applied to the commercial AZ91D alloy melt to investigate its effects on grain refinement. Alloy melts with and without melt shearing were also filtered using a pressurized filtration technique to concentrate the potential nucleating particles for electron microscopic examination. The results showed that intensive melt shearing resulted in significant refinement of both the Al8Mn5 intermetallics and the primary α-Mg phase in the as-cast AZ91D alloy, and that this grain-refining effect is insensitive to the superheat and can persist even after prolonged isothermal holding. The pressurized filtration experiments showed for the first time that oxide films and skins consist of nano-sized MgO particles populated densely in a liquid matrix. Intensive melt shearing can effectively disperse such MgO particles throughout the alloy melt. The HRTEM investigation and detailed crystallographic analysis confirmed that dispersed MgO particles act as potent heterogeneous nucleation sites for both the Al8Mn5 and α-Mg phase. 相似文献
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Intensive melt shearing has a significant grain refining effect on some light alloys.However,the persistence of the grain refining effect during isothermal holding and remelting is still unclear,although it is very important for the practical application.In this study,intensive melt shearing was achieved in a twin-screw mechanism to investigate its grain refining effect on AZ91D magnesium alloy.The refinement mechanism was discussed and the persistence of grain refinement after remelting and isothermal holding was also studied.A Zeiss imaging system with polarized light was used for quantitative measurement of grain size.The results show that the intensive melt shearing has a significant grain refining effect on AZ91D magnesium alloy.With the application of intensive melt shearing,the grain size of AZ91D magnesium alloy can be reduced from 530 μm(for a typical as-cast microstructure) to 170 μm,which is about 70% size reduction.The grain refinement achieved by the intensive melt shearing can be partially kept after isothermal holding and remelting.It is believed that the refinement effect was mainly due to the finer and well dispersed oxide particles formed by high intensive shearing.The smaller size of oxide particles and their slow motion velocity in the sheared melt could make important contributions to the remained grain refinement. 相似文献
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Influences of the three melt treatment processes (namely, refinement with carbon inoculation, electromagnetic stirring and "refinement & electromagnetic stirring" processing) on the microstructures of AZ91D alloy were explored experimentally. The results indicate that the micron carbon powders inoculation processing with 0.1% (mass fraction) addition level makes the grain size of the primary phase (a-Mg) decrease to approximate 40% that of the initial primary crystal, from about 530 μm to 200 μm around. The electromagnetic stirring processing not only decreases the grain sizes sharply, but also transfers the grain shape of a-Mg from coarse dendritic to nearly spheralitic with the shape factor from about 0.1 to approximate 0,8. And the "refinement & electromagnetic stirring" processing improves grain shape of a-Mg further and refines grain size to about 72 μm, less than 15% that of the initial primary crystal. 相似文献
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The effects of pulsed magnetic field on the solidified microstructure of an AZ91D magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied in the solidification of AZ91D alloy. The average grain size of the as-cast microstructure of AZ91D alloy is refined to 104 μm. Besides the grain refinement, the morphology of the primary α-Mg is changed from dendritic to rosette, then to globular shape with changing the parameters of the pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface by the magnetic pressure, which makes the nucleation rate increased and big dendrites prohibited. In addition, primary α-Mg dendrites break into fine crystals, resulting in a refined solidification structure of the AZ91D alloy. The Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms. 相似文献
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G. S. Peng Y. Wang K. H. Chen S. Y. Chen 《International Journal of Cast Metals Research》2018,31(2):99-107
The effects of intensive melt shearing and Ca concentration on grain refinement of commercial purity Mg have been investigated by standard TP-1 casting tests, X-ray diffraction combined with the observation of optical microscope and scanning electron microscope. It was found that, without intensive melt shearing, Ca addition greatly improved grain structure of Mg from columnar grain to equiaxed grain. With Ca concentration increasing from 0.01 to 1 wt. %, the average grain size of the alloy gradually decreased. When intensive melt shearing was applied, the grain structures of the alloy remained equiaxed grain with Ca concentration variation. The average grain size first decreased and then kept invariable with Ca concentration increasing to 1 wt. %. The grain refining mechanism of Ca concentration variable and intensive melt shearing was discussed. 相似文献
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G. S. Peng Y. Wang K. H. Chen S. Y. Chen 《International Journal of Cast Metals Research》2017,30(6):374-378
The low concentration Zr and intensive melt shearing effects on grain refinement of commercial purity Mg has been studied. It was found that the low concentration Zr addition, combined with intensive melt shearing, resulted in a significantly grain refinement. The mechanism of grain refinement on the intensive melt shearing dispersing MgO film into individual MgO particle and enhancing the adsorption of low concentration Zr on the surface of MgO particle was proposed. 相似文献
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采用坩埚扭摆振动法测量了添加少量钙的AZ91D镁合金熔体的黏度,获得了600~870 ℃温度区间内升温和降温过程中的黏度-温度关系曲线υ(t)和黏度-钙添加量关系曲线υ(w).结果表明:AZ91D镁合金熔体的曲线υ(t)发生了不可逆转变;曲线υ(t)发生转折的温度对钙元素的添加量具有强烈依赖性,钙添加量(质量分数)为0.4%时,升温和降温过程的曲线υ(t)出现多温度点的黏度值相符合现象;曲线υ(w)具有显著的区间性特征,钙添加量为0.7%~0.8%时,开始出现较多的新相. 相似文献
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《Acta Materialia》1999,47(7):2047-2057
The superplastic behavior of a fine-grained AZ91 alloy, processed by equal channel angular extrusion, has been investigated in a low temperature range of 423–523 K. The experimental results showed a stress exponent of 2 and the activation energy for superplastic flow was in agreement with that for grain boundary diffusion of magnesium. The alloy with non-equilibrium grain boundary structures exhibited lower superplastic elongation than the alloy with equilibrium grain boundaries. Furthermore, the strain rate for superplastic flow of the former was lower than that of the latter. These differences probably arise because the accommodation process for grain boundary sliding is hampered by the long-range stresses associated with the non-equilibrium grain boundaries. 相似文献
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Effects of grain refinement on mechanical properties and microstructures of AZ31 alloy 总被引:1,自引:0,他引:1
Cerium was added in AZ31 alloy with the contents of 0.4%,0.8%and 1.2%respectively to produce experimental alloys. The grain refinement of Ce in the as-cast and rolled AZ31 alloy were studied by using Polyvar-MET optical microscope with a VSM2000 quantitative analysis system,KYKY2000 SEM and Tecnai G~2 20 TEM.And the mechanical properties of AZ31+Ce alloy were tested on a CSS-44100 testing system with computerized data acquisition.The results show that the cerium has a good grain refinement effect on the ... 相似文献
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1 Introduction AZ91D magnesium alloy has received more attention due to its high specific strength, specific rigidity and good dimensional stability and so on[1]. Thixoforming is one of the best methods with regard to forming AZ91D magnesium alloy compone… 相似文献
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AZ91镁合金的半固态搅拌摩擦焊接连接形成机理 总被引:1,自引:0,他引:1
半固态连接被认为是一种连接合金的可能的方法。研究了AZ91镁合金半固态搅拌摩擦焊接的机理。将2块7.5 mm厚的AZ91镁合金试件和1块2 mm厚的 Mg?25%Zn中间层放在加热板上,加热到所需温度并保温3 min后,采用旋转搅拌头搅拌焊缝。将加热板在台车上以4.6 cm/min的恒定速度运动。同时,对一个样品进行无中间层焊接。使用扫描电子显微镜和光学显微镜研究焊接过程中搅拌速度、搅拌头形状和温度的影响。结果表明,中间层降低了焊接温度;升高温度、加快搅拌速度、采用圆形搅拌头代替槽形搅拌头都能增大搅拌区的宽度。在焊接过程中,可能存在某些机理,从而有助于获得良好的的冶金结合,例如氧化层消失、液相混合、液球连接、液体渗入基体、从大量液球基体金属进入焊缝区。 相似文献
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Effect of ultrasonic power on grain refinement and purification processing of AZ80 alloy by ultrasonic treatment 总被引:1,自引:0,他引:1
Zhiwen Shao Qichi Le Zhiqiang Zhang Jianzhong Cui 《Metals and Materials International》2012,18(2):209-215
Ultrasound with different powers was applied to treat AZ80 alloy melt to attain grain refinement or purification processing
of the alloy. The influence of ultrasonic powers from 0 W to 1400 W on microstructures of the AZ80 alloy with ultrasonic grain
refinement treatment was investigated. The average grain size of the alloy could be decreased from 387 μm to 147 μm after
the ultrasound with the optimal power 600 W was applied to treat the melt. The effect of ultrasonic powers from 0 W to 230
W on the inclusion distribution in the ingot that was treated by ultrasonic purification processing was also studied. The
optimal ultrasonic power in the ultrasonic purification processing was 80 W. In order to gain insight into the mechanism by
which ultrasonic power affected the microstructure of the alloy or inclusion distribution in the ingot, numerical simulations
were carried out and the ultrasonic field propagation in the melt was characterized. 相似文献
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G.R. Ebrahimi A.R. MaldarR. Ebrahimi A. Davoodi 《Journal of Alloys and Compounds》2011,509(6):2703-2708
Dynamic recrystallization of the AZ91 alloy was studied by conducting hot compression tests at temperature range of 325-400 °C and strain rate of 0.001-1 s−1. The influence of the hot deformation variables on flow stress as well as recrystallized grain size was investigated. The results showed that by decreasing temperature and increasing strain rate, flow stress increases while dynamically recrystallized grain size decreases. A power-law relation developed between the characteristic peak strain and Zener-Hollomon parameter and the exponent was determined as 0.17. Besides, the linear regression between the Zener-Hollomon parameter and dynamically recrystallized grain size developed another power law equation, with a stress exponent equivalent to −0.13. 相似文献