共查询到19条相似文献,搜索用时 250 毫秒
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金属半固态成形已有近50年的发展历史,因其加工优势和市场价值备受关注,并形成了很多加工方法,其中半固态流变成形工艺效率高、成本低,具有较好的发展前景。由于铜合金熔点普遍较高,目前针对其进行的半固态工艺研究较少。简要综述了针对铜合金的半固态流变成形及制备技术的研究新进展,包括各新工艺的加工过程、最优工艺参数选择及工艺过程的机理等,分析了各工艺目前尚存在的问题和原因。阐述了半固态流变制备工艺模型及机理的新进展,并对其发展趋势进行了分析和展望,认为半固态流变成形技术未来的研究方向有半固态浆料制备新方法、新型半固态合金和半固态组织演变机制及其控制方法等。 相似文献
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非晶复合材料具有高强度力学性能的同时又表现为宏观脆性,而半固态工艺可以提高非晶复合材料的宏观塑性。主要综述了非晶复合材料的发展历程和分类,简要介绍了半固态成形工艺。重点介绍了半固态成形技术制备半固态非晶复合材料坯料或浆料的主要方法和具体工艺,同时追踪了利用半固态成形技术(锻造成形、铸造成形、轧制成形)制备的非晶复合材料产品的最新研究,进而介绍了半固态等温热处理对非晶复合材料微观组织的影响规律。最后对比了半固态流变成形和触变成形的优缺点,展望了流变成形技术在非晶复合材料领域的推进和应用。 相似文献
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半固态金属(SSM)加工是金属成型的一项新技术。SSM加工以半固态金属浆料作原料。SSM浆料通常表现出两种独特的流变特性:假塑性和触变性。SSM各种加工方法都是在这两个特性的基础上发展起来的。所以,发展SSM加工方法要从掌握浆料的流变特性开始。总结比较了现有的流变学模型。 相似文献
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目的以2024铝合金为例,研究变形铝合金流变挤压铸造成形件的组织和力学性能,探讨采用流变挤压铸造的方法成形高性能变形铝合金结构件的可行性。方法采用机械搅拌法制备了2024铝合金半固态浆料,采用不同机械搅拌温度和时间进行半固态浆料的制备,并对半固态浆料进行流变挤压铸造。研究了机械搅拌温度和搅拌时间对筒形件组织和力学性能的影响。结果成功制备出了2024铝合金筒形件。随着机械搅拌温度和搅拌时间的提高,筒形件的微观组织能得到细化,同时组织中固液相分布更加均匀,因此筒形件的力学性能也有所提高。结论对变形铝合金2024采用半固态流变挤压铸造进行成形的方法是可行的。半固态浆料最佳制备工艺参数为625℃时机械搅拌25 min,在此工艺参数下,流变挤压铸造2024筒形件的抗拉强度可达264 MPa。 相似文献
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采用等温压缩实验,对Al2O3/Al复合材料在伪半固态下流变行为进行了研究.结果表明,Al2O3/Al复合材料在伪半固态下压缩时的流动应力随实验温度的提高而显著下降;并分析了复合材料伪半固态温度下的流变行为以及其影响因素. 相似文献
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电磁场技术在半固态合金加工中的应用促进了制备工艺的开发和创新,也为获得高质量的半固态合金制品提供了保障。电磁场引起的半固态合金熔体流动状态和性质对合金元素传输、晶粒长大、温度场分布、凝固组织等均有重要影响。主要综述了电磁场对半固态合金流动行为的影响、数值模拟技术在解析半固态合金流动行为中的应用等方面的研究进展,并结合笔者的研究经历介绍了电磁场搅拌技术在半固态合金浆料制备中的应用、熔体流动对半固态合金凝固组织的影响,以及在半固态合金熔体流动特性研究中的新发现。在这些研究工作的基础上,着重综述了应用商业软件和数学建模对半固态合金熔体中电磁场作用引起的流动行为进行模拟、仿真所做的工作和取得的成果。最后,对电磁场技术在半固态合金加工中的应用以及电磁场作用下半固态合金熔体流动特性对半固态合金凝固组织影响的研究进展进行了总结,并对其发展前景和主要发展方向进行了展望。 相似文献
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ZhaoYANG HaifengZHANG AimingWANG BingzheDING ZhuangqiHU 《材料科学技术学报》2003,19(3):209-212
The influence of stress and strain on the solid/liquid segregation formed in deformed semisolid metal was studied. The compression experiment at a low constant strain rate was conducted on a Gleeble 1500 thermo-mechanical simulator.The stress and strain fields of the samples were calculated by finite element method. The experiment results and the modeling results prove that the hydrostatic pressure gradient is the driving force for solid/liquid segregation. The segregated liquid phase usually agglomerates in the micropores and shear bands are created by sliding of equiaxed dendrite grains. The sliding among the grains is influenced by the solid fraction and grain size of the semisolid slurry,so as the solid fraction and grain size change, the morphology of the segregated liquid changes. 相似文献
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半固态成形技术充分利用金属材料在半固态温度区间特殊的微观组织和成形性能,能够在较低的成形载荷下实现复杂构件的高效近净成形,该技术的应用对于提高金属材料的质量利用率和性能利用率、延长模具寿命、节能减排等方面具有重要的作用。主要介绍了半固态成形技术的历史沿革、半固态成形技术的分类、半固态金属坯料浆料的制备工艺、有色金属材料和钢铁材料的半固态成形技术开发以及应用情况,最后提出了半固态成形技术所面临的挑战和机遇。 相似文献
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Jean Collot 《Materials and Manufacturing Processes》2001,16(5):595-617
There have been many challenges in aluminum die casting to establish casting processes to produce high-integrity components from aluminum alloys. Advances in new casting technology mainly have been in pressure die casting; in particular, to obtain mold filling at low speed. This can be achieved by using innovative filling processes with aluminum alloys in the liquid or semisolid state. Different techniques such as high-pressure die casting (HPDC), Cosworth process, low-pressure systems, squeeze casting, indirect squeeze casting, metal compression forming (MCF), and semisolid metal (SSM) processing have been developed. Semisolid forming includes thixoforming and rheoforming. During the semisolid casting process, preheating by induction is needed to obtain the same temperature and the same liquid fraction through the billet in a short time. Thixocasting in the semisolid state helps to avoid turbulence during mold filling. 相似文献
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W. T. Carter Jr. R. M. Forbes Jones R. S. Minisandram 《Journal of Materials Science》2004,39(24):7253-7258
Nucleated casting is a method of casting metal below its liquidus temperature, casting as a semisolid rather than as a liquid. In nucleated casting, a stream of liquid metal is directed into a gas atomizer, which converts it into a spray and accelerates the spray droplets from the atomization zone toward a collection mold. Because of the high surface-to-volume ratio, high relative velocity, and a large temperature difference between the gas and droplets, the droplets lose heat very efficiently to the surrounding gas.Droplet diameter and process parameters such as gas-to-metal flow ratio, process rate, and spray distance have significant impact on the solid fraction of the metal at the collection zone. Small particles lose all of their heat of fusion and are fully solid when they strike; they will likely remelt in the semi-solid pool. Large particles are fully liquid when they strike. Medium-size particles are partially solid. When the particles strike the surface of the pool, a large number of nucleation sites are available for further solidification. Each nucleation site grows until it strikes an adjacent site and all local liquid is consumed and a fine-grained metallurgical structure results. When operated at high gas-to-metal ratio the semisolid will have small (<30%) fraction liquid, and free-form casting is possible. This process is commonly called spray forming. When operated at low gas-to-metal ratio the semisolid will have a high (>75%) fraction liquid, and a mold is required to contain the metal as it continues to solidify. This process is termed nucleated casting.Alloy 718 metal has been cast in a prototype nucleated casting system for demonstrating the feasibility of the new process. Metallographic examination shows that the as-cast material possesses a uniform, equiaxed 0.075 mm (ASTM 4.5) grain structure. Macrosegregation-related defects were not found in the casting or in forgings that were obtained from the ingots. 相似文献
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This paper explores the possibilities of joining SiCp/A356 composites using semisolid Zn27Al filler metal with aid of mechanical stirring. Moreover, the effect of stirring rate on the macro-appearance, microstructure, bonded ratio, braze metal ratio of joints and the tensile strength of joints were investigated. Experimental results show that the bonded ratio of interface, braze metal ratio and the tensile strength of the joints is rise with increasing of stirring rate. It is indicated that increasing of stirring rate will promote the disruption of oxide film on surface of composites so as to enhance metallurgical bonds at joint interface. In addition, increasing of stirring rate will also promote formation to fine brittle η-Zn phase and its uniform distribution in bond. 相似文献
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目的为了有效抑制半固态成形过程中的液相偏析,改善半固态成形构件微观组织和力学性能的均匀性。方法提出了包括多段流变成形和多段触变成形在内的多段半固态成形工艺。多段半固态成形工艺均由半固态坯/浆料制备、预成形、控温冷却和终成形4个阶段组成,分别在热模拟试验机和机械伺服压机上开展了SKD11工具钢和6061铝合金的半固态触变成形和半固态流变成形试验。结果在初成形阶段,具有较高液相分数的半固态坯/浆料以较高的应变速率初步充填型腔,限制了液相外流的时间和空间;在控温冷却阶段,半固态坯/浆料的液相分数因部分凝固而降低;在终成形阶段,具有较低液相分数的半固态坯/浆料以较低的应变速率完成型腔的充填,由于固相晶粒在此阶段发生塑性变形而提高了成形构件的力学性能。结论获得了组织均匀性较好的钢铁材料和有色合金构件,验证了多段半固态成形工艺的可行性。 相似文献
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A new semisolid metal processing technology, rheo-diecasting (RDC) has been developed for production of Mg-alloy components
with high integrity. The RDC process innovatively combines the dispersive mixing power of the twin-screw mechanism for creation
of high quality semisolid slurry and the high efficiency, low cost nature of the high pressure die casting (HPDC) process
for component shaping. AZ91D Mg-alloy was used to optimise the RDC process and to establish its advantages over both the HPDC
process and other existing semisolid processing techniques. In this paper we present the RDC process for processing Mg-alloys
and the resulting microstructure and mechanical properties of RDC AZ91D alloy. The solidification behaviour of the Mg-alloys
in the RDC process and the co-relationships between microstructure and mechanical properties of the RDC AZ91D alloy are discussed.
It was found that the RDC process is capable of producing Mg-alloy samples with close-to-zero porosity and a fine, uniform
microstructure throughout the entire sample irrespective of the section thickness. Compared with those obtained by other existing
processing techniques, the RDC samples have substantially improved or equivalent mechanical properties, with the tensile elongation
showing more than 100% improvement. 相似文献