Semisolid metal processing
Semisolid metal processing
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DOI：
10.31399/asm.hb.v15.a0005224
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发表时间：
2002
影响因子：
4.4
通讯作者：
Z. Fan
中科院分区：
文献类型：
--
作者：
Z. Fan
在凝固过程中应用剪切产生非枝晶半固态浆料，从而可以对半固态金属（SSM）进行加工，是一种相对直接转移到模具或模具中给予金属最终成形的新技术。不同于产品。触变成形是用来描述一种接近传统的金属成形技术，它使用固体金属（部分熔化的非枝晶合金的固态净成形加工）或液态金属（铸造）作为金属模具内的起始段：在封闭模具中进行触变铸造，材料，SSM加工处理半固体或在开放模具中进行触变锻造。(这些过程是浆料，其中非枝状固体颗粒将在下面的“分散在液体基质中的技术”中详细描述。半固态金属部件成形。该技术很快使浆料表现出独特的流变性，并受到一系列专利的保护。早年的特点是：稳态行为是许多替代机械搅拌假塑性（或剪切变薄）的方法，而被建议实现所需的微瞬态行为是触变的。所有的结构。这些包括目前可用的SSM固体枝晶材料的等温粗化技术，粉末的混合，基于这些独特的流变特性开发的被动加工，依次混合，通过非枝晶微观结构产生的半固态放电。2001年是最初的枝晶固体材料冷加工30周年。SSM处理的概念。今天，SSM的这些探索在一定程度上是为了尝试环加工，它已经成为麻省理工学院强大的专利地位，但几乎是可靠的和商业上可行的技术，当然也是由于对金属部件生产的强烈好奇，铸造世界高，完整性的缺点，改进的机械性能，机械搅拌。然而，在所有这些建议中，复杂的形状和严格的尺寸控制。也许更重要的是，它已经证明了其生产非枝晶的公认方法具有进一步技术发展和商业开发的巨大潜力。在这种商业规模的原料中，虽然通过深入的塑性变形理解、技术发展和测试，在科学小规模生产上取得了进展，但今天一些部件正在使用。综述了SSM加工各种合金的可行性。该领域有待进一步研究，并已在过去30年进行了调查。首先，还讨论了发展问题。IMR/335的主要重点是高温合金，特别是钢，几乎没有注意©2002 IoM通信有限公司和ASM国际。铝和镁合金。这主要是作者在沃尔夫森中心材料加工，布鲁内尔大学，乌克斯桥，米德尔塞克斯UB8由于驱动完美的钢压铸3PH，英国（mtstzzf@brunel.ac.uk）。军事应用技术。半固态处理被认为是降低铸造温度的有效手段。然而，由于20世纪70年代的石油危机，以及20世纪80年代以来日益增加的环境问题，汽车市场的力量2001年标志着半固态金属（SSM）加工概念的30周年纪念日，人们一直在努力减轻重量。原装高性能轻金属部件。因此，自20世纪90年代实验导致流变铸造的发现以来，SSM加工主要是在1971年初由Spenser1作为铝合金的一部分进行的。在过去的十年中，他的博士研究在SSM加工的指导下经历了麻省理工学院Flemings教授的密集研究。斯宾塞正在研究开发和商业化。今天，SSM热撕裂在铸钢。他使用Sn-15Pb加工已经确立了自己作为一种科学合金*作为模型系统来评估粘度的声音和商业上可行的技术，部分凝固的合金使用Couette粘度计。生产具有高整合度的金属部件，这样做，他得到了剪切枝晶结构，强度大，机械性能提高，形状复杂，虽然这不是最初的意图。他发现了严格的空间控制。也许更重要的是，当枝晶结构被破坏时，它已经显示出进一步部分凝固合金具有机械技术发展和商业开发的流动性和触变行为的巨大潜力佛兰芒。这一发现的另一个重要方面是，到当年夏天，这一发现在过去没有被清楚地认识到，即进行了工业试验，证明了固化过程的可行性，这标志着第一次广泛的操作。从历史上看，几千年来，有两种铸造方式，即自金属铸造诞生以来被称为“流变铸造”、合金凝固铸造和“触点铸造”简而言之，流变铸造涉及到将给定的成分作为自然过程处理，具有所谓的快速凝固*合金成分在wt-%，除非另有说明。
application of shearing during solidification to produce a non-dendritic semisolid slurry that can be Semisolid metal (SSM) processing is a relatively transferred directly into a mould or die to give a final new technology for metal forming. Different from product. Thixoforming is used to describe the near the conventional metal forming technologies which use either solid metals (solid state net shaping of a partially melted non-dendritic alloy processing) or liquid metals (casting) as starting slug within a metal die: thixocasting if in a closed die, materials, SSM processing deals with semisolid or thixoforging if in an open die. (These processes are slurries, in which non-dendritic solid particles are described in more detail below in ‘Technologies for dispersed in a liquid matrix. Semisolid metal component shaping’.) The technology was quickly slurries exhibit distinctive rheological guarded by a series of patents. During the early years, characteristics: the steady state behaviour is many alternative approaches to mechanical stirring pseudoplastic (or shear thinning), while the were suggested to achieve the required microtransient state behaviour is thixotropic. All the structures. These include isothermal coarsening of currently available technologies for SSM solid dendritic materials, mixing of powders, passive processing have been developed based on those unique rheological properties, which in turn mixing, electrical discharge through a semisolid denoriginate from their non-dendritic microstructures. dritic material, electromagnetic stirring, and intensive Year 2001 marks the 30th anniversary of the cold working of initially dendritic solid materials. concept of SSM processing. Today, SSM Those explorations were partly an attempt to circumprocessing has established itself as a scientifically vent a strong MIT patent position, but almost cersound and commercially viable technology for tainly also a result of intense curiosity from the production of metallic components with high foundry world and perceived disadvantages of integrity, improved mechanical properties, mechanical stirring. Of all those suggestions, however, complex shape, and tight dimensional control. only electromagnetic stirring has become a widely Perhaps more importantly, it has demonstrated its accepted method for the production of non-dendritic great potential for further technological development and commercial exploitation. In this feedstock materials on a commercial scale, although paper, progress made on the scientific small scale productions via intensive plastic deformaunderstanding, technological development, and tion are being used for some components today.4 industrial applications of SSM processing are The feasibility of SSM processing of various alloys reviewed. The areas for further research and has been investigated in the past 30 years. Initially, development are also discussed. IMR/335 the primary focus was on high temperature alloys, notably steels, and practically no attention was given © 2002 IoM Communications Ltd and ASM International. to aluminium and magnesium alloys. This was mainly The author is in the Wolfson Centre for Materials Processing, Brunel University, Uxbridge, Middlesex UB8 due to the drive for perfection of steel die casting 3PH, UK (mtstzzf@brunel.ac.uk). technology for military applications. Semisolid processing was considered to be an effective means to reduce the casting temperature. However, because of the oil crises in the 1970s, and increasing environmenIntroduction tal concerns since the 1980s, automobile market forces Year 2001 marks the 30th anniversary of the concept have been pressing hard for weight reduction using of semisolid metal (SSM) processing. The original high performance light metal parts. As a consequence, experiment leading to the discovery of rheocasting since the 1990s, SSM processing has predominantly was performed in early 1971 by Spenser1 as a part of concentrated on aluminium alloys. In the past decade, his doctorate research under the supervision of SSM processing has experienced intensive research, Professor Flemings at MIT. Spencer was investigating development, and commercialisation. Today, SSM hot tearing during casting of steels. He used Sn–15Pb processing has established itself as a scientifically alloy* as a model system to evaluate the viscosity of sound and commercially viable technology for the partially solidified alloys using a Couette viscometer. production of metallic components with high integIn doing so, he was shearing the dendritic structure, rity, improved mechanical properties, complex shape, although that was not originally intended. He discoand tight dimensional control. Perhaps more importvered that when the dendritic structure is broken up, antly, it has demonstrated a great potential for further the partially solidified alloy has the fluidity of machine technological development and commercial exploitaoil and exhibits thixotropic behaviour.1,2 Flemings tion. and his team immediately recognised the importance Another significant aspect of SSM processing, of the discovery and, by the summer of that year, had which has not been clearly realised in the past, is that performed industrial trials demonstrating the feasibilit marks the first extensive manipulation of the solidification process. Historically, for thousands of years, ity of the two routes, which were termed ‘rheocasting’ since the birth of metal casting, solidification of alloys and ‘thixocasting’.3 In brief, rheocasting involves the of given compositions has been treated as a natural process, with the so called rapid solidification *Alloy compositions are in wt-% unless specified otherwise.