块体非晶合金超塑性成形的研究进展

简述了块体非晶合金的研究现状及其超塑性成形技术,重点介绍了温度及应变速率对非晶合金超塑性的影响、块体非晶合金过冷液相区本构模型研究概况以及超塑性成形的应用,提出了块体非晶合金超塑性研究中仍需解决的问题。     

大块非晶合金的超塑性研究进展

对大块非晶合金在过冷液相区内的超塑性变形特点进行了评述.介绍了在过冷液相区内的流变行为和变形后的组织结构变化,并解释了超塑性变形的机理.同时,对大块非晶合金的超塑性成形技术发展现状况进行了概述.     

块体非晶合金精密模锻成形流动行为

利用块体非晶合金在过冷液相区所表现出的超塑性特性,开发超塑性精密成形技术是解决其成形加工困难,拓宽其应用领域的关键。文章采用三维有限元数值模拟及物理模拟的方法,研究了不对称精密棘轮超塑性成形过程中材料的流动行为。研究结果表明,棘轮模腔结构的不对称性对材料的流动行为影响显著;在材料向齿形的充填过程中存在流动死区,死区的位置处于齿形分布较稀疏的部位;齿形尖角是成形的最后充填部位,在终成形阶段采用较小的压下速度或较长的保压时间,有利于齿形尖角的完全充满。在数值模拟与物理模拟的基础上,进行了Zr41.25Ti13.75Ni10Cu12.5Be22.5块体非晶合金超塑性模锻成形实验,获得了形状完整、轮廓清晰的块体非晶合金不对称精密棘轮。     

块体非晶复合材料超塑性成形研究现状

块体非晶复合材料克服了非晶合金的室温脆性，保留了非晶合金的高强度优势，是一种具备优异力学性能的结构材料。研究其在过冷液相区的超塑性变形行为能够指导理论模型的建立、发展和完善，也能加快推动材料的工程实际应用。简述了块体非晶合金及其复合材料超塑性成形的研究现状，并重点总结了近年来非晶复合材料在过冷液相区的超塑性流变行为、超塑性变形时的显微结构演变及力学性能的变化。提出了目前超塑性成形非晶复合材料方面亟待解决的技术难题。     

Zr基块体非晶合金的微塑性成形性能

采用自行研制的微成形系统进行热压缩实验,分别研究成形温度、成形时间和冲头速度等对尺寸为d1 mm×1.5 mm的Zr41.2Ti13.8Cu12.5Ni10Be22.5块体非晶合金(Vit.1)在过冷液相区微塑性成形性能的影响规律。进一步研究了不同坯料尺寸对Vit.1块体非晶合金在过冷液相区超塑性成形性能的影响程度,结果表明流动应力随坯料尺寸的减小而降低。在此基础上,利用闭式模锻方法成形了分度圆直径为d1 mm的微型齿轮,采用SEM观察成形件的表面形貌,结果表明采用微成形方法可以获得尺寸精度较高的Vit.1块体非晶合金微型齿轮。     

非晶合金的塑性成形

独特的长程无序、短程有序的微观结构使得非晶合金具有优异的力学、物理及化学性能,例如高硬度、高强度、优异的耐腐蚀以及大弹性极限,因此被认为是一种潜在的功能与结构材料,自问世以来一直是最热门的前沿性研究之一,并在体育、电子、航天、航空、军工、能源等领域具有明确而巨大的应用背景。随着制备技术的不断成熟,理论研究的不断深入,非晶合金作为一种性能优异的金属材料将翻开21世纪材料研究新篇章。然而,非晶合金在室温变形过程中呈现室温脆性及应变软化特征,致使其易于发生灾难性断裂,极大地限制了该先进材料的塑性成形。文章综述了非晶合金冷塑性成形及热塑性成形方面的研究进展,证实了非晶合金在多向复杂应力状态下可进行室温塑性成形,在过冷液相区内体现优异的超塑性成形能力,并就非晶合金塑性成形领域今后值得关注的问题进行了展望。     

Zr基大块非晶合金的超塑性成形性能

研究了Zr41.25Ti13.75Ni10Cu125Be22.5大块非晶合金的过冷温度区域范围、时间-温度-转变曲线及其在过冷温度区域的力学行为,并在此基础上,对精密凸轮零件进行了模锻成形实验,分析了不同温度和应变速率对成形结果的影响.结果表明:Zr41.25T13.75Ni10Cu12.5Be22.5大块非晶合金在635.6～710.4 K的过冷区域范围内,其应变速率敏感系数接近1,具有良好的超塑性性能;较理想的超塑性成形温度为653～668 K,应变速率为5.0×10-4～5.0×10-3s-1.在温度为668 K、应变速率为5.0×10-4s-1的工艺条件下,非晶合金的可成形时间大于1000 s,最大流动应力小于70 MPa.     

块体非晶合金搅拌摩擦焊研究现状及发展趋势

块体非晶合金具有高强度、高硬度、过冷液相区具有超塑性等优点,但其成形铸件尺寸小、形状简单的问题限制了其应用。搅拌摩擦焊过程中热量输入少,能在非晶过冷液相区内实现材料的连接,从而避免非晶合金的晶化。介绍了搅拌摩擦焊(FSW)的基本原理,综述了国内外块体非晶合金搅拌摩擦焊接的研究现状,指出了现有研究的不足并对未来的研究方向进行了展望。     

Zr基非晶合金力学性能的研究进展

Zr基非晶合金具有很强的非晶形成能力,可在小于103K/s临界冷却速率条件下获得.近年的研究表明,Zr基非晶合金具有高强度、超塑性、高弹性、高硬度、高耐磨性、高耐腐蚀性和优异的加工成形等性能,有着广阔的应用前景.本文总结了Zr基非晶合金的形成机理,着重对Zr基非品合金的力学性能、耐腐性能、加工性能等进行了综述.     

材料超塑性研究的现状与发展

对20世纪90年代以来国内外超塑性的研究工作进行了介绍和评述.主要介绍了新的超塑材料的开发及超塑性的应用,概述了国内外超塑性研究的最新进展,并对超塑性研究的热点问题进行了评述,重点评述了用超塑成型方法制作大型铝合金汽车零件、用分子动力学模拟超塑变形中的晶界滑动、新材料和纳米材料的超塑性开发及超塑微成形的研究等国内外超塑性研究的新进展.展望了超塑性的发展趋势,指出应开发材料的低温或高速超塑性,重视超塑性流动过程的理论研究,进一步拓展超塑性的应用领域.     

Cu基非晶合金的最新研究进展

Cu基非晶合金是一种高性能材料,本文从Cu基非晶合金体系、形成能力、影响因素、力学性能以及Cu基复合材料几个方面对Cu基非晶合金进展进行了综述,提出了Cu基非晶合金的发展方向,同时展望了Cu基块状非晶合金的工程应用前景。     

锆基块体非晶合金的力学性能研究进展

本文叙述了锆基块体非晶合金的制备方法，优异的性能，特别是对其力学性能研究领域的最新进展进行了综述。并与传统晶态合金作了适当的对比，锆基块体非晶合金具有优异的力学性能，如弹性比功、超塑性、断裂韧性等，此类合金的应用将不断拓宽。     

大块非晶态合金成形技术研究现状

介绍了两种非晶态合金材料成型技术的研究状况,一是超塑性精密净成形,另一是近净铸造成形技术.对其适应性做了评述:认为超塑性成形要求的温度区间很窄,应变速率很低,限制了它的进一步应用;近净铸造成形技术在较大尺寸非品器件成形方面具有更大优势,但其理论和应用研究尚需深入.     

Using equal-channel angular pressing for the production of superplastic aluminum and magnesium alloys

Equal-channel angular pressing (ECAP) is a useful tool for achieving exceptional grain refinement in bulk metallic alloys. Typically, the grain sizes produced through ECAP are in the submicrometer range, and thus they are smaller by up to an order of magnitude than the grain sizes attained through typical thermomechanical treatments. As a consequence of these ultrafine grains, the as-pressed alloys may exhibit superplastic ductilities at faster strain rates than in conventional superplastic alloys. This work initially describes the application of ECAP to two different alloys. First, results are presented for a commercial Al-2024 alloy where this alloy was selected because it contains no minor additions of either zirconium or scandium to assist in restricting grain growth. The results show that superplasticity is achieved through the use of ECAP. Second, results are described for a Mg-0.6%Zr alloy where this alloy was selected because it is the optimum composition for achieving a high damping capacity. Again, processing by ECAP produces superplastic ductilities not attained in the cast alloy. The second part of this work demonstrates that processing by ECAP may be extended from conventional rod or bar samples to samples in the form of plates. This is a very attractive feature for industrial superplastic forming applications. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Superplastic Response of Continuously Cast AZ31B Magnesium Sheet Alloys

Magnesium sheet is typically produced for commercial applications with the traditional DC-ingot casting method. As a result of the hexagonal close-packed crystallographic structure in magnesium, multiple rolling passes and annealing steps are required to reduce the thickness of the ingots. Thus, high fabrication costs characterize the creation of magnesium sheet suitable for common forming operations. Recently, continuous casting (CC) technology, where molten metal is solidified directly into sheet form, has been applied to magnesium alloys; this method has shown the potential to significantly reduce the cost of fabricating magnesium sheet alloys. In order to understand the viability of the CC process, a study was conducted to investigate the superplastic potential of alloys produced by this method. This study focused on AZ31B Mg that was continuously-cast on twin-roll casters from three different suppliers. These three materials were compared with a production DC-cast AZ31B alloy in terms of microstructure, elevated-temperature tensile properties, and superplastic forming response. The data from this study found that microstructural features such as grain size and segregation can significantly affect the forming response. Additionally, the CC alloys can have equivalent or superior SPF response compared to DC-cast alloys, as demonstrated in both elevated temperature tensile tests and superplastic forming trials using a rectangular pan die.     

Influence of magnesium on grain refinement and ductility in a dilute Al–Sc alloy

Experiments were conducted to determine the influence of magnesium additions on grain refinement and tensile ductility in an Al–0.2% Sc alloy processed by equal-channel angular pressing (ECAP). The experiments show ECAP reduces the average grain size to within the range of ∼0.70 to ∼0.20 μm for alloys containing from 0 to 3% Mg but the as-pressed grain size increases to ∼0.3 μm in an alloy with 5% Mg because it is then necessary to use additional annealing treatments during the pressing process. The ultrafine grains introduced by ECAP are stable to high temperatures in the alloys containing from 0 to 3% Mg: in all alloys, the average grain size is <5 μm after annealing for 1 h at temperatures up to ∼750 K. High superplastic ductilities were achieved in the alloy containing 3% Mg but alloys containing 0.5% and 1% Mg exhibited the enhanced ductilities generally associated with conventional Al–Mg alloys. The results suggest the addition of ∼3% Mg is optimum for achieving superplastic elongations at rapid strain rates in the Al–0.2% Sc alloy.     

Superplastic forming by decomposition of (CaCO3 + C) and MgCO3

An innovative method has been developed that replaces argon as the pressure source for superplastic forming. In this new process, several solid materials are placed in a closed system to generate pressure and are capable of forming superplastic alloy plates at specific temperatures. In the present study, the total pressures for the decomposition of ( CaCO₃+ C) and MgCO₃ have been theoretically calculated from thermodynamics. The results show that a pressure range of 40 to 396 psi can be obtained for the ( CaCO₃ + C) system between 850 and 1000 °, which is suitable for the superplastic forming of Ti-6Al-4V and Superdux 64 ( Nippon Yakin Kogy Co., Ltd., Sanei Bridge, Kyobasi 1-5-8, Chyuoku, Tokyo 104, Japan) stainless steel. The pressure for MgCO₃ system between 480 and 515 ° ranges from 78 to 160 psi, which is suitable for the superplastic forming of 8090 Al-Li and 7475 Al-Zn-Mg alloys. The calculated temperature dependence of pressure is consistent with the experimentally measured results. Furthermore, the forming rates, wall thickness distributions, tensile properties, and microstructures of the four alloys after forming have been shown to be very similar to those of conventional superplastic forming by argon pressurization.     

镁合金成形技术现状及展望

论述了镁合金材料的性能及特点,详细介绍了镁合金的成形工艺,包括压铸、熔模铸造、消失模铸造、塑性成形、超塑性成形和半固态成形技术,对镁合金生产中存在的问题及解决方法进行了讨论,并展望了其发展前景.