镁合金消失模铸造新技术研究

消失模铸造属于颇有特点的精密绿色铸造技术.但镁合金消失模铸造中存在充型能力差、孔洞缺陷严重、凝固组织粗大及力学性能偏低等问题.针对以上问题,国内外开发了几种镁合金消失模铸造新技术,本文主要介绍这些新技术的最新研究进展.真空低压消失模铸造技术,可保证金属液充型平稳,提高镁液充型和补缩能力,保护其充型过程,适于镁合金铸造成...     

镁合金真空低压消失模铸造的技术特征与实践

详细介绍了镁合金在真空低压消失模铸造下的技术特征.试验研究表明真空低压消失模铸造的流动性受充型气体的流量与压力、浇注温度、涂层厚度、泡沫密度、真空度等多方面的因素影响;在低充型速度和低真空度的条件下,液态镁合金在真空低压消失模铸造过程中的充型形貌均呈现以内浇道为中心的拱形层状推进流动,如充型速度加快,金属液流动前沿拱形形貌更加突出,而真空度增加会出现明显的"附壁效应";与重力消失模铸造比较,真空低压消失模铸造镁合金铸件凝固更呈现"同时凝固"特征;由于快速充型、压力下凝固,镁合金真空低压消失模铸造零件的铸态抗拉强度(σb=180.8MPa)、屈服强度(σ0.2=113.2 MPa)、伸长率(δ=4.4%),高于重力消失模铸造、树脂砂真空型铸造的铸态性能,达到了金属型铸造的铸态性能,经热处理达到了压力铸造镁合金的性能范围.浇注实践表明,真空低压消失模铸造对液态镁合金,具有良好的抗氧化保护能力、优良的浇注充型性能和力学性能,可铸造出高精度的、薄壁复杂的镁合金消失模铸件.     

镁合金真空低压消失模铸造的技术特征与实践

介绍了镁合金在真空低压消失模铸造下的技术特征。研究表明：真空低压消失模铸造的流动性受充型气体的流量与压力、浇注温度、涂层厚度、泡沫密度、真空度等多方面的因素影响；在低充型速度和低真空度的条件下，液态镁合金在真空低压消失模铸造过程中的充型形貌均呈现以内浇道为中心的拱形层状推进流动，如充型速度加快金属液流动前沿拱形形貌更加突出。而真空度增加会出现明显的“附壁效应”；与重力消失模铸造比较，真空低压消失模铸造镁合金铸件凝固更呈现“同时凝固”特征；由于快速充型、压力下凝固，镁合金真空低压消失模铸造零件的铸态抗拉强度（σh=180．8MPa）、屈服强度（σ0.2=113．2MPa）、伸长率（δ=4．4％），高于重力消失模铸造、树脂砂空型铸造的铸态性能，达到了金属型铸造的铸态性能，经热处理达到了压铸镁合金的性能范围。浇注实践表明，真空低压消失模铸造对液态镁合金，具有良好的抗氧化保护能力、优良的浇注充型性能和力学性能，可铸造出高精度的、薄壁复杂的镁合金消失模铸件，是一种极有潜力和优势的镁（铝）合金精密铸造技术。     

数值模拟在消失模铸造工艺中的应用

数值模拟技术对消失模铸造有着重要意义,本文介绍了近年来国内消失模铸造数值模拟技术的研究进展状况,以及数值模拟技术和商业化模拟软件在泡沫珠粒充填、金属液充型和凝固过程中的应用情况,指出了今后消失模铸造数值模拟技术的发展方向。     

《消失模铸造原理及质量控制》出版发行

由华中科技大学黄乃瑜教授主编的《消失模铸造原理及质量控制》，反映了我国当代消失模技术最新发展水平。本书对模具发泡成形和泡沫板材数控加工成形两种消失模铸造工艺的制模、涂料配制与干燥、造型紧实、金属液充型与铸件凝固等工艺过程的控制进行了系统、深入的论述。     

消失模铸造铁液及凝固特性对灰铸铁石墨组织的影响

在生产条件下,通过附铸阶梯试样的方法,研究了消失模铸造灰铸铁石墨形态的特点,结果表明,消失模铸造灰铸铁较易出现过冷石墨.讨论了消失模铸造特点及消失模铸造高温铁液及充型凝固特点对石墨形态的影响.     

基于ProCAST的消失模铸造工艺的数值模拟研究

运用ProAST软件对链轮铸钢件的消失模铸造工艺进行了充型和凝固过程的数值模拟评价,分析了缺陷产生的原因,对铸造工艺进行了优化,并结合实际生产情况,给出了影响消失模铸造的六大基本因素。     

仿真技术在消失模铸造中的应用

随着计算机技术的发展,装备数字化、网络化、智能化是铸造技术革命的核心技术之一,仿真装备和技术作为铸造装备重要部分在铸造中逐步被应用。芜湖新兴铸管研究所通过仿真分析,为后期量化和批量化生产提供依据。消失模铸造充型仿真虚拟,实现了液态金属充型与凝固过程虚拟的可视化,为反复再现液态金属充型与凝固过程、预测铸造缺陷提供了依据,对工艺改进起到了辅助作用,减少了通过实际浇注试验来确定其铸造工艺的次数,降低了成本和对环境的污染。     

镁合金真空低压消失模铸造充型能力的研究

利用自主开发的真空低压消失模铸造技术及其装备研究了AZ91D镁合金在不同工艺参数条件下的成型能力，成功地浇注出了电机外壳、排气管等复杂的镁合金铸件，试验研究表明，这种新的消失模铸造工艺大大提高了镁合金的充型能力，消除了重力下消失模铸造美合金充型能力差，易形成浇不足和冷隔缺陷的缺点。     

镁合金消失模铸造成形技术的研究现状及进展

消失模铸造成形技术作为镁合金一项有发展前途的铸造新技术,其开发成功对于推动镁合金的广泛应用具有重要的意义.本文综述了近年来国内外针对镁合金消失模铸造成形技术在充型过程、组织和性能控制等方面的研究概况,并重点分析了工艺因素对充型过程的影响,指出了该技术目前还存在的问题,并对其今后的研究方向进行了展望.     

消失模铸造技术现状及发展趋势

回顾了消失模铸造技术的发展历程,现今铸铁和铸钢消失模铸造技术在国内外已相当成熟、应用也较为广泛;而相比之下,铝合金和镁合金的消失模铸造技术发展相对缓慢,尤其在我国铝合金、镁合金消失模铸造技术的推广应用还任重道远.本文着重论述了铝(镁)合金消失模铸造技术的应用现状,指出了当前铝(镁)合金消失模铸造中存在的主要问题,对今后消失模铸造技术的发展趋势进行了展望,介绍了几种适合铝(镁)合金的特种消失模铸造新技术.研究特种消失模铸造新方法,结合金属材质、涂料、热处理工艺、新型泡沫材料和尾气净化技术等开发,是绿色消失模铸造技术的发展方向.     

Status quo and development trend of lost foam casting technology

Lost foam casting（LFC）technology has been widely applied to cast iron and cast steel.However,the development of LFC for Al and Mg alloys was relatively slower than that for cast iron and cast steel.The application of LFC to Al and Mg alloys needs more effort,especially in China.In this paper,the development history of LFC is reviewed,and the application situations of LFC to Al and Mg alloys are mainly discussed.Meanwhile,the key problems of LFC for Al and Mg alloys are also pointed out.Finally,the prospects for LFC technology are discussed,and some special new LFC technologies are introduced for casting Al and Mg alloys.In future,the development trends of green LFC technology mainly focus on the special new LFC methods,metal material,coating,heat treatment,new foam materials as well as purification technology of tail gas,etc.     

Effect of Al on Expansion Behavior of Mg–Al Alloys During Solidification

The cooling curves and the change of contraction/expansion during solidification and cooling were tested by using a selfmade device which could achieve the one-dimensional contraction instead of three-dimensional contraction of the casting.Then, the effects of Al content(0, 1.1, 3, 5, 10, 12.9, 15, 17, 19, 22, 24 and 30 wt%) on the thermal contraction/expansion of the binary Mg-Al as-cast alloys during solidification were obtained. The results showed that expanding instead of contraction was present in Mg-Al alloys with the addition of 0-30 wt% Al during solidification. The values of expansion significantly increased at first and then decreased with the increase in Al content. And the maximum expansion ratio of 0.44%(maximum expansion value: 0.841 mm) was present in the Mg-15 wt% Al alloy. Contraction instead of expansion occurred once the temperature drops to the temperature corresponding to the expansion value in total, indicating the occurrence of a continuous expansion during the solidification process in mushy zone for the Mg alloys with Al addition of 5-30 wt%. The expansion value in total consisted of two parts: the expansions occurring in the liquid-phase zone and mushy zone. The expansion in liquid zone was present in every Mg-Al alloy, and it contributed to the most proportion of the total expansion value when the Al content in Mg-Al alloy was lower than 10 wt% or higher than 22 wt%. However, the total expansion value was mainly determined by the solidification behavior in mushy zone when the Al content was among 10-22 wt% in Mg-Al alloys.     

Solidification microstructures of Al-Zn-Mg-Cu alloys prepared by spray deposition and conventional casting methods

High strength Al-Zn-Mg-Cu alloys were prepared by spray deposition and casting techniques. The microstructures of the Al-Zn-Mg-Cu alloys were studied using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Secondary phases in the microstructures of the alloys prepared by spray deposition and conventional cast were examined. The results indicate that under the conventional casting condition, the microstructure of the alloy revealed the presence of coarse Al/Mg（ZnCu）2 eutectic phases, and the spray deposited process causes an obvious modification in size, morphology, and distribution of secondary phases in the microstructure as well as reduction of segregation. The superior microstructure of the spray-deposited Al-Zn-Mg-Cu alloy was attributed to the high cooling rate, and associated with the rapid solidification process.     

Solidification behaviour of Al-7 %Si-Mg casting alloys

The effects of Mg content and cooling rate on the solidification behaviour of Al-7% Si-Mg(mass fraction)casting alloys have been investigated using differential scanning calorimetry, differential thermal analysis and microscopy. The Mg contents were selected as respectively 0.00%, 0.35% and 0. 70% (mass fraction). DTA curves of Al-7%Si-0.55%Mg(mass fraction) alloy at various cooling rates were accomplished and the alloy melt was cast in different cooling rates. The results indicate that increasing Mg content can lower the liquidus and binary Al-Si eutectic transformation temperatures. Large Fe-rich π-phases (AlsFeMg3Si6) are found in the 0.70% Mg alloys together with some small β-phases (Al5FeSi) ; in contrast, only β-phases are observed in the 0.35% Mg alloys. The test results of the Al-7%Si-0.55% Mg alloys identify that the liquidus and binary Al-Si eutectic transformation temperatures decrease, and the quantity of ternary Al-Si-Mg2 Si eutectic phase decreases as the cooling rate increases.     

镁合金铸造成形过程宏观／微观模拟

通过研究镁合金压铸过程中界面热,采用热传导反算法确定压铸过程的界面换热系数,研究镁合金压铸过程中工艺参数及凝固过程对铸件界面换热系数的影响规律,建立镁合金压铸过程界面换热边界条件的处理模型,以实现镁合金压铸过程中凝固过程的准确预测。通过实验研究镁合金压铸过程中凝固组织,建立了镁合金压铸过程中形核模型。采用CA方法,建立了镁合金枝晶生长模型,以实现镁合金凝固组织的预测。采用相场方法研究了镁合金枝晶生长形貌。     

镁合金真空低压消失模铸造影响因素及充型能力的研究

介绍了一种新的真空低压消失模铸造工艺,分析了该工艺的工作原理和影响因素,并采用窗体及电机壳体模样测试了AZ91D镁合金在该工艺条件下的充型能力。研究表明：充型气体的气压与流量、泡沫模样的密度与裂解特性、涂层厚度及透气性、浇注温度、真空度等是镁合金真空低压消失模铸造过程中的主要影响因素。窗体和电机壳体成功浇注试验证明了真空低压消失模铸造新工艺大大提高了镁合金的充型能力,消除了重力下消失模铸造镁合金充型能力差、易形成浇不足和冷隔缺陷的缺点。     

AZ91D镁合金反重力铸造充型及凝固过程计算机模拟

给出了AZ91D镁合金的相关热物性参数，采用ProCAST铸造模拟软件对镁合金力学试棒反重力铸造充型与凝固过程进行了模拟，并通过反重力铸造工艺实验对模拟结果进行了验证。结果表明：铸造模拟软件ProCAST可用于镁合金铸件反重力铸造充型及凝固过程的模拟，能够提供较为准确的流场、温度场等信息，实现缺陷及其位置的预测。     

基于Pro/Engineer平台的镁合金智能压铸模设计

以一种结构复杂，不易分型和出模的U形框架带底盘且有凸缘的镁合金压铸件为例，说明了利用Pro／Engineer进行镁合金压铸模设计的一般步骤和方法。实践证明，该系统大大提高了模具设计的效率，并对复杂压铸件的压铸模设计有参考价值。     

Evaluation of crucible and investment materials for lost wax investment casting of Ti and NiTi alloys

Abstract

The aim of this study is to assess the suitability of selected commercial ceramic crucibles for the investment casting of Ti6Al4V and NiTi alloys for jewellery purposes. A commercial vacuum tilt casting machine and a centrifugal casting machine were employed to cast the alloys in cold copper moulds or in refractory investment shells. The form filling of the shell and the crucible and investment reactions were assessed by microstructural investigation, chemical analysis and hardness profiles of the as cast items as a function of shell temperature. The reaction of the alloys strongly depended on the alloy, the crucible material, the coating of the crucibles and the temperature of the ceramic shell. Optimum results were achieved with yttria and yttria coated Al titanate crucibles for Ti6Al4V and NiTi alloys respectively. Improvement of the materials and process costs is necessary to allow the competitive casting of jewellery made from titanium alloys.