气压对定向凝固藕状多孔镁的气孔分布影响

采用统计分析方法,通过孔径分布、气孔最邻近距离和局部气孔率定量分析定向凝固藕状多孔镁横截面上的气孔分布特征,并在此基础上分析气压对藕状多孔镁气孔分布的作用规律。结果表明：纯氢条件下气压越高,孔尺寸分布越趋于一致、孔位置和气孔结构单元分布越均匀;氢气分压一定,选择合适的氩气分压可使熔体共晶凝固时,孔尺寸、孔位置和气孔结构单元的分布最均匀。     

气体压力对定向凝固多孔Cu气孔结构的影响

利用自行开发研制的Gasar装置,在H2和Ar的高压气氛中制备了具有规则气孔结构的定向凝固多孔Cu,并研究气体压力对多孔Cu气孔结构的影响.结果表明:当H2压力一定时,随着Ar压力增加,气孔率逐渐减小;当Ar压力一定时,随着H2压力的增加,气孔率呈现先增加后减小的趋势;随着H2压力的增加,气孔的平均直径减小,尺寸分布均匀性提高.     

Al-H系定向凝固制备多孔Al

传统多孔金属材料大多以Al为基,其气孔多为随机分布的不规则形状.而作为规则多孔金属的制备方法--金属/气体共晶定向凝固法(又称Gasar工艺)业已成功应用于Mg,Cu,Ni,Ag,Fe和Si等多种材料,但这一工艺对于Al却并不适用本工作对此进行的实验研究和理论分析认为,Al熔体中氢气溶解总量过少,加之目前Gasar工艺下Al-H体系的凝固速率较低,因此不能维持固、气两相协同共生生长,导致无法直接采用Gasar工艺制得藕状规则多孔Al.     

定向凝固制备镁单晶中杂质相的研究

采用自行设计的定向凝固装置制备了镁单晶,通过扫描电镜观察、能谱分析和软件统计分析,研究定向凝固工艺制备的镁单晶中杂质相的特性。结果表明,杂质相中含有多种元素,其主要成分是MgO,有球形、团簇形和块状。试样中MgO杂质相从下至上数量逐渐减少,尺寸逐渐增大,且镁组织中MgO平均直径在1μm以下。     

凝固模式对定向凝固多孔铜锰合金气孔结构的影响

采用金属-气体共晶定向凝固工艺（GASAR工艺）,制备气孔定向排列的多孔铜锰合金,并研究气孔结构的变化。结果表明：这种变化主要取决于合金的凝固模式（平面凝固、柱状胞晶凝固、柱状枝晶凝固、等轴枝晶凝固）,而合金凝固模式由合金的凝固过程决定。通过数值模拟发现,随着合金凝固的进行,合金的凝固模式从胞晶凝固向柱状枝晶凝固过渡,最终变为等轴枝晶凝固。通过升高合金熔体温度和铸型的预热温度,可以缩小等轴枝晶凝固的范围,扩大定向生长气孔的区域。     

凝固模式对Gasar多孔Cu-Cr合金结构及组织影响

在0.6 MPa纯H2气氛中,采用金属/H2共晶定向凝固(Gasar)技术制备得到Gasar多孔Cu-x Cr合金。研究了Cr含量、凝固模式以及凝固速率对Gasar多孔合金气孔结构和显微组织的影响。结果表明,当合金以平面、胞状及柱状枝晶凝固时,Gasar多孔Cu-x Cr合金能获得定向生长气孔。当凝固方式转变为等轴枝晶凝固时,定向生长气孔发生中断。Gasar多孔Cu-x Cr合金(x=0.8%、1.3%)气孔在共晶相前沿析出,与共晶组织协同定向生长。随Cr含量增加,共晶组织体积百分比增加,孔隙率和孔圆整度进一步增加;随多孔Cu-1.3 Cr合金试样凝固高度增加,凝固速率下降,界面生长方式转变为等轴晶生长方式,则无法得到定向生长气孔。     

藕状多孔金属Mg的Gasar工艺制备

金属／气体共晶定向凝固(Gasar)是一种制备规则多孔金属的新工艺．本文利用自行开发的Gasar装置,成功制备了具有规则气孔分布的藕状多孔金属Mg,并研究了气体压力对气泡形核、气孔率、气孔大小和分布的影响。     

金属-气体共晶定向凝固制备藕状多孔金属的研究

金属 气体共晶定向凝固 （Gasar）是一种制备规则多孔金属的新工艺。利用自行开发的Gasar装置 ,成功制备了具有规则气孔分布的藕状多孔金属Mg ,并研究了铸型预热温度和气体压力等工艺参数对气孔率、气孔大小和分布的影响。结果表明 :提高铸型预热温度可以完全消除无气孔金属壳 ;随着氢气压力的增大 ,铸锭的平均直径都在减小 ;在整个Gasar凝固中约有 8%左右的氢气溢出。     

磁场对锌合金定向凝固显微组织的影响

基于改进的自制Bridgman水平卧式定向凝固装置,研究了横向直流稳恒磁场对Zn-35Al-2.5Cu-1.5Ti合金显微组织的影响。通过金相显微组织观察、显微组织定量表征等方式,分析了磁场对锌合金显微组织的影响规律。结果表明,随着磁感应强度增加,因磁场存在而产生的热电磁流体动力学（TEMHD）效应增强,促进液-固界面糊状区熔体流动,有利于原子扩散迁移,显微组织粗化;牵引速度增加,TEMHD效应减弱,凝固组织细化。当磁感应强度为0.2T,定向凝固牵引速率为30μm/s时,锌合金显微组织粗化严重。施加磁场与未施加磁场的合金显微组织相比,其一次臂、二次臂间距增加最大幅度可达44.9%和52.2%。     

用金属/气体共晶二维定向凝固法制备放射状规则多孔Mg

采用热传导方向为径向的金属一气体共晶二维定向凝固方法（二维Gasar）,在纯氢和氢、氩混合气氛下制备了气孔沿径向规则分布的放射状多孔金属Mg．研究了放射状多孔金属结构的特点以及气体压力等工艺参数对孔隙率、孔径和气孔分布的影响．结果表明,在圆柱形试样的二维定向凝固过程中,金属一气体共晶形成的体积膨胀会在凝固前沿的液相中产生大的对流,影响气孔的生长方向和规则程度,同时还会导致气体的逸出．随混合气体中氩气分压的增大,逸出程度下降;当氩气分压大于氢气分压时,气体的逸出被完全抑止．由此可以准确地预测出放射状规则多孔金属的孔隙率．     

Pore structure and mechanical properties of directionally solidi ed porous aluminum alloys

Porous aluminum alloys produced by the metal-gas eutectic method or GASAR process need to be performed under a certain pressure of hydrogen, and to carry over melt to a tailor-made apparatus that ensures directional solidif ication. Hydrogen is driven out of the melt, and then the quasi-cylindrical pores normal to the solidif ication front are usually formed. In the research, the effects of processing parameters(saturation pressure, solidif ication pressure, temperature, and holding time) on the pore structure and porosity of porous aluminum alloys were analyzed. The mechanical properties of Al-Mg alloys were studied by the compressive tests, and the advantages of the porous structure were indicated. By using the GASAR method, pure aluminum, Al-3wt.%Mg, Al-6wt.%Mg and Al-35wt.%Mg alloys with oriented pores have been successfully produced under processing conditions of varying gas pressure, and the relationship between the f inal pore structure and the solidif ication pressure, as well as the inf luences of Mg quantity on the pore size, porosity and mechanical properties of AlMg alloy were investigated. The results show that a higher pressure of solidif ication tends to yield smaller pores in aluminum and its alloys. In the case of Al-Mg alloys, it was proved that with the increasing of Mg amount, the mechanical properties of the alloys sharply deteriorate. However, since Al-3%Mg and Al-6wt.%Mg alloys are ductile metals, their porous samples have greater compressive strength than that of the dense samples due to the existence of pores. It gives the opportunity to use them in industry at the same conditions as dense alloys with savings in weight and material consumption.     

Fabrication of lotus-type porous Mg−Mn alloys by metal/gas eutectic unidirectional solidification

Lotus-type porous Mg–xMn (x=0, 1, 2 and 3 wt.%) alloys were fabricated by metal/gas eutectic unidirectional solidification (the Gasar process). The effects of Mn addition and the fabrication process on the porosity, pore diameter and microstructure of the porous Mg−Mn alloy were investigated. Mn addition improved the Mn precipitates and increased the porosity and pore diameter. With increasing hydrogen pressure from 0.1 to 0.6 MPa, the overall porosity of the Mg−2wt.%Mn ingot decreased from 55.3% to 38.4%, and the average pore diameter also decreased from 2465 to 312 μm. Based on a theoretical model of the change in the porosity with the hydrogen pressure, the calculated results were in good agreement with the experimental results. It is shown that this technique is a promising method to fabricate Gasar Mg–Mn alloys with uniform and controllable pore structure.     

Theoretical analysis of bubble nucleation in GASAR materials

1　INTRODUCTIONPorousmaterialscanbeproducedbyusinganov elmethodcalledGASARdevelopedintheDne propetrovskMetallurgicalInstitute (DMI )ofUkraine[1] .Mostmetal hydrogenbinarysystemshaveaeutecticdecompositionsimilartotheclassicaleutecticsystem .Thesemetalscanbemelted ,saturat edwithhydrogen ,andthendirectionallysolidified ,asshowninFig .1[2 ] .TheporosityofthesolidifiedGASARmaterialscanbevariedthroughprocessvari ablessuchaspressure ,rateanddirectionofcoolinginaprocessbasedongas solideut…     

Nb42Ti21Co37包共晶合金定向凝固组织演化规律研究

包共晶转变兼具共晶转变和包晶转变双重特征,存在于众多的工业合金中。然而,迄今为止尚未建立起相对完整的包共晶凝固理论模型,关于其凝固机理的相关研究较少。基于此,本文针对Nb42Ti21Co37包共晶合金开展了不同抽拉速度(V=1, 3, 5, 15, 30, 70 μm/s)下的定向凝固实验,旨在研究不同抽拉速度下合金的微观组织演化规律,并构建相应的凝固机制。研究结果表明：Nb42Ti21Co37包共晶合金常规铸态和定向凝固组织中均含有α-Nb、Co6Nb7和TiCo＋Co6Nb7包共晶相,随着抽拉速率的逐渐增加,初生相α-Nb依次经历了圆球状→花瓣状→团簇状→枝晶状的转变;伴随着上述过程,淬火界面经历了胞状界面到胞枝晶状界面的转变,并且,在抽拉速率V=70 μm/s时固/液界面消失;其次,定向凝固稳态生长区内包共晶的组织逐渐细化,其层间距与生长速率呈指数线性关系,即λ=-1＋5×e2.5;当抽拉速率低于5μm/s时,合金的定向凝固过程与平衡凝固相类似;另外,各相在稳定生长区的生长机制为共生生长,随着抽拉速率的增加,包共晶组织的定向排列性逐渐变差。     

Microstructure of directionally solidified Cu-Cr composites

Cu-Cr composites were prepared by self-made directional solidification equipment with the high temperature gradient and double-zone heating. The microstructural evolution was investigated during the directional solidification with the different solidification rate for Cu-1.0%Cr, Cu-1.7%Cr and Cu-5.6%Cr alloys, respectively. It is shown that for the hypoeutectic Cu-1.0%Cr alloy, the general microstructures consist of primary α(Cu) phase and the rod-like or needle-like (α β) eutectics, and for the hypereutectic Cu-1. 7%Cr and Cu-5.6%Cr alloys, α(Cu)phase, primary β(Cr) phase and (α β) eutectics coexist. With the increase of the solidification rate, the morphology evolution of every phase is that, 1st cellular(dendrite) of α(Cu) phase thins and cellular(dendrite) spacing shortens gradually, (α β) eutectics set in α(Cu) cellular or dendrite, and primary β(Cr) phase distributes unevenly on α (Cu) matrix, whose morphology undergoes the change from dendrite to particle.     

AZ31镁合金定向凝固的有限元模拟

定向凝固技术是获得新型功能材料的一种重要手段。基于有限元算法,对采用传统法和定向凝固法铸造的AZ31镁合金内部温度、应力、应变分别进行了仿真模拟。结果表明,采用定向凝固法铸造的AZ31镁合金,其内部温度为单相分布,更有利于形成柱状晶,从而提高Az31镁合金的性能。     

低合金钢齿轮铸造工艺改进

分析了低合金钢齿轮铸件原工艺存在的问题,通过改进工艺方案,合理设计浇注系统、冒口及其补贴,实现顺序凝固;通过加强质量控制,包括热节部位采用铬铁矿砂,砂芯内部采用石灰石砂,热割冒口等工艺措施,成功地获得了表面质量良好的齿轮铸件。