快速凝固过共晶铝硅合金的显微组织及摩擦学行为研究现状

过共晶铝硅合金由于具有高耐磨性、低热膨胀系数和高比强度而广泛应用于汽车和飞机制造业.该类合金在常规铸造下易产生粗大的脆硬初生硅相,降低合金力学性能及耐磨性.而利用快速凝固技术能够有效细化硅相,制备出高耐磨的过共晶铝硅合金.过共晶铝硅合金的性能可以通过改变共晶硅和初晶硅的形态及其分布、二次枝晶胞的尺寸或臂间距等方式加以改善.目前过共晶铝硅合金的研究大多是关于控制共晶和初晶硅的形态和分布,而针对常规铸造的细化晶粒工艺只对25％(质量分数)硅含量以下的过共晶铝硅合金有明显效果,因此研究人员聚焦于能对高硅含量的过共晶铝硅合金实现晶粒细化的快速凝固技术.快速凝固技术区别于常规铸造的特点是高冷却速度,研究发现冷却速度对过共晶铝硅合金的相平衡和微观结构有着显著的影响.随着冷却速度的增加,过共晶铝硅合金的微观结构细化、化学均匀性提高、固溶度增加,形成非晶及亚稳相,极大地改善了过共晶铝硅合金的性能.根据不同快速凝固技术制备的过共晶铝硅合金,其细化的显微组织及对应的摩擦学行为也有所不同.这些差异对于完善快速凝固过程中硅晶粒形核长大机制、形态演化机制及其对过共晶铝硅合金性能影响的理论体系能够起到有效的补充作用.本文综述了快速凝固过共晶铝硅合金四种主要制备方法:衬底急冷技术、快速凝固-粉末冶金技术、喷射沉积技术和选择性激光熔化技术,分析了相关快速凝固工艺的研究现状,对比了不同工艺制备的过共晶铝硅合金的显微组织及耐磨性能,并从理论体系、性能预测和技术工艺三方面对其未来的研究方向提出了一些可行建议.     

变质剂对高硅铝合金标准样品组织均匀性的影响

采用金相观察和X射线衍射分析方法研究了Al-Sr,Al-P,Cu-P三种变质剂对高硅(22%,质量分数)铝合金标准样品组织均匀性的影响.结果表明:未添加变质剂的标准样品中初晶硅呈粗大板片状,且局部聚集成团,组织均匀性差;添加了Al-Sr变质剂后初晶硅得到了一定的细化,但共晶硅高度分枝,组织分布仍不够均匀;添加Al-P和Cu-P变质剂后,标准样品中出现了新相AlP,使得初晶硅由板片状变成了细小的多边形颗粒,且弥散分布于整个基体中,同时共晶硅析出明显减少,而初晶硅数量增多,标准样品的组织均匀性好.另外对比发现,添加Cu-P变质剂后的改善效果最为显著,组织均匀性最好,且其成分均匀性通过传统的极差法检测也完全符合标准样品的要求.本工作从组织均匀性上为高硅铝合金标准样品的制备提供了新的判据和参考.     

Si-Al-Sn合金熔体中块体硅定向生长行为研究

为从Si-Al-Sn合金中有效分离初晶硅, 本研究提出并实现了三元合金定向生长块体硅的技术。通过考察冷却速度、合金成分、温度梯度与晶体生长速度比值(G/R)等参数及其影响机制, 确定促进块体硅稳定生长的有利条件; 对比Si-Al、Si-Sn二元合金体系, 采用成分过冷理论分析金属Sn对三元合金中块体硅生长行为的影响; 采用电子探针显微分析仪考察块体硅微观组织形貌与杂质分布。研究结果表明: 定向凝固方法能有效分离块体硅, 同时抑制块体硅内金属夹杂物生成, 并将杂质含量控制在其固溶度范围内, 成为一种有效分离、回收高纯初晶硅的新途径。     

利用强磁场控制过共晶铝硅合金的凝固组织

研究了静磁场和梯度磁场的强度和方向对Al-15.7%Si合金宏观和微观凝固组织的影响.结果表明,在不同的磁场条件下,从过共晶合金中析出的初晶硅粒的分布状况和共晶硅的形态和密度有显著不同.通过改变磁感应强度和磁场梯度的大小和方向可有效控制初晶硅的分布;合理控制强磁场的操作参数可达到细化铝硅共晶体的目的.强磁场的磁化力和洛伦兹力通过控制初晶硅颗粒迁移行为来改变其在合金基体中的分布状态,通过影响凝固过程中的对流现象改变合金的凝固组织.     

钠盐变质及振动对Zn - 27Al - Si合金组织和性能的影响

为了提高锌铝合金在干摩擦条件下的耐磨性以进一步拓宽其应用范围,在Zn-27Al合金中加入3%～4%Si,并通过钠盐变质及振动处理,制得Zn-27Al-Si合金.利用显微镜和电镜观察分析了试验合金中硅相形貌,并对合金的力学性能进行了测定.研究结果表明:钠吸附在硅晶体的生长台阶上使初晶硅产生大量分枝,最终生长成为球团状;振动一方面改变了结晶的温度场,抑制了共晶硅的析出,另一方面产生的"扰动"作用使硅球表面辐射生长的杆状共晶硅机械碎断,从而减少了硅相对基体的割裂作用,使试验合金在其他性能不变的情况下耐磨性提高3～4倍.     

AlSi5合金的制备

铝硅合金是一种典型的共晶合金,组织中的β相的性能与纯硅相似,在常规铸态条件下,共晶硅呈片状,初晶硅呈多角形块状和板状.硅相很脆,大大降低了合金的强度和塑性.因此,AlSi合金的性能和β相的形态与分布密切相关,尤其对于Si含量高的AlSi合金.本文综述了各种改善A1Si合金性能的制备方法(包括变质熔炼、快速凝固以及粉末冶金方法等),比较了各种方法制得材料的组织性能特点.同时研究了铸态和加工态AlSi5合金的组织结构特点.实验结果表明,经过轧制+退火处理后,α相晶粒尺寸＜50μm,α相和硅相的分布得到改善.     

过共晶铝硅合金半固态挤压铸造近终成形技术研究

研究了AI-Si(质量分数为24.3%和AI-Si(质量分数为29.2%)合金在机械搅拌作用下初晶硅形貌变化的工艺参数,半固态料坯的制备方法和半固态挤压成形的工艺方法.实验结果表明:605℃是该成分范围的过共晶铝硅合金合适的半固态搅拌温度,在该温度下恒温搅拌50min可有效地改变板条状初晶硅的形态,获得平均直径为200μm的球状化的初晶硅;在上述优化的半固态工艺条件下采用挤压铸造工艺获得了优质的近终成形圆盘形零件.     

高硅铝合金几种常见制备方法及其细化机理

高硅铝合金根据制备方法的不同,其细化方法及原理也有所不同.主要综述了熔炼铸造、快速凝固粉末冶金和喷射沉积工艺制备高硅铝合金的方法及其细化机理.     

尺度可控纳米晶硅粉的液氮低温球磨制备及其光致发光性能研究

本文以市售高纯硅粉作为原料,采用液氮低温球磨方法,制备高纯、晶粒尺寸可控、表面钝化的纳米晶硅粉.重点研究球磨工艺(球磨时间、球磨转速)对纳米晶硅粉晶粒尺寸、物相、微观结构的影响,液氮低温球磨法对纳米晶硅粉的表面钝化,并测试制得的纳米晶硅粉的光致发光性能.结果表明:通过液氮低温球磨可制得物相单一、晶粒尺寸均匀可控、表面氮钝化的纳米品硅粉;同时,光致发光性能结果表明随着纳米晶硅粉晶粒尺寸的降低,其光致发光谱明显蓝移,峰值从605nm移至590hm,且峰强显著增强.     

快速凝固和直流电处理对铝硅合金中硅形态的影响

用氮气雾化法制取了Al-12.54%Si合金微粒并进行700℃重熔处理,对加Sr变质的Al-13.23%Si合金熔体进行了直流电处理.用扫描和透射电镜研究了不同处理条件对Al-Si合金中共晶硅生长形态的影响.结果表明,快速凝固法制取的合金微粒与重熔处理试样中,共晶硅呈球状和条状.加Sr变质的共晶硅为弯扭的纤维状,直流电熔体处理后共晶硅转变为圆球状,其颗粒尺寸为50～200nm.     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.