Spheroidization of Eutectic Silicon in Direct-Electrolytic Al-Si Alloy

The spheroidization process of direct-electrolytic Al-Si alloy (DEASA) containing Si content in the range of 7 to 12 pct heated at temperatures of 778 K to 803 K (505 °C to 530 °C) was studied. The width, length, and aspect ratio of Si particles were measured to quantitatively analyze the microstructural variety of Si phase during the heating process in terms of chemical composition and remelting. Compared to existing Al-Si alloy, the lower soaking temperature of 778 K to 783 K (505 °C to 510 °C) is required to obtain the full spheroidization of the Si phase of DEASA. When remelting DEASA, a satisfactory granulation rate can be achieved at a higher soak temperature of 788 K to 803 K (515 °C to 530 °C). The origin of the high spheroidizaton rate is attributed to the microstructural characteristic relative to the electrolysis process. It would be expected that high crystallographic defects of Si grain result in the complete spheroidization of Si phase at lower temperatures for a short period.     

Al—Si共晶合金的化学变质剂的概述

介绍了Al-Si共晶合金在生产中的的重要作用,并指出了Al—Si合金变质的原因及意义;研究了各个变质剂在变质处理中的优点和其缺点．分析了变质效果。结果表明：Sr的变质效果比较好,但仍有空洞,故可以采用钠和Sr或者钠、Sr以及稀土复合的变质剂进行变质.     

Influence of Mg on Grain Refinement of Near Eutectic Al-Si Alloys

Although the grain-refinement practice is well established for wrought Al alloys, in the case of foundry alloys such as near eutectic Al-Si alloys, the underlying mechanisms and the use of grain refiners need better understanding. Conventional grain refiners such as Al-5Ti-1B are not effective in grain refining the Al-Si alloys due to the poisoning effect of Si. In this work, we report the results of a newly developed grain refiner, which can effectively grain refine as well as modify eutectic and primary Si in near eutectic Al-Si alloys. Among the material choices, the grain refining response with Al-1Ti-3B master alloy is found to be superior compared to the conventional Al-5Ti-1B master alloy. It was also found that magnesium additions of 0.2 wt pct along with the Al-1Ti-3B master alloy further enhance the near eutectic Al-Si alloy’s grain refining efficiency, thus leading to improved bulk mechanical properties. We have found that magnesium essentially scavenges the oxygen present on the surface of nucleant particles, improves wettability, and reduces the agglomeration tendency of boride particles, thereby enhancing grain refining efficiency. It allows the nucleant particles to act as potent and active nucleation sites even at levels as low as 0.2 pct in the Al-1Ti-3B master alloy.     

电热法生产铸造用共晶铝硅合金的能耗分析

介绍了电热法生产铸造用铝硅合金的工艺流程,同时对兑掺法和电热法生产铸造用铝硅合金的能耗进行了分析,结果表明：电热法生产共晶铝硅合金与兑掺法相比可节能5%以上,成本可降低700元以上。     

Influence of Electric-Current Pulse Treatment on the Formation of Regular Eutectic Morphology in an Al-Si Eutectic Alloy

This article describes the influence of an electric current pulse (ECP) on the microstructure of an Al-Si eutectic alloy during directional solidification. Experimental results demonstrate that the ECP has a significant effect on the microstructure of the directionally solidified Al-Si eutectic alloy. Application of ECP can increase the number and area percentage of the complex regular structure (CRS). Furthermore, the area of single CRS increases first and then declines with the increase of the ECP density. Analysis results suggest that the change of the CRS is a result of the forced convection caused by Lorentz force and change of temperature gradient induced by the ECP. The growth process of the CRS is discussed.     

Physical Properties and Solidification Structure of Al－SiEutectic Alloy Melt with Cerium Modification

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Effect of Pulsed Magnetic Field on Microstructure and Mechanical Properties of Eutectic Al-Si Alloy

Pulsed magnetic field (PMF) processing has been employed for refining the microstructure of eutectic (Al-12.4Si) Al-Si alloy in the current study. The effect of PMF on microstructure and mechanical properties of eutectic Al-Si alloy was studied. The results show that the morphology of primary α-Al was refined from coarse columnar dendrites to fine equiaxed dendrites by PMF treatment. Fine short rod-like or rounded particle-like eutectic silicon was formed during solidification of eutectic Al-Si alloy treated by PMF. PMF treatment reduced the size of eutectic silicon from 49 to 2.3 μm in length, and the width from 3.1 to 0.6 μm. The aspect ratio of eutectic silicon was also reduced by PMF treatment from slightly less than 16 to slightly less than 4. The ultimate tensile strength and elongation of eutectic Al-Si alloy with PMF treatment at room temperature were about 201 MPa and 8.8 pct, respectively, which were increased by 47 and 73 pct, respectively, compared with the eutectic Al-Si alloy without PMF treatment.     

稳恒电磁场对铸造用共晶铝硅合金中铁相的影响研究

针对碳电热法生产的一次铝硅合金经稀释精炼后其主要杂质为铁,而传统加除铁剂过滤的方法除铁效率较低的问题,采用锰为除铁剂,研究了电磁场对铝硅合金中富铁相的影响.结果表明,加入直流磁场后铝硅合金中的铁相由针状长大到片状、球状,合金中的铁相体积随直流磁场强度的增大而增大,当磁场强度达到一定值时针状的铁相消失,从而使最终合金中的绝大部分富铁相被去除.     

X-Ray Videomicroscopy Studies of Eutectic Al-Si Solidification in Al-Si-Cu

Al-Si eutectic growth has been studied in-situ for the first time using X-ray video microscopy during directional solidification (DS) in unmodified and Sr-modified Al-Si-Cu alloys. In the unmodified alloys, Si is found to grow predominantly with needle-like tip morphologies, leading a highly irregular progressing eutectic interface with subsequent nucleation and growth of Al from the Si surfaces. In the Sr-modified alloys, the eutectic reaction is strongly suppressed, occurring with low nucleation frequency at undercoolings in the range 10 K to 18 K. In order to transport Cu rejected at the eutectic front back into the melt, the modified eutectic colonies attain meso-scale interface perturbations that eventually evolve into equiaxed composite-structure cells. The eutectic front also attains short-range microscale interface perturbations consistent with the characteristics of a fibrous Si growth. Evidence was found in support of Si nucleation occurring on potent particles suspended in the melt. Yet, both with Sr-modified and unmodified alloys, Si precipitation alone was not sufficient to facilitate the eutectic reaction, which apparently required additional undercooling for Al to form at the Si-particle interfaces.     

含齿形裂隙类岩石材料单轴压缩试验研究

为研究含齿形裂隙岩石在单轴压缩下的破坏特征及强度特性,制作了含不同裂隙倾角和起伏角的齿形裂隙类岩石材料试件,并采用岩石力学伺服试验机进行单轴压缩试验。试验结果表明：（1）试件主要产生拉伸、剪切和拉剪复合裂纹,且根据裂纹的扩展路径可划分为A型（拉伸破坏）、B型（剪切破坏）、C型（复合破坏）3种破坏模式,裂隙倾角对试件最终破坏模式影响显著;（2）当裂隙倾角较小时,试件应力—应变曲线为多峰曲线,随着裂隙倾角的增大,曲线呈单峰形式,表现为延性减弱,脆性增强,而裂隙倾角相同但起伏角不同的试件应力—应变曲线大致相同;（3）当裂隙起伏角相同时,试件当量峰值强度随裂隙倾角的增大呈先减小后增大的规律,且裂隙起伏角对试件当量峰值强度的影响小于裂隙倾角。     

Effect of Aging Time on Mechanical Properties and Wear Characteristics of Near Eutectic Al–Si–Cu–Mg–Ni Piston Alloy

Al–12Si–3Cu–1 Mg–1.78Ni alloy is widely used for piston parts in automobile industry. The present paper investigates the effect of aging time for 1–16 h at 180 °C after solution treatment of the alloy at 500 °C for 5 h, on alloys prepared by gravity casting and squeeze casting. The wear rate of the alloy shows a minimum at an intermediate aging time. The hardness and ultimate tensile strength showed a peak at intermediate aging time. Mechanical properties and wear resistance are found to be better in squeeze cast alloy. The result are explained based on the microstructure developed during casting process and on heat treatment for various durations.     

锌铝共晶合金丝研制

对含铝５％φ６ｍｍ的锌铝共晶合金丝进行了试验研究，解决了粗坯难于盘圆及生产过程中的增强锌铝合金塑性甚至超塑性的问题。阐述了合金丝的生产工艺，讨论了过程影响因素，文章最后概括了生产技术条件，为锌铝共晶合金丝的生产奠定了技术基础。     

NanoSIMS Analysis of Trace Element Segregation during the Al-Si Eutectic Reaction

The purpose of the present article was to test, for the first time, the potential of the NanoSIMS for quantifying the microscale spatial distribution of trace elements in aluminum alloys. As a suitable test case, two variants of an as-cast industrial A356 alloy have been chosen and analyzed quantitatively. The results show that Sr segregates preferentially to the α-Si particles rather than to the Al matrix. The Na segregates preferentially to α-Si, but in contrast to Sr, Na is inhomogeneously distributed in the particles and tends to accumulate at parts of their surfaces. The Ca segregates preferentially to the Al matrix and was not found in α-Si. This suggests that impurity-induced twinning is probably not the mechanism responsible for the flake-to-fibrous transition observed in Ca-modified Al-Si-alloys. The P was difficult to analyze as the ³1P-peak was close to the peak of the molecule fragment ³1Si + ¹H. The complication can probably be resolved in future studies. The present work demonstrated that NanoSIMS is a tool with great potential for providing new insight into microscale trace element segregation in Al alloys. This article is based on a presentation made in the symposium entitled “Solidification Modeling and Microstructure Formation: In Honor of Prof. John Hunt,” which occurred March 13–15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.     

铝硅合金低温加硅研究

扼要介绍了铝硅合金生产中的五种熔配工艺,以共晶型与过共晶型两种不同牌号的铝硅合金为例阐述了低温加硅熔炼技术,获得了最佳工艺,该方法质量稳定、节约能源、环境友好。     

Tensile and Fracture Properties of Cast and Forged Composite Synthesized by Addition of Al-Si Alloy to Magnesium

Cast Mg-Al-Si composites synthesized by addition of Al-Si alloy containing 10, 15, and 20 wt pct of Si, in molten magnesium, to generate particles of Mg₂Si by reaction between silicon and magnesium during stir casting has opened up the possibility to control the size of these particles. The microstructure of the cast composite consists of relatively dark polyhedral phase of Mg₂Si and bright phase of β-Al₁₂Mg₁₇ along the boundary between dendrites of α-Mg solid solution. After hot forging at 350 °C, the microstructure has changed to relatively smaller sizes of β-Al₁₂Mg₁₇ and Mg₂Si particles apart from larger grains surrounded by smaller grains due to dynamic recovery and recrystallization. Some of the Mg₂Si particles crack during forging. In both the cast and forged composite, the Brinell hardness increases rapidly with increasing volume fraction of Mg₂Si, but the hardness is higher in forged composites by about 100 BHN. Yield strength in cast composites improves over that of the cast alloy, but there is a marginal increase in yield strength with increasing Mg₂Si content. In forged composites, there is significant improvement in yield strength with increasing Mg₂Si particles and also over those observed in their cast counterpart. In cast composites, ultimate tensile strength (UTS) decreases with increasing Mg₂Si content possibly due to increased casting defects such as porosity and segregation, which increases with increasing Mg₂Si content and may counteract the strengthening effect of Mg₂Si content. However, in forged composite, UTS increases with increasing Mg₂Si content until 5.25 vol pct due to elimination of segregation and lowering of porosity, but at higher Mg₂Si content of 7 vol pct, UTS decreases, possibly due to extensive cracking of Mg₂Si particles. On forging, the ductility decreases in forged alloy and composites possibly due to the remaining strain and the forged microstructure. The initiation fracture toughness, J _IC , decreases drastically in cast composites from that of Mg-9 wt pct. alloy designated as MA alloy due to the presence Mg₂Si particles. Thereafter, J _IC does not appear to be very sensitive to the increasing presence of Mg₂Si particles. There is drastic reduction of J _IC on forging of the alloy, which was attributed to the remaining strain and forged microstructure, and it is further lowered in the composites because of cracking of Mg₂Si particles. The ratio of the tearing modulus to the elastic modulus in cast composites shows a lower ratio, which decreases with increasing Mg₂Si content. The ratio decreases comparatively more on forging of cast MA alloy than those observed in forged composites.     

镧镨铈混合稀土金属在Al-Si合金中的作用

本文研究了一种新型的镧镨铈混合稀土对铝硅合金中共晶硅的变质作用和铁相的作用。研究证明 ,镧镨铈混合稀土对 Al- Si合金中共晶硅有着比富铈混合稀土更强的变质能力 ,其残余量在 0 .17%和 0 .2 4%之间即可使硅含量接近 12 %的铝硅二元合金得到良好变质 ;镧镨铈混合稀土有促进 Al- Si合金中针状铁相析出的作用 ,为保证铝硅合金中不出现针状铁相 ,镧镨铈混合稀土的加入量以不超过 0 .45 %为好。     

Influence of Phosphorus on the Nucleation of Eutectic Silicon in Al-Si Alloys

The role of phosphorus (P) in the heterogeneous nucleation of eutectic silicon (Si) and the evolution of eutectic grains in hypoeutectic aluminum-silicon alloys were investigated. Systematic additions of P in the range of 0.5 to 20 ppm to Al-7 wt pct Si alloys of different purities have shown that the morphology of the eutectic Si changes from a fine plate- to a coarse flake-like structure. The growth of eutectic grains was investigated by interrupting the eutectic reaction by quenching experiments. Moreover, the macroscopic growth mode of the eutectic grains was characterized by electron backscatter diffraction. An increase in P concentration from 2 to 3 ppm resulted in a transition of the macroscopic growth mode of the Al-Si eutectic in high purity alloys from growth with a planar front with a strong dependence of the thermal gradient, to nucleation in the vicinity of the primary Al dendrites and subsequent growth of distinct eutectic grains. It is suggested that AlP particles are the key impurities acting as potential nucleation sites for eutectic Si. This is further substantiated as with increasing P concentration nucleation and growth of the Al-Si occurred at higher temperatures close the equilibrium Al-Si eutectic solidification temperature at 850 K (577 °C). In addition, the recalescence undercooling ΔT _R,eu was reduced from 4.5 K (0.5 ppm P) to 1.5 K (20 ppm P) in high purity alloys. This was accompanied by a drastic increase of the nucleation rate of the eutectic grains.     

铝硅合金的液态模锻

本文阐述了铝硅合金液态模锻过程中施加压力对结晶组织和机械性能的影响,提出了合理选择工艺参数的原则,此外还讨论了液态模锻模具结构设计方面应考虑的特点。     

Fe-C共晶合金的液态结构和粘度

用θ-θ液态金属X射线衍射仪研究了Fe-4,30C共晶合金的液态结构。结果表明，温度在1200～1400℃范围内时，液态Fe-4.30C共晶合金原子间的最近邻距离为0.259～0.260nm。径向分布函数的高斯分解曲线表明，液态Fe-4，30C共晶合金在1200℃具有类似面心立方结构的特征。采用回转振荡粘度仪测试的结果表明，随着温度的降低，该合金的粘度有规律地增加；而且在1150℃（熔点附近），粘度变化异常，这种异常与碳聚集成石墨原子团有关。     

Characteristics of Eutectic α(Cr,Fe)-(Cr,Fe)23C6 in the Eutectic Fe-Cr-C Hardfacing Alloy

Metallurgical and Materials Transactions A - A specific eutectic (Cr,Fe)-(Cr,Fe)23C6 structure had been previously reported in the research studies of Fe-Cr-C hardfacing alloys. In this study, a...