复合变质对Al-20%Si合金耐磨性能的影响

在不同P、RE添加量下对P-RE复合变质和未变质的过共晶铝硅合金的耐磨性进行了研究。结果表明:P-RE复合变质明显提高了合金的耐磨性,当加入0.08%P和0.6%RE时,合金的耐磨性达到最佳,磨损失重量从未变质的5.2mg降低到4.225mg,减少了19%。磨损主要为磨粒磨损,磨粒来源是硅相的破碎剥落。合金耐磨性能的改善与复合变质引起的共晶硅和初晶硅颗粒的细化和合金强度、塑性的提高有关。     

The Origins of Primary Silicon Particles in Hypereutectic Aluminium-Silicon Alloys

Castings of hypereutectic aluminium-silicon alloys were produced in order to examine the mechanisms of primary silicon particle formation. In castings made using cold moulds, primary silicon particles are shown to originate from transient eutectic colonies which form as the molten metal comes in contact with the mould walls and are subsequently disrupted by local reheating, releasing eutectic silicon particles to serve as nuclei for primary silicon particles. Impurity elements also serve as heterogeneous nucleating agents for primary silicon particles. It is shown that small additions of strontium greatly reduce the influence of these elements.     

电热法生产过共晶Al-Si合金的组织与性能研究

对电热法生产铝硅合金配制的Al-20Si合金进行了P-RE复合变质处理,对变质后的微观组织和力学性能进行了分析.结果表明,合金经复合变质后,合金的初晶硅尺寸得到明显细化,共晶硅由长针状变为短杆状或者细小的颗粒状;其抗拉强度由182MPa提高到205MPa,提高12.6%了,其伸长率由0.22%提高到0.26%,提高了18.2%.然而与纯铝配制的过共晶铝硅合金相比,其抗拉强度和伸长率都相对较低,原因在于电热法生产铝硅合金配制的过共晶铝硅合金中Fe含量较高.     

多主元高熵合金AlTiFeNiCuCrx微观结构和力学性能

研究了不同Cr含量的AlTiFeNiCuCrx多主元高熵合金的微观组织和力学性能特点.结果表明,Cr含量的增加使合金的凝固模式从亚共晶向过共晶凝固转移,铸态组织由先析出枝晶相、菊花状共晶组织和枝晶间相组成.合金仅由简单的体心立方结构和面心立方结构两相组成.Cr含量的增加对合金硬度的提高较小.该合金为低温脆性材料,但在1073 K高温时具有很好的塑性变形能力和较高的强度,当x=1-1.5时,合金具有最优的压缩强度和塑性组合.     

Spray forming of hypereutectic Al–Si alloys

To develop advanced aluminum alloys with high silicon content, hypereutectic aluminum silicon alloys AlSix (x = 18, 25, and 35 wt.%) in the form of cylindrical billet have been spray formed under different thermal conditions. To help in spray forming parameter selection and interpretation of experimental results, phase diagram of the alloys and their thermochemical data such as liquid fractions and enthalpies in function of temperature have been calculated. The spray formed hypereutectic Al–Si alloys are typically composed of refined and uniformly distributed primary silicon and modified eutectic. Thermal conditions and silicon content of the deposited materials have significant influence on the metallurgical quality of the spray formed Al–Si alloys. Strong cooling condition is required for spray forming Al–Si alloys with high silicon content.     

Role of scandium additions in primary silicon refinement of hypereutectic Al–20Si alloys

This study investigates the effect of Sc on the formation of primary silicon during the solidification of hypereutectic Al–20Si alloys. The evolution of the microstructure was studied using thermal analysis. The results show that the addition of 0·2 and 0·4 wt-% Sc suppresses the nucleation of primary silicon due to the formation of ScP particles instead of AlP particles. For large Sc additions, at the centre of the samples, the primary silicon has a star-shaped morphology with thin branches. The addition of Sc decreases the P refinement ef?ciency in hypereutectic Al–20Si alloys, which may be a result of the formation of a ScP phase. The results suggest that the addition of Sc poisons the nucleant particles of the primary and eutectic silicon.     

Influences of complex modification of P and RE on microstructure and mechanical properties of hypereutectic Al-20Si alloy

P and RE complex modification of hypereutectic A1-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3μm and the eutectic silicon can be refined from 8.3 μm to 5.2μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.     

Microstructural evolution during containerless rapid solidification of Ni–Mo eutectic alloys

Ni–45%Mo hypoeutectic, Ni–47.7%Mo eutectic and Ni–50%Mo hypereutectic alloys are rapidly solidified during containerless processing in drop tube. The microstructures of Ni–47.7%Mo eutectic alloy are composed of lamellar eutectic plus anomalous eutectic of Ni and NiMo phases. When the droplet size decreases, the volume fraction of anomalous eutectic becomes larger. The structural morphology transforms into Ni dendrite plus lamellar eutectic in very small droplets which are highly undercooled. The microstructures of Ni–45%Mo hypoeutectic alloy are characterized by primary Ni dendrite plus lamellar eutectic, whereas those of Ni–50%Mo hypereutectic alloy consist of NiMo dendrite plus lamellar eutectic. For both off-eutectic alloys, the experimental results show that the microstructure evolution depends mainly on droplet size. In the case of Ni–45%Mo hypoeutectic alloy, with the decrease of droplet size, the primary Ni phase transforms from dendrites to equiaxed grains. As for Ni–50%Mo hypereutectic alloy, when droplets become smaller and smaller the microstructural transition proceeds from primary NiMo dendrite plus lamellar eutectic to anomalous eutectic. The calculated highest undercoolings of the three alloys are 226, 182 and 135 K, respectively. By classical nucleation theory, Ni phase is the primary phase to nucleate for Ni–47.7%Mo eutectic alloy. The TMK eutectic growth and LKT/BCT dendritic growth theories are applied to analyze the rapid solidification process and investigate the microstructural transition mechanisms. The coupled zone of Ni–Mo eutectic alloy has also been calculated on the basis of TMK and LKT/BCT models, which covers a composition range from 45.7% to 57.1% Mo.     

Effect of Slow Cooling Rate on the Microstructure of Sr-modified Al-Si Eutectic Alloys

A technique to obtain a fully-modified eutectic (fibrous silicon) structure without primary crystals in commercial purity Al-12.7% Si-0.04% Sr is described. The alloy was solidified at a cooling rate of 1.5 K/min, that is lower than the usual cooling rate in sand casting. The structures, and calculated solid-liquid interface velocities, are in agreement with the classification in diagrams for directionally solidified eutectic alloys. The ultimate tensile strength of the fully modified eutectic samples is as high as 255 MN/m², that is higher than that of chill-cast alloys of similar composition.     

Microstructural Characteristic and Mechanical Behavior of Nodular Silicon Hypereutectic Al-Si Alloys

The microstructure and mechanical properties of Al-Si-Cu-Mg alloys containing 12 wt.% to 30 wt.% Si are discussed. The eutectic and primary silicon particles are nodulized by a designed modification practice followed by a solution heat treatment of 6 h to 8 h at 510°C to 520°C. Metallographic analysis was used to measure structural characteristics of the Si-rich structures. Spheroidization of silicon phase leads to an increase in tensile strength and ductility of alloys at room temperature and 300°C compared with commercial Al-Si alloy. Increasing Si concentration causes the ultimate tensile strength and elongation at room temperature to fall due to the appearance of coarse silicon particles, but the ultimate tensile strength at 300°C remains unchanged.     

Variation of microstructure of RE-containing AlSi20Cu2Ni1RE0.6 alloy with different cobalt contents

Cobalt is generally considered as the element that can promote the high-temperature mechanical properties of Al-Si alloys. In order to develop new hypereutectic Al-Si alloys that can be used at high temperature, the changes of microstructure of Al-20Si-2Cu-1Ni-0.6RE-xCo alloy with different contents of Co were studied in this paper. The results show that, under P-RE complex modification of the alloy melt, the content of Co varying from 0 to 1.5% had little influence on the refining effect of primary Si and modification effect of eutectic Si, but the amount of acicular RE-bearing Al-RE-Ni-Co-Si compounds gradually increased with the increase of Co content. In addition, Co could also modify the morphology of Fe-bearing phases, which solidified as particles instead of long needles. The addition of Co even has an adverse effect on the tensile strength of this RE-containing hypereutectic Al-Si alloy.     

电磁搅拌对铝硅合金显微组织的影响

研究电磁搅拌对亚共晶、共晶及过共晶Al—Si合金显微组织的影响，并对其在EMS作用下的液淬组织和凝固组织进行研究。试验表明：电磁搅拌能够改变正常的铝硅合金凝固行为。本试验条件下EMS作用下非树枝晶存在异常长大、聚集和缩颈熔断现象；对亚共晶Al-Si合金凝固主要表现为共晶组织发生粗化；对过共晶Al-Si合金凝固主要表现为初生硅的聚集与偏聚。     

压力铸造对Al-Si-Cu合金组织的影响

本文研究了压力铸造条件下Al-Si-Cu多元合金的显微组织,通过与重力铸造条件下的比较发现：压力铸造不仅能明显细化Al-Si-Cu合金中的共晶组织和初生相(初生α-Al或初生硅),而且可以改善Al-Si-Cu多元合金中金属问化合物的形态和分布,甚至改变析出相的构成。     

Rapidly solidified hypereutectic Al-Si alloys prepared by powder hot extrusion

Rapidly solidified hypereutectic Al-Si alloys were prepared by powder hot extrusion.By eliminating vacuum degassing procedure.the fabrication routine was simplified.The tensile fracture mechanisms at room temperature and elevated temperature were investigated by SEM fractography.Compared with KS282 casting material,the tensile strength of rapidly solidified Al-Si alloy is greatly improved due to silicon particles refining while its density and coefficient of thermal expansion are lower.than those of KS282.The wear resistance of RS AlSi is better than that of KS282.     

锶在Al-Si合金LM6中的变质作用

用Ｓｒ对Ａｌ－Ｓｉ合金ＬＭ６（英国牌号,我国相近牌号为ＺＬ１０２）进行变质处理,当ＬＭ６合金处于过共晶成分范围时,获得细小弥散分布的共晶Ｓｉ组织,但初晶Ｓｉ尺寸较大,呈多角形块状。将ＬＭ６合金调整为亚共晶成分后,几乎没有初晶Ｓｉ析出,从而得到变质效果良好的细小,弥散共晶Ｓｉ组织。     

Semi-solid processing of hypereutectic A390 alloys using novel rheoforming process

The feasibility of semi solid processing of hypereutectic A390 alloys using a novel rheoforming process was investigated. A combination of the swirl enthalpy equilibration device (SEED) process, isothermal holding using insulation and addition of solid alloy during swirling was introduced as a novel method to improve the processability of semi solid slurry. The effects of isothermal holding and the addition of solid alloy on the temperature gradient between the centre and the wall and on the formation of α(Al) particles were examined. In additional tests, phosphorus and strontium were added to the molten metal to refine the primary and eutectic silicon structure to facilitate semi solid processing. The results show that the combination of the SEED process with two additional processing steps can produce semi-solid A390 alloys that can be rheoprocessed. The microstructure reveals an adequate amount of non-dendritic α(Al) globules surrounded by liquid, which greatly improves the processability of semi-solid slurry.     

Microstructure and mechanical properties of hypereutectic Al-Si alloy modified with Cu-P

The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The results indicate that the Cu-P master alloy possesses not only obvious modification effect,but also longevity effect with more than 8 h on the hypereutectic Al-Si alloy.It is shown from thermal calculation,scanning electron microscope（SEM）,and energy dispersive analysis of X-rays（EDAX） that the modification mechanism of Cu-P on primary silicon in the castings is heterogeneous nucleation around AlP particles.The Cu-P master alloy has no or little modifying effect on eutectic silicon,even though it has obvious modification on primary silicon in the castings.This may be because of the fast transformation of eutectic silicon at a very narrow temperature,which will notably weaken the role of AlP particles as heterogeneous nuclei for eutectic silicon.     

MICROSTRUCTURE ANALYSIS AND MECHANICAL PROPERTIES OF Zn—Al ALLOY ROD PRODUCED BY HEATED MOLD CONTINUOUS CASTING

The new technology of continuous casting by heated mold was used to produce directional solidification ZA alloy lines to eliminate the inter defects of these lines and increase their mechanical properties. The results are as follows: (1) The microstruc-ture of the ZA alloy lines is the parallel directional dendritic columnar crystal. Every dendritic crystal of eutectic alloy ZA5 was composed of many layer eutectic β and η phases. The micro structure of hypereutectic ZA alloys is primary dendritic crystal and interdendritic eutectic structure. The primary phase of ZA8 and ZA12 is β, among them, but the primary phase of ZA22 and ZA27 is a. (2) Through the test to the as-cast ZA alloy lines made in continuous casting by heated mold, it is found that the tensile strength and hardness increase greatly, but the elongation decreases. With the increase of aluminum amount from ZA 5 to ZA 12, ZA22 and ZA27, the tensile strength increases gradually. ZA27 has the best comprehensive mechanical properties in these     

代铜用硅相增强铸造锌铝复合材料的研究

选择多种成分的锌铝合金，以硅为增强相，扩大硅的成分范围，采用复合钠盐和稀土混合物对合金中的硅进行变质处理，测定试验合金的冲击韧度、硬度、抗拉强度、耐磨性以及高温耐磨性等力学性能，探讨钠盐和稀土对锌铝硅合金中硅的变质机制，优选综合力学性能较好的试样进行高温磨损测试，并观察其显微组织。结果表明，锌铝合金中加入硅相并进行复合变质后，其综合力学性能进一步提高，这归功于硅相的骨架作用。     

Microstructural change in gravity cast Mg−Ni alloys with Ni contents

The effects of Ni content on the microstructures of gravity cast Mg−Ni alloys were examined. Different shapes of primary solid particles and microstructures of the eutectic matrix were observed with varying Ni content. The eutectic matrix in the hypoeutectic alloy consisted of rod-like Mg₂Ni phase with a small amount of α-Mg phase. The eutectic matrix in the near-eutectic and hypereutectic alloys consisted of eutectic cells oriented in different directions. A transition of lamellae to fiber occurred. The formation of cellular structure and transition of lamellae to fiber resulted from two-phase instability in the coupled region induced by constitutional undercooling.