Sc和Si相互作用对铸造Al-Si-Sc合金组织和性能的影响

通常在铸造Al-Si合金加入Sc来改善合金的性能,但是Si和Sc的相互作用对合金组织和性能影响仍需要进一步深入研究。本文研究了不同含量的Si和Sc对合金组织和性能的影响,结果表明,Sc通过原位形成初生Al_(3)Sc作为α-Al异质形核质点从而细化α-Al晶粒;在凝固过程中,共晶反应生成了网格状AlSi_(2)Sc_(2)相,包晶反应形成了块状AlSi_(2)Sc_(2)相;两种AlSi_(2)Sc_(2)相都会消耗合金中Sc原子,从而降低了Al_(3)Sc的细化效果;Sc还变质共晶Si为更有序的纤维/片状结构,适当的Si与Sc的比可以避免AlSi_(2)Sc_(2)的形成;Al-6Si中Sc含量从0.3%增加至1%时,抗拉强度和屈服强度均上升,但由于AlSi_(2)Sc_(2)相的存在,其伸长率下降;当Sc含量为1%、Si含量从6%降至3%时,抗拉强度、屈服强度和伸长率分别上升2%、12%和21%,主要是凝固过程中析出了Al_(3)Sc而非AlSi_(2)Sc_(2)相。最后,还讨论了Si-Sc交互作用对组织演变的机制。

富Ce稀土对多元Al-Si活塞合金凝固组织的影响

采用DSC以及光学显微镜与扫描电镜研究了富Ce稀土(0.1wt%,0.3wt%,0.5wt%)对多元近共晶Al-11.5Si-4Cu-2Ni-1Mg-0.5Fe(wt%)活塞合金凝固组织的影响。发现富Ce稀土加入对该合金的共晶硅和多种第二相的凝固温度、形态与体积分数均有明显影响。富Ce稀土的加入,使Al-Si共晶温度降低,T-Al_(9)FeNi相和δ-Al_(3)CuNi相析出温度升高。富Ce稀土加入量0.3wt%时,共晶硅变质效果最佳,T-Al_(9)FeNi相由初始的板条状转变为小块状,体积分数减小到3.22vol%,δ-Al_(3)CuNi相由初始的片状转化为鱼骨状,体积分数增加到6.47vol%。富Ce稀土中La、Ce原子在凝固过程中富集在固液界面前沿,增大了成分过冷,细化共晶组织。当富Ce稀土含量为0.5wt%时,合金中出现长针状富稀土相。

Al-3Y-2B中间合金对Al-20Si铸态组织和力学性能的影响

研究了Al-3Y-2B中间合金对过共晶Al-20Si二元合金铸态组织及性能的影响规律,基于冷却曲线分析(CCA)方法,测得了Al-20Si二元合金中加入Al-3Y-2B中间合金前后的冷却曲线。实验结果表明:Al-20Si合金熔体加入1.0%的Al-3Y-2B中间合金后,初生硅的生成温度降低约13℃;铸态组织的初生硅平均尺寸由110μm减小到33μm,初生硅形貌由粗大的多边形结构转变为尺寸细小的板状结构;共晶硅形貌由细长针状转变为短针状和短棒状;铸态合金的伸长率(EL)由1.62%提升到1.98%,极限抗拉强度(UTS)由120 MPa提升到162 MPa。Al-3Y-2B的添加量为0.5%时,组织中的初生硅和共晶硅被很好的细化;Al-3Y-2B的添加量提高到1.0%时,Al基体中开始出现脆性相,影响合金的机械性能。

THERMAL RATE TREATMENT AND ITS EFFECT ON MODIFICATION OF Al-Si ALLOYS

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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 Al-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 23.3 μm and the eutectic silicon can be refined from 8.3 μm to 5.2 μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.

Al-Si-P master alloy and its modification and refinement performance on Al-Si alloys

An Al-Si-P master alloy has been developed by an in-situ reaction and the electron probe microanalyzer （EPMA） results show that there are many pre-formed AlP particles contained in the master alloy. Silicon introduced into the system plays an important role in remarkably improving the distribution and content of AlP particles due to their similar crystal structure and lattice parameters. ZL109 alloys have shown fast modification response to the addition of 0.5% Al-15Si-3.5P master alloy at 720℃, with a mass of primary Si precipitating in size of about 15 μm. Also, coarse primary Si grains in AI-30Si alloy can be refined dramatically from 150 μm to 37 μm after the addition of 2.0% Al-15Si-3.5P master alloy at 850℃. The P recovery of the Al-15Si-3.5P master alloy is much higher than that of a Cu-8.5P master alloy due to the pre-formed AlP particles.

Modification and refinement mechanism of Mg_2Si phase in Sr-containing AZ61-0.7Si magnesium alloy

The effect of Sr on modification and refinement of the Mg 2 Si phase in an AZ61-0.7Si magnesium alloy has been investigated and analyzed.The results indicate that Sr can effectively modify and refine the Chinese-script shaped Mg2Si phase in the AZ61-0.7Si alloy.By adding 0.06wt.%-0.12wt.%Sr to AZ61-0.7Si alloy,the Mg2Si phase in the alloy can be changed from the initial coarse Chinese-script shape to fine granule and/or irregular polygonal shapes.Accordingly,the Sr-containing AZ61-0.7Si alloy exhibits higher tensile and creep properties than the AZ61-0.7Si alloy without Sr modification.The mechanism on modification and refinement of the Mg2Si phase in Sr-containing AZ61-0.7Si alloy is possibly related to the following two aspects:(1)adding Sr may form the Al4Sr phase which can serve as the heterogeneous nucleus for the Mg2Si particles and/or(2)adding Sr may lower the onset crystallizing temperature and increase the undercooling level.

Modification mechanism of hypereutectic Al-Si alloy with P-Na addition

Effect of P-Na united modification on Al-22%Si-1.0%Cu-0.5%Mg-0.5%Mn alloy was studied. The results show that the refining effect of P-Na addition on primary silicon is superior to that of P and the former could modify eutectic silicon at the same time. Effects of P-Na modification on crystallization and microstructure of hypereutectic Al-Si alloys were studied with Electron-Scanning Microscope, Electron-Probe and X-ray diffractometer. The modification mechanism represents that on one hand, the primary silicon is refined by AlP as heterogeneous nucleus; on the other hand, when Na is added at the same time, P atoms are difficult to diffuse in the melt, and then enrichs on the growing faces of silicon phase. Moreover, a SiP compound was also discovered in Si crystals, which prevents the growth of silicon phase and refines the primary silicon.

Modification ofβ-Al_5FeSi Compound in Recycled Al-Si-Fe Cast Alloy by Using Sr,Mg and Cr Additions

The effects of Sr,Mg,Cr,Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated.The experimental results show that the additions of Cr and Sr/Cr successfully modified the platelet and flake-likeβ-Al-5FeSi phases （β-compound） into the fibrousα-Al-8Fe-2Si （α-compound）.The additions of Sr and Sr/Mg were less effective to modify theβ-compound into theα-compound,while the eutectic Si was fully modified into the fibrous morphology.A small secondary dendrite arm spacing （DAS） was found in the Sr-added,Cr-added and Sr/Cr-added alloys,especially in a steel mold.The Sr,Sr/Cr and Sr/Mg combined additions modify the eutectic Si simultaneously.A sludge phase was found in the addition of Cr-added,Sr/Cr-added and Mg-added alloys,especially in the graphite mold casting.The volume fraction ofβ-compounds was decreased by the addition of various modifying elements. The Cr and Sr/Cr combined additions are very effective to modify theβ-compound for the recycled Al-Si-Fe based alloys.

Modification effect of pure rare earth metal La on as-cast hypereutectic Al-17%Si alloys

The modification effect of La addition on the microstructural characteristics of hypereutectic Al 17%Si alloys was studied. Microstructures were examined using conventional optical microscopy and electron probe X ray microanalyzer. The morphology of Si crystal was evaluated by quantitative metallographical analysis. The results indicate that simultaneous modification to both primary and eutectic Si crystals is obtained by the addition of pure rare earth metal La in the hypereutectic Al 17%Si alloys while the optimal effect of La is obtained at a rather large scale. La begins to form intermetallic compound when its concentration exceeds approximately 1%, which appears as dark platelets in etched specimens. Electron probe X ray microanalysis experiment shows that La rich platelet could be represented as Al 1Si 2La 2 consisting of LaSi 2 and some unknown ternary Al x Si y La phase.

Modification mechanism of cerium on the Al-18Si alloy

The effect of the rare earth cerium （Ce） on the hypereutectic Al-Si alloy under different casting states have been studied by optical microscope and quantitative image analysis. It is found that the size and the quantity of primary silicon in castings decrease with the increase of added Ce in the melt. Meanwhile primary silicon changes from branched shape to fine facetted shape. Although the modification on eutectic silicon in castings also improves with the increase of added Ce in the melt, the effect of modification on eutectic silicon away from primary silicon is more obvious than that on eutectic silicon close to primary silicon. The modification mechanism was analyzed in detail by means of scanning electron microscope equipped with energy dispersive analysis of X-ray and thermodynamics analysis, which included the analysis on the change in standard Gibbs energy of reaction and reaction equilibrium.

Effect of mixed rare earth oxides and CaCO_3 modification on the microstructure of an in-situ Mg_2Si/Al-Si composite

The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive spectrum analysis. The results showed that the morphol-ogy of the primary Mg2Si phase particles changed from irregular or crosses to polygonal shape,their sizes decreased from 75 μm to about 25 μm,and the compound of both the oxide and CaCO3 was better than either the single mixed rare earth o...

Thermodynamics of effect of modification on microstructure of Al-Si alloy melt

Thermodynamic law of interaction between modification element and alloy melt has been analyzed, and the effect of modification element on electrical resistivity of melt has been studied. It was found that, in a certain range of concentration, there exists a ‘node’ where the alloy melt reconstruction will occur. An extreme value appeared in the relationship curve of melt’s resistivity and modification element’s concentration corresponding to the ‘node’, where the solidified structure of the alloy changed remarkably.

Functions and mechanism of modification elements in eutectic solidification of Al-Si alloys:A brief review

Being used more and more widely in engineering,AlSi alloys comprise about 80%of all kinds of aluminum alloys,which are the most widely utilized nonferrous alloys.Although most Al-Si alloys consist of multiple components,the eutectics in the structure accounts for 50%-90%of the sum volume of such alloys.Therefore,understanding the modification mechanism and function rules of the AlSi eutectic solidification is the technical key in controlling the structures and properties of such casting alloys.The present paper chiefly reviews recent investigation developments and important conclusions along the lines of the functions of modification elements and their modification mechanism in the eutectic solidification of Al-Si alloys.

United modification of Al-24Si alloy by Al-P and Al-Ti-C master alloys

The modification effect of a new type of Al-P master alloy on Al-24Si alloys was investigated. It is found that excellent modification effect can be obtained by the addition of this new type of Al-P master alloy into Al-24Si melt and the average primary Si grain size is decreased below 47 μm from original 225 μm. It is also found that the TiC particles in the melt coming from Al8Ti2C can improve the modification effect of the Al-P master alloy. When the content of TiC particles in the Al-24Si melt is 0.03%, the improvement reaches the maximum and keeps steady with increasing content of TiC particles. Modification effect occurs at 50 min after the addition of the Al-P master alloy and TiC particles, and keeps stable with prolonging holding time.

Effects of Solution Treatment Time and Sr-Modification on Microstructure and Mechanical Property of Al-Si Piston Alloy

The purpose of this paper was to investigate the effects of solution treatment time and Sr-modification on the microstructure and property of the Al-Si piston alloy.It was found that as-cast microstructures of unmodified and Sr-modified Al-Si alloys consisted of a coarse acicular plate of eutectic Si,Cu_3NiAl_6 and Mg_2Si phases in theα-Al matrix but different in size and morphology.Both size and inter-particle spacing of Si particles were significantly changed by increasing the solution treatment time.After a short solution treatment,the coarse acicular plate of the eutectic Si appears to be fragmented.Fully modified microstructure of Sr-modified alloy can reduce the solution treatment time compared to unmodified alloy.The maximum of a peak hardness value is found in the very short solution treatment of both Al-Si piston alloys.Compared to 10 h solution treatment,the solution treatment of 2-4 h is sufficient to achieve appropriate microstructures and hardness. The short solution treatment is very useful to increase the productivity and to reduce the manufacturing cost of the Al-Si piston alloys.

Effects of high magnetic field on modification of Al-Si alloy

Effects of high magnetic field on modification of Al-6%Si hypoeutectic alloy, Al-12.6%Si eutectic alloy and Al-18%Si hypereutectic alloy were studied. For the Al-6%Si alloy, it is found that the sample modified by Na-salt does not lose efficacy after remelting under high magnetic field. For the Al-12.6%Si alloy, if the sample modified by Na-salt is kept at the temperature of modification reaction, high magnetic field can postpone the effective time of the modification. For Al-18%Si alloy modified by P-salt, the primary Si in solidified structure concentrates at the edge of the sample and eutectic Si appears in the center of the sample under the condition without high magnetic field, while the primary Si distributes evenly in the sample when the high magnetic field is imposed. It is thought that the high magnetic field restrains the convection of the melt.

Distributions of Sr and Fe and their influence on modification of hypoeutectic Al-Si alloy

The influence of cooling rate and Fe-containing phases on Sr-modification of Si phases in hypoeutectic Al-Si alloys, a problem with great industrial importance, was investigated. The microstructures of samples were examined using scanning electron microscopy(SEM) with energy-dispersive X-ray spectroscopy(EDX). A new method of electron probe microanalysis(EPMA) map scanning was used to analyze the Sr distribution, which gave quantitative results covering more Si particles. EPMA map scanning, together with SEM with EDX, was also used in analyzing the distribution of Fe phases. Results show that Fe-containing phase was related to the unmodified Si particles in samples with partial modification failure and the plate-like Si phases in samples without modification failure. Such a relationship was further confirmed by the microstructure observation.In conclusion, a partial failure of Sr-modification can be caused by both slow cooling rate and Fe-containing phases.

Assessment of modification level of hypoeu- tectic Al-Si alloys by pattern recognition of cooling curves

Most evaluations of modification level are done according to a specific scale based on an American Foundry Society (AFS) standard wall chart as qualitative analysis in Al-Si casting production currently. This method is quite dependent on human experience when making comparisons of the microstructure with the standard chart. And the structures depicted in the AFS chart do not always resemble those seen in actual Al-Si castings. Therefore, this qualitative analysis procedure is subjective and can introduce human-caused errors into comparative metallographic analyses. A quantization parameter of the modification level was introduced by setting up the relationship between mean area weighted shape factor of eutectic silicon phase and the modification level using image analysis technology. In order to evaluate the modification level, a new method called "intelligent evaluating of melt quality by pattern recognition of thermal analysis cooling curves" has also been introduced. The results show that silicon modification level can be precisely assessed by comparison of the cooling curve of the melt to be evaluated with the one most similar to it in a database.

MODIFICATION EFFECT OF Sr ON Al-Si ALLOYS

By inserting the single crystal silicon seeds into Sr modified Al-22wt-% Si alloy melts,the fact that nucleation and growth of Si-phase are affected by Sr addition has been confirmed.It is suggested that this effect is caused by the adsorption of Sr on{111}_(si),and the modification of eutectic structure results from the variation of leading phase in the eutectic from Si to α-Al.