On the modification of hypereutectic Al-Si alloys using rare earth Er

Hypereutectic Al-17.5Si (wt pct) and Al-25Si (wt pct) alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.     

Co对Al-20Si-2Cu-1Ni-0.5Mn合金微观组织和力学性能的影响

采用扫描电镜(SEM)、图像定量分析软件等,研究了在Al-20Si-2Cu-1Ni-0.5Mn合金中分别添加质量分数为0.5%、0.9%、1.5%的Co对合金微观组织和力学性能的影响。结果表明,随着Co含量的增加,合金中的含Co金属间化合物的体积分数和平均直径均有所增加,其形态也由小团块状转变为发达的树枝晶。合金的力学性能随Co含量的增加逐渐降低。Co元素对于初生Si没有明显的变质作用。     

压铸条件下过共晶铝硅合金P变质的必要性

在铝合金压铸生产过程中,Al-P中间合金变质处理和压力铸造工艺都能够使过共晶铝硅合金中的初晶硅晶粒细化.探讨Al-P中间合金变质处理,分别在压铸工艺条件下和普通金属型条件下,对过共晶Al-15Si合金组织的不同影响.试验表明,压铸条件下未经Al-P变质的和经Al-P变质的Al-15Si合金与金属型条件下未经Al-P变质的Al-15Si相比,初晶Si尺寸分别减小50%和75%左右;在相同的压铸工艺条件下,Al-P变质后Al-15Si合金初晶Si尺寸,比未经过Al-P变质的Al-15Si合金初晶Si尺寸减小40%左右.论证了在Al-Si系过共晶铝合金压铸件生产过程中,Al-P中间合金进行变质处理的必要性.     

P变质对不同冷速下过共晶压铸铝合金初晶Si的影响

以过共晶压铸铝合金为对象，研究了P变质对不同冷却速度下初晶Si组织的影响。发现P变质处理前后随冷却速度的增加，初晶Si尺寸减小的变化趋势十分相似，并且都存在一个明显的突变区域。对于不同冷却速度下合金组织的细化，P变质都有很好的促进作用。同一冷却速度下，P变质后细化效果可增加42．7％，在冷却速度很高（铸件厚度达到1mm）时，P变质对初晶Si仍然具有很好的细化作用。在快速凝固和P变质双重作用下，初晶Si组织得到更加明显的细化。Al—P中间合金是一种良好的过共晶压铸铝合金变质剂。     

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.     

Effects of P+Cr complex modification and solidification conditions on microstmcture of hypereutectic Al-Si alloys by wedge-shaped copper mould casting

Large and segregated primary Si particles may drastically decrease the mechanical properties of Al-Si alloys. To solve this problem, a P-Cr complex modif ier was added into the alloy, and the effects of P-Cr complex modification and solidification conditions on the microstructure of hypereutectic Al-Si alloys casting produced in wedge-shaped copper mould were studied. The thermal analysis technique was applied to calculate the cooling rate during solidification. The microstructures were observed by means of optical and scanning electron microscopies. Results showed that the primary Si segregates in the as-cast hypereutectic Al-Si alloys. The segregation of primary Si can be inhibited by adding a P+Cr complex modif ier and increasing the cooling rate during solidif ication. The ref inement of primary Si particles by P+Cr complex modif ication is due to the formation of CrS i2 and AlP particles which act as the heterogeneous nuclei for the primary Si phase. The segregation of Si was also inhibited through the adherence of heavier CrS i2 particles to the primary Si particles.     

Effect of phosphor addition on eutectic solidification and microstructure of an Al-13％Si alloy

As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidification and microstructure of the Al-13%Si alloy, an investigation has been undertaken by means of thermal analysis and micro/macro-structure observation. Results indicate that addition of phosphor in near eutectic Al-Si alloy promotes the nucleation of eutectic but has little refinement impact on primary Si particles as expected. Conversely, both primary Si particles and eutectic Si flakes become slightly coarser in P-rich alloys. The coarsening of eutectic Si flakes ties closely to the increased eutectic growth temperature with phosphor addition. The eutectic solidification of the alloy proceeds from the near mold zone towards the center, and it is also found that a few independent nucleation regions emerge in liquid at the solidification front due to the addition of phosphor.     

P+RE变质对过共晶Al-Si合金组织的影响

采用P+RE对过共晶Al-Si合金进行复合变质。结果表明,P+RE复合变质对初晶硅和共晶硅均有很好的变质效果。五心瓣状初晶Si尺寸明显减小且棱角钝化,共晶Si由原来的长针状变为短杆状,微观组织得到明显的细化。同时也对P+RE的变质机理进行了论述。     

Influence of Si and Ti contents on the microstructure, microhardness and performance of TiAlSi intermetallics in Al-Si-Ti alloys

In this study, the influence of Si and Ti contents on the microstructure, microhardness and morphology of TiAlSi intermetallics in ternary Al-Si-Ti alloys was investigated. The increase of Si addition in Al-xSi-2Ti alloys leads to an increase of Si content in TiAlSi phase as well as an increase of microhardness. A phase evolution from Ti(Al_1−xSi_x)₃ to Ti₇Al₅Si₁₂ at about 14 wt.% Si was detected, while all the TiAlSi intermetallics exhibit flake-like. The increase of Ti content promotes the morphological transformation of TiAlSi from flake-like to block-like and primary Si particles are replaced by blocky TiAlSi particles in hypereutectic Al-Si alloy. The high-temperature strengthening effect of TiAlSi particles in a piston alloy was investigated and the strength is increased by 11.9% in this article, while the elongation and yield strength are increased by 17.6% and 10.1%, respectively.     

过共晶Al-Si合金快速凝固组织演变

以群体动力学模型为基础,在充分考虑合金的热物性参数、过饱和度以及第二相形核率变化的基础上,提出描述该合金快速凝固组织演变的数学模型,并结合A390合金进行计算。结果表明:随着雾化合金液滴尺寸的减小,平均冷却速度增加,而初生Si相长大时间减少,所析出初生Si相的尺寸及体积分数也不断减小;当粉末尺寸减小到某一临界值时,初生Si相消失,从而使不同尺寸粉末的微观组织发生很大的变化。计算结果与实验结果吻合较好,说明此提出的模型可以较好地预测过共晶Al-Si合金快速凝固组织的形成,从而为进一步研究高硅合金材料的组织演变奠定基础。     

稀土元素对过共晶铝硅合金的变质机理

过共晶铝硅合金具有很多优良的特性,是一种极有发展前途的结构材料,但合金中粗大的初晶硅和细长的共晶硅组织会影响其力学性能,研究表明添加稀土元素可以有效的细化初晶硅和共晶硅。本文总结了目前几种主要的变质理论,并对其以后的研究和发展方向进行了展望。     

Novel image analysis to determine the si modification for hypoeutectic and hypereutectic Al-Si alloys

The aim of this research is to develop a novel analytical approach to determine the level of modification of silicon in Al-Si hypoeutectic and hypereutectic alloys. Two standards to determine the level of modification of silicon particles were investigated: the AFS Si Modification Standard and the Primary Si Grade.^1,2 The first method can only be used for Al-Si hypoeutectic alloys and the second one for Al-Si hypereutectic alloys. In both methods, the determination of the level of modification of silicon is carried out by comparing micrographs of the test sample with the respective standards by simple observation. This results in a method with a bias error and does not take advantage of the analytical accuracy made possible by modern image analysis techniques. This paper presents a method known as image-analysis-based silicon modification level, which provides highly reliable results to determine the level of silicon modification for Al-Si hypoeutectic and hypereutectic alloys. He is formerly a member of the Light Metals Casting Technology Group (LMCTG) at the University of Windsor. For more information, contact J.H. Sokolowski, Mechanical, Automotive and Materials Engineering, University of Windsor, Room 209, Essex Hall, 401 Sunset Avenue, Windsor, Canada, N9B 3P4; jerry@uwindsor.ca.     

不同Si/Al比和变质处理对ZA27合金中Si相形态的影响

分析了Al-Si合金中初生Si相的变化规律，并与相同Si／Al比的ZA27合金中析出的Si相作比较，提出了将Al-Si合金中对Si相的变质工艺应用到ZA27合金中，细化组织中的Si相。结果表明，在ZA27合金中Si相的变化规律与Al-Si合金中的Si相大致相同，用1．5％的Cu-P中间合金对ZA27合金进行变质处理，可获得良好的变质效果。     

半固态过共晶Al-Si合金的制备技术

论述了半固态过共晶Al-Si合金的制备技术,包括半固态搅拌、喷射沉积与触变成形、双重铸造、变质与等温处理等。这些技术可有效地改善初晶Si形态,细化初晶Si,获得一定量的球状α相,并控制浆料中的固相率,使合金具有预期的半固态组织。     

Al-Si合金熔体热处理的结构转变

用示差扫描量热分析了Al-Si合金温度处理的熔体结构变化规律及结构变化温度。结果表明,在升温阶段的Al-7%Si亚共晶、Al-12%Si共晶及Al-20%Si过共晶合金的熔体中均存在额外的热效应,范围均在798～850℃之间,额外热效应温度范围与含硅量无关,结构转变焓值随合金的硅含量增加而增加,氢含量不影响结构转变的温度;而在降温过程中仅在Al-20%Si过共晶合金中发现了额外热效应,额外热效应的出现及温度范围取决于降温速度。分析认为,升温阶段的额外热效应体现了Al的熔体结构变化,降温阶段的额外热效应与熔体中的Si-Si原子团簇的行为有关。     

倾斜板振动熔体处理技术研究与应用进展

论述了一种金属组织细化与制备半固态金属浆料的熔体处理方法,总结了近年来的研究与应用进展。倾斜板振动技术可以显著细化金属坯料组织,使纯铝的细化晶粒度很容易达到1级细化标准,该技术对过共晶Al-Si合金中初晶Si与共晶Si也具有较好的细化效果;采用该技术可制备具有细小球形晶或等轴晶组织的A356、Al-6Si-2Mg、A2017、AZ91、AZ31、过共晶Al-Si合金等金属坯料,实现了触变成形;通过连续流变挤压制备了6201、A2017、AZ31、AZ61合金管材、型材和线材,通过流变轧制制备了A356、A2017、AZ91、AZ31、AZ61、Mg-Sn合金板带材;倾斜板振动熔体处理技术具有成本低、效率高的特点,在流变压铸、流变挤压、流变轧制及金属组织细化等方面具有很好的应用前景。     

Microstructure and mechanical properties of laser melting deposited Ti2Ni3Si/NiTi Laves alloys

Two Ti2Ni3Si/NiTi Laves phase alloys with chemical compositions ofNi-39Ti-11Si and Ni-42Ti-8Si （%, mole fraction, the same below）, respectively, were fabricated by the laser melting deposition manufacturing process, aiming at studying the effect of Ti, Si contents on microstructure and mechanical properties of the alloys. The Ni-39Ti-llSi alloy consisting of Ti2Ni3Si primary dendrites and Ti2Ni3Si/NiTi eutectic matrix is a conventional hypereutectic Laves phase alloy while the Ni-42Ti-8Si alloy being made up of NiTi primary dendrites uniformly distributed in Ti2Ni3Si/NiTi eutectic is a new hypoeutectic alloy. Mechanical properties of the alloys were investigated by nano-indentation test. The results show that the decrease of Si and the increase of Ti contents change the microstructures of the alloys from hypereutectic to hypoeutectic, which influences the mechanical properties of the alloys remarkably. Corrosion behaviors of the alloys were also evaluated by potentiodynamic anodic polarization curves.     

稀土对过共晶Al-Si合金P变质效果的影响

研究了加入稀土元素La对P变质Al-18Si合金中Si的形态及尺寸的影响，结果表明：稀土元素La的加入优化了P的变质效果，在细化初晶Si的同时变质了共晶Si，并且明显减缓了P变质初晶Si的粗化趋势，使变质效果至少可维持6h以上，通过扫描电镜测定了稀土元素La在合金中的分布，并分析讨论了稀土元素La对P变质效果影响的机理和作用。     

Sb对过共晶Mg-4.8%Si合金中Mg_2Si初晶变质的影响

利用Mg-20%Sb中间合金对过共晶Mg-4.8%Si合金进行变质处理,考察Sb的含量对Mg2Si初晶变质效果(主要包括形态和尺寸)的影响规律,并讨论其变质机制。结果表明:Sb的加入量是决定其能否有效变质过共晶Mg-4.8%Si合金中Mg2Si初晶的重要因素;在未变质的过共晶Mg-Si合金中,Mg2Si初晶以粗大的树枝晶状为主;当Sb加入量低于0.8%(质量分数)时,Mg2Si初晶形态无明显改善,其平均尺寸略有降低;当Sb加入量达到并超过1.2%后,Sb才能有效变质过共晶Mg-4.8%Si合金中Mg2Si初晶,且Mg2Si初晶呈细小的颗粒状弥散分布,其平均尺寸迅速减小;其变质机制应与残留在熔体中弥散分布的Mg3Sb2粒子作为Mg2Si初晶的形核核心有关。     

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

1　INTRODUCTIONAsastructuralmaterialhavingmanymeritssuchashighfrictionresistance ,highheatresistanceandlowexpansioncoefficient[13] ,hypereutecticAl Sial loyhasbeenattractingattentionofmanyresearchers .However ,forthehypereutecticAl Sialloysproducedwithtraditionalcasting process ,thereareusuallymanycoarseSiparticlesinthematrix ,whichleadtolowtensilestrength ,poorturning propertiesandroughsurfaceaftermechanicalworking[4 ] .Thepre viousresearches[5,6 ] indicatedthat ,forparticulatere inforc…