Effects of ZnS modification on primary Si in hypereutectic Al-Si alloy

A new modifying agent, ZnS, was used as a refiner to modify primary silicon in hypereutectic AlSi alloy. The factors affecting the modification results, including addition level of ZnS and holding time, were investigated. The results showed that the average size of the most effectively modified primary silicon was 28.5 μm when the ZnS mixed powder addition was 0.15 wt.% with a holding time of 10 min. More important, the average size of primary silicon could remain below 40 μm despite the holding time extending to 120 min, which means ZnS is a promising modifying agent of primarySi in industrial applications.

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.

Effects of individual and combined additions of phosphorus,boron and cerium on primary and eutectic silicon in an Al-30Si alloy

The modification of silicon in an Al-30Si alloy was studied using optical microscopy, electron probe micro-analysis, transmission electron microscopy and differential scanning calorimetry. It is found that phosphorus master alloys combined with boron master alloys have good modification effect on primary silicon but no evident modification effect on eutectic silicon, while boron combined with cerium has good modification effect on eutectic silicon. The results of differential scanning calorimetry show that phosphorus, boron or cerium addition and their combined addition have different undercooling effects on eutectic silicon. Many scholars thought that AlP particles were the nuclei of eutectic silicon when phosphorus was enough in the alloy. Our results show that β-（Al,Si,Fe） can still be the nucleus of plate-like entectic silicon while AlP is the nucleus of primary silicon when there is enough phosphorus in the melt. In addition, the mechanism about the modification was also discussed.

Effect of Nd on Microstructure and Mechanical Properties of Hypereutectic Al-25Si Alloy

The modification mechanism of Nd on Al-25Si alloy was studied. The result showed that pure Nd (0.3%) could significantly refine primary silicon in hypereutectic Al-25Si alloy. And the morphology of primary silicon was transformed from star-shaped to block and the size of primary silicon changed from 150～200 μm to 40～80 μm after modification. The morphology of silicon and elements presence was detected by means of SEM-EDS, XRD was carried out to detect the phase constitution before and after modification. It was found that no new phase formed and the lattice of silicon and aluminum increased after modification and most of Nd may exist as solids solute element of silicon and absorb on the surface of silicon. Mechanical property test results showed that after modification with 0.3% Nd, Tensile strength increased about 33% from 138 to 184 MPa, yield strength increased about 15% from 126 to 145 MPa, and elongation change was not obvious. The improvement of mechanical property should attribute to fine grain strength and purification of base metal after modification.

Effect of Y_2O_3 on microstructure and mechanical properties of hypereutectic Al-20%Si alloy

The effect of Y2O3 on the microstructure and mechanical properties of the hypereutectic Al-20%Si(mass fraction) alloy was investigated. The results show that, with the addition of Y2O3 into the Al-P-Ti-TiC modifier, the average size of primary silicon in the Al-20%Si alloy modified by Al-P-Ti-TiC-Y2O3 modifier (approximately 15μm or less) is significantly reduced, and the morphology of eutectic silicon changes from coarse acicular and plate like to refined fibrous. The Brinell hardness (HB189) and tensile strength (301 MPa) of Al-20%Si alloy modified by the Al-P-Ti-TiC-Y2O3 increase by 11.6% and 10.7%, respectively, for the alloys after heat treatment.

Al-10%LaCe中间合金制备及对过共晶Al-Si合金的变质作用

采用混熔法制备Al-10%LaCe中间合金,并对Al-25%Si合金进行变质处理,研究不同添加量的LaCe对Al-25%Si合金的变质作用。LaCe对Al-25%Si合金中的初晶硅和共晶硅都有着比较明显的细化作用,当LaCe的添加量达到1.0%时,初晶硅组织仍呈现出不规则五瓣星状及其他较复杂形状,其晶粒尺寸细化作用明显,共晶硅由长针状变为颗粒状。X射线衍射和扫描电镜分析结果表明,在变质后的合金中生成了新的含LaCe多元相。

Effect of neodymium on primary silicon and mechanical properties of hypereutectic Al-15%Si alloy

The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase.So,optical microscopy(OM) and X-ray diffraction(XRD) were adopted to study affection of Nd on primary silicon of hypereutectic Al-15%Si alloy in this paper.The results of OM showed that pure Nd could effectively refine primary silicon of hypereutectic Al-15%Si alloy.When Nd addition was 0.3%,the average size of primary silicon reduced from 20-40 μm of initial sample to 10-20 μm of modified sample.XRD pattern showed that no new phase was formed after Nd modification.The results of mechanical properties test showed that whole properties of modified samples were significantly improved.Tensile strength increased about 32.6% from 147 MPa to 195 MPa.Elongation was increased about 160% from 1.0% to 2.6%.The improvement of mechanical properties should attribute to primary silicon refinement after modification.

B对过共晶Al-Si合金初晶Si的细化作用

研究了B对过共晶Al-20Si合金中初晶Si的细化作用。结果表明,B对过共晶Al-Si合金初晶Si有较好的变质效果。初晶Si的尺寸先随B含量的增加而减小,当B的添加量为0.065%时达到最佳的细化效果,之后初晶硅的尺寸开始随B含量的增加而增大。

Al-P变质对过共晶Al-Si合金组织与力学性能的影响

介绍了磷变质处理对过共晶铝硅合金显微组织的影响。首先采用不同含量的磷变质剂细化变质初晶硅,然后采用热处理的方式细化共晶硅,得到了磷变质剂的最佳加入量,并介绍了细化后合金的组织和力学性能。结果表明,通过该工艺能得到完全粒化的共晶硅,初晶硅晶粒较小,平均晶粒尺寸约为15μm。经T6处理后材料的抗拉强度可以达到358.367 MPa。

Characterization of high-pressure die-cast hypereutectic Al-Si alloys based on microstructural distribution and fracture morphology

The fracture behavior of high-pressure die-cast hypereutectic(HPDC) Al-Si alloys was investigated using a high-resolution laboratory CT and synchrotron X-ray tomography with a particular focus on the influence of HPDC microstructure. Results showed that microstructure of the alloy was mainly comprised of primary silicon particles(PSPs), Al dendrites, Cu-rich phases and pores. Most of the coarse PSPs, Cu-rich phases and pores were located in the center of the specimen. The rapid solidification of HPDC led to a heterogeneous microstructural feature. Elemental Cu was enriched in the frontiers of solid-liquid interface, causing the formation of large size dendritic arms. The pores were formed in the interdendrites which endured high stress intensity under high applied stress. Microcracks were originated from pores and further connected Cu-rich phases causing intergranular fracture. PSPs worked as obstacles causing piling-up dislocations in the phase interface. In the regions where large size of PSPs enriched in, PSPs ruptured rather than debonded from matrix, indicating transgranular fractures of PSPs. Microcracks originated around pores and PSPs tended to converge on the main cracks to decrease the energy required for crack propagation.

过共晶Al-Si合金的变质处理试验

根据Sr、P对过共晶Al-Si合金的变质机理,用Al-Sr(10%)合金、Al-P(3.5%)合金和C还原磷酸钠(赤P∶Na_3PO_4∶石墨C=1∶5.3∶2.5)分别对过共晶Al-Si合金进行变质处理。结果表明,过共晶Al-Si合金用Al-P(3.5%)合金变质效果最佳,显微组织下初生硅数量增多且呈球形均匀弥散分布,Al-P(3.5%)合金加入量在总量的1.1%~1.2%之间,最佳变质时间为20min左右,最稳定的变质温度应控制在780~810℃温度区间。

P-LaCe复合变质对过共晶Al-25%Si合金的变质效果

文章分别采用1.0%LaCe、0.8%P以及1.0%LaCe-0.8%P复合变质对Al-25%Si合金进行变质处理,研究不同变质剂对Al-25%Si合金的变质效果。经变质处理后,Al-25%Si合金中的初晶硅都有着不同程度的细化作用,0.8%P的变质效果为最佳,初晶硅由未变质的粗大的五瓣星状及其他较复杂形状转变为细的多边形状和板片状,平均晶粒尺寸由150μm~200μm细化至30μm~50μm,共晶硅以长针状分布,分布密度明显降低。单纯加1.0%LaCe处理后,合金中初晶硅形态上无变化,平均晶粒尺寸略有减小,共晶硅发生明显变化,从长针状变为颗粒状或短棒状,尺寸大幅减小。P-LaCe复合变质需控制好二者的添加量的配比,否则易产生过变质现象,降低变质效果。力学性能测试结果表明,经变质处理后的Al-25%Si合金的抗拉强度与硬度均不同程度增加,以0.8%P变质后的合金力学性能为最佳,与金相组织细化程度相对应。

Nd变质过共晶Al-17.5%Si合金的微观组织和断口形貌

采用单一稀土元素Nd对过共晶Al-17.5%Si合金进行变质;采用扫描电镜、金相显微镜、电子探针、透射电镜及X射线衍射等方法对变质前后合金的微观组织、成分和相组成进行分析;并对变质前后合金的断口形貌进行分析。结果表明：加入0.3%Nd（质量分数）到过共晶Al-17.5%Si合金中可同时变质初生硅和共晶硅,经过变质处理后,初生硅的形状由星形和不规则形状变为块状,尺寸由40~60μm减小到10~30μm,共晶硅由长针状变成球状或短棒状;初生硅区域的主要成分是硅,中心边缘几乎检测不到Nd元素,Nd沿晶界分布;与未变质合金相比,经0.3%Nd变质后的Al-17.5%Si合金硅相上孪晶密度增大,变质后的合金中没有生成新相,α（Al）相和硅相的晶格常数变大;经0.3%Nd变质后,合金的整体性能大幅度提高,抗拉强度提高了35.8%,从120 MPa提高到163 MPa,伸长率从0.8%提高到2.2%,提高了175%。

过共晶铝硅合金的研究进展

过共晶铝硅合金具有密度和线膨胀系数小,铸造性能好,可获得高的耐磨性和热稳定性,是发动机活塞等轻质耐磨件的理想材料。本文对近年来过共晶铝硅合金的研究,主要在合金中硅相细化方面的研究进展进行了综述。

Al-P中间合金对过共晶铝硅合金组织及切削性能的影响

采用Al-P中间合金变质过共晶铝硅合金,在室温下通过刀具耐用度对比实验和表面质量对比实验评价切削加工性.实验表明:经过Al-P中间合金变质后,初晶硅变得细小、分散且圆钝化,变质后刀具耐用度是变质前的1.75倍、摩擦力-时间曲线变得平滑、失重量变小,说明经变质后,材料中硬质点对刀具的磨损变小,改善了切削加工性.

重熔次数对P-RE-Sr变质细化A390铝合金组织的影响

本文研究了不同重熔次数对不同复合变质A390合金组织的影响,实验结果表明:P、RE、Sr复合变质时,在相同重熔次数条件下,三元复合变质合金中的初晶硅的尺寸最小;当合金重熔次数小于2次时,初晶硅变质重熔效果较好,随着重熔次数不断增加,合金中初晶硅尺寸随之增大.

二次加热控制高硅铝合金中初生硅形态的研究

用光学显微镜(OM)及Image Pro Plus金相分析软件对半固态二次加热处理后的过共晶铝硅合金的初生硅组织特征进行分析。结果表明,在过共晶铝硅合金中,通过磷盐变质处理可以让初生硅相细化,平均直径由117μm降至31μm,并通过半固态二次加热使初生硅的形态得到显著的改善,其形状因子为0.67。

过共晶铝硅合金硅相复合变质的研究进展

提出了过共晶铝硅合金硅相复合变质处理存在的问题及挑战,综述了目前硅相复合变质处理的物理法及化学法,并从理论上对硅相变质机制进行了总结和概括。指出今后复合变质的发展方向是深入了解硅相的变质机制,开发出新型高效率、低成本的化学复合变质剂。

Al-5Ti-B对过共晶Al-18Si合金的变质效果

采用Al-5Ti-B变质剂对过共晶Al-18Si合金进行反向变质处理,用光学显微镜观察合金的组织与形貌,研究变质剂加入量、变质温度和冷却速度对初晶硅的尺寸、形态和面积分数以及共晶组织的影响。研究表明:当Al-5Ti-B加入量(质量分数)为0.3%时,变质处理后Al-18Si合金中的初晶硅和共晶硅尺寸明显减小,初晶硅的面积分数减小;与其相比,变质剂加入量增加到0.6%时,初晶硅尺寸变化不明显,但共晶硅进一步细化;随冷却速率降低,变质处理后Al-18Si合金中初晶硅相的数量减少,但Si颗粒尺寸明显增大,并且共晶硅细化;与Al-18Si合金在720℃变质相比,该合金在780℃变质处理时,初晶硅的尺寸增大,但初晶硅的面积分数显著减小;合金在850℃变质处理后初晶硅的尺寸、面积分数都比720℃变质处理后明显减小;随变质温度升高,Al-Si合金中的共晶硅明显细化。

LaCe混合稀土添加量对A390合金的组织和硬度的影响

采用LaCe混合稀土对A390合金进行了变质处理。研究了LaCe混合稀土添加量对A390合金组织和硬度的影响。结果表明,LaCe混合稀土对过共晶A390合金具有良好的变质作用,其最佳添加量为0.5%。此时,合金中初生硅由未变质的板块状或板条状变成了细的多角形和近球形,平均尺寸由65μm减小到18μm;继续增加稀土添加量,初生硅形态和尺寸有粗化的趋势。变质后的A390合金中检测到富稀土针状相。当LaCe混合稀土加入量为0.5%时,合金的硬度达到最大值。继续增加LaCe混合稀土的添加量,合金的硬度呈现下降趋势。