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.

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.

Hydrogen Content and Porosity Behavior of Hypereutectic Aluminum-silicon Alloy with Phosphorus

By making castings that pick up gas from moisture in red sand molds,the porosity generated at different cooling rates was discussed during solidification of hypereutectic Al-25%Si alloy without and with phosphorus additions. The effect of phosphorus addition on hydrogen content in the melt was also studied. It was observed that the phosphorus addition made hydrogen content in alloy melts present a “see-saw' tendency.In addition to primary silicon refinement,the phosphorus promoted gas porosity formed not only in slowly cooled sections, but also in rapidly cooled sections. There was a small difference in density of full dense sample between P-refined and unrefined castings, with a larger density associated with phosphorous addition. The change of the surface tension seemed more reasonable to explain the mechanism of porosity behavior.

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.

Improvement in mechanical properties of hypereutectic Al-Si-Cu alloys through sonosolidified slurry

For the wider applications,it is necessary to improve the ductility as well as the strength and wear-resistance of hypereutectic AlSi-Cu alloys,which are typical light-weight wear-resistant materials.An increase in the amounts of primary silicon particles causes the modified wear-resistance of hypereutectic Al-Si-Cu alloys,but leads to the poor strength and ductility.It is known that dual phase steels composed of hetero-structure have succeeded in bringing contradictory mechanical properties of high strength and ductility concurrently.In order to apply the idea of hetero-structure to hypereutectic Al-Si-Cu alloys for the achievement of high strength and ductility along with wear resistance,ultrasonic irradiation of the molten metal during the solidification,which is called sono-solidification,was carried out from its molten state to just above the eutectic temperature.The sono-solidified Al-17Si-4Cu alloy is composed of hetero-structure,which are,hard primary silicon particles,soft non-equilibrium a-Al phase and the eutectic region.Rheo-casting was performed at just above the eutectic temperature with sono-solidified slurry to shape a disk specimen.After the rheo-casting with modified sonosolidified slurry held for 45 s at 570 oC,the quantitative optical microscope observation exhibits that the microstructure is composed of 18area%of hard primary silicon particles and 57area%of soft a-Al phase.In contrast,there exist only 5 area%of primary silicon particles and no a-Al phase in rheo-cast specimen with normally solidified slurry.Hence the tensile tests of T6 treated rheo-cast specimens with modified sono-solidified slurry exhibit improved strength and 5%of elongation,regardless of having more than 3 times higher amounts of primary silicon particles compared to that of rheo-cast specimen with normally solidified slurry.

Transformation of microstructure after modification of A390 alloy

A hypereutectic aluminum-silicon alloy with content of 17%Si,designed as A390,was modified. The change of microstructure was identified by optical microscopy. The results show that phosphorus can change the morphology and size of the primary silicon and control the length of needle-like eutectic silicon or dendrite. After modified by phosphorus,the primary silicon of star-like and coarse platelet is changed to polygonal with less cute angles and decreasing average size. The eutectic silicon is also changed because it grows from the tip of angles on the primary silicon and is influenced by the morphology and size of primary silicon. The eutectic silicon changes from needle-like or dendrite shape to short bars and dots with less average length.

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.

ECAP变形及半固态等温处理对Al-25%Si合金组织和性能的影响

对铸态Al-25%Si合金进行等通道转角挤压(ECAP),并结合半固态等温处理技术,研究了ECAP挤压及半固态等温处理工艺参数对合金微观组织和室温拉伸性能的影响。利用光学显微镜观察分析微观组织,拉伸试验机测试室温拉伸性能,以及扫描电子显微镜分析断口形貌。研究结果表明,ECAP变形能够有效地细化Al-25%Si合金中的初生硅相,其平均直径由铸态的117.9μm降至31.9μm,同时形状因子也由0.12提升至0.40。ECAP后的常温力学性能也得到明显提升,其抗拉强度也由铸态的96 MPa提升至200 MPa,伸长率由1.04%提升至3.25%。在半固态加热过程中,初生硅的形状因子随等温温度的提升和时间的延长呈先增后降的趋势。在590℃保温10min,其形状因子最高为0.62。

Sr添加量对过共晶Al-20%Si合金铸态组织和硬度的影响

采用Al-10%Sr对Al-20%Si合金进行变质处理,研究Sr对Al-20%Si合金的铸态组织和硬度的影响。Sr可以同时细化Al-20%Si合金中的初晶硅和共晶硅,当Sr的添加量达到0.4%时,初晶硅晶粒细化效果最明显,初晶硅的形貌由大的板块状变为变态后的细的鱼骨状,共晶硅由长针状变为颗粒状。X射线衍射分析表明,在变质后的合金中生成了Al_(2)Si_(2)Sr相。扫描电镜分析表明,当Sr添加量为0.4%时,Al-20%Si合金样品中出现了白色的菱形组织Al_(2)Si_(2)Sr相,即XRD测试分析中的Al-Si-Sr三元相。硬度试验表明,当Sr的添加量为0.4%时,Al-20%Si合金的硬度达到最大值64 HB,随着Sr添加量的进一步增加,其硬度呈现下降趋势。

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%。

高硅铝合金初晶硅变质效果的热分析研究

利用新开发的热分析技术研究了Al-20Si-1.5Cu-1Ni-0.5Mn合金的初晶Si变质效果。通过对不同的P变质剂加入量和保温时间下的热分析曲线和金相组织的分析表明,随着P加入量的增加(≤0.08%),初晶Si平均晶粒尺寸减小,初晶生长温度TG及其差值ΔTG不断增大;在变质处理后不同的保温时间下平均晶粒尺寸及ΔTG都变化不大。初晶生长温度差值ΔTG与平均晶粒尺寸具有很好的对应关系,ΔTG可以作为初晶Si变质效果的评判依据。

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-Mn-Ti-P-Cu及Mg对过共晶Al-25Si合金组织及耐磨性能的影响

采用真空感应熔炼炉制备一种新型绿色中间合金Al-Mn-Ti-P-Cu,并添加金属Mg共同作用于过共晶Al-25Si合金,再对其进行适当热处理,最后检测实验效果,分析变质、强化、磨损机制。结果表明:该中间合金对组织中粗大的初、共晶硅及α(Al)均有明显细化作用;变质后,添加适量Mg可将Mg2Si强化相以相对细小形态引入基体,并最终在热处理后呈颗粒状均匀弥散分布基体中;随着组织的细化以及基体强度和硬度的提高,合金的磨损机制由磨粒磨损和粘着磨损的混合型磨损转化为单一的磨粒磨损,同时磨损质量损失降幅达46.6%,从而获得一种较理想的高强耐磨活塞材料。

等温电磁搅拌对半固态Al-25%Si合金组织的影响

研究了A l-25%Si合金在半固态等温电磁搅拌条件下合金显微组织的变化行为.分别在580℃、600℃下等温搅拌0 m in、10 m in、20 m in和30 m in,实验结果显示:随着搅拌时间的增加,初生硅发生细化,尺寸明显变小且边角更加钝化,分布也更加均匀;当搅拌时间超过20 m in后,初生硅尺寸变化不大,分布趋于均匀.

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。

搅拌温度对半固态过共晶铝硅合金中初生硅形貌的影响

采用等温搅拌法制备过共晶铝硅合金半固态浆料,研究了搅拌温度对初生硅形貌的影响。结果表明,搅拌可明显改善初生硅的形貌,使其细化、球化。搅拌温度过高,熔体内部过冷度较小,先析出的初生硅晶核较少,初生硅长大时相互间抑制作用较小,易择优长成较粗大的初生硅,这些较粗大的初生硅不易碎化、磨圆而得以保留。降低搅拌温度,熔体内过冷度增大,利于提高熔体内部的形核率,初生硅长大时相互间抑制作用较大,长成的初生硅较细小,易被碎化、磨圆细化、球化。但搅拌温度过低,尽管制备的初生硅更细小,却由于初生硅间易出现团聚,球化程度会变差。

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.

REAlTiBP多元复合变质ZL117铝硅合金

研究了REAlTiBP多元复合变质剂对ZL117合金组织和性能的影响。经变质处理后 ,ZL117合金中的初晶硅平均尺寸由变质前的 2 5 0变为 3 0 μm ,室温抗拉强度由变质前的 168变为 2 45MPa ,高温 (3 0 0℃ )抗拉强度由变质前的 88变为 12 0MPa ,冲击韧性由变质前的 6.5提高到16.5J·cm- 2 ,耐磨性由变质前的 0 .0 0 80下降到 0 .0 0 42g ,变质效果良好。

液淬和变质工艺对过共晶铝硅合金的影响

过共晶铝硅合金中的初晶硅由于晶粒粗大并且有尖锐的棱角,严重削弱了合金的机械性能,通常我们采用变质处理工艺来改善这一现象。液淬工艺主要用于得到非晶组织,通过液淬工艺能得到超细非晶结构。如果把液淬工艺加入到变质工艺的过程中,这对实验的结果一定能产生影响。本文中,我们分别对过共晶铝硅合金采用了变质和变质液淬的混合工艺。通过实验我们证实磷元素能够显著改变组织的尺寸,通过对磷元素的扫描分析,发现磷元素不仅分布在中心,在初晶硅的内部也分布大量的磷元素,这说明了磷元素除了在异质形核中起作用外,它还可以把初晶硅分割为很多小的初晶块,不同的小初晶块生长方向各不相同,那么在宏观上观察,经过磷元素变质的初晶硅,形状上开始变得比较圆滑。如果我们在变质过程中引入液淬工艺,变质效果能得到显著的提高,结果表明晶粒尺寸变小,晶粒形状变为椭圆,这说明冷却速度促进了磷元素对初晶硅尺寸和形状的影响。

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.