过共晶铝硅合金的细化变质

根据Ａｌ－Ｓｉ二元系相图〔１〕分析了过共晶铝硅合金的主要性质。介绍了过共晶铝硅合金的细化变质方法和进展。     

铝硅合金低温加硅研究

扼要介绍了铝硅合金生产中的五种熔配工艺,以共晶型与过共晶型两种不同牌号的铝硅合金为例阐述了低温加硅熔炼技术,获得了最佳工艺,该方法质量稳定、节约能源、环境友好。     

共晶Al-18Si-2Cu合金组织及性能的研究

通过研究不同体系的变质剂和热处理工艺对过共晶铝硅合金中初生硅和共晶硅的作用,探讨复合变质以及T6热处理对过共晶Al-18Si-2Cu合金组织及性能的影响;并研究了不同变质温度下,过共晶铝硅合金组织及性能的变化规律,研究最适合Al-P和Ni基非晶复合变质剂的变质温度。实验分析发现,Al-P对初生硅有明显的细化变质作用,使过共晶Al-18Si-2Cu合金中的初生硅的平均尺寸由未变质时的130μm降低到20μm;非晶能增加共晶硅的形核数量,使针状和板片状的共晶硅得到细化,其中,Ni非晶的变质效果比Fe非晶好;T6热处理能使初生硅圆钝化,且使针状和板片状的共晶硅粒化,从而使Al-18Si-2Cu合金的抗拉强度和延伸率都有一定提高;通过控制变量法,经对比分析,最适合Ni非晶的变质温度为820℃。     

稀土和磷复合变质对过共晶铝——硅合金硅晶体形貌与力学性能的影响

采用扫描电镜、Ｘ射线衍射、材料性能检测等实验手段对复合变质处理后的过共晶铝硅合金显微组织、形貌和力学性能进行了分析。结果表明：磷和稀土复合变质后，使粗大块状、条状的初晶硅的尺寸明显缩小且棱角钝化；较大针状的共晶硅变为颗粒状，使显微组织明显细化，从而导致过共晶铝硅合金的力学性能显著提高。     

铝钇共晶反应及其产物对亚共晶铝硅合金初生相的细化研究

研究了稀土Y在亚共晶铝硅合金中诱发稀土-铝共晶反应对铝合金初生α相的细化效应;应用Bramfitt提出的方法,计算了Al-Y共晶反应产物Al3Y与α-Al界面的二维点阵错配度,结果显示两者的二维错配度<6%,即Al3Y可作为α-Al的异质形核质点,且能达到中等有效形核而起到细化晶粒的作用,并通过实验验证计算结果如下:选用稀土元素Y作为A356合金细化剂的同时,将A356-Y熔体分别在稀土钇-铝共晶温度上、下10℃左右保温2 min后快速冷却,获得试样的金相组织照片后利用图像分析工具得到A356-Y合金初生α相的平均晶粒尺寸和平均形状因子。实验结果表明:A356-Y合金在Al-Y共晶温度之下保温,可获得较理想的初生α相形貌和较小的晶粒尺寸;结合二维错配的计算结果,可推断初生α相细化的主要原因为异质形核质点的增加:Al-Y共晶反应产物Al3Y与α-Al的二维点阵错配度在中等有效形核范围内,具有细化合金初生α相的作用;另一共晶产物α-Al与初生α相具有相同的晶体结构和点阵常数,则其也可作为异质形核质点而起到细化合金的作用。稀土Y可作为半固态A356合金中初生α相的优质细化剂。     

电热法生产铸造用共晶铝硅合金的能耗分析

介绍了电热法生产铸造用铝硅合金的工艺流程,同时对兑掺法和电热法生产铸造用铝硅合金的能耗进行了分析,结果表明：电热法生产共晶铝硅合金与兑掺法相比可节能5%以上,成本可降低700元以上。     

快速凝固喷射沉积制备Al-40Si组织分析

针对应用广泛的低密度、低膨胀、高热导、高比强的高硅铝合金,采用快速凝固喷射沉积技术制备了Al-40Si高硅铝合金锭坯,通过光学显微镜及扫描电镜对其组织进行了分析.结果表明：合金组织特征为初生Si相均匀弥散分布于α-Al基体中,未出现共晶Si组织;随着合金中Si含量的增加,初生硅相的数量增加,平均尺寸增大;本试验所制备的Al-40Si合金中初晶硅粒子大小为5～30μm,并随合金锭坯部位的不同,初生Si大小不同,中心部位最小,底部次之,边部最大.     

过共晶铝硅合金新型变质剂的研究

通过拉伸实验和金相观察,研究了过共晶铝硅合金新型变质剂的时效性,以及不同变质时间和添加顺序对变质效果的影响。试验表明:自制新型变质剂对过共晶铝硅合金具有良好的变质效果。     

过共晶铝硅合金的研究进展

文章从变质处理、快速凝固、超声波处理、半固态处理等方面对过共晶铝硅合金组织的影响和力学性能的改善进行了介绍,为过共晶铝硅合金的研究人员提供参考。     

Zr-Sr复合变质对高硅Mg-Si-Zn镁合金组织的影响

为了改善高硅Mg-Si-Zn合金的性能,通过实验添加元素Sr、Zr,对Mg-Si-Zn合金进行单一和复合变质.分析了Mg_2Si初生相和共晶Mg_2Si的形貌与尺寸,研究了高硅Mg-4Si-4Zn合金的组织变化规律.结果表明:Sr可将Mg-4Si-4Zn合金中粗大的初生Mg_2Si枝晶变为规则的块状,树枝晶尺寸由长90～130μm,宽50～70μm变为对角线长度为20～50μm,复杂汉字状的共晶Mg_2Si变质为细小的棒状;Sr在凝固过程中通过在Mg_2Si表面占位来阻碍其生长,当Sr加入量超过0.75%后合金组织中出现Mg_xSr_ySi_z相,使Sr变质效果下降.经过Zr-Sr复合变质,Mg-4Si-4Zn镁合金初生Mg_2Si相形貌由不规则状转变为对称的六边形状,具有尖锐棱角的初生相逐渐减少,当Zr添加量达到0.9%时,变质效果最好,Mg_2Si相最为圆整.     

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.     

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.     

P、Sr、RE变质对过共晶Al-Si合金组织形态的影响

采用P、Sr、混合RE对含Si量22%～26%的过共晶铝硅合金进行变质处理,利用金相显微镜分析了单一元素变质及复合变质对合金初晶硅和共晶硅组织形态的影响。结果表明,P为初晶硅变质元素,Sr为共晶硅变质元素,RE能同时细化初晶硅和共晶硅;试验发现Sr虽然不能细化初晶硅,但对初晶硅有明显的裂解作用;P和RE复合变质使得初晶硅尺寸减小到25μm,而加入Sr后,由于Sr对初晶硅的裂解作用,使得初晶硅的尺寸减小到15μm,共晶硅大部分呈蠕球杆状或团球状,均匀弥散分布;试验得到了一种初晶硅和共晶硅细化效果均良好的复合变质剂。     

Review of Microstructure Evolution in Hypereutectic Al–Si Alloys and its Effect on Wear Properties

Al–Si alloys with silicon content more than 13 % are termed as hypereutectic alloys. In recent years, these alloys have drawn the attention of researchers due to their ability to replace cast iron parts in the transportation industry. The properties of the hypereutectic alloy are greatly dependent on the morphology, size and distribution of primary silicon crystals in the alloy. Mechanical properties of the hypereutectic Al–Si alloy can be improved by the simultaneous refinement and modification of the primary and eutectic silicon and by controlling the solidification parameters. In this paper, the effect of solidification rate and melt treatment on the evolution of microstructure in hypereutectic Al–Si alloys are reviewed. Different types of primary silicon morphology and the conditions for its nucleation and growth are explained. The paper discusses the effect of refinement/modification treatments on the microstructure and properties of the hypereutectic Al-Si alloy. The importance and effect of processing variables and phosphorus refinement on the silicon morphology and wear properties of the alloy is highlighted.     

Low-Cost Process for Silicon Purification with Bubble Adsorption in Al-Si Melt

The primary silicon and Al-Si alloy have been separated in hypereutectic Al-Si melt by the electromagnetic stirring and directional solidification processes. During the electromagnetic separation process, the behavior of a hydrogen bubble in Al-Si melt has been discussed. Furthermore, the bubble adsorption effect for the Si purification has been revealed. The results show that the bubble cavity formed in the lower part of the sample by pulling it up. The scanning electron microscope along with energy dispersive spectrometer (SEM-EDS) analysis indicated that a lot of impurities were adsorbed onto the surface of the bubble cavity that may be beneficial for the Si purification. By decreasing the pulling-up rates, the size of the bubble cavity in Al-Si alloy increased, which results in the decreasing of the impurity contents in primary silicon. In this work, the impurity content in primary silicon is 10.8 ppmw, which is obviously improved compared with the 777.57 ppmw in metallurgical silicon. It is a low-cost technology that will be a potential route for the Si purification.     

Simultaneous Primary Si Refinement and Eutectic Modification in Hypereutectic Al–Si Alloys

A solid?Cliquid duplex casting process was applied to achieve simultaneous refinement and modification of silicon phases in hypereutectic Al?CSi alloys. In this process P-treated Al-24Si (wt%) solid alloy is mixed with Sr-treated eutectic Al-12.6Si molten alloy to provide an Al-18Si alloy in the Liquid?+?Primary Si phase field and then cast. By using this process the mean particle size of primary silicon was reduced from 50???m to less than 15???m (refinement) and the eutectic structure changed from a plate-like to a fibrous structure (modification) when compared with conventional casting process. The results of mechanical testing showed that the tensile strength increased by about 14?% from 153.5 to 175.1?MPa and the elongation more than doubled from 1.64 to 3.76?%. The improvement of mechanical properties is attributed to the combination of refined primary silicon and the fibrous structure of the modified eutectic Al?CSi matrix.     

Effects of AlMnCa and AlMnFe Alloys on Deoxidization of Low Carbon and Low Silicon Aluminum Killed Steels

 To confirm the effects of AlMnCa and AlMnFe alloys on the deoxidization and modification of Al2O3 inclusions, experiments of 4 heat low carbon and low silicon aluminum killed steels deoxidized by AlMnCa and AlMnFe alloys were done in a MoSi2 furnace at 1 873 K. It is found that the 1# AlMnCa alloy has the best ability of deoxidization and modification of Al2O3 inclusions than 2# AlMnCa and AlMnFe alloys. Steel A deoxidized by 1# AlMnCa alloy has the lowest total oxygen content in the terminal steel, which is 37×10-6. Most of the inclusions in the steel deoxidized by 1# AlMnCa alloy are spherical CaO containing compound inclusions, and 891% of them are smaller than 10 μm. The diameter of the inclusion bigger than 50 μm is not found in the final steels deoxidized by AlMnCa alloys. Whereas, for the steels deoxidized by AlMnFe alloys, most inclusions in the terminal steel are Al2O3 or Al2O3 MnO inclusions, and a few of them are spherical, and only 768% of them are smaller than 10 μm. Some inclusions bigger than 50 μm are found in the steel D deoxidized by AlMnFe alloy.     

Computer Aided Cooling Curve Analysis and Microstructure of Cerium Added Hypereutectic Al–Si (LM29) Alloy

Thermal analysis of LM29 alloy and Ce added LM29 alloys was carried out. The effect of cerium addition on solidification parameters and microstructural features of hypereutectic Al-Si (LM29) alloy was studied using Newtonian analysis technique. Thermal analysis parameters such as primary and eutectic phase nucleation and solidus temperatures were determined. The addition of Ce to LM29 alloy decreased the nucleation temperature of primary silicon and eutectic silicon. The microstructural examination of Ce added LM29 alloys revealed the presence of a polyhedral shaped Al–Si–Ce compound that might have caused the refinement of primary and eutectic silicon. The dendrite coherency point temperature of LM29 alloy was found to be suppressed on addition of Ce.     

Nucleation on ceramic particles in cast metal-matrix composites

In order to understand the nucleation on ceramic particles in the melts of metal-matrix composites (MMCs), the effect of segregation of solute on the surface of reinforcement particles in the melt has been analyzed as a function of particle temperature and the surface energy of the particle/liquid melt. The temperature of the particle in the melt, calculated analytically, was found to become close to the melt temperature within a very short time of contact between the particle and the melt. The solute concentration near the particle surface will, therefore, primarily be influenced by the surface energy of the particle and the melt. Based on this, the undercooling due to solute segregation around the particle and the chemical free-energy change due to the formation of the new solid phase on the particle were calculated in selected hypo- and hypereutectic Al-Si alloy melts containing (1) SiC particles or (2) graphite particles. The chemical free-energy change (driving force for nucleation) due to the formation of the new phase on the particle is lower for hypoeutectic compositions than for hypereutectic compositions in the aluminum-silicon alloy systems; this is due to the higher undercooling in the hypereutectic alloys due to solute segregation on the surface of the particle. This suggests that the formation of the primary phase on the surfaces of particles in the melt should be more favorable in the hypereutectic compositions than for hypoeutectic compositions. This also indicates that even when the particle temperature is not significantly lower than the liquidus temperature, nucleation on the particles can take place due to the segregation of the solute on the particles. Experimental observations of the microstructure of several cast metal-matrix composites, including Al-Si-SiC and Al-Si-graphite, show (1) the presence of silicon in contact with the reinforcement particles in hypereutectic alloys, suggesting that nucleation and growth of primary silicon under certain conditions occurs on silicon carbide and graphite particles, possibly due to solute segregation on the surface of the particles, and (2) the presence of reinforcement particles in the last-freezing interdendritic regions of the primary phases in hypoeutectic alloys, suggesting the absence of nucleation of primary phases on the reinforcement surface, as predicted by the analysis.     

Effect of Electromagnetic Vibration on the Agglomeration Behavior of Primary Silicon in Hypereutectic Al-Si Alloy

An experimental apparatus that enables the simultaneous application of an alternating electric field and a stationary magnetic field was developed. Electromagnetic vibration was induced in a hypereutectic Al-Si alloy melt during solidification at a constant cooling rate. The results showed that the silicon particles collide with each other and agglomerate into clusters with the application of an electromagnetic vibration. With the increase of the electromagnetic force F, the sizes of the silicon clusters decrease and the clusters become more compact.