不同Sr添加量对Al-20%Si合金组织和性能的影响

研究了Sr对Al—20％Si合金组织和力学性能的影响。结果表明，随着Sr量的增加，初晶硅先由角块状或大板片状变为小块状再到多角的大块状，板片上出现大量蜂窝点，块状初晶硅角边发生钝化；共晶硅先由长针叶状变为细短纤维状或枝状再变为粗短枝状或蠕虫状；α枝晶不断柱状化，数量不断增多。另外，随Sr量的增加，合金伸长率逐渐增大，但有起伏，抗拉强度先急剧增加后变化不大，硬度呈抛物线变化。Sr量在0．04％～0．06％间，组织形貌最为理想，综合力学性能最优，强度和硬度增加2倍多，塑性增加近4倍。

超声波处理对过共晶Al-20%Si合金组织的影响

采用高能超声波对Al-20%Si合金进行熔体处理,研究超声波处理对Al-20%Si合金微观组织形貌的影响。控制Al-20%Si合金熔体温度在620～680℃之间时,研究合金凝固组织随熔体温度和超声波处理参数的变化规律。结果表明,随着导入超声波输出功率的增大和处理时间的延长,Al-20%Si合金的初晶硅形貌由粗大的板片状逐渐变成细小的球状颗粒;超声波处理熔体的温度控制在660℃左右时,可以获得最佳的效果,初晶硅的尺寸细小、圆整度高、分布均匀。

高能超声波处理对细化过共晶Al-20%Si合金中硅相的影响

采用高能超声波对过共晶Al-20%Si合金进行熔体处理,研究超声波对Al-20%Si合金微观组织的细化效果和作用规律。结果表明,在Al-20%Si合金凝固过程中对其进行超声波处理,可以破碎组织中粗大板片状初晶硅,使晶粒尺寸变小,圆整度提高、分布均匀;提高超声波功率,可以增强对铝硅合金微观组织的细化效果并使熔体中组织细化的区域扩大;实验结果还表明,在熔体中不同位置导入超声波进行处理,对整体组织的作用效果有较大区别,在熔体中心位置较浅深度导入超声波时,所获得的组织细化区域较大,并且组织分布均匀。

超声驻波作用下Al-20%Si合金的微观组织演变

采用超声驻波处理Al-20%Si合金熔体,研究不同超声驻波处理功率下Al-20%Si合金的微观组织演变,探讨超声驻波对Al-20%Si合金凝固过程的作用和组织细化的机理。结果表明:超声驻波能抑制初晶硅的析出,但声辐射力的作用使已析出的初晶硅偏聚长大;超声驻波处理能实现共晶硅"片状.纤维状"明显的形态转变,凝固后共晶硅转变为频繁分支细小的纤维状;超声功率越大,共晶硅"片状.纤维状"的形态转变越明显;超声驻波可以用于亚共晶Al-Si合金的变质处理中。

Bi对Al-20%Si合金微观组织及摩擦磨损性能的影响

研究不同Bi含量对Al-20%Si合金微观组织及摩擦性能的影响。借助金相显微镜(OM)、扫描电镜(SEM)、X射线衍射(XRD)对Al-20%Si合金进行观察分析。结果表明,随着Bi含量的增加,Al-20%Si合金组织中初晶硅和共晶硅都有不同程度的细化。添加0.75%Bi,块状初晶硅的棱角钝化,尺寸小于50μm;当Bi含量达到1.5%时,初晶硅近似不规则多边形,尺寸进一步减小,棱角更加圆润,共晶硅呈弥散分布,部分呈颗粒状。摩擦磨损试验表明,Bi对Al-20%Si合金摩擦系数以及摩擦力产生影响,摩擦系数从0.73降为0.58,磨损量减少20%。

稀土磷复合变质剂对Al-20%Si合金的细化处理研究

采用EPMA、XRD与DSC等分析手段,对制得的AlTiCREP(含2%P)进行物相分析,研究不同P(以AlTiCREP形式加入)添加量、熔体处理温度及保温时间对Al-20%Si初生硅的变质效果的影响,并探讨其细化机理。结果表明:制得的AlTiCREP中间合金含有TiAl3、TiC、AlP及稀土复合相;经AlTiCREP中间合金变质的初生硅颗粒明显细化且较圆整。添加0.03%AlTiCREP的变质效果最佳,初生Si尺寸细化至26.40μm,相对AlTiCRE细化的晶粒尺寸减小了10.8%,这归因于变质剂中的TiC在硅的作用下易于反应形成的Al4C3。该相可作为AlP的基底,在细化过程形成的Al4C3·AlP为初晶硅提供更多的形核质点,提高了AlP变质效果。最佳熔体处理温度为800℃,细化时效长达120 min。

搅拌时间对P变质的Al-20%Si合金初生硅尺寸与力学性能的影响

对Cu-9%P中间合金变质的Al-20%Si合金熔体进行了搅拌处理,研究了搅拌时间对P变质的Al-20%Si合金初生硅尺寸与力学性能的影响。研究表明:机械搅拌使Cu-P合金周围形成的Al P细小,同时使其弥散地分布于Al-Si合金熔体中,作为初生硅的结晶核心。随着搅拌时间的增加,初生硅由棱角尖锐、粗大的块状变为尖角钝化的颗粒状,搅拌时间从8 min增加到28 min时,初生硅尺寸由56.56μm减小到21.74μm,试样的抗拉强度由96.2 MPa增加到164.3 MPa,提高了70.8%,伸长率由1.5%提高到2.5%,提高了66.7%。

Study on Steel-Mushy Al-20Sn Alloy Bonding

Steel-mushy Al-20Sn alloy bonding was studied for the first time. The relationship model about preheat temperature of steel plate, solid fraction of Al-20Sn alloy mushy, rolling speed and interfacial shear strength of bonding plate could be established by artificial neural networks perfectly. This model could be optimized with a genetic algorithm. The optimum bonding parameters were: 505 degreesC for preheat temperature of steel plate, 34.3% for solid fraction of Al-20Sn alloy mushy and 10 mm/s for rolling speed, and the largest interfacial shear strength of bonding plate was 71.2 MPa.

Effects of ZrO_2 Nanoparticles on the Microstructure and Thermal-protective Properties of PEO Coating on Al-12.5%Si Alloy

PEO ceramic coatings including ZrO_2-Al_2O_3-SiO_2 in three phases were prepared on an Al-12.5%Si alloy in electrolyte solutions containing ZrO_2 nanoparticles. The microstructures and phases of the coatings were analyzed by SEM and XRD, and the heat insulation performance and the thermal shock resistance of the coatings were investigated. The compactness of the coating increased significantly and the hindrance of the Si element on plasma electrolytic oxidation process was effectively weakened. The growth rate of the coating was improved substantially with the addition of ZrO_2 nanoparticles. The PEO ceramic coatings are primarily composed of SiO_2 and high temperature steady phases such as a-Al_2O_3 and c-ZrO_2. Both the content of c-ZrO_2 and the heat-insulating property of the coating increased significantly. The ceramic coatings with special microstructure and composition formed in the solutions containing ZrO_2 nanoparticles possess excellent heat insulation performance and thermal shock resistance.

MICROSTRUCTURE AND MACROSEGREGATION OF Al-7%Si ALLOY SOLIDIFIED UNDER COMPLEX EFFECTS OF ELECTROMAGNETIC AND CENTRIFUGAL FORCES

Macrosegregations and microstructures of Al-7%Si alloy solidified under complex of fects of magnetic field and centrifugal forces are studied by means of a set of selfdesigned electromagnetic centrifugal casting (EMCC) device. It is shown that electromagnetic field (EMF) has an important effect on the macrosegregation of centrifugal casting specimen of Al-7%Si alloy in two respects: one is that there exists always a kind of convection in the liquid in front of the S/L interface caused by effect ofthe electromagnetic force; the other is that different atomic clusters of solidparticles with different physical characteristics are subjected to quite different electromagnetic (Lorentz) force. Therefore, their movements get changed. In addition, the formation process of a complex band structure consisting of primary α-Al dendrites and (α-Al+β-Si) eutectics in hypoeutectic Al-Si alloys during EMCC and the effect of EMF are discussed.

高导热低热膨胀Al-20%Si/石墨片复合材料的制备与性能研究

采用真空热压烧结工艺制备高导热、低热膨胀的Al-20%Si/石墨片复合材料,探讨了热压强度、烧结温度和时间、石墨含量等工艺参数对复合材料导热性能的影响。采用金相显微镜观察复合材料的微观形貌,采用激光热导仪、膨胀系数分析仪以及电子万能测试机测试复合材料的导热系数、热膨胀系数和三点抗弯曲强度。结果表明:Al-20%Si/石墨片复合材料结构较为致密,石墨片在铝基基体中分散均匀;不同的工艺参数对复合材料的导热性能有明显影响,热压强度和温度越高,烧结时间越长,复合材料的导热性越好。当石墨质量分数为5%,热压强度45 MPa,烧结温度450℃,时间60 min时,垂直方向z导热系数约44 W·m^(-1)·K^(-1),热膨胀系数约15×10^(-6)/℃;但复合材料在三点弯曲压力下呈脆性断裂,抗弯曲强度仍待提高。

Structural evolution of spray-formed Al-70wt.%Si alloys during iso-thermal holding in the semi-solid state

The grain growth behavior of spray-formed Al-70wt.%Si alloys was studied in the semi-solid state. The specimens were isothermally heat-treated at various temperatures between the solidus and liquidus of Al-Si alloys and then quenched in water. The microstructure of reheated specimens was characterized using optical and scanning electron microscopies. The isothermal holding experiment was carried out to investigate grain growth behavior as a function of holding time and temperature in the semi-solid state. The coarsening mechanism and the effect of porosity on microstructure were also studied.

STRUCTURAL TRANSFORMATION AND ITS REVERSIBILITY IN LIQUID Al-13%Si ALLOY AT HIGH TEMPERATURES

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Mg、Ni元素添加及热处理对Al-20%Si合金组织和力学性能的影响

研究了不同Mg、Ni合金元素添加和T6热处理对过共晶Al-20%Si合金组织和力学性能的影响。结果表明:合金中主要有初生硅相、α-Al相和共晶硅相,随着合金元素Mg、Ni含量的增加,合金中初生硅数量逐渐减少,而部分共晶硅变短和颗粒化。T6热处理后,合金中初生硅和共晶硅数量进一步减少。随着添加合金元素Mg∶Ni比值的增加,经T6热处理后,合金的抗拉强度和硬度值均随之增加。当添加合金元素Mg∶Ni比值为1.6时,经T6热处理后,该合金的抗拉强度和硬度值最高分别可达264 MPa和128 HBS。

Static and Dynamic Precipitation Behavior of the Al-20wt.% Zn Alloy

The static and dynamic precipitation behavior of solution-treated binary Al-20 wt.% Zn alloy is investigated via artificial aging, cold rolling and artificial aging combined with cold rolling. The solution-treated Al-Zn alloy exhibits high thermal stability during aging, and low densities of nano-sized Zn particles are precipitated along with AI grain boundaries after aging at 200℃ for 13 h. Compared with static precipitation, dynamic precipitation occurs more easily in the Al-Zn alloy. Zn clusters are obtained after cold rolling at an equivalent plastic strain of 0.6, and the size of the Zn phase reaches hundreds of nanometers when the strain is increased to 12.1. The results show that the speed of static precipitation can be significantly enhanced after the application of 2.9 rolling strain. Grain refinement and defects induced by cold rolling are considered to promote Zn precipitation. The hardness of Al-Zn alloy is also affected by static and dynamic precipitations.

太阳能热发电换热管在Al-12.07%Si中的腐蚀研究

在太阳能热发电站中,选择Al-12.07%Si作为储能材料,20G钢作为换热管材料,并将20G钢沉浸在Al-12.07%Si中进行长达1080h的腐蚀研究。通过SEM、EDAX、XRD方法分别对腐蚀后试样腐蚀层的形貌、成分和腐蚀试样的物相进行分析。研究结果发现,20G钢的腐蚀层形状不平整规则,试样表面均出现了Fe2Al5和FeAl3相。随着腐蚀时间延长,腐蚀试样的失重和腐蚀层厚度逐渐稳定,试样的腐蚀速率下降。

Modification and aging precipitation behavior of hypereutectic AI-21wt.%Si alloy treated by P+Ce combination

In the present study, the tested hypereutectic Al-21wt.%Si alloys were prepared by modifying the melt using different proportions of P and Ce, and then applying T6 heat treatment. The modification effects and mechanism of P＋Ce complex modifier on the Si phase of hypereutectic Al-21wt.%Si alloy were studied, and the aging precipitation behavior after modification was characterized by means of tensile strength measurement, OM, SEM and TEM analysis. The results show that the massive primary silicon phase particles are significantly refined after modification, while the needle-like eutectic silicon crystals become fibrous and short. It was found that the mechanism of phosphorus modification on the primary silicon can be attributed to heterogeneous nucleation of AlP, while the modification mechanism of Ce can be explained by adsorbing-twinning theory. In the aged microstructure of the modified hypereutectic Al-21wt.%Si alloy, there existed some strengthening phases such as AI4Cu9, Al2Cu, AlCu3, and Al57Mn12. The P＋Ce complex modifier not only affected the size of primary silicon and eutectic silicon, but also the aging behavior of alloys under the heat treatment process. When Al-21wt.%Si alloy was modified using 0.08%wt.P ＋ 0.6wt.% Ce, the aging precipitates were dispersed uniformly in the alloy, and its mechanical properties at room and elevated temperatures are optimized （Rm = 287.6 MPa at RT, Rm = 210 MPa at 300 ℃）.

Effect of Gd on microstructure and refinement performance of Al-5Ti-B alloy

Al-5Ti-B and Al-5Ti-B-Gd master alloy refiners were fabricated by fluorine salt casting method.The microstructure and phase constitution of the master alloys were investigated by scanning electron microscopy (SEM),transmission electron microscopy (TEM) and X-ray diffraction (XRD).The results show that Al-Ti-B alloy refiner consists of Al_(3)Ti phase and TiB2 phase.After Gd is introduced into the intermediate alloy,Ti_(2)Al_(20)Gd phase appears in the alloy,the size of Al_(3)Ti is significantly reduced,and Ti-Al-Gd phase is found in the edge of Al_(3)Ti phase.At the same time,some independent Ti-Al-Gd phases appear in local areas,which are Ti_(2)Al_(20)Gd phase determined by micro-area electron diffraction analysis.Analysis and calculation results of the high-resolution images of the Ti_(2)Al_(20)Gd/Al structure show that there is no other compound at the junction between the Ti_(2)Al_(20)Gd phase and Al,and Ti_(2)Al_(20)Gd phase has a great difference in atomic space with the α-Al,which cannot be directly used as heterogeneous nucleus.But,after being decomposed in the aluminum melt,the Ti_(2)Al_(20)Gd phase can promote the refinement effect of the refiner.In the Al-Ti-B-Gd master alloy,there are many dispersed Al_(3)Ti particles with a size of less than 1 μm,which can promote the Al-5Ti-B refining effect.

高温扩散对过共晶Al-Si合金组织的影响

研究w(Si)=20%的过共晶Al-Si合金在高于共晶点温度进行热处理后的组织形貌变化.结果表明:热处理温度610℃,保温时间分别为5、10、15min时,随保温时间的延长,粗大的柱状树枝晶α-Al变为近球状组织;不规则的多边形状和花瓣状的初晶Si会逐渐熔断、钝化,最后以15μm小块状和近球状组织出现;粗大的针片状共晶Si先发生熔断变为细小的颗粒状,然后全部熔化,最后在水淬中析出细小颗粒状和纤维状的共晶Si包围α-Al相;热处理温度580℃,保温时间分别为5、15、30、40min时,随保温时间的延长,初晶硅尺寸变细小,直径达到30μm,圆整度不断得到提高,当保温时间达到40min时,共晶硅变为纤维状.

稀土复合变质处理对Al-Si合金性能的影响

采用Ce-La复合稀土对Al-20%Si合金进行变质处理,考察了稀土复合变质对Al-Si合金力学性能、耐磨性能的影响,研究了冷却速度对合金力学性能的影响。结果表明:Ce-La复合变质剂对Al-20%Si合金具有双变质作用,当稀土Ce的添加量为0.5%,La的添加量为0.6%时,Al-Si合金的力学性能最好,抗拉强度和伸长率分别为268.5 MPa、0.52%;Ce-La复合变质剂能细化合金,提高合金耐磨性;稀土共晶硅对冷却速度一定程度上较为敏感,冷却速度的提高可以有效细化合金。