INFLUENCES OF TRACE ADDITIONS OF STRONTIUM AND PHOSPHORUS ON ELECTRICAL RESISTIVITY AND VISCOSITY OF LIQUID Al-Si ALLOYS

The electrical resistivity and viscosity of liquid hypoeutectic Al 7%Si and hypereutectic Al 18%Si alloys, and the influences of trace strontium and phosphorus on them were investigated. The trace additions of the two elements increase the electrical resistivity. At the precipitation temperatures of primary phase, the electrical resistivity exhibits a discontinuity for all experimental Al Si alloys. In the discontinuity the electrical resistivity, respectively, decreases and increases abruptly for Al 7%Si alloys and Al 18%Si alloys. Phosphorus and strontium both have some effects on the discontinuity temperature and the jump value of electrical resistivity of Al 18%Si alloys, but strontium hardly has effect on them in Al 7%Si alloys. The trace additions of strontium and phosphorus increase the viscosity of the experimental alloy.

Electrical resistivity and structural heredity of hypereutectic Al-Si alloy melt

The variation rule of the sensitive physical properties of Al 16%Si alloy melt was studied. The results show that within a certain temperature range, the electrical resistivity of Al 16%Si alloy melt changes abruptly in the forms of inflection points or platforms, which is ascribed to the changes in the internal microstructure of the melt. Based on this rule, the variation characteristics of microstructure can be revealed. When remelting and overheating Al 16%Si alloy to 1 050 ℃, the hereditary effects of different original structure on solidification structure after remelting can be eliminated, which can provide scientific foundation for properly controlling the hereditary factors transmitting the structural information of melt.

Process and properties of electroless Ni-W-B amorphous electrical resistance film

The process and properties of electroless plating Ni-W-B alloy have been studied. The results show that the deposits containing W and B are obtained, and the deposition rate of the bath is increased with increase of W content when a certain amount of sodium tungstate solution is added in the Ni-B bath. The Ni-W-B alloy is amorphous as deposition and its resistivity increases directly with the increase of W content in the coating, but decreases gradually with increasing the deposit thickness. XRD and SEM show that the distributions of W and B in the Ni-W-B alloy film are very uniform and dispersed without any segregation.

Effects of electric parameters on corrosion resistance of anodic coatings formed on magnesium alloys

Anodic coatings were obtained by micro-arc oxidation on AZ91HP magnesium alloys in a solution containing 10 g/L NaOH and 8 g/L phytic acid.The effects of electric parameters including frequency,final voltage,duty cycle and current density on the corrosion resistance of anodic coatings formed on the magnesium alloys were investigated by using an orthogonal experiment of four factors with three levels.The results show that the final voltage plays a main role on the coating properties.The orders of affecting corrosion resistance and coating thickness are separately ranked from high to low as,final voltage>duty cycle>current density>frequency and final voltage>current density>frequency>duty cycle.The final voltage influences the corrosion resistance of the anodized samples mainly by changing the surface morphology and coating thickness.

Mechanical, electrical, and thermal properties of the directionally solidified Bi–Zn–Al ternary eutectic alloy

A Bi-2.0Zn-0.2A1 （wt%） ternary eutectic alloy was prepared using a vacuum melting furnace and a casting furnace. The samples were directionally solidified upwards at a constant growth rate （V= 18.4 μm/s） under different temperature gradients （G = 1.15-3.44 K/mm） and at a constant temperature gradient （G = 2.66 K/mm） under different growth rates （V= 8.3-500 μm/s） in a Bridgman-type directional so- lidification furnace. The dependence ofmicrostructure parameter （2） on the solidification parameters （G and V） and that of the microhardness （Hv） on the microstructure and solidification parameters were investigated. The resistivity （ρ） measurements of the studied alloy were per- formed using the standard four-point-probe method, and the temperature coefficient of resistivity （α） was calculated from the ρ-Tcurve. The enthalpy （AH） and the specific heat （Cp） values were determined by differential scanning calorimetry analysis. In addition, the thermal conductivities of samples, obtained using the Wiedemann-Franz and Smith-Palmer equations, were compared with the experimental results. The results revealed that, the thermal conductivity values obtained using the Wiedemarm-Franz and Smith-Palmer equations for the Bi-2.0Zn-0.2Al （wt%） alloy are in the range of 5.2-6.5 W/Km and 15.2-16.4 W/Km, respectively.

Influence of Zn content and annealing process on electrical property of CuZn alloy

The relationship among annealing temperature, microstructure and electrical resistivity of Cu (8%～13%)Zn (mole fraction) alloys was studied. The results show that the relationship between the electrical resistivity of cold deformation CuZn alloy and annealing temperature is related to the recovery and recrystallization of the processes. The increments of electrical resistivity due to strain are restored mainly on the process of recovery and recrystallization. The room temperature resistivity of soft state alloys is linear to the Zn contents. The extended application of Matthissen rule on high concentration solid solution was discussed. [

Microstructure formation and electrical resistivity behavior of rapidly solidified Cu-Fe-Zr immiscible alloys

The immiscible Cu-Fe alloy was characterized by a metastable miscibility gap.With the addition element Zr,the miscibility gap can be extended into the Cu-Fe-Zr ternary system.The effect of the atomic ratio of Cu to Fe and Zr content on the behavior of liquid-liquid phase separation was studied.The results show that liquid-liquid phase separation into Cu-rich and Fe-rich liquids took place in the as-quenched Cu-Fe-Zr alloy.A glassy structure with nanoscale phase separation was obtained in the as-quenched(Cu0.5Fe0.5)40Zr60 alloy sample,exhibiting a homogeneous distribution of glassy Cu-rich nanoparticles in glassy Fe-rich matrix.The microstructural evolution and the competitive mechanism of phase formation in the rapidly solidified Cu-Fe-Zr system were discussed in detail.Moreover,the electrical property of the as-quenched Cu-Fe-Zr alloy samples was examined.It displays an abnormal change of electrical resistivity upon temperature in the nanoscale-phase-separation metallic glass.The crystallization behavior of such metallic glass has been discussed.

引线框架Cu-Fe-P合金的加工工艺研究

研究了热处理与冷变形对引线框架材料Cu-Fe-P合金导电率、显微硬度、耐热性的影响。结果发现,低温时效时,极为细小的析出物在冷轧过程中可以溶入铜基体,从而使得导电率大幅度下降;同时耐热性主要依赖于固溶处理温度以及随后的时效条件。精整变形后合金性能可达:导电率68%IACS、显微硬度165HV;在450℃加热5min合金未观察到软化。

Effects of aging in electric field on 2024 alloy

The effect of heat treatment in an electric field on micro plastic deformation characteristics of 2024 Al alloy was investigated. The mechanism of aging in an electric field affecting the micro plastic deformation behavior was preliminarily discussed. The results show that the resistance to micro plastic deformation of the alloy can be greatly increased by aging in an electric field. Aging temperature, aging time and electric field strength are selected by adopting the orthogonal design method and the optimum technological parameters are obtained.

Microstructure and properties of deformation-processed Cu-Fe in-situ composites

The effects of intermediate annealings on the microstructure, the strength and the electrical resistivity of deformation-processed Cu-Fe in-situ composites were studied. The results show that intermediate annealings favour the formation of uniform tiny fibres from the iron dendrites but they have no obvious effect on the strength of the composite. The bigger the strain is, the higher the strength is. As the strain increases, the resistivity increases due to the increase of interface density. Intermediate annealings result in notable decreasing resistivity due to the precipitation of the iron atoms from the Cu matrix and decrease of solute scattering resistivity. The doping with Zr improves the strength of the composite slightly and the ultimate tensile strength(UTS) increases about 10%. The colligated performances of deformation-processed Cu-11.5%Fe and Cu- 11.5%Fe-Zr composites at strain η= 5.37 are 64.6% IACS/752MPa and 61.4% IACS/824MPa respectively.

基于电接触强化的铝合金表面电刷镀镍层改性研究

[目的]对铝合金进行表面处理可提高其硬度和耐磨性,拓宽铝合金材料在机械零件方面的应用。[方法]采用电刷镀技术在1060铝合金表面制备Ni镀层,再通过电接触强化技术对Ni镀层进行改性。采用扫描电子显微镜和维氏硬度计考察了Ni镀层电接触强化前后的微观组织和显微硬度。通过摩擦磨损试验对比了1016铝合金及Ni镀层电接触强化前后的耐磨性。[结果]经电接触强化后,Ni镀层内部的裂纹及孔洞类缺陷减少,晶粒间隙减小,致密性提高,显微硬度增大到524.4~560.3 HV0.1范围内。1016铝合金在摩擦磨损试验后存在较深的犁沟和剥落,耐磨性较差。Ni镀层的耐磨性优于1016铝合金,但在摩擦过程中会发生剥落。经电接触强化的Ni镀层在摩擦过程中摩擦因数平稳,表面只是轻微擦伤,耐磨性最佳。[结论]结合电刷镀镍和电接触强化技术可显著提高铝合金的表面性能。

电爆喷涂FeCoCrNiAl_(x)高熵合金涂层的形成机制与性能

采用电爆喷涂技术在TC4钛合金表面制备FeCoCrNiAl_(x)(x=0,0.5,1.0,摩尔比,下同)涂层。使用XRD,SEM,EDS,显微硬度计以及摩擦磨损实验等材料分析手段,研究Al含量对高熵合金涂层物相结构、表面形貌、显微硬度和耐磨性能的影响。结果表明:涂层的晶粒尺寸为纳米级,均形成了简单的FCC,BCC及FCC+BCC结构固溶体。随Al元素的增加,物相结构由FCC相逐渐向BCC相转变。涂层表面平整、致密,没有明显的裂纹等缺陷,且各元素分布均匀,并没有发现元素偏聚现象。划痕测试表明,FeCoCrNiAl_(1.0)涂层出现失效的平均临界载荷为37.2 N;涂层与基体呈冶金结合。涂层的硬度和耐磨性与Al含量呈正相关关系,x=1.0时,平均显微硬度达到最大值531.8HV,约为基体的1.62倍;FeCoCrNiAl_(1.0)涂层的磨损量最小,耐磨性约为基体的3.9倍,磨损机制主要为磨粒磨损。

AZ91D镁合金表面钼-钛-锰导电膜化学转化工艺及其性能研究

[目的]对镁合金进行表面处理可获得兼具导电性和耐蚀性的膜层,进而满足电子通信领域的使用要求。[方法]采用以(NH_(4))_(2)MoO_(4)、H_(2)TiF_(6)和KMnO_(4)为主成分的溶液,在AZ91D镁合金表面通过化学转化技术制备了钼−钛−锰(用MTM表示)导电膜。研究了前处理工艺和化学转化液的KMnO_(4)质量浓度对MTM膜层外观、形貌、组成、耐蚀性和导电性的影响。[结果]对AZ91D镁合金进行打磨、碱洗、酸洗、表调等前处理后在含4.2 g/L KMnO_(4)的转化液中处理所得的MTM膜层表面拥有最大面积分数的β相导电斑点,耐蚀性较好,导电性最佳(禁带宽度和接触电阻分别为2.556 eV和0.428Ω/in^(2))。[结论]本工艺制备的MTM膜层耐蚀性和导电性良好,在电子通信领域具有很好的应用前景。

Influence of Surface Condition on Expulsion in Spot Welding AZ31B Magnesium Alloy

Experiments were carried out to study the influence of surface condition on expulsion during the spot welding of AZ31B Mg alloy. A general electrical contact resistance theory for conductive rough surfaces and the relation between maximum temperature Tm in the contact and voltage-drop V across interface of two surfaces were employed to understand the reason of expulsion in Mg alloy spot welding. The main reason of expulsion is that the high electrical contact resistance induced by large roughness of the surface and oxide film covered on the surface leads to local melting of metal in the interface of two surfaces, and liquid metal of the local area ejected from the specimen under electrode force forms expulsion.

Microstructure and electrical resistivity in the GdNi_(5–x)Cu_x intermetallic series

The effect of the Ni/Cu substitution on the electrical resistivity and microstructure of the polycrystalline GdNi5-xCux series was studied. The value of temperature of phase transition（T_（ph）） estimated from temperature dependence of electrical resistance varied non-linearly across copper doping from 32.5 K（x=0.0） to 29.1 K（x=5.0）. The value of residual resistivity（ρo） estimated at low temperature range decreased from 27.28 μΩcm（x=0.0） to 9.44 μΩcm（x=5.0）, which was discussed as the influence of microstructure. In order to describe the temperature dependence of resistivity ρ（T） a variety of approaches were applied due to different scattering mechanisms occurring at high and low temperature ranges. The change within ρ（T） curvature was evidenced at low temperature range across copper doping. The temperature variation of the resistivity was quite peculiar for Cu-rich compounds（x=4.8, x=5.0）, which might be correlated with the incommensurate magnetic structure derived from the weakly negative interaction between the nearest neighbours of Gd. The correlation between microstructure and resistivity was observed.

Characterizations of precipitation behavior of Al-Mg-Si alloys under different heat treatments

The solidification-precipitation behavior of Al-Mg-Si multicomponent alloys has long been an absorbing topic. Experiments were carried out to analyze the precipitation behaviors of Al-Mg-Si alloys under different heat treatments. All specimens were homogenized at 570 °C for 8 h, and then solution treated at 540 °C for 55 min. Subsequently, the specimens were age treated for different times at temperatures of 100 °C, 150 °C and 180 °C, respectively. The experimental results show that the occurrence of dispersed free zones(DFZ) is caused by the uneven distribution of dispersed phase. During the aging process, pre-β″ phases form at the initial stage and an aging temperature of 100 °C is too low to complete the transformation of pre-β″ to β″. At 150 °C, the precipitation sequence is concluded as SSSS-pre-β″-pre-β″+β″-β″-β′-β. Moreover, changes in sizes and densities of the pre-β″, β″and β′ phases during the aging process has an important influence on the evolution of microhardness and electrical resistivity. The microhardness peak value of 150 °C is similar to that of 180 °C, which is ~141 HV. While, at 100 °C, the microhardness increases slowly, and the attainable value is 127 HV up to 19 days. When the aging temperature is 100 °C, the electrical resistivity has the highest average value. When the aging temperature exceeds 100 °C, with the occurrence and growth of β″and β′, the resistivity has a distinct decrease with prolonged aging time.

Thermal stability and microstructure development of cast and powder metallurgy produced Mg-Y-Zn alloy during heat treatment

Response to isochronal annealing up to 440 ℃ of squeeze cast Mg–Y–Zn alloy and of the same alloy prepared by powder metallurgy(PM)and extruded at 280 ℃ was studied by resistivity and microhardness measurement,differential scanning calorimetry(DSC)and microstructure investigation.Electrical resistivity was measured at 77 K and microhardness was measured at room temperature after each annealing step.DSC measurement was performed at various heating rates.Transmission and scanning electron microscopy and optical microscopy revealed ribbons of long-period ordered structure(LPSO)18R and planar defects within grain boundaries.Relatively high density of planar defects was found in grain interiors of the cast alloy with the grain size approximately 50μm.Well pronounced subgrains were observed in the PM prepared alloy.Secondary phase particles decorate grain boundaries in this alloy.Three precipitation processes were detected in the cast alloy during repeated isochronal annealing up to 440 ℃,whereas only one significant process was revealed in the PM alloy.These processes were identified as embedding of stacking faults by solutes,development and rearrangement(18R→14H)of LPSO phase and development of grain boundary particles.A coarsening of grain boundary particles rich in Y and Zn only proceeds in the PM alloy.Activation energies of the precipitation processes were determined.Microhardness exhibits good thermal stability against annealing up to 360 ℃ in the PM alloy.

A Novel High-Entropy Amorphous Thin Film with High Electrical Resistivity and Outstanding Corrosion Resistance

This study explores a novel WNbMoTaV high-entropy thin film(HETF)in amorphous structure via pulsed laser deposition system.The formation of amorphous structure of this high-entropy alloy is ascribed to the high cooling rate during the deposition process.The HETF shows a smooth surface with a height fl uctuation of less than 13 nm.This film has a high electrical resistivity of~320.6μΩ·cm and a low corrosion current density of 0.088μA/cm 2.The corrosion resistance of the HETF at ambient temperature is superior to the conventional AISI 316 L stainless steel.The high electrical resistivity and excellent corrosion resistance of the HETF are mainly attributed to its chemical disorder,cocktail effect and homogeneous amorphous structure.This experimental phenomenon not only provides a basis for the preparation of amorphous alloy films with low glass forming ability by pulsed laser deposition system,also promotes the potential application of WNbMoTaV HETF in the microelectronic components as resistivity sensors.

Influence of Rare Earth(Ce and La) Addition on the Performance of Al-3.0 wt%Mg Alloy

The influences of rare earth elements（cerium and lanthanum） on the microstructure and phases of Al-3.0 wt%Mg alloys used for electromagnetic shielding wire were characterized by scanning electron microscopy（SEM）, energy-dispersive spectroscopy（EDS）, X-ray diffraction（XRD） and differential scanning calorimetry（DSC）. The mechanical properties and electrical resistivity were also investigated. The results indicated that a certain content of rare earth could improve the purification of the aluminum molten, enhance the strength, and reduce the electrical resistivity of Al-3.0 wt%Mg alloys. The strength reached the top value when RE content was 0.3 wt% while the alloy with 0.2 wt% RE addition had the smallest electrical resistivity. The elongation varied little when RE addition was no more than 0.2 wt%. But the excessive addition of rare earth would be harmful to the microstructure and properties of Al-3.0 wt%Mg alloys.