Determination of thermal conductivities of solid and liquid phases for rich-Sn compositions of Sn-Mg alloy

The variations of thermal conductivities of solid phases versus temperature for pure Sn and Sn-1 wt% Mg, Sn-2 wt% Mg, and Sn-6 wt% Mg binary alloys were measured with a radial heat flow apparatus. Thermal conductivity variations versus temperature for pure Sn and Sn-1 wt% Mg, Sn-2 wt% Mg, and Sn-6 wt% Mg binary alloys were found to be 60.60 ± 3.63, 61.99 ± 3.71, 68.29 ± 4.09, and 82.04 ± 4.92 W/Km, respectively. The thermal conductivity ratios of liquid phase to solid phase for pure Sn and eutectic Sn-2 wt% Mg alloy at their melting temperature were found to be 1.11 and 1.08, respectively, with a Bridgman type directional solidification apparatus. Thus the thermal conductivities of liquid phases for pure Sn and eutectic Sn-2 wt% Mg binary alloy at their melting temperature were evaluated to be 67.26 ± 4.03 and 73.75 ± 4.42 W/Km, respectively, by using the values of solid phase thermal conductivities and the thermal conductivity ratios of the liquid phase to the solid phase.     

Experimental determination of thermal conductivity of solid and liquid phases in Bi−Sn and Zn−Mg binary eutectic alloys

The thermal conductivities of solid phases, K_s, for Bi-43 wt.% Sn and Zn-0.15 wt.%Mg binary alloys at their eutectic temperature are found to be 28.0 τ 1.4 and 137.4–6.9 W/Km, respectively, with a radial heat flow apparatus. The thermal conductivity ratios, R, of liquid phase to solid phase for the same alloys at their eutectic temperature are found to be 0.93 and 0.78, respectively, with a Bridgman type directional solidification apparatus. Thus, the thermal conductivities of the liquid phases, K_L, for Bi-43 wt.%Sn and Zn-0.15 wt.%Mg binary alloys at their eutectic temperature are evaluated to be 26.0−1.3 and 107.2−5.4 W/Km, respectively, from the measured values of K_s and R.     

Sn-6Bi-2Ag(Cu, Sb)无铅钎料合金微观组织分析

利用差示扫描量热计 (DSC)测定了Sn 6Bi 2Ag ,Sn 6Bi 2Ag 0 .5Cu ,Sn 6Bi 2Ag 2 .5Sb三种新无铅钎料合金的熔化温度。结果表明 ,少量Cu的加入能降低Sn Bi Ag系无铅钎料合金的熔化温度 ,而Sb的加入使合金的熔化温度升高。利用光学显微镜 (OM )、扫描电子显微镜 (SEM )、能谱分析 (EDX)对合金的微观组织进行了分析与比较 ,钎料合金的微观组织与冷却条件和合金元素的含量有关 ,Sb的加入使析出相的尺寸细化。硬度测定表明Sn Bi Ag(Cu ,Sb)无铅钎料合金的硬度远大于纯Sn的硬度 ,加入少量的Cu(0 .5 % ) ,Sb(2 .5 % )对Sn Bi Ag系钎料合金的硬度影响较小     

Combined effects of Bi and Sb elements on microstructure,thermal and mechanical properties of Sn-0.7Ag-0.5Cu solder alloys

This research investigated the combined effects of addition of Bi and Sb elements on the microstructure, thermal properties, ultimate tensile strength, ductility, and hardness of Sn-0.7Ag-0.5Cu (SAC0705) solder alloys. The results indicated that the addition of Bi and Sb significantly reduced the undercooling of solders, refined the β-Sn phase and extended the eutectic areas of the solders. Moreover, the formation of SbSn and Bi phases in the solder matrix affected the mechanical properties of the solder. With the addition of 3 wt.% Bi and 3 wt.% Sb, the ultimate tensile strength and hardness of the SAC0705 base alloy increased from 31.26 MPa and 15.07 HV to 63.15 MPa and 23.68 HV, respectively. Ductility decreased due to grain boundary strengthening, solid solution strengthening, and precipitation strengthening effects, and the change in the fracture mechanism of the solder alloys.     

Design and preparation of aluminum alloy with high thermal conductivity based on CALPHAD and first-principles calculation

To obtain the aluminum alloy with high thermal and mechanical properties, the effects of alloying elements and the second phases on the thermal conductivity of Al alloys were investigated by CALPHAD and first-principles calculation, respectively. The properties of the second phases, including Young’s modulus, Poisson’s ratio and minimum thermal conductivity, were systematically studied. Results show that the ranking order of the effects of the alloying elements on the thermal conductivity is Mg>Cu>Fe>Si, and for Al-12Si alloys, the mathematical model of the relationship between the alloying elements and the thermal conductivity can be expressed as λ=ax²-bx+c when the second phase precipitates in the matrix. All kinds of ternary phases of Al-Fe-Si have higher deformation resistance, rigidity, theoretical hardness, Debye temperature and thermal conductivity than the other phases which possibly exist in the Al-12Si alloys. Based on the guidance of CALPHAD and first-principles calculation, the optimized chemical composition of Al alloy with high conductivity is Al-11.5Si-0.4Fe-0.2Mg (wt.%) with a thermal conductivity of 137.50 Wm⁻¹·K⁻¹ and a hardness of 81.3 HBW.

     

Dependency of the thermal and electrical conductivity on temperatures and compositions of Zn in the Al−Zn alloys

The variations of thermal conductivity (K) with temperature for Al–xZn (x = 5, 10, 20, 30, 50 and 60 wt. %) alloys were measured by using a radial heat flow furnace. The variations of electrical conductivity (σ) of solid phases with temperature for the studied alloys were determined from the Wiedemann-Franz and Smith-Palmer equations by using the measured values of K from the plots of K. The thermal temperature coefficient (α_TTC) and the electrical temperature coefficient (α_ETC) were obtained. Dependency of the α_TTC and α_ETC on the composition of Zn in the Al?Zn alloys was also investigated. According to the present experimental results, K of Al–Zn alloys linearly decrease with increasing temperatures up to the melting temperature for each composition and exponentially decrease with the increasing Zn content. On the other hand, the σ of Al based Al-Zn alloys exponentially decrease with increasing temperature and Zn content.     

Determination of interfacial energies for solid al solution in equilibrium with Al-Cu-Ag liquid

The equilibrated grain boundary groove shapes of a solid Al solution in equilibrium with Al-Cu-Ag liquid were observed from a quenched sample using a radial heat flow apparatus. The Gibbs-Thomson coefficient, solid-liquid interfacial energy, and grain boundary energy of the solid Al solution were determined from the observed grain boundary groove shapes. The thermal conductivity of the solid phase for Al-16.42 at.% Ag-4.97 at.% Cu and Al-16.57 at.% Ag-11.87 at.% Cu alloys and the thermal conductivity ratio of the liquid phase to the solid phase for Al-16.57 at.% Ag-11.87 at.% Cu alloy at the melting temperature were also measured with a radial heat flow apparatus and a Bridgman-type growth apparatus, respectively.     

化合物相的析出对Mg-Sn二元合金导热性能的影响

研究了添加不同含量的Sn(3%,6%,9%,质量分数)对铸态、固溶态及时效态Mg-Sn二元合金导热性能的影响。结果表明,铸态及固溶处理态Mg-Sn合金的热导率均随着Sn元素含量的增加不断降低,其中Sn含量最多的固溶态Mg-10Sn合金所对应的热导率降低至52.6 W/(m·K);同固溶态合金相比,相同溶质含量的铸态合金的热导率更高。Mg-Sn合金的热导率随时效的进行逐渐升高,Mg-3Sn、Mg-6Sn及Mg-10Sn合金的热导率分别最终可达到125、120及110 W/(m·K)。分析表明,镁合金热导率的不断升高可以归结于基体的纯化效应,Sn元素的原子大小、核外电子分布以及化合价等均会对Mg-Sn合金的导热性能产生影响。     

Microstructure and Electro-Physical Properties of Sn-3.0Ag-0.5Cu Nanocomposite Solder Reinforced with Ni Nanoparticles in the Melting-Solidification Temperature Range

The electrical conductivity of nanocomposite Sn-3.0Ag-0.5Cu alloys with two different weight percentages of Ni nanoparticles (1.0 and 2.0 wt.%) was measured over a wide temperature range. The samples were produced using a cold pressing method: Sn-3.0Ag-0.5Cu powder and Ni nanopowder were mechanically mixed and pressed into 8 mm diameter rods. Ni nanoparticles were synthesized via a chemical reduction method and characterized by a core/shell structure. Temperature dependencies of the electrical conductivity revealed a hysteresis between the heating and cooling curves in a wide temperature range above the melting temperature. This fact is connected with structure transformations accompanied by a dissolution of Ni nanoparticles, which should be retarded due to an oxide/hydroxide shell on the surface of the nanoparticles. A microstructure analysis of the samples in the solid state showed a fine distribution of intermetallic compounds in the Sn-based matrix. The Ni atoms substituted for Cu atoms in the Cu₆Sn₅ compound forming a (Cu,Ni)₆Sn₅ phase.     

Effects of rare earth La on the microstructure and melting property of（Ag-Cu28）-30Sn alloys prepared by mechanical alloying

To obtain novel intermediate temperature alloy solders with a melting temperature of 400-600°C,nominal(Ag-Cu28)-30Sn alloys without or with a trace addition(0.5 or 1.0 wt.%) of rare earth(RE) element La were prepared by mechanical alloying.The aim of this research is to investigate the effects of the addition of La on the microstructures,alloying process and melting properties of(Ag-Cu28)-30Sn alloys.The results show that the addition of La produces no new phase.A trace amount of La addition can effectively refine the grain size,but the excessive addition of 1.0 wt.% La inhibits the alloying process.The influence of La on the melting temperatures of solder alloys is negligible.However,the trace addition of 0.5 wt.% La can distinctly reduce the fusion zone and improve the melting property of(Ag-Cu28)-30Sn alloys.     

热循环对Sn58Bi(纳米Ti)/Cu焊点界面与性能影响

为了改善Sn-58Bi低温钎料的性能,通过在Sn-58Bi低温钎料中添加质量分数为0.1%的纳米Ti颗粒制备了Sn-58Bi-0.1Ti纳米增强复合钎料。在本文中,研究了纳米Ti颗粒的添加对-55～125 _^oC热循环过程中Sn-58Bi/Cu焊点的界面金属间化合物(IMC)生长行为的影响。研究结果表明：回流焊后,在Sn-58Bi/Cu焊点和Sn-58Bi-0.1Ti/Cu焊点的界面处都形成一层扇贝状的Cu₆Sn₅ IMC层。在热循环300次后,在Cu₆Sn₅/Cu界面处形成了一层Cu₃Sn IMC。Sn-58Bi/Cu焊点和Sn-58Bi-0.1Ti/Cu焊点的IMC层厚度均和热循环时间的平方根呈线性关系。但是,Sn-58Bi-0.1Ti/Cu焊点的IMC层厚度明显低于Sn-58B/Cu焊点,这表明纳米Ti颗粒的添加能有效抑制热循环过程中界面IMC的过度生长。另外计算了这两种焊点的IMC层扩散系数,结果发现Sn-58Bi-0.1Ti/Cu焊点的IMC层扩散系数(整体IMC、Cu₆Sn₅和Cu₃Sn IMC)明显比Sn-58Bi/Cu焊点小,这在一定程度上解释了Ti纳米颗粒对界面IMC层的抑制作用。     

Effect of Alloying Element on Electromagnetic Interference Shielding Effectiveness of Binary Magnesium Alloys

The microstructure,electrical conductivity and electromagnetic interference shielding effectiveness of Mg-X(X=Al,Sn,Y and Gd)alloys in as-cast and solution states were systematically investigated in this study.The electrical conductivity and electromagnetic shielding capacity of binary magnesium alloys decrease linearly with alloying element content.The electromagnetic shielding effectiveness of the binary magnesium alloys with the same alloying element content is as follows:Mg-GdMg-SnMg-YMg-Al.The main reason for the differences in electromagnetic interference shielding of the binary magnesium alloys is the change in conductivity,which is mainly affected by volumetric difference of solute atoms and magnesium atoms,solute atomic valence and configuration of extranuclear electron.     

Preparation, deformation, and failure of functional Al-Sn and Al-Sn-Pb nanocrystalline alloys

Changes in the structure, hardness, mechanical properties, and friction coefficient of Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb (wt %) alloys subjected to severe plastic deformation by equal-channel angular pressing (with a force of 40 tonne) and by shear at a pressure of 5 GPa have been studied. The transition into the nanocrystalline state was shown to occur at different degrees of plastic deformation. The hardness exhibits nonmonotonic variations, namely, first it increases and subsequently decreases. The friction coefficient of the Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys quenched from the melt was found to be 0.33; the friction coefficients of these alloys in the submicrocrystalline state (after equal-channel angular pressing) equal 0.24, 0.32, and 0.35, respectively. The effect of disintegration into nano-sized powders was found to occur in the Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys after severe plastic deformation to ? = 6.4 and subsequent short-time holding.     

Measurements of electrical and thermal properties with growth rate,alloying elements and temperature in the Al–Si–X alloys

In this work, effect of alloying elements (X = Cu, Co, Ni, Sb and Bi) and growth rates on the microstructure, physical properties (electrical resistivity, enthalpy and specific heat) of the directionally solidified Al–Si eutectic alloy have been investigated. Al–12.6Si–2X (wt. %) samples were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified under constant temperature gradient, G (7.80 K/mm) and different growth rates, V (8.3–166.0 μm/s). Flake spacing (λ) and electrical resistivity (ρ) were measured from the solidified samples. The variation of electrical resistivity with temperature in the range of 300–500 K for alloying elements in the Al–Si eutectic cast alloy was also measured. The enthalpy of fusion (ΔH) and specific heat (C_p) for the same alloy were determined by a differential scanning calorimeter from the heating curve during the transformation from solid to liquid.     

Pb-Free solders: Part II. Application of ADAMIS database in modeling of Sn−Ag−Cu alloys with Bi additions

The ADAMIS database was used for calculation of the surface tension of the quaternary Sn−Ag−Cu−Bi liquid alloys by Butler's model. The resultant data were compared with those from the maximum bubble pressure measurements from Part I. The same thermodynamic database was next applied for the calculation of various phase equilibria. It was established that the Bi addition to the ternary Sn−Ag−Cu alloys (Sn-2.6Ag-0.46Cu and Sn-3.13Ag-0.74Cu in at.%; Sn-2.56Ag-0.26 Cu and Sn-2.86Ag-O.40Cu in mass%) causes lowering of the melting temperature and the surface tension to make the tested alloys closer to, traditional Sn−Pb solders. The simulation of the solidification by Scheil's model showed that the alloys with the higher Bi concentration are characterized by the lifting-off failure due to the segregation of Bi at the solder/substrate boundary. Thus, in modeling of new Pb-free solders, a compromise among various properties should be taken into consideration.     

Improved tensile properties of Mg-8Sn-1Zn alloy induced by minor Ti addition

In this study, the influence of minor titanium(Ti) addition on the microstructure and tensile properties of Mg-8Sn-1Zn based alloys were investigated by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and tensile tests. The results showed that Ti can decrease the secondary dendrite arm spacing(SDAS). The tensile strength of the Mg-8Sn-1Zn-Ti alloys is initially increased by increasing the Ti content up to 0.09 wt.%, but subsequently decreased for further increase of Ti content. The improved tensile properties are attributed to the decreased SDAS and refi ned Mg_2Sn phases, as well as the increased fraction of tin(Sn) segregated regions. The tensile fracture surface of the studied alloys shows mixed characteristics of cleavage and quasi-cleavage fracture. Adding Ti does not significantly change the fracture mode of the studied alloys.     

含RE铝阳极中析出相的电化学行为研究

用电子探针和能谱分析技术，观察了Al-5Zn-0．05In-0．1Sn-1Mg-0．3RE阳极中主要析出相的成分，并熔炼了析出相合金．电位测量和腐蚀后铝阳极表面的电子探针面扫描分析表明：富Sn相为阳极相，富Fe相、富RE相为阴极相；Fe相是铝阳极自腐蚀微电池中的主要阴极相，温度对析出相的电化学行为有影响．     

Effect of Sr modification on microstructure and thermal conductivity of hypoeutectic Al−Si alloys

Trace amount of Sr (0.05 wt.%) was added into the hypoeutectic Al−Si (3−12 wt.% Si) alloys to modify their microstructure and improve thermal conductivity. The results showed that the thermal conductivity of hypoeutectic Al−Si alloys was improved by Sr modification, and the increment and increasing rate of the thermal conductivity gradually increased with Si content increasing. The improvement of thermal conductivity was primarily related to the morphology variation of eutectic Si phases. In Sr-modified Al−Si alloys, the morphology of eutectic Si phases was a mixed morphology of fiber structure and fine flaky structure, and the proportion of the fine flaky eutectic Si phases gradually decreased with Si content increasing. Under the Si content reaching 9 wt.%, the proportion of fine flaky eutectic Si phases was nearly negligible in Sr-modified alloys. Correspondingly, the increment and increasing rate of thermal conductivity of Sr-modified alloys reached the maximum and tended to be stable.     

合金化元素对纳米晶铝合金热稳定性的影响

为研究加入Fe和Ti扩散系数有限的元素对纳米晶铝合金热稳定性的影响,制备Al?10％Fe(质量分数)和Al?10％Fe?5％Ti(质量分数)合金.将初始混合粉末在真空下球磨100 h,用高频感应加热烧结系统将球磨后的粉末制备成块体样品.采用X射线衍射仪、维氏显微硬度仪、场发射扫描电子显微镜和透射电子显微镜对球磨后的粉末...