Microstructures of an AlSi_7Mg alloy by near-liquidus casting

Semi-solid ingots of an A1SiTMg alloy were obtained using the method of near liquidus casting. Their microstructures exhibit the characteristics of free, equiaxed, and non-dendrite, which are required for semi-solid forming. The influences of casting temperature, heat preservation time, and cooling rate on the microstructure were also investigated. The results show that in the temperature region near liquidus the grain size becomes small with a decrease in casting temperature. Prolonging the heat preservation time makes grain crassitude at the same temperature. And increasing the cooling rate makes grain fine. The microstructure of the alloy cast with iron mould is freer than that with graphite mould.

MICROSTRUCTURE AND PROPERTIES OF ZL201 ALLOY OBTAINED BY NEAR-LIQUIDUS ELECTROMAGNETIC CASTING

The microstructures of ZL201 alloy slurry prepared by near-liquidus electromagnetic casting （NLEMC）, electromagnetic casting（EMC）, and near-liquidus casting（NLC） were investigated by means of electron microscopy and image analysis. Mechanical properties of as-cast alloys were determined. The results show that the NLEMC induces a fine, uniform, and equiaxed grain structure with a mean equal-area-circle grain diameter of 32.8μm. The as-cast aUoy has a hardness of HV122.8 and a tensite strength of 368MPa. Both of them are betterthan those of the alloys prepared by EMC and by NLC. The mechanism of grain refinement in the NLEMC alloy slurry was discussed.

REHEATING TEMPERATURE CONTRAST AND MICROSTRUCTURES OF 7075 Al ALLOY CAST BY LIQUIDUS SEMI-CONTINUOUS CASTING

In this study, reheating of liquidus semi-continuous cast billets of 7075 Al alloy was carried out in a resistance furnace, and the temperature contrast of the outer and the center of the reheated billets was investigated, then the reheating microstructures were investigated. Results show that: the difference of temperature between the outer and center is small and the difference of their microstructures are also small. During reheating at 576℃ the spheroidization of grains is significant after 5min and no rosettes are visible after 20min by optical microscopy. Similar observations were madeon materials reheated at 596℃, but the ripening process is faster. The grains growup to 30-60μm, fine enough for thixoforming.

Non-dendritic structural 7075 aluminum alloy by liquidus cast and its semi-solid compression behavior

Fine, equiaxed, non dendritic structure needed by semi solid processing was obtained by liquidus cast, i.e. 7075 wrought aluminum alloy cast from liquidus temperature. The microstructures after heat treatment at different temperatures and time in the semi solid range were observed, and the compression deformation behavior at different temperatures (490～600 ℃) and strain rates (5×10 -3 ～5s -1 ) was investigated by means of Gleeble 1500 thermal mechanical simulator. The results show that the deformation resistance of the non dendritic structure attained by liquidus cast in semi solid is remarkably lower than that of conventional dendritic structure. The formability of non dendritic structure is better than that of dendritic structure.

Liquidus Temperatures of System Na_3AlF_6-K_3AlF_6-AlF_3 for Aluminum Electrolysis at Lower Temperature

Liquidus temperatures in the molten salt system Na3AlF6-K3AlF6-AlF3 of interest for aluminum electrolysis were determined by thermal analysis method. The results were presented and an empirical equation describing liquidus temperatures for primary crystallization was derived t=1003.5–0.081×A2.3159–5.87×B0.657–0.024×A2.22×B1.14＋ 0.035×A2.17×B1.084, where t is the liquidus temperature in degree Celsius, A denotes the mass fraction of AlF3 in system Na3AlF6-K3AlF6- AlF3, and B denotes K3AlF6/（Na3AlF6＋K3AlF6 ） in mass（%, the value was defined as KR in this paper）. The composition limitations are 0w（AlF3）30%, and 0KR50%. The isothermal diagram of molten salt system Na3AlF6-K3AlF6-AlF3 was obtained in this composition limitation.

Partial Remelting of Thixotropic Magnesium-Rare Earth Alloy from Near Non-Equilibrium-Liquidus Casting

After the investigation on partial remelting of thixotropic magnesium serial alloys （ZK60） by near non-equilibrium liquidus casting （NNLC）, the primary solid grains of ZK60-2Ca alloy spheroidized notably during partial remelting processing, however, coarsening and polygonization as occurred holding time prolonged. The refining and globularity of the thixotropic alloys are promoted after further alloyed by Y, RE, Nd and/or Ag, and the results vary with those addition. The remelting structure of ZK60-2Ca-1Y alloy is finer than its base alloy. And the effect of RE, especially Ag, on the refinement of microstrueture is notable, but Nd does nothing on it. There is little impact of remelting temperature fluctuation on partial remelted microstrueture as holding time in general. On the contrary, it is more sensitive at longer holding time. The quality thixotropic silver-contained alloy can be achieved by remelted partially at 600℃ for 10 min.

THE LIQUIDUS OF THE TERNARY Ag-Cu-Si ALLOY SYSTEM

The liquidus of the ternary Ag-Cd-Si alloy system in the Ag-Cu rich region was determined by DTA. The ternary Ag-Cd-Si system was divided into two ternary systems Ag-Cu-Cuo.76Si0.24 and Ag-Cu0.76Si0.24-Si by the section of Ag-Cu0.76 Si0.24.There is one ternary eutectic point for both the systems with the composition of 12. 5at. %Ag+71. 7at.%Cu+15.8at. %Si and 30at.% Ag+44.7at.%Cu+25.3at.%Sirespectivelg and the temperatures of the eutectic points are 740 and 705℃ respectively.

Semi-solid slurry of AZ91 magnesium alloy prepared by electromagnetic stirring near liquidus temperature

An electromagnetic stirring process near liquidus temperature was designed and demonstrated experimentally to produce semi-solid slurry of AZ91 magnesium alloy,in order to avoid not only contamination from mechanical stirring but also the inflammation of Mg alloy melt at elevated temperature. AZ91 alloy feedstock was isothermally heat treated at 600-610 for 20 min,and then stirred by electromagnetic field. Globular primary particle characteristic was observed optically in the castings. Mechanical properties were also studied.

LIQUIDUS OF Au-Cu-Si SYSTEM

The diagram of system Au-Cu-Si was constructed from data of 9 internal sections by DTA in an atmosphere of dry N_2.The composition of ternary eutectic point melting at 337℃ lies in Au(74.7)-Cu(6.1)-Si(19.2) at.-%.The liquidus of the 3 side-binary systems have been redetermined.

Calculation and application of liquidus projection

Liquidus projection usually refers to a two-dimensional projection of ternary liquidus univariant lines at constant pressure. The algorithms used in Pandat for the calculation of liquidus projection with isothermal lines and invariant reaction equations in a ternary system are presented. These algorithms have been extended to multicomponent liquidus projections and have also been implemented in Pandat. Some examples on ternary and quaternary liquidus projections are presented.

LIQUIDUS OF NdCl_3-MgCl_2-LiCl SYSTEM

The liquidus of ternary system NdCl_3-MgCl_2-LiCl has been determined by means of DTA.It was found that there are two surfaces corresponding to the primary crystallization of NdCl_3 and α-(MgCl_2,LiCl)respectively,and a univariant line related to the secondary crystallization with a minimum M(68.5 wt-% NdCl_3,2.7 wt-% MgCl_2,28.8 wt-% LiCl_2 441℃)in the system.

LIQUIDUS OF SYSTEM Ag-Cu-Ge

The diagram of Ag-Cu-Ge system was constructed from the investigation of 13 internal sec- tions by DTA heating as well as cooling curves in an atomsphere of dry N_2 . The phase dia- gram is subdivided into two pseudo-ternary systems shown as Ag-Cu-Cu_3Ge and Ag-Cu_3Ge-Ge. Both systems belong to simple eutectic type. The ternary eutectic points lie in.' E_1, Ag(22.0)-Cu(58.8)-Ge(19.2), 632℃ and E_2 , Ag(44.3)-Cu(29.5)-Ge(26.2), 533℃. The three side binary systems were redetermined.

LIQUIDUS OF Ag-Cu-Bi SYSTEM

The diagram of Ag-Cu-Bi system was constructed from the investigation of 12 internal sec- tions by DTA heating as well as cooling curves in an atmosphere of dry N_2.The composi- tion of ternary eutectic point melting at 258℃ lies in Ag(5.0)-Cu(0.5)-Bi(94.5) at.-%.The liquiduses of Ag-Cu,Ag-Bi and Cu-Bi binaries were reinvestigated.

Determination of the liquidus and solidus temperatures of FeCrAl stainless steel

The liquidus and solidus temperatures of FeCrAl stainless steel were determined by differential scanning calorimetry（DSC） at different heating rates. They were also calculated by Thermo-calc software and empirical formulae separately. The accuracy of calculation results was assessed by comparison with the corresponding DSC results. The liquidus temperatures calculated by empirical formulae, which exhibited a maximum deviation of 8.6℃ were more accurate than those calculated using Thermo-calc, which exhibited a maximum deviation of 12.11℃. On the basis of Thermo-calc calculations performed under the Scheil model, the solidus temperature could be well determined from solid fraction（fS） vs. temperature（t） curves at fS = 0.99. Furthermore, a theoretical analysis to determine the solidus temperature with this method was also provided.

Liquidus and phase equilibria in CaO-SiO2-5%MgO-20%Al2O3-TiO2 system

The single hot thermocouple technique(SHTT) and high temperature equilibrium technique were combined to investigate the phase diagram of the CaO-SiO_2-5%MgO-20%Al_2O_3-TiO_2 system.The 1300 ℃ to 1500 ℃ liquidus lines are calculated according to the thermodynamic equations based on the pseudo-melting temperatures measured by the single hot thermocouple technique.The phase equilibria relationships are experimentally determined at 1400 ℃ using the high temperature equilibria technique followed by X-ray fluorescence(XRF),X-ray diffraction(XRD),scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDX) analysis.The liquid phase(L),melilite solid solution phase((C_2MS_2,C_2AS)_(ss)),diopside phase(CMS_2) and perovskite phase(CaOTiO_2) are found.Coupled with the liquidus lines and equilibria results,the phase diagram is constructed for the specified region of the CaO-SiO_2-5%MgO-20%Al_2O_3-TiO_2 system.

液相线铸造Al-18Si合金的凝固组织与力学性能研究

采用光学显微镜、Image-Pro Plus软件、X射线衍射仪和万能拉伸试验机等研究液相线铸造Al-18Si合金的凝固组织与力学性能。结果表明,随着液相线温度下保温时间的增加,Al-18Si过共晶铝硅合金中初生硅的尺寸呈现先减小后增大的趋势,力学性能则呈现先增大后减小的趋势。与普通铸造相比,液相线铸造可使Al-18Si合金中初生硅平均尺寸减小30.6%,使该合金抗拉强度和伸长率分别提高27%和108%。因此,液相线铸造是改善过共晶铝硅合金凝固组织和力学性能的有效方法。

关于素Near-环的微商

本文将魏宗宣关于原环求导的一个定理推广到素Near-环上．主要结果是：设N是一个2-扭自由的素Near-环，d是N的一个非平凡微商．Z为N的中心，I是N的非零理想，如果d（I）Z，则N是可换环．

环及Near-环中的微商

本文首先考虑了near-环中的一个交换性定理,然后利用Leibniz公式讨论了根在微商下的不变性及幂零、诣零微商,最后作为特例,给出在结合环中有关的几个新结果。

弱对称near-环的J-型根环类

本文讨论弱对称near-环,它是以零对称near-环作为特殊情形的一类near-环,对于弱对称near-环,证明了J_ν={N|N～N′≠{0}■J_ν(N′)≠{0}},ν∈{2,*,3}是Amitsur-Kurosh意义下的Jacobson-型根环类(简称“J-型根环类”),从而突破了J-型根环类局限于零对称near-环的范围。另外,对于一般near-环,证明了J.真介于J_5/2与J_3之间。

COUNTING ROOTED NEAR-4-REGULAR EULERIAN MAPSON SOME SURFACES

In this article the rooted planar near-4-regular Eulerian trails are enum erated and an explicit form ula for such m aps is presented. Further, the rooted near-4-regular Eulerian m aps on the torus are counted in an exact w ay.