Study on casting composite ingot of 4045/3004/4045 aluminum alloys

Two kinds of equipments were designed for casting composite ingots, and three‐layer ingots of 4045/3004/4045 aluminum alloys were prepared by direct‐chill (DC) semi‐continuous casting process, macro‐morphology, microstructure, temperature distribution near the interface, elements distributions and tensile strength of the interface were investigated. The equipment suitable for casting composite ingots was determined, and results show that solid supporting layer with uniform temperature distribution forms near the interface, which ensures the stable casting process. The two different aluminum alloys are well bonded. The criterion for temperature control of solid supporting layer is founded based on the relationship between the interface bonding strength and the temperature of solid supporting layer when contacted by 4045 alloy melt.     

Third order elastic constants of hexagonal boron nitride

Third order elastic constants of hexagonal Boron Nitride have been evaluated using the Lannard-Jones potential. The results obtained are presented and compared with the only available measurement ofC ₃₃₃ for this material.     

电磁铸造5182铝合金锭的组织与性能研究

采用电磁铸造技术铸造了易拉罐用5182变形铝合金，采用光学显微镜和扫描电镜分析了其显微组织，而且对其进行了均匀化处理和对比实验。结果表明，电磁铸造锭有更加良好的内部组织和优良的力学性能，电磁铸造试样的硬度大约是普通连续铸造试样的两倍，疲劳性能是普通连续铸造铸锭的3倍，电磁铸造铸锭还有良好的耐磨性，电磁铸造锭的优良性能得宜于电磁搅拌的作用使整个铸锭获得均匀细小的晶粒组织，电磁铸造技术是一种无模铸造技术，它依靠电磁力约束液体金属成型，液体金属不与铸模接触，铸锭表面光滑如镜；相反，普通连续铸造锭表面因存在振动痕和亚表面偏析等铸造缺陷，力学性能大大降低。     

Characterization of intermetallics in aluminum alloy 3004

The evolution of intermetallics in aluminum alloy 3004 from the casting to the thin-sheet stages is examined. Two casting types have been utilized: 650-mm-thick D.C. ingot and 12-mm-thick stationary-mold-cast strip. Size, shape, density, and area fraction of intermetallics are characterized in their matrix environment using the standard optical, scanning electron microscopy and scanning transmission electron microscopy metallographic techniques. The results are discussed in terms of a) the effect of processing parameters on the intermetallic structure and b) the impact of primary and secondary intermetallics on the microstructure development (grain size and texture) and the performance (anisotropy, bendability, metal finish, and metal transfer during forming). The strip-sourced alloy is characterized by a smaller primary intermetallic size but it affords a greater flexibility in developing a variety of primary and secondary intermetallic area fractions and size distributions. Hence it can be tailored more readily to a specific set of performance criteria.     

Simulation analysis of thermal stress during casting process of large-sized alloy steel ingot

To quantitatively analyze the main reasons of common crack in the surface of alloy steel ingot with 5% Cr during production and to propose the direction of improvement, a physical model system, which consisted of steel ingot mold, casting, riser of heat insulation, slag layer, sprue pipe, and runner, was primarily established by three-dimensional CAD software. The joint simulation method concerned with pouring, solidification, temperature field, and cast stress was determined by using ADSTEFAN cast simulation software. The stress distribution of casting and the quantitative effect of shake-out timing were analyzed in detail. An effective plan of decreasing stress was proposed in cooling mode.     

4045/3004/4045层状铝合金复合材料连铸制备方法

本文旨在开发出制备复合锭坯的新技术,在新型热顶石墨环结晶器中安装冷却板,采用直接水冷半连续铸造法实现了4045/3004/4045铝合金三层复合锭的实验室制备,研究了复合锭坯的宏观形貌、微观组织,并考察了界面两侧元素分布以及铸造过程中界面附近3004合金熔体的温度分布.结果表明:在冷却板的作用下界面附近形成了一层温度分布较为均匀的固态支撑层,从而保证复合铸造过程的顺利实现,复合界面结合较好,且为一种冶金结合;由界面抗拉强度测试结果可知界面的结合强度均高于96 MPa,进一步证明了两种合金的结合是一种冶金结合.     

Study on dynamic strain aging phenomenon of 3004 aluminum alloy

3004 Aluminum alloy has been subjected to tension test at a range of strain rates (5.56 × 10⁻⁵ to 5.56 × 10⁻³ s⁻¹) and temperatures (233–573 K) to investigate the effect of temperature and strain rate on its mechanical properties. The serrated flow phenomenon is associated with dynamic strain aging (DSA) and yield a negative strain rate dependence of the flow stress. In the serrated yielding temperature region a critical transition temperature, T_t, was found. The critical plastic strain for the onset of serrations has a negative or positive temperature coefficient within the temperature region lower or higher than T_t. According to the activation energy, it is believed that the process at the temperature region lower than T_t is controlled by the interaction between Mg solute atom atmosphere and the moving dislocation. In the positive coefficient region, however, the aggregation of Mg atoms and precipitation of second phase decrease the effective amount of Mg atoms in solid solution and lead to the appearance of a positive temperature coefficient of the critical plastic strain for the onset of serrations.     

Structure and property evolution during drawing and wall ironing of aluminum alloy 3004

The evolution of mechanical properties and dislocation substructure during the commercial-scale can making (deep drawing, wall ironing, and “baking”) operations of the aluminum alloy 3004 H19 has been investigated. At each stage the samples were obtained from the deep-drawn cup or wall-ironed can wall and subjected to tensile tests and transmission electron microscopy characterization. The strength decreased (and ductility increased) during deep drawing and increased during wall ironing. The “sizing” of can wall during drawing superimposes a strain hardening effect on these strength and ductility variations. The corresponding changes in dislocation density and cell or microband boundary configuration were observed at each stage. The strain localization and microstructural inhomogeneities were particularly prevalent in the upper parts of the cup and can wall. The cell size and bank thickness did not vary significantly during can making.     

ZL201合金液相线铸造与二次加热的合金组织

为了研究半固态金属的成型规律,采用电子显微镜及图像分析仪,研究了近液相线半连续铸造ZL201合金的微观组织及其在二次加热过程中的变化.研究表明,在液相线温度下半连续铸造的ZL201合金组织为均匀、细小的蔷薇状组织,晶粒的平均等积圆直径为43.6μm,晶粒平均圆度为1.88.经二次加热后,铸造组织逐渐转变为等轴晶.在620℃下加热20min后,晶粒平均等积圆直径为111μm,晶粒平均圆度1.42.在640℃下加热20min后,晶粒平均等积圆直径为108μm,晶粒平均圆度1.58.研究表明,近液相线半连续铸造可以获得理想的ZL201合金半固态坯料.     

3004铝合金晶格和织构演化的原位X射线衍射研究

为探究3004铝合金板材在拉伸变形过程中晶粒取向变化和晶格应变行为,明确两者在塑性变形过程中的竞争机制和作用,本文首次将原位拉伸方法用于铝合金织构演化和晶格应变行为的研究中,利用试验装置对3004铝合金进行定量应变拉伸,并在不同变形量下对样品进行X射线衍射物相和织构测试分析.实验结果表明:样品在弹性变形区晶格常数随应变...     

SiC_P/Al复合材料晶面衍射弹性常数的两相模型计算

通过分析外载荷作用下,SiCP/Al复合材料中Al基体相和SiC相的相互作用关系,运用自洽方法和Eshelby夹杂理论,建立了一套预测SiCP/Al复合材料"晶面衍射弹性常数"的两相模型。运用该模型计算SiC相和Al相若干晶面的"晶面衍射弹性常数",并与实验测量值进行比对。结果显示,SiC相的{101}及{116}晶面和Al相的{222}晶面的模型计算值均与实验值高度吻合,偏差小于6%。其他晶面的弹性常数值与实验值的偏差均在15%之内。说明该理论模型具有较好的预测性,可靠性较高。通过这一理论预测模型来计算复合材料的"晶面衍射弹性常数"既能避免实验测量的繁琐,减少人力和物力资源浪费,又能得到难以通过实验测量获得的"晶面衍射弹性模量"。     

Acoustic microscopy measurement of elastic constants and massdensity

A method is presented to determine the elastic constants and the mass density of isotropic and anisotropic solids and anisotropic thin films. The velocity and attenuation of leaky surface acoustic waves (SAWs) have been obtained for specified propagation directions from V(z) curves measured by line-focus acoustic microscopy (LFAM). The experimentally obtained velocities have been compared to velocities obtained from a measurement model for the V(z) curve which simulates the experiment. Since the measured and simulated V(z) curves have the same systemic errors, the material constants are free of such errors. For an isotropic solid, Young's modulus E, the shear modulus G and the mass density ρ have been determined from the leaky Rayleigh wave velocity and attenuation, measured by LFAM, and a longitudinal wave velocity measured by a pulse-echo transit-time technique. For a cubic-crystalline solid, the ratios of the elastic constants to the mass density (c₁₁ /ρ, c₁₂/ρ, c₄₄/ρ) have been determined from the directional variation of measured SAW velocities, using a preliminary estimate of ρ. The mass density ρ has subsequently been determined by additionally using the attenuation of leaky SAWs in crystal symmetry directions. For a cubic-crystalline thin film deposited on a substrate, the elastic constants and the mass density (c₁₁, c₁₂, c₄₄, ρ) of the film have been determined from the directional variation of the measured SAW velocities, and a comparison of the corresponding attenuation coefficient with the measured attenuation coefficient has been used to verify the results     

Improved properties of A319 aluminum casting alloy modified with Zr

The beneficial effects of 0.15 wt.% Zr addition on mechanical properties and wear resistance of A319 aluminum casting alloy were investigated. The cast alloys were given a solutionizing treatment followed by artificial aging in the temperature range 175 to 235 °C for different period of times. Mechanical properties and wear behavior of the Zr-containing material were determined and compared to those of the base A319 alloy in both as-cast and age-hardened conditions. It is shown that minor addition of Zr results in the precipitation of Al₃Zr particles in the aluminum matrix. These particles are stable upon heating due to the low solubility of zirconium in aluminum matrix. The main effects of such particles are an increase in hardness, strength, quality index and wear resistance. This is very promising where these aluminum cast alloys are to be used at relatively high temperatures.     

A new method of semi-continuous casting of AZ80 Mg alloy billets by a combination of electromagnetic and ultrasonic fields

The influence of low frequency electromagnetic field and power ultrasonic field on the microstructure of AZ80 Mg alloy billets was studied. The magnetic flux density and time average electromagnetic volume force density were obtained by numerical simulation. The acoustic pressure distribution was also numerically calculated in order to characterize the ultrasonic field propagation. After comparison of the different effects of grain refinement by low frequency electromagnetic casting (LFEC) and ultrasonic casting (UC), a new method (LFEC + UC) was developed by simultaneously applying ultrasonic vibration to the melt during low frequency electromagnetic semi-continuous casting of AZ80 Mg alloy billets. With the application of the compound field under the optimum conditions, the as-cast macrostructure and microstructure were refined and homogeneously distributed. An obvious improvement of mechanical properties was finally obtained. The mechanisms of grain refinement and interaction of low frequency electromagnetic field and power ultrasonic field with the melt were discussed.     

基于遗传算法的低压铸造铝合金车轮工艺优化

为解决低压铸造铝合金车轮质量控制难度大的问题,采用遗传算法对工艺参数进行优化.基于铸造数值模拟结果,利用BP人工神经网络建立了铸造工艺参数与质量控制目标缩松缺陷和凝固时间的非线性关系,采用遗传算法实现了铸造工艺参数的优化.以某型低压铸造A356铝合金车轮为例,对浇注温度、上模温度、下模温度、侧模温度、模芯温度5个参数进行优化,得到的最佳工艺组合,可有效控制缩松缺陷和凝固时间.利用数值模拟结果、建立神经网络模型,采用遗传算法优化的方法,获得近似最优解,有助于优化低压铸造工艺.     

A theory of acoustic measurement of the elastic constants of a general anisotropic solid

An acoustic wave approach is presented for the measurement of the twenty-one independent elastic constants of the most general linearly elastic anisotropic solid. The method requires that one be able to measure the density of the material, the velocities of the three modes of wave propagation in each of six directions, and the particle displacements associated with each of those modes.