消失模铸造制备镁合金表面复合材料的研究

以AZ91D合金为基体,金属铝粉作为主要的合金化元素,自制了性能优良的合金化涂料,利用消失模铸造工艺制备了表面复合材料.在温度780℃、负压度-0.02MPa条件下进行浇注,研究发现在镁合金基体表面有大量的新相生成,利用扫面电镜和电子能谱对组织进行分析,当合金化涂料厚度从0.3mm增加到0.5mm时,复合层的厚度也随之增加,可达到300微米,并且组织均匀、致密.硬度测试和模拟海水腐蚀试验表明,表面复合层最高硬度可以达到基体的3倍左右;并且腐蚀速率与铸态的AZ91D相比降低了5倍左右.     

离心铸造WCp/Fe-C复合材料及其应用研究

通过扫描电镜、电子能谱分析,研究了离心铸造复合材料辊环的机械性能,微观组织及其应用.结果表明在离心铸造条件下制备的WCp/Fe-C复合材料辊环,其复合材料工作层的硬度达到HRA80～85,接近了粉末冶金辊环的硬度(HRA81～88),复合材料工作层和芯部贝氏体基体的冲击韧性ak值分别达到5.4和14.8J/cm2.高于粉末冶金辊环的韧性(1.6～3.0J/cm2).辊环复合材料工作层中增强颗粒的体积分数和复合材料工作层厚度均受离心转速和浇注温度影响.在离心转速＞1200r/min、浇注温度＞1500℃时,可制备复合材料工作层厚度18～24mm、WCp体积分数80%、界面结合良好没有微观和宏观裂纹缺陷的复合材料辊环.     

Mechanical behavior of cast and forged magnesium alloys and their microstructures

Effects of manufacturing processes on microstructure and mechanical properties of magnesium alloys AM60 and AZ31B were investigated. The magnesium alloy AM60 was produced by high-pressure die cast (HPDC) with two different casting processors but AZ31B was produced by forging. Casting defects were investigated with SEM observations for the specimens obtained from the two casting processors. The fatigue tests were conducted by load control according to ASTM E466 standard procedure with zero to max loading. The failed surfaces of the specimens were also observed by using SEM. The microstructural analyses were conducted for the specimens obtained from the casting and forging processors. Micro-hardness values in the cross-section of a forged specimen were relatively consistent compared to those of cast specimens. From this study, it was clearly observed that the production methods affect to the microstructures and mechanical behavior of the magnesium alloys.     

Rotating cylinder manufacturing method and investment casting of SiCp/AZ91HP magnesium composites

Abstract

This paper describes the rotating cylinder method for manufacturing, and investment casting for forming, composite slurry. Microstructural features, such as SiC particle distribution and grain refinement of the as cast composites, were investigated. Also the effect of SiC particle fraction and size, and process parameters on the microstructure and the mechanical properties are discussed. Attempts were made to evaluate the thermal stability of oxides against molten AZ91HP magnesium alloy. The oxides examined included CaO, CaZrO₃, and silica bonded Al₂O₃ and zircon flour. Finally, the tensile properties, hardness, and wear resistance of the as cast composites were evaluated and the results are compared with those of the as cast alloy.     

碳纤维增强树脂基复合材料与铝/镁合金连接研究进展EI北大核心CSCD

运载工具的轻量化是解决当前能源危机和环境问题的重要手段之一,得到国内外学者的高度重视。碳纤维增强树脂基(carbon fiber-reinforced polymer,CFRP)复合材料和以铝镁为代表的轻合金具有一系列优异的力学性能与加工特性,是极具应用前景的轻量化材料,实现这两种材料之间的有效连接,成为当下研究的热点。然而由于异种材料之间理化性能差异较大,在生产过程中混合应用多种轻量化材料仍面临巨大挑战。本文通过对胶接、机械紧固、搅拌摩擦及其变种工艺连接技术的研究进展、优缺点、发展趋势进行汇总分析,考察不同连接方式下获得接头的微观形貌,总结了CFRP与铝镁轻合金搅拌摩擦连接的三种机理包括宏观锚定、微观机械嵌合与化学键连接。最后,基于以上三种连接机理,指出进一步提升混合接头性能的关键在于增大金属母材表面粗糙度,增加熔融高分子面积和采用混合连接工艺。     

The interfacial characteristic of SiCp/AZ91 magnesium matrix composites fabricated by stir casting

The particle/matrix interfaces in SiCp/AZ91 composite fabricated by stir casting were investigated using transmission electron microscope (TEM) equipped with ultra-thin window energy dispersive X-ray analysis (EDAX) system. Chemical reactions indeed occurred at the interfaces. According to EDAX results, the interfacial reaction products are considered to contain Al₄C₃, MgO, and Mg₂Si phases. The interfaces can be classified into three types (interfaces I, II, and III) according to morphological features of the interfaces: (1) for interface I, interfacial reaction products were in direct contact with the surface of SiCp; (2) for interface II, interfacial reaction products were not in direct contact with the surface of SiCp; (3) for interface III, interfacial reaction products were not observed at the interfaces, i.e., interface III was simply formed by the two surfaces of SiCp and matrix. Mg₁₇Al₁₂ and Al₈Mn₅ precipitate phases heterogeneously nucleated at the particle/matrix interfaces.     

Bone-like matrix formation on magnesium and magnesium alloys

Mg metal and its alloys have promise as a biocompatible, degradable biomaterials. This work evaluates the potential of in vitro cell culture work with osteoblast-like cells on Mg based materials, and investigates cell differentiation and growth on Mg alloyed with various non-toxic or low-toxicity elements. Mg based substrates support the adhesion, differentiation and growth of stromal cells towards an osteoblast-like phenotype with the subsequent production of a bone like matrix under in vitro conditions. No significant difference in the final tissue layer is observed on pure Mg, an AZ21 alloy or a 0.5 wt% Ca alloy. Only a 0.8 wt% Ca alloy which shows complete structural disintegration shows minimal cell growth. Due to association of non-soluble degradation products formed when Mg is incubated in physiological-like fluid, mass changes typically used to report Mg degradation are not viable estimates of degradation. Methods quantifying the time dependent change in the mechanical integrity of samples as a function of incubation time are required for a proper assessment of Mg degradation. We conclude that in vitro cell culture of bone cells on Mg substrates is expected to be a viable screening technique to assess the relative biological activity of Mg-based materials.     

镁系准晶与高性能镁合金

综述了Mg-Al-X(X=Cu,Zn,Pd,Ag,Pt)、Mg-Zn-(Ga,Al)、Mg-Zn-RE(RE=Y,以及Gd到Er的稀土元素)等系列的镁系准晶的结构、形成机理、准晶形成的成分范围,以及准晶的力学性能.介绍了近年来利用镁系准晶的优异性能,采用各种制备工艺,开发含准晶的高性能镁基材料的研究进展.     

Artificial ageing of Al-Si-Cu-Mg casting alloys

The T6 heat treatment is commonly used for gravity cast Al-Si-Cu-Mg alloys. The influence of the alloying elements Cu and Mg and the artificial ageing temperature on the age hardening response were investigated. Artificial ageing was conducted at 170 °C and 210 °C for various times for three alloys, Al-7Si-0.3Mg, Al-8Si-3Cu and Al-8Si-3Cu-0.5Mg, cast with three different solidification rates (secondary dendrite arm spacing of about 10, 25 and 50 μm). The coarseness of the microstructure has a small influence on the yield strength, as long as the solution treatment is adjusted to obtain complete dissolution and homogenisation. The peak yield strength of the Al-Si-Mg alloy is not as sensitive to the ageing temperature as the Al-Si-Cu and Al-Si-Cu-Mg alloys are. The ageing response of the Al-Si-Cu alloy is low and very slow. When 0.5 wt% Mg is added the ageing response increases drastically and a peak yield strength of 380 MPa is obtained after 20 h of ageing at 170 °C for the finest microstructure, but the elongation to fracture is decreased to 3%. The elongation to fracture decreases with ageing time in the underaged condition as the yield strength increases for all three alloys. A recovery in elongation to fracture of the Al-Si-Cu-Mg alloy on overageing is obtained for the finest microstructure, while the elongation remains low for the coarser microstructures. The quality index, Q = YS + K?, can be used to compare the quality of different Al-Si-Mg alloys. This is not true for Al-Si-Cu-Mg alloys, as K depends on the alloy composition. Overageing of the Al-Si-Mg alloy results in a decrease in quality compared to the underaged condition.     

Solidification and precipitation behaviour of Al-Si-Mg casting alloys

The effect of Mg content on the solidification and precipitation behaviour of both unmodified and Sr-modified Al-7Si-Mg casting alloys has been investigated at various solidification rates using cooling curve analysis, differential scanning calorimetry (DSC) and optical and electron microscopy. The Mg concentrations covered the range from 0.3 wt% to 0.7 wt%. The results indicate that increasing Mg content or cooling rate lowers the liquidus and binary Al-Si eutectic transformation temperatures. The latent heat of fusion of these alloys is strongly dependent on the level of Si present, but there is no observed dependence on Mg content. The solidification reactions observed under DSC are identified and it is noticed that the ternary eutectic solidification reaction L Al + Si + Mg₂Si is only observed at Mg levels of 0.6% and higher. The minor phases formed on solidification are identified and their response to solution heat treatment is examined. Increasing Mg content usually enhances precipitate hardening. However when Mg levels are increased above 0.5wt%, no apparent increase of yield strength with Mg is observed. This is correlated with dissolved Mg levels and energy released during reprecipitation.     

Structural durability of magnesium alloys and components

The fatigue behaviour of the magnesium die cast alloys AZ91, AE42 and AM50 was investigated at constant amplitude and in variable amplitude tests. The ambient conditions of these tests varied between laboratory air at room temperature, at 125 °C and a permanent influence of NaCl‐solution at room temperature. More than 40 test series were analysed in a generalized way to determine standardized slopes of S‐N curves and mean stress sensitivity. The behaviour of the three alloys was investigated also in strain‐controlled cyclic tests at normal and elevated temperature. Based on this substantial data set several variants of methods following both the nominal‐stress concept and the local‐strain approach were applied to determine guidelines to improve the reliability of lifetime estimation of components made of magnesium. The corrosion fatigue behaviour of these magnesium alloys was extensively investigated under rotating bending to clarify the damaging influence of the corrosive load component. Under simultaneous action of corrosion and cyclic mechanical loading several influencing factors have to be considered which attain special importance during the testing of magnesium alloys.     

The mould-filling capacity of two casting alloys

The mould-filling capacities of an Au-Ag-Cu alloy and a Ni-Cr-Be alloy for dental use have been studied by measuring the lengths of cast helices of a constant cross-section as a function of the supertemperature of the melt. A vacuum-pressure casting machine was applied in the experiments. Assuming that the conduction of heat through the investment is rate-controlling for the heat flow, the heat of fusion was calculated for the two alloys. These values were found to be close to those obtained by differential thermal analysis measurements. The lengths of the helices are strongly influenced by the deliberated heat of fusion during solidification. The substantially higher mould-filling capacity of the Ni-Cr-Be alloy compared with that of the Au-Ag-Cu alloy can be explained to a large extent by the corresponding difference in their latent heat of fusion. A calculation of the lengths of the helices requires a knowledge of the speeds of the melts. So far there are only indications of a higher speed for the Ni-Cr-Be alloy than for the Au-Ag-Cu alloy with the casting machine employed. The highest slope for the length of helix against supertemperature curve was observed for the Au-Ag-Cu alloy, indicating a smaller heat transfer coefficient for this alloy than for the Ni-Cr-Be alloy.     

Macrosegregation in direct-chill casting of aluminium alloys

Semi-continuous direct-chill (DC) casting holds a prominent position in commercial aluminium alloy processing, especially in production of large sized ingots. Macrosegregation, which is the non-uniform chemical composition over the length scale of a casting, is one of the major defects that occur during this process. The fact that macrosegregation is essentially unaffected by subsequent heat treatment (hence constitutes an irreversible defect) leaves us with little choice but to control it during the casting stage. Despite over a century of research in the phenomenon of macrosegregation in castings and good understanding of underlying mechanisms, the contributions of these mechanisms in the overall macrosegregation picture; and interplay between these mechanisms and the structure formation during solidification are still unclear. This review attempts to fill this gap based on the published data and own results. The following features make this review unique: results of computer simulations are used in order to separate the effects of different macrosegregation mechanisms. The issue of grain refining is specifically discussed in relation to macrosegregation. This report is structured as follows. Macrosegregation as a phenomenon is defined in the Introduction. In “Direct-chill casting – process parameters, solidification and structure patterns” section, direct-chill casting, the role of process parameters and the evolution of structural features in the as-cast billets are described. In “Macrosegregation in direct-chill casting of aluminium alloys” section, macrosegregation mechanisms are elucidated in a historical perspective and the correlation with DC casting process parameters and structural features are made. The issue of how to control macrosegregation in direct-chill casting is also dealt with in the same section. In “Role of grain refining” section, the effect of grain refining on macrosegregation is introduced, the current understanding is described and the contentious issues are outlined. The review is finished with conclusion remarks and outline for the future research.     

High pressure die casting of non-ferrous alloys

Abstract

High pressure die casting is a ‘traditional’ process which, over the last 15 years, has completely modernised its technology. In this paper, it is described how basic research has led to fundamental changes in die design techniques which, coupled with improved process control and alloy development, have extended the scope of the process and improved the quality of the castings produced.

MST/768     

Directional pressure quench casting of aluminium alloys

Abstract

A novel method of casting is described in which liquid metal in permeable moulds is subjected to high ambient pressure and quenching simultaneously. A small pressure quenching chamber was used and shapes of two different geometries cast into sand moulds. Two non-heat treatable alloys, LM6M and LM21M, comprised the raw material. The results show that increasing ambient pressure alone up to a value of 2 MPa (20 bar) can reduce porosity of castings, has a limited effect on tensile strength, and little effect on dendrite arm spacing. Casting under pressure with quenching increased tensile strength by up to 30% compared with conventional castings and virtually eliminated porosity. The dendrite arm spacing is also considerably reduced. Pressure quench casting is a potentially inexpensive means of improving the mechanical and microstructural properties and integrity of a wide range of aluminium alloys made by existing sand casting methods. For heat treatable alloys it offers the possibility of solution treating in the mould, thus eliminating one operation in a production process.

MST/3099     

Effect of silicon on damping capacities of pure magnesium and magnesium alloys

A new idea of using a stiffer metallic compound Mg₂Si to enhance the damping capacities of pure magnesium and its alloys is successfully attempted. The present paper focuses on the relation between damping capacities and the addition amount of Si. The results show that damping capacities increase with increasing amount of Si. Particular emphasis is placed on the increasing dislocation density around matrix-particulate interface and the refinement of grain size promoted by big growth restriction factor of Si.     

铸造钛合金及其熔炼技术的发展现状

钛合金具有密度低、高温性能好、耐腐蚀性能好等优点,逐渐成为一种优异的航空航天结构材料.综述了钛合金的成形特点和发展现状,以及钛合金熔炼技术的发展现状.