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.     

7050铝合金铸锭裂纹形成及控制分析

从合金特性、铸造工艺、铸态组织等方面出发,分析了各种因素对7050铝合金铸锭铸造过程中裂纹产生的影响,对铸坯裂纹的形成条件、机理进行了综述和总结,并提出了防止铸锭产生裂纹的控制措施.     

AA5052板材准静态/动态平面应变成形极限试验研究

为建立磁脉冲辅助冲压成形(EMAS)工艺的有效性,采用准静态平面应变预拉伸和动态磁脉冲成形相结合的方法对5052-O铝合金板材的准静态/动态平面应变状态复合成形极限进行了试验研究.结果表明:准静态/动态复合加载过程能显著改善该铝合金板材的室温成形性;准静态/动态平面应变复合成形极限比准静态平面应变成形极限有显著提高,相似或者略高于完全磁脉冲平面应变成形性,且随着准静态预应变水平的增加,准静态/动态复合变形成形极限变化不大.预变形的存在不会削弱复合成形过程的极限变形能力.     

双金属复合管固-液铸轧复合工艺环形布流器设计及其流场模拟

为解决双金属复合管固-液铸轧复合（SLCRB）工艺覆层熔体金属的环形均匀稳定布流问题,提出并设计了一种带有三级环形阶梯分流和锥形缓冲的环形布流器,并且基于商用软件Fluent建立了稳态布流过程的流体动力学模型,分析了布流器结构和铸轧速度对系统流场的影响,给出了获得均匀、稳定出口流场的布流器内部结构和布流条件,并用水模实验进行验证。结果表明:布流器内通道高宽比不小于1有利于均匀分流,并且锥形缓冲区的均流缓冲作用至关重要。以1.2 m/min的铸轧速度成功制备了外径为38 mm、内径为26 mm的铅-铝双金属复合管,覆层金属厚度均匀、界面结合效果良好。      

液固铸造4343/3003/4343铝合金复合锭的界面组织EI北大核心CSCD

采用液固铸造法制备4343/3003/4343铝合金复合锭,研究了复合锭的界面组织、元素分布和界面结合强度,分析了复合锭的界面结合机理。结果表明：在725-750℃浇注4343铝合金,复合锭的界面冶金结合良好,复合界面清晰平直。复合界面由Al-Si固溶体层和Si,Mn元素扩散层构成,Al-Si固溶体层厚薄均匀,Mn,Si元素的扩散距离分别为10μm和32μm,复合界面的结合强度高于3003铝合金的抗拉强度。液固铸造4343/3003/4343铝合金复合锭的界面复合机理为：4343铝合金熔体首先在3003铝合金锭表面急冷形成Al-Si固溶体,Al-Si固溶体中的Si和3003铝合金中的Mn相互扩散,形成牢固冶金结合的复合锭。     

直接冷却半连续铸造铝合金圆锭温度场的数值模拟

通过试验方法测定直接冷却半连续铸造铝合金圆锭凝固过程的温度变化曲线,利用逆向法计算出铸锭表面热流和换热系数;然后采用数值方法模拟直接冷却半连续铸造过程温度场,实测结果和模拟数据基本吻合。     

n-SiCp/1350复合材料低频电磁铸锭挤压材组织与性能的研究

利用低频电磁铸造(LFEC)-热反挤压方法制备了n-SiCp/1350复合材料挤压材。通过金相组织观察(OM)、扫描电镜(SEM)、室温拉伸性能以及硬度、导电率等测试手段,研究了该复合材料热反挤压前后的显微组织、拉伸性能以及硬度、导电率的变化情况。结果表明:低频电磁铸造(LFEC)铸锭表面质量显著优于传统直冷半连续铸造(DC)铸锭表面;LFEC制备n-SiCp/1350复合材料铸锭组织中n-SiCp较DC铸锭组织显著均匀弥散,n-SiCp在凝固过程中发生团聚,尺寸为1.0~3.5μm;LFEC制备复合材料铸锭晶粒较DC制备铸锭晶粒细小;拉伸试验结果表明,热挤压变形后LFEC制备复合材料的抗拉强度140.5MPa、延伸率24.7%均优于DC铸锭挤压材的抗拉强度132.5MPa、延伸率20%;热挤压后,LFEC制备复合材料的硬度32HV略高于DC铸锭挤压材硬度30HV,导电率54.3%IACS略低于后者的54.6%IACS。     

铸锻联合成形工艺晶粒分布预测协同仿真技术

开发了一种铸锻联合成形工艺的协同仿真技术.采用ProCAST软件的CAFE模块进行铸造模拟,获得初始不均匀的铸态晶粒尺寸.编译了一组Fortran程序作为Deform-3D软件的功能模块,用以建立初始不均匀铸态晶粒尺寸的分布与Deform-3D锻造模型之间的耦合.通过对Deform-3D的二次开发,实现了锻造过程中微观组织演变的数值模拟.最终实现了对动态再结晶晶粒尺寸和动态再结晶体积分数的预测.采用开发的协同仿真技术对截齿齿体的铸锻联合成形工艺进行了数值模拟分析.模型分别采用了初始均匀的晶粒尺寸和由铸造模拟获得的初始不均匀的晶粒尺寸,获得了两种模型的动态再结晶晶粒尺寸和动态再结晶体积分数的分布.通过对比分析,证明了铸锻联合成形工艺晶粒分布预测协同仿真技术的可行性.     

铸锻联合成形工艺晶粒分布预测协同仿真技术

开发了一种铸锻联合成形工艺的协同仿真技术。采用ProCAST软件的CAFE模块进行铸造模拟,获得初始不均匀的铸态晶粒尺寸。编译了一组Fortran程序作为Deform-3D软件的功能模块,用以建立初始不均匀铸态晶粒尺寸的分布与Deform-3D锻造模型之间的耦合。通过对Deform-3D的二次开发,实现了锻造过程中微观组织演变的数值模拟。最终实现了对动态再结晶晶粒尺寸和动态再结晶体积分数的预测。采用开发的协同仿真技术对截齿齿体的铸锻联合成形工艺进行了数值模拟分析。模型分别采用了初始均匀的晶粒尺寸和由铸造模拟获得的初始不均匀的晶粒尺寸,获得了两种模型的动态再结晶晶粒尺寸和动态再结晶体积分数的分布。通过对比分析,证明了铸锻联合成形工艺晶粒分布预测协同仿真技术的可行性。     

7050铝合金高温变形过程中的微观组织特征

研究了7050铝合金在温度为460℃,应变速率分别为1.0×10-4s-1和 0.1s-1条件下的高温拉伸变形过程.结果表明:7050铝合金在高温拉伸过程中平均晶界取向差角与真应变之间保持比例关系,晶粒尺寸随变形的进行而增加.晶粒的长径比在变形条件为460℃/1.0×10-4s-1变形时基本保持不变;而变形条件为460℃/0.1s-1时,晶粒长径比则随着变形的进行而增加.微观组织结果表明,7050铝合金在460℃/1.0×10-4s-1的变形过程中,软化机制为连续动态再结晶,而变形条件为460℃/0.1s-1时,软化机制为动态回复.连续动态再结晶过程中平均晶界取向差角的持续增加与亚晶界的迁移和变形过程中晶界吸入位错有关.     

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.     

Analysis of zonal shrinkage in alloy steels

Abstract

Thermal behaviour of the solidifying steel structure is important for understanding of the defects during ingot solidification. During solidification and cooling, most metals shrink. As a consequence in upper part of solid ingot, pores and pipes of typical shapes and size are formed. Forming of pipes is closely related to the casting and solidification processing parameters. In the present paper the influence of liquid temperature, chemical composition and temperature gradient on the shrinkage intensity are investigated. The ratio of the pipe depth to total ingot height as a criterion of the pipe size is used. The values of the temperature gradients on the base of the numerical model solidification are obtained. The experimental measurements of temperature change have been carried out on laboratory steel ingot. The results by numerical model are compared with the experimental ones and showed a good agreement.     

电磁场对7050铝合金凝固组织和元素分布影响

为了研究中频电磁场对7050铝合金凝固组织和元素分布的影响,在未施加电磁场,施加1000Hz、6000A电磁场和1000Hz、4000A电磁场下进行7050铝合金凝固试验.利用金相显微镜和电子背散射衍射分析技术分析了锭坯微观组织,利用化学分析方法测定溶质元素沿锭坯边部到中心的分布情况.结果表明:外加中频电磁场有效地细化晶粒,影响溶质元素分布.未施加电磁场下,锭坯晶粒最大,发生反偏析;1000Hz、4000A电磁场下,锭坯晶粒次之,发生反偏析;1000Hz、6000A电磁场下,锭坯晶粒最细,发生正偏析.     

In-situ observation of solid-liquid interface transition during directional solidification of Al-Zn alloy via X-ray imaging

The morphological instability of solid/liquid(S/L) interface during solidification will result in different patterns of microstructure. In this study, two dimension(2 D) and three dimension(3 D) in-situ observation of solid/liquid interfacial morphology transition in Al-Zn alloy during directional solidification were performed via X-ray imaging. Under a condition of increasing temperature gradient(G), the interface transition from dendritic pattern to cellular pattern, and then to planar growth with perturbation was captured. The effect of solidification parameter(the ratio of temperature gradient and growth velocity(v), G/v) on morphological instabilities was investigated and the experimental results were compared to classical "constitutional supercooling" theory. The results indicate that 2 D and 3 D evolution process of S/L interface morphology under the same thermal condition are different. It seems that the S/L interface in 2 D observation is easier to achieve planar growth than that in 3 D, implying higher S/L interface stability in 2 D thin plate samples. This can be explained as the restricted liquid flow under 2 D solidification which is beneficial to S/L interface stability. The in-situ observation in present study can provide coherent dataset for microstructural formation investigation and related model validation during solidification.     

Composition segregation in semi-solid metal cast AA7075 aluminium alloy

The composition distribution and microstructural evolution associated with the characteristic globular grain structure in semi-solid metal cast AA7075 aluminium alloy has been investigated. The primary globular grains possess uniform composition over nearly 90% of their diameter with fluctuations only occurring in the near surface of the individual grains. The inter-globular regions are solute rich and contain non-equilibrium eutectic. The segregation pattern in semi-solid cast structures occurs over a much greater length-scale than the dendritic pattern prevalent in conventional castings and it is proposed that the distinction arises from predominant planar growth of the α-primary globular grains during the SSM conditioning stage. Examination of the in-grain structure using electron backscattered diffraction revealed a quasi-periodic fluctuation in misorientation that may have arisen from local perturbations on the planar solid interface as solidification progressed. Homogenisation prior to artificial ageing is severely compromised by the undesirable segregation pattern.     

Effect of combined application of electromagnetic fields on horizontal direct chill casting of 7050 aluminium alloy

Abstract

Influence of combined electromagnetic field application on horizontal direct chill casting of 7050 aluminium alloy is investigated. Temperature measurement and structure observation are carried out to analyse the casting process under different electromagnetic fields. Combined electromagnetic field can reduce the harmful gravitational thermal effect in the horizontal direct chill casting process and improve the ingot properties. With application of combined electromagnetic field, temperature distribution in the melt is more uniform, sump of the ingot becomes flat and symmetric, surface quality of ingot improves markedly, grain morphology changes from feathery grains to equiaxed grains and grain size decreases. Distribution of copper and zinc in the transverse section of the ingot becomes more uniform.     

基于数值模拟的大型复杂灰铁铸件工艺设计

为防止某大型复杂铸件产生缩孔缺陷并降低铸造成本,采用数值模拟方法对其铸造工艺参数进行定量化设计.应用Pro CAST软件对铸件进行凝固分析,通过提取凝固结果中的各参数(温度场、固相温度的密度、焓变化等)对模数进行求解,定量得到铸件的高模数分布区域,而后通过分析模数分布区域并结合均衡凝固理论设计了冒口、冷铁与浇注系统,运用Pro CAST软件对铸件的充型及凝固过程进行模拟.研究表明:该大型铸件应采用底注式浇注系统为宜,对铸件中部与底部模数达到2.5 cm的热节处采用冷铁和铬铁矿砂处理热节,对铸件顶部模数达到2.5 cm的部位采用飞边冒口进行补缩;提取凝固模拟结果中热节处的平均模数和金属液体积,即可对冒口尺寸进行定量化设计;通过观察模拟结果中浇口杯金属液水平高度的变化,可得出浇注系统进行液态补缩的时段.     

Influence of a non-rotating shoulder on heat generation,microstructure and mechanical properties of dissimilar AA2024/AA7050 FSW joints

Friction stir welding (FSW) and stationary shoulder friction stir welding (SSFSW) were carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with thicknesses of 2 mm. A comparison between the two processes was performed by varying the welding speed while keeping the rotational speed constant. Through the analysis of the force and torque produced during welding and a simple analytical model, it was possible to show that in SSFSW there is more effective coupling with the tool and the heat produced is more efficiently distributed. This process decreases both the welding area and the diffusion at the interface of the two alloys compared with FSW. The minimum microhardness occurred at the advancing side (AS) at the interface between the thermo-mechanically affected zone (TMAZ) and the stir zone (SZ) in both processes, although the decrease was more gradual in SSFSW. This interface is also where all specimens failed for both welding technologies. An increase in tensile strength was measured in SSFSW compared with standard FSW. Furthermore, it was possible to establish the mechanical performance of the material in the fracture zone using digital image correlation.     

Effect of magnesium content on thermal and structural parameters of Al–Mg alloys directionally solidified

In this study, the influence of magnesium content on thermal and structural parameters during the unsteady-state unidirectional solidification of Al–Mg alloys is analyzed. Using a special device, Al–Mg alloys containing 5, 10, and 15 wt% Mg were submitted to unidirectional solidification. Using a data acquisition system, the temperature variations along the casting during solidification were measured. From these results, the variations of solidification parameters as growth rate of dendrite tips, thermal gradient, cooling rate, and local solidification time were determined. The variation of global heat transfer coefficient at metal/mould interface was estimated through the adjustment of experimental temperature variation close to the interface and numerical predictions. Primary and secondary dendrite arms spacing variations during solidification were measured by optical microscopy. From these results, comparative analysis were developed to determine the influence of magnesium content.