钕对AZ61镁合金铸态显微组织和力学性能的影响

主要研究了Nd对AZ61合金铸态组织和力学性能的影响。研究结果表明Nd元素对AZ61镁合金有明显的细化作用,当加入1．0％Nd时,细化效果最为显著,而且有最佳的力学性能。经分析,Nd与合金中的镁铝元素形成热稳定性较高的金属间化合物,在α-Mg晶粒内和晶界均有分布。     

铸态AZ61镁合金热压缩变形组织变化

利用Gleeble-1500对铸态AZ61镁合金在变形温度200~500℃,应变速率0.001~1s-1的条件下进行压缩变形;利用显微结构分析和硬度测试等研究不同变形条件下AZ61镁合金的组织和性能,引用Z值(Zener-Hollomon系数)研究温度和应变速率对AZ61镁合金组织的影响,建立再结晶晶粒尺寸与Z值之间的关系。结果表明:铸态AZ61镁合金在热变形时表现出动态再结晶特征,随温度上升,再结晶容易发生且峰值应力降低,再结晶晶粒尺寸随温度升高而增大;随应变速率上升,峰值应力增大且峰值应力对应的应变量增大,再结晶晶粒尺寸减小;硬度大小的变化也与动态再结晶密切相关。     

挤压态HAl61-4-3-1合金高温本构模型构建及其加工图

采用Gleeble-3500热模拟实验机在变形温度为600～800℃和应变速率为0.01～10 s-1时对HA161-4-3-1铝黄铜合金进行等温热压缩实验,对实验所获得真实应力-应变曲线进行摩擦修正,并以修正后的应力应变数据构建了考虑应变补偿的Arrhenius本构模型.其次,根据修正的应力应变数据构建了应变为0.3...     

基于倾角传感器的帆板自动控制系统的设计

以全国大学生电子设计竞赛为背景,采用模块化的设计方法,完成了基于倾角传感器的帆板自动控制系统.详细论述了该系统设计原理及硬件组成,给出了系统的软件流程.利用倾角传感器实现高精度检测和采用PID算法实现高精度控制是该系统设计的主要特点.实验表明,该系统工作稳定可靠,达到了预期的设计要求,并可为类似系统的设计提供有益的借鉴.     

Internal migration and wages of Italian university graduates*

In this paper, we estimate wage gains due to geographic mobility of Italian university graduates three years after graduation. By means of a matching procedure we quantify wage premia associated with the choice of studying far from home, moving after graduation and moving back home after graduation. We find evidence of large heterogeneity in the returns to different migration patterns. The results show large gains for those who move after graduation and smaller gains for those who migrate to study. Conversely, those who choose to go back home after having studied in regions different from that of origin suffer small losses. Our findings are robust to a finer definition of mobility and to the subsample of individuals originating from the South.     

Optioneering: A New Basis for Engagement Between Architects and Their Collaborators

Conventionally, architects are somewhat tardy when inviting engineers to join their projects. By only introducing consulting engineers to participate in the later stages of the design process, engineers are commonly assigned a fixing role. This provides little opportunity for creative engineering solutions at the generative stage. Optioneering, a new business management model, however, offers the possibility of a new collaborative method for interaction between designers and their partners. Dominik Holzer and Steven Downing describe how a research project between the Spatial Information Research Laboratory (SIAL) at the Royal Melbourne Institute of Technology (RMIT) and the engineering firm Arup investigated the capability of this new form of collaboration. Copyright © 2010 John Wiley & Sons, Ltd.     

自孕育法制备AZ61镁合金的微观组织

采用AZ91D镁合金母液与纯Mg熔体混合的自孕育法制备AZ61镁合金半固态坯料,研究了液-液熔体混合和导流.器角度改变对AZ61镁合金组织的影响.试验结果表明:液-液混合熔体经导流器浇注到铸型中后,可以使AZ61镁合金组织明显细化.相比未混合制备的AZ61,熔体混合有利于能量起伏、结构起伏、浓度起伏,增加有效形核,使晶粒细化;经倾斜导流器激冷、冲刷进一步细化晶粒,同时熔体流经导流器产生的二次混合又促进了有效形核,使平均晶粒尺寸大幅减小(约50％).随导流器角度增加,组织有粗化的趋势,但影响不大.     

基于感应加热的镁合金带内筋筒形件热强旋旋前温度场研究

对于镁合金带内筋筒形件的热强旋成形,旋前管坯的温度场分布对成形过程中的材料流动及旋压件的成形质量具有重要影响.基于多物理场耦合软件COMSOL,建立了ZK61镁合金带内筋筒形件热强旋旋前管坯电磁感应加热模型,模拟分析了不同感应加热参数条件下管坯温度场的分布情况,并通过实验验证了模型的可靠性.研究结果表明:相比电流强度,...     

新SIMA制备坯料触变挤压AZ61镁合金零件的组织与性能(英文)

新应变诱导熔化激活法被用来制备高质量的AZ61镁合金半固态坯料。利用光学显微镜和拉伸实验,研究触变挤压成形零件的微观组织与力学性能。结果表明:当施加的压力为784MPa,保压时间为90s,模具温度为450℃时,半固态坯料能够完全充填模具型腔。与半固态等温处理方法相比,新SIMA法制备的半固态坯料触变挤压成形零件的抗拉强度和伸长率分别为300.5MPa和22%;并且成形零件的微观组织晶粒细小、组织均匀。随着等温处理温度的升高和保温时间的延长,成形零件的抗拉强度和伸长率先增加后降低。当挤压道次从1增加至4时,成形零件的抗拉强度和伸长率明显增加。     

Effect of Al5Ti1B master alloy on microstructures and properties of AZ61 alloys

AZ61 alloys with different levels of Al5Ti1B master alloy additions were prepared by conventional casting method.The effects of Al5Ti1B contents and holding time on microstructures and microhardness of AZ61 alloys were studied by XRD,OM and microhardness testing techniques.The results show that when the addition level of Al5Ti1B master alloy is less than 0.5%(mass fraction),the average grain size of the alloys decreases with the increase of Al5Ti1B content at the same holding time.But the grain size increases somewhat with further addition of Al5Ti1B.The average grain size of the alloys decreases with the increase of the holding time as it is less than 30 min at the same addition level of Al5Ti1B.It is considered that TiB2 particles can serve as the heterogeneous nucleation sites ofα-Mg during solidification,and heterogeneous nucleation is the main reason for the grain refinement of AZ61 alloys.The microhardness of the refined AZ61 alloys with 1.0%Al5Ti1B addition is increased by about 8%.