NdFeB合金铸锭组织及均匀化退火

研究了NdFeB合金的铸锭组织,并对NdFeB合金进行了均匀化退火。研究表明,NdFeB铸锭中Nd2Fe14B相以片状晶方式生长,经退火后,α-Fe基本消除,片状晶变为等轴晶并粗化。X-射线衍射结果显示,经退火处理后,Nd2Fe14B在某些方向上的各向异性更为明显。     

Al-7.5Zn-1.6Mg-1.4Cu合金的均匀化处理

利用光学显微镜、扫描电镜、能谱分析、X射线衍射分析和差示扫描量热分析等研究了Al-7.5Zn-1.6Mg-1.4Cu合金铸态与均匀化态的显微组织演化与元素分布,确定了该合金的均匀化温度与过烧温度。结果表明,合金铸态组织中存在严重的枝晶偏析,经470℃保温24h后,枝晶网络变稀,共晶相与η相回溶至基体,偏析基本消除。470℃保温24h是该合金较为理想的均匀化工艺。     

铸锭均匀化退火对2Al2合金薄壁管冷加工性能的影响

2Al2合金铸锭如果不进行均匀化退火或均匀化不充分，生产薄壁管时．管坯在冷拔前打头时端头破碎严重，打头困难；在冷轧管时端头破裂严重。管材表面易出现横向裂口。分析认为，其主要原因是铸造时的不平衡结晶所产生的锰偏析、镁偏析。没有得到有效的消除。     

稀土La对Al-10Mg合金铸态组织与性能的影响

研究了添加稀土La对Al-10Mg合金铸态显微组织和力学性能的影响,结果表明:加入质量分数为0.3%-0.5%的La能够细化铸态Al-10Mg合金的晶粒,并形成颗粒状及短杆状Al-La化合物,提高合金力学性能,当La添加量超过0.7%时,合金晶粒出现粗化,Al-La化合物转变为沿晶界连续分布的粗大网络状形态,La对合金的强化效果减弱。     

2524铸态合金均匀化过程中微观组织的变化

在不同温度和不同保温时间条件下对2524铸态合金进行均匀化处理,利用扫描电镜(SEM)、透射电镜(TEM)、差示扫描量热法(DSC)和金相显微镜(OM)等,研究2524铸态合金在均匀化过程中微观组织的变化,并分析在不同的均匀化处理状态下T相(即Al20Cu2Mn3相)的析出情况。结果表明:2524铸态合金中存在严重的枝晶偏析,大量的非平衡共晶相连续地沿晶界分布,主要的第二相为Al2Cu和Al2Cu Mg;主要合金元素不同程度地富集在晶界,富集程度为CuMgMn;最佳的均匀化处理制度为500℃/48 h,均匀化处理后,Al2Cu和Al2Cu Mg基本回溶至基体,只余少量难溶的Al Cu Fe Mn相散布在晶界,该均匀化制度与均匀化动力学方程的计算结果基本一致;随均匀化处理温度升高,T相粒子的尺寸逐渐增大而数目逐渐减少。     

喷射成形Al11.4Zn2.6Mg1.7Cu合金沉积态显微组织分析

利用喷射成形工艺制备了Al1 1 .4Zn2 .6Mg1 .7Cu超高强铝合金材料 ,用金相、SEM、TEM等测试方法对其显微组织进行了分析。研究结果表明 :沉积坯件主要由等轴晶粒构成 ,晶粒平均直径约为 2 3μm ,添加的合金元素Zn ,Mg和Cu呈有规律的分布 ,通过XRD和TEM分析 ,Al1 1 .4Zn2 .6Mg1 .7Cu铝合金沉积坯件中第二相主要包括六方结构的MgZn2 相、四方结构的Al2 Cu相和斜方晶格的Al2 CuMg相。     

Al-2.3Cu-1.7Mg-1.2Fe-1.2Ni合金的时效行为研究

采用硬度测试、电导率测试、常温力学性能测试等方法研究了单级时效处理过程中时效温度和时效时间对Al-2.3Cu-1.7Mg-1.2Fe-1.2Ni合金力学性能和电导率的影响规律,并利用金相显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、选区电子衍射(SAED)等手段对合金淬火态以及几种不同时效处理制度下的显微组织进行了研究.结果表明,合金经固溶淬火处理后仍残留有较多的大尺寸第二相,淬火态组织存在的第二相主要有Al9FeNi,Al7 Cu2 Fe,Al7 Cu4 Ni等.单级时效处理过程中,时效处理的温度越高,达到峰时效所需的时间越短,材料的峰时效硬度值越低;电导率随时效时间的延长而不断上升,时效温度越高,电导率的增长速率越快.峰时效条件下合金内主要沉淀强化相包括S’相和S"相,晶界上有明显的链状析出物存在,呈不连续分布;峰时效条件下,合金棒材的极限抗拉强度、屈服强度和延伸率分别为455 MPa,391 MPa和10.6％,电导率可达到21.6 MS·m-1.     

Al10Zn2.9Mg1.7Cu超高强铝合金的喷射成形制备研究

采用喷射成形技术制备了Al10Zn2.9Mg1.7Cu高强高韧铝合金沉积坯件，研究了喷射成形制备过程中各工艺参数对沉积坯件的成形性、显微组织、致密度的影响，确定了适当的工艺参数，研究了沉积坯件的热挤压及热处理工艺，对材料的组织进行了分析并对不同状态的材料性能进行了比较。研究结果表明：当喷射成形工艺参数合理时，沉积坯件具有良好的成形性与致密度，在随后的热挤压过程中，通过较低的挤压比即可使材料达到全致密；通过对合金进行适当的热处理，材料的极限抗拉强度达到810MPa，同时延伸率保持在8％-11％，该材料是一种理想的轻质高强结构材料。     

均匀化处理对Cu-Cr-Zr合金显微组织的影响

采用OM、SEM和TEM分析手段对Cu-Cr-Zr合金的铸态和均匀化组织进行研究.结果表明,Cu-Cr-Zr合金的铸态组织呈典型的枝晶状组织,主要由网状的Cr枝晶、共晶组织和基体组成,其中共晶组织是由基体和层片状的Cu5Zr相组成.在Cu-Cr-Zr合金的均匀化退火过程中,发生共晶组织的溶解和Cr相的析出.随着均匀化退火温度和时间的升高和延长,共晶组织逐渐溶解,Cr相的析出体积分数逐渐减小.合理的均匀化退火制度为900℃×12 h.     

合金元素及均匀化工艺对Al-5Mg合金力学性能的影响

通过在Al-5Mg合金中加入弥散相形成元素,在均匀化过程中能获得均匀细小的弥散相,热变形后能获得细小亚晶结构的组织。力学性能测试结果表明,利用固溶强化、弥散强化和细晶强化等综合方式强化后的铝合金,与传统的5083合金相比,挤压后的抗拉强度提高20%。但铸造过程形成的初晶相(Ti,V)Al3在拉伸和疲劳断裂过程中易成为裂纹源,降低铝合金的延伸率和疲劳寿命。     

Atom-probe analysis of GP zones in an Al-1.7 At. pct Cu alloy

Guinier-Preston (GP) zones in an Al-1.7 at. pct Cu alloy aged at 383 K for 8000 minutes were analyzed by atom-probe field ion microscopy (AP-FIM). Layer-by-layer concentration profiles in the 〈100〉 direction were obtained from several GP zones. Generally, the GP zones were found to consist of several copper-enriched layers, with the highest measured concentration of copper in any of these layers being 50 at. pct. Although some uncertainty exists as to the copper content of the GP zones, these results appear to be inconsistent with the existence of layers that approach 100 pct copper. Some GP zones showed two well-separated copper-enriched regions; others showed a broad single peak in copper concentration. Therefore, it was concluded that aging at 383 K for 8000 minutes causes a transition from GP 1 to GP 2. The present results together with the previous atom-probe data indicate that there is a distinct stage for GP 2 zones which have two separated copper-enriched layers of 200 planes. Formerly Graduate Student, Department of Materials Science and Engineering, The Pennsylvania State University     

Al-5Ti-B对过共晶Al-18Si合金的变质效果

采用Al-5Ti-B变质剂对过共晶Al-18Si合金进行反向变质处理,用光学显微镜观察合金的组织与形貌,研究变质剂加入量、变质温度和冷却速度对初晶硅的尺寸、形态和面积分数以及共晶组织的影响。研究表明:当Al-5Ti-B加入量(质量分数)为0.3%时,变质处理后Al-18Si合金中的初晶硅和共晶硅尺寸明显减小,初晶硅的面积分数减小;与其相比,变质剂加入量增加到0.6%时,初晶硅尺寸变化不明显,但共晶硅进一步细化;随冷却速率降低,变质处理后Al-18Si合金中初晶硅相的数量减少,但Si颗粒尺寸明显增大,并且共晶硅细化;与Al-18Si合金在720℃变质相比,该合金在780℃变质处理时,初晶硅的尺寸增大,但初晶硅的面积分数显著减小;合金在850℃变质处理后初晶硅的尺寸、面积分数都比720℃变质处理后明显减小;随变质温度升高,Al-Si合金中的共晶硅明显细化。     

Grain refining of Al-4.5Cu alloy by adding an Al-30TiC master alloy

A particulate Al-30 wt pct TiC composite was employed as a grain refiner for the Al-4.5 wt pct Cu alloy. The composite contains submicron TiC particles. The addition of the TiC grain refiner to the metal alloy in the amount of 0.1 Ti wt pct effected a remarkable reduction in the average grain size in Al-4.5 wt pct Cu alloy castings. With the content of over 0.2 Ti wt pct, the grain refiner maintained its refining effectiveness even after a 3600-second holding time at 973 K. The TiC particles in the resulting castings were free of interfacial phases. It is concluded that the TiC are the nucleating agents and that they are resistant to the “fading effect” encountered with most grain refiners.     

Microstructural changes in a mechanically alloyed Al-6.2Zn-2.5Mg-1.7Cu alloy (7010) with and without particulate SiC reinforcement

Elemental powders of Al, Zn, Mg, and Cu (corresponding to the composition of 7010 aluminium alloy) were milled in a high-energy attritor with and without additions of SiC particulates. The microstructural changes taking place in the milled powders (which eventually lead to mechanical alloying) are found to be retarded by SiC additions. High-resolution techniques such as electron probe microanalysis (EPMA) and transmission electron microscopy/energy-dispersive X-ray analysis (TEM/EDX) revealed the presence of localized solute-rich regions long after the diffraction line from these solutes had ceased to appear in the X-ray diffractograms. Zinc appears to be more difficult to be mechanically alloyed into aluminum than either Cu or Mg in spite of its comparatively larger diffusivity in aluminum.     

Effect of excess Au on antiphase domain growth in Cu3Au

The kinetics of antiphase domain growth have been studied in three nonstoichiometric Cu₃Au alloys containing nominally 26, 28, and 31.5 at. pct Au. During isothermal annealing of disordered samples below the critical temperatures, the domain growth in all of the alloys initially followed the samet ^1/2 dependence found previously for stoichiometric Cu₃Au. At long times, the two alloys furthest off stoichiometry reached limiting domain sizes which decreased with increasing Au content. Although the role of the excess Au in determining these limiting sizes is not clear, it is evident that most of the excess Au is accommodated within the domains. The antiphase domain size distributions in the alloys agree with those found for the stoichiometric alloy.     

Solution kinetics of CuAl2 in an Al-4Cu alloy

The results of a recently-developed, spherical, finite geometry, mathematical model using numerical methods are compared to existing closed-form models. The geometry and boundary conditions imposed by the closed-form models are shown to be restrictive in the application of these models to the solution kinetics of second phases. A quantitative metallography study of the solution kinetics of CuAl₂ in an Al-4 wt pct Cu alloy was undertaken to provide data on the changes in second-phase particle size distributions as a function of solution treatment time. The size distributions were shown to vary according to the proposed spherical, finite model formulated using numerical methods. Formerly Undergraduate Student, Department of Metallurgical Engineering, Drexel University, Philadelphia, Pa. Formerly Graduate Student, Department of Metallurgical Engineering, Drexel University This paper is based in part on a thesis submitted by D. L. BATY to Drexel University in partial fulfillment of the requirements of the degree of Bachelor of Science in Metallurgical Engineering.     

Local atomic arrangements in the solid solution Al-1.7 at.% Cu,at 793 K

The absolute diffuse X-ray intensity, scattered from a crystal of Al-1.7 at.% Cu, was measured in the solid solution region at 793 K. This intensity was separated into terms associated with local order and those due to displacements of atoms from the sites of the average lattice. Computer simulations with the measured short-range order parameters and for a pseudo-random alloy were compared. The actual alloy has few isolated Cu atoms, compared to the random configuration. Instead the Cu is present in small composition fluctuations; more than half the solute content is in tiny plate-like regions which resemble the larger G.P. zones that form upon quenching and aging. Also, the density of these embryonic regions is similar to the zone density for short aging times. Therefore, there is no apparent nucleation barrier for zone formation. The electrical resistivity immediately after quenching can be calculated from the cluster population and the result agrees with experiment. The pair potentials in the system were determined from the X-ray scattering.     

High-temperature creep in an Al-8.5Fe-1.3V-1.7Si alloy processed by rapid solidification

The creep behavior of an Al-8.5Fe-1.3V-1.7Si alloy processed by rapid solidification is investigated at three temperatures ranging from 623 to 723 K. The measured minimum creep strain rates cover seven orders of magnitude. The creep behavior is associated with the true threshold stress, decreasing with increasing temperature more strongly than the shear modulus of aluminum. The minimum creep strain rate is controlled by the lattice diffusion in the alloy matrix, and the true stress exponent is close to 5. The apparent activation energy of creep depends strongly on both applied stress and temperature and is generally much higher than the activation enthalpy of lattice self-diffusion in aluminum. Also, the apparent stress exponent of minimum creep strain rate depends on applied stress as well as on temperature and is generally much higher than the true stress exponent. This behavior of both the apparent activation energy and apparent stress exponent is accounted for by the strong temperature dependence of the threshold stress-to-shear modulus ratio. The true threshold creep behavior of the alloy is interpreted in terms of athermal detachment of dislocations from fine incoherent Al₁₂(Fe, V)₃Si phase particles, admitting a temperature dependence of the relaxation factor characterizing the strength of the attractive dislocation/particle interaction.