预时效对6022合金成形性能和力学性能的影响

对6022合金板材分别进行555℃固溶30 min+自然时效5 d,以及555℃同溶30 min+140℃不同时间预时效+自然时效5 d的处理.通过显微硬度测试、拉伸实验、DSC分析和透射电镜观察,研究在140℃预时效对该合金的成形性能、模拟烤漆(175℃时效30 min)后的力学性能和微观组织的影响.结果表明:随着预...     

Cu含量对Al-1.0Mg-1.0Si-0.6Mn薄板成形性及烤漆硬化性的影响

采用拉伸、杯突实验结合DSC分析系统研究了Cu含量对汽车车身用Al-1.0Mg-1.0Si-(0.1~0.7)Cu-0.6Mn合金T4态薄板各类成形性指标及模拟烤漆处理后性能变化的影响规律.结果表明:随着Cu含量增加,T4态合金板材的强度单调增大,n值呈现出略有增大的趋势,延伸率、r值变化规律不明显,IE值单调下降,板材的拉胀成形性能变差;随着Cu含量增加,T4态合金板材烤漆前后的强度均单调增大,但合金板材模拟烤漆后表现出烤漆软化现象,且其软化量随Cu含量增加而逐渐增大,说明Cu含量增加不利于铝板烘烤硬化性能的发挥.     

A calorimetric study of precipitation in aluminum alloy 2219

Precipitate microstructures in aluminum alloy 2219 were characterized using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The DSC signatures of individual precipitate phases were established by comparing the DSC and TEM results from samples that had been aged such that only one precipitate phase was present. These signatures were then used to analyze the commercial tempers. It was found that DSC could readily distinguish between the T3, T4, T6, T8 and O tempers but could not distinguish amongst T81, T851 and T87. Small amounts of plastic deformation between solution treatment and aging had a significant effect on the thermograms. Aging experiments at 130 and 190 °C showed that the aging sequence and DSC response of this alloy were similar to those of pure Al-Cu when the increased copper content is taken into account. Further aging experiments at temperatures between room temperature and 130 °C showed pronounced changes of the GP zone dissolution peak as a function of aging conditions. These changes were found to be related to the effect of GP zone size on the metastable phase boundary and on the GP zone dissolution kinetics.     

Cu precipitation in a prestrained Fe-1.5 wt pct Cu alloy during isothermal aging

The control of Cu precipitation at low temperatures, e.g., bake hardening of Cu bearing steels, has recently attracted considerable attention due to the potential of achieving good formability and high strength. An Fe-1.5 wt pct Cu alloy, solution treated and 10 pct prestrained, exhibits a two-step age-hardening behavior, i.e., a smaller, but substantial hardening around 200 °C to 300 °C and a major hardening around 500 °C, while only the latter hardening occurs in undeformed specimens. The precipitation behavior of nanoscale Cu particles or bcc Cu clusters that plays a major role in age hardening was simulated by Cahn-Hilliard nonclassical nucleation theory and the Langer-Schwartz model. Simulation results are compared with the distribution of Cu particles observed under three-dimensional atom probe field ion microscope (3-D APFIM) and transmission electron microscope (TEM), and age hardening behavior as well. The increase in hardness in prestrained specimens at low temperatures (≤400 °C) can be ascribed to Cu particles nucleated preferentially at dislocations or to Cu particles that were formed in the matrix as early as at dislocations presumably due to excess vacancies introduced by prestraining.     

Effects of SiC whiskers and particles on precipitation in aluminum matrix composites

The age-hardening precipitation reactions in aluminum matrix composites reinforced with discontinuous SiC were studied using a calorimetric technique. Composites fabricated with 2124, 2219, 6061, and 7475 alloy matrices were obtained from commercial sources along with unreinforced control materials fabricated in a similar manner. The 7475 materials were made by a casting process while the others were made by powder metallurgy: the SiC reinforcement was in the form of whiskers or particulate. It was found that the overall age-hardening sequence of the alloy was not changed by the addition of SiC, but that the volume fractions of various phases and the precipitation kinetics were substantially modified. Precipitation and dissolution kinetics were generally accelerated. A substantial portion of this acceleration was found to be due to the powder metallurgy process employed to make the composites, but the formation kinetics of some particular precipitate phases were also strongly affected by the presence of SiC. It was observed that the volume fraction of GP zones able to form in the SiC containing materials was significantly reduced. The presence of SiC particles also caused normally quench insensitive materials such as 6061 to become quench sensitive. The microstructural origins of these effects are discussed.     

Effect of Cu contents on aging precipitation behaviors of Cu-rich phase in Fe-Cr-Ni alloy

 Abstract: The precipitation characteristics and effect on strengthening mechanism of Cu-rich phases during short-time and long-time aging in the Super 304H steels with different Cu contents were investigated by the use of X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the size of Cu-rich phase particles increases, the distance of Cu-rich phase particles decreases and the density of Cu-rich phases increases with the increase of Cu content during short-time aging (~ 800 h) at 650℃ in the Super 304H steels. During long-time aging (>2000 h) at 650℃, Cu-rich phases precipitate sufficiently and the strengthening effect of Cu-rich phases is preferable in the Super 304H steel with 4% Cu. The strengthening effect of Cu-rich phases in the Super 304H steels with 2.2 % Cu or 5 % Cu is weaker than that with 4% Cu during long-time aging (>2000 h).     

The effects of preaging treatments on aging kinetics and mechanical properties in AA6111 aluminum autobody sheet

The automotive paint bake cycle is used to impart a modest artificial aging response, referred to as the paint bake response (PBR), in Al-Mg-Si-Cu autobody sheet alloys following stamping. This aging response acts to increase the dent resistance of exterior automotive panels and allows for greater down gaging. Unfortunately, the short duration of the paint bake cycle (as dictated by production demands) is generally insufficient to exploit more than a small fraction of the age-hardening potential of the alloys. The application of a preaging treatment immediately after quenching from solution heat treatment has been shown to be effective in increasing the PBR by up to a factor of 4, while at the same time improving the formability of the alloy and reducing the natural aging rate. Through the use of atomic resolution microscopy and differential scanning calorimetry, the mechanism of preaging can be shown to be the result of changes in the precipitation sequence of metastable variants of Mg₂Si, resulting in an increase in the precipitation kinetics during the aging cycle and a finer distribution of strengthening precipitates. The model proposes that preaging biases the formation of disordered clusters, which subsequently undergo partial dissolution during higher temperature thermal excursions. The cluster dissolution is associated with both an increase in the matrix concentration of elemental solute (Mg and Si) and a transient flux in vacancies that were previously entrained with the disordered clusters. The dissolution results in the formation of an intermediate metastable phase and an enhancement in the aging kinetics of β″ precipitates. The enhancement in aging kinetics allows superior final component strength at higher production rates, as well as allowing for lower automotive paint bake temperatures.     

The effect of strontium on the Mg2Si precipitation process in 6201 aluminum alloy

A transmission electron microscopy (TEM) study of a 6201 aluminum alloy to which controlled strontium additions were made has revealed important differences compared to the same alloy free of strontium. In the as-cast state, strontium favors the formation of α-AlFeSi (Al₈Fe₂Si) rather than β-AlFeSi (Al₅FeSi) phase, resulting in a greater quantity of excess silicon present in the strontium-treated alloy. During heat treatment, the excess silicon allows a greater density of finer β″-Mg₂Si precipitates to form, leading to increased tensile strength values and increased electrical resistivity. Strontium also retards the growth of the precipitates formed during heat treatment and inhibits formation of the equilibrium β-Mg₂Si phase. As a result, the strontium-treated alloy exhibits a resistance to overaging.     

Ti-Mg复合脱氧和硫含量对钢中夹杂物特征及MnS析出行为的影响

采用扫描电镜/能谱仪表征了管线钢中夹杂物的形貌、尺寸、成分及数量,考察了不同Ti/Mg比的钢中夹杂物特征、硫含量及脱氧产物数量对MnS析出行为的影响,并进行了热力学计算.结果表明：Ti-Mg脱氧钢中夹杂物以MgO-Al₂O₃-Ti₂O₃、MgO-Ti₂O₃或MgO为核心,表面包裹或局部析出MnS,粒径小于1.3μm,数量为300~450 mm^-2,形貌为圆形、多边形和方形;夹杂物中Ti/Mg原子数比为0.05~0.2时,夹杂物细小且近圆形;随硫含量减少,凝固过程中MnS析出倾向减小,MnS在夹杂物表面由包裹析出向局部析出转变,提高氧化物夹杂数量,有利于细小MnS的包裹或局部异质形核;Ti-Mg复合脱氧产物细小、弥散,可作为MnS异质形核核心,可同时降低MnS及氧化物的危害.     

Low temperature specific heat and magnetic study of precipitation in a Cu−Co alloy

Specific heat measurements between 1.4° and 4.2°K and magnetization measurements from 4.2° to 300°K with a Cu+0.7 at. pct Co alloy, solution treated at 1000°C and aged at 400°C, give the concentration and dipole moment of precipitated cobalt-rich particles as a function of aging time.     

The effect of Cu additions on the precipitation kinetics in an Al-Mg-Si alloy with excess Si

The microstructural evolution during age hardening of a Cu-bearing Al-Mg-Si alloy has been investigated by the three-dimensional atom probe (3DAP) and transmission electron microscope (TEM) techniques, in order to clarify the effect of Cu on the initial age-hardening response. After 30 minutes of artificial aging at 175 °C, the alloy shows a significant increase in hardness. The TEM observations have revealed that very fine, needle-shaped β″ precipitates are formed in addition to spherical Guinier-Preston (GP) zones, whereas only the spherical GP zones are observed in the Al-Mg-Si ternary alloy using the same aging condition. The number density of the precipitates is significantly affected by the preaging conditions. The 3DAP analysis shows that the distribution of Cu atoms is uniform after 30 minutes of artificial aging at 175 °C, whereas Cu atoms are incorporated into the needle-shaped β″ precipitates after 10 hours of aging at 175 °C. Based on these microanalytical results, the effect of Cu additions on the age-hardening response of Al-Mg-Si alloys is discussed.     

The effect of cathodic polarization on the corrosion fatigue behavior of a precipitation hardened aluminum alloy

Fatigue experiments were conducted on polycrystalline and monocrystalline samples of a high purity Al, 5.5 wt pct Zn, 2.5 wt pct Mg, 1.5 wt pct Cu alloy in the peak-hardened heat treatment condition. These experiments were conducted in dry laboratory air and in 0.5N NaCl solutions at the corrosion potential and at applied potentials cathodic to the corrosion potential. It has been shown that saline solutions severely reduce the fatigue resistance of the alloy, resulting in considerable amounts of intergranular crack initiation and propagation under freely corroding conditions for polycrystalline samples. Applied cathodic potentials resulted in still larger decreases in fatigue resistance and, for poly crystals, increases in the degree of transgranular crack initiation and propagation. Increasing amounts of intergranular cracking were observed when applied cyclic stresses were reduced (longer test times). The characteristics of cracking, combined with results obtained on tensile tests of deformed and hydrogen charged samples, suggest that environmental cracking of these alloys is associated with a form of hydrogen embrittlement of the process zones of growing cracks. Further, it is suggested that stress corrosion cracking and corrosion fatigue of these alloys occurs by essentially the same mechanism, but that the often observed transgranular cracking under cyclic loading conditions occurs due to enhanced hydrogen transport and/or concentrations associated with mobile dislocations at growing crack tips.     

Texture clustering and long-range disorientation representation methods: application to 6022 aluminum sheet

Two new graphical methods are presented for microstructural analysis of crystalline material. These analyses are intended to aid an understanding of deformation behavior at scales larger than the grain size. The correlation of orientation over large distances has rarely been investigated, since a long-range correlation has been assumed to be negligible, if present at all. The first method reveals orientation clustering by calculating the variance of the orientation distribution function (ODF). The second addresses orientation ordering or orientation autocorrelation and is named the disorientation correlation function (DCF). We show that both analyses can be derived from the two-point autocorrelation functions of the orientation field.     

C含量对690合金M23C6相析出行为的影响

摘要：为了研究0.011%～0033%范围内C质量分数对690合金M23C6相析出行为的影响规律,采用SEM、TEM、物理化学相分析和热力学计算等手段,考察了不同C含量与M23C6相析出数量及析出位置关系。结果表明,随着C含量增加,M23C6析出相质量分数增加、完全固溶温度提高,前者与C质量分数呈线性关系变化,后者则符合抛物线关系。C含量升高,M23C6相的吉布斯自由能下降,从基体中析出M23C6相这一固态相变过程的驱动力增大,在相同的保温时间下,促进M23C6相在更多位置上的析出及其析出形貌的显著变化。对于较高C含量的690合金,除在晶界和孪晶端部外,还可在孪晶内部观察到M23C6相析出现象,其析出相颗粒发生粗化的同时,相质量分数也逐渐增加。     

Effect of doping aluminum and yttrium on high-temperature oxidation behavior of Ni-11Fe-10Cu alloy

Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10 Cu at 750 and 950 °C in air were investigated. The oxidation kinetics of Ni-11Fe-10 Cu alloy followed parabolic law at 750 °C without spallation and linear law at 950 °C with severe spallation, while that of Ni-11Fe-10Cu-6Al-3Y alloy followed parabolic law at 750 and 950 °C without spallation. The parabolic rate constant(k_p) of Ni-11Fe-10 Cu was smaller than that of Ni-11Fe-10Cu-6Al-3Y at 750 °C. The oxide scale formed on Ni-11Fe-10 Cu at 750 °C was composed of a CuO outer layer, a NiFe_2O_4 middle layer and a NiO inner layer. The oxide scale formed on Ni-11Fe-10Cu-6Al-3Y at 750 °C was also composed of the similar triplex layers in addition to an internal oxidation zone containing Al, Ni and Cu oxide and the microstructure of the scale changed with increasing temperature. Although the doping Al and Y could improve the adherence of oxide scale, it could aggravate the extent of internal oxidation. Based on the combination of X-ray diffraction(XRD), scanning electron microscopy/energy dispersive spectroscopy(SEM/EDX) analysis, the microstructure and growth mechanism of the multi-layer oxide scale was studied and the effect of doping Al and Y on the oxidation behavior of Ni-11Fe-10 Cu alloy was also discussed.     

固溶温度对Al-Zn-Mg-Cu系铝合金组织与应力腐蚀的影响

对7B50铝合金热轧板在460～490℃范围内进行固溶处理、室温水淬及人工时效,通过室温力学性能测试、慢应变速率拉伸实验及电导率测试,结合光学显微镜,扫描电镜和能谱分析,研究固溶温度对Al-Zn-Mg-Cu铝合金组织与应力腐蚀的影响。结果表明,提高固溶温度能有效减少残留相,增加再结晶的体积分数。当固溶温度从460℃提高到490℃时,屈服强度(σ0.2)和抗拉强度(σb)分别提高20.9%和23.5%,固溶温度从480℃升高到490℃时,强度变化不大,但随着固溶温度升高,伸长率先提高后降低,抗应力腐蚀性能先升高后降低。当固溶温度为480℃时,应力腐蚀敏感性最低,综合性能较好。残留相增多和再结晶程度提高是引起应力腐蚀敏感性提高的主要原因。在腐蚀溶液中,应力腐蚀断口形貌为典型的沿晶断裂。     

Effect of trace additions of cadmium,silver and zirconium on the precipitation hardening behavior of aluminum 6061 alloy

Age hardening response was investigated in Aluminum 6061 alloy to determine the influence of trace additions of 0.01 and 0.1 % of cadmium, 0.01, 0.1 and 0.5% of silver, 0.05 and 0.1% of zirconium, as well as 0.1% each of Cd + Zr and Ag + Zr. Thermo-mechanical stabilization treatment followed by artificial aging of these alloys were carried out at 313 K, 353 K, 393 K and 453 K. Vickers hardness was used to monitor the progress of age hardening. The Precipitate morphology, distribution and size were studied by Scanning Electron Microscopy. Tensile tests on selected alloys after selected treatment conditions assisted in determining the UTS, YS and % elongation. Fractography of the tensile fractures by scanning electron microscopy was used to delineate the effect of trace element addition on the fracture type. The trace addition effects observed seem to be caused by the precipitate size refinement and distribution. The observed effects seem to corroborate results obtained by several other techniques. The present work strengthens, both qualitatively and quantitatively, the viewpoint that it is possible to choose an age hardenable aluminum base alloy and improve it significantly by making judicious additions of trace elements.     

Crystallization characteristics of the Ti53Cu47 amorphous alloy

A thin Ti₅₃Cu₄₇ amorphous ribbon was prepared by rapid quenching from the melt. The crystallization behavior was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The DSC results indicated that the activation energy for crystallization was 170 or 150 kJ/mole (1.76 or 1.55 eV/atom) based on the Kissinger or Arrhenius plot, respectively, which is close to that of chemical diffusion in the TiCu alloy: 166 kJ/mol (1.72 eV/atom). The Johnson-Mehl-Avrami (JMA) plot exhibited a linearity, with an exponent of n=2.0 ±0.2. The XRD patterns revealed the transformation to the equilibrium γ-TiCu phase. However, broad peaks due to nanocrystalline grains were not observed. From the TEM analysis, there was a metastable phase with an fcc structure based on the Cu structure pre-existing in the as-quenched ribbon. Only a few TiCu particles in the nanoscale dimension were observed to precipitate from the amorphous matrix upon both continuous and isothermal heatings. A theoretical calculation demonstrates that amorphous Ti₅₃Cu₄₇ has a very low nucleation frequency and thus, a low tendency to form nanocrystals.     

Al-6.1Zn-2.6Mg-1.6Cu 铝合金的回归再时效热处理

The effects of the retrogression temperature and time of retrogression and re-aging heat treatment(RRA) on the hardness and electrical conductivity of Al-6.1Zn-2.6Mg-1.6Cu aluminum alloy were studied. Samples were pre-aged at 120℃ for 24h as the first-stage treatment. Then, retrogression was performed at a temperature range of 170～250℃ for times of between 1min and 180min, followed by re-aging at 120℃ for 24h. Hardness (H) and electrical conductivity (EC) measurements were used to characterize the samples after RRA treatment. Analysis of the results shows: (1)The re-aging treatment at 120℃ for 24 h increases both H and EC of the retrogressed alloy in the RRA process;(2) RRA with retrogression at higher than 200℃ result in EC higher than that of peak-aged, but H lower; The change of H and EC with respect to retrogression temperature (T) and time (t) can be seen as functions of H (t) = H0 A1e(-t/s) ,EC(t) =A(1-e(-k·(t-Xc)));(3) RRA treatments with retrogression at 190℃ for 4～30min result in H and EC which are both higher than those of the peak-aged temper, and retrogression at 190℃for 30min is the industrial application that yields H of 190 HV and EC of 33.5%IACS.     

热处理制度对7039铝合金冲击性能及组织的影响

将7039铝合金热轧板材在470℃/2 h条件下固溶后,分别进行T6处理、T73处理以及RRA处理.利用Hopkinson压杆技术对3种热处理态的7039铝合金进行冲击压缩实验,用光学显微镜和透射电镜对冲击后的试样进行组织观察,分析热处理制度对合金动态应力-应变行为和微观组织的影响.结果表明:经T6处理的7039铝合金在高速冲击加载时的绝热剪切敏感性明显低于T73和RRA处理的合金,经RRA处理的合金绝热剪切敏感性最大;不同热处珲状态的合金在应变率为3 000 s-1时,组织中均产生绝热剪切带以及变形带;合金在高速冲击加载过程中产生的绝热剪切带内部组织主要是一种强同复组织.