Aging Strengthening in Rapidly Solidified Cu-Cr-Sn- Zn Alloy

It is known that the strength of alloys can be successfully improved by rapid solidification. The paper presents a process where Cu-Cr-Sn-Zn lead frame alloy is produced by rapid solidification and aging. The microcrystalline structure of rapidly solidified Cu-Cr-Sn-Zn alloy is smaller grain structure examined by optical metallography. The effects of aging processes on the microstructure and properties of the lead frame alloy were investigated. Aged at 500°C for 15 min the fine coherent precipitates Cr dist...     

Strengthening mechanisms in a rapidly solidified and aged Cu-Cr alloy

A single-roller melt spinning method was used to produce Cu-Cr microcrystal alloy ribbons. Upon proper aging treatment, the strength and hardness of the alloy were remarkably enhanced while the conductivity only had a minimal decrease. Grain refinement and coherent dispersion strengthening were proved to be the major factors contributing to the improvement of strength and hardness of the alloy after aging. The degree of coherent strengthening was almost identical with that calculated by the Gerold equation. Compared with the solid solution quenched Cu-Cr alloy, the peak hardness was increased 2.6 times, in which about 27% was attributed to the grain refinement and 73%, in turn, provided by coherent strengthening due to aging precipitation. Neither the solid solution strengthening nor vacancy strengthening had detectable effect on the strength and hardness of the rapidly solidified Cu-Cr alloy.     

机械合金化制备Cu-Fe过饱和固溶体及其时效分解

采用机械合金化工艺制备Cu-xFe(x=1,2,4,质量分数/%)过饱和固溶体,研究时效对其硬度和导电性能的影响.X-ray衍射分析结果表明:机械合金化显著提高了Fe在Cu中的固溶度,Cu-4Fe复合粉末经32h球磨.Fe完全固溶于Cu基体中,此时Cu晶粒尺寸为20nm,点阵常数降低到0.3621nm.硬度和导电率测试结果表明:时效处理能促进过饱和固溶体发生分解,Cu-4Fe过饱和固溶体冷压成型压坯在400℃保温8h后显微硬度HV由时效前的175降低到96,电导率由35%IACS(国际退火铜标准)提高到60%IACS.     

Microstructure,precipitates and mechanical properties of powder bed fused inconel 718 before and after heat treatment

IN718 alloy was fabricated by laser powder bed fusion (PBF) for examination of microstructure, precipitates and mechanical properties in the as-built state and after different heat treatments. The as-built alloy had a characteristic fine cellular-dendritic microstructure with Nb, Mo and Ti segregated along the interdendritic region and cellular boundary. The as-built alloys were then subjected to solution heat treatment (SHT) at 980 °C or 1065 °C for 1 h. SHT at 980 °C led to the formation of δ-phase in the interdendritic region or cellular boundary. The segregation was completely removed by the SHT at 1065 °C, but recrystallization was observed, and the carbides decorated along the grain boundaries. The as-built alloy and alloys with SHT at 980 °C and 1065 °C were two-step aged, which consisted of annealing at 720 °C for 8 h followed by annealing at 620 °C for 8 h. Transmission electron microscopy revealed the precipitation of γ' and γ” in all alloys after two-step aging, but the amount and uniformity of distribution varied. The Vickers hardness of the PBF IN718 alloy increased from 296 HV to 467 HV after direct aging. The hardness decreased to 267 HV and 235 HV after SHT at 980 °C and 1065 °C, respectively, but increased to 458 HV and 477 HV followed by aging. The evolution of Young’s modulus after heat treatment exhibited similar trend to that of hardness. The highest hardness was observed for IN718 after SHT at 1065 °C and two-step aging due to precipitation with greater amount and uniform distribution.     

Effects of Sc Addition and Direct Aging Treatment on Microstructure and Hardness of AlSi10Mg Alloy

Cu-mold centrifugal cast processing is employed as a rapid solidification method for producing samples with and without Sc. The Al–Si–Mg and Al–Si–Mg–Sc alloy samples are exposed to direct aging treatments varying temperature and time to verify the microstructural changes. Both rapidly solidified samples and as-aged samples are characterized by a number of methods, including optical microscopy, SEM–EDS, transmission Electron Microscopy (TEM)–EDS, TEM–HAADF, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Vickers hardness. At first, the results point to a strong precipitate-related hardening effect formed as a result of the Sc addition to the alloy. All samples containing Sc show a higher hardness value when compared to their respective treated samples without Sc. Second, when comparing the Al–10Si–Mg–0.4Sc alloy samples among themselves after being treated at different conditions, high temperatures, and excessive treatment times are recognized as detrimental to the hardness. This is due to the growth of larger Sc-bearing precipitates of approximately 1 μm in size under such conditions, having lower efficiency in pinning dislocations during loading. The best aging condition is 255 °C for 60 min, which produces a very fine dispersion of Mg and Sc intermetallics (200 nm in size) with a peak hardness of 110 HV.     

时效早期Al-Mg-Si合金的组织和析出相的演变

用显微硬度测试、差示扫描量热法(DSC)和高分辨透射电镜(HRTEM)观察等手段研究了Al-Mg-Si合金人工时效过程中的硬化、组织变化以及早期析出相的演变。结果表明：在170℃时效的合金具有更高的峰值硬度。在时效初期晶内析出高数量密度的溶质原子团簇和GP区,合金的硬度显著提高。在170℃处理4 h后合金的硬度达到峰值,此时晶内析出相以针状β″相为主,β″相与Al基体界面三维共格应变是合金强化的主要原因。同时,晶界析出相呈断续分布状态。随着时效时间的增加β″相开始粗化,晶界析出相的连续程度降低。在过时效阶段晶内析出相的严重粗化和数量密度的降低,使合金的硬度剧烈降低。在时效的初始阶段,合金的析出序列为过饱和固溶体→球形原子团簇→针状GP区→针状β″相。     

Cr分布对Cu-Cr合金性能的影响

Cu-Cr合金是一种很好的时效强化型合金,其性能主要取决于Cr在Cu基中的分布.对Cu-0.2Cr合金研究发现,当Cr固溶于铜中时硬度和导电性最低,通过时效后的衍射和性能分析,析出相为fcc(face-centered cubic) 的Cr且与基体保持着共格关系,其硬度和导电性分别提高了32.8Hv和39.9IACS%.对时效后合金的强度按共格弥散强化造成的切变应力的增量进行估算,其估算值与实测值相差6%.用马提申定则对固溶和时效后合金的导电性进行估算,估算结果与实测结果相差较小,因此在低固溶条件下,可以利用马提申定则对固溶和时效后Cu-Cr合金的导电性进行估算.     

Cu-3.0Ni-0.75Si合金时效析出动力学分析

为研究Cu-3.0Ni-0.75Si合金时效过程中沉淀相的析出与长大规律,及其对合金硬度的影响,采用涡流电导仪和布氏硬度计分别测量合金的电导率和硬度,根据导电率与新相析出量之间的关系分析合金的时效析出动力学过程.结果表明,在350℃下时效,合金硬度随时效时间的延长,先升高后趋于平缓;在450℃、550℃下时效,合金硬度随时效时间的增加快速上升,到达峰值后缓慢下降;时效温度越高,合金硬度峰值越低,但硬度达到峰值所需的时间越短.温度一定,随时效时间的增加,合金电导率在时效初期快速升高,至峰值后趋于平缓.根据Cu-3.0Ni-0.75Si合金在450℃时效过程中电导率的变化,通过Avrami方程推导出相应的相变动力学方程及电导率方程分别为f=1-exp(-0.052 2t0.717 61)和σ=15.2+16.3[1-exp(-0.052 2t0.717 61)],采用相关系数检验法及F检验法对电导率方程的可信性进行检验,结果说明时效析出动力学方程和电导率方程具有一定的可靠性.对比由电导率经验方程得出的电导率理论值与测量得出的实验值,该理论值与实验值有良好的吻合度.     

热处理工艺及冷变形对CuNiSiCr合金组织与性能的影响

研究了引线框架用CuNiSiCr合金不同热处理工艺及冷变形量对组织与性能的影响,研究表明,新型CuNiSiCr合金在930℃保温1 h进行固溶处理,然后进行30%的冷变形,随后在510℃下进行2.5 h的时效处理,合金的硬度与导电性能达到较好的配合,能满足引线框架的技术性能要求。     

Effect of cooling aging on microstructure and mechanical properties of an Al–Zn–Mg–Cu alloy

In the present work, Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT). At high initial aging temperature (IAT), the hardness was decreased with the decreased cooling rate. However, when IAT was lower than 180 °C, the hardness was increased with the decreased cooling rate. Conductivity was increased with the decreased cooling rate regardless of IAT. The tensile strength, yield strength and conductivity of Al alloy after (200–100 °C, 80 °C/h) CAT were increased 2.9%, 8.1% and 8.3% than that after T6 treatment, respectively. With an increase of IAT and decrease of cooling rate, the fine GP zone and η′ phase were transformed to be larger η′ and η precipitates. Moreover, continuous η phase at grain boundary was also grown to be individual large precipitates. Cooling aging time was decreased about 90% than that for T6 treatment, indicating cooling aging could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption.     

Cu-Ni-Si合金冷变形及动态再结晶行为研究

研究了时效温度和时效时间对不同冷变形条件下Cu-2.0Ni-0.5Si合金性能的影响。在Gleeble-1500D热模拟试验机上,采用高温等温压缩试验,对Cu-2.0Ni-0.5Si合金在高温压缩变形中的流变应力行为进行了研究。结果表明,合金经900℃固溶,当变形量为40%,时效温度达到450℃时,其显微硬度达到201HV,导电率达到34%IACS。随变形温度升高,合金的流变应力下降,随应变速率提高,流变应力增大。在应变温度为700、800℃时,合金热压缩变形流变应力出现了明显的峰值应力,表现为连续动态再结晶特征。从流变应力、应变速率和温度的相关性,得出了该合金高温热压缩变形时的变形激活能Q。     

铸造Mg-Gd-Y-Nd-Zr合金在时效过程中的组织与性能演变

采用金相观察、硬度测试、单轴拉伸、扫描电镜观察、能谱分析、透射电镜观察等手段,研究了铸造Mg-Gd-Y-Nd-Zr合金在时效过程中的组织与性能演变。结果表明,经固溶处理后,合金具有较强的塑性变形能力,延伸率可达10%以上,但强度较低。随时效程度增加,合金强度升高塑性降低,经225℃/3h时效处理后,合金为欠时效状态,与基体共格的β″相是主要的强化相,断口以解理面、韧窝、撕裂棱和晶界为主要特征。经峰值时效处理后,与基体呈半共格关系的β′相是主要的强化相,合金抗拉强度超过300 MPa,但塑性急剧降低,断口以解理面、撕裂棱和晶界为主要特征,与欠时效样品相比,解理面所占比例明显增加,且解理面及晶界光滑。进入过时效状态后,合金的强度降低,但延伸率有所提升,断口以晶界和解理面为主要特征。     

压铸(Al63Cu25Fe12)p/AZ91复合材料的组织、性能和热处理特征

在CO2/SF6气氛保护下,采用压铸的方法将-200目的Al63Cu25Fe12准晶粉末注入到熔融的AZ91镁合金中,于720℃和一定的压力下保压30min,制备了新型的(Al63Cu25Fe12)p/AZ91镁基复合材料.结果表明,在复合过程中,准晶相分解出的自由Cu向基体扩散并与基体中的Al发生反应,生成的金属间化合物分布在准晶颗粒周围,同时Mg向颗粒中浸渗填充到颗粒的孔隙中;复合材料具有不同于基体镁合金的固溶时效特征,需要更长的时间才能达到时效峰值;复合材料经过热挤压和热处理后的力学性能显著提高,抗拉强度从AZ91铸态材料的189.54MPa提高到359.38MPa,但塑性有所降低.     

Aging Behaviors of W-Ni-Fe Ternary Alloys with High Ni-to-Fe Ratios

The hardness variation of two kinds of alloys with 36 wt pct W content and 7/3, 9/1 Ni-to-Fe ratios during strain aging at 800℃ was studied. The microstructures of the aged alloys were analyzed by X-ray diffraction and TEM. The results show that the strain aging hardness of W-Ni-Fe ternary alloy with 7/3 Ni-to-Fe ratio decreases monotonically with the increase of aging time. Under the same conditions, the hardness of 9/1 Ni-to-Fe ratio alloy decreases in the initial aging stage, but then increases as aging process goes on. X ray diffraction and TEM analysis show that there is not any precipitation depositing from the alloy with 7/3 Ni-to-Fe ratio during aging. The monotonic decrease in hardness of this alloy during aging process results from the recovery, recrystallization and solid solubility declining. In the alloy of 9/1 Ni-to-Fe ratio, the fine β phase precipitates dispersively during aging which hardens the alloy. The two different kinds of mechanisms (the softening one and the hardening one) decide the hardness variation of the alloy with 9/1 Ni-to-Fe ratio mentioned above.     

蠕变时效对7050铝合金板材组织与性能的影响

通过金相显微、透射电子显微、电子拉伸和剥落腐蚀实验研究了7050铝合金板材蠕变时效与人工时效的微结构及性能。结果表明:蠕变时效过程中施加的应力使板材不断产生变形,为η′析出相提供了大量形核点,析出相尺寸更加细小,特别是晶界无沉淀带较人工时效明显变窄,晶界析出相不连续。与人工时效相比,蠕变时效试样的抗拉强度和抗剥落腐蚀性能略有提高。     

微量Cu和形变热处理对Al-Fe合金性能的影响

观察Al-Fe合金的显微组织并测量其力学性能和导电性能,研究了Cu元素和形变热处理对其性能的影响。结果表明：在铸态Al-Fe-Cu合金组织中,Cu元素在基体内均匀分布,而Fe元素在晶界处偏析;挤压态的Al-0.7Fe-0.2Cu合金其性能最优：导电率为59.90%IACS,抗拉强度为108 MPa,硬度为31.2HV;随着退火温度的提高Al-0.7Fe-0.2Cu合金的抗拉强度急剧降低,在400℃退火时其抗拉强度最低(100 MPa),伸长率最高(31.3%);在250℃退火时导电率出现峰值(62.61%IACS)。在退火Al-0.7Cu-0.2Cu合金中有许多细小针状的θ(Al₂Cu)相析出,并与位错交互缠结。随着退火温度的提高合金中的位错密度降低,晶粒细化。     

时效及冷变形对Cu-3.2Ni-0.75Si-0.30Zn合金组织及性能的影响

本文分析了时效及时效后的冷变形对合金组织及性能的影响 ,并探讨了二级时效对变形后合金的硬度和导电率的影响规律 ,结果表明 ,经适当的分级时效工艺处理后 ,合金的硬度可达 2 4 0Hv以上 ,导电率可达4 5 %IACS以上     

热处理对网状结构TiB_W/Ti60复合材料组织与性能的影响

使用大尺寸球形Ti60钛合金粉与细小TiB2粉,通过低能球磨与反应热压烧结,成功制备了增强相呈网状分布的TiB晶须增强Ti60合金基(TiB_W/Ti60)复合材料。对TiB_W/Ti60复合材料进行热处理,以改善其组织结构与力学性能。结果表明:随着固溶温度的升高,TiB_W/Ti60复合材料基体中初生α相(密排六方相)含量减少,相应地转变β组织(α′(马氏体)+残留β相(体心立方相))含量增加,TiB_W/Ti60复合材料的抗拉强度升高,塑性降低;经过1 100℃/1h固溶处理之后,TiB_W/Ti60复合材料的室温抗拉强度为1 470 MPa,延伸率为1.9%。经过时效处理后,转变β组织中的α′相分解成细小α+β相。经过1 100℃/1h固溶+600℃/8h时效处理后TiB_W/Ti60复合材料的硬度达到HV538,抗拉强度达到1 552 MPa,延伸率为1.5%,经过1 000℃/1h固溶+600℃/8h时效处理,其抗拉强度达到1 460 MPa,延伸率为2.2%。     

Accelerated precipitation behavior of cast Mg-Al-Zn alloy by grain refinement

This study demonstrates that the precipitation behavior of β-Mg₁₇Al₁₂ phase during aging and the resultant variation in hardness and mechanical properties of cast Mg-Al-Zn alloy are strongly dependent on initial grain size. Grain size reduction accelerates discontinuous precipitation at the early stage of aging treatment by increasing the area fraction of grain boundaries that can act as nucleation sites for discontinuous precipitates (DP), but it does not influence DP growth rate. Grain refinement also prematurely terminates continuous precipitation because the formation of a large number of DP reduces the amount of Al dissolved in the matrix, which is required for the formation of continuous precipitates (CP). This promotion of DP formation and early termination of CP formation significantly decrease the peak-aging time to one-third. The enhanced precipitation behavior also leads to an additional hardness improvement in the aged alloy, along with an increase in hardness owing to grain boundary strengthening by grain refinement. The amount of increase in hardness changes with aging time, which is determined by the variation of three variables with aging time: DP fraction difference between refined and nonrefined alloys, hardness difference between DP and matrix, and matrix hardness difference between the two alloys. Grain refinement improves both tensile strength and ductility of the homogenized alloy owing to grain boundary strengthening and suppression of twinning activation, respectively. However, the loss of ductility after peak-aging treatment is greater in the refined alloy because of the larger amount of DP acting as a crack source in this alloy.     

Grain size-dependent Mg/Si ratio effect on the microstructure and mechanical/electrical properties of Al-Mg-Si-Sc alloys

Al-Mg-Si-Sc alloys with different Mg/Si ratio (<1.73 in wt.% vs>1.73 in wt.%) and different grain size (coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200 °C. In the coarse-grained Al-Mg-Sc-Sc alloys, the β″ precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio, while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β″ precipitation was found in the case of Si excess (Mg/Si ratio <1.73), much greater than in the case of Mg excess (Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-Si-Sc alloys, based on present understanding of the predominant factors on strengthening and conductivity, respectively.