高体积分数SiCp/7075Al复合材料的时效析出行为

高体积分数SiC颗粒增强7系铝基复合材料(SiCp/7XXXAl)具有高比强度比刚度等特点,因此适宜作为结构件在航空航天、汽车等领域应用。本文采用压力浸渗法制备了45vol.%的SiCp/7075Al复合材料,并对复合材料和基体合金的时效行为进行了系统的研究。DSC分析结果发现复合材料的η′相和η相的放热峰分别比基体7075合金降低了4.4℃和0.5℃。复合材料与7075铝合金达到峰时效的时间均为9h,峰时效时复合材料与基体7075铝合金的硬度分别提高了38.7%(从213.4到296HB)和107.6%(从98.2到203.9HB)。颗粒的加入使得基体中的位错密度显著增加,这有利于析出相的形核。但另一方面,合金元素在界面的偏聚会抑制析出相的析出。因此,SiCp/7075Al复合材料的析出行为是两方面共同作用的结果。     

亚微米Al2O3P/Al-Mg-Si复合材料时效行为

为了研究亚微米级Al₂O₃颗粒对基体合金时效过程的影响规律,在 6061 铝合金基础上调整Mg、Si含量,采用压力浸渗法,制备了Al₂O₃体积分数为30%的亚微米级Al₂O_3P/Al-2.26Mg-0.63Si复合材料。通过硬度试验、SEM和TEM等手段,研究了复合材料及其基体合金的时效行为。结果表明,Al-2. 26Mg-0.63Si 合金的时效过程比较明显,随时效温度的提高峰时效时间提前,190℃时出现时效软化现象。亚微米Al₂O₃颗粒的加入强烈抑制复合材料的时效过程,时效曲线未出现明显时效峰。分析认为,由于大部分Mg 元素被消耗在界面形成MgAl₂O_4,且基体中位错稀少,不利于溶质原子扩散,因此复合材料中沉淀相在过时效阶段仍停留在GP区状态,没有充分长大,时效析出受到抑制。     

微量Mg元素添加对Cu-Cr合金析出行为及性能的影响

通过熔炼铸造工艺制备了Cu-Cr和Cu-Cr-Mg合金,评价了Mg元素对Cu-Cr合金硬度、导电和抗软化性能的影响,研究了Mg元素对Cu-Cr合金析出相的细化作用,探讨了Mg元素的迁移行为。结果表明,相比于Cu-Cr二元合金,时效态Cu-Cr-Mg合金具有更高的硬度和软化温度,且保持较高的导电性能。两种合金的主要时效强化相均为纳米Cr析出相,Mg元素的加入抑制了纳米沉淀相的长大和结构转变,峰时效态Cu-Cr-Mg合金的析出相与基体可能仍保持共格界面关系,过时效态合金中出现与Heulser相结构相同的析出相,且峰时效态Cu-Cr-Mg合金经过高温保温处理后,其强化相的尺寸明显小于Cu-Cr合金析出相。EDS的结果表明,在时效初期Mg和Cr共存于析出相内部,而在时效后期析出相内部只有Cr元素存在,Mg元素发生迁移,同时理论估算结果显示,Mg元素可明显降低Cu(fcc)/Cr(bcc)之间的界面能,导致其偏聚于基体/析出相界面处,这可能是Mg元素能够细化析出相和提高合金性能的主要原因。     

Cu-Ni-Si合金的时效析出与再结晶

通过分析时效期间Cu-Ni-Si合金显微硬度、导电率及微观组织的变化,研究了析出相和再结晶行为的相互作用,以期为该合金多级复合工艺的制定提供参考.研究发现,时效初期析出相对随后的再结晶过程具有强烈阻碍作用.在450、550℃较低温度时效时,合金发生原位再结晶,析出相在其体积分数略微升高或不变的情况下发生粗化;导电率上升趋势为先快后慢并趋于稳定,因而其变化曲线上无峰值出现;显微硬度则由于时效后期析出颗粒粗化,析出强化效果降低而出现峰值.在750℃高温时效时,合金发生不连续再结晶,析出相在体积分数略有降低的情况下发生粗化;导电率先快速上升后缓慢下降,因而出现峰值,而显微硬度由于析出物迅速粗化,一开始就表现为持续下降.     

SiCw／6061Al复合材料时效机制的研究

研究了ＳｉＣ晶须增６０６１铝基复合材料及基体合金在１７０℃和１９０℃时效时的析出行为,结果表明：复合材料达到峰时效的时间均较基体合金有所提前。ＴＥＭ观察发现：复合材料基体中的位错密度明显高于相应铝合金;达到峰时效时前者析出相的数量明显少于后者,而前者析出相的尺寸却明显大于后者,分析了复合材料基体中高密度位错析出相形核和长大的影响。     

添加Sn对不同Mg/Si比Al-Mg-Si合金时效硬化和析出行为的影响

采用硬度测试和透射电镜研究Sn对不同Mg/Si比Al-Mg-Si合金时效硬化与析出行为的影响。结果表明：添加Sn虽然增加了低Mg/Si比合金峰值时效的析出相密度，但也降低了β″相的析出速度，从而降低了低Mg/Si比合金峰时效前的硬化速度和峰时效硬度。过时效阶段，含Sn合金的高析出相密度提高了低Mg/Si比合金过时效硬度。对于高Mg/Si比合金，添加Sn不仅增加合金的析出相密度，同时也提高了β″相的析出速度，从而增加了合金的硬化速度和峰时效硬度。     

AlNp/LY1 2复合材料时效行为及微观组织

采用粒径为0.5μm和10μmAlN颗粒用挤压铸造法制备出两种体积分数为50％的AlNp/LY12复合材料,研究了两种材料的时效硬化行为及微观组织结构。结果表明：AlN颗粒的存在未改变基体合金的沉淀析出次序,但加速了基体合金的时效析出速率,且大颗粒的促进作用比小颗粒更明显。透射电镜观察表明,复合材料中基体内的位错密度高于基体LY12合金,并随增强体颗粒增大而增多,颗粒加入后引入的大量相界面和高密度位错是时效硬化速率加快的主要原因。     

时效温度对Mg-12Gd-3Y-1Sm-0.5Zr合金组织和力学性能的影响

采用X射线衍射、光学显微镜、透射电子显微镜、显微硬度和拉伸性能测试等手段,研究时效热处理温度对Mg-12Gd-3Y-1Sm-0.5Zr合金组织和性能的影响。结果表明,Mg-12Gd-3Y-1Sm-0.5Zr合金在200,250℃和300℃峰时效时,晶粒大小随时效温度的升高而逐渐增大,晶内颗粒状的第二相数量增多,硬度峰值出现的时间逐渐缩短。合金时效温度在200,250℃时,析出相为β′相,时效温度在300℃时,析出相为β相。合金在250℃峰时效时力学性能最优。在200,250℃峰时效热处理的合金在从室温到200,250℃和300℃拉伸过程中抗拉强度随拉伸温度的升高先升高后降低,出现了抗拉强度反常温度效应,而在300℃峰时效热处理后的合金未出现该反常现象。     

Mullite／Al-Mg-Si复合材料时效行为研究

选用挤压铸造法制备Mullite／Al-Mg-Si复合材料，采用用硬度测试（HB）、扫描电镜（SEM）、差示扫描量热仪（DSC）和透射电镜（TEM）等手段，研究了莫来石短纤维增强不同镁硅比（Mg／Si=2，Mg／Si〈2，Mg／Si〉2）成份的Al-Mg-Si复合材料及其基体合金的时效行为。结果表明：复合材料具有和基体舍金相似的时效硬化曲线，相同的析出序列；Mullite纤维的引入提高了基体合金的时效硬度，并一定程度地加速了基体合金的时效硬化过程，但对GP区的抑制不明显；Si或Mg元素的富余都加速了复合材料及其基体合金的时效硬化过程，且两类材料的时效峰明显提前。Mullite短纤维与富余的甄或Mg元素对复合材料的时效硬化过程具有交互促进作用。     

热处理对Al-Cu合金电导率的影响

通过电导率测量、硬度分析和金相组织观察,研究了不同热处理工艺对Al-4.0%Cu(质量分数,下同)合金电导率的影响,分析了析出相、合金硬度和电导率之间的关系。实验结果表明,Al-4.0%Cu合金的电导率主要受基体中Cu固溶度和析出相状态的影响;双级时效处理对电导率和硬度的决定因素主要为二级时效的温度与时间,一级时效后合金的电导率和硬度会随着二级时效发生改变;退火后的Al-4.0%Cu合金于350℃保温24h后,可获得较高的电导率,此时基体中的析出相为细小、弥散的θ相。     

Aging behavior and precipitation kinetics of SiCp/6061AI composites

The aging behavior of SiC particle reinforced 6061 aluminum matrix composites was investigated with Brinell hardness measurement, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For 40 vol%SiCp/6061Al composite, the age-hardening efficiency was lower than that of monolithic 6061Al alloy and its high strength was mainly attributed to the introduction of high volume fraction particles. At low aging temperature, the aging process of composite was more accelerated than that of 6061Al alloy. With temperature increasing, the time to reach the peak hardness was shortened and the precipitation processes became accelerated. Moreover, precipitation process observed in the matrix alloy was altered by the addition of SiC particles. Formation of G.P. region was severely suppressed and the activation energy of phase decreased, which made the precipitation of phase easier than that of 6061Al alloy.     

Aging Behavior of High Volume Fraction SiC Particles Reinforced 2024Al Composite

2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1μm diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices. Therefore, the aging peak of the composite appears earlier than that of 2024AI alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.     

Aging Behavior of High Volume Fraction SiC Particles Reinforced 2024Al Composite

2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1 μm diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024Al composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices.Therefore, the aging peak of the composite appears earlier than that of 2024Al alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.     

Aging behavior of a 2024 Al alloy-SiCp composite

In the present research work the 2024 aluminum alloy was reinforced with SiC particles via powder metallurgy method. The effect of heat treatment conditions on artificial aging kinetics was investigated. The solution treatment of the composite sample and the unreinforced alloy was carried out at 495 °C for 1, 2 and 3 h followed by aging at 191 °C for various aging times between 1 and 10 h. The existence of SiC particles led to increasing the peak hardness of the alloy. The peak hardness of the composite sample took place at shorter times than that of the unreinforced alloy for the samples solution treated for 2 and 3 h, but took place at longer times for the samples solution treated for 1 h. The suitable solution treating time was about 2 h for both the composite and the unreinforced alloy that led to the fastest aging kinetics and the maximum hardness. At the solution treating time shorter than 2 h due to incomplete dissolution of precipitates, the aging kinetics decelerated and the hardness values decreased. X-ray diffraction studies indicated the presence of precipitation phases such as CuAl₂ and CuMgAl₂ in the composite in both as-extruded and solutionized conditions. For the samples solution treated more than 2 h, hardness values decreased due to the grain growth of matrix but no change occurred in the aging kinetics.     

27vol%-SiCw/6061Al复合材料170℃时效的双硬度峰现象

本文采用挤压铸造法制备27%vol-SiC_w/6061Al复合材料,并对该种复合材料在170℃时效的动力学过程进行了研究,结果发现在时效动力学曲线上出现了双硬度峰现象。DSC分析结果表明复合材料中β'相及β相的析出温度与6061合金相对比分别降低56℃和76℃,由此讨论了SiC晶须加入对复合材料脱溶过程的影响,并认为双时效峰现象与材料中的析出由G.P.区向β'相的转化有关,通过TEM观察,发现复合材料时效过程中析出相形貌的变化,在组织结构上提供了确凿的证据。     

位错对高体积分数SiCP/2024Al时效行为的影响

采用粒径为1μm的SiC颗粒,用挤压铸造法制备出体积分数为45 %的SiC_P/2024Al复合材料,研究了位错对高体积分数SiC_P/2024Al时效行为的影响。结果表明,复合材料中的高密度位错可以湮灭大量的淬火空位,这在一定程度上抑制了GP区的析出。但是,高密度位错的存在降低了其它析出相的热扩散激活能,促进了析出相形核;还能为原子的管道扩散提供通道,促进了溶质原子的扩散,加速析出相的长大,在宏观上表现为对时效行为的促进,使峰时效提前。高密度的位错为强烈依赖于位错等缺陷形核的θ'和S'相提供许多优先形核的场所,使复合材料中的形核密度增加,同时使析出相的尺寸减小,所以复合材料中的析出相呈现细小弥散的分布特点。      

Production and properties of SiCp-reinforced aluminium alloy composites

A vacuum infiltration process was developed to produce aluminium alloy composites containing various volume fractions of ceramic particles. The matrix composites of aluminium with 9.42 wt%Si and 0.36 wt%Mg containing up to 55 vol% SiCp were successfully infiltrated and the effect of infiltration temperature and volume fraction of particle on infiltration behaviour was investigated. In addition to aluminium powder, magnesium was used to improve the wetting of SiC particles by the molten aluminium alloy. The infiltration rate increased with increasing infiltration time, temperature and volume fraction of particle, but full infiltration appeared at the optimum process parameters for the various volumes of fraction composite compacts. In addition, the microstructure, hardness, density, porosity and wear resistance of the composites were also examined. It is observed that the distribution of SiC particles was uniform. The hardness and density of the composite increased with increasing reinforcement volume fraction and porosity decreased with increasing particle content. Moreover, the wear rate of the composite increased with increasing load and decreased with increasing particle content.     

Precipitation characteristics of Cu–15Cr–0·15Zr in situ composite

Abstract

The precipitation characteristics of Cu–15Cr–0·15Zr in situ composite made by cold drawing have been studied using analytical TEM and hardness measurement. It has been observed that the in situcomposite reaches peak hardness at a lower aging temperature than the corresponding alloy which is not subjected to cold working prior to aging treatment. The Cr rich precipitates in the peak aged composite are much smaller than those in the peak aged alloy. Under peak aging conditions, precipitation free zones adjacent to the grain boundaries of the Cu matrix are also observed in both the alloy and the composite. The addition of Zr enhances the precipitation hardening effect in the alloy and the composite. The major mechanism of this enhancement may be through increasing the Cr rich precipitate nucleation rate and precipitate/matrix interfacial energy.     

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%。     

Incorporation of new technique for processing of Al/SiCp composites based on evaporative pattern casting (EPC) method

Abstract

A336 Al matrix composites containing different volume fraction and mean mass particle size of SiC particles as the reinforcing phase were synthesised by evaporative pattern casting (EPC) route. The process consisted of fabricating of EPS/SiC_p composite pattern followed by EPC of A336 Al alloy. The EPS/SiC_p pattern was made by blending SiC particles with expandable polystyrene (EPS) beads and placing them in expanding mould heating with steam until EPS beads expand completely. Uniform distributed SiC particles around the EPS beads and locally movement of them during pouring and degradation leads to homogenous distribution of particles in final Al/SiC_p composite. Higher modulus, strength and hardness were observed in the composites than the unreinforced Al alloy part. The fracture surfaces of the composite samples exhibited dimple surfaces and fracture in SiC particles.