Effect of heat treatment on microstructure and corrosion behavior of Al6061 alloy weldment

In this research, the corrosion behavior and microstructure of Al6061 alloy welded by GTAW (Gas tungsten arc welding) and followed by various heat treatments have been investigated. The microstructure of both weld metal (WM) and base metal (BM) was studied using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Corrosion behavior was investigated in 3.5 wt.% NaCl aqueous solution. Results indicated that BM consists of Fe-rich coarse intermetallic particles. These particles were found to act as cathodic regions with respect to surrounding matrix. Potentiodynamic polarization curves confirmed that WM is cathode rather than BM in different heat treatment cycles. Moreover, it was found that heat treatment led to displacement of the BM corrosion potential to noble direction. Observations of corroded surfaces confirmed localized corrosion.     

Ti particle-reinforced surface layers in Al: Effect of particle size on microstructure,hardness and wear

Two types of Ti particles are used in an ultrasonic impact peening (UIP) process to modify sub-surface layers of cp aluminium atomized, with an average size of approx. 20 μm and milled (0.3–0.5 μm). They are introduced into a zone of severe plastic deformation induced by UIP. The effect of Ti particles of different sizes on microstructure, phase composition, microhardness and wear resistance of sub-surface composite layers in aluminium is studied in this paper. The formed layers of a composite reinforced with smaller particles have a highly misoriented fine-grain microstructure of its matrix with a mean grain size of 200–400 nm, while reinforcement with larger particles results in relatively large Al grains (1–2 μm). XRD, SEM, EDX and TEM studies confirm significantly higher particle/matrix bonding in the former case due to formation of a Ti₃Al interlayer around Ti particles with rough surface caused by milling. Different microstructures determine hardness and wear resistance of reinforced aluminium layers: while higher magnitudes of microhardness are observed for both composites (when compared with those of annealed and UIP-treated aluminium), the wear resistance is improved only in the case of reinforcement with small particles.     

Effect of T6 heat treatment on damping characteristics of Al/RHA composites

In the present work, effect of T6 heat treatment on the damping behaviour of aluminum/rice husk ash (RHA) composites fabricated by vortex method was studied using dynamic mechanical analyser (DMA) at frequencies ranging from 1 Hz to 25 Hz at room temperature under three-point bending test mode. The matrix material for the present work was A356·2 and reinforced with different weight % of 4, 6 and 8 rice husk ash particles. It was observed that composite exhibits high damping capacities than unreinforced alloy and increases with increase in weight % and the storage modulus increases with the addition of RHA particles but decreases with the increase in weight %. The heat treated composites exhibit higher damping capacity than the composites without heat treatment and increases with the increase in weight % of the reinforcement and loss in the storage modulus was observed and further decreases with the increase in the weight % of reinforcement. The related mechanisms were also discussed.     

Effect of heat treatment temperature on microstructure and electromagnetic shielding properties of graphene/SiBCN composites

Three-dimensional (3D) graphene/SiBCN composites (GF/SiBCN) were prepared by depositing SiBCN ceramics in 3D graphene foam via the chemical vapor infiltration technique. The effect of the heat treatment temperature on the microstructure, phase composition, and electromagnetic properties of the GF/SiBCN composite was investigated. The SiBCN ceramics maintained an amorphous structure in the composite below 1400 °C above which the crystallinity of the free carbon phase gradually increased. While the Si₃N₄ and B₄C phases started to crystallize at 1500 °C and their crystallinity increased with temperature, SiC was observed at 1700 °C. The electromagnetic shielding effectiveness of GF/SiBCN increased with the heat treatment temperature.     

热处理对热等静压Sip/Al-Cu复合材料显微组织和力学性能的影响

采用元素粉作为原料,通过热等静压技术(HIP)制备出50％ SiP/Al-Cu和70％SiP/Al-Cu(体积分数)复合材料,研究固溶处理和峰值时效处理对复合材料显微组织、Al2Cu相溶解过程及力学性能的影响.结果表明:热等静压技术制备的SiP/Al-Cu复合材料完全致密,组织均匀细小,材料由Si相、Al相和Al2 Cu组成,白色Al2Cu相产生于原始的Cu粉与Al粉界面处.在516℃固溶处理2h后,70％ SiP/Al-Cu复合材料中的Al2Cu相全部溶入Al基体中,而50％ SiP/Al-Cu复合材料中还残留少量Al2Cu相.经过峰值时效处理后,50％ SiP/Al-Cu和70％ SiP/Al-Cu复合材料的抗弯强度为548 MPa和404 MPa,相对于热等静压态分别提高了38.81％和13.51％,复合材料的强度显著增强.     

Effect of heat treatment on microstructure and interface of SiC particle reinforced 2124 Al matrix composite

The microstructure and interface between metal matrix and ceramic reinforcement of a composite play an important role in improving its properties. In the present investigation, the interface and intermetallic compound present in the samples were characterized to understand structural stability at an elevated temperature. Aluminum based 2124 alloy with 10 wt.% silicon carbide (SiC) particle reinforced composite was prepared through vortex method and the solid ingot was deformed by hot rolling for better particle distribution. Heat treatment of the composite was carried out at 575 °C with varying holding time from 1 to 48 h followed by water quenching. In this study, the microstructure and interface of the SiC particle reinforced Al based composites have been studied using optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), electron probe micro-analyzer (EPMA) associated with wavelength dispersive spectroscopy (WDS) and transmission electron microscopy (TEM) to identify the precipitate and intermetallic phases that are formed during heat treatment. The SiC particles are uniformly distributed in the aluminum matrix. The microstructure analyses of Al–SiC composite after heat treatment reveal that a wide range of dispersed phases are formed at grain boundary and surrounding the SiC particles. The energy dispersive X-ray spectroscopy and wavelength dispersive spectroscopy analyses confirm that finely dispersed phases are CuAl₂ and CuMgAl₂ intermetallic and large spherical phases are Fe₂SiAl₈ or Al₁₅(Fe,Mn)₃Si. It is also observed that a continuous layer enriched with Cu and Mg of thickness 50–80 nm is formed at the interface in between Al and SiC particles. EDS analysis also confirms that Cu and Mg are segregated at the interface of the composite while no carbide is identified at the interface.     

Effects of microstructure on optimum heat treatment conditions in metal-matrix composites

It is well known that the microstructure of metal-matrix composite materials is significantly different from that of the unreinforced matrix. Heat treatments which optimized strength values in the matrix therefore, no longer do so in the composite. It is thus beneficial to find these variations in the heat treatment process, and to pinpoint the microstructural mechanisms responsible. It is known that, in addition to a higher dislocation density, the composite also has a very fine grain size and many whisker interfacial nucleation sites. This study has found that the time required for solutionizing appears to be much shorter in the composite primarily due to the very small grain size. It was also observed that artificial ageing was not very effective in the composite since the precipitates nucleated and grew on the whisker interfaces, therefore, only natural ageing was necessary to achieve peak tensile and yield strengths.     

热处理对热等静压SiP/Al-Cu复合材料显微组织和力学性能的影响

采用元素粉作为原料, 通过热等静压技术(HIP)制备出50%Si_P/Al-Cu和70%Si_P/Al-Cu(体积分数)复合材料, 研究固溶处理和峰值时效处理对复合材料显微组织、 Al₂Cu相溶解过程及力学性能的影响。结果表明: 热等静压技术制备的Si_P/Al-Cu复合材料完全致密, 组织均匀细小, 材料由Si相、 Al相和Al₂Cu组成, 白色Al₂Cu相产生于原始的Cu粉与Al粉界面处。在516 ℃固溶处理2 h后, 70%Si_P/Al-Cu复合材料中的Al₂Cu相全部溶入Al基体中, 而50%Si_P/Al-Cu复合材料中还残留少量Al₂Cu相。经过峰值时效处理后, 50%Si_P/Al-Cu和70%Si_P/Al-Cu复合材料的抗弯强度为548 MPa和404 MPa, 相对于热等静压态分别提高了38.81%和13.51%, 复合材料的强度显著增强。     

Effect of heat treatment on the microstructure and property of cold-sprayed nanostructured FeAl/Al2O3 intermetallic composite coating

It is difficult to deposit dense intermetallic compound coatings by cold spraying directly using compound feedstock powders due to their intrinsic low temperature brittleness. A method to prepare intermetallic compound coatings in-situ employing cold spraying was developed using a metastable alloy powder assisted with post heat treatment. In this study, a nanostructured Fe(Al)/Al₂O₃ composite alloy coating was prepared by cold spraying of ball-milled powder. The cold-sprayed Fe(Al)/Al₂O₃ composite alloy coating was evolved in-situ to FeAl/Al₂O₃ intermetallic composite coating through a post heat treatment. The effect of heat treatment on the phase formation, microstructure and microhardness of cold-sprayed Fe(Al)/Al₂O₃ composite coating was investigated. The results showed that annealing at a temperature of 600 °C results in the complete transformation of the Fe(Al) solid solution to a FeAl intermetallic compound. Annealing temperature significantly influenced the microstructure and microhardness of the cold-sprayed FeAl/Al₂O₃ coating. On raising the temperature to over 950 °C, diffusion occurred not only in the coating but also at the interface between the coating and substrate. The microhardness of the FeAl/Al₂O₃ coating was maintained at about 600HV_0.1 at an annealing temperature below 500 °C, and gradually decreased to 400HV_0.1 at 1100 °C.     

脉冲电流密度对Ni-SiC镀层微观结构和显微硬度的影响

采用脉冲电沉积方法,在压缩机阀片表面制备Ni-SiC镀层。利用原子吸收分光光度计、透射电镜和硬度计研究脉冲电流密度对Ni-SiC镀层SiC粒子复合量、微观结构和显微硬度的影响。结果表明,随着脉冲电流密度的增大,Ni-SiC镀层SiC粒子的复合量先增加后略有降低。在脉冲电流密度为7A/dm2时,镀层SiC粒子的复合量高达9.92%(质量分数)。脉冲电流密度为7A/dm2时,镀层致密、晶粒细小,SiC粒子均匀分布于镀层中,且团聚现象较少。当脉冲电流密度为7A/dm2时,镀层的显微硬度高达842.9Hv。     

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%。     

Effect of Ca additions on microstructure and microhardness of an as-cast Mg-5.0 wt.% Al alloy

The effects of Ca additions (0.5-2.0 wt.%) on the microstructure and the microhardness of an as-cast Mg-5.0 wt.% Al alloy have been investigated. The coarse microstructure of the base alloy can be refined through adding Ca. DSC and TEM results showed that, as Ca additions increased up to 1.5 wt.% Ca, the β-Mg₁₇Al₁₂ phase was completely replaced by a (Al, Mg)₂Ca phase. The Vickers microhardness of the as-cast Mg-Al-Ca alloys increased with increasing Ca content. Tests on the Mg-5.0Al-2.0Ca (wt.%) alloy showed an indentation size effect, which was well described by Meyer's Law.     

Effects of cooling rate and heat treatment on the microstructure of iron-based titanium carbide composites

The microstructural response of iron-carbon-TiC components produced by a liquid route to changes in cooling conditions and post-solidification heat treatments has been investigated. Heat treatments of pure Fe-TiC composite materials have been found to produce only minor changes in the TiC morphology and distribution with reduction in hardness resulting from some TiC precipitation and depletion of the iron matrix of titanium and carbon. As-cast composites containing Fe-2.4% C/10% TiC and Fe-3.27% C/10% TiC exhibit a white cast iron matrix containing dispersed TiC. Subsequent heat treatment of this material at 750° C renders the matrix malleable, replacing the cementite by free graphite with no apparent alteration to the TiC morphology or distribution.     

T6热处理对复式连通双连续相SiC/Al复合材料性能的影响

研究了T6热处理(固溶处理 时效)对复式连通双连续相SiC/A1复合材料的组织和压缩性能的影响.结果表明,经T6热处理后,复合材料基体中第二相共晶硅从粗大的针状变成了细小的粒状,增强了弥散强化效果,时效析出相Mg2Si强化了基体;界面附近的基体中残余应力增大,使复合材料的压缩强度显著提高,材料的弹性模量和塑性稍稍降低.随着固溶时间的延长,复合材料的压缩强度先升高后降低.其影响机制是,随着固溶时间的延长共晶硅扩散充分,球化完全,继而粗化长大,从而提高了弥散强化效果.随着时效时间的延长,材料中的残余应力减小,位错密度降低,时效强化相Mg2Si的强化能力减弱,使复合材料的压缩强度降低.     

真空退火对原位Al2O3/Fe-Cr-Ni增强复合材料性能的影响

铁铬镍合金具有良好的高温强韧性和抗蠕变性,被广泛应用于制造航空发动机、工业燃气轮机等设备。利用原位合成和热压烧结工艺制备Al2O3/Fe-Cr-Ni复合材料。为减少脆性相对复合材料性能的影响,将热压烧结试样在1000℃下真空保温2h后退火。采用XRD和SEM等测试方法,研究热处理后Al2O3/Fe-Cr-Ni复合材料的微观结构和常温力学性能。结果表明:Al2O3/Fe-Cr-Ni复合材料主要由Fe-Cr-Ni合金相、Fe-Cr相和Al2O3陶瓷增强相组成。热压烧结试样的维氏硬度、抗弯强度和断裂韧度分别为4.16GPa、298.31MPa和8.04MPa·m1/2。经1000℃高温热处理后,复合材料中Fe-Cr相发生奥氏体转变和合金基体晶粒长大,导致硬度下降至2.98GPa。Fe-Cr-Ni合金基体中韧性相含量和基体连续性增加,使该复合材料的抗弯强度和断裂韧度明显上升,其值分别为459.33MPa和12.81MPa·m1/2。     

SiCp表面化学镀对SiCp/Al复合材料微结构及热性能影响

为了改善SiCp与Al基体之间的界面,在碱性条件下,甲醛作为还原剂,采用化学镀的方法在SiCp表面沉积铜层,然后采用无压渗透方法制备SiCp/Al复合材料。采用X射线衍射仪、3D立体视频显微镜、扫描电子显微镜来分析化学镀后SiCp和复合材料的表面、界面形貌、组织结构及物相,并通过EDS能谱对复合材料表面元素成分分析,利用激光闪光法测定复合材料导热系数。结果表明,相比酒石酸钾钠单一络合剂,采用酒石酸钾钠和EDTA-2Na组成的双络合剂的SiCp镀层更致密,且镀层未被氧化,复合材料界面结合良好,界面厚度为2.5~3μm,有AlCu2相生成,无Al4C3脆性相存在。室温下,镀铜后的复合材料热导率达到181 W/(m·K),远高于没有表面改性的复合材料热导率102 W/(m·K)。     

石墨化处理对不同高织构含量C/C复合材料微结构的影响

采用化学气相沉积工艺制备出炭毡增强炭/炭(C/C)复合材料和3K炭布叠层增强C/C复合材料,并对材料进行2500℃高温石墨化处理。利用X射线衍射仪;偏光显微镜及拉曼光谱仪对所制材料进行表征。结果表明,炭毡C/C复合材料基体是单一的高织构(HT)热解炭,3K炭布叠层C/C复合材料的基体是带状组织,从纤维表面向外依次为各向同性热解炭、HT和中织构(MT)热解炭,其中HT含量低于50%;沉积态和热处理后,两种C/C复合材料都具有相似的石墨化度,且热处理后的石墨化度超过80%,但Lc值差异明显,炭纤维、MT和HT热解炭的La值均升高,其中HT热解炭升幅明显大于炭纤维和MT热解炭。HT热解炭的含量是导致这两种C/C复合材料具有相似石墨化度而Lc值却显著差异的原因。     

热处理对TiAl基合金相变和显微组织的影响

TiAl基合金净形成形是克服其难加工成形的有效方法，但该合金铸态组织较粗大，不利于提高其综合性能，如何细化该合金的微观组织成为当前研究热点之一。本文重点讨论了通过热处理改变TiAl基合金微观组织的技术途径，包括双相区热处理，双温热处理，循环热处理，快速加热循环热处理等，并分析了各种热处理条件下组织演变的微观机制，其中快速循环热处理对细化原始组织效果最为显著。     

热处理对Mn-Cu合金微观组织和阻尼性能的影响

通过X射线衍射仪（XRD）、扫描电子显微镜（SEM）和动态机械热分析仪（DMA）的相结构、微观结构和阻尼性能的测试结果,研究了热处理工艺对轧制态CuMn50合金的微观组织和阻尼性能的影响。结果表明合金的阻尼性能随着应变振幅先缓慢增加而后迅速增加;随着冷速提高,Mn-Cu合金开始出现晶粒,阻尼性能降低,缓慢冷却有利于富锰区的产生,起到了时效的作用;炉冷时效后,阻尼性能进一步提高,时效时间对炉冷试样的微观结构和阻尼性能没有影响;水冷时效后,随着时效时间的增大,合金的晶粒先变得粗大随后析出第二相α-Mn,阻尼性能先增大到峰值随后略为减低,840℃固溶0.5h又420℃时效8h后,合金的阻尼性能达到最好。     

Research on heat treatment of TiBw/Ti6Al4V composites tubes

Heat treatment with different parameters were performed on the hot-hydrostatically extruded and swaged 3.5 vol.% TiBw/Ti6Al4V composites tubes. The results indicate that the primary α phase volume fraction decreases and transformed β phase correspondingly increases with increasing solution temperatures. The α + β phases will grow into coarse α phases when the aging temperature is higher than 600 °C. The hardness and ultimate tensile strength of the as-swaged TiBw/Ti6Al4V composite tubes increase with increasing quenching temperatures from 900 to 990 °C, while they decrease with increasing aging temperatures from 550 to 650 °C. A superior combination of ultimate tensile strength (1388 MPa) and elongation (6.1%) has been obtained by quenching at 960 °C and aging at 550 °C for 6 h. High temperature tensile tests at 400–600 °C show that the dominant failure modes at high temperatures also differ from those at room temperature.