ZL系列铸铝合金的微弧氧化

对含硅量为 8 %～ 12 %的ZL系列铸铝合金的微弧氧化工艺条件、膜层结构以及成膜过程进行了研究。结果表明 :采用不对称交变电压和在以硅酸钠为主要成分的复合电解液体系中 ,铸铝合金表面可获得一层性能优异的微弧氧化膜层。电子能谱 (EDS)和X射线衍射 (XRD)分析结果表明微弧氧化膜主要由Al,Si和O元素组成 ,膜的相结构主要为 η Al2 O3 ,α Al2 O3 和SiO2 ,并含有γ Al2 O3 和Mg ,W ,Cu等元素的氧化物。扫描电镜 (SEM)分析表明微弧氧化膜由致密层 (内层 )和疏松层 (外层 )构成 ,疏松层表面存在许多气孔 ,而致密层完整光滑 ,具有较高的显微硬度和优异的耐磨耐蚀性能     

Definition of quality in cast aluminum alloys and its characterization with appropriate indices

In this paper, the issue of “quality” of cast aluminum alloys from various viewpoints is interpreted. Many methods to characterize the quality of materials are available; the methods used currently for the quality evaluation of cast aluminum alloys include nondestructive testing, characterization of the microstructure, and mechanical testing. With regard to mechanical testing, a number of quality indices have been devised to evaluate and characterize the quality of cast aluminum alloys. As these quality indices use different mechanical properties for the quality evaluation, they are expected to lead to different results. In this work, the application of proposed quality indices and their suitability is discussed for a number of situations, including minor variations in chemical composition, different solidification rate, solid solution and artificial aging heat treatments.     

Ti-Al合金高温氧化膜的形态及形成

利用Pt丝标记法和定量成分分析等研究方法,研究Ti-Al(2%~75%Al,摩尔分数)合金在1 173 K的大气中经24 h氧化形成的氧化膜的组织形态和生长过程。结果表明:在氧化膜中观察到Al2O3存在3种不同分布形式,即当2%65%时,氧化膜由单一的Al2O3构成。Ti-Al合金高温氧化膜中Al2O3和TiO2的分布可分为4种组织形态。采用Pt标记可清晰观察到氧化膜内、外层,外层氧化膜的形成与Al离子向外扩散有关,内层氧化膜的形态受MO/M界面热力学平衡控制。     

不锈钢表面高温热处理氧化皮的常温去除机理研究

在高温使用环境或热处理中,不锈钢表面容易形成氧化皮,影响了不锈钢零件的应用.利用超声电化学方法去除不锈钢表面的高温热处理氧化皮,即在超声波的辅助作用下,电解不锈钢表面氧化皮,并研究了电解和超声波对氧化皮去除作用规律.试验结果表明:辅以超声波作用的电化学技术可以在常温下快速去除不锈钢表面的高温热处理致密氧化皮,恢复了不锈钢的金属色泽表面.超声波不仅可以对不锈钢表面氧化皮产生力学效应,而且可以明显加快电化学阳极反应速率和氧化皮的脱落速度.     

Evaluation of the effects of variations in chemical composition on the quality of Al-Si-Mg,Al-Cu,and Al-Zn-Mg cast aluminum alloys

The effect of slight variations in chemical composition on the quality of cast aluminum alloys from three different major alloy systems was evaluated. For the evaluation of the alloy quality, an index Q _D adjusted to damage tolerance requirements that are currently involved for the design of advanced lightweight structures is used. The quality index Q _D accounts for tensile strength and ductility as well as for material failure through yielding or fracture. For this investigation, experimental results obtained for variations in chemical composition of the alloy systems Al-Si-Mg, Al-Cu, and Al-Zn-Mg were exploited. In total, castings from 37 different batches from 10 aluminum alloys, varying in chemical composition, were evaluated. Quality characterization and alloy quality ranking were made by evaluating results of 512 tensile tests using the index Q _D as well as, for comparison, the quality index Q, which is currently used by the industry. The results obtained involving the index Q _D seem to be more realistic, from the viewpoint of damage tolerance design requirements.     

AC8C铸造铝合金的组织缺陷分析

采用化学成分分析、断口扫描、金相检验、硬度测试等方法,对AC8C铸造铝合金内燃机活塞断裂原因进行了分析.结果表明,活塞显微组织中d-固溶体粗大、共晶硅和Al2Cu相聚集,导致合金力学性能降低,使共晶硅和Al2Cu相集中分布的区域发生早期脆性断裂.铸造和固溶时效处理工艺不当是造成铝合金组织缺陷的原因.     

Effects of acetic acid on microstructure and electrochemical properties of nano cerium oxide films coated on AA7020-T6 aluminum alloy

Nano cerium oxide films were applied on AA7020-T6 aluminum alloy and the effects of acetic acid concentration on the microstructure and electrochemical properties of the coated samples were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), crack-flee films with well-developed grains were obtained and grain sizes of the films decreased. Elimination of cracks and decreasing grain size of the nano cerium oxide films caused corrosion resistance to increase.     

机械振动对铸造铝合金组织和性能的影响

分析振动方式对ZL101铝合金消失模铸件组织和力学性能的影响。结果表明,机械振动后合金组织明显细化;垂直振动时,合金晶粒尺寸最小,孔隙率最低,抗拉强度最大;ZL101合金垂直振动后,不同厚度处的组织存在较大差别,厚度越大,振动细化效果越显著。     

Non-dendritic structural 7075 aluminum alloy byliquidus cast and its semi-solid compression behavior

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Formation of unidirectional nanoporous structures in thickly anodized aluminum oxide layer

A series of anodic aluminum oxide(AAO) was grown on the commercially pure 1050 aluminum sheet by controlling electrolyte temperature (2–15 °C) and an odizing time (0.5–6 h), using a fixed applied current density of 3 A/dm² in diluted sulfuric acid electrolyte. A crack-free thick AAO with the thickness of 105–120 μm and containing unidirectional nano sized pores (average pore diameter of 5–7 nm) is successfully achieved in the specimens anodized for 2 h, irrespective of electrolyte temperature. When anodizing time reaches 6 h, very thick AAO with the thickness of 230–284 μm is grown, and average diameter of unidirectional pores is in the range of 6–24 nm. The higher values in both the AAO thickness and pore diameter are attained for the specimens anodized at higher temperatures of 10–15 °C. A crack is observed to exist in the AAO after anodizing up to 4 h and more. A higher fraction (more than 9%) of the crack is shown in the specimens anodized at higher temperatures of 10–15 °C for 6 h and a considerable amount of giant cracks are contained.     

Strength distribution at interface of rotary-friction-welded aluminum to nodular cast iron

The morphology, size and composition of intermetallic compound at the interface of AI 1050 and nodular cast iron were studied by electron microprobe analysis（EMPA） and scan electron microscopy （SEM）, respectively. The bond strength of the interface was measured by the tensile tests and the morphology of the fracture surface was observed by SEM. The observation of the interface reveals that there are two distinct morphologies： no interrnetallic compound exists in the central area at the interface; while numbers of intermetallic compounds （FexAly） are formed in the peripheral area due to the overfull heat input. The tensile tests indicate that the distribution of strength in radial direction at the interface is irdaomogeneous, and the central area of the interface performs greater bond strength than the peripheral area, which proves directly that the FexAly intermetallic compounds have a negative effect on the integration of interface. The morphology on the fracture surface shows that the facture in the central area at the interface has characteristic of the ductile micro-void facture. So it is important to restrain the form of the intermetallic compound to increase the bond strength of the AI 1050 and nodular cast iron by optimizing welding parameters and the geometry of components.     

Formation of zinc aluminum mixed metal oxide nanostructures

We report a method for synthesizing zinc aluminum layered double hydroxide (ZnAl:LDH) nanostructures at room temperature. The ZnAl:LDH nanoplates could be converted into zinc aluminum mixed metal oxide (MMO) nanostructures by calcination in air. The crystalline nature and morphology of the MMO nanostructures could be tuned by varying the calcination temperature. At low calcination temperatures (450-650 °C), nanostructures were composed of crystalline ZnO regions and amorphous regions. The crystalline orientations of the ZnO crystal grains were almost identical throughout the nanostructure. At calcination temperatures above 750 °C, ZnAl₂O₄ crystal grains appeared and amorphous regions could not be found in MMO nanostructures. As the calcination temperature increased, the crystal grain size and surface roughness of MMO nanostructures increased. Calcination at 950 °C resulted in the formation of MMO nanoparticles. The optical properties of the MMO nanostructures were probed by UV-vis diffuse reflectance spectroscopy. The spectra varied depending on their dimensions and crystalline natures.     

Non-isothermal annealing of a cold rolled commercial twin roll cast 3003 aluminum alloy

It is shown that the recrystallization behavior of a cold rolled twin roll cast, commercial 3003 aluminum alloy under non-isothermal conditions, can be satisfactorily modeled by combining the approaches developed by Semiatin et al. and Puchi et al. The first approach allows the determination of the apparent activation energy for recrystallization without any ambiguity, information that can then be used in the second approach to define clearly the search range for the value of the apparent activation energy for recrystallization and to determine simultaneously the Avrami constants, from experiments conducted at a single heating rate. It is also shown that the apparent activation energy for recrystallization in this alloy varies between approximately 34 and 79 kJ/mol, with the trend being to find smaller values of this parameter as the strain applied to the material increases. Such low values of this energy were corroborated by isothermal experiments conducted in samples of the same material. The microstructural evolution of the samples annealed under non-isothermal conditions indicates that the rate of growth of the recrystallized grains in the rolling direction is significantly higher that in the short transverse direction, due to the pinning effect of the second phase particles aligned along the rolling direction, which leads to recrystallized structures with an aspect ratio significantly higher than 1. The effect of the strain applied to the material on the recrystallization kinetics is quantified by expressing the time required to achieve a given recrystallized fraction as a function of the effective strain, by a simple parametric relationship that involves three numerical constants. Recrystallization experiments conducted under non-isothermal conditions are found to be more suitable for the evaluation of the effect of the strain applied on the recrystallization kinetics in comparison with isothermal tests, since larger strains can be applied to material before the annealing treatment.     

A356铸造铝合金的疲劳裂纹萌生及短裂纹扩展研究

研究了A356-T6铸造铝合金的缺口疲劳裂纹萌生与早期扩展行为及机制.结果表明,热等静压试样的疲劳抗力优于非热等静压试样.对于钝缺口试样,疲劳裂纹萌生于缺口根部附近的多个平面,最终哪个裂纹源扩展成主裂纹取决于局部微观组织.对于缺口几何形状不同的热等静压和非热等静压疲劳试样,在疲劳过程中,不管是在高应力状态下,还是在低应力状态下,都出现了铝基体的循环塑性变形和共晶硅粒子断裂导致疲劳裂纹萌生.对于非热等静压试样,铸造缩孔在构件的疲劳过程中起着重要作用,但即使缺口根部存在较大尺度的铸造缩孔,导致了疲劳裂纹萌生,但也同时观察到疲劳裂纹从共晶硅粒子、金属间化合物、铝基体的滑移带和铁基金属间化合物等处萌生.对于脆性的A356铸造铝合金可采用修正的断裂力学参量ΔKn、局部应力范围Δσ或局部应变幅Δε/2作为控制参量来表征疲劳裂纹萌生行为,而缺口有效应力强度因子范围ΔKneff和ΔJs参量可用来表征缺口场中短裂纹扩展行为.     

新型超高强铝合金铸态及均匀化态组织研究

通过相图计算和试验相结合的方法,研究了一种航空用新型高损伤容限型超高强铝合金的铸态及均匀化态组织。结果表明,合金铸态组织第二相主要为MgZn2型晶体结构的σ相,还存在MgZn2相及极少量A17Cu2Fe相。新型超高强铝合金在7055铝合金成分基础上,通过合理调整Zn、Mg、Cu元素含量及其配比,使合金组织中不生成S相,在保证合金强度的前提下,能提高合金的断裂韧度、抗腐蚀等损伤容限性能,同时能简化均匀化、固溶等热处理工艺。     

Research progress on microstructure evolution of semi-solid aluminum alloys in ultrasonic field and their rheocasting

The effects of ultrasonic vibration（UV）treatment on microstructure of semi-solid aluminum alloys and the application of UV in rheocasting process are reviewed.Good semi-solid slurry can be produced by high-intensity UV process for aluminum alloys.The microstructures of Al-Si,Al-Mg and Al-Cu alloys produced by rheocasting assisted with UV are compact and with fine grains.The mechanical properties of the UV treated alloys are increased by about 20%-30%.Grain refinement of the alloys is generally considered because of cavitation and acoustic streaming caused by UV.Apart from these mechanisms,a hypothesis of the fuse of dendrite root caused by capillary infiltration in the ultrasonic field,as well as a mechanism of crystallites falling off from the mould-wall and crystal multiplication by mechanical vibration effect in indirect ultrasonic vibration are proposed to explain the microstructure evolution of the alloys.     

高纯超细氧化铝粉末的制备(Ⅲ) --团聚消除的研究

本文对沉淀法制备超细氧化铝粉末过程中的团聚现象进行了研究；利用表面活性剂的起泡性能使颗粒与表面活性剂及空气形成固、液、气三相混合物泡沫，从而使颗粒之间距离增大，同时采用非离子型高分子表面活性剂的稳定作用和空间位阻作用来消除粉末的团聚。通过采用表面活性剂等不同方法消除团聚的比较，发现采用表面活性剂能够有效地消除粉末的团聚并且经济、方便。     

Low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg alloys

Fatigue failure is one of the main failure forms of Al-Si-Cu-Mg aluminum alloys.To feature their mechanical aspect of fatigue behavior,the low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg alloys at room temperature was investigated.The experimental results show that both permanent mold cast and die-cast Al-Si-Cu-Mg alloys mainly exhibit cyclic strain hardening.At the same total strain amplitude,the die-cast Al-Si-Cu-Mg alloy shows higher cyclic deformation resistance and longer fatigue life than does the permanent mold cast Al-Si-Cu-Mg alloy.The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior,and can be described by the Basquin and Coffin-Manson equations,respectively.     

Reflectance spectroscopy of oxide films. I. A theoretical study

Theoretical reflectance spectra for a thin film on an infinite substrate (such as an oxide layer on a metal) have been calculated, to assess the combined effects of absorption bands, interference and surface structure on film identification and the accuracy of film thickness measurements.