浇注温度对ZL210A铸造铝合金铸态力学性能和微观组织的影响

通过研究浇注温度对砂型铸态ZL210A合金力学性能、金相组织和断口形貌的影响.结果表明,浇注温度对ZL210A合金力学强度、硬度值和合金断口形貌影响不大,对合金延伸率略有影响,晶界上析出的共晶相随着浇注温度的提高而增多,合金铸态组织主要为α(Al)和θ(Al2Cu)相.     

ZL211A合金组织与性能研究

研究了ZL211A合金的铸造状态和热处理状态的组织和力学性能,进行了合金熔炼、铸造、热处理、力学性能测试、微观组织和拉伸断口形貌观察等试验.结果表明,ZL211A合金的铸态金相组织主要由α(Al)、CuAl2和T(Al12CuMn2)相组成,力学性能较低,不能满足航空结构材料的要求,必须经热处理强化后才能使用;热处理状态的金相组织主要由α(A1)、T(Al12 CuMn2)相、θ″相和θ′相组成,经过二级固溶处理再人工时效后,即在535℃±5℃,保温7h,再升温到545+3-5℃,保温7h,淬入50～60℃的热水中,然后在165℃±5℃人工时效7h,可获得优良的综合力学性能.ZL211A合金拉伸试样断口表现为延性断裂,其微观形貌均为韧窝和撕裂棱,韧窝的大小和深浅有所不同.     

金属型重力铸造高强度铝铜合金

目的 针对铝铜合金热裂敏感性高、难以进行金属型铸造的难题,研究其合金成分、铸造工艺、组织与性能的关系。方法 首先充分分析铸造铝铜合金的凝固机制与特点,在ZL205A合金基础上,设计了新型合金成分以及两种铸造试样模,经过熔炼、铸造与热处理,获得砂型铸造与金属型铸造试样,进行力学性能测试、组织分析,并观察试样的抗热裂性。结果 两种铸造试样都获得了较高的力学性能,铸态及T6态全部为等轴晶组织,成功避免了热裂问题,并提高了合金的力学性能;金属型铸造试制了油马达铸件。结论 证明了通过铝铜合金的成分优化设计,以及含钪复合细化剂的合理匹配,采用金属型铸造获得等轴晶组织,进而避免粗大枝晶组织,是克服热裂问题的关键,从而实现金属型铸造高强度铝铜合金。     

Ti60合金近β锻造后微观断口形貌研究

采用光学显微镜和扫描电子显微镜观察了Ti60合金近β锻造后的显微组织和室温拉伸试样、热稳定试样的断口形貌并确定断裂方式。结果表明:Ti60合金采用近β锻造,获得三态组织;室温拉伸试样断口裂纹源起源于试样中心,断面凹凸不平,既有韧窝形貌又有解理断裂特征,为混合型断口;热稳定试样断口裂纹源位于试样边缘,断口表面平整,为典型的解理断裂特征;试样经热暴露后,强度变化不大,塑性明显降低。     

显微共晶偏析对ZL205A合金力学性能的影响

对ZL205A合金中显微共晶偏析按轻重程度进行了分级,研究了各级偏析对试样室温力学性能的影响,并对试样断口进行了分析.结果表明:ZL205A合金Ⅰ级偏析对该合金试样室温力学性能无明显影响,满足一般力学性能(切取)设计使用要求;与Ⅰ级偏析相比,Ⅱ级偏析对合金试样室温力学性能有影响,其合金σb,σ0.2和δ5值分别下降了1%,3%和52%,主要表现为对延伸率影响程度较大.     

稀土及锶对铸造铝硅合金的协同变质作用EI

本文介绍了稀土和锶对ZL102及ZL104两种合金的协同变质作用。这两种铝硅合金只用稀土变质在砂型铸造时,其金相组织和力学性能与未变质的相差不多;若仅用锶变质,两种合金砂型铸造试样针孔度在5级以上,均不能满足砂型铸造生产要求。在这两种合金中加入0.2％稀土及0.04％锶时,变质效果良好,针孔度也低。     

高强铸造铝铜合金显微组织与力学性能的研究

研究了T6态ZL205A合金的显微组织和高低温力学性能.结果表明:经过T6处理后的ZL205A合金主要由α固溶体和呈弥散质点状析出的二次T相组成,另外,在组织中还有少量的Al3Ti的偏析物和未完全溶解而残留在晶界上的Al2Cu相.通过测试T6态ZL205A合金在-100℃、-50℃、0℃、23℃、50℃、100℃、150℃、200℃、250℃和300℃下的拉伸性能,得出各温度点的抗拉强度、屈服强度、伸长率和断面收缩率,并分析各力学性能指标随温度的变化规律,做出各温度点下的应力应变曲线.同时观察断口形貌,分析其断裂机制.     

往复挤镦对Mg-Sn-Al-Zn-Si合金组织性能的影响

将铸态Mg-5Sn-1.5Al-1Zn-0.8Si镁合金进行往复挤镦变形,采用OM、SEM和EDS等分析合金组织,重点研究了往复挤镦对该合金显微组织、力学性能及断口形貌的影响。结果表明:多道次往复挤镦可显著细化实验合金的显微组织,经过挤镦变形后,平均晶粒尺寸由铸态的50μm细化至3μm左右,组织中的第二相被破碎且呈现弥散分布。往复挤镦可大幅度提高实验合金的力学性能,其硬度、抗拉强度和延伸率分别比铸态试样提高了47%、155%和110%,挤镦变形合金的拉伸断口出现大量韧窝,断裂方式为典型的韧性断裂。     

ZL205A铝合金铸件偏析缺陷的断口形貌和化学成分

以实际生产过程中铝铜系ZL205A铸件的偏析缺陷为研究对象,研究了偏析缺陷对铸件本体力学性能和断口形貌的影响,同时研究了偏析面积与试样性能的关系.结果表明:偏析缺陷对试样抗拉强度和伸长率影响较大,对试样屈服强度影响较小,且偏析缺陷试样伸长率均值为3.7%,略低于I级指标4%要求,而抗拉强度和屈服强度均值分别为391.3MPa和343.5MPa,均高于I级指标360MPa和280MPa要求;无缺陷试样断裂为韧性断裂,偏析缺陷试样断裂为沿晶脆性断裂,偏析相呈网络状并连成片均布在晶界上,其主要成分为Al2Cu低熔点共晶相;试样抗拉强度σb值与其偏析面积能较好地满足线性关系.     

不同热处理条件下30CrMnSiNi2A钢的组织性能研究

为考察热处理工艺对材料性能的影响,对不同回火温度下三种碳含量的30Cr Mn Si Ni2A钢的性能进行实验研究,并分析其组织和断口形貌.研究结果表明:低温回火时30Cr Mn Si Ni2A钢具有较高的强度和硬度,其内部组织为回火马氏体,断口形貌为韧窝断口;当碳含量增大,30Cr Mn Si Ni2A钢的强度也增大;随着回火温度升高,30Cr Mn Si Ni2A钢的强度和硬度逐渐下降,伸长率和断面收缩率却总体呈上升趋势,其组织向索氏体转变,断口形貌变为解理和沿晶断口,回火脆性与其内部形核有关.     

固化条件对热塑增韧环氧树脂的固化动力学和相分离的影响

Thermoplastic toughened epoxy resins are widely used as matrices in modern prepreg systems.Different curing conditions play a great role in affecting the cure kinetics and phase behaviour of thermoplastic modified epoxies which further result in different mechanical properties of polymer matrix composites.Since the morphology of the cured thermoplastic/epoxy blends is directly related to the mechanical properties,it is essential to control processing conditions for obtaining desirable morphology.A polyethersulphone (PES) modified multifunctional epoxies,triglycidylaminophenol (TGAP) and tetraglycidyldiaminodiphenylmethane (TGDDM),was used for investigation.The cure kinetics and cured morphology of polymer blends heated at different heating rates and cured at different temperature were studied.It is shown that higher cure temperature and higher heating rate display similar effects in the epoxy conversion and the domain size of phase separated structure.     

Study on thermoplastic-modified multifunctional epoxies: Influence of heating rate on cure behaviour and phase separation

The effect of heating rate on the cure behaviour and phase separation of thermoplastic-modified epoxy systems was investigated. Polyethersulphone (PES) modified multifunctional epoxies, triglycidyl-aminophenol (TGAP) and tetraglycidyldiaminodiphenylmethane (TGDDM), as well T300/914 prepreg were used. It was shown that heating rate had a significant influence on the cure kinetics and phase structures of investigated systems. Greater heating rate causes higher epoxy conversion. The domain size of the macrophases formed from phase separation increases with the increase of heating rate. A more complete phase separation is achieved by fast heated thermoplastic-modified epoxy blends.     

Designing of epoxy resin systems for cryogenic use

The mechanical and thermal properties of several types of epoxy systems were designed based on the chemical structure, network structure and morphology aiming at cryogenic application. In this research di-epoxies or multifunctional epoxies were cured by several kinds of hardeners such as anhydride, amine or phenol and were blended with polycarbonate, carboxyl-terminated butadiene acrylonitrile copolymer or phenoxy. The mechanical properties and thermal properties of these cured epoxies were measured at room and liquid nitrogen temperature. It was found that the two-dimensional network structured linear polymer shows high performance even at cryogenic temperature. It was concluded that the controls of the structures are very important to optimize epoxy systems for cryogenic application.     

Thermodynamically reversible and irreversible control on morphology of multiphase systems

Morphology and properties of polymer alloys can be controlled by thermodynamically reversible (structure freeze-in) or irreversible (structure lock-in) processes via simultaneously manipulating miscibility, mechanisms of phase separation, glass transition (structural relaxation), and cure kinetics of polymer systems. Using phase diagrams consisting of binodal and spinodal curves, the morphology of epoxy/carboxyl-terminated butadiene acrylonitrile copolymer (CTBN) systems can be controlled by the mechanism of nucleation and growth or by spinodal decomposition. We have found that the particle size of the rubber reinforcement in epoxies is affected by the mechanisms of phase separation. Phase separation by nucleation and growth gives larger rubber particles than the corresponding phase separation by spinodal decomposition. This contrast in the morphology development is the consequence of controlling phase separation through chemorheological behaviour. Modification of the phase separation kinetics in epoxy/CTBN systems was extremely effective at altering both morphology and properties of these alloys. This technique offers a means to shift the glass transition temperature of the rubber-rich phase while leaving the glass transition temperature of the epoxy-rich phase intact. Such control over morphology is the key to ultimately controlling material properties.     

混合比及后处理对混合环氧/热塑性树脂复相体系动态力学特征的影响

以热塑性树脂(TP)/双酚A二缩水甘油醚(DGEBA)及二苯基甲烷四缩水甘油胺(TGMDA)混合环氧树脂的复相体系为基础,采用动态力学分析手段研究了在相同热塑性树脂含量的条件下,混合比例对混合环氧/热塑性树脂的动态力学性能中tanδ曲线的特征峰位置、峰形等的影响,以及在经高温后处理后曲线特征峰的变化.结合树脂断口分析,结果显示:混合环氧在固化反应过程中对热塑性树脂的高粘度高阻碍性的响应是不同的,tanδ曲线上的主峰主要由TP的转变构成而次级峰则主要由DGEBA环氧固化物的转变构成.高温后处理使树脂体系有利于分相及固化网络的完善.在复相体系中,连续相主要由TP及TGMDA环氧固化网络构成,DGEBA环氧主要存在于分散相中.     

Epoxy resin/liquid natural rubber system: secondary phase separation and its impact on mechanical properties

An investigation was carried out to explore the morphology and mechanical properties of diglycidyl ether of bisphenol A epoxy resin (DGEBA) with liquid natural rubber possessing hydroxyl functionality (HLNR). Though modification of epoxies by synthetic rubber has been extensively studied not much attention has been paid to liquid natural rubber. Photo depolymerisation of natural rubber enables us to synthesise low molecular weight oligomers by varying the experimental parameters. Epoxy resin was cured using nadic methyl anhydride as hardener in presence of N,N-dimethyl benzyl amine accelerator. Hydroxylated natural rubber of different concentrations is used as modifier for epoxy resin. The addition of such chemically modified liquid rubber to an anhydride hardener–epoxy resin mixture has given rise to the formation of a two-phase microstructure in the cured systems, consisting of spherical particles of liquid natural rubber strongly bonded to the surrounding matrix, there by providing the required mechanism for toughness enhancement. Subinclusions of epoxy resin were present in the elastomer domains as secondary particles (particle in particle morphology) as evidenced from the SEM (scanning electron micrograph) photomicrographs. The origin of the so-called secondary phase separation is due to the combined effect of hydrodynamics, viscoelastic effects of rubber phase, diffusion, surface tension, polymerisation reaction and phase separation. In a dynamic asymmetric system, the diffusion of the fast dynamic phase is prevented by the slow dynamic phase, and hence the growth of fast dynamic phase gets retarded due to the slow dynamic phase. In the case of low viscosity blends the growth of fast dynamic phase turns fast and hence diffusion of fast dynamic phase cannot follow geometrical growth and cannot establish local concentration equilibrium and hence double phase separation takes place. The double phase separation is responsible for the enhanced impact and toughness behaviour of the blends. The mechanical behaviour of the liquid rubber-modified epoxy resin was evaluated in terms of tensile and flexural properties.     

Investigating of polysulfide and epoxy‐polysulfide copolymer curing

Polysulfide can be cured in various methods. In this work, the effect of various oxidative curing agents (manganese dioxide and para quinonedioxime) in presence of curing accelerator (Diphenylguanidine) on mechanical‐dynamical properties and cure time of polysulfide resin (G4) was investigated. Results showed that mentioned oxidative curing agents have no remarkable effect on mechanical properties and cure time. But preferred method is preparation of polysulfide‐epoxy copolymer. This copolymer is a new class of liquid polymer composition containing block copolymers, with alternating blocks of polysulfide and polyepoxide. in different epoxy/polysulfide ratio, the epoxy‐polysulfide copolymer showd different tensile strenght, elongation, hardness, gel time, viscosity and Tg, but epoxy free polysulfide approximately revealed constant mechanical and dynamical properties so that epoxidized polysulfide had excellent mechanical properties and suitable curring times in comparison with those samples which were cured in other methods. FT‐IR spectroscopy, viscometry and GPC were used to verify the formation of epoxy‐polysulfide copolymer. Results obtained from DMTA and SEM showed that phase separation of epoxy resin from the copolymer matrix took place and The glass transition temperature (Tg) of the cured copolymer was between the cured epoxy and polysulfide glass transition temperatures.     

Morphology, dynamic mechanical and thermal studies on poly(styrene-co-acrylonitrile) modified epoxy resin/glass fibre composites

Poly(styrene-co-acrylonitrile) (SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRPs) in order to get improved mechanical and thermal properties. E-glass fibre was used as the fibre reinforcement. The morphology, dynamic mechanical and thermal characteristics of the systems were analyzed. Morphological analysis revealed heterogeneous dispersed morphology. There was good adhesion between the matrix polymer and the glass fibre. The dynamic moduli, mechanical loss and damping behaviour as a function of temperature of the systems were studied using dynamic mechanical analysis (DMA). DMA studies showed that DDS cured epoxy resin/SAN/glass fibre composite systems have two T_gs corresponding to epoxy rich and SAN rich phases. The effect of thermoplastic modification and fibre loading on the dynamic mechanical properties of the composites were also analyzed. Thermogravimetric analysis (TGA) revealed the superior thermal stability of composite system.     

Effects of modified hyperbranched polyester as a curing agent on the morphology and properties of dynamically cured polypropylene/polyurethane blends

The dynamic vulcanization process, usually used for the preparation of thermoplastic elastomers, has been applied to prepare polypropylene (PP)/polyurethane (PU) blends. Boltorn^TM H20 (H20) hyperbranched polyester containing 16 hydroxyl end gropus and pentaerythritol are used as curing agents, respectively, for curing PU oligomer during blending with molten PP. To improve the compatibility of cured PU particles with PP matrix, H20 is partly functionalized with stearic acid. The morphology, mechanical properties, thermal properties and melt flow index (MFI) of the PP/PU blends with different curing agent are investigated. Compared with pentaerythritol, SEM photographs show that H20 partly functionalized with stearic acid effectively reduces the size and size distribution of cured PU particles in PP/PU blends which also is proved by MFI measurement. Consequently, the dynamically cured PP/PU blends with modified H20 have better mechanical properties than those cured with pentaerythritol. The shifts of crystallization peaks to higher temperatures for all PP/PU blends indicate that PU particles in the blends can act as effective nucleating agents. Moreover, due to the smaller size of PU particles PP/PU blends cured with modified H20 have higher crystallization temperatures than those blends cured with pentaerythritol at the same PU content.     

Micro-crack behavior of carbon fiber reinforced thermoplastic modified epoxy composites for cryogenic applications

Three different types of thermoplastics, poly(ether imide) (PEI), polycarbonate (PC), and poly(butylene terephthalate) (PBT) were used to modify epoxy for cryogenic applications. Carbon fiber reinforced thermoplastic modified epoxy composites were also prepared through vacuum-assisted resin transfer molding (RTM). Dynamic mechanical analysis (DMA) shows that the storage moduli of PEI, PC, and PBT modified epoxies are 30%, 21%, and 17% higher than that of the neat epoxy respectively. The impact strength of the modified epoxies at cryogenic temperature increases with increasing thermoplastic content up to 1.5 wt.% and then decreases for further loading (2.0 wt.%). The coefficient of thermal expansion (CTE) values of the PBT, PEI, and PC modified epoxies also decreased by 17.76%, 25.42%, and 30.15%, respectively, as compared with that of the neat epoxy. Optical microscopy image analysis suggests that the presence of PEI and PC in the carbon fiber reinforced epoxy composites can prevent the formation of micro-cracks. Therefore, both the PEI and PC were very effective in preventing micro-crack formation in the composites during thermal cycles at cryogenic condition due to their low CTE values and high impact strength.