LC4CS棒材阳极氧化膜表面局部发黑分析

LC4CS棒材零件硫酸阳极化后表面出现发暗、发黑的非正常现象,影响产品质量和性能。采用SEM、金相、氧化膜分析等手段,经综合分析得出产生此现象的主要原因是：热处理不当引起的合金组织异常,产生大量的T相、S相和残留杂质相,使阳极氧化膜中出现空洞和夹杂,造成氧化膜出现局部发黑现象。可以采用二次热处理解决此问题。     

异常粗大的奥氏体晶粒对表面晶间裂纹的影响

在大方坯连铸中,经常出现的缺陷是表面网状裂纹.由于铸坯表面存在网状裂纹导致轧制过程中出现严重的纵裂纹.通过微观检测、热模拟等手段分析了表面网状裂纹产生的原因及机理,由实验结果可以看出,表面网状裂纹沿异常粗大的奥氏体晶粒开裂,其实质是奥氏体晶间裂纹;异常粗大的奥氏体晶粒、残余元素Cu的富集以及AlN、BN等氮化物和先共析铁素体薄膜的析出是导致该钢种产生晶间裂纹的主要原因;大的奥氏体晶粒是残余元素富集以及氮化物和先共析铁素体薄膜析出的先决条件,因此表面网状裂纹是第Ⅱ和第Ⅲ脆性区间相互作用的结果,经常出现在存在凹陷和鼓肚的部位;异常粗大的奥氏体晶粒产生的主要原因是高的过热度和不均匀冷却.     

PS版铝板基组织条纹缺陷的研究

通过对有组织条纹缺陷的PS版铝板基进行脱脂、碱洗、中和、阳极氧化处理,并对缺陷区域和正常区域作金相对比分析,结合来料电解铝液制备的半连续铸扁锭对应部位的晶粒度分析和成分分析．指出直接采用电解铝液制备PS版铝板基热轧用半连续铸造大扁锭容易产生浮游晶．而浮游晶是PS版铝板基发生组织条纹的根本原因,严重影响PS版基产品质量,通过对电解铝液直接铸造PS版铝板基扁锭的铸造工艺进行优化,可以使PS版基组织条纹缺陷得到根本的预防。     

汽车加油管用6082零部件氧化膜品质探讨

通过化学成分、导电率分析、金相显微组织观察及SEM/EDS等方法,对6082-T6零部件硬质阳极氧化品进行了分析研究。结果表明,产生硬质阳极氧化品盐雾试验不过关的原因是零部件有粗大杂质存在,这些粗大杂质颗粒在阳极预处理过程掉落或残留,产生氧化膜缺陷,从而导致盐雾测试不合格。     

铁硅钇合金的高温氧化行为

通过光学显微镜、X射线衍射、扫描电镜和热重分析等研究了添加钇对Fe-Si合金在900℃和1000℃、0.1 MPa纯氧气中高温氧化行为的影响。结果表明,随着元素钇含量的增加,Fe-3Si-0.5Y和Fe-3Si-5.0Y合金的晶粒尺寸较Fe-3Si-0Y合金降低约80%和94%,同时,根据X射线分析结果,合金表面氧化膜的晶粒尺寸随着合金晶粒尺寸的降低明显减小。晶粒细化使合金及其氧化膜中的晶界数量增加,并进一步地促进了合金元素和氧在其中的扩散以及SiO2和Y2O3的形成。然而,含钇合金在900℃和1000℃氧化时均未生成单一连续的SiO2或Y2O3氧化层,但晶粒细化后硅和钇氧化物的快速形成及部分地横向连接对元素的扩散仍起到了比较有效的抑制作用,含钇合金的氧化抗力因此得到了提高。讨论了添加元素钇导致的合金晶粒细化对Fe-Si合金氧化行为的影响机制。     

固溶工艺对6061铝合金硬质阳极氧化膜层质量的影响

采用显微硬度测试、金相和扫描电子显微分析,研究了固溶工艺对6061硬质阳极氧化膜层厚度、硬度、均匀性、致密度的影响。结果表明:阳极氧化膜因内外表面受到电解液的腐蚀程度不同而表现为氧化膜的硬度自膜层表面到基体逐渐升高。固溶工艺的改变对阳极氧化膜的厚度均匀性无显著影响,氧化膜自身的成分结构决定了其膜层厚度的均匀性。试样在530℃×3 h下采用水冷的方式所获得的硬质氧化膜与基体结合平整,不存在针孔、疏松等缺陷,表面无孔残蚀现象。提高固溶温度,虽然能使强化相Mg2Si、第二相质点等全部回溶到基体里,但因形成粗晶组织,使晶粒度极为不均匀。在而后的阳极氧化过程中造成氧化膜的成长速度不一致,生长快的氧化膜和生长慢的氧化膜之间存在一定的内应力,这种内应力在一定条件下转化为微裂纹,因而使得氧化膜层质量下降,硬度降低。     

晶粒细化对Zr-4合金均匀腐蚀性能的影响

通过超声喷丸处理在Zr-4合金表面获得细晶组织,400 ℃高压釜实验表明其耐蚀性能优于原始组织.采用场发射扫描电镜和X射线衍射,观察并计算了细晶组织的晶粒形貌与尺寸分布.采用金相显微镜、原子力显微镜和X射线衍射,分析了不同腐蚀时间的氧化膜形貌和结构的演变.结果表明,喷丸处理在细化晶粒的同时会增加样品表面微观缺陷,从而促进保护性氧化膜的形成,提高Zr-4均匀的耐腐蚀性能.     

低碳钢热连轧钢板表面铁素体晶粒异常粗大试验研究

本文采用“THERMECMASTOR—Z”型热加工模拟试验机和“SX—8—16”型高温箱式电阻炉,在实验室对1700热连轧机生产工艺进行模拟,找出了低碳钢SPCC、SPCD热连轧板卷沿厚度方向铁素体晶粒异常不均的原因;分析了终轧温度、终轧变形量和卷取温度对晶粒异常不均的影响,初步提出了避免表面铁素体晶粒异常粗大应采取的措施。     

砂面铝型材不同表面预处理对比研究

对砂面铝型材不同表面预处理条件下砂面形成机理以及由此引起的型材表面微观形貌和表层组织结构的不同作了分析,指出了它们对阳极氧化膜层性能可能产生的影响.     

织构对5005A铝合金阳极氧化条纹的影响

研究了织构与5005A铝合金阳极氧化后条纹之间的关系,并分析了热轧工艺和中间退火工艺对材料织构的影响。通过调整材料织构的组成,找出影响5005A铝合金阳极氧化条纹的关键因素。     

Abnormal grain growth behavior of an

To obtain a superior high temperature creep strength, the transformation of fine-grained structure to large elongated grains by abnormal grain growth is an important process for oxide dispersion strengthened superalloys. The present study investigated the abnormal grain growth behavior of TMO-2, an experimental alloy possessing higher creep strength than existing ODS alloys. It was found that abnormal grain growth was triggered by oxide dispersoid coarsening rather than γ^′ dissolution. Preanneal increased the grain growth temperature and decreased the grain growth rate in the same manner as low-γ^′ or γ^′-free ODS alloys. However, with regard to stored energy, far fewer dislocations were found, and grain growth was considered to be driven predominantly by surface energy. The allowance of normal grain growth during preanneal or hot work to preserve abnormal grain growth ability was investigated and correlated with the amount of softening.     

Effects of lanthanum ion-implantation on microstructure of oxide film formed on Co-Cr alloy

Isothermal and cyclic oxidizing behavior of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000 ℃ in the air by thermal-gravimetric analysis （TGA）. Scanning electronic microscopy （SEM） and transmission electronic microscopy （TEM） were used to examine the morphology and structure of oxide film after oxidation. Secondary ion mass spectrum （SIMS） method was used to examine the binding energy change of chromium caused by La-doping and its influence on the formation of Cr2O3 film. laser Raman spectrum was used to examine the stress changes within the oxide film. It was found that lanthanum implantation remarkably reduced isothermal oxidizing rate of Co-40Cr and improved anti-cracking and anti-spalling properties of Cr2O3 oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide and increased high temperature plasticity of the oxide film. Lanthanum mainly existed on the outer surface of Cr2O3 oxide film in the form of fine La2O3 and LaCrO3 spinel particles.     

Structure Analysis of Oxidation Film of Ignition-Inhibition AZ91D Magnesium Alloy Added with Cerium

The effect of cerium on ignition temperature of AZ91D magnesium alloy was studied. By the addition of cerium of 1%, the ignition temperature is raised by 180℃, so the magnesium alloy added with cerium can be melted in air. The burning temperature increases with the increasing of cerium. The structure and chemical compositions of the surface oxide film were investigated by XRD and Auger electron spectrometry(AES). The results of XRD indicate that the oxide film of the surface of ignition-inhibition magnesium alloy can change from loose structure of simple magnesia to compact composite structure consisting of magnesia, cerium oxide, Mgl7 A112 and aluminum oxide, which has excellent ignition-inhibition effect. AES depth profile analysis shows that the oxide film can be divided into three layers. The outside layer is mainly made up of magnesia, the middle layer, which consists of cerium oxide, magnesia, and aluminum oxide, is compound and compact. Thermodynamic analysis indicates that the structure of the surface oxide film is accordant to the change of free energy and high vapor pressure of magnesium.     

Microstructure evolution and densification behaviour of powder metallurgy Al–Cu–Mg–Si alloy

ABSTRACT

An Al–Cu–Mg–Si alloy was prepared by conventional press-sintering powder metallurgy using elemental Al powder. The phase transformation process of Al–Mg, Al–Si alloy and Cu during the sintering process was investigated in details. It was found that a series of phase transitions take place in the alloy to disrupt the oxide film of Al particle and enhance the densification process. The relative density of the sintered samples reached 98%. A new Al–Mg–Cu–O compound was found at the grain boundaries except the MgAl₂O₄ phase, it is speculated that the disruption of the oxide film was also associated with the other alloy compositions except for Mg. Furthermore, no detectable AlN compound was found at the grain boundary region although sintering with flowing nitrogen atmosphere, which is benefit from the high density of the green compact and the excellent wettability between the liquid phase and the aluminium.     

碳含量对Cr25Ni20型奥氏体耐热钢高温氧化性能的影响

对两种不同碳含量的Cr25Ni20型奥氏体耐热不锈钢分别加热到800 和1 100 ℃循环氧化96 h后，进行了循环氧化分析，并利用扫描电镜观察钢材表面氧化膜形貌；利用X射线衍射仪对氧化膜进行物相分析；采用划痕法测量氧化膜与金属基体的黏附力。结果表明，氧化膜是由菱形结构的Cr2O3晶粒和尖晶石结构的MnCr2O4晶粒组成，随着氧化温度的升高，氧化物晶粒变得粗大并由菱形结构向尖晶石结构转变；碳含量的增加造成“贫铬”现象的发生，减缓保护性氧化膜的生成，降低氧化膜与金属基体的黏附力；随着氧化温度的升高，氧化膜横截面的厚度不断增加，氧化膜受破坏程度也不断加剧。     

镍基合金C276在超临界水中的腐蚀行为

研究镍基合金C276在550~650℃/25 MPa超临界水中的腐蚀特性.采用腐蚀增重、扫描电镜、能谱和X射线衍射方法分析材料的氧化动力学、氧化膜形貌、合金元素分布和组织结构.结果表明,C276合金在超临界水中以均匀腐蚀为主,其腐蚀增重服从抛物线生长规律.当温度由550℃升高到600℃时,材料的腐蚀增重大约升高到3倍;当温度进一步升高到650℃时,材料的腐蚀增重反而下降.C276合金表面氧化膜分层不明显,氧化膜的主要成分为（Ni,Fe）Cr₂O₄,同时其表层离散分布着大量的NiO氧化物颗粒.C276合金表面氧化膜的保护性能主要取决于氧化膜内Cr含量,Cr含量越高其结构越致密,从而保护性能也越好.     

稀土铁铬铝合金的高温氧化TEM研究

通过透射电镜对Fe-25%Cr-6%Al-RE(富镧)合金氧化行为进行研究.结果表明:经1200℃恒温2h纯氧中氧化,合金中镧以六方La₂O₃微小颗粒沉淀在氧化膜中α-Al₂O₃晶粒的顶端及晶界上。它们阻碍铝向表面扩散,抑制氧化膜的侧向生长;在1200℃/室温之间热循环氧化历程.稀土组元加快了合金的内氧化。它们以氧化铝、氧化镧形式出现,在靠近氧化膜/金属界面,立方La₂O₃颗粒平行于晶界并在合金基体上沉积。     

Influence of Lanthanum Ion-Implantation on Adhesive Property of Oxide Film Formed on Co-40Cr Alloy

The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1 000 ℃ in air by thermal gravimetric analysis（TGA）.Scanning electron microscopy（SEM）was used to examine the Cr2O3 oxide film＇s morphology after oxidation.Secondary ion mass spectrum（SIMS）method was used to examine the binding energy change of chromium caused by La-doping and its influence on the formation of Cr2O3 film.Acoustic emission（AE）method was used in situ to monitor the cracking and spalling of oxide films during oxidizing and subsequent air-cooling stages.Laser Raman spectrum was used to examine the stress changes within oxide films.A theoretical model was proposed relating to the film fracture process and was used to analyze the AE spectrum both on time domain and AE-event number domain.It was found that lanthanum implantation remarkably reduced the isothermal oxidizing rate of Co-40Cr and improved the anti-cracking and anti-spalling properties of Cr2O3 oxide film.The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide,increased the high temperature plasticity of oxide film,and remarkably reduced the number and size of Cr2O3/Co-40Cr interfacial defects.     

Kinetics of grain growth in the weld heat-affected zone of alloy 718

Grain-boundary liquation occurs in the weld heat-affected zone (HAZ) of the Ni-base superalloy 718 at locations where the peak temperatures are greater than about 1200 °C. The evolution of the grain structure at these HAZ locations depends upon the interaction between the grains and the grain-boundary liquid. The evolution of grain structure in the presence of grain-boundary liquid was simulated by subjecting samples to controlled thermal cycles using resistance heating. A measurement of grain size as a function of isothermal hold at two peak temperatures of 1200 °C and 1227 °C indicated that in alloy 718, the kinetics of grain growth depended upon the prior thermal history of the alloy. In the solution-treated alloy, the presence of grain-boundary liquid did not arrest grain growth at either peak temperature. In the homogenized and aged alloy, a grain refinement was observed at the peak temperature of 1227 °C, while an arrest of grain growth was observed at a peak temperature of 1200 °C. Liquid film migration (LFM) and subgrain coalescence, either acting alone or simultaneously, are shown to explain most of the observed microstructural phenomena and the kinetics of grain growth in the alloy. B. Radhakrishnan, formerly Research Associate, with the Department of Materials Science and Engineering, University of Alabama at Birmingham, Birmingham, AL.