铝合金铸造过程中析氢动力学研究

铝及其合金在熔炼过程中,往往存在吸氢现象.当熔体温度下降时,氢在熔体中的溶解度下降,会从熔体中析出,导致铸锭或工件产生气孔、疏松等缺陷.采用不同模具预热温度浇注和减压凝固,分析了模具预热温度对熔体中氢扩散速度及扩散距离的影响,凝固压强对氢气泡临界形核半径和长大的影响.结果表明,低的模具预热温度抑制熔体中氢的扩散和析出;凝固压力大时氢气泡的临界形核半径较大,抑制气泡的形核和长大.所以低的模具预热温度和高的凝固压强可使氢固溶在铝合金中,从而提高其组织的致密性.     

DZ125高温合金熔体过冷度对γ′相的影响

采用熔融复合熔盐净化和循环过热相结合的方法,获得了过冷度达180 K的DZ125高温合金深过冷熔体,分析了DZ125高温合金过冷度对γ′相的影响情况。结合经典形核与生长理论,DZ125高温合金深过冷快速凝固组织中γ′相的尺寸及分布规律亦受熔体过冷度控制。随熔体过冷度提高,快速凝固过程中γ′相形成元素在基体中的固溶度大大提高,进而增大了强化相γ′相析出的驱动力,提高其析出量,促使其细化;而且,快速凝固导致大量晶格缺陷如位错,以及晶界的形成,它们作为γ′相析出的形核点,大大降低其临界形核功,从而有利于其析出。     

电磁场下近液相线高温合金熔体处理非枝晶组织的形成

采用电磁场近液相线熔体保温工艺对Ni-20Cr-18W(质量分数,%)高温合金进行处理,获得了平均晶粒尺寸d=127μm,凝固组织为球状晶粒的60 kg铸锭.借助于OM,SEM和EBSD等手段,针对所获得的电磁场对原子团簇、界面稳定化以及树枝晶向球状晶转变的研究结果,从形核热力学方面对近液相线处理后高温合金铸锭晶粒细化机制进行了研究.结果表明:该工艺能够细化凝固组织;其细化机制为原子团簇与球晶分别作为后续凝固过程中的形核核心,促进凝固过程中晶粒形核,细化组织.此外,在改善熔体宏观温度场均匀性的基础上,电磁场促进了球晶稳定化以及树枝晶向球状晶的转变,并提高其形核率.     

Al-25％Si合金过热处理后的凝固行为和组织研究

研究了熔体过热温度、冷却速度及浇注温度对Al-25％Si合金凝固形核温度、初生硅尺寸和数量分布的影响.结果显示,过热温度增加、冷却速度增大均会影响初生硅形核温度.随过热温度升高,形核温度增加,直至1 000℃过热后形核温度降低.增加冷却速度使形核温度进一步升高.不同冷却速度下,初生硅相尺寸和数量随过热温度增加以相同规律变化,1 000℃时尺寸细化达到最小值,数量达到最大值.冷却速度对初生硅尺寸的影响与过热温度有关,低过热温度下,增加冷却速度有利于初生硅相尺寸细化,过热温度升高,冷却速度对尺寸的影响逐渐减小.熔体过热处理对初生硅相的影响还与浇注温度有关,降低浇注温度,初生硅尺寸粗化,同时硅颗粒数量减少.Al-25％Si合金熔体高温过热处理后在850℃浇注,能够将初生硅相尺寸细化至30μm以下.     

Fe-Ti-N形核合金对工业纯铁凝固组织的细化作用

通过在铁钛熔体中引入氮气,制备了形核Fe-Ti-N合金.扫描电镜和能谱仪观察结果表明,该形核合金中均匀分布着大量的TiN粒子.应用该形核合金对熔态工业纯铁进行凝固组织细化实验,结果发现,添加2wt%合金后,纯铁铸锭的等轴晶区比例从30%提高到60%,平均晶粒尺寸从700μm降低到400μm.     

U-2.5% Nb合金表面的氢蚀特性

利用气固反应系统对U-2.5%Nb合金表面进行了氢化,采用体视显微镜原位观察U-2.5%Nb合金的氢蚀,利用X射线衍射(XRD)、激光扫描共聚焦显微镜(LSCM)和扫描电镜(SEM)表征该合金氢化前后的成分及形貌。结果表明:在70℃、氢压为一个大气压的气氛中,U-2.5%Nb合金的氢化反应速率很高,氢化后形成了UH3化合物;合金表面氢蚀点边缘并非圆滑,而是呈条状优先形核相向外凸出。U-2.5%Nb合金表面氢化腐蚀的机制是:贫铌α相的氢蚀速率大于富铌γ1-2相的而优先发生氢蚀,随后贫铌α相之间的γ1-2相也相继发生氢蚀而连成一片后迅速长大。     

轴类零件外圆表面锡基合金浇铸工艺研究

通过对双金属轴承零件制造工艺的分析研究,制定了轴类零件在浇铸锡基合金层时浇铸表面的处理工艺和凝固顺序的控制要点,有效地预防了其合金层脱粘、疏松及气孔等铸造缺陷.     

Zr对Mg-Gd-Er合金晶粒细化机理的影响

利用OM、EBSD对比分析了Zr的加入对Mg-Gd-Er合金凝固组织的影响,采用DSC测试了Mg-11Gd-2Er和Mg-11Gd-2Er-0.4Zr 2种合金熔体的过冷度,计算了Zr的加入对合金熔体润湿角及形核激活能的影响,利用HRTEM分析了Zr与Mg的界面关系及Zr的加入对界面能的影响。结果表明,Zr的加入能明显细化Mg-Gd-Er合金的晶粒尺寸,晶粒尺寸由大概率的1000 mm降到了50 mm,细化效果明显;Zr的加入使合金熔体的润湿角由18.3°降到了11.1°,熔体的形核激活能降低了44.4%;Mg的(1010)面与Zr的(1100)面完全共格,降低了Mg和Zr之间的界面能。熔体润湿角的降低和Mg与Zr的完全共格界面关系是细化Mg-Gd-Er合金晶粒尺寸的有效机制。     

物理变质处理对消失模铸造AZ91合金组织及力学性能的影响

在消失模铸造条件下,分别采用机械振动及熔体混合处理对AZ91合金的组织形貌和力学性能进行了研究,并分析了凝固过程中细化晶粒的机制。试验结果表明:采用机械振动及熔体混合处理都能显著地细化消失模铸造AZ91合金的组织,并显著提高力学性能。当机械振动激振力为1.5kN时,AZ91合金综合力学性能最优,其主要通过增大过冷度、枝晶臂熔断等作用细化组织。熔体混合处理其效果强于传统的熔体高温处理,熔体混合处理通过在混合液体中产生更多的核胚以增加形核位置,来细化枝晶组织。     

SCR技术制备半固态合金非枝晶组织形成机制

采用单辊搅拌冷却技术制备A2017半固态合金,对半固态合金非枝晶的形成及演变过程进行了研究.结果表明,随着合金熔体浇注温度的降低或者辊靴行腔高度的减小,半固态合金组织逐渐从粗大的枝晶转变为细小的等轴晶.从辊靴行腔入口到出口,靠近靴子面侧半固态合金组织依次为枝晶、退化枝晶和等轴晶,而靠近工作辊面侧合金组织主要为细小的等轴晶和球形晶.合金组织的演变过程为合金熔体首先在靴子和工作辊内表面凝固形核并长大成枝晶,在工作辊的剪切搅拌作用下,枝晶从辊靴表面破碎脱落进入熔体,在工作辊对高固相率半固态合金的剪切搅拌下,枝晶进一步发生断裂破碎最终形成细小的等轴晶和球形晶.     

Purifying effect of new flux on magnesium alloy

1　INTRODUCTIONAsoneofthelighteststructurematerials ,mag nesiumalloysofferlightmass(ρ<2 g·cm- 3) ,specif icstrength (higherthanthatofthealuminumalloysandsteels) ,specificstiffness ,excellentmachinabili ty ,superiordampingandmagneticshieldingcapaci ties,whichleadstoagrowinginterestinmagnesiumanditsalloys .Inrecentyears ,magnesiumalloyshavebeenwidelyusedinaviation ,spaceflight,automobileandelectronicsindustries[1] .Since 1990 stheirappli cationhassteadilyextendedanditispredictedthatitwill…     

Effects of processing variables on melt cleanliness of AZ31B magnesium alloy investigated by quantitative evaluation of Fe and non-metallic inclusions

Impurities such as Fe, Ni and Cu and non-metallic inclusions such as oxides, nitrides, carbides, sulfides and fluorides are harmful to the quality and various properties of magnesium alloy sheets produced by twin-roll casting. In this study, the changes of the content of Fe and non-metallic inclusions in AZ31B magnesium alloys with melt temperature and isothermal holding time were quantitatively evaluated using EPMA and the metallographic method. The Fe content did not increase above the Fe content in the raw material, which implies that the dissolution of Fe from a steel crucible was suppressed effectively. The content of non-metallic inclusions, mainly consisting of oxide, fluoride and Fe-rich intermetallic compounds, did not change remarkably with the melt temperature but it increased with the isothermal holding time due to the continuous oxidation of the magnesium alloy melt on the melt surface.     

Characterization and analysis of non-metallic inclusions in Ni42-Fe expansive alloy

Cracks and ruptures always occur during wire drawing process of 42% nickel-iron expansive alloy. In order to study the reasons of these phenomena, a method of metallographic observation in combination with sample electrolysis was used to characterize the non-metallic inclusions in the alloy wire. The results indicate that the inclusions in the alloy are oxidation products during the process of melting. There are single or complex phase inclusions composed of elements such as Al, Si, Ca, Ti, Fe, and O2. Among them, the macro-inclusions are TiO2 compound inclusions formed by the adhesion of Al and Si oxides on them. These inclusions are fragile ones with a low strain rate, as well as a rather high hardness, so that they are the main reason that leads to the surface cracks and ruptures in the alloy wires. The analysis has educed that the key point to enhance the product quality is to promote the cleanliness of the melt, control the types and quantity of non-metal inclusions in the alloy.     

AlMg5及AlMg5-Zr电弧喷涂涂层的组织和性能研究

目的在铝镁涂层中加入微量的Zr元素,对AlMg5及AlMg5-Zr电弧喷涂涂层的组织和性能进行对比研究。方法采用体视显微镜观察涂层的表面形貌,采用拉伸试验机、维氏显微硬度计测量涂层的结合强度及表面硬度。通过海水浸泡试验和中性盐雾试验研究涂层的耐腐蚀性能,采用电位仪测量涂层在海水腐蚀过程中的腐蚀电位,采用SEM观察涂层经中性盐雾腐蚀后的表面微观形貌,采用失重法计算涂层的中性盐雾腐蚀速率。结果微量Zr元素的加入,改善了铝镁涂层的组织结构,降低了涂层的孔隙率。相比于AlMg5涂层,AlMg5-Zr涂层的结合强度及表面硬度分别提高了13.8%和10.8%。海水浸泡腐蚀过程中,AlMg5-Zr涂层的自腐蚀电位表现较正,发生腐蚀较难,浸泡2880 h后,AlMg5-Zr涂层表面失光变色较少。中性盐雾腐蚀过程中,AlMg5-Zr涂层的腐蚀速率较小,腐蚀1920 h后,AlMg5涂层的微观腐蚀痕迹较明显,表面疏松,且出现连续的白色腐蚀产物。结论 Al Mg5-Zr电弧喷涂涂层的组织结构、与基体的结合强度、表面显微硬度及耐腐蚀性能均优于AlMg5涂层。     

Metallkundliche und elektronische Untersuchungen über die interkristalline Korrosion an einer AlMg-9,56 Knetlegierung

Metallographic and electrochemical investigations into intercrystalline corrosion of AlMg 9,56 wrought alloy The intercrystalline corrosion has been studied with a 50% cold worked AlMg9,56 wrought alloy in 1 N sodium chloride solution; the metal has been used in various heat treatment states. Electron transmission photographs were made of the grain boundary precipitates formed by heat treatment. The electrochemical behaviour was studied by potentiostatic and galvanostatic methods. The corrosion behaviour of a heterogeneous alloy having a high proportion of intermetallic AlMg ß-equilibrium phase was compared with the behaviour of heat treated specimens of the alloy. The current potential curve could be traced for the ß-equilibrium phase. Indications were found of two different rate controlling and potential dependent reactions for the dissolution of the ß-equilibrium phase and of the grain boundary precipitates of the heat treated wrought alloy. In the course of heat treatment two different typs of precipitates are found which show different corrosion behaviour. After a short time heat treatment the grain boundaries are covered with continuous precipitates of unknown composition. After extended precipitation coagulation takes place which results in isolated globulites of the intermetallic ß-equilibrium phase. Intercrystalline corrosion of the AlMg9,56 wrought alloy is thus consistently due to the selective corrosion of grain boundary precipitates.     

不锈钢焊缝中气孔形成机理研究及其进展

以金红石型铬镍奥氏体不锈钢焊条焊缝为研究对象，以气泡浮出速度理论为基础，综合介绍了不锈钢焊缝中气孔形成机理研究的几种观点：药皮中水分影响理论、熔滴中非金属夹杂物影响理论、焊缝金属凝固模式影响理论和熔滴过渡形态影响理论，为后续研究及工程应用提供了必要的理论依据。     

Effects of pre-treatments on the corrosion properties of electroless Ni-P layers deposited on AlMg2 alloy

Amorphous Ni-P layers with 8-10 wt.% phosphorus were deposited by sodium hypophosphite onto AlMg2 type aluminium alloy substrates after different pre-treatments. Prior to the electroless nickel-phosphorus (ENP) deposition in an acetate and lactic acid based nickel bath, the widely applied Zn (zincate) or Ni displacement (Ni strike) pre-treatments for aluminium substrates as well as a non-conventional surface conditioning one (soaking in a warm solution containing only hypophosphite and lactic acid) were all tested and their effects evaluated on the corrosion and other properties of the Ni-P layers developed right afterwards. The surface morphology and structure of the ENP layers were characterized by scanning electron microscopy and X-ray diffraction analysis. Polarization resistances were measured in 0.5 mol dm^− 3 Na₂SO₄ solution at pH 3. Compared to the direct electroless plating on the bare aluminium alloy AlMg2, it was found, that the hypophosphite adlayer (hypophosphite immersion pre-treatment) have also increased the corrosion resistance as the displacement pre-coatings, but without decreasing the deposition rate unlike conventional displacement methods. In the studied ENP deposition systems the decrease of corrosion rate could mainly be attributed to the lower microporosity and smoother morphology of the nickel-phosphorus coatings.     

Zur Korrosion der Legierung AlMg 2 Mn 0,8 in hochkonzentrierter Salpetersäure

Corrosion of the alloy AlMg 2 Mn 0,8 in highly-concentrated nitric acid The purpose of the study was to investigate the corrosion of the alloy AlMg 2 Mn 0.8 in highly-concentrated nitric acid at temperatures between 5 °C and 50°C. The corrosion rates follow the Arrhenius equation the apparent activation energy was calculated to be ?60.8 kJ/mol. The ratio of the dissolved alloy components aluminum and magnesium indicates that magnesium had accumulated near the surface of the metal before the exposure to nitric acid. This finding is confirmed by surface analysis.     

镁合金熔剂净化研究现状与展望

镁合金化学性质极其活泼，极易与氧、氮、水汽等发生化学作用，产生大量的非金属夹杂物和金属夹杂物，严重恶化了镁合金的铸造性能、力学性能及耐腐蚀性能。阐述了镁合金中的夹杂物来源及其危害，综述了镁合金净化熔剂的研究现状，并对熔剂的研究发展方向进行了展望。     

对铸铁件气孔和气缩孔防止措施的认识

气孔是由铁液内部的气体形成的。降低型砂、芯砂发气量、增加和增大排气眼、平稳浇注等常用气孔防止措施只能排除和减少铁液外围的气体和有限地减少进入铁液内部的气体,但未必能排除已进入铁液内部的气体,因此这些措施防止气孔的作用往往是有限的,并不能彻底消除气孔。排除铁液内部气体是防止气孔的关键,因而要尽量提高液面温度,使液面推迟形成氧化膜,使铁液内部气体在液面被氧化膜封闭之前有充分时间排出。对防止气孔应当注意的其它问题也进行了介绍,指出气缩孔的根源不是气孔而是缩孔,因此不可能采用防止气孔的方法,只能采用防止缩孔的方法消除气缩孔。还例举了防止气孔和气缩孔的实例。