自孕育剂参数对自孕育铸造法制备AM60镁合金半固态浆料的影响(Ⅱ)

采用加入与母合金液具有相同成分的自孕育剂方法,研究孕育剂参数(孕育剂加入方式、孕育剂尺寸、孕育剂加入量和孕育剂组织)对AM60镁合金组织细化的影响。结果表明:加入自孕育剂后,熔体经导流器浇注到铸型中,可以明显细化AM60镁合金的组织。当孕育剂加入量为11%(质量分数)时,效果最好,平均晶粒尺寸仅为43.4μm,且分布均匀。孕育剂的原始组织对合金凝固组织有明显的影响,孕育剂本身的组织越细小,合金凝固组织越细小。孕育剂的加入使合金液中形成大的能量起伏和成分起伏,在合金凝固过程中起到吸热、形核、促进凝固和阻止二次相连续长大的作用,有助于形成细晶组织。     

自孕育法流变压铸AZ91D镁合金微观组织特征

采用一种新的自孕育法制备AZ91D镁合金半固态浆料,研究了AZ91D镁合金半固态浆料的流变压铸成形,并对半固态浆料和压铸件的微观组织进行研究分析。结果表明,自孕育法可以制备出组织细小、均匀的半固态浆料。将自孕育法制备半固态浆料短时保温后,浆料中初生α(Mg)内部没有液相夹裹,平均晶粒尺寸为70.4μm;在增压压力为180 MPa,压射充型速度在2~5 m/s内,经585℃保温10 min的AZ91D镁合金半固态浆料能顺利进行流变压铸,能够改善AZ91D镁合金铸件的微观组织,获得性能良好的半固态压铸件。     

高强韧稀土镁合金大型复杂铸件制造技术研究现状及展望

在介绍高强韧稀土镁合金(Mg-RE)大型复杂铸件研制技术瓶颈的基础上,指出了制造过程中熔体纯净化/细化孕育与熔体纯净化/成分均匀化之间的相互制约以及铸件本体强韧性不足的影响因素,综述了国内外稀土镁合金熔体纯净化、细化孕育、均匀化、凝固组织模拟与调控、缺陷抑制、热处理组织调控等技术的研究现状。明确了未来研究需要关注的两大科学问题:解决大熔量稀土镁合金熔体"均匀化-纯净化-细化孕育"冶金交互作用机理,稀土镁合金大型复杂铸件"溶质场-流动场-能量场"传输规律及其对组织和缺陷演变的影响机理。     

熔体处理在制备Mg-9Zn-2Al镁合金半固态浆料中的作用

采用自孕育法制备新型Mg-9Zn-2Al高锌镁合金半固态浆料,研究孕育剂加入量为5%(质量分数)、导流器角度为45°时熔体处理温度对Mg-9Zn-2Al镁合金组织的影响。对孕育剂加入熔体后的熔化状况进行分析,并从原子团簇角度探讨熔体处理温度对一次孕育的作用机理。结果表明:熔体处理温度过高或过低时,组织平均晶粒尺寸较大;在695~710℃范围内,晶粒平均尺寸较小,约为47.5~48.8μm。根据所推导出的孕育剂在导流器入口处的温度表达式,可以确定自孕育法铸造的最佳熔体处理温度,提出用固相率fS描述自孕育剂的熔化状况。     

自孕育法制备AZ31镁合金半固态流变成形组织(英文)

采用新型自孕育流变铸造技术对变形镁合金半固态组织进行控制。该工艺过程为将合金熔体与一定量的合金固体颗粒(自孕育剂)混合,然后将混合金属通过一个多流股导流器浇入铸型或收集器。结果表明:采用自孕育工艺,合金熔体处理温度690~710℃,孕育剂的加入量为3%~7%时能有效将AZ31镁合金传统铸造中的粗大枝晶组织转变为细小、近球状的非枝晶组织;当合金熔体处理温度较高时,增加孕育剂的加入量或减小导流器的倾斜角度有利于获得非枝晶组织。自孕育工艺制备的AZ31镁合金半固态浆料在620℃等温保温30s后能有效改善初生α-Mg颗粒的圆整度;延长保温时间有助于减小颗粒的圆整度,但同时颗粒发生粗化。利用Lifshitz-Slyozov-Wagner(LSW)理论对初生相颗粒在等温保温过程中的组织圆整、粗化过程进行了分析。     

物理场细化镁合金凝固组织研究新进展

常规铸造条件下,镁合金凝固组织为发达、粗大的枝晶,铸件的强度和塑性均较低,影响其使用性能。组织细化对于提高镁合金铸件的力学性能极为重要。本文着重综述了外场孕育法细化晶粒方法,如机械振动、机械搅拌、电流、超声波和磁场等方法对镁合金微观组织的影响。     

自孕育工艺参数对ZA96镁合金半固态组织的影响及其交互本质

采用自孕育法制备ZA96镁合金半固态组织,研究自孕育工艺参数对ZA96镁合金半固态组织的影响,并从温度场的角度分析工艺参数之间相互作用的本质。结果表明:采用自孕育法铸造,能够获得合格的半固态坯料和浆料。工艺参数对半固态坯料组织影响较大,但对从导流器出口处收集到的浆料在半固态区间进行保温后,发现自孕育剂加入量对组织影响不大,而导流器角度的影响较大。熔体过热度为80~95℃、自孕育剂加入量为5%、导流器角度为45°时,半固态坯料组织的晶粒平均尺寸较小,约为35.6μm;或经552℃、20 s保温后,其晶粒尺寸为45μm,圆整度为1.7。自孕育工艺参数交互作用的本质在于通过自孕育参数的调整从而达到控制其形核的目的。推导出了熔体在导流器出口处的温度与自孕育工艺参数之间的关系式。     

用轻稀土镁球化剂生产厚断面球墨铸铁件

在生产大型离心复合铸铁轧辊时,对一些要求高强度的轧辊,我们以球墨铸铁作辊芯材料,其辊颈处直径为550~650mm。对于厚断面球墨铸铁件,国内多采用钇基重稀土镁合金进行球化处理。但考虑到该合金价格约为轻稀土镁合金的十倍多,所以我们最后选用轻稀土镁合金作球化剂、以75Fe－Si作孕育剂,来处理大型离心复合铸铁轧辊的辊芯。只要正确地选用原铁水成分及最终成分、适当的球化剂用量和处理温度,并进行多次孕育,用轻稀土镁合金处理厚断面球墨铸铁,同样能得到良好的机械性能。我们对几个大型轧辊的下辊颈进行心部取样,测得其铸态机械性能为σb~450MPa,δ~5%。     

浇注温度对自孕育铸造法制备AM60镁合金半固态浆料的影响(Ⅰ)

采用新型的自孕育法制备AM60镁合金半固态浆料,研究浇注温度对自孕育法制备AM60镁合金半固态浆料的影响。结果表明:随着浇注温度的降低,组织中发达和粗大的树枝晶逐渐减少;在接近液相线温度时出现小块状或蔷薇状晶粒,晶粒的尺寸逐渐减小;分布逐渐趋向正态分布,且存在一个合适的温度加工区间,即630～680℃,对应的晶粒尺寸为58.4～63.1μm。加入的孕育剂在熔体中起到内冷铁作用,加快熔体的冷却速率,使熔体快速到达半固态区间。采用自孕育法制浆时,合金熔体中晶核主要来源于熔体中的高熔点质点(Al8Mn5)、孕育形核和晶粒游离与增殖。     

AZ91D镁合金自孕育流变压铸组织及性能

采用自孕育制浆结合高压压铸制备了AZ91D镁合金流变压铸件,研究了浆料保温时间对其凝固组织及力学性能的影响,采用能谱分析了液态压铸和半固态压铸组织及成分差异的原因,利用光学显微镜和扫描电镜观察了压铸件不同部位的凝固组织。结果表明:自孕育流变压铸能够细化AZ91D镁合金液态压铸组织,获得近球状初生α-Mg晶粒,且自孕育流变压铸过程形成的二次α-Mg晶粒相比液态压铸过程形成的细小激冷晶,Al元素含量显著升高;浆料保温时间只影响流变压铸件初生α-Mg晶粒,不影响二次凝固组织;采用自孕育流变压铸能够显著提高压铸件力学性能,并在保温3 min时达到最佳综合力学性能。     

阿莫西林与庆大霉素或奈替米星联合应用PAE的比较

目的 阿莫西林(AMPC)与庆大霉素(GM)或奈替米星(NTL)联合应用抗生素后效应(PAE)的比较。方法 应用光密度法测定PAE。结果 AMPC单用时对金黄色葡萄球菌和粪肠球菌有较长的PAE,对大肠埃希氏菌PAE甚小;GM和NTL单用对G'球菌的PAE亦很明显,对大肠埃希氏菌PAE稍短,但比单用AMPC要长。NTL的PAE比GM长,可能与受试菌对NTL敏感性高于GM有关。三种药物PAE均有随药物浓度增加而延长的趋势。AMPC与4倍MIC的GM或NTL联用时对受试菌的PAE均呈协同或相加效应;对G⁺球菌的联合PAE比G^-杆菌明显延长;AMPC与NTL的联合PAE长于与GM联合的PAE。结论 AMPC与GM或NTL联用时延长给药间隔,仍可维持强大的抗菌活性,减轻不良反应,AMPC与NTL联用优于与GM联用。     

Assessment of 3D printed steels and composites intended for wear applications in abrasive,dry or slurry erosive conditions

The design of earth cutting and machining tools generally requires the application of several types of materials with different wear resistance: (1) base metal with low wear resistance, (2) extremely resistant cutting inserts made of ceramics (or even diamond), cemented carbides or cermets and (3) thick coatings with average wear resistance to protect base metal or thin (PVD or CVD) coatings to improve wear resistance of inserts. The production of such tools is complicated, tedious and not very efficient (tool life depends on the interface bonding, brazed inserts can be severely damaged after impact, base material wear, etc.). The novel approach is to exclude the steps of brazing or coating and to produce steels or composites with similar wear resistance as that of inserts or coatings using the promising approach of additive manufacturing (AM i.e. 3D printing). Moreover, benefits of AM like near net shape part building with complex internal features (internal cooling channels) are desired for cutting tools. The aim of the current research is to assess novel commercially available 3D printed steels and composites in several relevant tribological conditions where these materials could be applied. The comparison with conventional Hardox 400 wear resistant steel and AISI 316 stainless steel is provided. Results report significant improvement in the wear resistance of AM produced steels and composites against reference materials. The performance of 3D printed materials lie between WC- based bulk cemented carbides and hardfacings. The characteristic features of wear mechanisms are presented and discussion is supported by Scanning Electron Microscope images.     

铝合金铸造用磷酸盐粘结剂砂的研究

研究了适用于铝等低熔点金属或合金铸造用砂型或型芯粘结剂及硬化工艺,其铸型的特点是表层有较高的强度,而心部强度较低,从而满足型砂或芯砂良好的溃散性,有利于铸件清砂,该粘结剂与有机粘结剂相比,不仅溃散性好,而且没有污染.     

ADI的疲劳强度

论述了ADI的疲劳强度。ADI的疲劳强度优于普通球铁,具有与锻钢相当或比锻钢更好的疲劳强度。表面滚压或喷丸可以进一步增加ADI的疲劳抗力而与气体氮化钢和表面碳化处理钢相匹敌,使ADI完全可以在一定应用中替代碳钢和低合金钢铸件,锻钢件。     

Effects of alternating current imposition and alkaline earth elements on modification of primary Mg2Si crystals in hypereutectic Mg-Si alloy

The effects of alternating current imposition and/or alkaline earth elements on modification of the primary Mg₂Si crystals in the hypereutectic Mg-Si alloy were investigated. An alternating current of 60 A with frequency of 1 kHz was applied into the hypereutectic Mg-Si melt which was alloyed with alkaline earth elements or not in the fixed temperature range from 700 to 630 °C. The results show that the primary Mg₂Si crystals could be refined by imposing alternating current or adding alkaline elements. Compared with the samples treated by adding 0.4% Ca or 0.4% Sr, higher modification efficiency could be obtained for the samples treated by imposing alternating current. No further modification efficiency could be obtained for the samples treated by imposing alternating current combined with 0.4% Ca or 0.4% Sr addition.     

Salt fog corrosion behavior of high-velocity oxygen-fuel thermal spray coatings compared to electrodeposited hard chromium

The corrosion behavior of several coating/substrate combinations was determined using the ASTM B117 Salt Fog Test. The coatings were electrodeposited hard chromium (EHC) and two high-velocity oxygen-fuel (HVOF) thermal-sprayed coatings, tungsten-carbide/cobalt (WC/Co) and Tribaloy 400 (T400). The substrates were 4340 steel, 7075 aluminum alloy, and PH13-8 stainless steel. On the 7075 Al alloy, a sulfamate nickel layer was deposited prior to the deposition of hard chromium. The results indicated that on the 4340 steel none of the coatings provided significant protection, with equivalent performance between the EHC and WC/Co coatings and slightly poorer performance for the T400. On the 7075 Al alloy, the EHC with sulfamate nickel exhibited excellent performance as no pits or blisters were noted on the faces or edges of the samples. The WC/Co showed no pitting or blistering on the faces but had a significant amount of pitting along the edges. The EHC and WC/Co coatings performed well on the 13-8 stainless steel as no pits or blisters were noted on the faces or edges. The T400 coatings had rust stains on the faces and edges but defects could not be seen with the unaided eye or at a 7× magnification.     

KINETICS OF REDUCTION IRON OXIDE IN CaO-SiO_2-Al_2O_3-Fe_tO SLAGS WITH CARBON SATURATED IN MOLTEN IRON

1.IntroductionItisimportanttoinvestigatethekineticsofreductionofironoxideinslagswithcarbonsaturatedinmoltenironforunderstandingboththeslag-metalreactioninthehearthofblastfurnaceandthefinalreductionbehavioursofprereductionironorepelletscontainingcarboninironbathreactor.Theprevious.......h..sll--7]focusedtheirattentionsmainlyonthereductionrateofpureironoxideortheredlltionrateofironoxideinsimpleslags.Thoseresultsarenotconsistentwiththatoftilerealsituation.Throughanalyzinggascompositionattheoutlet…     

A SOLUTION OF SHAPE EXTRUSION OR DRAWING BASED ON DEFORMATION THEORY

ＡＳＯＬＵＴＩＯＮＯＦＳＨＡＰＥＥＸＴＲＵＳＩＯＮＯＲＤＲＡＷＩＮＧＢＡＳＥＤＯＮＤＥＦＯＲＭＡＴＩＯＮＴＨＥＯＲＹＹｕａｎＸｉ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｅｒｉｎｇ，ＣｅｎｔｒａｌＳｏｕｔｈＵｎｉｖｅ...     

Magnetic properties and microstructures of SnO2 doped Mn-Zn ferrites

The effects of additive SnO2 (0.4wt.%), with and without SiO2 (0.02wt.%) and/or CaO(0.04wt.%), on the microstructure and magnetic properties of Mn-Zn ferrites were reported. The results reveal that SnO2 on its own increases the initial permeability ( μi) slightly, but SnO2 with SiO2 and/or CaO decreases the values of μi. However, ferrites with SnO2 additions have reduced power losses. The separate contributions of hysteresis loss and eddy current loss to the total power loss show that SnO2 (with or without SiO2 and/or CaO) doping increases the hysteresis loss slightly, but SnO2 doping alone reduces the eddy current loss significantly (～14%). The additions of SiO2 or CaO further decrease the eddy current loss, and by interaction of SnO2-CaO-SiO2, the eddy current loss is reduced by more thaN20%. These magnetic and microstructural effects were discussed in terms of the additive-impurity interaction, the existence of grain boundary phases, and the effective bulk and grain boundary resistivities of the ferrites.     

Interfacial defects of hard magnetic Pr2Fe14B phase from amorphous to nanostructures

The interfacial defects of hard magnetic Pr2Fe14B phase from amorphous to nanostructures have been investigated by positron lifetime spectroscopy. The nanostructure was produced by melt-spinning and nanocrystallization route. The two main components can be ascribed to vacancy-like defects in the intergranular layers or the interfaces, and microvoids or large free volumes with size compared to several missing atoms at the interactions of the atomic aggregates or the crystallites. The remarkable changes in the positron lifetimes from the amorphous structure to the nanocrystructure with varied sizes can be interpreted, indicating that the structural transformation and the grain growth induce the defect changes occurring at the interfaces with different shapes and sizes.