Sr、RE对A356合金组织结构和力学性能的影响

A356合金重熔过程中通过混合添加适量Sr、RE来改善合金的微观组织结构。采用金相分析、X射线衍射分析(XRD)及力学性能测试等试验方法,分析了Sr、RE混合添加对合金的初晶晶胞特征参数、共晶Si相形貌和力学性能的影响。研究发现,A356合金重熔过程中,Sr、RE混合添加能够强化合金的细化效果及共晶Si相的变质效果。Sr、RE的添加,能够大幅度提高合金的综合力学性能,合金抗拉强度由变质前的153MPa提高到变质后的252MPa,伸长率由不足5%提高到超过13%。     

Y和Sc对A356合金组织与性能的影响

对比研究了微量稀土元素Y、Sc对A356合金铸态显微组织和力学性能的影响。结果表明,0.3%的Y、0.3%的Sc均能明显减小合金中α-Al枝晶间距,细化α-Al晶粒,使片状共晶Si部分纤维化,但对Si变质效果均不如Sr。等量Y和Sc细化变质效果相比,Y的细化效果不如Sc,但Sc对共晶Si的变质效果不如Y;与之相对应,Y提高A356合金铸态力学性能的幅度优于等量Sc。     

Sr对Sb变质Mg-5Sn-1.5Al-1Zn-1Si合金组织的影响

用重力铸造法制备Sb及Sr+Sb联合变质Mg-5Sn-1.5Al-1Zn-1Si合金,再进行不同的固溶处理,研究Sr对Sb变质Mg-5Sn-1.5Al-1Zn-1Si合金组织的影响。结果表明:Sb和Sr+Sb联合变质均可以使初生Mg_2Si和Mg_2(Si,Sn)颗粒发生不同程度的球化,而Sr+Sb联合变质比Sb单变质具有更好的细化和球化效果;Sr+Sb联合变质后,共晶Mg_2Si和Mg_2(Si,Sn)相由汉字状变为细小近似球形或多边形颗粒状;Sb变质Mg-5Sn-1.5Al-1Zn-1Si合金在较低固溶温度和较短保温时间下即可使大部分Mg17Al12相和部分Mg_2Sn相固溶到基体中,而Sr+Sb联合变质合金组织中,Mg_(17)Al_(12)和Mg_2Sn依然清晰可见,未完全溶解的Mg_(17)Al_(12)相发生球化,均匀的分散在基体中;Sr+Sb联合变质Mg-5Sn-1.5Al-1Zn-1Si合金固溶温度要比Sb单变质时略高一些,但对固溶时间的影响并不明显。     

Ti、B、Sr、RE联合细化及变质对A356铝合金微观组织的影响

采用金相显微镜、SEM、EDAX等试验方法,研究添加Ti、B、Sr、RE元素细化及变质对A356铝合金显微组织的影响,得出RE的添加并未与合金中的Mg形成高Mg含量化合物,Mg的分布仍很均匀,同时含铁相得到细化;对于0.10%Ti细化的A356铝合金,RE的添加使二次枝晶间距明显减小;0.01%Ti与0.03%B联合细化对A356铝合金的细化作用明显优于0.10%Ti的细化作用,晶粒为细小等轴晶,且Al-Fe-Si-Mg、Al-Si-RE相得到明显的细化;Ti、B、Sr、RE联合细化及变质的合金获得了最佳的硅颗粒变质效果。     

Sr和Sb变质AZ61-0.7Si合金的铸态组织和力学性能

Mg2Si相的变质和细化被认为是改善含Si镁合金力学性能的关键因素之一.研究了Sr和Sb变质AZ61-0.7Si镁合金的铸态组织和力学性能.研究结果表明:添加0.4%(质量分数)Sb对AZ61-0.7Si镁合金中的汉字状Mg2Si相有一定细化作用,但没有明显变质效果.相反,添加微量Sr对AZ61-0.7Si合金中的汉字状Mg2Si相有明显变质和细化作用.在AZ61-0.7Si合金中添加0.03%～0.09%Sr(质量分数)后,合金中的Mg2Si相从粗大汉字状形貌变为细小的颗粒状和/或多边形状.相应地,合金的抗拉性能和蠕变性能得到显著提高.     

细化变质处理对铸造A356铝合金组织性能及共晶硅生长机制的影响

研究了采用新型Al-5Ti-1B-1RE中间合金和Al-10Sr中间合金对A356铝合金进行单一或复合细化变质处理后的组织、力学性能和共晶硅生长机制的影响。结果表明：单一细化变质处理中Al-5Ti-1B-1RE中间合金对A356铝合金中α-Al相有明显的细化作用,合金的强度和维氏硬度显著提高；Al-10Sr 中间合金对共晶硅有强的变质作用,合金的伸长率明显提高；而经复合细化变质处理后α-Al相形状和尺寸变得更均匀细小,晶界更清晰,共晶硅相几乎都转变成更弥散、更细小的纤维状,片层状共晶硅也几乎完全消失,共晶硅长度由铸态40-60 μm降低到1-2 μm之间,达到完全变质效果,其力学性能显著高于铸态、单一细化变质剂处理的A356铝合金。未细化变质的A356铝合金中的共晶Si的生长方式为典型的小平面台阶生长,复合细化变质处理的共晶硅以孪晶凹槽机制生长为主,小平面生长特征逐渐减弱直至消失。     

细化变质处理对A356.1合金组织和力学性能的影响

通过光学显微镜(OM)、扫描电镜(SEM)、拉伸性能测试和DSC差热分析等方法系统研究Al-5Ti-1B、Sr、La、Ce对A356.1铝合金组织和性能的影响。结果表明:Al-5Ti-1B对A356.1合金中初生α(Al)晶粒的细化作用十分显著,而对共晶硅和富铁相没有明显变质作用。Sr能有效地将A356.1合金中粗大、狭长的板条状转变为细小的颗粒状和短纤维状,从而大幅降低共晶硅的长度,并显著改善共晶硅的形状系数,但对初生α(Al)相和富铁相没有明显的细化变质作用。La、Ce对A356.1合金中初生α(Al)、共晶硅和富铁相均有一定的细化变质作用,但细化效果远不及Al-5Ti-1B,变质效果明显不如Sr。加入RE元素后,富铁相的形态未发生明显变化,但长度大幅减小,说明RE对富铁相的长大具有显著的抑制作用。当采用Sr变质时,合金的综合力学性能达到最佳,其中伸长率较添加Al-5Ti-1B、La、Ce时的分别提高56.8%、32.7%和21.1%。     

变质处理对A356合金性能的影响

研究了稀士Ce变质及Ce+Sr复合变质对A356合金性能的影响.分析了变质剂加入量对A356合金组织和性能的影响.研究结果表明,在采用金属型铸造的条件下,加入0.5％Ce变质或者采用0.05％Sr+0.45％Ce的复合变质均能达到最佳的变质效果.由于变质剂的加入,使得合金的晶粒尺寸减小,晶粒平均尺寸由未变质时的约4mm降低到变质后的约1mm.扫描电镜结果表明,共晶硅的产生都是在铝相的狭缝中,同时也证明复合变质的效果更优.     

RE-Sr复合变质对轮毂用A356合金组织性能的影响

针对汽车轮毂用A356合金在Sr变质处理时熔体的吸气性增大,造成铸件气孔疏松、针孔度不合格等问题,采用主要成分为La和Ce的混合稀土RE与Sr联合对A356合金进行复合变质实验。结果表明,复合变质相比单一Sr变质,熔体中的氢含量显著降低。在一定范围内,RE和Sr具有协同变质作用,当采用0.2%Sr+0.2%RE时,铸件的微观组织、力学性能和导电率达到最优。     

A356合金的组织与热疲劳性能研究

以A356合金为研究对象,采用复合细化变质、微合金化和T6热处理的方法制备了5种A356合金,研究了合金的力学性能、显微组织和不同温度幅下的热疲劳性能,并分析了热疲劳裂纹的生长行为和产生机理。结果表明,经过复合细化变质、微合金化和T6热处理可以使A356合金的力学性能得到提高;经过T6热处理后,复合细化变质和复合细化变质+微合金化的A356合金中共晶Si的形态由针片状转变为颗粒状,共晶Si棱角圆整化程度提高提高,铸态A356合金的热疲劳寿命得到延长;在温度幅下限不变的前提下,合金的热疲劳寿命随着温度幅上限的提高而逐渐降低;经过复合细化变质+微合金化+T6热处理后合金的裂纹萌生和扩展速率最低,热疲劳寿命最长。     

Features of formation of the structure in production of blanks of disks of heat-resistant nickel alloys

Conclusions To provide a high level of mechanical properties in wrought blanks of cast ÉP741NP and ÉP962 alloys it is necessary to form controlled structures. A necklace-type structure formed in homogenizing isostatic treatment, subsequent thermomechanical working including alternation of the operations of deformation in the (+)-area and recrystallization anneals, and final heat treatment is preferable. The temperature conditions of all stages of thermomechanical working are strictly controlled, especially the final operation of deformation and heating for hardening. To eliminate hardening cracks and distortions it is necessary to use molten salts at t=600°C as quenchants. The use of multiple production operations makes it possible to significantly reduce the structural inhomogeneity related to inhertance of the original dendritic structure. However, the structure of the final semifinished product is nevertheless characterized by a difference in occurrence of the processes of polygonization and recrystallization between the former dendritic cells and the interdendritic spaces in deformation and heat treatment.To obtain structurally homogeneous blanks for gas turbine engine parts it is necessary to use basically new methods of remelting such as vacuum double electrode remelting and electron beam remelting with an intermediate vessel.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 25–29, December, 1991.     

Ab-initio calculation of enthalpies of formation of intermetallic compounds and enthalpies of mixing of solid solutions

A large number of ab-initio calculations of energies of formation of intermetallic compounds have been performed in the last 15 years. The currently used methods are listed. The paper presents a review of the aluminium based compounds which have been studied. Comparisons of calculated and experimental enthalpies of formation are provided for aluminim-3d and-4d transition metal alloys at equiatomic composition. The modelling of the enthalpies of mixing of solid solutions based on a given lattice is described.     

试论洋务派教师聘任的思想

洋务派在洋务学堂的办学活动中,为了解决西学专业学科的教学困难,采用了聘请外籍教师的应急措施.他们以真才实学,合同制管理作为主导思想,并认为这种解决师资的途径只是权宜之计,并非久远.从客观上看,洋务派的教师聘任思想有深刻的历史影响.     

Prospects of the Use of Synergetic Approach to Solution of Problems of the Science of Nanomaterials

A synergetic approach to solution of problems of self-controlled synthesis of nanostructures and creation of self-organizing nanotechnologies is considered in connection with the superproblem of creation of materials with functional properties resembling those of biosystems. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 55 – 61, July, 2005.     

Kinetics of the oxidation of metals — Influence of self-diffusion of metal

The importance of the self-diffusion of a metal during its oxidation by a gas is treated for the cases of nonstoichiometric oxides having either interstitial cation or cation vacancies. We have established a general relationship for the reaction rate when a mixed diffusion process occurs. From this relationship, we have shown that the pressure dependence can be different, according to whether the rate-determining process is the self-diffusion through the metal or through the product.     

胫骨生物陶瓷复合材料的微结构增韧机理

扫描电镜观察显示胫骨是一种由羟基磷灰石和胶原蛋白组成的自然生物陶瓷复合材料.羟基磷灰石具有层状的微结构并且平行于骨的表面排列.观察也显示这些羟基磷灰石层又是由许多羟基磷灰石片所组成,这些羟基磷灰石片具有长而薄的形状,也以平行的方式整齐排列.基于在胫骨中观察到的羟基磷灰石片的微结构特征,通过微结构模型分析及实验,研究了羟基磷灰石片平行排列微结构的最大拔出能.结果表明,羟基磷灰石片长而薄的形状以及平行排列方式增加了其最大拔出能,进而提高了骨的断裂韧性.     

Analysis of microporous structure of carbon adsorbents in terms of the theory of volume filling of micropores

A methodology of using the theory of filling the volume of micropores when evaluating the porous structure of carbon nanomaterials and adsorbents, as well as describing the adsorption of different species, is considered. Potentialities of the mathematical means of a theory of filling the volume of micropores when differentiating homogeneous and irregular microporous structure of activated carbon, determining the micropores’ parameters (their volume and size), evaluating the degree of heterogeneity of microporous structures, and describing adsorption over wide concentration range are analyzed. The perspectives of this approach, based on the theory of filling the volume of micropores, in the prognosis of the microporous structures’ parameters and the activated carbons’ adsorbability in the process of their synthesis are demonstrated. Original Russian Text ? G.A. Petukhova, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 2, pp. 170–176.