Effect of solid fraction on steel-mushy Cu-graphite pressing bonding

The pressing bonding of steel plate to QTi3.5-3.5graphite slurry was studied. The bonding conditions were 620℃ for preheating temperature of steel plate, 530℃ for preheating temperature of dies, 50 MPa for pressure and 2 min for pressing time. The relationship between the solid fraction of QTi3.5-3.5graphite slurry and the interracial mechanical property of bonding plate was obtained. The results show that when the solid fraction of QTi3.5-3.5graphite slurry is smaller than 45.8%, the interracial shear strength of bonding plate increases with the increasing of solid fraction. When the solid fraction is larger than 45.8%, the interracial shear strength decreases with the increasing of solid fraction. When the solid fraction is 45.8%, the largest interracial shear strength of bonding plate 127 MPa can be got, and the interface is made up of Fe-Cu solid solution.     

石墨粉表面镀镍工艺研究

采用电镀法对石墨粉表面进行了镀镍.采用正交试验的方法研究了镀镍过程中阴极电流密度、搅拌间隔时间、润湿剂加入量和吸附剂加入量对石墨粉镀镍效率的影响,并对结果进行了方差分析和信噪比分析,以选取镀镍效率高且稳定的工艺组合.用镀镍石墨粉在浓硝酸中充分腐蚀前后的质量差计算镀镍石墨粉中镍的含量,并以此表征镀镍效率.试验结果表明:吸...     

TiAl基合金金属型真空吸铸成形方法研究

提出了一种钛铝基合金金属型真空吸铸成形新方法,并通过数值模拟研究了TiAl基合金薄板、叶片的充型规律.研究表明,在真空吸铸过程中,充型速度和石墨吸口直径的增加,有利于充型分数的提高,另外石墨吸口直径与反向充填出现的位置密切相关.在凝固过程中,合金从下而上逐层凝固,但随着铸型温度的增加,凝固了的合金在金属液中所占的比例减少.以数值模拟结果指导试验,得到质量良好的TiAl基合金薄板和叶片铸件.     

60Si2Mn半固态浆料的制备和流变轧制的组织形貌

以弹簧钢（60Si2Mn)为研究对象，采用电磁搅拌的方式制备半固态浆料，研究了搅拌参数对半固态浆料组织形貌的影响；同时对半固态浆料进行了流变轧制，观察和分析了半固态浆料在轧制过程中的组织演变及轧制产品可能存在的组织缺陷。结果表明：在变温连续搅拌条件下，随着搅拌时间的延长，半固态浆料的固相率提高，初生固相颗粒的直径减小，组织更均匀；经过1道次的轧制，半固态浆料中的液相从固相颗粒间挤出，流向轧件的表面，大部分固相集中在轧件的中心，产生宏观偏析现象，提高固相率可减小偏析程度。此外，轧件中还可能出现缩孔、分层组织等缺陷。     

QAl-9-2合金在3.5%NaCl溶液中脱合金腐蚀研究

利用扫描隧道显微镜（ＳＴＭ）对ＱＡｌ－９－２合金在３．５％ＮａＣｌ溶液中脱合金腐蚀的早期过程进行了原位观察,结合ＳＥＭ,ＥＤＸ分析ＱＡｌ－９－２合金的脱合金腐蚀首先发生在α基体和亚稳β相的界面,并在亚稳β相内的继续扩展,α相不发生脱合金腐蚀,ＳＴＭ原位观察没有发现铜在表面再沉积的现象。     

热处理对喷射成形ZA35-3.5Mn合金电化学腐蚀性能的影响

为了探索热处理对喷射成形ZA35-3.5Mn合金电化学腐蚀性能的作用规律,采用组织观察、能谱分析及电位扫描技术对不同固溶和时效时间下合金的电化学行为进行了研究.结果表明:在3.5％NaCl溶液中,与未热处理合金相比,经过385℃/4h固溶处理,富锰相全部回溶到基体,增大合金阳极极化,消除腐蚀微电池作用,腐蚀电流密度减小41.2％;再进行120℃/15 h时效处理,合金的腐蚀电流密度减小30.0％,耐腐蚀性增强.     

含镀铜石墨颗粒铜基复合材料研究

采用化学镀铜工艺在石墨颗粒表面镀上一层金属铜,通过粉末冶金方法制备了铜/石墨复合材料,研究了石墨颗粒表面铜镀层在不同处理温度下的球化问题和改善复合材料界面结合的作用效果.结果表明,石墨颗粒表面铜镀层有利于改善铜基石墨复合材料的界面结合,使复合材料力学性能提高;处理温度较高时,表面铜镀层有熔融球化的趋势,当复合材料烧结温度超过石墨镀铜层的完全球化温度时,镀铜石墨粉改善界面结合的效果逐渐降低,直至消失.     

特殊钢连铸大方坯末端电磁搅拌位置研究与应用

采用有限元法,建立了大方坯凝固传热过程的数学模型。基于射钉试验验证了该模型的正确性。基于该凝固模型,分析了中心固相率与不同定义下凝固率的关系,提出了中心固相率在0～0.2范围内作为末端电磁搅拌的合理位置,适用于所有钢种;而面积凝固率在0.6～0.8范围内作为末端电磁搅拌的合理位置,只适用于高碳特殊钢。工业性生产试验进一步验证了这一观点,并取得了较好的冶金效果。     

Wear properties and effect of molds on microstructure of graphite reinforced copper alloy composites made by centrifugal casting

Graphite reinforced copper alloy composites were cast using gravity and centrifugal casting techniques to identify the effect of graphite particles on microstructural formation and the effect of the casting techniques on the distribution of the particles. Melt containing either 5 or 120 μm size graphite particles were gravity cast in both steel and graphite molds. Melts containing 5 μm graphite particles were also cast in a horizontal centrifugal casting machine. Samples cast in the graphite molds exhibited much greater pore size than that found in the samples cast in the steel molds. Graphite particles moved to the inner periphery when influenced by centrifugal force, resulting in the formation of graphite-rich and graphite-free zones. The volume fraction of graphite particles near the inner periphery was 13%, which is higher than the initial volume fraction of graphite particles (7 vol.%) added into the melt. The results of wear testing showed that the friction coefficient of the pin from the graphite-rich zone is 0.49 and 0.69 for the pin from the graphite-free zone. The size of the machining chips from the graphite-rich zone was much smaller than those from the graphite-free zone. These results suggest that this composite may be an attractive substitute for copper alloys containing lead.     

Relationship between solid fraction and distribution of Pb in Al-Pb ingot

ＩＮＴＲＯＤＵＣＴＩＯＮＡｌ Ｐｂｈｙｐｅｒｍｏｎｏｔｅｃｔｉｃａｌｌｏｙｉｓａｎｅｗｔｙｐｅｂｅａｒ ｉｎｇｍａｔｅｒｉａｌ[1] .Ｇｒｅａｔｅｍｐｈａｓｉｓｈａｓｂｅｅｎｐｕｔｏｎｉｔｅｓ ｐｅｃｉａｌｌｙｓｉｎｃｅ 1990ｓ[2～ 4 ] .ＰｂｈａｓｅｘｃｅｌｌｅｎｔｌｕｂｒｉｃａｔｉｎｇｐｒｏｐｅｒｔｙｗｈｉｃｈｃａｎｍａｔｃｈｔｈａｔｏｆＳｎ ,ｂｕｔｉｔｓｃｏｓｔｉｓｍｕｃｈｌｏｗｅｒｔｈａｎｔｈａｔｏｆＳｎ ,ｓｏＡｌ ＳｎａｌｌｏｙｉｓｒｅｐｌａｃｅｄｂｙＡｌ Ｐｂａｌｌｏｙｉｎｔｈｅｆｉｅｌｄｏ…     

掺杂金属对天然鳞片石墨电化学嵌/脱锂性能的影响

研究化学镀Ni、Cu和混合掺杂Zn处理后天然鳞片石墨的电化学嵌/脱锂性能。结果表明:金属微粒Ni、Cu与Zn的掺入可有效改善天然鳞片石墨的循环性能与大倍率充放电特性,金属微粒有效降低石墨电极内阻、保证石墨颗粒之间紧密的电接触是掺入金属微粒后石墨大倍率充放电性能得到改善的重要原因之一。Ni与Cu微粒改善石墨循环性能的机理与Zn的不同,Cu、Ni通过阻止溶剂化锂离子嵌入维持石墨结构稳定性,来达到提高材料循环性能的目的;金属Zn改善石墨循环性能的原因则可能是嵌锂过程中,Zn锂化所形成Li-Zn合金维持材料表面所形成SEI膜的稳定性。     

Effects of A-EMS processing parameters on semisolid slurry production

A computational model coupling an electromagnetic model with a macroscopic heat and fluid flow model in semisolid Al alloy slurry preparation by A-EMS was developed.The effects of A-EMS processing parameters such as stirring current,stirring frequency and stirring gap width on macroscopic transport phenomena during solidification were analyzed.Both the computational and experimental results showed that more intensively uniform stirring fields and uniformly fine microstructures were obtained by optimizing processing variables.     

Cu-Cr合金在3.5％NaCl+H2SO4溶液中脱铬腐蚀行为

通过金相、扫描电镜(SEM／EXD)，结合X射线衍射(XRD)研究了Cu-Cr合金在3.5％NaCl+H2SO4溶液中脱铬腐蚀行为。结果表明，Cu-Cr合金脱铬腐蚀首先发生在Cr相的界面处，并向Cr相内继续扩展，随H2SO4浓度增大及温度升高，其脱铬腐蚀倾向加大。     

Study on numerical simulation of nodular graphite iron microstructure formation

In this paper, the mathematical and physical model was developed based on thermodynamics and solidification theory before the eutectoid transformation of nodular graphite iron occurred. The Local Element Substitute and Magnification Method was brought forward and 3-dimensional numerical simulation program based on the model and the new assistant algorithm was developed and used to calculate the samples. Results of calculation have good agreement with experimental data. To display the microstructure formation during solidification of nodular graphite iron, a 2-dimensional numerical simulation program combined with the result of the 3-dimensional numerical simulation of experimental samples was compiled.     

Effect of graphite content on electrochemical performance of Sn-SnSb/graphite composite powders

Sn-SnSb alloy was synthesized by reducing a aqueous solution containing Sn（Ⅱ） and Sb（Ⅲ） salts with NaBH4 in the presence of sodium citrate. The product was characterized by X-ray diffractometry（XRD） and scanning electron microscopy（SEM）. Sn-SnSb/graphite composite powders were prepared by mechanical milling and the mass fraction of graphite was increased from 20% to 50%. The effect of graphite content on the electrochemical performance of Sn-SnSb/graphite composite electrode was investigated. The results show the increase of graphite content is in favor of enhancing the first charge-discharge efficiency and improving the cycle performance, but the capacity of the composite electrode decreases with increasing content of graphite.     

Ag-Cu-Ti活性钎料真空钎焊钼和石墨结合质量研究

为了实现石墨与钼的高强连接,实验采用活性钎料Ag-Cu-Ti作为填充材料,研究了钎焊过程中采用的工艺及不同种类石墨对真空钎焊接头组织结构和性能的影响,进一步探讨了界面结合机理.利用光学显微镜分析了接头微观形貌,采用能谱仪确定了接头的成分分布,采用自行设计的模具测试了接头的剪切强度.结果表明,Ag-Cu-Ti钎科与两侧钼和石墨基体均形成了良好的结合界面,接头抗剪强度达到了石墨基材强度的80%以上;石墨密度对接头性能的影响比较大,导致钎缝区出现不同的界面形貌.可以通过表面物理改性的方法改善接头质量.     

TA15合金在3.5%NaCl盐雾下的腐蚀疲劳性能

研究TA15合金在3.5%NaCl盐雾环境和不同应力比(R=-1、0.06,0.5)条件下的腐蚀疲劳性能,并建立合金腐蚀疲劳的Sa-Sm-N曲面方程:N=1.83×1013/[888Sa/(888-Sm)-329.51]3.65。根据疲劳过程中试样循环位移响应得出,TA15合金的循环硬化/软化行为与施加应力比有关。对腐蚀疲劳断口的SEM观察进一步表明,合金在盐雾环境下的裂纹萌生呈现多源特征,且裂纹源区大多呈解理形貌,裂纹扩展区材料抗力变化与应力比相联系。     

Effects of cooling rates on microstructure and microhardness of lead-flee Sn-3.5%Ag solders

The microstructure and microhardness of Sn-3.5%Ag solders were explored in the cooling rate ranging from 0.08 to 10^4 K/s. Under rapid cooling condition, the strong kinetic undercooling effect leads to the actual solidification process starting at the temperature lower than the equilibrium eutectic point, and the actual metastable eutectic point shifts to the higher Ag concentration. Hence, the higher the applied cooling rate is, the more the volume fraction of primary β-Sn crystal forms. At the same time, the separation of primary β-Sn crystal favors restraining the formation of bulk Ag3Sn intermetallic compounds （IMCs） in solder due to the mismatch crystalline orientation relationship, those Ag3Sn phase separating through the eutectic reaction could hardly cling to the primary β-Sn crystal and grow up. Additionally, the Vickers hardness test shows that free β-Sn and spherical Ag3Sn phase in the rapidly solidified alloy strongly improves the microhardness of the Sn-3.5%Ag solder.     

Influence of graphite on concentration of carbon vacancies in ball-milled TiCx

In this work,the influence of graphite on the ball-milled TiCx was studied.The results show that the lattice parameter of TiCx is increased when TiCx particles are ball-milled with graphite,which indicates a decrease in the concentration of carbon vacancies in the TiCx.It is considered that this decrease in the concentration of carbon vacancies results from the diffusion of carbon atoms from graphite into the TiCx.When the TiCx is ball-milled with more graphite,the effectiveness of the ball-milling is better,and the diffusion process of carbon becomes much easier.Furthermore,besides diffusion into the TiCx,some graphite has transformed into amorphous carbon after the ball-milling.