Multi-scale Simulation on Bonding Mechanism of Solid-Liquid Cast-Rolling of Cu/Al Cladding Strip based on FEM and MD

To explore the complex thermal-mechanical-chemical behavior in the solid-liquid cast-roll bonding(SLCRB) of Cu/Al cladding strip, numerical simulations were conducted from both macro and micro scales. In macro-scale, with birth and death element method, a thermo-mechanical coupled finite element model(FEM) was set up to explore the temperature and contact pressure distribution at the Cu/Al bonding interface in the SLCRB process. Taking these macro-scale simulation results as boundary conditions, we simulated the atom diffusion law of the bonding interface by molecular dynamics(MD) in micro-scale. The results indicate that the temperature in Cu/Al bonding interface deceases from 700 to 320 ℃ from the entrance to the exit of caster, and the peak of contact pressure reaches up to 140 MPa. The interfacial diffusion thickness depends on temperature and rolling reduction, higher temperature results in larger thickness, and the rolling reduction below kiss point leads to significant elongation deformation of cladding strip which yields more newborn interface with fresh metal and make the diffusion layer thinner. The surface roughness of Cu strip was found to be benefit to atoms diffusion in the Cu/Al bonding interface. Meanwhile, combined with the SEM-EDS observation on the microstructure and composition in the bonding interface of the experimental samples acquired from the castrolling bite, it is revealed that the rolling reduction and severe elongation deformation in the solid-solid contact zone below kiss point guarantee the satisfactory metallurgical bonding with thin and smooth diffusion layer. The bonding mechanisms of reactive diffusion, mechanical interlocking and crack bonding are proved to coexist in the SLCRB process.

Evolution of bonding interface in solid-liquid cast-rolling bonding of Cu/Al clad strip

Cu/Al clad strips are prepared using solid?liquid cast-rolling bonding(SLCRB)technique with a d160mm×150mm twin-roll experimental caster.The extent of interfacial reactions,composition of the reaction products,and their micro-morphology evolution in the SLCRB process are investigated with scanning electron microscope(SEM),energy dispersive spectrometer(EDS),and X-ray diffraction(XRD).In the casting pool,initial aluminized coating is first generated on the copper strip surface,with the diffusion layer mainly consisting ofα(Al)+CuAl2and growing at high temperatures,with the maximum thickness of10μm.After sequent rolling below the kiss point,the diffusion layer is broken by severe elongation,which leads to an additional crack bond process with a fresh interface of virgin base metal.The average thickness is reduced from10to5μm.The reaction products,CuAl2,CuAl,and Cu9Al4,are dispersed along the rolling direction.Peeling and bending test results indicate that the fracture occurs in the aluminum substrate,and the morphology is a dimple pattern.No crack or separation is found at the bonding interface after90°-180°bending.The presented method provides an economical way to fabricate Cu/Al clad strip directly.

Microstructural Characterization of Novel Ni-Containing Nd-Fe-B Strips by Strip Casting

The characteristics of novel Nd-Fe （Ni, Co, Al ）-B microstructure prepared by strip casting technique were studied. The novel microstructure was observed using scanning electron microscope （SEM） and transmission electron microscope （TEM）. Along the direction of heat flow, there are two kinds of different microstructures. Close to the wheel side, there is a thick layer containing many polygonal Nd2Fe14B grains. Near the free surface side, however, there are relative uniform platelike Nd2Fe14B grains whose growth direction is not completely the direction of the heat flow during solidification. The formation of the novel microstructure is presumed to be the contribution of the special temperature field and Ni component.

Heat transfer analysis and experimental study of unequal diameter twin-roll casting process for fabricating Cu/Al clad strips

Unequal diameter twin-roll casting(UDTRC)can improve the formability,surface conditions,and production efficiency during the fabrication of clad strips.Using Fluent software,a numerical simulation is used to study the asymmetric heat transfer characteristics of Cu/Al clad strips fabricated by UDTRC.The effects of roller velocity ratio,Cu strip thickness,and inclination angle on the kissing point position,as well as the entire temperature distribution are obtained.The heat transfer model is established,and the mechanism is discussed.The Cu strip and rollers are found to be the main causes of asymmetric heat transfer,indicating that the roller velocity ratio changes the liquid zone proportion in the molten pool.The Cu strip thickness determines the heat absorption capacity and the variations in thermal resistance between the molten Al and the big roller.The inclination angle of the small roller changes the cooling time of big roller to molten Al.Moreover,the microstructure of Al cladding under different roller velocity ratios is examined.The results show significant grain refinement caused by the shear strain along the thickness direction of Al cladding and the intense heat transfer at the moment of contact between the metal Al cladding and Cu strip.

Interfacial pressure distribution and bonding characteristics in twin-roll casting of Cu/Al clad strip

The mechanical properties and product thickness specifications of bimetallic clad strip prepared by twin-roll casting are tightly related to the mechanical behavior of bonding interface interaction.The thermal−flow coupled simulation and the interface pressure calculation models are established with the cast-rolling velocity as the variable.The results show that the interface temperature decreases,the interface pressure and the proportion of the thickness of the Al side increase with the decrease in cast-rolling velocity.The thinning of Cu strip mainly occurs in the backward slip zone.The higher pressure and longer solid/semi-solid contact time make the interface bonded fully,which provides favorable conditions for atomic diffusion.The inter-diffusion zone with a width of 4.9μm is attained at a cast-rolling velocity of 2.4 m/min,and the Cu side surface is nearly completely covered by aluminum.Therefore,the ductile fracture occurs on the Al side,which prevents the propagation of interface delamination cracks effectively.Meanwhile,shear effect becomes more significant at high interfacial pressure and large plastic strain,and the microstructure on Al side is composed of slender columnar crystals.Thus,the metallurgical bonding and refinement of grains on the Al side can result in higher bonding strength and tensile properties of the clad strip.

激光熔覆镍基合金与铝反应合成Ni-Al金属间化合物覆层的研究

以镍基合金和铝为原料,利用激光熔覆技术在低碳钢表面反应合成Ni-Al金属间化合物覆层。采用SEM,EDX,TEM和XRD等表征手段对试样的组织和相结构进行分析。结果表明:激光熔覆镍基合金与铝反应合金覆层由β-Ni Al和γ′-Ni3Al两相构成,两相中均固溶有一定量Fe,Si元素。β-Ni Al相含量较多,为细小、均匀、交错分布的树枝晶,Ni,Al间的反应放热使树枝晶呈现等轴化趋势;γ′-Ni3Al相含量较少,呈连续网状分布于β-Ni Al树枝晶周围,这种结构有利于降低覆层脆性。在1.5kW功率下,激光熔覆镍基合金及铝反应合成的β-Ni Al和γ′-Ni3Al两相合金覆层致密,有少量气孔但无裂纹现象,覆层与基体实现完全冶金结合。

激光反应合成Ni-Al金属间化合物涂层

以镍包铝、镍基自熔性合金以及铝的混合粉为原料,利用激光工艺与镍、铝之间的反应合成相结合,制备了Ni-Al金属间化合物涂层。实验结果表明,涂层显微组织主要由NiAl和Ni3Al两相构成,其中NiAl相呈树枝晶形貌,Ni3Al相有两种形态,一种沿NiAl树枝晶间呈连续网状分布,另一种在NiAl相上析出,呈细小不规则角状。与直接熔覆镍包铝相比,镍包铝中添加镍基合金与铝后,多道熔覆功率由2.4 kW下降为2.1 kW,涂层质量改善,同时降低了基底中铁元素的熔入;涂层硬度由410~440 HV提高到490~540 HV。

退火对层状复合Ni-Al双金属带界面化合物和性能的影响

层状复合Ni-Al双金属带作为连接材料被广泛应用于锂离子电池中,该复合带需要2层金属间具有良好的结合性能,这与结合界面上的金属间化合物的形成及其性质有很大的关系。研究不同退火温度时Ni-Al双金属层状复合带的复合界面上金属间化合物的生长情况及力学性能。研究结果表明:当达到一定的热力学条件后,金属间化合物首先在界面局部区域生成并迅速完成长大,新生的化合物主要有NiAl3和Ni2Al3,这些相沿界面呈层状分布,并且随温度升高而变厚。但过高的扩散温度会使复合界面上生成较厚的脆性化合物。制备组织和性能较好的Ni-Al双金属层状复合带最佳工艺为:退火温度420℃,退火时间3 h。

等离子原位合成Ni-Al基金属间化合物涂层的研究

通过高温等离子光束激发不同配比的Ni、Al、Fe混合粉产生原位反应,利用扫描电镜(SEM)对原位反应获得的涂层的显微结构进行观察,并利用XRD进行成分分析。结果表明,实验获得的金属间化合物结构致密,并与基体呈冶金结合,其中质量比为1∶1的Ni、Al混合粉末熔覆涂层的主要成分为NiAl,而加入Fe后得到的涂层成分为NiAl和Fe3Al两种金属间化合物涂层。

铬铸铁表面激光熔敷Ni-Al-WC合金层及组织性能研究

研究了铬铸铁表面激光熔敷Ni Al WC合金层及其组织性能 ,分析了熔敷层的化学成分、相的组成、显微结构、平均显微硬度、耐磨性及耐蚀性等。结果表明 :熔敷层与基体完全实现了冶金结合 ,其化学成分、显微组织发生了根本性转变 ,使表面硬度。

扫描速度对激光熔覆Al-Ni-TiC-CeO_2复合涂层组织与性能的影响

目的解决S355海洋钢在海洋环境中的腐蚀、磨损问题,制备良好的涂层结构,并延长其使用寿命。方法采用激光熔覆工艺在S355海洋钢表面制备Al-Ni-Ti C-CeO_2复合涂层,研究扫描速度对涂层组织与性能的影响,利用扫描电镜观察涂层的微观组织形貌,结合X射线衍射仪对涂层物相进行分析。采用显微硬度计、摩擦磨损试验机和电化学工作站对涂层的硬度、耐磨性和耐蚀性进行测试分析。结果不同扫描速度制备的涂层均出现Al-Fe相,涂层与基体有良好的冶金结合。随着扫描速度的增加,涂层厚度逐渐降低,涂层内组织由短棒状向颗粒状转变,裂纹和气孔逐渐减少,稀释率逐渐降低。涂层表面硬度最高为846.6 HV0.2。涂层磨痕宽度最低为449.4μm,深度为15.5μm,磨损速率最低为3.88×10^(–6)mm^3/(N·s)。涂层自腐蚀电位最大为–0.60396V,最小自腐蚀电流密度为2.3753×10^(–8)A/cm^2,阻抗最大能达到2.5kΩ,腐蚀速率最低为0.0725mm/a,约为基材的33.6%。结论在S355海洋钢表面激光熔覆Al-Ni-TiC-CeO_2复合涂层,可有效提高其耐磨与耐蚀性能。当扫描速度为7.5 mm/s时,性能最佳。

Cr元素含量对TC21钛合金表面激光熔覆Ni-Al涂层组织与性能的影响

目的研究Cr元素含量对TC21钛合金表面激光熔覆Ni-Al涂层组织与性能的影响,改善其表面性能。方法利用激光熔覆技术在TC21钛合金表面制备不同Cr含量的Ni-Al涂层,采用带有能谱仪(EDS)的扫描电子显微镜(SEM)、X射线衍射仪(XRD)对熔覆层的显微组织、物相组成进行分析,采用显微硬度计和材料表面性能综合测试仪测试熔覆层的硬度分布和耐磨性能。结果熔覆层表面质量良好,未添加Cr元素时,熔覆层主要由Ni(Al,Ti)、Ni2AlTi、TiNi等物相组成;添加Cr元素后,熔覆层中有α-Cr沉淀相析出,并且随着Cr元素含量的逐渐提高,TiNi、Ni2AlTi、α-Cr等物相的相对含量逐渐增加。熔覆层主要由Ni(Al,Ti)枝晶组织与其周围呈网状分布的TiNi、Ni2AlTi、α-Cr晶间组织构成。熔覆层的显微硬度均提高到基体的2倍左右,Cr元素对提高Ni-Al涂层显微硬度的影响不大,但能使其显微硬度波动减小,趋于平稳,熔覆层的韧性随着Cr元素含量的增加而不断提高。当Cr元素添加量为20%(原子数分数)时,耐磨性最好,约为基体的2.948倍。结论Cr元素的添加,有利于熔覆层中α-Cr相的析出和TiNi/Ni2AlTi共晶组织的生成,能有效降低熔覆层的室温脆性,提高塑韧性及耐磨性能。

TC21钛合金表面激光熔覆Ni/Al-Cu涂层的组织与性能

利用激光熔覆技术在TC21钛合金表面制备Cu含量为0、4、8at%的Ni/Al熔覆层。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、显微硬度计以及材料表面性能综合测试仪。研究了Cu元素对Ni/Al熔覆层微观组织和性能的影响。结果表明:当Cu元素含量为0at%时,熔覆层物相主要由TiNi、Ti_(2)Ni、TiAl、AlNi_(2)Ti组成,熔覆层显微组织存在孔洞。随Cu元素的加入,Cu原子取代了TiNi晶体结构中的Ni原子,形成了新的三元相TiNi_(0.8)Cu^(0.2),熔覆层组织致密。当Cu元素含量为4at%时,熔覆层有最高的显微硬度和耐磨性,硬度约为基体的2.3倍,耐磨性为基体的4.1倍。磨损机制主要为粘着磨损和磨粒磨损。

Cu/Al双辊异温铸轧复合界面局部熔合机理

以传统双辊铸轧工艺为基础,采用金属熔体触辊凝固制备Cu、Al带坯并轧制复合,利用高温Cu带与Al带强压接触传热及其产生的Al带表面浅层熔化现象,提出一种基于界面"局部熔合"的Cu/Al双辊异温铸轧复合工艺。利用非线性热-力耦合有限元方法,数值模拟分析了Cu带和Al带初始温度Tc和Ta、层厚比K、压下率ε对Cu/Al复合界面接触换热与温度分布的影响规律,给出了实现界面"局部熔合"的工艺条件。在自制的物理模拟装置上进行Cu/Al异温压力复合实验,并通过界面的SEM、EDS分析,验证了Cu/Al界面"局部熔合"的工艺条件,揭示了Cu-Al二元合金反应扩散是"局部熔合"作用下Cu/Al界面冶金结合的主要机制。

铝合金表面激光熔覆AI-Y-Ni合金涂层的组织与性能研究

通过对铝合金表面激光熔覆的工艺和材料配方的研究,在铝合金表面上制备了具有良好冶金结合的Al-Y-Ni合金层。应用扫描电镜、XRD衍射和显微硬度计分析了熔覆层组织和性能。结果表明,熔覆层内成分和硬度分布较为均匀,物相组成以Al、Al2Ni6Y3和Al3Ni2相为主。

铝(4A60)-钢(08Al)复合带材界面化合物形成及结合性能

采用金相显微镜、扫描电镜和X射线衍射仪，研究电站空冷用铝（4A60）？钢（08Al）复合带材在不同模拟钎焊工艺下界面化合物的生长特性。通过界面剥离实验，分析不同钎焊条件下复合带材结合性能的变化规律。结果表明：在钎焊保温时间20 min内，铝（4A60）？钢（08Al）复合带材生成界面金属间化合物（IMC）的临界温度范围为605~615℃，界面相主要成分为Fe 2 Al 5。界面金属间化合物厚度随保温时间的增长满足抛物线规律，在615℃时，生长常数k为0.69＆#215;10？12 m2/s。界面金属间化合物厚度在12μm以下时，复合带材仍保持良好的界面结合强度（大于45 MPa）。随着金属间化合物厚度继续增加，界面结合强度显著下降，当金属间化合物厚度为25~43μm时，结合强度降至10~20 MPa；当金属间化合物厚度为54~68μm时，界面结合强度只有5~10 MPa。

退火工艺对镍/铝复合带金属间化合物的影响

研究了镍，铝复合带的退火热处理工艺，探讨了退火温度和时间对复合界面上金属间化合物生长的影响。结果表明：退火中温度过高会使界面上生成较厚的金属间化合物，退火温度在450～460℃时，镍，铝复合带的综合组织性能较为理想。当达到一定的热力学条件后，金属间化合物首先在界面局部区域生成并迅速完成长大，随退火时间延长，各区域的化合物新生相沿界面连接为一个整体。延长退火时间对金属间化合物层的相组成和各相厚度影响不大。综合复合带组织与性能的要求，得到优选退火工艺为460℃退火1h。

退火对轧制包覆碳钢/铝夹层带材组织与性能的影响

研究了轧制包覆法制备的碳钢/铝夹层带材的退火热处理工艺.利用OM,SEM,X射线衍射仪等分析了退火温度、退火时间等对复合界面金属间化合物生长的影响,在材料力学试验机上测试了复合带的主要力学性能.结果表明:退火过程中碳钢/铝复合带界面金属间化合物生成的临界温度为420℃,生成的金属间化合物主要为FeAl3相,化合物层的厚度约为10μm.420℃退火20 min是本实验得到的复合带最佳退火制度,退火后复合带的延伸率可达18.28%.退火后,当脆性金属间化合物层沿复合界面连续分布时,复合带的延伸率低于5%.

镍铁铝混合粉末的激光熔覆冶金研究

为了利用高能激光束将镍、铁、铝金属单质的混合粉末快速熔融,得到高性能的镍铁铝合金,并直接用于熔覆,采用激光3-D打印的金属粉末成型的方法,用一台中低功率的光纤激光器,以工程中常用的轧制不锈钢板为基底,研究了一定比例的镍、铁、铝混合粉末的熔覆冶金情况。通过优化激光工艺参量(激光频率、扫描速率、激光功率和离焦量)组合,得到了质量良好的单道熔覆结果。通过激光共聚焦显微镜、晶相显微镜以及扫描电子显微镜等检测手段,对熔覆条的宏观形貌和微观组织进行观察。结果表明,可获得良好的无气孔无裂纹的合金组织,且合金与基板形成了良好的冶金结合;熔覆层硬度低于基板硬度30HV左右,但截面硬度分布均匀。该研究有助于得到各向性质统一的冶金层。

在线高频电阻加热工艺对碳钢/铝复合带组织与力学性能的影响

研究了2种母材在线高频电阻加热生产碳钢/铝复合带的生产工艺,对产品的金相形貌与元素扩散进行了观察和分析。结果表明:在复合界面上没有生成采用传统热轧工艺所产生的金属间化合物FeAl3和Fe2Al5;碳钢/铝复合带的最佳退火工艺为450℃退火1h;复合带的综合性能得到了明显的优化,在线高频电阻加热工艺在双金属复合带的生产中具有广阔的应用前景。