Cast-rolling force model in solid-liquid cast-rolling bonding(SLCRB) process for fabricating bimetal clad strips

Based on twin-roll casting, a cast-rolling force model was proposed to predict the rolling force in the bimetal solid-liquid cast-rolling bonding(SLCRB) process. The solid-liquid bonding zone was assumed to be below the kiss point(KP). The deformation resistance of the liquid zone was ignored. Then, the calculation model was derived. A 2D thermal-flow coupled simulation was established to provide a basis for the parameters in the model, and then the rolling forces of the Cu/Al clad strip at different rolling speeds were calculated. Meanwhile, through measurement experiments, the accuracy of the model was verified. The influence of the rolling speed, the substrate strip thickness, and the material on the rolling force was obtained. The results indicate that the rolling force decreases with the increase of the rolling speed and increases with the increase of the thickness and thermal conductivity of the substrate strip. The rolling force is closely related to the KP height. Therefore, the formulation of reasonable process parameters to control the KP height is of great significance to the stability of cast-rolling forming.

Bonding strength of Invar/Cu clad strips fabricated by twin-roll casting process

Based on traditional twin-roll casting process,Invar/Cu clad strips were successfully fabricated by using solid Invar alloy strip and molten Cu under conditions of high temperature,high pressure and plastic deformation.A series of tests including tensile test,bending test,T-type peeling test and scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)measurements were carried out to analyze the mechanical properties of Invar/Cu clad strips and the micro-morphology of tensile fracture surfaces and bonding interfaces.The results indicate that no delamination phenomenon occurs during the compatible deformation of Invar/Cu in bending test and only one stress platform exists in the tensile stress-strain curve when the bonding strength is large.On the contrary,different mechanical properties of Invar and Cu lead to delamination phenomenon during the uniaxial tensile test,which determines that two stress platforms occur on the stress-strain curve of Invar/Cu clad strips when two elements experience necking.The average peeling strength can be increased from13.85to42.31N/mm after heat treatment at800℃for1h,and the observation of the Cu side at peeling interface shows that more Fe is adhered on the Cu side after the heat treatment.All above illustrate that heat treatment can improve the strength of the bonding interface of Invar/Cu clad strips.

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.

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.

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.

Microstructure and corrosion resistance of 304 stainless steel electroslag strip cladding

The 304 stainless steel strips were deposited one layer on carbon steel base metal by electroslag strip cladding （ESC） and submerged arc cladding （SAC）, respectively. The solidification microstrueture of ESC metal was analyzed by the optical microscopy, scanning electron microscope and energy dispersive spectroscopy. The corrosion resistance studies of strip cladding metals were carried out in 10% oxalic acid electrolytic etching test. The results showed that the cladding metal obtained by ESC presented low content of C, high content of Cr and enough alloying element of Ni in the chemical composition. The transition zone of ESC with small width was almost parallel with the base metal, leading to a lower dilution. There are three types of solidification modes （ A→AF→FA ） occurred in the ESC metal due to the decrease of cooling rate and degree of dilution from the transition zone to the top of ESC metal. As a result, the microstructure of ESC metal exhibited mainly austenite with a small amount of ferrite, contributing to achievement of better corrosion resistance.

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.

热连轧机轧制力成比例负荷分配的CLAD算法

为了实现热连轧精轧机组负荷分配的在线优化设定,提出一种轧制力成比例负荷分配的新算法CLAD算法(change load ratio by adjusting draft).其要点是通过调整压下量的偏差来使当前轧制力与目标轧制力的偏差最小化.根据轧制力成比例原则建立非线性方程组,结合假设条件,将系数矩阵简化为对角阵,经数学推导给出了新算法的迭代公式和收敛条件.提出一种经验插值法确定初始值,使得负荷分配迭代计算能快速收敛.对宝钢典型轧制案例的模拟计算验证了新算法具有计算速度快、收敛性好等优点,可用于在线计算.

Improvement of material properties and cladded flat product productivity with roll-bonding technology

Taking advantage of the progress of roll-bonding technology, the integrity of the material technology, and the development of the production and examination facilities of all the main carbon steels, stainless steels and specialty alloys in Baosteel, the cladded flat new products, which combined both properties of base material and clad material ,have been developed and produced in large quantities. The product categories includes heavy plates with high alloy content and homogeneous distribution in thickness and carbon steel plates cladded with all kinds of stainless steels ,nickel alloys ,and titanium alloys. The double-sided and single-sided cladding hot roiled strips and cold rolled sheets were also commercially produced. Due to the combined properties of both the cladding material and backing material, all products show obvious improvement in properties when compared with solid material. The comparability with the existing production process and equipment laid a very solid foundation for high productivity.

Effect of cold-rolling and annealing on interfacial structures and properties of A500/steel bimetal strip

The effect of cold-rolling, by both a series of small passes and single-pass with different deformations as well as the subsequent annealing, on the interfacial structures and properties of A500（AlSn8Pb2Si2.5Cu0.8Cr0.2）/steel bimetal strip produced by liquid-solid roll cladding was investigated. Experimental results of the cold-rolling by a series of small passes show that the interfacial bonding strength increases slightly when the total deformation is less than 7.32% and then decreases gradually with the increase in deformation. Subsequent annealing has no effect on the interfacial structures and properties. The effect of cold-rolling by single-pass less than 33.2% deformation on the interfacial structures and properties is the same as that of multi-pass cold-rolling, whereas cold-rolling by single-pass more than 33.2% deformation followed by annealing at 350℃ for 2.5h can make the interfacial bonding strength increase to a great extent. Metallographic examination of the interface shows that there exist only transverse cracks within the interfacial layer and the clad strip does not split along the interface during cold-rolling if the thickness of interfacial layer is less than 45μm. The thick interfacial layer（>56μm）, however, crumbles during cold-rolling, thus resulting in the splitting of the clad strip.

铝基覆铜板表面感光膜退除工艺

以2 g/L氢氧化钠(Na OH)为主要退膜反应剂,12 mL/L氨水和6 mL/L乙醇胺为加速剂,0.2~1.0 g/L 358DR为铝面保护剂,退除铝基覆铜板表面的感光膜。通过单因素实验研究了退膜温度、时间和铝面保护剂浓度对退膜效果和铝面情况的影响。结果表明,在铝面保护剂358DR质量浓度为0.8 g/L、温度为40℃的条件下,20 s能够将感光膜完全退除,并且铝面没有被攻击。该退膜工艺用于实际产线时的退膜效果甚至优于小试结果。

薄带连铸结晶辊涂层研究进展

双辊薄带连铸结晶辊兼有铸辊和结晶器的双重作用,在连铸过程中同时受到高温磨损、热应力以及压应力的多重作用,因此,原来的辊体铜质基质材料不能满足正常的连铸需要,必须选择合适的涂层材料和工艺对其表面进行涂层处理。目前,采用电镀、化学镀、热喷涂、冷喷涂以及激光熔覆等技术手段可以在结晶辊表面制备一种或多种材料的涂层。电镀、热喷涂以及激光熔覆技术相对成熟,应用最为广泛。涂层材料有单一金属、各类合金,同时可以加入各种添加剂。选用W、Cr、Ni、Co等单质金属以及WC-Co、Cr_(2)C_(3)-Ni-Cr、Ni-Cr等合金可以获得更好的综合性能;添加Cu的合金,如WC-Cu、W-Cu、Cu-Ni等,可以获得与铜基体相近的导热系数以及膨胀系数,添加稀土元素可以细化晶粒、降低裂纹倾向。通过表面涂层处理可以大幅度提高薄带连铸结晶辊的使用寿命。

热处理工艺对钎焊复合带材耐熔蚀性能的影响

采用金相显微镜、拉伸试验、模拟冲杯和钎焊试验等手段,研究了两种热处理工艺制得的蒸发器管片料用复合带材钎焊前后的力学性能、断面晶粒组织和微观组织。结果表明:对于0.27 mm厚的蒸发器管片用复合带材,H24态成品钎焊后更容易获得粗大的芯材晶粒组织。带材及模拟冲杯件钎焊时,钎料向芯层渗透主要以晶界渗透为主,熔蚀轻微;而经过芯材高温均热处理的O态成品钎焊后芯材晶粒细小,模拟冲杯件钎焊时,钎料向芯层渗透主要以晶内渗透为主,熔蚀比较严重。

带极电渣堆焊奥氏体不锈钢耐晶间腐蚀性能

用带极电渣堆焊和带极埋弧堆焊2种方法堆焊了Cr-Ni不锈钢,研究了这两种方法和焊接速度对堆焊层金属显微组织及耐晶间腐蚀性能的影响.显微组织观察表明,带极电渣堆焊和带极埋弧堆焊层的显微组织都为奥氏体+δ铁素体.带极电渣堆焊层金属中δ铁素体随着焊速的提高而增多,含量由6.8%增加到20.4%,带极埋弧堆焊金属中的δ铁素体含量比带极电渣堆焊的高,达到了23.6%;电化学动电位再活化试验结果表明,焊接速度8 m/h的带极电渣堆焊层金属的再活化率仅为3.22%,耐晶间腐蚀的性能最佳,焊速快慢或焊接方法改变都将使带极电渣堆焊层金属的再活化率升高,耐晶间腐蚀性能下降.10%草酸溶液电解浸蚀试验的结果与EPR曲线结果一致.

反向凝固连铸碳素钢带中复合层的凝固生长规律

在实验室条件下 ,用市售碳素钢板作为母带 ,用 0 8Al低碳钢作为复合层材料 ,对反向凝固连铸薄带生产过程中复合层在母带表面的凝固生长规律进行了研究。研究结果表明 ,母带在钢水中的浸渍时间、母带厚度和钢水过热度对复合层厚度有显著影响 ,而且这些工艺参数之间存在交互作用 ;复合层的变化经历了“快速生长”、“平衡相持”和“迅速回熔”三个阶段 ,这三个阶段在复合层厚度 -浸渍时间图上共同组成具有较长平台的反向凝固“∩”形特征曲线 ;较低的钢水温度和较厚的母带有利于增加复合层厚度。

同轴电缆用铜铝复合带中间退火工艺的研究

研究了中间退火工艺对同轴电缆用铜铝复合带力学性能的影响。结果表明,随着退火温度的升高或退火时间的延长,复合带的伸长率先增加后降低,在340℃×3h退火后,伸长率达到最大值35.80%。温度升高或时间延长都会导致复合带的抗拉强度降低。同轴电缆用铜铝复合带合理的中间退火工艺为310℃×1.5h。

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。

不锈钢带极电渣堆焊层金属耐腐蚀性能

采用带极电渣堆焊(ESW)和带极埋弧堆焊(SAW)两种方法在Q235母材上熔敷不锈钢层,分析了这两种方法和不同焊接速度下得到的堆焊层金属的电化学腐蚀及晶间腐蚀性能.电化学腐蚀结果表明,9.8%H2SO4溶液中,当扫描电位低于-300 mV时,堆焊层金属即可进入钝化状态,堆焊层金属(ESW v=8 m/h)的电化学腐蚀性能最佳;5%HCl溶液中,由于穿透性强的Cl-使堆焊层表面形成的钝化膜溶解破坏,导致堆焊层金属在扫描电位-800～200 mV范围内处于活化状态,发生点腐蚀.10%草酸溶液晶间腐蚀试验表明,带极电渣堆焊层金属的抗晶间腐蚀性能明显优于带极埋弧堆焊层金属.

激光宽带熔覆碳化钨/钴基合金的组织与性能

利用积分镜对激光束进行整形获得宽带激光束,进行宽带激光熔覆获得无裂纹WC/钴基合金层。对激光熔覆层用扫描电境(SEM)进行形貌观察,并进行能谱成分分析,用XRD进行合金物相表征。结果表明,熔覆层组织主要是由Co的过饱和固溶体、WC、W2C、CoCr、Cr7C3等相组成。W2C相的出现说明WC相发生了分解,WC等硬质相的存在导致熔覆层硬度的非均匀性。

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。