【作者】 李伟轩；

【导师】 任忠鸣； 邓康；

【作者基本信息】 上海大学 ， 钢铁冶金， 2009， 博士

【摘要】 本文围绕电磁场在铜坯两种主要连铸工艺,即水平连铸和垂直半连铸中的应用开展研究,包括板带坯水平连铸的电磁搅拌,电磁复合作用下的金属凝固和连铸,以及高性能无氧铜的软接触电磁连铸,期望通过实验室模拟、现场试验和工业实践,开发新技术,推动电磁技术在金属铜坯连铸中的推广和应用。本文针对超薄板坯宽厚比大、电磁搅拌时感应效率低下,铜制结晶器对交变电磁场屏蔽强烈,水冷感应线圈在生产中易产生安全事故,以及交变电磁场对生产现场控制设备有干扰等问题,提出了施加静磁场和与其正交的直流电,形成定向电磁搅拌的新模式,设计了工业试验和试生产用的铜合金超薄板坯(板带坯)水平连铸电磁搅拌结晶器,对其搅拌特点和规律进行了深入研究,掌握了基本规律,进而开展了Cu-Fe-P系KFC合金和Cu-Ni-Zn系锌白铜合金的板带坯水平连铸电磁搅拌的工业试验和试生产。结果显示,在电磁搅拌作用下,铜合金超薄板坯(板带坯)水平连铸的凝固界面形状发生很大变化,搅拌对流对凝固前沿的溶质富集产生强烈的抑制作用,使板带中的Fe元素偏析现象大幅度下降(当输入电流达到800A时偏析近零);同时,电磁搅拌使凝固组织细化,中心层出现明显等轴晶带并使疏松等缺陷消失,而铸坯边缘区域的柱状晶组织则变细且生长方向趋向铜液来流方向(发生偏移),柱状晶一次主轴之间间距随搅拌电流增高而减小,铸坯的抗拉强度比普通连铸时提高39%。本文开发了采用稳恒强磁场与工频小电流复合作用产生电磁振荡的方法,在实验时中进行了较高熔点的纯铝及Al-4.5%Cu合金的电磁振荡下的凝固实验,发现电磁振荡技术可以明显细化金属的凝固组织。对于纯铝,同一交变电流强度(10A)下,当磁感应强度为6T时,试样细化程度存在峰值,晶粒数最多,但是在纵截面上存在明显的细化衰减现象。6T磁感应强度和5A交变电流时两者的复合作用的细化晶粒作用最明显。对于Al-4.5%Cu合金,单一稳恒磁场或单一的交变电流均不能改变合金的树枝晶形貌。只有当磁场和电流复合时枝晶才有可能被打碎,复合作用小时合金凝固组织为等轴状和颗粒状混合的凝固组织,复合作用大时凝固组织以颗粒状为主。在10T磁感应强度下,随着交变电流的增加液体波动加剧,枝晶被打碎的程度增加,直至完全转变为颗粒状组织。揭示晶粒细化的原因主要是电磁复合作用造成的波动力对初始晶核的冲刷,以及电磁压力折断枝晶臂引起的晶核增值,而并非通常认为的空化效应。工业试生产证明了在实际生产中利用电磁复合作用细化晶粒改善铸坯质量的可行性。本文在理论计算和实验室模拟实验的基础上,设计出铜坯连铸用软接触电磁结晶器,并且在无氧铜的生产中得到成功应用,在此基础上提出“电磁(搅拌)脱氧-电磁连铸”的无氧铜生产方法,实现了国内铜加工企业现有装备条件下的大尺度、高性能无氧铜材料的非真空、低成本、连续性生产。该方法生产的无氧铜材的铜含量≥99.97%,氧含量在5-10ppm,超过国家TU1标准(部分达到TU0标准),完全满足国际上电真空领域用高性能无氧铜的性能指标,并且物理、力学性能均优于同类产品,其中,铸坯密度8.92~8.94g/cm3(接近铜的理论密度8.96g/cm3),屈服强度51MPa,抗拉强度155MPa,延展率45%,断面收缩率70%;材料电阻率0.01712?mm2/m(国际退火无氧铜材料的标准电阻率为0.01742?mm2/m,国内的行业标准为0.01777Ωmm2/m),电导率为104%IACS,比国际上同类材料的电导率标准提高1.75%,比国内行业标准提高3.80%;同时,在高温真空条件下,材料的全排气量为5.6mPa·m3/g,仅为日本采用常规方法所生产的同类产品的40%。综合上述研究成果,本文在超薄板坯(板带坯)水平连铸电磁搅拌和电磁振荡结晶器及连铸工艺等方面开辟了新的思路和有实用意义的工业试验,为今后的发展和新技术开发建立了基础。在有色金属连铸用软接触电磁结晶器设计与实用化,高性能无氧铜材料制备的电磁(搅拌)脱氧-电磁连铸新方法等方面实现了技术创新,形成了大尺度、高性能无氧铜材料的低成本和规模化生产,其产品在应用领域和物理、力学性能等方面均达到国际前沿标准,更多还原

【Abstract】 In this paper, we focus on the study of application of electromagnetic field in the main two copper continuous casting technologies: horizontal continuous casting and vertical semi-continuous casting, including the electromagnetic stirring in thin slab horizontal continuous casting, electromagnetic vibration in liquid metal solidification and continuous casting, and soft-contact electromagnetic continuous casting of high quality oxygen-free copper We hope these experiment investigations in laboratory and factory could brought out new techniques and promote the industry application of electromagnetic technology in copper continuous casting.Because of the disadvantages, including large width-height ratio of super thin slab, the weaken stirring effect of electromagnetic induct in EMS, the strong shielding effects of copper mould on the alternated electromagnetic field, the unsafety of brass water-cooling induct coil using in practice and the interference effects of alternated electromagnetic field on the control equipment, a kind of new stirring mode under the condition of static magnetic field coupled with orthogonal directional current was brought forward. EMS mould used in copper thin slab horizontal continuous casting for industry experiments and production was designed out and its stirring characteristics were studied deeply. Then, it was applied to Cu-Fe-P series KFC and Cu-Zn-Ni alloy horizontal continuous casting successfully. It showed that the solidification interface of copper alloy thin slab changed obviously after EMS process, the solute accumulation in solid liquid interface was repressed strongly via the electromagnetic stirring, and the segregation of Fe was reduced greatly (achieved to zero when stirring current is 800A). At the same time the solidification structure of the billet was refined, equiaxed grain zone appeared in the mid-zone and the porous shrinkage disappeared. While the column grain became thinner at the edge of the billet, its growth direction changed towards to the metal flow. The primary dendrite spacing reduced with the increasing of stirring current, and the billet’s tensile strength enhanced 39% after EMS process.In lab, alloys with higher melting point such as pure aluminum and Al-4.5%Cu alloy were solidified in vibrated condition which generated by static high magnetic field with 50 Hz alternating current orthogonally. The results showed that the solidification structures were refined obviously by the electromagnetic vibration. For pure aluminum, the sample has the most grain number per area when the magnetic flux strength was 6T and the alternative current strength keeping at 10A, but on vertical section, the refine effect attenuated from top to bottom. When the magnetic flux strength was 6T and alternative current strength was 5A, the sample had the most refined solidification structure. For Al-4.5Cu alloy, the shape of dendritic crystal would not be changed by only imposing static magnetic field or alternative current singly. While it would be changed via a static magnetic field interacted with alternating current, which called electromagnetic vibration. When this multiple action was weak, the solidification structure was equiaxed crystal mixed with granular grain. Once this action was strong, the main structures were granular. When the magnetic flux strength was 10T, the liquid metal’fluctuation aggravated with the raise of alternating current strength, more and more dendritic crystal were broken up and finally changed to granular grain entirely. We found that the main cause of crystal refinement were the crystal nucleus multiplication which generated by the electromagnetic vibration and the broken up of dendritic arm by electromagnetic pressure during the dendritic crystal growth, but not the cavitations effects in general. The industry experiment using H65 brass testified the feasibility of electromagnetic vibration, which showed the refine grain and improved billet’s quality.Based on the theoretical calculation and simulation experiment in laboratory, a kind of soft-contact electromagnetic mould used in copper alloy continuous casting is designed and applied successfully in the production of copper and magnesium alloy. Furthermore, a new technique acquiring oxygen-free copper called“electromagnetic (stirring) deoxidization - electromagnetic continuous casting”is proposed. By using this technique, the copper with the characters of high quality, large size and oxygen-free could be realized in the domestic enterprises under the condition of non-vacuum, low cost and continuous production. The copper content exceeds 99.97% and oxygen content lies between 5 and 10 ppm, which meet the TU1 standard, even the TU0 standard and reach the copper standard used in international vacuum electron field. The physics and mechanical property are better than that in similar products, its density reach to 8.92-8.94 g/cm3 (the copper density in theory is 8.96 g/cm3) , the mean yield strength is 51 MPa, the tensile strength is 155 MPa, the elongation percentage is 45 %, reduction of cross section area is 70 %, resistance is 0.01712 ?mm2/m(the value of annealed oxygen-free copper standard international is 0.01742Ωmm2/m), conductivity exceeds 104 % IACS which enhanced 1.75% above that in the similar production world wide,the full exhaust gas content in high temperature and vacuum is 5.6 mPa·m3/g, just about 40 % of the value in traditional Japanese production.As a sum, the research on electromagnetic stirring mould used in thin slab horizontal continuous casting, electromagnetic vibration mould and new continuous casting technique broken a new path and have practical values and establish the basis for the future development, the design and utilization of copper electromagnetic soft-contact continuous casting mould , new technique acquiring oxygen-free copper called“electromagnetic (stirring) deoxidization - electromagnetic continuous casting”were technique innovations, high quality oxygen-free copper billet with large size could produced in industry with low cost, and high physical and mechanical property.更多还原