【作者】 查吉利；

【导师】 龙思远；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2018， 博士

【摘要】 目前,镁及镁合金熔体的制备均采用氯盐熔剂对熔体进行炉次式精炼、再转移到气体保护静置炉的工艺模式。熔剂在高温下易释放腐蚀性气体,污染环境,腐蚀车间建筑和设备,同时容易在熔体中产生夹杂,降低镁合金的力学和抗蚀性能。随着镁产业的持续增长,该工艺存在的品质、环保、能耗三大制约性问题也日趋突出。为了解决上述问题,业界一直在寻求镁熔体的无熔剂精炼方法,即,在保护气氛下,通过“气体精炼+过滤+静置”等物理方法综合应用,去除熔体污染物。但是,因熔体污染物间的巨大性状差异和介质过滤效能的维持及价格两个瓶颈,最终制约了无熔剂精炼方法的成熟应用。针对上述问题,本文提出了一套创新的研究方案,即:1、研发新型熔体过滤净化方法及装置,实现稳定持续有效的过滤,并实现过滤介质的重复使用;2、研究镁熔体污染物性态差异和单元无熔剂净化技术,根据熔体连续净化要求,合理配置单元技术、实现污染物的逐步去除,最终达成熔体连续精炼。3.设计和建造集成控制的无熔剂连续熔化精炼设备样机,并用该样机进行镁熔体精炼的实验生产并取样备检;4.合理应用检测手段,对试样进行综合实验检测分析,确定净化效果。本研究取得如下成果。1.在工艺原理研究方面:针对过滤介质堵塞和成本及排放难题,本研究基于“镁熔体的氧化夹杂区域团聚和沉降”的发现,提出了钢质过滤介质逆向过滤方法,实现了镁熔体的低成本持续稳定过滤净化。为实现熔炼的连续化,本研究针对镁熔体污染物的性状特征,研发了独具特色、集“气体保护、连续熔化、气体搅拌精炼、惯性分离、自净化过滤、自然沉降、凝析降铁、定量浇注、铸锭”等单元技术为一体的“镁熔体无熔剂连续熔化精炼工艺”。2.在设备设计建造方面:根据研发的无熔剂熔炼工艺,设计和构建了每小时熔炼能力为50公斤的原型设备。同时,开发“模糊控制+PID控制”相结合的工艺过程及工艺参数PLC集成控制系统,实现了设备的连续自动运行。与现行炉次式熔剂熔铸系统相比,除绿色环保连续自动外,设备集成度高而占地少、易操作、运行稳定。3.在检测分析方面:1)采用样机对ZM6镁合金进行的熔炼和精炼实验,结果表明,所研发设备熔炼保护效果稳定,熔体品质不随熔炼时间延长变差。精炼系统的除杂效能稳定,且在考核范围内与精炼速率无关。2)采用无熔剂重熔精炼工艺生产镁合金再生铸锭时,冷室压铸块状废镁的收得率为93%~96%,热室压铸块状废镁的收得率为88%~92%;废镁无熔剂再生锭的微观组织中夹杂数量偏多但尺寸小,且没有异常大尺寸夹杂。3)采用所研发设备以100%块状压铸废镁为原料进行废镁无熔剂回收。同商品镁合金锭相比,回收锭在成分和杂质元素含量方面,完全满足相关国际、国内镁合金铸锭标准的要求;回收锭在酸水溶液中腐蚀速率和总量更低,具有更优异的耐蚀性能。4)除消除废镁长途运输成本、废镁收集储运潜在安全隐患、解除熔炼再生对人员控制的依赖外,吨废镁制备吨再生锭的成本为1400~3000元,和现行吨废料换取吨镁锭的5000~6000元加工费相比,技术经济效益显著。更多还原

【Abstract】 Currently,Mg and Mg alloy melt preparation remains its traditional flux patch purification followed by gas protected melt settlement.Besides the heavily pollutive exhausts and melt contamination,the use of chloride salt leads to the generation of gases corrosive to workshop and equipments.With the continuous growth of Mg industry,solving the quality,environment protection and energy consumption problems in flux based melt preparation process becomes more and more prominent.Naturely,a lot of attention was paid to development of a non-flux method,i.e.,to purify melt under gas protective via integral use of "inert gas + filtration + settlement" purification mechanism.However,due to great property difference of melt contaminants,the rapid degrading filtration efficiency and high filter cost,no mature non-flux refining method is developed for industrial use.In order to solve the problems inherited in non-flux purification,a comprehensive approach is proposed in present study to achieve continuous and effective melt purification,i.e.: A.developing a novel filtering method to realize a continuous and low cost Mg melt filtration;B.developing a sequential contaminants removal process in accordance to the specific properties of contaminants.C.design and construct non-flux Mg melt continuous melting and purification prototype system with integral control mechanism,with which,conducting bulk Magnesium melt non-flux refining to provide samples for further investigation.D.proper use of modern analysis methods to characterize the samples in terms of inclusion geometry and related purification quality.The achievements and conclusions are specified as follows.1.Processing Research and Development“Inclusions suspending in Mg melt tend to agglomerate and settle” was observed and a unique "Mg melt self-clean filtering with reusable steel filter” is developed to provide Mg melt low cost and continuous filtration.Based on in-depth study on the properties of the melt contaminants and the performance of unit melt non-flux purification techniques,a novel continuous non-flux purification process was put forward,which is characterized by its sequentially use of unit purifying mechanisms of “gas refining,inertia separation,self-clean filtration,settlement,dosed pouring" to form “Mg melt non-flux continuous melting and purifying process”.2.Prototype equipment design and constructionAccording to the process principle,a unique "Mg non-flux continuous melting and purifying system" was designed and constructed.At meantime,a PLC integrated control system based on "fuzzy control + PID control" was developed to realize monitoring and control of the melt preparation and supply process as a whole.Compared with the traditional fluxed Mg melting and purification facility,the non-flux one needs less install and operation space,stable,easy to use and maintain,besides its green and continuity in nature.3.Experimental investigation with prototype equipment1)Using a prototype to conduct smelting and refining experiments on ZM6 magnesium alloys,the results show that the melting and protection effect of the developed equipment is stable,and the melt quality does not deteriorate as the smelting time is prolonged.The impurity removal efficiency of the refining system is stable,and is independent of the refining rate within the assessment range.2)When magnesium alloy reclaimed ingots are produced by the non-flux refining process,the yield of cold-house die-casting waste magnesium is 93%~96%,and the yield of hot-chamber block magnesium waste is 88%~92%.The recycled ingot contains more inclusions of smaller size,and there are no abnormally large inclusions.3)Compared with commercial magnesium alloy ingots,the 100% scrap recycled ingots by the non-flux refining process comply with relevant international and Chinese standards for Mg die casting ingots;the recycled ingots have lower corrosion rate and total amount in the acid aqueous solution,and have more excellent corrosion resistance.4)Due to lower processing cost and high reclaiming rate,the processing cost of the recycled ingot is about 1400~3000 Yuan RMB per ton,beside the eliminated logistic cost and potential danger.Compared with the current market price of 5000 ~ 6000 Yuan RMB for recycling of 1 ton scrap into 1 ton ingot,the scrap fluxless continuous recycling technique possesses very attractive technical and economic significance.更多还原