【作者】 李亚宁；

【导师】 龙思远；

【作者基本信息】 重庆大学 ， 材料加工工程， 2009， 硕士

【摘要】 面对常规锻造成形工艺生产镁合金锻件所存在的工艺冗长、变形不均匀、材料利用率低、无性价比优势,难以实现规模生产应用的现实,本论文在“镁合金复合成形方法”专利的基础上,通过试验、数值模拟和理论分析相结合的方法,进行了“镁合金挤压预成形坯模压近终成型工艺”研究,以期为高品质镁合金锻件的低成本生产奠定技术基础。为此,本研究以拉伸试样为对象,先挤压生产具有试样二维几何特征的预成形挤压型材,然后根据试样厚度截取一段挤压型材,一次热模压获得几何形状、尺寸和表面质量满足要求的近终成型拉伸试样锻件。通过对该过程中材料的组织特征、拉伸性能、试样工艺品质、成形工艺技术指标等进行分析和检测,系统考核了该工艺的技术经济特征。研究表明:镁合金挤锻复合成型方法与常规锻压成型相比,具有以下特点:①短流程、高效率:将常规锻造工艺生产镁合金构件所经历的挤压开坯、多道次加热锻压和切边,缩短为一次挤压预成形后一次模压成型,大幅度缩短了工艺流程,提高了生产效率;②低能耗:挤锻复合工艺实现了一次加热模压近终成型,减少了加热、锻造道次,并省略了切边,在简化锻造工艺的同时,降低了生产能耗;③高材料收得率:因采用一次等体积封闭模压成形,基本消除了工艺废料,锻造工艺收得率达到95%、综合工艺收得率达85%以上,远高于常规锻造的30%～60%;④变形组织、性能分布均匀:和常规锻件因锻造变形分布不均导致组织均匀性较差不同,挤锻复合工艺因采用大挤压变形率,在挤压预成形坯内获得了均匀细小的等轴细晶组织,模压成型后组织晶粒度和均匀性得到了有效保证,故工件内部组织、性能均匀。综上所述,和常规锻造工艺相比,挤锻复合近终成型工艺具有显著的技术经济优势。作为研究总结,本文还确定了“挤锻复合构件生产工艺开发路线”、提出了“挤锻复合工艺及最佳参数组合”,为该工艺的应用奠定了基础。挤锻复合构件生产工艺开发路线:锻件图→锻坯工艺数字分析→模压工艺优化→挤压预成形坯截面设计→挤压工艺及模具设计→铸坯设计挤锻复合工艺最佳参数组合:铸坯均质化工艺:入炉加热到400℃后保温4个小时;挤压预成形工艺:变形率≥16%,挤压模具预热温度400℃;模压坯截取工艺:余量～3%,在挤压预成形坯型材上截取模压坯料;挤压预成形坯段模压工艺:坯料入炉加热到400℃后保温30分钟,迅速移入400℃模具中以100～1000 mm/min的速度等温模压。更多还原

【Abstract】 The present forge forming is characterized by its lengthy process, deformation non-uniformity, low material utilization ratio and high processing cost, and is therefore hard to be used to produce Mg forging parts for mass commercial application. To explore a new cost effective, high efficiency process with potential of stable offering quality products, based on a patented technique, the present study is devoted to do systematic research on“Near-net-shape Hot-pressing of Mg Extruded Preform”via experiments, numerical virtual reality and theoretical analysis.Aiming to produce tensile specimens with the technique, a preform extrusion profile with the 2D geometrical feature of the specimens was first produced. Then, the profile was sectioned, and net-shapely forged into the specimens with the required geometry and surface quality. Finally, the microstructure, tensile properties, processing quality, and processing parameters were empirically determined. Meanwhile, the technical and economic characteristics of the process are also examined in this paper.The obtained results show that, as compared with conventional forging forming process, the new process has the following characteristics:①Short and efficient: The new process replace the multiple forging followed by trimming with one shot close-die press forming, which consequently reduces the process sequence and increases the processing efficiency or productivity.②Low energy consumption: the new process reduces the multiple heating and forging in a conventional forge forming process to one-shot net-shape pressing of the extruded preform, which, in turn, largely reduces the energy consumption besides the processing simplification.③High material utilization ratio: the one-shot close-die pressing almost eliminates the need for residual material. Consequently, the material utilization ratio in press forming is as high as more than 95%, and the comprehensive material utilization ratio from extrusion to press remains more than 85%, far higher than 30～60% for the conventional forge forming process.④Uniform microstructure and properties: the employment of high deformation rate of≥16% during extrusion preforming ensure the obtainment of affine and equiaxed grains throughout the preform, which ensures a fine, equiaxial grains and the consequently good and uniform properties in the products. The results detailed above indicate that the newly developed process is obviously technically and economically advantageous as compared with the conventional forge forming process. As a summary, flow-chart of processing design for a Mg part and the optimal processing parameters of the new process were proposed as well to lay a sound base for its industrialization.The proposed flow-chart of processing design is: forged part drawing→forging numerical analysis→forging optimization→cross-section design of the extruded preform (profile)→design of extrusion die→design of casting billet.The optimized processing parameters for the new process are:The billet homogenization: heating at 400℃for 4 hours;Extrusion: deformation rate≥16%, die preheating temperature 400℃;Preform Sectioning: extruded profile sectioning for close die pressing with weight allowance less than 3%Close-die pressing: profile sections heated to 400℃for 30 minutes and, then, quickly removed into the die preheated to 400℃and forged with ram speed of 100～1000 mm/min.更多还原