【作者】 谭建波；

【导师】 邢书明；

【作者基本信息】 北京交通大学 ， 载运工具运用工程， 2007， 博士

【摘要】 鉴于半固态合金触变成形技术成本高、坯料加热易造成二次夹渣等,而半固态合金熔体流变成形技术具有流程短、成本低等优点,因此,半固态合金熔体流变成形技术越来越受到世界同行的重视。半固态合金熔体流变充型理论是半固态流变成形技术的工艺理论之一,目前,流变充型理论的研究还不系统、不完善,其完善与否将直接影响到半固态合金流变成形技术的推广和应用。本文对半固态合金熔体流变充型能力、沿程流动过程中初生相的演变规律、流变充型极限长度、充满型腔的临界条件等进行了比较系统的研究。采用实验的方法研究了半固态合金熔体原始组织特征参数对充型能力的影响,分析了原始组织初生固相率、晶粒尺寸和形状因子对充型能力的影响。通过回归分析,建立了原始组织特征参数与充型长度的数学表达式。研究了充型压力、充型速度对充型能力的影响,并分别建立了充型压力、充型速度与充型长度的关系。以半固态挤压铸造螺旋线试样为对象,用定量金相的方法研究了充型过程中半固态合金熔体初生固相率、晶粒尺寸和形状因子的演变规律;揭示了充型压力、充型速度对沿程流动初生相组织演变的影响;对半固态合金熔体充填螺旋线的流变充型方式进行了分析,结果表明,其流变方式属于均匀流变。在本实验条件下充型前半固态合金熔体的原始组织、充型压力和速度不会引起均匀流变向分离流变转变。以半固态合金熔体在圆管、矩形管中充型为例,结合半固态合金熔体具有宾汉体的流变特性,通过理论分析提出了可以定量计算半固态合金熔体流变充型极限长度的数学模型,并通过半固态挤压铸造实验进行了验证,计算值与实际测量值相比较,最大相对偏差≤7.8%。通过对半固态合金熔体流变充型过程的物理分析,结合半固态合金熔体的流变特性,根据充型驱动力大于或等于充型阻力和阻流通道内不可流动层厚度小于阻流截面最小厚度的1/2这两个充型临界条件,运用不可压缩粘性流体流动理论,提出了半固态合金熔体充满型腔的临界条件。该条件包括了设备参数、工艺参数、材料参数和模具参数,通过实验验证,可以用来指导半固态流变成形工艺设计、设备选型,并能进行缺陷预测和充型过程控制。更多还原

【Abstract】 Because the cost of semi-solid alloy thixoforming technology is high, and heating of ingot causes easily second inclusion, but the semi-solid alloy melt rheoforming technology has some advantages, such as short filling process, low cost and so on, so it has become more and more respected in colleague in the worldwide. Semi-solid alloy melt rheologic mold filling theory is one of the technologic theories of the semi-solid alloy melt rheoforming technology. Now the semi-solid alloy melt rheologic mold filling theory has not been researched systematically and completely, which will directly affect the popularization and application of the semi-solid alloy melt rheoforming technology. The rheologic filling ability of semi-solid alloy melt, the evolving rule of the original structure phase along filling process, the limit length of rheological mold filling of semi-solid alloy melt and the critical conditions of the mould cavity filled with the semi-solid melt were studied systematically in this paper.The influence of the characteristic parameters of the semi-solid alloy melt original structure on the mold filling ability was studied through experimental method; The influence of solid phase fraction, grain size and shape factor of original structure phase on the mold filling ability was analyzed; The mathematical representation between original structure character parameters and filling length was established through regression analysis. In addition, the influence of filling pressure and filling speed on the filling ability was studied, and the relationship between filling length and filling pressure and speed respectively was established.Using the spiral sample of semi-solid squeeze casting, the evolving rule of solid phase fraction, grain size and shape factor of the semi-solid alloy melt original phase was investigated by the method of quantitative metallic phase. The influence of filling pressure and speed on the original structure evolution along filling process was found. The rheological filling mode of the semi-solid alloy melt filling the spiral sample was analyzed. The results show that rheological mode was uniform, and the original structure of semi-solid alloy melt before filling, filling pressure and filling speed will not bring the conversion from uniform rheology to separate rheology in the condition of this experiment.Taking semi-solid alloy melts filling in circle pipe and rectangular pipe as example,更多还原