基于热焓补偿法的高强铝合金半固态制浆装置及工艺研究

STUDY ON SEMI-SOLID SLURRY PREPARATION DEVICE AND TECHNOLOGY OF HIGH-STRENGTH ALUMINUM ALLOY BASED ON ENTHALPY COMPENSATION METHOD

葛秋霜

11849021

硕士

机械工程领域工程

卢宏兴

2020-06-02

2020-07-20

哈尔滨工业大学

深圳

半固态成形技术是近年来发展迅速的一种金属材料近净成形技术，它结合了固态成形和液态成形的优点，能够以较低的生产成本获得较高的产品性能，其产品广泛应用于汽车、航天、通信等领域。现有的流变制浆技术主要存在适用合金材料少，温度场分布不均匀，工艺参数优化慢等难点。本课题基于本实验室自主开发的热焓补偿法流变制浆技术，以半固态成形工艺窗口较窄、难以实现半固态加工的7075高强铝合金材料为研究对象，开展了对此制浆技术的一系列研究，主要完成工作如下：利用有限元分析软件模拟了部分参数对浆料温度场的影响情况，为实验装置设计和实验方案设计提供参考。数值模拟结果表明：坩埚底部越薄，浆料温度场越均匀。适当增大坩埚底部到感应线圈底部的距离，可以使浆料温度分布更均匀。其他参数相同时，随着加热时间增大，浆料整体温差先减小后增大。不同工艺参数条件下确定温差随时间变化的拐点对于均匀浆料温度场很重要。根据热焓补偿法制浆工艺特点和数值模拟结果，设计了一套自动化制浆装置。选取坩埚初始温度、熔体重量、加热功率和加热时间四个工艺参数进行实验研究。分别探究了单因素变化时对半固态浆料径向、轴向以及整体温度场的影响规律，对工艺参数的优化进行讨论。实验结果表明：热焓补偿法能够有效减小温差，均匀温度场，制备出合格的40%-50%固相分数的7075铝合金半固态浆料。坩埚初始温度、熔体重量、加热功率和加热时间四个工艺参数均能对浆料平均温度产生较大影响。加热时间是影响浆料温差的最主要因素，其他因素对温差影响相对较小。其他工艺参数相同时，随着加热时间增加，浆料平均温度先降低后升高。加热功率、坩埚初始温度、熔体重量这三个工艺参数中任一参数增大均会导致浆料平均温度升高。随着加热时间增加，浆料整体温差先减小后缓慢增大。加热功率越大，浆料温差随加热时间变化的拐点出现得越早。采用中等加热功率（5-10 kW）更易同时获得合适的浆料平均温度和较小的温差。通过机器学习的数据处理方法，建立了神经网络预测模型，成功对热焓补偿法半固态制浆过程中温度场情况进行准确预测。分别建立了平均温度和最大温差两个预测模型。两个预测模型的决定系数均大于0.99，平均温度预测模型的平均绝对误差为0.16 ºC，最大温差预测模型的平均绝对误差为0.52 ºC。

Semi-solid forming technology is a near net forming technology that has developed rapidly in the decades. It combines the advantages of solid forming and liquid forming to obtain high product performance at low production costs. The semi solid formed products are widely applied in automotive, aerospace and communication industries. The currently existed technologies of making semi-solid slurries mainly have limitations such as only applicable for a few alloy materials, non-uniform distribution of temperature in a slurry and slow process of optimizing parameters. This project is to develop a novel technology to make high quality semi-solid slurry based on so the called Enthalpy Compensation Method. A series of studies on 7075 high-strength aluminum alloy materials have been carried out using the developed technology. The detailed results are presented as follows:The finite element analysis software was used to simulate the influence of the key process parameters on the slurry temperature distribution, thus assisting the design of experimental equipment and experimental procedure. The simulation results show that the thinner the bottom of the crucible the more uniform the slurry temperature distribution. Appropriately increasing the distance between the bottom of the crucible and the bottom of the induction coil can make the slurry temperature distribution more uniform. As the heating time increases while other parameters keep constant, the maximum temperature difference within the slurry initially decreases and then increases. It is important to detect the inflection point of the maximum temperature difference changes with time and to determine the appropriate heating time at different process parameters for uniform slurry temperature distribution. According to the characteristics of Enthalpy Compensation Method and the analysis of numerical simulation results, an automatic device of making semi-solid slurries has been designed. The process parameters of initial crucible temperature, melt weight, heating power and heating time were selected for experimental studies. The influence of single parameter on the radial, axial and overall temperature distribution within the semi-solid slurry was investigated. The experimental results show that the Enthalpy Compensation Method can be successfully applied to effectively obtain a uniformly distributed temperature within semi-solid slurry, to reduce the maximum temperature difference and to make high quality semi-solid slurries of 7075 aluminum alloy with solid fraction of 40% to 50%. Initial crucible initial temperature, melt weight, heating power and heating time all have great influence on the average slurry temperature, while heating time is the most important parameter for the slurry maximum temperature difference. With increase of the heating time, the average temperature of the slurry initially decreases and then increases. With increase of the heating power, the initial crucible temperature and the melt mass, the average temperature of the slurry gradually increases. Furthermore, with increase of the heating time, the overall temperature difference of the slurry initially decreases and then increases slowly. The higher the heating power, the earlier the inflection point of the slurry temperature difference change with the heating time is reached. A medium heating power ( 5-10 kW ) can be used to obtain desirable average temperature and small temperature difference of the slurry. Concept of machine learning in terms of a neural network prediction model has been established in this study. Changes of the slurry temperature distribution within a semi-solid slurry made by the Enthalpy Compensation Method was accurately predicted. Two prediction models, namely the average temperature model and the maximum temperature difference model, were established. The two prediction models can give both determination coefficients of greater than 0.99. The average absolute error is 0.16 ºC by the average temperature prediction model and the average absolute error is 0.52 ºC by the maximum temperature difference prediction model.

热焓补偿法 半固态 工艺参数 温度场 预测模型

enthalpy compensation method semi-solid slurry process parameter temperature field prediction model

中文

联合培养

南方科技大学

葛秋霜. 基于热焓补偿法的高强铝合金半固态制浆装置及工艺研究[D]. 深圳. 哈尔滨工业大学,2020.