铝硅合金变质处理的热分析技术研究

华中科技大学

硕士学位论文

过共晶铝硅合金变质处理的热分析技术研究

姓名：曾勇

申请学位级别：硕士

专业：材料加工工程

指导教师：吴树森

20090527

华 中 科 技 大 学 硕 士 学 位 论 文

摘 要

过共晶Al-Si合金广泛运用于制造汽车发动机活塞等零件，但其组织中存在的粗大多角形块状初晶Si以及大量针片状共晶Si，严重影响了合金的力学性能。工业中常通过变质处理来提高合金性能，在各种检测变质效果的方法中，热分析法有着很大的理论和实际意义。本文在本研究室原有的亚共晶Al-Si合金热分析系统基础上，对原有系统的软硬件进行改进和完善，使其能在5min内完成过共晶Al-Si合金变质效果的评判。

利用I-7018数据采集模块以及I-7520信号转换模块建立起了新的热分析系统，通过串口通信完成对原始温度数据的精确采集，比较了VC++环境下三种常用的串口通信方式，选用多线程下的CSerialPort类来完成对串口通信的控制，在热分析设备和计算机的接口问题上，除了通过RS232串口直接通信，采用RS232协议转USB的转换线，使系统能通过USB接口和计算机进行通信，极大提高了数据传输速度、灵活性以及方便性。在原始温度数据的处理上采用平均值滤波法，选用三点中心差分法计算微分曲线，然后再选用相邻平均时域滤波法来对微分曲线进行平滑滤波。根据过共晶Al-Si合金冷却凝固特点，通过相应算法完成初晶阶段和共晶阶段热分析特征值的识别。

使用热分析系统对本课题组新开发的新型Al-20Si-1.5Cu-1Ni-0.5Mn高硅铝合金进行初晶Si的P变质的热分析研究，研究变质效果和合金初晶段热分析特征值之间的关系，结果表明ΔTG(初晶生长温度的差值)和初晶Si平均晶粒大小之间有很好的对应关系，当ΔTG为35℃到45℃之间时，初晶硅有着较好的变质效果，当ΔTG<30℃时，没有明显的变质效果。

使用热分析系统进行Al-20Si-1.5Cu-1Ni-0.5Mn-0.4Mg高硅铝合金Re变质的热分析研究，结果表明，在未发生过变质的前提下，当ΔTEG(共晶生长温度差值)为6.5℃到7.6℃之间时，共晶Si有着较好的变质效果，当ΔTEG<4.3℃时，没有明显的变质效果，ΔTEG和共晶变质效果有较好的对应关系。

关键词： 热分析 过共晶铝硅合金 串口通信 冷却曲线 变质 特征值

华 中 科 技 大 学 硕 士 学 位 论 文

Abstract

The hypereutectic Al-Si alloy is widely used in manufacture of automotive engine piston and other parts, but the large primary silicon and the long acicular eutectic silicon exist in the unmodified alloy, which affect the mechanical properties of the alloy greatly. Modifications are widely used in industry in order to improve the mechanical properties. Among the methods of detecting the effect of the modification, thermal analysis has great theoretical and practical significance. In this paper, with the improvement of the hardware and software of the original eutectic Al-Si alloy thermal analysis system, a new system which can measure the modification effect of the hypereutectic Al-Si alloy within 5 minutes was developed.

By the use of the I-7018 data acquisition module and the I-7520 signal converter module, a new system was developed. The collection of the original temperature data could be completed accurately through serial communication, three commonly used methods of serial communication under VC environment had been compared, the multi-threaded category–CserialPort was selected to control the serial communication. The serial communication could be completed not only through the RS232 serial port but also through the USB interface with the conversion line, so that the speed, flexibility and convenience of the data transmission were greatly improved. The filtering of the original temperature data was implemented by calculating average and medial value, the derivative curve was calculated using three points central difference method, then the adjacent average filtering method was chosen to filter the derivative curve. According to the cooling characteristics of the hypereutectic Al-Si alloy, corresponding algorithm was adopted to identify the thermal analysis characteristic values of the alloy.

Using the thermal analysis system, the effect of primary silicon modification of the Al-20Si-1.5Cu-1Ni-0.5Mn alloy newly developed by our group was studied in order to

华 中 科 技 大 学 硕 士 学 位 论 文

find the relationship between the effect of the modification and the thermal analysis characteristic values, it is found that, ΔTG ( the difference of the primary silicon growth temperature) has a good relationship to the average grain size of the primary silicon, if ΔTG was between 35℃ and 45℃, the primary silicon was well modified, if ΔTG was lower than 30℃, the alloy was unmodified.

The effect of eutectic silicon modification of the Al-20Si-1.5Cu-1Ni-0.5Mn -0.4Mg alloy had also been studied, it is found that, if ΔTEG(the difference of the eutectic silicon growth temperature) was between 6.5℃ and 7.3℃, the eutectic silicon was well modified, if ΔTEG was lower than 4.3℃, the alloy was unmodified, ΔTEG had a good relationship to the effect of the modification of the eutectic silicon.

Key words: thermal analysis, hypereutectic Al-Si alloy, serial communication,

cooling curve, modification, characteristic values

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本人声明所呈交的学位论文是我个人在导师指导下进行的研究工作及取得的研究成果。尽我所知，除文中已经标明引用的内容外，本论文不包含任何其他个人或集体已经 …… 此处隐藏：9344字，全部文档内容请下载后查看。喜欢就下载吧 ……