超声振动—溶质对铸造铝合金内耗的影响研究

发布时间：2018-08-29 19:37

【摘要】：铸造铝合金具有良好的流动性,导热加工性能好,铸造周期短,化学稳定性好以及比强度高等一系列的优点,在制造业的各个领域都得到了非常广泛的应用。常用的铸造零件如活塞、旋转支架、轴承、缸体等由于其产生的振动大,噪声严重等原因,不能完全满足生产和生活的需求。现有的工艺一般只能改善这些影响,并不能从根本上满足人类对防噪减振的需求,因此如何提高材料的阻尼性能,从根本上起到防噪减振的效果,成为人们探究的课题。内耗技术作为研究材料微观机制,了解材料微观特性的有效手段,对于我们研究材料的内部结构,了解材料物理性能,以及如何改变材料组成使其拥有更好的、符合生产生活需求的性质等方面具有重要的研究意义和实际价值。本文在超声与未超声条件下,分别将添加有Cu、Mg、Zn、Cr四种溶质元素的铝液进行铸造,利用多功能内耗仪对四种不同的铝合金进行不同频率的内耗性能测试,并通过光学显微镜观察晶粒尺寸的大小,运用扫描能谱分析晶体内部元素含量,进行必要的热处理等工艺,研究不同合金内部的微观结构、了解内耗峰的特点、形成机制及其变化规律,探究内耗峰在研究合金晶粒尺寸、内部结构、相变、杂质等方面的作用。得出如下实验结论:(1)不同的溶质元素的添加能一定程度地改变铝合金的内部结构。通过对内耗—温度曲线显示出的信息进行分析,能够在一定程度上了解合金材料的微观机制,如晶界尺寸大小,沉淀相是否存在,杂质元素是否存在以及其含量的多少等一系列微观信息。(2)施加超声振动与改变溶质元素含量都能在一定程度上改变合金晶粒的尺寸,从而对晶界内耗峰产生影响,施加超声比未施加超声的合金晶粒尺寸更小,对应的内耗峰的峰温与峰高会更低。改变溶质元素含量,当其使晶粒尺寸减小时,对应的晶界内耗峰的峰高和峰温降低,反之,峰值和峰温均升高。若元素含量的添加达到形成沉淀时,则会产生新的沉淀型的相变内耗峰。(3)四种不同的铝合金中的内耗峰的种类各不一样,铝铜合金中只存在晶界内耗峰以一种类型,铝镁合金中存在晶界内耗峰以及过饱和相变型内耗峰两种,铝锌合金中只存在一种由不连续沉淀引起的相变内耗峰,铝铬合金中存在晶界内耗峰以及Snoek内耗峰两种。(4)不同的内耗峰的产生原理不一样,铝镁合金中的相变内耗峰则是过饱和相在回复温度以上形成脱熔的中间相β'相而产生的,铝锌合金中的相变内耗峰是不连续的沉淀在晶界偏析沉淀下来,并向晶界发展而产生的。铝铜、铝镁、铝铬三种合金中的晶界内耗峰都是加热过程下强迫振动导致的晶界的滞粘性滑动引起的。铝铬合金中的Snoek内耗峰是由于合金内部非金属元素(C、O)的增多而导致的点缺陷引起的。
[Abstract]:The cast aluminum alloy has a series of advantages such as good fluidity, good thermal conductivity, short casting period, good chemical stability and high specific strength. It has been widely used in various fields of manufacturing industry. The commonly used casting parts such as piston, rotary support, bearing, cylinder block and so on can not fully meet the needs of production and life because of its large vibration and serious noise. The existing technology can only improve these effects and can not satisfy the demand of human being for noise and vibration control fundamentally. So how to improve the damping property of materials and how to improve the effect of noise and vibration reduction has become a research topic. Internal friction technology is an effective means to study the microscopic mechanism of materials, to understand the microscopic properties of materials, to study the internal structure of materials, to understand the physical properties of materials, and to change the composition of materials to make them better. It is of great significance and practical value to meet the needs of production and life. In this paper, the aluminum liquid with four solute elements of Cu,Mg,Zn,Cr was cast under ultrasonic and non-ultrasonic conditions, and the internal friction properties of four different aluminum alloys were tested by multi-function internal friction instrument. The grain size was observed by optical microscope, element content in crystal was analyzed by scanning energy spectrum, heat treatment was carried out, the microstructure of different alloys was studied, and the characteristics of internal friction peak were understood. The mechanism of formation and its changing law are discussed, and the effect of internal friction peak on the grain size, internal structure, phase transformation and impurity of the alloy is studied. The experimental results are as follows: (1) the internal structure of aluminum alloy can be changed to some extent by adding different solute elements. By analyzing the information shown in the internal friction temperature curve, the microscopic mechanism of the alloy material, such as grain boundary size, the existence of precipitation phase or not, can be understood to a certain extent. The existence of impurity elements and the amount of impurity elements are a series of micro information. (2) applying ultrasonic vibration and changing the content of solute elements can change the grain size of the alloy to a certain extent, thus having an effect on the internal friction peak of grain boundary. The grain size of the alloy with ultrasonic is smaller than that without ultrasonic, and the peak temperature and peak height of the corresponding internal friction peak are lower. When the content of solute element is changed, the peak height and peak temperature of grain boundary internal friction peak decrease when the grain size is reduced, whereas the peak value and peak temperature increase. If the content of elements reaches to precipitate, there will be a new precipitation-type internal friction peak. (3) the types of internal friction peaks in four different aluminum alloys are different, and there is only one type of internal friction peak at grain boundary in Al-Cu alloy. There are two kinds of internal friction peaks at grain boundary and supersaturated phase transition in Al-Mg alloy, but there is only one internal friction peak caused by discontinuous precipitation in Al-Zn alloy. There are two kinds of internal friction peaks at grain boundaries and Snoek peaks in Al-Cr alloys. (4) the different internal friction peaks are produced by the formation of 尾 'phase in the demelted mesophase in the supersaturated phase when the recovery temperature is above the recovery temperature. The internal friction peak of phase transformation in Al-Zn alloy is formed by the precipitation of discontinuous precipitation at grain boundary and its development towards grain boundary. The internal friction peaks of grain boundary in Al-Cu, Al-Mg and Al-Cr alloys are all caused by hysteretic slip of grain boundary caused by forced vibration during heating. The internal friction peak of Snoek in Al-Cr alloy is caused by the point defect caused by the increase of non-metallic elements (Co) in the alloy.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG292

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