si对za38锌铝合金组织和热疲劳性能的影响.doc

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摘要 本课题主要介绍了加Si后的ZA38锌铝合金的微观组织及力学性能，研究了Si含量变化对ZA38锌铝合金的微观组织及力学性能的影响，同时研究了Si含量的变化对锌铝合金热疲劳性能的影响。本课题主要通过光学显微镜、万能拉伸试验机、SEM、自约束全自动冷热疲劳试验机等仪器对加Si的ZA38锌铝合金组织及热疲劳性能进行系统地研究。

    实验结果表明：ZA38合金由初生α相、α相间的（α+η）共析体和ε相组成。ZA38合金中加入不同含量的Si元素后，合金的组织形态有较大差异，Si元素的加入量为0.55%时，合金组织细化程度最大，由未添加Si元素时的粗大树枝晶转化为细小等轴晶，且分布均匀。

ZA38合金中Si含量达到0.55%时，抗拉强度达到最大值405Mpa，比不加Si时提高了2.5%，延伸率达到最大值4.33%，增加了18.6%。随着Si含量的增加，ZA38合金的硬度随之增大。但合金中的Si含量过高时，合金组织中大块Si相明显增多，会割裂基体，从而造成应力集中，使其力学性能变差。

ZA38合金的热疲劳裂纹的扩展程度主要受两方面的影响：一是合金的强度和塑性；二是合金中的Si相的分布情况。当ZA38合金中Si元素含量为0.55%时，Si相尺寸适中，均匀分布在基体上，合金组织得到最大细化，在热循环应力作用时，会阻碍位错运动，使合金的热疲劳抗性得到提升。当Si的含量过高时，初生Si相粗化，以块状和长条状分布在基体上，合金的强度和塑性都变差，热疲劳抗力大大降低。ZA38合金热疲劳性能由好到坏依次为：0.55%Si，0.3%Si，0.8%Si，0%Si，1.3%Si，1.05%Si。

关键词：ZA38；显微组织；合金力学性能；热疲劳性能

 

Abstract  This subject mainly introduces the microstructure and mechanical properties of the ZA38 zinc aluminium alloy through addition Si, and study The effect of Si content on the microstructure and mechanical properties of ZA38 Zn-Al alloy and The effect of Si content on the thermal fatigue properties of Zn-Al alloy, This subject mainly through optical microscope, universal tensile testing machine, SEM, self constraint automatic cold and hot fatigue testing machine and other equipment to study on the microstructure and thermal fatigue property of ZA38 Zn Al alloy with Si.

The experimental results show that the ZA38 alloy consists of primary α phase, (α +η) eutectoid and ε phase composition. After adding different content of Si element in ZA38 alloy, microstructure morphology have big difference, when Si addition amount is 0.55%, the degree of alloy organization’s refinement is the largest, from coarse dendritic structure without adding Si element is transformed into fine equiaxed grains and uniform distribution.

When the content of Si reached 0.55%, the tensile strength reached the maximum 405Mpa, compared with the alloy without Si element, it increased by 2.5%, and the elongation reached 4.33%, increased by 18.6%.. With the increase of Si content, the hardness of ZA38 alloy will increase.. However, when the content of Si in the alloy is too high, the bulk Si encounter in the alloy is obviously increased, which will separate the matrix, resulting in the stress concentration, and it will make the mechanical properties worse..

The thermal fatigue crack growth of ZA38 alloy is mainly influenced by two aspects: one is the strength and plasticity of the alloy, the other is the distribution of Si phase in the alloy. When the content of Si element in ZA38 alloy is 0.55%, the size of Si phase is moderate and uniform distribution in the matrix,. the microstructure of the alloy obtained maximum refinement, with the effect of thermal cycling should force, dislocation motion will be hindered, the thermal fatigue resistance of the alloy are improved. When the content of Si was too high, the primary Si phase was coarsening and distributed by the form of bulk and the strip on the matrix, the strength and ductility of the alloy were decreased, and the thermal fatigue resistance decreased greatly.. The thermal fatigue properties of ZA38 alloy are arranged from good to bad, followed by 0.55%Si, 0.3%Si, 0.8%Si, 0%Si, 1.3%Si, 1.05%Si.

Key Words  ZA38 alloy; microscopic structure; alloy mechanical properties; thermal fatigue property

 

 

第1章 绪 论

1.1 锌基合金的简介

1.1.1 锌基合金的发展历史

1930年，美国新泽西锌合金公司研制出了Za2mak3和Zamak5锌铝压铸合金。二战期间，德国为解决铜资源紧缺问题，成功的用重力铸造锌铝合金代替铜合金制造轴瓦、轴套等轴承材料。1959-1962年，国际铅锌组织ILZRO发起了一项旨在开发新型的、先进的压铸锌铝合金研制计划，促使了薄壁锌铝合金压铸技术和ILZRO-16、ILZRO-12铸造锌合金的出现，ILZRO-12（后经改进发展成ZA12合金）的蠕变性能与Zamak3和Zamak5相当，但其铸造性能和力学性能更好[1]。上世纪70年代初期，加拿大Normand Mines Limited研究中心与美国 Zestern公司合作，研制出锌基long-s metal减摩合金ZA8、ZA12、ZA27等。目前，美国、加拿大等发达国家有很多成功应用锌铝合金的范例。