时效Mg-4Y-3Nd合金微观组织转变及性能研究

发布时间：2018-05-02 06:34

本文选题：镁铱钕合金 + 时效处理　；参考：《吉林大学》2015年硕士论文

【摘要】：镁合金以质轻、比强度高、耐热性好和减震性能好等优点，成为现代替代钢铁、铝合金和塑料以实现轻量化的理想材料，被日益广泛的应用在交通工具、“3C”产品和航空航天等领域。但由于高温蠕变性能差，制约了其发展应用范围，因此镁合金的强化及其强化机理成为镁合金研究的一个重要方向。各种稀土被作为合金元素加入到镁合金中来改善其常温高温性能、耐热蠕变性等，含有钇和钕元素的WE系列合金是耐热镁合金中应用最广泛的合金，如WE54和WE43等，300℃其性能可保持1000h，250℃下能够长期工作，在飞机和赛车发动机的汽缸上得到应用。最常用的的强化手段是固溶时效处理，但是，到目前为止，Mg-Y-Nd合金的时效强化机制还不太清楚，所以，本课题通过高温时效处理，研究Mg-4Y-3Nd合金不同时效阶段的析出相的析出规律、析出相的物相转变，从而明确其时效强化机制。研究工作中，采用先金属模铸造法再热挤压加工制备的Mg-4Y-3Nd合金。并对其进行固溶时效处理。利用光学显微镜、X射线衍射仪（XRD）、扫描电子显微镜（SEM）和能谱仪（SEM-EDS）、透射高分辨（HTEM）、维氏硬度计研究了不同时效阶段的金相组织、第二相析出规律、物相结构、时效硬化，从而明确其时效强化机制。结果表明：T6态Mg-4Y-3Nd合金的第二相优先在晶界处形核，向晶内非连续析出，随着时效时间的增加，，第二相会在晶内连续析出，并且第二相在基体组织上呈均匀分布状态，不存在铸态组织中的连续树枝晶，时效过程中，最先析出的第二相细小，然后体积有稍微长大，时效4h后的第二相体积逐渐长大，直到32h时有明显的长大。物相结构研究表明：T6态Mg-4Y-3Nd合金的显微组织由α-Mg固溶体、二元析出相Mg24Y5、Mg2Y、Mg41Nd5和三元析出相Mg14Nd2Y组成。随着析出相的生成，基体的晶格常数也随之变化，同一晶面的2θ减小，晶面间距d增大。时效硬度曲线表明：0.5-32h时效过程中存在3次时效硬化峰，包括0.5h时的一次很快消失的小幅时效，4h和24h时两次明显的时效硬化，每个时效硬化峰的出现，都表明析出相之间发生了物相转变，时效0.5h时，Mg-Y-Nd合金中主要存在β″相，因为β″相存在的时间极短，会很快转化为β′相，这个现象表现为时效1h时合金的硬度有下降；然后β′相不断的形成，在时效4h时出现一次明显的时效硬化现象，时效8h硬度明显下降，这是β′相开始转变为β1相；到时效24h时又一次出现明显的时效硬化现象，这时β1相开始转化为β相，导致时效32h出现硬度的明显下降，在8-32h时效过程中存在β′相、β1相和β相共存的现象。
[Abstract]:Magnesium alloy, with the advantages of light quality, high strength, good heat resistance and good damping property, has become an ideal material to replace steel, aluminum alloy and plastic to realize light weight. It is widely used in the fields of transportation, "3C" products and Aeronautics and Astronautics. But because of poor high temperature creep performance, it restricts its development and application, so magnesium is limited. The strengthening and strengthening mechanism of the alloy has become an important direction in the study of magnesium alloys. All kinds of rare earth elements are added to magnesium alloys as alloy elements to improve their temperature and temperature properties at normal temperature, heat resistance, and so on. WE series alloys containing yttrium and neodymium are the most widely used alloys in heat-resistant magnesium alloys, such as WE54 and WE43, and their properties at 300. 1000h can be maintained at 250 C for a long time and can be applied to the cylinder of aircraft and car engine. The most commonly used reinforcement means is solution aging treatment. However, so far, the aging hardening mechanism of Mg-Y-Nd alloys is not very clear. So, this subject has studied different aging stages of Mg-4Y-3Nd alloys by high temperature aging treatment. The precipitation mechanism of precipitates and the phase transformation of precipitates are identified, so as to clarify the mechanism of aging strengthening.
In the research work, the Mg-4Y-3Nd alloy prepared by reheat extrusion of the first metal mold casting method was used. The solid solution and aging treatment was carried out. The optical microscope, X ray diffractometer (XRD), scanning electron microscope (SEM) and energy spectrometer (SEM-EDS), transmission high resolution (HTEM), and Vivtorinox hardness meter were used to study the metallographic structure of different aging stages, second Phase precipitation, phase structure and age hardening can clarify the aging strengthening mechanism.
The results show that the second phase of the T6 state Mg-4Y-3Nd alloy is first nucleated at the grain boundary and discontinuous in the crystal. As the aging time increases, the second phase will continuously precipitate in the crystal, and the second phase is uniformly distributed in the matrix structure, and there is no continuous dendrite in the cast structure. The first precipitate phase is first precipitated during the aging process. The volume is slightly older and the volume of the second phase after aging 4H grows gradually. The phase structure of the T6 state Mg-4Y-3Nd alloy shows that the microstructure of the T6 state Mg-4Y-3Nd alloy is composed of a solid solution of alpha -Mg, Mg24Y5, Mg2Y, Mg41Nd5 and three elements precipitated in the precipitate phase of the alloy. With the formation of the precipitated phase, the lattice lattice of the matrix is constant. The number also varies with the 2 D of the same plane decreasing, and the distance between the crystal faces increases.
The aging hardness curve shows that there are 3 time hardening peaks in the aging process of 0.5-32h, including a small amplitude aging that quickly disappeared at the time of 0.5h, two apparent aging hardening at 4H and 24h, and the occurrence of each hardening peak indicates that the phase transition occurs between the precipitates, and when the time effect 0.5h is the main existence of the beta "phase in the Mg-Y-Nd alloy, because The existence of the beta "phase is very short, and it will quickly transform into beta phase. This phenomenon shows that the hardness of the alloy decreases when the aging 1H is aged; then the phase of the beta phase is constantly formed, and a obvious aging hardening occurs at the aging 4h, and the hardness of the aging 8h decreases obviously. This is the transformation of beta 'phase to beta 1 phase, and another appearance to the aging 24h. The phenomenon of aging hardening occurs when the beta 1 phase begins to be transformed into beta phase, which leads to a significant decrease in the hardness of the aging 32H. In the aging process of 8-32h, there is a phase of beta 'and the coexistence of beta 1 and beta phase.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.22;TG166.4

【参考文献】