Mn对Mg-5Sn-2Al-Zn变形合金组织演变及力学性能的影响

发布时间：2019-03-25 19:40

【摘要】：本文利用纯镁锭、锡锭,纯铝粒、锌粒及含锰10%的镁-锰中间合金,在实验室条件下完成Mg-5Sn-2Al-Zn-xMn(x=0、0.2、0.5及0.8)合金的制备。因为合金在浇铸时结晶较快,得到非平衡组织,存在严重的成分偏析。为了平衡组织、均匀成分,也为后续塑性变形做准备,必须对合金采取固溶处理。通过X射线衍射仪(XRD)进行物相分析,采用光学显微镜、扫描电子显微镜(SEM)辅以能谱仪(EDS)以及透射电镜(TEM)对不同Mn含量的Mg-5Sn-2Al-Zn(TAZ521)合金进行微观组织分析,利用万能压缩机对以上合金进行室温抗压强度测试,用维氏硬度仪对合金进行表面硬度测试,研究不同Mn含量对合金铸态、固溶后组织及力学性能的影响。在热模拟压力机上采取不同的变形温度和变形速率,对经过均匀化处理的TAZ521-xMn(x=0、0.2、0.5及0.8)镁合金进行热变形实验,分析了变形温度、变形速率对热压缩变形过程流变应力的影响,并建立了TAZ521镁合金高温变形时的应力-应变关系模型。同时分析了Mn的加入对TAZ521合金高温变形应力及动态再结晶组织的影响。分析结果表明:TAZ521合金组织主要由α-Mg相、Mg2Sn相以及较少量的β-Mg17Al12相组成;Mn含量的增加促进了Mg2Sn相和β-Mg17Al12相在枝晶间的析出分布,并使枝晶细化。在含有Mn的TAZ521固溶态合金中弥散分布着一定数量的Al-Mn相,主要以颗粒状的Al8Mn5相和细长杆状的Al11Mn4相存在,一些细小的颗粒状或块状Al-Mn相作为异质形核的核心,分布于原始晶界处。对不同Mn含量的TAZ521合金进行室温压缩实验,当Mn含量在0.2%和0.5%时室温力学性能较好,当含Mn达到0.8%时,颗粒状的第二相分布明显增多,其力学性能也急剧下降。随着Mn含量的增加,TAZ521合金的硬度总体呈现一定程度的上升趋势,但提高幅度不大。当Mn含量从0.2%提高到0.5%时,TAZ521合金硬度有小幅提高,而继续增加到0.8%时,改善效果则不够显著。Mn的添加使得TAZ521合金在热变形下的流变应力显著降低,并且在保持较高的温度条件下,变形速率越低,应力的降低效果越显著。少量的Mn也可以促进TAZ521合金在高温变形下的动态再结晶形核,随着Mn含量的逐渐增加,对TAZ521镁合金再结晶促进效果更加明显,因此Mn在TAZ521合金高温塑性变形过程中可以起到一定细化晶粒的作用。
[Abstract]:In this paper, pure magnesium ingots, tin ingots, pure aluminum grains, zinc particles and magnesium-manganese master alloys containing 10% mn were used to prepare Mg-5Sn-2Al-Zn-xMn (x 0, 0.2, 0.5 and 0.8) alloys under laboratory conditions. Because the alloy crystallizes rapidly during casting, the non-equilibrium structure is obtained, and there is serious component segregation. In order to balance the microstructure, uniform composition, and prepare for the subsequent plastic deformation, the alloy must be treated with solid solution. Phase analysis was carried out by X-ray diffractometer (XRD), and optical microscope was used. The microstructure of Mg-5Sn-2Al-Zn (TAZ521) alloy with different Mn content was analyzed by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The compressive strength of the above alloys at room temperature was measured by universal compressor, and the surface hardness of the alloys was tested by Vickers hardness instrument. The effects of different Mn content on the as-cast, solid solution microstructure and mechanical properties of the alloys were studied. The deformation temperature of TAZ521-xMn (x 0, 0. 2, 0. 5 and 0. 8) magnesium alloy treated by homogenization was studied by using different deformation temperature and deformation rate in the thermal simulation pressure machine, the deformation temperature was analyzed, and the deformation temperature of magnesium alloy TAZ521-xMn (x 0, 0. 2, 0. 5 and 0. 8) The effect of deformation rate on the flow stress during hot compression deformation was studied. The stress-strain relationship model of TAZ521 magnesium alloy during high temperature deformation was established. The effects of the addition of Mn on the high temperature deformation stress and dynamic recrystallization microstructure of TAZ521 alloy were also analyzed. The results show that the microstructure of TAZ521 alloy is mainly composed of 伪-Mg phase, Mg2Sn phase and a small amount of 尾-Mg17Al12 phase, and the increase of Mn content promotes the precipitation and distribution of Mg2Sn phase and 尾-Mg17Al12 phase between dendrites, and refines the dendrite. In the TAZ521 solid solution alloy containing Mn, a certain number of Al-Mn phases are dispersed, mainly in granular Al8Mn5 phase and slender rod Al11Mn4 phase. Some fine granular or massive Al-Mn phases are the core of heterogeneous nucleation. Distributed at the original grain boundary. The mechanical properties of TAZ521 alloys with different Mn content were studied at room temperature. When the content of Mn was 0.2% and 0.5%, the mechanical properties at room temperature were better. When the content of Mn was 0.8%, the distribution of the second phase of particles increased obviously. Its mechanical properties also decreased sharply. With the increase of Mn content, the hardness of TAZ521 alloy increases to a certain extent, but the increase of hardness is not significant. When the content of Mn is increased from 0.2% to 0.5%, the hardness of TAZ521 alloy increases slightly, but when the content of mn increases to 0.8%, the improvement effect is not significant. The addition of mn makes the flow stress of TAZ521 alloy decrease significantly under hot deformation. Under the condition of high temperature, the lower the deformation rate, the more significant the effect of stress reduction. A small amount of Mn can also promote the dynamic recrystallization nucleation of TAZ521 alloy under high temperature deformation. With the increasing of Mn content, the effect of promoting recrystallization of TAZ521 magnesium alloy is more obvious. Therefore, Mn can play a role of grain refinement in the process of high temperature plastic deformation of TAZ521 alloy.
【学位授予单位】：沈阳理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22

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