Mg-3.5Sr-1Mn基镁合金的显微组织和力学性能研究

发布时间：2018-08-26 13:58

【摘要】：镁合金作为一种轻质的工程材料,越来越受到人们的关注和重视。目前,研究较为成熟且价格低廉的镁合金的力学性能尤其高温性能较差,这严重阻碍了镁合金在汽车行业以及其他行业的应用。而一些高温性能比较好的镁合金,大多是以稀土为主要添加元素的稀土镁合金,而稀土高的价格同样会限制稀土镁合金的推广和应用。正是由于这种原因,国内外开始关注成本低廉且又具有良好高温性能的碱土镁合金的研究和开发。目前,国内外对于碱土镁合金的研究大多集中在含Ca镁合金上,而对于含Sr镁合金的研究主要集中在Mg-Al-Sr基镁合金上,对于其他含Sr新型碱土镁合金的研究还非常少。因此,进一步针对含Sr新型碱土镁合金的设计及其显微组织和力学性能展开研究对于碱土镁合金的发展以及加大镁合金的推广应用具有非常重要的理论意义和实际意义。本文基于设计的Mg-3.5Sr-1Mn(wt%)新型含Sr碱土镁合金作为研究对象,利用光学显微镜、DSC差热分析仪、X射线衍射仪、扫描电镜、拉伸试验机和显微硬度计等手段,研究了Ce、Sc和Nd合金化和/或微合金化及热处理对Mg-3.5Sr-1Mn镁合金显微组织和力学性能的影响,并得到了以下主要研究结果:1)Mg-3.5Sr-1Mn试验镁合金的铸态组织主要由α-Mg、α-Mn和Mg17Sr2三种相组成,并且合金经T4处理(520℃×24 h+淬水)后,合金组织中的α-Mn和Mg17Sr2相仍然存在。此外,在Mg-3.5Sr-1Mn镁合金中分别添加0.5-1.5 wt%Ce、0.15-0.45wt%Sc和0.5-1.5 wt%Nd后,合金铸态组织和T4(520℃×24 h+淬水)热处理组织中的合金相种类均没有发生变化,但合金的铸态晶粒被细化。2)在Mg-3.5Sr-1Mn试验镁合金中添加0.5-1.5 wt%Ce可以改善合金的室温抗拉性能,并且随着Ce添加量从0.5 wt%增加到1.5 wt%,含Ce合金的抗拉强度、屈服强度和延伸率均呈先下降然后上升的趋势。在添加了0.5 wt%、1.0 wt%和1.5 wt%Ce的三个试验合金中,以添加1.5 wt%Ce的合金具有相对较佳的室温抗拉性能。此外,在Mg-3.5Sr-1Mn试验镁合金中添加0.5-1.5 wt%Ce对合金的断裂方式没有明显影响,均呈典型的解理和/或准解理断裂。3)在Mg-3.5Sr-1Mn试验镁合金中添加0.15-0.45 wt%Sc可使合金组织中第二相的分布更加均匀。同时,添加0.15-0.45 wt%Sc到Mg-3.5Sr-1Mn镁合金中还可改善合金的室温抗拉强度、屈服强度和延伸率,但随着Sc添加量从0.15 wt%增加到0.45wt%,合金的抗拉强度和延伸率呈下降趋势,而屈服强度却稍有增加。总体而言,在添加了0.15 wt%、0.30 wt%和0.45 wt%Sc的三个试验合金中,以添加0.15 wt%Sc的合金具有相对较佳的的室温抗拉性能。此外,在Mg-3.5Sr-1Mn试验镁合金中添加0.15-0.45 wt%Sc对合金的断裂方式没有明显影响,均呈典型的解理和/或准解理断裂。4)在Mg-3.5Sr-1Mn试验镁合金中添加0.5-1.5 wt%Nd可使合金组织中第二相的分布更加分散。同时,添加0.5 wt%、1.0 wt%和1.5 wt%Nd对Mg-3.5Sr-1Mn合金的室温抗拉性能存在不同的影响,其中0.5 wt%和1.0 wt%Nd可使合金的抗拉强度、屈服强度和延伸率增加,而添加1.5 wt%Nd后,虽然合金的延伸率增加但抗拉强度和屈服强度降低。在添加了0.5 wt%、1.0 wt%和1.5 wt%Nd的三个试验合金中,以添加1.0 wt%Nd的合金具有相对较佳的室温抗拉性能。此外,在Mg-3.5Sr-1Mn试验镁合金中添加0.5-1.5 wt%Nd对合金的断裂方式没有明显影响,均呈典型的解理和/或准解理断裂。
[Abstract]:Magnesium alloys, as a kind of lightweight engineering materials, have attracted more and more attention. At present, the mechanical properties of magnesium alloys with relatively mature and low price are especially poor at high temperature, which seriously hinders the application of magnesium alloys in automotive industry and other industries. Rare earth magnesium alloys with rare earth as the main additive element, and the high price of rare earth will also restrict the promotion and application of rare earth magnesium alloys. The research on Mg-Al-Sr-based magnesium alloys is mainly concentrated on Mg-Al-Sr-based magnesium alloys, while the research on other new alkaline-earth magnesium alloys containing Sr is very few. Therefore, further research on the design, microstructure and mechanical properties of new alkaline-earth magnesium alloys containing Sr is carried out to study the development and increase of alkaline-earth magnesium alloys. The popularization and application of magnesium alloys have very important theoretical and practical significance.Based on the new type of Mg-3.5Sr-1Mn(wt%) containing Sr alkaline soil magnesium alloys designed in this paper,the alloying of Ce,Sc and Nd was studied by means of optical microscope,DSC differential thermal analyzer,X-ray diffraction,scanning electron microscope,tensile tester and microhardness tester. The effects of and/or microalloying and heat treatment on the microstructure and mechanical properties of Mg-3.5Sr-1Mn magnesium alloys were investigated. The main results were as follows: 1) The as-cast microstructure of Mg-3.5Sr-1Mn alloy was mainly composed of three phases, namely, a-Mg, a-Mn and Mg17Sr2, and the microstructure of the alloy after T4 treatment (520 *24 H + quenching water). In addition, after adding 0.5-1.5 wt% Ce, 0.15-0.45 wt% Sc and 0.5-1.5 wt% Nd to Mg-3.5Sr-1Mn alloy respectively, the as-cast microstructure and T4 (520 *24 H + quenched water) heat treatment microstructure of the alloy have not changed, but the as-cast grains of the alloy have been refined.2) by adding 0.5-1.5 wt% in Mg-3.5Sr-1Mn test magnesium alloy. The tensile strength, yield strength and elongation of the alloys with Ce content increased from 0.5 wt% to 1.5 wt%. Among the three alloys with Ce content of 0.5 wt%, 1.0 wt% and 1.5 wt% Ce, the alloys with 1.5 wt% Ce have relatively better room temperature properties. In addition, the addition of 0.5-1.5 wt% Ce to M g-3.5Sr-1Mn alloy has no obvious effect on the fracture mode of the alloy, which is typical cleavage and/or quasi-cleavage fracture. 3) The addition of 0.15-0.45 wt% Sc to M g-3.5Sr-1Mn alloy can make the distribution of the second phase more uniform. The tensile strength, yield strength and elongation of the alloy at room temperature were also improved in g-3.5Sr-1Mn magnesium alloy. However, with the increase of Sc content from 0.15wt% to 0.45wt%, the tensile strength and elongation of the alloy decreased, while the yield strength increased slightly. In addition, the addition of 0.15-0.45 wt% Sc to Mg-3.5Sr-1Mn test magnesium alloy has no obvious effect on the fracture mode of the alloy, and both of them show typical cleavage and/or quasi-cleavage fracture. 4) Adding 0.5-1.5 wt% Nd to Mg-3.5Sr-1Mn test magnesium alloy can make the second-order fracture in the alloy structure. At the same time, the addition of 0.5 wt%, 1.0 wt% and 1.5 wt% Nd has different effects on the tensile properties of Mg-3.5 Sr-1Mn alloy at room temperature. Among them, 0.5 wt% and 1.0 wt% Nd can increase the tensile strength, yield strength and elongation of the alloy, while the addition of 1.5 wt% Nd can increase the elongation but decrease the tensile strength and yield strength. Among the three test alloys with 0.5 wt%, 1.0 wt% and 1.5 wt% Nd, the alloys with 1.0 wt% Nd have relatively better tensile properties at room temperature. In addition, the addition of 0.5-1.5 wt% Nd to Mg-3.5 Sr-1 Mn test magnesium alloys has no obvious effect on the fracture mode of the alloy, showing typical solution and / or quasi-solution fracture.
【学位授予单位】：重庆理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.22;TG166.4

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