Mg-Sn系合金微观组织及力学性能的研究

发布时间：2018-05-08 22:35

本文选题：Mg-Sn-Zn-Al + 变形　；参考：《重庆大学》2015年硕士论文

【摘要】：随着镁合金的应用不断增多,特别是交通业、航空航天、3C产品的需求,迫切需要开发出新型镁合金。Mg-Sn是典型的时效强化型合金,其存在偏析严重、Mg2Sn易粗化以及时效硬化需时较长等问题,所以关于Mg-Sn体系合金的研究有待进一步深入。本文拟以Mg-Sn合金为基础,采用电磁感应熔炼炉在氩气保护下制备出了Mg-3Sn-x Zn-1Al(x=0.5~2.0wt.%)、Mg-x Sn-2Zn-1Al(x=3.0~10.0wt.%)和Mg-5Sn-2Zn-1Al-0.1Ba合金,通过X射线荧光光谱仪(XRF)、金相显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)、透射电镜(TEM)、维氏显微硬度计及力学性能测试仪器等手段方法研究了合金的显微组织和力学性能,研究合金中析出相的成分、结构及组织演变规律,扩大镁合金的应用范围,对建立一种新型高强高韧的Mg-Sn系合金具有重要的意义。研究了Mg-3Sn-x Zn-1Al合金的显微组织与力学性能,发现0.5-2.0 wt.%Zn的添加可以逐渐细化Mg-3Sn-1Al合金的晶粒,使Mg2Sn相增多,但会使Mg2Sn相粗化。在凝固过程中,固相中高浓度的Sn元素能够阻止Mg原子的扩散,进而阻碍晶粒的长大。随Zn含量的增加,挤压态合金晶粒显著地细化,力学性能有了显著的提高,且塑性都出现了一定程度的增加。特别是合金的加工硬化能力(1/YR)也随Zn含量的增加而略有提高,这意味着Zn元素能改善合金的强度和塑性变形能力,其主要原因是晶粒细化效应和第二相的弥散均匀分布。在对合金进行时效处理后,Zn的存在可以缩短合金到达时效峰值时间,提高峰值硬度。Zn的添加会增加Mg2Sn相的数量,其阻碍晶界滑移和位错的运动,有利于提高合金的强度,但却降低了塑性。研究了Mg-x Sn-2Zn-1Al合金的显微组织与力学性能。随着Sn量的增加,合金枝晶逐渐细化,并且树枝晶形态更加明显,即Sn元素发生了明显的偏析,且Mg2Sn相逐渐增加,呈断续网状分布于晶界处,但Sn含量增加至7%后,Mg2Sn的数量和尺寸都大幅度增加,在晶界上呈半网络状分布。经热挤压后,合金发生动态再结晶,再结晶晶粒尺寸较为均匀,挤压过程中析出的Mg2Sn相也逐渐增多。合金在经过180℃×60h时效后,合金达到峰值硬度,随Sn含量的增加,其到达峰值的时间未发生明显的变化,但是硬度峰值从74.5增至78.9。经T5时效处理,合金具有较高的强度和延伸率,其强化效果主要源于Mg2Sn相的增多。挤压态Mg-5Sn-2Zn-1Al和Mg-10Sn-2Zn-1Al合金经过轧制后,合金具有细小的晶粒,低的织构和部分孪晶,尽管合金塑性有所下降,但合金仍然显示较高的强度,其中,Mg-10Sn-2Zn-1Al合金的抗拉强度、屈服强度和延伸率分别达到369Mpa,263Mpa和8.4%。经过300℃下退火1h后,合金发生完全再结晶,孪晶消失,晶粒大小均匀,强度,特别是屈服强度急剧下降,但塑性有很大的提高。研究了Mg-5Sn-2Zn-1Al-0.1Ba合金的显微组织与力学性能,结果表明:微量Ba的添加显著地细化了合金的枝晶,并且形成了Sn3Ba5和Sn Ba2相。经过挤压变形后,合金发生了晶粒的再结晶,晶粒转变为均匀的等轴晶,尺寸较小,合金组织较为均匀,合金的力学性能得到进一步改善。合金在经过180℃时效后,微量的Ba使Mg-5Sn-2Zn-1Al的峰值时效硬化时间从60h缩短到20h,促进了Mg2Sn相的析出,合金的力学性能有所提高,特别是屈服强度提升较为明显。
[Abstract]:With the increasing application of magnesium alloys, especially the demand of transportation, aerospace and 3C products, it is urgent to develop a new type of magnesium alloy.Mg-Sn as a typical aging hardening alloy, which has many problems such as serious segregation, easy to coarsening of Mg2Sn and longer time hardening. So the research on Mg-Sn alloy needs further research. In this paper, based on Mg-Sn alloy, Mg-3Sn-x Zn-1Al (x=0.5~2.0wt.%), Mg-x Sn-2Zn-1Al (x=3.0~10.0wt.%) and Mg-5Sn-2Zn-1Al-0.1Ba alloy are prepared under the protection of argon gas by electromagnetic induction melting furnace. The X ray fluorescence spectrometer (XRF), metallographic microscope (OM), X ray diffractometer, transmission electron microscope, and dimension are used. The microstructure and mechanical properties of the alloy are studied by means of microhardness tester and mechanical properties testing instrument. The composition, structure and microstructure evolution of the precipitated phase in the alloy are studied, and the application range of the magnesium alloy is expanded. It is of great significance for the establishment of a new type of Mg-Sn alloy with high strength and high toughness. The study of Mg-3Sn-x Zn-1Al combined with the alloy is of great significance. The microstructure and mechanical properties of gold show that the addition of 0.5-2.0 wt.%Zn can gradually refine the grain of Mg-3Sn-1Al alloy, make the phase of Mg2Sn increase, but make the Mg2Sn phase coarsened. In the solidification process, the high concentration of Sn elements in the solid phase can prevent the diffusion of Mg atoms, and then obstruct the grain growth. With the increase of Zn content, the extruded alloy grains are increased. The mechanical properties have been significantly improved and the plasticity of the alloy increased to a certain extent. Especially, the working hardening ability (1/YR) of the alloy increased slightly with the increase of the content of Zn, which means that the Zn element can improve the strength and plastic deformation ability of the alloy. The main reason is the grain refinement effect and the dispersion of the second phase. After aging treatment, the existence of Zn can shorten the peak time of aging and increase the number of Mg2Sn phase with the increase of the peak hardness.Zn. It hinders the movement of grain boundary slip and dislocation, which is beneficial to improve the strength of the alloy, but reduces the plasticity. The microstructure of Mg-x Sn-2Zn-1Al alloy is studied and the microstructure of the alloy is studied. With the increase of Sn, the dendrite gradually refined, and the dendrite morphology is more obvious, that is, the Sn element has obvious segregation, and the Mg2Sn phase increases gradually, showing a intermittent network distribution at the grain boundary. But after the increase of the Sn content to 7%, the number and size of Mg2Sn increase greatly, and the grain boundary is distributed in a semi network shape. Hot extrusion has been made. After pressure, the alloy has dynamic recrystallization, the recrystallized grain size is more uniform and the precipitated Mg2Sn phase increases gradually during the extrusion process. The alloy reaches the peak hardness after 180 C 60H aging. With the increase of Sn content, the peak time has not changed obviously, but the peak of hardness increases from 74.5 to the aging place of T5. The alloy has high strength and elongation, and its strengthening effect is mainly due to the increase of Mg2Sn phase. After rolling, the alloy has fine grain, low texture and partial twins after the extrusion of Mg-5Sn-2Zn-1Al and Mg-10Sn-2Zn-1Al alloy. Although the alloy plasticity decreases, the alloy still shows high strength, of which, Mg-10Sn-2Zn-1Al The tensile strength, yield strength and elongation of the alloy reached 369Mpa, respectively, when 263Mpa and 8.4%. were annealed at 300 C for 1h, the alloy was completely recrystallized, the twins disappeared, the grain size was uniform, the strength, especially the yield strength decreased sharply, but the plasticity was greatly improved. The microstructure and mechanical properties of the Mg-5Sn-2Zn-1Al-0.1Ba alloy were studied. The results show that the addition of trace Ba significantly refines the dendrite of the alloy and forms the phase of Sn3Ba5 and Sn Ba2. After the extrusion, the alloy has the recrystallization of the grain, the grain is transformed into uniform equiaxed crystal, the size is smaller, the alloy structure is more uniform, and the mechanical properties of the alloy are further improved. The alloy is at 180 C. After the effect, the micro Ba shortens the time of peak hardening of Mg-5Sn-2Zn-1Al from 60H to 20h, which promotes the precipitation of Mg2Sn phase and improves the mechanical properties of the alloy, especially the increase of yield strength.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.22

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