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研究了Zn含量和热处理工艺对挤压态Mg-x%Zn-1%Mn(x=4,5,6,7,8,9,质量分数)镁合金组织和力学性能的作用规律。结果表明:Zn含量增加,挤压时动态再结晶趋于完全且小晶粒容易长大,同时第二相流线亦随之增加并阻碍其长大;再结晶晶粒在固溶过程中会长大,但Zn含量越高长大越困难,最终其晶粒更细小。通过透射电子显微镜(TEM)研究发现,时效态合金中主要存在2种亚稳相,即:长轴沿[0001]α的杆状相(β1′相)和(0001)α上的盘状相(β2′相),它们与基体之间存在共格或半共格界面,杆状β1′相对位错运动的阻碍更加强烈;根据X射线衍射(XRD)的分析结果,可知2种相都是具有Laves结构的MgZn2相。双级时效处理在低温预时效阶段从过饱和固溶体析出G.P.区,为第二级时效提供形核核心,从而细化了β1′和β2′相,增加了其弥散度。高Zn含量合金在180℃时效16h后发生了过时效,通过消耗β1′和β2′而形成了大块的Mg-Zn化合物。在时效态组织中,Mn以杆状析出,可以作为β1′和β2′相的形核核心,使二者发生粗化。挤压态合金的力学性能对Zn含量的变化不敏感;时效态合金的强度随Zn含量的增加呈抛物线增加,当Zn含量大于6%时,强度增加缓慢,延伸率急剧降低,这与高锌合金容易过时效且存在残余流线有关。故含6%Zn合金具有最佳的力学性能。
The effects of Zn content and heat treatment process on the microstructure and mechanical properties of Mg-x% Zn-1% Mn (x = 4, 5, 6, 7, 8, 9, The results show that when the content of Zn increases, the dynamic recrystallization tends to be complete and the small grains grow easily at the time of extrusion, while the second phase flow line also increases and hinders the growth of recrystallized grains. Grow up, but the higher the Zn content grows more difficult, the final smaller grains. Transmission electron microscopy (TEM) study found that there are mainly two kinds of metastable phase in the aged alloy, namely, the long axis along the rod-shaped phase (β1 ’) and (0001) α of [0001] (β2 ’phase), there is a coherent or semi-coherent interface between them and the matrix, rod β1’ relative dislocation movement impeded more strongly; according to the X-ray diffraction (XRD) analysis results, we can see that the two phases are MgZn2 phase with Laves structure. The two-stage aging treatment precipitates the G.P. zone from the supersaturated solid solution at the low temperature pre-aging stage, providing nucleation sites for the second-stage aging, thereby refining the β1 ’and β2’ phases and increasing their dispersion. The high Zn content alloy was overaged after 16 h aging at 180 ° C, forming massive Mg-Zn compounds by consuming β1 ’and β2’. In the aged microstructure, Mn precipitates as a rod and can act as nucleation sites for β1 ’and β2’ phases, causing both to coarsen. The mechanical properties of the as-extruded alloy are not sensitive to the change of Zn content. The strength of the aged alloy increases parabolically with the increase of Zn content. When the Zn content is more than 6%, the strength increases slowly and the elongation decreases sharply. The alloys are easily aged and have residual flow lines. Therefore, 6% Zn alloy has the best mechanical properties.