Dy对Mg-Y-Nd系合金组织和性能影响规律研究

发布时间：2018-04-06 20:39

  本文选题：Mg-4Y-3Nd　切入点：Dy　出处：《哈尔滨工业大学》2015年博士论文

【摘要】：镁合金作为具有高比强度和比刚度的结构材料,在汽车、电子等领域已被大量应用,但较低的高温性能限制了其在航天航空工业上的应用。稀土元素可以明显提高镁合金的性能,尤其是高温拉伸和高温蠕变性能,因此稀土镁合金为当前世界镁合金领域的一个研究热点。本文在Mg-4Y-3Nd-0.5Zr合金基础上,添加Dy稀土元素,开发新型Mg-4Y-3Nd-x Dy-Zr镁合金。研究了合金中Dy对合金组织形态、相组成及结构、室温及高温力学性能等的影响。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3,5)合金铸态组织研究表明,合金铸态组织由基体a-Mg、存在于晶界的骨状的共晶相Mg5RE(f.c.c.,a=2.2~2.3nm)和沿骨骼状相边缘及其内部形成的块状相RE17Mg3(f.c.c.,a=0.5~0.6nm)组成。Dy未影响铸态相结构类型,但对相的晶格常数有微弱影响。随着合金中Dy含量的增加,骨状相体积增多,尺寸增大,形貌更加复杂。在合金凝固过程中,Dy替代了部分Nd析出形成骨状相,而对骨状相中的Y没有影响。在形成块状相时,Dy对Nd基本没有影响,块状相中Dy/Y随着合金中Dy含量的增加而不断增大。在铸态组织中Nd主要集中分布在骨状相中,而Y和Dy在晶界和骨状相中有微弱的富集。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3,5)合金固溶态组织研究表明:骨状相在500℃温度下结构稳定,而在525℃和550℃温度下快速消融;块状相在525℃以下温度时相结构稳定,Nd从块状相中不断扩散到基体中直至与基体中的含量一致,但在550℃固溶处理过程中,块状相在缓慢消融,对晶界的钉扎作用逐渐减弱导致晶粒快速长大。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3,5)合金时效硬化曲线和时效析出行为研究结果表明,该系合金具有明显的时效硬化效应,并随着时效温度的升高,合金时效硬度略有下降。加入Dy大大提高了合金硬度,同时也使到达峰时效提前、析出相更加细小弥散。在250℃时效处理过程中,Mg-4Y-3Nd-0.5Zr合金时效析出顺序为:β″、β′、β。但Mg-4Y-3Nd-0.5Z合金中加入Dy,促进了β′相的形核析出,这也是导致峰时效提前原因。对Mg-4Y-3Nd-0.5Zr(WN43)合金和Mg-4Y-3Nd-2Dy-0.5Zr(WND432)合金固溶态的基体固溶体脱溶沉淀析出的转变驱动力进行了分析,并计算得出了在250℃下的WN43DG=-85J/mol,WND432DG=-101J/mol。较低的脱溶沉淀析出转变驱动力促使β￠相的形核析出。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3)合金性能研究结果表明,Dy能显著提高合金拉伸性能,尤其是高温抗拉性能。在300℃下,加入3%Dy的Mg-4Y-3Nd-3Dy-0.5Zr合金的抗拉强度和屈服强度分别提高了43.2%和37.6%。但由于合金加入Dy较少,对合金蠕变性能影响很小,尤其是较低温度的蠕变性能。Mg-4Y-3Nd-2Dy-0.5Zr合金在蠕变温度为250℃时,应力敏感性指数为2.3,滑移机制主要为基面滑移和棱柱面滑移;在蠕变应力为40MPa和80MPa时,激活能分别为94k J/mol和195k J/mol。细小弥散的块状相RE17Mg3对合金具有第二相强化作用,但其强化作用弱于块状相中稀土固溶进基体后产生的固溶强化作用。
[Abstract]:Magnesium alloys, as structural materials with high specific strength and specific stiffness, have been widely used in automotive, electronic and other fields, but their low high temperature properties limit their application in aerospace industry.Rare earth elements can obviously improve the properties of magnesium alloys, especially the tensile and creep properties of magnesium alloys at high temperature. Therefore, rare earth magnesium alloys have become a research hotspot in the field of magnesium alloys in the world.On the basis of Mg-4Y-3Nd-0.5Zr alloy, a new type of Mg-4Y-3Nd-x Dy-Zr magnesium alloy was developed by adding Dy rare earth element.The effect of Dy on microstructure, phase composition and structure, mechanical properties at room and high temperature.With the increase of Dy content in the alloy, the volume of bone phase increases, the size increases and the morphology becomes more complex.During the solidification of the alloy, Dy replaced some ND precipitates to form bone-like phase, but had no effect on Y in the bone-like phase.Dy/Y in bulk phase increases with the increase of Dy content in bulk phase.In the as-cast microstructure, ND is mainly concentrated in the bony phase, while Y and Dy are weakly enriched in the grain boundary and the bone-like phase.The aging hardening curve and precipitation behavior of Mg-4Y-3Nd-x Dy-0.5Zrd-x Dy-0.5ZrxO0 ~ (2 +) alloy are studied. The results show that the aging hardening effect of the alloy is obvious.With the increase of aging temperature, the aging hardness of the alloy decreases slightly.The addition of Dy can greatly improve the hardness of the alloy, at the same time, the peak aging is advanced, and the precipitate phase is more fine and dispersed.During aging treatment at 250 鈩，

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