镁合金中LPSO结构在搅拌摩擦加工过程的演变机制

As one of the strengthening factor in Mg alloys, LPSO(Long Period Stacking Order) structure has great potential for improving the strength and ductility of magnesium alloys，leading to excellent mechanical properties of LPSO-containing Mg-RE-Zn alloys, with great potential applications. However, in all these LPSO-containing Mg-RE alloys, the distribution of LPSO in the grains is non-uniform, and the X phase(LPSO structure) at grain boundaries are very coarse, which obviously restricts the further improvement of strength and ductility of these alloys. Meanwhile, it is much hard to modify the morphology of these phases by conventional composition adjustment, solidification and forming techniques. In this project, Mg-Gd-Zn alloy will be selected as representative research material and processed by friction stir processing (FSP). The aims of this project is to reveal the evolution rule and mechanism of LPSO structure and its effects on dynamic recrystallization behavior and texture characteristics of Mg-Gd-Zn alloy during FSP. At last, some theoretical guidelines for the design and development of high-performance Mg-RE alloys containing LPSO structure will be provided in this project by research reports.

长周期有序结构（LPSO）强化的镁合金已显示了优异的力学性能和显著的应用前景。但是，该类合金中存在的粗大且不均匀的晶界X相(LPSO结构)及晶内LPSO，严重限制了合金强度和韧性的进一步提高，而且这种分布形态难以采用常规的成分设计、制备或加工方法来进行有效调控。本项目选择含LPSO 结构的Mg-Gd-Zn 合金为研究对象，利用具有大塑性变形特征的搅拌摩擦加工（FSP）方法实现对合金中第二相的显著细化与均匀化，通过对FSP 合金微观结构的研究，揭示LPSO结构在FSP 过程的演变规律与机制，阐明LPSO 结构演化对合金的动态再结晶以及织构特征的影响，为高性能镁合金材料的开发与应用提供理论指导。

长周期有序结构（LPSO）强化的镁合金已显示了优异的力学性能和显著的应用前景。但是，该类合金中存在的粗大且不均匀的晶界X相(LPSO结构)及晶内LPSO，严重限制了合金强度和韧性的进一步提高，而且这种分布形态难以采用常规的成分设计、制备或加工方法来进行有效调控。本项目选择含LPSO 结构的Mg-Gd-Zn 合金为研究对象，利用具有大塑性变形特征的搅拌摩擦加工（FSP）方法实现对合金中第二相的显著细化与均匀化，通过对FSP 合金微观结构的研究，揭示LPSO结构在FSP 过程的演变规律与机制，阐明LPSO 结构演化对合金的动态再结晶以及织构特征的影响，为高性能镁合金材料的开发与应用提供理论指导..项目研究结果表明：LPSO结构在FSP过程中由于受到巨大的剪切作用，发生了扭折、变形甚至破碎，这能够在一定程度上抑制了FSP后再结晶晶粒的长大。由于晶界X相（LPSO结构）相对于β相具有更高的韧性，可以保持形态尺寸不发生明显变化，故而在动态再结晶过程中作为颗粒促进PSN形核，促进了动态再结晶的发生。通过对Mg-Gd-Zn合金的搅拌摩擦加工，能够较好的实现“细晶+析出相+细小弥散相”的显微组织调控，再结合后续热处理，材料的屈服强度、抗拉强度和延伸率分别达到298Mpa、390Mpa和4.4%。这为新型高性能镁合金的设计奠定了基础。