低成本超高强非稀土Mg-Al-Ca-Mn变形镁合金的多尺度多相显微组织调控及强韧化机理

Up to now, the developed ultra-high-strength wrought magnesium alloy are mostly based on the magnesium alloys containing high content of rare earth (RE) elements, the very high cost limits its promotion and application. In this project, to meet the demand of low-cost ultra-high strength magnesium alloys in high-tech fields such as aerospace and transportation industries, ultrahigh strength RE-free Mg-Al-Ca-Mn alloys will be developed. The microstructure, including the eutectic phase Mg2Ca, dynamic precipitated nano Al2Ca phase, GP zone, recrystallization zone ratio, grain size and texture, etc. of the Mg-Al-Ca-Mn alloys under different alloy composition, homogenization and extrusion processing will be characterized quantitatively, the formation mechanism and evolution of the microstructure of the low-cost ultra-high-strength Mg-Al-Ca-Mn wrought magnesium alloys containing multi-scale multiphases will be revealed. The relationship between microstructure and mechanical properties of the Mg-Al-Ca-Mn alloys will be determined quantitatively, and the optimum mode of multi-scale heterogeneous microstructure for the low cost ultrahigh-strength wrought magnesium alloys will be established. The deformation and fracture behavior of the low cost ultra-high strength Mg-Al-Ca-Mn magnesium alloys will be investigated, the strengthening and toughening mechanism of the alloys will be revealed, the strengthening and toughening models of low-cost ultra-high strength Mg-Al-Ca-Mn alloys containing multi-scale multiphases will be established. The research results will enrich the alloy design theory of high performance magnesium alloys and provide theoretical guidance for the develop of low cost ultrahigh-strength RE-free magnesium alloys.

目前开发的超高强变形镁合金基本均为高稀土含量的稀土镁合金，昂贵的成本限制了其推广应用。本项目将针对航空航天及交通等高技术领域对低成本超高强镁合金的需求，开发低成本超高强不含稀土的Mg-Al-Ca-Mn变形镁合金；定量表征不同合金成分、均匀化处理和挤压变形条件下合金中的共晶Mg2Ca相、动态析出纳米Al2Ca相、GP区、及基体再结晶区比例、晶粒尺寸及织构等，揭示低成本超高强Mg-Al-Ca-Mn变形镁合金多尺度多相显微组织的形成机理与演变规律；建立合金的显微组织与力学性能的定量关系，确立低成本超高强变形镁合金的多尺度多相适配微结构的最佳模式；研究低成本超高强Mg-Al-Ca-Mn镁合金的变形断裂行为，揭示其强韧化机理，建立多尺度多相适配超高强Mg-Al-Ca-Mn合金的强韧化模型。研究成果将丰富高性能镁合金的合金设计理论，为低成本超高强非稀土型镁合金的合金开发提供理论指导。

本项目针对航空航天及交通等高技术领域对低成本超高强镁合金的需求，通过合金的成分设计、热处理和挤压变形实现了对Mg-Al-Ca-Mn合金中微米尺度初生第二相和纳米尺度动态析出第二相的调控，利用常规挤压工艺制备了超高强低成本非稀土变形镁合金，揭示了合金的强塑性机理。.可通过Ca/Al比调控Mg-Al-Ca-Mn合金中初生相的种类和形貌。在Ca和Al总含量约为6 wt.%的Mg-Al-Ca-Mn合金中，随着Ca/Al质量比从0.25增加至1.30，合金的初生相由粗大C36-(Mg,Al)2Ca相转变为细小层片状共晶C14-Mg2Ca相。挤压后初生相被挤碎成细小颗粒，呈条带状沿着挤压方向分布，条带附近为细小的再结晶组织，远离条带的位置为粗大的变形晶粒。高Ca/Al比的挤压态合金中，动态析出相更致密和细小。随着Ca/Al比例的增加，挤压态合金的强度显著提高，延伸率明显下降。挤压态Mg-2.7Al-3.5Ca-0.4Mn合金具有438 MPa的超高屈服强度，延伸率为2.5%，其主要强化机制是细晶强化和析出强化。.挤压态Mg-Al-Ca-Mn合金的主要强化相为亚稳态的纳米级C14-Mg2Ca动态析出相。Mn和Al的含量影响合金挤压态合金中C14动态析出相的尺寸与分布。0.1wt.%的微量Mn元素添加可有效细化挤压态Mg-5Al-3Ca合金中的C14相，从而显著提高合金的屈服强度。在Mg-(5-7)Al-3Ca-0.3Mn中，Al含量增加减少挤压态合金中Mg2Ca动态析出相的数密度，降低合金的屈服强度。挤压态Mg-5Al-3Ca-0.3Mn合金的屈服强度高达420 MPa，抗拉强度高达451 MPa，延伸率为4.1%。.硬脆的初生Laves相是Mg-Al-Ca-Mn合金在加载过程中的裂纹源，导致合金的塑性降低，调控初生相的形貌和分布可以改善合金的塑性。对铸态Mg-3.0Al-2.7Ca-0.4Mn合金500oC/20h均匀化处理后挤压的合金中，初生层片状C14相球化，均匀分散在α-Mg基体中，合金的延伸率显著增加至10.2%，屈服强度为322 MPa。基于合金的断裂行为，建立了含有微裂纹产生相颗粒合金的断裂模型，定量描述了合金塑性与C14初生相颗粒的形貌和分布之间的关系。.本项目的研究成果丰富了高性能镁合金的合金设计理论，为低成本非稀土型超高强镁合金的合金开发提供了理论指导。