Mg-Gd-Y-Zn-Zr-Li-X合金设计及其形变热处理与强韧化机制研究

The new generation of missile weapon system have an urgent demand for lightweight. Mg alloys, which are the lightest metal structural materials, act as the key factor to realize the lightweight of missile weapon system. High strength Mg alloys with long period stacking ordered structure (LPSO type Mg alloys) exhibit excellent mechanical properties, therefore they have a great potential for producing the components of missile weapon system. However, high rare earth concentration of the LPSO type Mg alloys increases the density, reduces the advantage on lightweight and limits their board applications in engineering. The proposed project aims to develop new Mg-Gd-Y-Zn-Zr-Li-X(Ag，Ca，Sn) alloys with low density and high performance via proper alloying method and thermomechanical treatment. Finally, the yield strength of new Mg alloys will be higher than 300 MPa, the elongation will be greater than 10 %, and the density will be less than 1.70 g/cm3. The proposed project will investigate the effects of Li and X (Ag, Ca, Sn) elements on the characteristics of matrix, grains and precipitates in the LPSO type Mg-Gd-Y-Zn-Zr alloy, and essentially evaluate the strengthening effect of these alloying elements. The microstructural evolution during the thermomechanical treatment and the strengthening and toughening mechanisms will be systemically studied. In addition, the proposed project aims to solve the contradiction between low density and high performance, develop new Mg-Gd-Y-Zn-Zr-Li-X(Ag，Ca，Sn) alloys, and clarify the structure-property relationships in studied Mg alloys. The proposed project will provide important data and scientific guidance for the application of Mg alloys in missile weapon systems.

新型导弹武器装备对轻质化的需求迫切，镁合金作为最轻的金属结构材料成为了导弹武器装备实现轻质化的关键。长程有序堆垛结构型（LPSO型）高强镁合金有优异的力学性能，是制备导弹武器结构件的潜在材料，但大量稀土元素的添加导致密度提高，弱化了轻质化优势，限制了其广泛的工程应用。本项目研究目的是通过合金化和形变热处理手段，开发新型低密度高强度Mg-Gd-Y-Zn-Zr-Li-X（Ag，Ca，Sn）合金，使其屈服强度高于300MPa，延伸率大于10%，密度小于1.70 g/cm3。此外，本项目深入研究Li与X元素对LPSO型Mg-Gd-Y-Zn-Zr合金基体、晶粒和析出相的影响规律，阐明这些合金元素对合金强化的本质；系统研究合金在形变热处理过程中微观组织演变规律及强韧化机理，解决LPSO型镁合金低密度与高性能之间的矛盾，建立新型低密度高强度Mg-Gd-Y-Zn-Zr-Li-X（Ag，Ca，Sn）合金体系

随着新型导弹武器装备主承力结构件对材料力学性能和低密度化的要求不断提高，低密度高强度稀土镁合金的开发势在必行。然而，稀土镁合金的低密度和高性能存在此消彼长的矛盾，而这一科学问题尚待解决。本项目就是在以上应用和科学背景下提出的，同时这也是本项目的科学意义所在。本项目证实了在稀土镁合金中添加少量的Li元素既可以同时提高合金的强度和韧性，并降低合金密度。本项目的开展为解决稀土镁合金的低密度和高性能之间的矛盾提供了重要指导理论。.本项目得出以下结论：（1）在GWZL831x(x=0，1，3，6，12wt%)中，GWZL8311合金具有最优的力学性能，屈服强度为307MPa，延伸率为13.8%，峰值时效后屈服强度为350MPa，延伸率为7%，其优异的力学性能归因于双峰晶粒组织，晶粒细化，β1R相，γ’相和Mg3RE相以及峰值时效后产生的β’H相带来的强化作用。（2）Li元素（含量范围为1-6wt%）导致合金中产生孤岛状β1R相，当Li含量为12wt%时合金中不产生β1R相。Li元素促进Mg3RE相的析出，抑制LPSO相和γ’相的析出。（3）Li含量为0-1wt%时，合金表现出时效硬化现象，峰值时效态1Li合金的主要析出相为β’H相。Li含量为3wt%-12wt%时，合金表现出时效软化现象，基体内无亚稳相析出。Ag， Sn和Ca元素均不能导致亚稳相析出，无法将合金的时效软化现象转变为时效硬化现象。（4）Ag具有GWZL8313合金提高再结晶比例和细化晶粒的作用，并促进β1R相析出，但消耗溶质原子，弱化了固溶强化作用，因此Ag提高合金韧性降低强度。Sn也提高了再结晶比例因此降低了合金强度，但Sn对韧性影响不大，因为Sn不能改变合金裂纹源Mg3RE相的数量和尺寸。与Sn相似，Ca也不能提高合金韧性。此外，Ca促进再结晶的能力较弱，合金再结晶比例较低，含Ca合金与不含Ca合金的强度相近。（5）预热+挤压工艺提高GWZL8313合金再结晶比例，细化晶粒，增加Mg3RE相数量，使合金保持强度的基础上提高了韧性。热挤压+轧制工艺提高GWZL8313合金再结晶比例提高，细化晶粒，导致β1R相消失并转变为Mg3RE相，使合金的强度下降但韧性增加。