低成本高强塑镁合金板材的合金设计与异步轧制变形的基础研究

In order to expand widely industrial applications of Magnesium alloys, it becomes more and more important to develop the Mg sheet with low-cost, high strength and high elongation simultaneously. Recently, Rare-Earth free Mg-Ca-Sn alloys with high yield strength of ~ 409 MPa has been successfully developed by extrusion, and novel microstructures with high densities of nano-lamella and Ca segregations were observed. Thus, the project would at first thoroughly investigate stacking fault (SF) energy and solute segregation energy around SFs for Mg-Ca based alloys. The purpose is to design Mg alloy systems with low SF energy. Composition of the Mg-Ca based alloy was designed according to the calculation result above, and the alloy was then extruded and rolled in differential speed. Formation mechanism of the nano-lamellas and their effects on grain growth behaviors would be studied, to reveal the grain refinement hardening mechanism. Effect of solute elements on nucleation and growth of compressive twinning would be investigated to reveal mechanism of the twinning induced dynamic recrystallization and also formation mechanism of the Rare-Earth texture. Combined with annealing, clarify the static recrystallization behaviors of the as-rolled Mg-Ca based alloys, and also the mechanism of abnormal grain growth to produce the bi-modal grain structure and improve ductility of sheets. Finally, the relationships between deformation processing, microstructures and mechanical properties of Mg-Ca based alloys would be established, to provide basis of designing newly low-cost, high strength and ductile Mg alloys sheets.

开发出低成本、高强和高塑性兼备的镁合金板材是支撑其规模化应用的前提。根据最近发现的挤压态Mg-Ca-Sn非稀土高强合金(屈服强度~409MPa)以及高密度的富Ca纳米层片组织，本项目拟首先通过第一性原理计算，系统研究Mg-Ca系合金的层错能和溶质原子在层错处的偏聚能，据此设计低层错能Mg-Ca基合金体系；进而针对上述设计的挤压态Mg-Ca基合金板材进行异步轧制变形，研究形变诱导纳米片层形成的关键因素，揭示其限制晶粒长大及细晶强化的机理；研究溶质元素调控压缩孪晶形核和扩展的行为，明晰“孪晶诱导”动态再结晶的作用机制，进而阐述Mg-Ca基合金中“稀土织构”形成的内在机理。结合后续退火，明确Mg-Ca基合金的静态再结晶行为，尤其可能发生晶粒异常长大的微观机制，以期获得双组态的晶粒组织进一步改善合金的塑性。最终建立变形工艺-微观组织-强度/塑性的构效关系，为设计新型低成本高强塑镁合金板材提供依据。

本项目基于四年前申请人发现了Mg-Ca-Sn镁合金在常规挤压下实现了亚微米的异常超细晶和高强化现象，但是该超细晶组织形成机理以及如何解决镁合金强塑性互斥难题并没有解决。在国家自然科学基金委-山西省煤基低碳联合基金重点项目（No. U1610253）的资助下，课题组在理论上系统研究了Mg-X二元体系中不同溶质元素在镁合金缺陷处（层错和亚晶界）的偏聚行为和强化效应，据此设计了系列Mg-Ca基非稀土合金；系统研究了Al、Zn、Mn、Ca等元素对缺陷处偏聚、纳米第二相析出以及变形过程中的动态再结晶行为，发现了Ca、Zn等元素在晶界和亚晶界的偏聚，实现了在常规的挤压/轧制过程中亚微米镁合金基体和显著的高强化，其中挤压态Mg-2Ca-2Sn（wt.%）合金获得当前报道的最高强度的微合金化非稀土镁合金（~460MPa），Mg-1.0Ca-1.0Al-0.3Zn-0.1Mn挤压变形镁合金的屈服强度~ 425 MPa，抗拉强度~ 442 MPa，延伸率~ 11 %；Mg-0.6Ca-0.8Mn三元变形镁合金板材抗拉强度400 ~ 420 MPa，Mg-1.0Ca-1.0Al-0.2Zn-0.5Mn板材抗拉强度340 MPa，同时延伸率~ 5.8%。并在镁合金时效强化中，意外发现了不同于晶体和准晶的新型凝聚态物质结构的纳米第二相，为我们理解物质结构开辟了新的方向。. 反映上述研究内容的部分成果已在国内外学术期刊发表论文41篇，其中SCI论文32篇，影响因子大于3.0的21篇，JCR一区论文20篇（包括Physical Review Letters, Acta Materialia, Journal of Magnesium and Alloys, Journal of Materials Science and Technology等期刊）。申请国家发明专利24件，其中已授权8项。撰写《镁合金板带轧制工艺基础研究》专著一部（机械工业出版社）。项目组团队成员在国内外大型学术会议做特邀报告8人次；培养硕士生18人(已毕业13人)，博士生4人（已毕业2人），博士后1人；项目组成员秦高梧教授获得教育部长江学者特聘教授；马立峰教授荣获第十届中国金属学会冶金青年科技奖，任玉平教授荣获中国体视学会青年科技奖，潘虎成副教授荣获中国科协青年托举人才。