大压下量衬板控轧镁-铝-锌合金多尺度混晶组织形成及强塑性同时提高机制

The present project focuses on a key challenge that Mg alloys usually suffer from low ductility, aiming to overcome the key difficulty, i.e., achieving a simultaneous high strength and high ductility, for Mg alloys. The innovation of this project lies in the fact that a new preparation method, i.e., hard-plate rolling (HPR), was utilized to promote heterogeneous plastic deformation, achieving a multimodal grain structure (the coexistence of ultrafine- and micron grains) and weakened basal texture, in Mg-Al-Zn alloys. Based on the fact that the multimodal grain structure favors for enhanced work hardening while a weakened basal texture promotes the plasticity of Mg alloys, a simultaneous high strength and ductility can be achieved in Mg-Al-Zn alloys. Studying the formation mechanism of the multimodal grain structure, and accordingly providing preparing principle for multimodal-grain-structured Mg alloys; Investigating the influence of the multimodal grain structure and weakened basal texture on the mechanism for the simultaneous increase in strength and ductility, and accordingly, establishing HPR processing-multimodal grain structure-strength and ductility relations, optimizing the multimodal grain structure (grain size, volume fractions) and basal texture, realizing the controllable fabrication of Mg-Al-Zn alloys with both high- strength and ductility. The theoretical innovation of this project includes revealing formation mechanisms for the multimodal grain structure and weakened basal texture in HPR Mg-Al-Zn alloys; clarifying effects of multimodal grain structure and weakened basal texture on mechanisms for the simultaneous high- strength and ductility of Mg alloys; providing necessary basis for the development of new high strength and high ductility Mg alloys.

针对镁合金室温塑性差关键科学问题，通过混晶结构及弱基面织构解决“Mg合金强塑性同时提高”瓶颈难题。创新思路在于巧妙利用大压下量衬板控轧（HPR）新方法促进微观非均匀变形，实现Mg-Al-Zn合金混晶结构(超细晶、微米晶)和发散织构协同调控制备；基于混晶结构促进加工硬化、弱基面织构改善塑性新机制，实现强塑性同时提高；通过研究混晶结构形成机制，提供镁合金弱织构混晶结构组织设计准则；基于混晶结构及基面织构特性对强塑性同时提高影响规律的研究，建立HPR制备-混晶组织-强塑性的定性关系，优化出较佳混晶结构（尺寸、比例）及基面织构特性（强度、分布），实现高强塑性Mg-Al-Zn合金可控制备。在理论上的创新：揭示衬板控轧镁合金混晶结构组织形成及基面织构弱化机制；阐明混晶结构和弱基面织构对镁合金强塑性同时提高的作用机制，为开发高性能Mg-Al-Zn合金提供借鉴。

镁合金作为最轻的结构金属材料，在电子通信、汽车、航空航天等领域的轻量化应用具有显著优势。然而，镁为密排六方（hcp）结构、独立滑移系少、室温下塑性变形难，容易形成强基面织构。如何同时提高其强度和塑性是困扰镁合金领域的重大国际性难题。.本项目针对镁合金室温塑性差、强塑性同时提高难关键科学问题，通过巧妙利用大压下量衬板控轧（HPR）新方法促进微观非均匀变形，基于合金成分和热加工耦合调控实现混晶组织（超细晶、微米晶）和弱基面织构控制。本项目主要研究了大压下量控轧Mg-Al-Zn合金混晶组织形成机制、基面织构弱化机制、混晶结构Mg-Al-Zn合金高塑性变形行为及强塑性同时提高机制、高强塑性Mg-Al-Zn合金的短流程可控制备等。.本项目揭示了HPR过程中高密度亚微米级动态析出相可促进非均匀再结晶并稳定再结晶超细晶/细晶粒组织，从而促进Mg-Al-Zn合金混晶组织和弱基面织构形成机制；揭示了混晶结构中具有弱基面织构的细晶/超细晶在变形前期改善塑性、具有强基面织构的粗晶在变形后期稳定塑性变形，细晶/超细晶与粗晶的协同作用促进加工硬化因而同时提高镁合金强塑性机制；阐明了在高温拉伸前期粗晶发生连续动态再结晶（CDRX）协调变形、后期细晶晶界滑移（GBS）主导超塑性变形机制；实现了高性能混晶结构Mg-Al-Zn合金短流程可控制备。.通过本项目研究，实现了难变形镁合金高强塑混晶组织及弱织构演化协同控制；提出了混晶结构提高镁合金室温强塑性及高温超塑性变形机制，丰富了混晶结构镁合金强韧化及超塑性变形理论；建立了大压下量控轧制备-混晶组织-强塑性能的定性关系，为开发具有室温高强塑性能和高温超塑性的混晶结构镁合金及其组织控制提供借鉴。