Characterization and modeling in light alloys and nano-bainitic steels

汽车、航空航天、铁路和国防工业对先进材料和加工技术的要求不断增加和严格，这对科学和技术提出了巨大的挑战。较新的先进的高强度钢合金具有大大改善的显微组织，如纳米贝氏体钢，有可能将钢的使用扩展到运输，能源和国防部门的更高要求的应用中。在这些应用中，焊接是主要的连接工艺，最近的努力是将非熔焊技术（如超声波焊接）应用于较新的轻质结构材料，如汽车和航空航天应用中的镁合金。本研究计划的总体目标和长期目标是继续在组织-性能-转变关系领域取得重大进展，特别强调创新的固态焊接工艺和新的有前途的纳米贝氏体钢。具体而言，在本建议中，将研究以下内容：(i)不同材料的超声波点焊工艺优化，特别关注涉及界面层结合，结构特征和性能的潜在机制；（ii）开发具有优异强度和抗断裂性组合的纳米贝氏体钢的新成分和经济有效的热处理工艺。将采用实验和建模两种方法，在这些领域取得进展，以进一步科学理解，并通过先进的研究和通过培训工业界和学术界对HQP的高需求来满足工业界的需求。

Ever-increasing and stringent demands on advanced materials and processing technology in the automotive, aerospace, rail and defense industries pose enormous scientific and technological challenges. The newer advanced high strength steel alloys with vastly improved microstructures such as nano-bainitic steels have the potential to extend the use of steel to even more demanding applications in transportation, energy and defense sectors. Welding is the primary joining process in many of these applications and recent efforts have been directed in applying non-fusion welding techniques such as ultrasonic welding to the newer lightweight structural materials such as magnesium alloys in automotive and aerospace applications. The overall goal and long-term objective of this research program is to continue to make significant advances in the area of structure-property-transformation relationships with particular emphasis on the innovative solid-state welding processes and new promising nano-bainitic steels. Specifically, in this proposal the following will be studied: (i) process optimization of ultrasonic spot welding of dissimilar materials with special attention to the underlying mechanisms involving interface layer bonding, structure characteristics and properties, and (ii) development of new compositions and cost-effective heat treatment procedures for the nano-bainitic steels with superior combinations of strength with fracture resistance. Both experimental and modeling approaches will be adopted to make advances in these areas to further scientific understanding and to meet the demands of industry both through advanced research and through the training of HQP who are in high demand in industry and academia.