Characterization and modeling in light alloys and nano-bainitic steels

汽车、航空航天、铁路、国防等行业对先进材料和加工技术的需求日益增长和苛刻，带来了巨大的科技挑战。具有极大改善组织的新型先进高强度钢合金，如纳米贝氏体钢，有可能将钢的使用扩展到交通、能源和国防等更苛刻的应用领域。焊接是其中许多应用中的主要连接过程，最近的努力是将非熔化焊接技术(如超声波焊接)应用于汽车和航空航天应用中的镁合金等较新的轻质结构材料。这项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，特别是创新的固态焊接工艺和新的有前途的纳米贝氏体钢。具体地说，在这项建议中，将研究以下内容：(I)不同材料的超声点焊工艺优化，特别关注涉及界面层结合、组织特征和性能的潜在机制，以及(Ii)为具有优异强度和抗断裂性能组合的纳米贝氏体钢开发新的成分和经济高效的热处理工艺。我们将采用实验和模拟两种方法，通过高级研究和培训工业界和学术界急需的HQP，在这些领域取得进展，加深科学认识，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.