Fatigue and deformation aspects of lightweight materials

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In today's rapidly evolving energy crisis, improvements in fuel efficiency and reductions in greenhouse gas emissions are prime concerns and urgent topics to be solved in the automotive and aerospace industries. Lightweighting is one of the most important strategies, with every 10% reduction in weight leading to a 6.6% to 8% increase in fuel efficiency. Magnesium is the lightest of structural metals - it weighs 75% less than steel and is about one third lighter than aluminum. It is now regarded as a strategic lightweight material in the automotive and aerospace sector. However, there exist a number of issues that severely limit the widespread applications of magnesium alloys, including fatigue and reliability, welding and joining, corrosion resistance, and formability. Other issues remain as to how the twinning and detwinning occur during cyclic deformation, and if the anisotropy and strong tension-compression yield asymmetry in wrought magnesium alloys can be reduced or eliminated. The objectives of the proposed research are to address these critical issues and barriers building upon the applicant's extensive and pioneering research experience and knowledge in this area, and develop a fundamental understanding of fatigue and fracture of magnesium alloys and other types of lightweight materials. Specifically, the following topics will be examined: i) the underlying fatigue deformation and twinning-detwinning mechanisms in wrought magnesium alloys will be elucidated and modeled, ii) the texture and residual stresses will be analyzed and evaluated using a unique high-temperature X-ray diffractometer which permits in-situ measurements as a function of temperatures, iii) the effect of welding and protective coatings on fatigue deformation resistance will be examined, iv) new processing approach and models will be developed to weaken textures and reduce anisotropy. These projects will improve fundamental understanding of long-term performance in magnesium alloys, provide a basis for further development of lightweight alloys for aerospace, automotive and electronic applications, and lead to the training of Ph.D. and master's students who are in high demand from industry, academe, and government laboratories.