The Microstructure and tensile properties of a splat-quenched Al-Cu-Li-Mg-Zr alloy
- PDF / 7,103,542 Bytes
- 11 Pages / 594 x 774 pts Page_size
- 37 Downloads / 231 Views
I.
INTRODUCTION
BOTH the
efficiency and performance of aircraft would greatly benefit from the use of lighter-weight materials. A study by Lewis and co-workers I illustrated the design advantages of the use of low density, high specific modulus and high strength materials for airframe components. Although aluminum alloys presently comprise as much as 80 pct of the weight of a commercial airliner, current design projections forecast the increased use of lighter, stiffer materials, such as carbon fiber composites. 2 However, the conversion of current manufacturing facilities, which are designed for metal fabrication, to production of nonmetallic matrix materials would require a large investment in capital equipment and operator training. The prospect of developing low density, high strength aluminum alloys has, therefore, generated much interest in the aerospace industry. Lithium additions to aluminum provide the greatest reduction in density and increase in elastic modulus of any alloying element, and A1-Li-X systems have been the subject of much recent study. 3"4 The historical development of A1-Li alloys, reviewed recently by Balmuth and Schmidt, 5 dates back to the 1920's. However, early attempts at their commercialization were short-lived because of difficulties in obtaining adequate fracture toughness and ductility. The low ductility of AI-Li-X alloys has been associated with either grain boundary segregation of impurity elements 6 or the development of intense strain localization during plastic deformation. 7 Impurity elements such as Na, K, and S have low solubilities in aluminum and when present segregate to interfaces and grain boundaries. They have been detected in high concentrations on the intergranular fracture surfaces of A1-Li alloys, 6 and improvements in toughness have been claimed to occur when Na levels are reduced or when the Na is tied up in compounds by the addition of Bi. 8 However, Vasudevan et al. 9 have illustrated that while Na reduces the toughness in unaged A1-Li alloys, it does not affect the fracture behavior, ductility, and toughness of peak-aged alloys. Strain localization, associated with the shearing of coherent and partially coherent strengthening precipitates and the presence of R. E. CROOKS is a Research Scientist, Technical Center, ARCO Metals Company, Arlington Heights, IL 60004. E.A. STARKE, Jr. is Earnest Oglesby Professor of Materials Science, Department of Materials Science, University of Virginia, Charlottesville, VA 22901. Manuscript submitted January 9, 1984. METALLURGICALTRANSACTIONS A
large precipitate free zones (PFZ's), 1~ is more likely the reason for the intergranular fracture and concomitant low ductility and fracture toughness observed for most AI-Li-X alloys. Recent studies by Sanders and Starke lj on A1-Li binary alloys, Lin et al.12 on A1-Li-Cu alloys, and Starke and Lin ~3 on the A1-Cu-Li-Mn alloy 2020 have clearly shown this to be the case. Strain localization due to precipitate shearing can be minimized by overaging to produce incoherent precipitates,
Data Loading...
