The Evolution of Al-Li Base Products for Aerospace and Space Applications
- PDF / 1,418,867 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 58 Downloads / 225 Views
TION
HISTORICALLY, improvements in the performance of aerospace and space craft have been based on improvements in the performance of metallic materials. The specific properties (property/density) of aluminum-based alloys and products* have increased over time as the aerospace *For the purposes of this article, an alloy is a mixture of chemical elements as defined by the Aluminum Association designation. A product consists of an alloy with a temper and has a physical shape and measurable attributes.
industry has evolved. Starting with the Wright brothers’ flight in 1903, an Al-9 wt pct Cu cast product was used in the crankcase of the engine. This alloy had specific yield strength of 43 (MPa/gm/cm3).[1] Today’s strongest aerospace aluminum plate product is 7055-T7751, which is used for upper wings. The specific compressive strength of 7055T7751 plate product is 229 (MPa/gm/cm3),[2] i.e., more than five times stronger. The space tanks used to propel payload into space have undergone a similar evolution. The Saturn IB, which was present at the start of the space race, had fuel tanks made with 5456–H116 plate. The specific yield strength of 5456H116 is 96 (MPa/gm/cm3). In comparison, the fuel tanks of the space shuttle made with 2195-T8M4 plate show a specific yield strength of 211 (MPa/gm/cm3). Improvements in specific strength are not the only indicator of improved performance for aerospace materials. Durability (e.g., corrosion and fatigue resistance)
ROBERTO J. RIOJA, Alcoa Technical Fellow, and JOHN LIU, Director of Aerospace and Materials Technology, are with the Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069. Contact e-mail: [email protected] Manuscript submitted October 28, 2011. Article published online March 31, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
and damage tolerance (e.g., residual strength and fatigue crack growth) properties often determine the size of the aircraft components. The properties of most importance are a function of the aircraft component (e.g., upper or lower wing, fuselage, empennage, etc.) and position on the aircraft.[2] The Al-Li products offer opportunities for significant improvements in aerostructural performance through density reduction, stiffness increase, increases in fracture toughness and fatigue crack growth resistance, and enhanced corrosion resistance. However, previous generations of Al-Li alloy products (e.g., 2090-T81 plate, 8090-T86 plate, and 2091-T84 sheet) exhibited significant in-plane and through-thickness anisotropy in mechanical properties. These yielded undesirable design and manufacturing characteristics such as crack deviation and microcracking during cold hole expansion. In addition, they showed low short-transverse fracture toughness, poor corrosion resistance, and poor thermal stability. In this article, the results of intense research and development (R&D) are discussed to demonstrate the understanding of the underlying metallurgical causes for the undesirable characteristics. This work has culminated in key alloy design principles
Data Loading...
