M. J. Caton, Air Force Research Laboratory, Wright-Patterson AFB, OH; O. N. Senkov, S. V. Senkova, UES, Inc., Dayton, OH

Summary:

High strength aluminum alloys are being examined as a potential replacement for titanium alloys currently used in cryogenic applications within rocket propulsion systems. Aluminum alloys offer reduced weight, lower susceptibility to hydrogen embrittlement, and lower production and processing costs. The tensile and fatigue properties, at both room and cryogenic temperatures, of a developmental Sc-modified 7XXX series alloy are presented in cast, extruded and forged conditions. The specific tensile strengths of the developmental alloy extrusions and forgings exceed that of the Ti-5Al-2.5Sn alloy currently used in cryogenic fuel pump applications, both at room and cryogenic temperatures. The room temperature stress-life behavior at a stress ratio of 0.1 shows a sharp fatigue limit at a maximum stress of approximately 300 MPa for lifetimes exceeding 10⁷ cycles. Fatigue crack initiation and early crack growth were monitored using a standard replication method. The mechanisms controlling strengthening and fracture of the Sc-modified alloy will be discussed.