Ti‐6Al‐2Sn‐2Zr‐2Mo‐2Cr Alloy for High Strength Aerospace Fasteners

Abstract

Next generation demanding aerospace systems requirements are pushing the titanium alloy performance needs beyond the upper limits of the workhorse alloy Ti 6Al-4V (Ti 6-4), necessitating the use of advanced solutions. This paper provides an overview of Arconic’s lightweight solution to address the needs of future aerospace fastening systems. The key attributes for aerospace fasteners are strength (tensile, double shear, and fatigue) and manufacturability (ability to forge heads and roll threads while meeting metallurgical and dimensional requirements) at an affordable cost. In particular, increasing double shear strength (DSS) while meeting other requirements is very challenging. Typically, DSS is about 60% of the tensile strength for Ti 6-4, restricting Ti applications to moderate strength levels. Limited deep hardenability of Ti 6-4 (≤0.5”) also restricts the usage to smaller diameter fasteners. Beta Ti alloys (e.g. Beta C) capable of achieving high tensile strengths suffer from shortfalls in DSS and producibility. There is a need for an affordable high strength Ti alloy that can extend titanium fastener usage to higher strength levels and larger size (up to 1”), which will enable reduction in number of joints and weight reductions by replacing higher density nickel/steel fasteners. Ti 6Al-2Sn-2Zr-2Cr-2Mo (Ti 6-22-22), a judiciously balanced α + β Ti alloy, designed and developed by RMI Titanium Company in the early 1970s for thick-section aerospace structural applications with a need for higher strengths than Ti 6-4, is capable of meeting demanding fastener requirements of next generation aerospace systems. Superior producibility and ability to tailor processing-microstructure-property relationships in Ti 6-22-22 for achieving performance improvements will be discussed in this paper.