In December 2017, SAE released an updated and much-needed version of AMS 6931. Before we dig into some major changes in AMS 6931D, let’s take a look at where AMS 6931C left off.
AMS 6931 is a specification for titanium bar, forgings, and forging stock. AMS 6931 is specific to the 6AL-4V alloy.
AMS 6931C covered products up to 6” in diameter or least distance between parallel sides. However, it is commonly requested for products larger than 6” to be certified to AMS 6931. Since larger sizes were not specifically covered in the specification, AMS 6931C left it up to the purchaser and producer to determine what mechanical requirements could be satisfied for any products outside of the range identified in the specification. Usually manufacturers interpreted this as either (1) product manufactured in a size outside of the range of AMS 6931C would be manufactured to meet the properties of the largest size that is covered, or (2) since there are no specific requirements for products outside of the range of the specification, test results would be for information only, and not cause for rejection.
AMS 6931D recognizes that purchasers and end users are looking for assurances of what mechanical properties can be achieved in larger section sizes, by extending the coverage to 10” in diameter or least distance between parallel sides. Also, while AMS 6931C defined properties for products with a maximum cross-section of 48 square inches, AMS 6931D extends to 79 square inches. This allows titanium AMS 6931D products in this extended range to be certified without a “for information only” caveat; we now have firm requirements. For products larger than 10” diameter or least distance between parallel sides, and beyond a 79 square inch cross-section, the spec still does mandate the purchaser and producer to agree on the properties. [Read more…]