Aluminum-Lithium Light Weight Frangible Collar Development

Light weight aerospace fastening collars were manufactured from 2099 alloy which is a new generation Al-Li alloy developed by Alcoa. The collars studied in this work are threaded self-locking collars with controlled torque-off feature and are to be used in a fastener assembly with a treated pin.  The mechanical properties of 2099 collars were measured and compared to the ones made of incumbent alloys such as 7075 and 2024. It was found that the 2099 collars were 16% lighter but provided the equivalent mechanical properties. In addition, the corrosion characteristics of the 2099 collars were studied using the salt spray (NASM 1312-1) and alternate immersion (NASM 1312-9) test methods. It was observed that 2099 collars exhibited an improved corrosion performance as compared to 7075 collars.  This paper presents the results obtained from the mechanical and corrosion testing of the Al-Li collars along with the cost-value analysis of the new product.