INVESTIGATION OF ABNORMAL GRAIN GROWTH IN A FRICTION STIR WELDED AND SPIN-FORMED Al-Li ALLOY 2195 CREW MODULE

摘要

In order to improve manufacturing efficiency and reduce structural mass and costs in the production of launch vehicle structures, NASA is pursuing a wide-range of innovative, near-net s hape m anufacturing t echnologies. A t echnology t hat c ombines friction s tir welding (FSW) and spin-forming has been applied to manufacture a single-piece crew module us ing A luminum-Lithium (Al-Li) a Hoy 2195. P late s ize limitations for A 1-Li alloy 2195 r equire that two plates be FSW together to produce a spin-forming blank of sufficient s ize t o form the c rew m odule. S ubsequent forming of t he FSW r esults i n abnormal gr ain gr owth (AGG) w ithin t he w eld r egion upon s olution heat t reatment (SHT), w hich d etrimentally imp acts s trength, d uctility, a nd f racture to ughness. T he current study seeks to identify microstructural factors that contribute to the development of AGG. Electron backscatter diffraction (EBSD) was used to correlate driving forces for AGG, such as stored energy, texture, and grain size distributions, with the propensity for AGG. Additionally, developmental annealing treatments prior to SHT are examined to reduce or eliminate the occurrence of AGG by promoting continuous or uniform grain growth.