Multiple passes of friction stir processing for the creation of superplastic 7075 aluminum

A staggered pass sample of friction stir processed (FSP) 7075 aluminum was created to make samples with one through four passes of FSP under identical conditions. The tensile testing temperatures ranged from 673 to 763 K with initial strain rates ranging from 1 × 10−3 to 1 × 10−1 s−1. Materials processed by single as well as multiple passes exhibited superplasticity across various testing temperatures and strain rates while the as received materials exhibited elongations below 200%. This study demonstrated the effectiveness of four consecutive FSP passes in creating large areas of superplastic material. However, the largest elongations were observed for the single pass material.