Effect of Strain Rate on Tensile and Fracture Behavior of Ultrafine grained Al6061 processed through Cryorolling and Warm rolling

Abstract

The present study is focused on investigating strain rate sensitivity of UFG Al 6061 subjected to different rolling conditions and heat treatment. The different conditions used in this study were: (i) Solution treatment, (ii) Cryo-rolling + Warm rolling (CR+WR), (iii) Cryo-rolling + Warm rolling + Peak Ageing (CR+WR+PA), and (iv) Cryo-rolling + Peak Ageing (CR+PA). The rolled specimens were tested for tensile and K1c (three point bend test) at three different strain rates used in tensile tests were (0.6x10-3 /s, 1.0x10-2 /s and 5.0x10-2 /s) and three point bend tests were conducted at ram velocity of 1 mm/min, 20 mm/min and 100 mm/min. Among all tests, CR+PA samples showed good tensile strength of 257 MPa and fracture toughness of 50 MPa(m)1/2. Increased strength is attributed to the formation of ultrafine grains and high dislocation density. The tensile samples takes less load at higher strain rate when compared to lower strain rate. However, in three point bend test, no appreciable change in load taken by specimen at higher strain rates was observed compared to lower strain rate. Which indicates that loading rates selected were not high enough. The variation in strength at higher strain rate is supported by fractography studies, where failure mechanism has changed from dimple fracture to cleavage at higher strain rates.