Influence of cryorolling and followed by annealing on high cycle fatigue behavior of ultrafine grained Al 2014 alloy

Abstract

Effects of cryorolling (CR) and followed by annealing (CR+AN) on the high cycle fatigue strength of bulk ultrafine grained (UFG) Al 2014 alloy were investigated in the present work. Al 2014 alloy was cryorolled (CR) for the thickness reduction of 75% at liquid nitrogen temperature (−196°C). The cryorolled (CR) samples were heat treated for the temperature range of 100–250°C for the duration of 45min in order to investigate its influence on tensile strength, yield strength and high cycle fatigue behavior. The microstructural characterization of the alloy was made through TEM and FESEM. The cryorolled (CR) sample shows the improved high cycle fatigue strength as compared to ST alloy due to the formation of ultrafine grain (UFG) microstructure. The reduced flaw size in UFG prevents accumulation of stress concentration near the crack tip. However, the improvement in high cycle fatigue properties of cryorolled followed by annealed (CR+AN) alloy up to 200°C as compared to solution treated (ST) alloy observed is due to improvement in crack growth resistance facilitated by crack tip/precipitate interaction at grain boundaries (GBs). The high cycle fatigue strength gradually decreases with increasing annealing temperature from 100 to 250°C, due to gradual coarsening of metastable precipitate (θ′ phase), which transformed in to stable coarser precipitate ‘θ’ phase at 250°C.