Embrittlement mechanism on tensile fracture of 7075 Al alloy with friction stir process (FSP)

Abstract

7075-T6 Al alloy plates had a friction stir process (FSP) and then performed the natural aging to investigate the effects of various tool rotation speeds (1230rpm, 1450rpm, 1670rpm) and natural aging (40°C, 96h) on the microstructures and tensile fracture properties. The experimental results showed that the grain size became fine equiaxed and the average grain size were 5.2, 5.1, 4.2 μm from low to high tool rotation speeds in the stir zone (SZ). The tensile strength varied with the different rotation speeds of FSP. After natural aging, higher tool rotation speeds had an embrittlement phenomenon on the SZ (detected by nanoindenter) due to the contribution of stirred metal flow and precipitates. Decreasing the tool rotation speeds, the metal flow zones were refined and restrained the brittle behavior to improve the ductility. ©2011 The Japan Institute of Metals.