Influence of Cold Work on the Microstructural Evolution and Hardness During Aging of AA6061 Alloy

It is well known that the kinetics of precipitation is altered with the degree of cold working and this study aims to bring out the effect of cold working on the aging response of the alloy AA6061 along with the studies of microstructural evolution. The as-received samples were initially solutionized at 530 °C and subsequently aged at 160 °C for varying time from 2 to 28 h at intervals of 2 h. A peak hardness of 124 HV was observed at 15 h beyond which the hardness decreased due to overaging. The solutionized samples were also subjected to various degrees of cold working and the increase in hardness by virtue of strain hardening was observed. The samples that were cold worked to various levels (10, 20, 30% etc.) were subsequently aged at 160 °C for 4 h. A peak hardness of 134 HV was obtained for the sample cold worked to 75% and subsequently aged for 4 h and this was attributed to the increase in the dislocation density that improved the kinetics of precipitation. The evolution of microstructure for various samples during the course of aging was observed using transmission electron microscopy and the changes in the properties were correlated to the obtained microstructure.