Change in the Uniform Elongation and n-Value of 6061 Aluminum Alloy Sheets during Isothermal Strain Aging

6061 commercial aluminum alloys sheets are used as outer panels for automobiles, because of their age-hardenability. The present study investigates the effect of uniaxial tensile prestrain on the change in tensile properties during isothermal aging at 448 K. The relationship between the uniform elongation epsilon sub u and the n-value was examined. The value of epsilon sub u /n was slightly higher than 1 for the stretched specimens. The value is lower than 1 at the beginning of the aging, and becomes nearly 1 at the final stage of the aging for the unstretched specimens. A new approach for obtaining the newly defined n-value was proposed to obtain a good correlation between the uniform elongation epsilon sub u and the n-value for the unstretched and stretched specimens isothermally aged.