The Effect of Very Short Time-at-Temperature on the Yield Stress of 6061-T651 Aluminum

This paper describes the experimental methods and the results of an investigation of the effect of short time-at-temperature (achieved by using high heating rates) on the yield stress of 6061-T651 aluminum in uniaxial tension. Specimens were heated to 260°C at rates from about 10−3 to 103°C/s and then immediately pulled to failure at a constant strain rate of about 10/s. These heating rates, which correspond to approximate times-at-temperature in the range of 10−1 to 105 s, produce a large change in yield stress between times-at-temperature of 102 to 105 s. This change is explained in terms of precipitate coarsening and is substantiated by metallographic evidence. Extrapolation to times-at-temperature in the order of 10−5 s is discussed, and it is suggested that at these rates changes in yield stress would be due to strain rate effects only.