Creep Mechanisms of an Al-Cu-Mg Alloy at the Macro- and Micro-Scale: Effect of the S′/S Precipitate

A novel methodology combining the macro- and micro-creep techniques was employed to study the effect of S '/S precipitate growth on the creep mechanism of an Al-Cu-Mg alloy. An AA2524 alloy was pre-aged at 180 degrees C to obtain S '/S precipitates with various sizes. The results showed that the precipitate size increased approximately linearly to approximate to 32 nm, approximate to 60 nm, and approximate to 105 nm after 3 h, 6 h, and 12 h of pre-aging, respectively. The growth of precipitate could significantly shorten the primary creep stage, despite the fact that the steady-state creep behavior was similar to that of the as-received alloy, as revealed by the macro tensile creep tests at 180 degrees C and 180 MPa. This led to a stress exponent (2.4-2.5) of the Al alloy with various precipitate sizes that was quite close to that of the as-received Al alloy, implying a steady-state creep mechanism dominated by grain boundary sliding and dislocation interactions. Finally, the micro-creep tests showed a minor role of the precipitate size on the steady-state creep mechanism, as evidenced by the similar strain rate sensitivity (0.0169-0.0186), activation volume (approximate to 27 b(3)), and the results of a detailed transmission electron microscopy analysis of all tested alloys.