The change of the state of Mg-Si cluster with aging time at 303 K and 323 K after pre-aging at 363 K was studied by means of tensile test focusing on yield stress, 3DAP (3 Dimensional Atom Probe) and DSC (Differential Scanning Calorimetry) measurement. Mg-Si clusters formed during isothermal aging at the temperature of 363 K after solution treatment were different from the ones formed at the temperatures of 303 K and 323 K. During aging at 303 K and 323 K following pre-aging at 363 K, the cluster that was once formed at 363 K grew in size together with the new nucleation of another type of cluster formed at 303 K and 323 K. The increment of yield stress with aging time at 303 K and 323 K after pre-aging at 363 K was greater than the one without pre-aging at 363 K. This was considered to stem from the fact that the cluster formed during pre-aging at 363 K further grows during aging at 303 K and 323 K but at the same time the another type of cluster is supposed to newly nucleate and grow at 303 K or 323 K after pre-aging, both of which are inferred to contribute to the larger increase in yield strength.
