Effect of two-step aging on cluster formation in Al-Mg-Si alloys

Abstract

The change in the state of a Mg-Si cluster with pre-aging at 363 K, followed by aging at 303 or 323 K, was studied by means of a tensile test, three-dimensional atom probe (3DAP), and differential scanning calorimetry (DSC) measurements. Mg-Si clusters formed during isothermal aging (one-step aging) at 363K after solution heat treatment were different from the ones formed at 303 and 323 K. Furthermore, during aging at 303 and 323K following pre-aging at 363K (two-step aging), the clusters that were originally formed at 363K (high-temperature clusters) grew in size and a new type of clusters (low-temperature cluster) were newly formed at 303 and 323 K. The increase in yield stress with aging time at 303 and 323K was greater with the pre-aging at 363K than without the pre-aging. The greater increase in the yield strength was attributed to the growth of the high-temperature clusters formed in the pre-aging and the nucleation and growth of the low-temperature clusters, both of which proceeded during the aging at 303 or 323 K. © 2014 The Japan Institute of Metals and Materials.