Formation Behavior of Nanoclusters in Al-Mg-Si Alloys with Different Mg and Si Composition

Two types of nanoclusters are formed during low temperature aging and play important roles in age-hardening of Al-Mg-Si alloys. The formation behavior of these nanoclusters depends on the alloy composition and heat-treatment process. In this work, the various alloys with different Mg and Si concentration were used in order to clarify the influence of alloy composition on the nanocluster formation using differential scanning calorimetry (DSC), hardness and electrical resistivity measurements. Based on the DSC results, two overlapped exothermic peaks were clearly detected, showing the formation of Cluster (1) and Cluster (2) in all examined alloys with different alloy composition. These two overlapped peaks are separated by the Gaussian function method to analyze the volume fraction of nanoclusters quantitatively. It is found that the Si and Mg concentration of Al-Mg-Si alloys has a marked effect on the nanocluster formation. The formation of Cluster (1) is more related with the Si concentration, whereas Cluster (2) is correlated with both of the Mg and Si concentration. Furthermore, the important point is that the formation behavior of nanoclusters strongly depends on the Mg/Si ratio of the alloys. The formation of nanoclusters is most enhanced when the Mg/ Si ratio is approximately 1.0.