Influence of Mg/Si Ratio on Nanocluster Formation in Al-Mg-Si Alloys with Constant Mg plus Si Concentration

Two types of nanoclusters are formed during low temperature aging and play significantly important roles in age-hardening of Al-Mg-Si alloys. The formation behavior of nanoclusters markedly depends on the alloy composition. In this paper, alloy specimens with different Mg/Si ratios in the constant Mg + Si concentration of 1.1, 1.3 and 1.5 mol% were used in order to investigate the influence of the Mg/Si ratio on the nanocluster formation using differential scanning calorimetry (DSC), hardness and electrical resistivity measurements. Two overlapped peaks obtained by the DSC analysis are separated using the Gaussian function method and it is clarified that the volume fraction and formation kinetics of nanoclusters change with the Mg/Si ratio even though in the constant Mg + Si concentration. It is found that the most favorable Mg/Si ratio for the nanocluster formation is almost 1.0 even for the different values of the Mg + Si concentration. The influence of the Mg/Si ratio on the nanocluster formation is discussed in terms of interactions among the solute Mg and Si atoms and vacancies in the matrix.