Improvement of strength and elongation balance of Al-Mg-Si alloy utilizing Mg-Si cluster and its mechanism

Tensile properties of Al-Mg-Si alloy with Mg-Si clusters was compared with that withβ precipitate with the same strength. It was found that the elongation of the alloy with Mg-Si cluster was greater than the alloy with β precipitate because of high work hardening rate, in particular at large strain region. Decomposition of Mg-Si cluster into solute Mg and Si atoms during the tensile deformation test were also shown by differential scanning calorimetry (DSC). Three types of dislocation characteristics were observed from these alloys by transmission electron microscopy (TEM), homogeneous distribution of dislocation with β precipitate, cell structure with Mg and Si in solid solution, and combination of them with Mg-Si cluster. For the case of alloy with Mg-Si cluster, the yield strength was significantly increased due to the cutting mechanism. Simultaneously, the elongation was greatly improved due to the presences of decomposed solute Mg and Si atoms with plastic strain, which are inferred to prevent dynamic recovery in the later stage of tensile test. Consequently, the alloy with clusters has advantages from both alloys with precipitates and solutes, in terms of strength and elongation balance among the conventional 6000 series and 7000 series Al alloys.