The compositions of metastable phase precipitates observed at peak hardness condition in an Al–Mg–Si alloy

The metastable-phase precipitates which appear at the peak condition of hardness in an Al–0.83 at%Mg–0.4 at%Si alloy were investigated, using a combination of Vickers microhardness tests, DSC calorimetry, and field-emission STEM observations with EDX analyses. EDX and elemental mapping revealed that both Si-rich and Mg–Si precipitates with needle-shapes were present. EDX analysis showed that needle-shaped β″precipitates protruding from the specimen foils were composed mainly of Si. The present results on structures, compositions and thermal stabilities of the precipitates suggest that Si-rich precipitates co-exist with complex Mg–Si precipitates also of needle-shape.

Research highlights▶ The present EDX analysis revealed that both Si-rich and Mg-Si precipitates with needle-shapes were present at peak hardness condition in Al–Mg–Si alloys.