Makoto Saga

Precipitation Morphology and Tensile Properties of Al‐0.62Mg‐0.32Si Alloy Aged at Low Temperature

The influence of aging precipitates on tensile properties and dislocation substructure in Al-0.62Mg-0.32Si (mass %) alloy has been investigated by tensile tests and microstructural observations. Cold-rolled sheets of the alloy were aged under the following conditions: 453 K for 20 h (sample A), 373 K for 120 h (sample Bl), 373 K for 7200 h (sample Bh) and 323 K for 14688 h (sample C). Values of Vickers hardness of samples A, Bl and C were about 75 HV. However, characters of precipitates were different among the samples: needle-like β′′ precipitates about 50 nm in length and 4 nm in diameter were observed in sample A using transmission electron microscopy (TEM), and Mg-Si clusters below 2 nm in size were observed in samples Bl and C by three-dimensional atom probe (3DAP). In sample Bh showing the maximum hardness (103HV) after 373 K aging, fine β′′ particles about 5 nm in length were observed. Samples A and Bh with the β′′ precipitation exhibited higher values of yield stress than those for samples Bl and C, and the β′′ precipitates pinned dislocations. On the other hand, samples Bl and C with the cluster formation had excellent ductility and showed different dislocation substructure from each other. Electron tomography observations revealed that dislocations in sample Bl was wavy in three dimensions, while dislocations in sample C tended to be linear in shape. These results suggested that the tensile properties and dislocation motion were dependent on the aging products, such as clusters and β′′ precipitates.