Effect of pre-straining on structure and formation mechanism of precipitates in Al-Mg-Si-Cu alloy

The effect of pre-straining on the structure and formation mechanism of precipitates in an Al-Mg-Si-Cu alloy was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Elongated and string-like precipitates are formed along the dislocations in the pre-strained Al-Mg-Si-Cu alloy. The precipitates formed along the dislocations exhibit three features: non-periodic atomic arrangement within the precipitate; Cu segregation occurring at the precipitate/alpha(Al) interface; different orientations presented in one individual precipitate. Four different formation mechanisms of these heterogeneous precipitates were proposed as follows: elongated precipitates are formed independently in the dislocation; string-like precipitates are formed directly along the dislocations; different precipitates encounter to form string-like precipitates; precipitates are connected by other phases or solute enrichment regions. These different formation mechanisms are responsible for forming different atomic structures and morphologies of precipitates.

Automated summary

The effect of pre-straining on the structure and formation mechanism of precipitates in an Al-Mg-Si-Cu alloy was investigated using high-resolution HAADF-STEM. Elongated and string-like precipitates formed along the dislocations in the pre-strained alloy, exhibiting non-periodic atomic arrangement, Cu segregation at the precipitate/alpha(Al) interface, and different orientations. Four different formation mechanisms were proposed, leading to different atomic structures and morphologies of the precipitates.