Effect of pre-straining on structure and formation mechanism of precipitates in Al-Mg-Si-Cu alloy
(1. School of Materials Science and Engineering, Nanjing Institute of Technology, Nanjing 211167, China;
2. Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, Nanjing Institute of Technology, Nanjing 211167, China;
3. Key Laboratory for Light-weight Materials, Nanjing Tech University, Nanjing 211816, China;
4. International Joint Laboratory for Light Alloys (Ministry of Education), College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China)
2. Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, Nanjing Institute of Technology, Nanjing 211167, China;
3. Key Laboratory for Light-weight Materials, Nanjing Tech University, Nanjing 211816, China;
4. International Joint Laboratory for Light Alloys (Ministry of Education), College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China)
Abstract: 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/α(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.
Key words: Al-Mg-Si-Cu alloy; pre-straining; Cu segregation; precipitate; HAADF-STEM