MICROSTRUCTURE CHANGE AND ENERGY RELEASE OF FRICTION STIR WELDED Al-Mg-Si ALLOY DURING DSC TEST
DAI Qilei1, LIANG Zhifang2, WU Jianjun1, MENG Lichun3, SHI Qingyu1()
1 Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Department of Mechanical Engineering, Tsinghua University, Beijing 100084 2 Fundamental Industrial Training Center, Tsinghua University, Beijing 100084 3 CSR Sifang Locomotive and Rolling Stock Co. Ltd., Qingdao 266000
Cite this article:
DAI Qilei, LIANG Zhifang, WU Jianjun, MENG Lichun, SHI Qingyu. MICROSTRUCTURE CHANGE AND ENERGY RELEASE OF FRICTION STIR WELDED Al-Mg-Si ALLOY DURING DSC TEST. Acta Metall Sin, 2014, 50(5): 587-593.
During friction stir welding, the nugget zone (NZ) underwent severe plastic deformation and high temperature. This process resulted in high density of dislocations and dissolving of the precipitation. In this study, the stored energy of the NZ in friction stir welded Al-Mg-Si joint was quantitatively analyzed by means of differential scanning calorimetry (DSC). The microstructure of the NZ was investigated by electron back scattering diffraction (EBSD) and transmission electron microscope (TEM). DSC analysis showed that the energy stored in the NZ was about 8.565 J/g. Microstructure investigation showed that the NZ was composed of low-angle grain boundary (42%) and high-angle grain boundary (58%). Meanwhile, there were high density dislocations in the NZ. The stored energy was quantitatively analyzed based on EBSD data and dislocation density. The results showed that the stored energy resulting from the grain boundary and dislocations was about 0.0247 J/g and 0.0712 J/g, respectively. These results proved that the precipitation played dominant role in stored energy while the contribution of grain boundary and dislocations are negligible.