The morphological evolution of the precipitates in Al–7.4Zn–1.7Mg–2.0Cu（wt%） alloy was studied by highresolution transmission electron microscopy（HRTEM）. Statistics reveal that the hardness of the alloy changes...The morphological evolution of the precipitates in Al–7.4Zn–1.7Mg–2.0Cu（wt%） alloy was studied by highresolution transmission electron microscopy（HRTEM）. Statistics reveal that the hardness of the alloy changes accordingly with the change of the average thickness–diameter ratio of precipitates. The GPII zones are mainly responsible for the first and also the highest hardness peak. They grow in diameter and keep 7-atomic-layer in thickness. Once the thickness changes, the phase transformation from GPII zone to g0 or g-precursor would occur. The resultant metastable g0 and g-precursor precipitates grow in both diameter and thickness, but much faster in the former. After the first hardness peak,the metastable g0 precipitates and g-precursor, coexisting with part of GPII zones, are counted as the main hardening precipitates.展开更多
基金financially supported by the National Basic Research Program of China (No. 2009CB623704)the National Natural Science Foundation of China (Nos. 51171063, 10904034, 51071064 and 51301064)+1 种基金Instrumental Innovation Foundation of Hunan Province (No. 2011TT1003)the Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province and the Aid Program for Young Teachers (No. 531107040548)
文摘The morphological evolution of the precipitates in Al–7.4Zn–1.7Mg–2.0Cu（wt%） alloy was studied by highresolution transmission electron microscopy（HRTEM）. Statistics reveal that the hardness of the alloy changes accordingly with the change of the average thickness–diameter ratio of precipitates. The GPII zones are mainly responsible for the first and also the highest hardness peak. They grow in diameter and keep 7-atomic-layer in thickness. Once the thickness changes, the phase transformation from GPII zone to g0 or g-precursor would occur. The resultant metastable g0 and g-precursor precipitates grow in both diameter and thickness, but much faster in the former. After the first hardness peak,the metastable g0 precipitates and g-precursor, coexisting with part of GPII zones, are counted as the main hardening precipitates.
