The microstructure of the as-cast 7A55 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and differential scanning calorimetry （DSC） analysis. The results indicate that the microstructure of the as-cast 7A55 aluminum alloy mainly consists of the dendritic network of aluminum solid solution, Al/AIZnMgCu eutectic phases, and intermetaUic compounds MgZn2, Al2CuMg, Al7Cu2Fe, and Al23CuFe4. After homogenization at 470℃ for 48 h, Al/AlZnMgCu eutectic phases are dissolved into the matrix, and a small amount of high melting-point secondary phases were formed, which results in an increasing of the starting melting temperature of 7A55 aluminum alloy The high melting-point secondary phases were eliminated mostly when the homogenization time achieved to 72 h. Therefore, the reasonable homogenization heat treatment process for 7A55 aluminum alloy ingots was chosen as 470℃/72 h.
The effect of quenching rate on the electrical conductivity and microstructure of thick plates of incumbent AA7050 was investigated by employing Jominy end quench test. The electrical conductivity measurement and microstructural observation were conducted at different distances from the quenched end. The results indicate that the average cooling rates decrease with increasing the distance from the quenched end of the bar in the quench sensitive temperature range. However, the electrical conductivity increases with the increase of distance from the quenched end. The surface parts of the plate were fully recrystallized, while partial recrystallization took place at the quarter and center parts of the plate. The quench induced grain boundary precipitates became remarkably coarser and discontinuously distributed with increasing distance from the quenched end of the bar. Plenty of heterogeneous precipitates were observed to nucleate on A13Zr dispersoids when the distance from the quenched end was greater than 38mm.
Temperature variation and solution treatment of high strength aluminum alloy were investigated with temperature data acquisition system,microstructural observation,mechanical properties test,electrical conductivity measurement and differential scanning calorimetry（DSC） analysis.Specimens with two dimensions were employed in the experiment.The results indicate that the specimens with large size undergo low solution temperature and short time,giving rise to the reduction of hardening precipitates.The optimized solution treatments for specimens with dimensions of 25 mm×25 mm×2.5 mm and 70 mm×60 mm×20 mm are（480 ℃,30 min） and（480 ℃,90 min）,respectively.The densities of GP zones and η＇ phases of the small specimen are higher than those of the large specimen,which is consistent with the properties of the alloys.
