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The hardness, conductivity and room temperature tensile test were used to study the properties of the new aluminum alloy aged at 110-140 ℃ for different time.The microstructure of the alloy was observed by transmission microscope (TEM).The results show that the optimum aging process of the new aluminum alloy is aging at 110 ℃ for 24 h.Tensile strength, yield strength and elongation are 808,785 MPa,6.9%, respectively.Aging temperature is the main factor affecting the type, density and size of precipitates.When aged at 110 ℃,the main precipitations are GPⅠ zones,GPⅡ zones and metastable η' phase. After aging at 110 ℃ for a long time (up to 96 h), GPⅠ zones and GPⅡ zones still exist stably.Compared with aging at 110 ℃, the precipitation process accelerates at 140 ℃.After aging at 140 ℃ for 4 h, no GP zone is observed, and the main precipitate phase is η'.After aging at 140 ℃ for 24 h, the main precipitates are η' phase and η phase.

Mechanical properties of 2124 aluminum alloy thick plate in short-transverse direction were investigated when ageing at 170-180℃ for different time by room temperature tensile test.The microstructure morphology of alloy after different ageing processes was studied by TEM and SEM.The results show that the suitable ageing process of 2124 aluminum alloy plates is 175℃ for 10h.Yield strength, tensile strength and elongation are 372,422MPa and 2.9%, respectively.The main precipit-ation is S' phase, and also a small quantity of GPB zone and coarse T phase exist at this moment.Ageing temperature is the main factor affecting the density and size of the alloy precipitation.The higher the ageing temperature is, the quicker the rising of strength, the shorter time to reach the maximum strength.The increasing strength difference between the matrix and grain boundary is the main cause for the decrease of the elongation.

Microstructure evolution during hot deformation of a new Al-Zn-Mg-Cu alloy was investigated by Gleeble-1500D thermal-mechanical simulator at 300-450℃ and strain rate of 0.001-10s-1.The microstructure features at different hot deformation conditions were analyzed with optical microscope (OM) and transmission electron microscope (TEM).The results show that the dislocation density decreases and the subgrain sizes increase with the increase of deformation temperature and the decrease of the strain rate;the main softening mechanism of the alloy is dynamic recovery and dynamic recrystallization.Only dynamic recovery occurs when the temperature is 300-400℃.Dynamic recrystallization occurs when the strain rate is 0.001-10s-1 at 450℃.The nucleation mechanism is grain boundary bowing,subgrain growing and subgrain incorporation during dynamic recrystallization.

A non-isothermal ageing process was proposed for an Al-Zn-Mg-Cu alloy aiming to accommodate the slow heating/cooling procedure during the ageing of large components. The evolution of microstructure and microchemistry was analyzed by using transmission electron microscopy, high-angle annular dark field imaging, and energy dispersive spectrometry. The age-hardening of the alloy was examined to evaluate the strengthening behavior during the non-isothermal process. The corrosion behavior was investigated via observing the specimens immersed in EXCO solution (solution for Exfoliation Corrosion Susceptibility test in 2xxx and 7xxx series aluminum alloys, referring ASTM G34-01). Secondary precipitation was observed during the cooling stage, leading to increased precipitate number density. The distribution of grain boundary precipitates transits from discontinuous to continuous at the cooling stage, due to the secondary precipitation’s linking-up effect. The solutes’ enrichment on grain boundary precipitates and the depletion in precipitate-free zones develops during the heating procedure, but remains invariable during the cooling procedure. The corrosion in NIA (Non-isothermal Ageing) treated specimens initiates from pitting and then transits to intergranular corrosion and exfoliation corrosion. The transition from pitting to intergranular corrosion is very slow for specimens heated to 190 °C, but accelerates slightly as the cooling procedure proceeds. The transition to exfoliation corrosion is observed to be quite slow in all specimens in non-isothermal aged to over-aged condition, suggesting a corrosion resistance comparable to that of RRA condition. [ABSTRACT FROM AUTHOR]