| As Al-Zn-Mg-Cu alloy has high mechanical strength and corrosion resistance,it has been widely used in aerospace,transportation,oil drill pipe and other fields.With the development of industry,the demand for its performance is higher and higher.Al-Zn-Mg-Cu alloy is a kind of aluminum alloy that can be hardened by heat treatment.Therefore,in order to improve the comprehensive properties of Al alloy to meet the requirements,many new heat treatment methods have been explored.However,the traditional aging treatment generally used at present requires a longer time,consumes more energy,and has certain limitations.In order to reduce energy consumption and improve the comprehensive performance of aluminum alloy,this paper studies the performance change and microstructure evolution of Al-4.47Zn-2.13Mg-1.20Cu alloy system in the non-isothermal aging process.The non-isothermal aging processes with different temperature and rate are designed,the microstructure of alloy after non-isothermal aging is analyzed by SEM,DSC and TEM.The results show that GP zone and??are the main phase in the grain,stable?phase is distributed on the grain boundary with a narrow precipitation-free zone;with the decrease of aging rate,the size of precipitated increases,and the grain boundary precipitations are distributed as a small island.According to the hardness and tensile properties tests,the alloy has obtained excellent mechanical properties after non-isothermal aging,and reduce the aging time by about 50%,which is of practical significance to improve the production efficiency and energy saving and emission reduction of aluminum alloy.For the heating aging treatment,the yield strength,ultimate tensile strength,and elongation of the Al alloy after(100-200°C,20°C/h)are increased by 6.6%,12.8%,and 9%as compared with those samples after T6treatment.Because the bulky precipitation with a wider PFZ under the cooling aging treatment is obtained,the strengthening effect of the alloy is not obvious.In the simulated seawater solution,the effects of heating aging treatment on the corrosion performance of Al-Zn-Mg-Cu alloy are investigated by electrochemical,microbial corrosion,SSRT and other experiments.The results show that the self-corrosion potential,corrosion current density and stress corrosion sensitivity Iscc of the alloy are increased by heating aging treatment.Sulfate reducing bacteria(SRB)promotes the corrosion of the alloy by metabolism,which makes the main mechanism of stress corrosion cracking changed from anodic dissolution to hydrogen-induced cracking.With the decrease of aging rate,the precipitates at the grain boundaries gradually became intermittent,preventing grain boundary precipitates from anodic dissolution effectively,and enables the rapid diffusion and enrichment of Cu at the grain boundaries and reduces the potential difference between the grain boundary and matrix,thereby decreasing the intergranular corrosion susceptibility. |
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