Study On The Microstructure Evolution Of7050Aluminum Alloy During Non-isothermal Aging Process

Currently, there is little research for the ageing treatment of the thick aluminumplate. The paper investigated the non-isothermal ageing treatment for the7050aluminum thick plate.The effect of the process parameters and micristructure hasbeen obtained via the transformation of microstructure and performances in thedifferent non-isothermal aging treatmentt. The process parameters for the thickaluiminum plate has been got by the measurement of the temperature field and theinvestigation to the thin aluminum alloy.The resutlts show that: the hardness and conductivity increase with the increaseof aging time under the1inear heating treatment. When the temperature increased to190℃，the alloy get the peak value of182HV, which is closed to the hardness of thealloy through T6heating treatment. Under the condition of linear he ating treatmentfrom higher temperature to the lower temperature, the7050aluminum alloy is ableto get balance of high hardness and conductivity. In this process, it only need1.5hour to obtain the ideal mechanical properties. This improve the efficienc y of ageingtreatment.The G.P. zones and η’ phase existed in the matrix when the alloy was heatedfrom room temperature to140℃by the heating rate of20℃per hour。 Theprecipitates growed up in the subsequent heating process. When the heatingtemperature was up to200℃, the alloy came to over-aged state. The η phasedeposed directly from the matrix when the alloy get the linear cooling process fromup to190℃. With the temperature decrease，the precipitated phase gradually growin the experience of the short-term cooling. When the temperature decreased to160℃， there are density and fine precipitates deposed from the matrix. Thesesecondary precipitates made the alloy get an added strengthening。The secondaryprecipitation ales appear in the grain boundary and PFZ, which is benefit to thecombination property of the7050alloy.The precipitation behavior of the alloy was analyzed by differential scanningcalorimeter in the non-isothermal heating treating. The resutlts showed that: thedissolve peak of the η’ phase in the DSC curve moved to higher temperature withliner heating process which means the precipitates growed up to a bigger size. Thereexisted a secondary precipitation in the liner cooling treatment from190℃to140℃。The temperature field was analyzed by the actual measurement and simulation.It showed that there exist a non-isothermal heating process in the aging treatment. It need a temperature compensation when the non-isothermal aging was put to thickplates. The thick plates of200millimetre will get a approximate cooling process tothe thin alloy from190℃when the thick plates get a liner cooling process from250℃to room temperature by20℃per hour.