Study On Heating Aging Process Of 7050 Aluminum Alloy

Heating aging is a new type of aging treatment,which belongs to non isothermal aging.It can obtain good comprehensive properties with mechanical properties close to T6 aging treatment while having better corrosion resistance.Moreover,the time required for heating aging is much shorter than that for isothermal aging,the efficiency is high.At the same time,for thick plate and other large parts,the uniformity of properties is better after heat aging treatment.In this paper,the microstructure and properties of heat aging were studied,we mainly chose the initial temperature of 100 ℃,the heating rate of 20 ℃ / h,40 ℃ / h and 60 ℃ / h,and the termination temperature of 160 ℃,180 ℃,200 ℃ and 220 ℃.TEM was used to observe the morphology of intragranular precipitates,grain boundary precipitates and precipitate-free zone.the effects of heating rate and termination temperature on the microstructure were analyzed.The changes of hardness,conductivity and strength under different heating aging conditions were analyzed.The main conclusions are as follows:(1)The change of hardness and conductivity was studied,the heating aging process is analyzed by comparing the isothermal aging.The results show that they all experience under-aging,peak-aging and over-aging.The variation of hardness is affected by heating rate and termination temperature.The higher the heating rate is,the faster the hardness reaches the peak value,and then the hardness begins to decrease.The conductivity increases with the heating aging,and the influence of heating rate is small.(2)The microstructure was analyzed by TEM,HRTEM and electron diffraction patterns.The precipitation process of heating aging is as follows:Supersaturated solid solution-GP-η’-η.The average size and size range of intragranular precipitates increase with the increase of termination temperature,and the distribution density first increases and then decreases.The higher the heating rate is,the faster the nucleation and growth rate of intragranular precipitates is.However,when the heating aging reaches a higher temperature,the high heating rate makes the small-size precipitates more likely to dissolve,resulting in low distribution density.(3)With the increase of termination temperature,the tensile strength and yield strength first increase and then decrease,and the elongation first decreases and then increases.The proportion of intergranular fracture increases first and then decreases,the proportion of transgranular shear fracture decreases,and the proportion of transgranular ductile fracture increases.When the heating rate is 20 ℃ / h,there are more transgranular ductile fractures.