Study On Microstructure Evolution And Mechanical Properties In 6082 Aluminum Alloy During Long-term Thermal Exposure

Long-term thermal stability is essential for the use of 6082aluminium alloy in battery packaging.In this paper,the microstructure evolution and mechanical properties change of 6082 alloy during 1000 h of thermal exposure at 100,125,150 and 175°C were systematically studied experimentally and theoretically.The microstructure before and after thermal exposure was characterized by metallographic microscopy（OM）,scanning electron microscopy（SEM）,X-ray diffraction（XRD）and transmission electron microscopy（TEM）.the mechancial properties were revealed by tensile test and hardness test.And the relationship between microstructure and mechanical properties was discussed.The size of precipitates was quantitatively analyzed,and the coarsening mechanism and coarsening rate of precipitates were determined.Different coarsening models were used to predict the coarsening rate of precipitates,and a method to predict the strength of alloy after thermal exposure was provided.The main conclusions are as follows:（1）The alloy exhibits excellent thermal stability at 100-125°C,and the yield strength remains above 340 MPa after thermal exposure for 1000h.When the temperature exceeds the threshold 150°C,the strength decreases rapidly.After thermal exposure at 175°C for 1000 h,the tensile strength and yield strength of the alloy decrease from 361 MPa and 340MPa to 231 MPa and 178 MPa,respectively,while the elongation increases from 11.75%to 13.83%.With the extension of thermal exposure time,the strength decline rate slows down.Elongation increases slowly with thermal exposure time.（2）During thermal exposure,the morophology and size of grains did not change significantly,but the width of PFZ gradually increased.After thermal exposure at 175℃/1000 h,the grain size of the alloy is 40μm,which increases by 8%compared with peak aging.The width of PFZ is0.35μm,increasing by 400%.（3）The size of precipitates increased for higher exposure temperatures and longer exposure times.After thermal exposure at100-125°C,the size of precipitates increases slightly,but the average length remains below 35 nm.When the temperature exceeds 150°C,the size of precipitates increases rapidly.After thermal exposure at 175°C for1000 h,the average length of precipitates increases from 31 nm to 328 nm.（4）The precipitate coarsening rate is sensitive to temperature.The coarsening rates of precipitates are 1.31×10^-33 m³s^-1 and 1.28×10^-32 m³s^-1when exposed at 100°C and 125°C,respectively.At 150°C and 175°C,the coarsening rates of precipitates are 3.30×10^-31 m³s^-1 and 2.22×10^-30m³s^-1,respectively.（5）The precipitate coarsening receptor diffusion control in 6082alloy.LSW model and KV model were used to calculate the coarsening rate of precipitates in 6082 alloy.The KV model is the best coarsening model,and the ratio between the calculated theoretical coarsening rate and the actual coarsening rate is 1-1.4.A convenient method for predicting the strength of alloy under different thermal exposure conditions was proposed by coupling KV model with strength model.