Study On Rapid Solution And Aging Treatment Process And Mechanism Of 6061 Aluminum Alloy Sheets

With the problem of energy and environment becoming increasingly prominent,energy conservation and emission reduction has become a major trend in the development of the automotive industry.Lightweight technology is an important way to promote energy saving,emission reduction,and the production and application of new energy vehicles.In recent years,hot press quenching and off-line aging of aluminum alloy have been widely concerned.However,the outstanding problem is that the heat treatment of aluminum alloy is long,and the cost of alloy production is high.Based on the above process ideas,this paper attempts to explore a feasible rapid solution aging process of aluminum alloy,which is helpful to reduce the process cost of hot pressing forming and aging of high strength aluminum alloy.In this paper,taking 6061 aluminum alloy sheets as the research object,the influence factors of different heat treatment parameters on the microstructure and properties of the alloy are explored,the mechanism of rapid solution aging heat treatment is revealed,and the ideal rapid heat treatment parameters are obtained,which provides technical support for the actual aluminum alloy production process.The evolution of microstructure and properties of 6061 aluminum alloy under different solution heating methods,temperature and holding time were studied by using uniaxial tensile test,OM,SEM and XRD.It is found that there are mainly Mg₂Si and Al Fe（Mn Cr）Si distributing on the 6061 aluminum alloy matrix.With the solution temperature and holding time increasing,Mg₂Si,which plays the role of solution strengthening,gradually dissolves into the matrix.The time required for the salt solution to reach the same strength at the same solution temperature is shorter than that of the conventional resistance furnace,which indicates that the solution efficiency of salt bath is higher and the second phase of Mg₂Si dissolves more quickly.When the heating method is fixed,the higher the temperature of salt bath,the faster the re solution of Mg and Si alloy elements,the greater the strength of the alloy after solid solution treatment.However,the temperature should not be too high.The grains of aluminum alloy are easy to recrystallize and grow up or even get over-burning at high temperature,which leads to the decrease of alloy strength.With the increase of solution time,the strength of alloy increases rapidly and then tends to be stable.Because of the rapid solid solution of alloy elements in the early stage,the effect of solid solution strengthening of a small amount of elements in the later stage is not obvious.The ideal rapid solution heat treatment is rapid heating by salt-bath at 560℃for 1.5min.The heating curves of 6061 aluminum alloy sheets in salt bath,oil bath and conventional air resistance furnace were measured by a standard thermocouple.As for the solution heating method,the heating rate of salt-bath solution is much higher than that of conventional air furnace solution.The rapid heating to solution temperature in a short time is conducive to the diffusion of alloy elements,increase the hole concentration and accelerate the T4/T6 heat treatment process.The heating rate of oil bath in aging heating is also higher than that of air furnace,which can increase the effective aging holding time,enhance the atomic activity rapidly,and accelerate the aging process.The effects of different aging heating methods,aging temperature and aging time on the mechanical properties of T6 aluminum alloy were studied by tensile test and microhardness test.Under the same aging temperature and holding time,the strength of alloy by oil bath aging is higher;However,the aging temperature should not be too high.When the aging temperature exceeds 200℃,the peak aging strength and hardness will decrease.The ideal rapid aging heat treatment method is aging by oil bath aging at 200℃for 1h.At this time,the tensile strength of T6 alloy is 362Mpa,the yield strength is327MPa,the elongation is 13.1%,and the hardness is 131HV.The microstructure of 6061 aluminum alloy aged at 200℃and 230℃was analyzed by TEM,HRTEM,SAED and STEM.It was found that the precipitates were different at different aging temperature and time.While aged at 200℃for1h,The precipitates of alloy are mainly acicularβ’’,which is completely coherent with the matrix,and its size is about20～50nm,resulting in a large elastic strain field.While the aging time was prolonged to3 h,The precipitates grows and become semi-coherentβ’.The results show that the dispersion strengthening effect is weakened,and the strength and hardness of the alloy are reduced.When aging temperature rises to 230℃for 30 min,the strength is the highest,and the precipitated phase structure of the alloy containsβ’’andβ’.This indicates the content ofβ’’decreased,leading to the weakening of the final aging strengthening effect.