Residual Stress And Sensitivity Analysis Of 7075 Aluminum Alloy Plate Quenching

With the rapid development of aviation industry in China,people have more and more requirements for the performance of materials.Quenching plays an important role in improving the performance of materials,and is widely used in aerospace.The deformation,rupture,residual stress distribution and size and mechanical properties of the sheet metal after quenching are always the focus of our attention.Although the quenching process can greatly strengthen the performance of aluminum alloy,but the strong temperature gradient leads to the complex residual stress distribution,which directly results in the subsequent processing deformation.In order to reduce the residual stress after quenching,choose reasonable quenching process is necessary to ensure the follow-up processing,Therefore,it is an urgent problem to study the effect of heat treatment on the residual stress of aluminum thick plate.In view of the above problems,the residual stresses are respectively investigated in the processes of spraying quenching and immersion quenching with the same medium in this paper.First,the numerical simulation of spray-and immersion-quenching process is carried out by finite element method.The blind-hole method and crack compliance method are respectively done to measure the residual stresses for validate the FEM of quenching process.The comparison analysis show that the simulated values of the residual stress distribution are good agreement with the experimental measurement data.Secondly,the influence of plate thickness on the residual stress distribution is revealed for the spray quenching and immersion quenching.Obviously,the quenching cooling rate and plate thickness are critical to residual stresses.The residual stress can keep unchanged when the plate thickness is more than 70 mm in the immersion quenching.However,the spray quenching can make the residual stress increase uniformly.In addition,the residual stress can increase with the incensement of cooling rate.The residual stress in plates with thickness of less than 30 mm is small.The surface compressive stresses,induced by the spray quenching,decrease faster than the interior tensile stresses when the plate thickness varied from 30 mm to 100 mm.But the interior tensile stress decreased rarely if the plate thickness is from 30 mm to 60 mm.Again,the difference between spraying quenching and immersion quenching is smaller and smaller,and it is down.Moreover,the advantage of spray quenching on immersion quenching is gradually decreased with the increase of plate thickness.The temperature-time-property(TTP)curve of 7075 aluminum alloy was measured by the method of interrupted quenching and aging.The quenching process was divided into three stages: the spray quenching process in high temperature area and low temperature area,by immersion quenching at medium temperature.The finite element simulation of interrupted quenching and immersion quenching was carried out respectively.The nose temperature of the 7075 aluminum alloy is about 340?,and the quenching sensitive temperature range is between 219 and 407?;The compressive stress of the aluminum alloy plate after immersion quenching is 53.2% higher than that of the interrupted quenching,and the tensile stress will be higher than 70.6%.The time required for quenching to room temperature is longer than that of immersion,and reasonable quenching process can keep good alloy performance while reducing residual stress.