Research On The Effect Of Stress Triaxiality On Damage During Hot Power Backward Spinning For High-strength As-casting Aluminum Alloy Tube

High-strength aluminum alloy is the preferred material for aerospace and other high-tech industries because of its small density,good plasticity,light weight and corrosion resistance.The thin-walled tube manufactured by spinning for 7075 as-cast aluminum alloy blank,the manufacturing method can overcome the shortcomings of traditional tubes and realize the lightweight,this kind of tube of high performance,high reliability,high efficiency and green forming has become one of the main method of manufacturing the tubes.However,7075 as-cast aluminum alloy is considered to be high strength aluminum alloy with poor plasticity,difficult deformation and poor axial fluidity,so it is difficult to form and process at room temperature.Cracking defects are easily produced during the process of spinning,which seriously affects the forming quality of tubes.Stress triaxiality is one of the main factors that affect the cracking.Therefore,the finite element numerical simulation is applied in this paper.Combined with theoretical and experimental methods,the influence of stress triaxiality on the damage in the spinning forming process is systematically researched.The research contents and conclusions obtained in this paper are as follows:(1)Based on Lemaitre damage criterion,the hot power backward spinning of 7075 as-cast aluminum alloy tube with stress triaxiality is established,its reliability is verified by finite element simulation and spinning.(2)The key technology of thermomechanical coupling finite element modeling for 7075 as-cast aluminum alloy tube is solved.The hot power backward spinning model of 7075 as-cast aluminum alloy tube with stress triaxiality is established,and its reliability is verified by the tube spinning.(3)The stress triaxiality characteristics along the axial and circumferential direction of the tu are obtained:The characteristics of the axial and circumferential stress triaxiality of each pass are obtained by the analysis of the end,the middle,and the root in the circumferential path and the axial path in each pass:Axial path: The tube is subjected to the pressure of the roller,the inside an d outside stress triaxiality at the end of the tube is negative when the roller in contact with the tube in the first pass.The inside and outside stress triaxiality hasrelatively large volatility,and the variation trend of stress triaxiality on the inside and outside is basically similar in the second,third,fourth pass.Circumferential path: The stress triaxiality at the end and root of tube have the largest variation,and the change of stress triaxiality in the middle of tube is relatively stable.(4)The relationship between damage and stress triaxiality,the relationship between damage and the process parameters,the relationship between stress triaxiality and process parameters are obtained by orthogonal test and regression analysis with quadratic polynomial fitting.