Research On Double-sided Pressure Of Thin-walled5A02Aluminum Alloy Rectangular Section Tube

The tube hydroforming process is a typical representative method of thelightweight structure technology. The formability of tubes can be increasedsubstantially by combined axial force with internal pressure. But bursting is still amajor defect during hydroforming of aluminum alloy or other materials with poorformability. Double-sided pressure forming is a new method for tube forming basedon increasing the material hydrostatic pressure which would improve theformability. External pressure was added to improve the formability of the tube.Research on double-sided pressure forming of tubular part with rectangular sectionswas carried out in this paper.The theoretical formulas of limit effective strain with and without externalpressure were established through the equilibrium equations and concentrationinstability theory. The effective strain distribution of straight side area was analyzed.The limit effective strain is a fixed value when there is not the external pressure.when the external pressure is added, the limit effective strain increased with theexternal pressure.Experiment on double-sided pressure forming of tube with rectangular sectionwas carried out. The tube material is5A02aluminum alloy which the outer diameteris63mm and thickness is2mm. External pressure was kept constant during theforming process and the value of external pressure is from0MPa to80MPa. Theinternal pressure was increased until bursting occured. The effect of externalpressure on fillet radius and the rate of expansion were analyzed. With the externalpressure increased, the fillet radius decreases, the maximum thickness reduction isincreasedThe strain distribution of the straight side area was measured by using ASAMEstrain test system. It is shown that the strain is concentrated in the transition region.The Gape for different external pressure forming parts were analyzed by SEM.Initiation and growth of crack is inhibited when external pressure increased. Theoriginal tube and the transition zone of different external pressure of the grainmorphology and the number of different phase of the grain boundary were analyzedvia EBSD. Low angle grain boundaries increased when the external pressureincreasing.Numerical simulation on double-sided pressure forming of tube withrectangular section was carried out using the ABAQUS software. The effect of theexternal pressure on hoop stress, axial stress, thick stress and hydrostatic stress wereanalyzed. Exert external pressure reduce the stress values integrity.The influence of external pressure and lubrication on hydroforming of tube with rectangular section was compared. The uniformity of thickness distributionwas improved with improving the tribology. The hoop stress was decreased byadding the external pressure, but thickness distribution is unchanged for addingexternal pressure.