Research On Formability Of High Strength Aluminum Alloy Sheets For Warm Incremental Forming Process

Modern aerospace equipment is constantly developing towards high reliability,long life and light weight,so the material requirements in aerospace field are becoming more and more stringent.AA2024,as a light weight and high strength material,has been widely used in aerospace field due to its excellent performance.The parts in this field have the characteristics of multi-varieties and small batches.Incremental forming technology eliminates the stage of die preparation in the traditional stamping process,and can adapt to the characteristics of aerospace parts with multi-varieties and small batches.Taking AA2024 as the research object,the properties of warm incremental forming were studied in detail.The main research contents and related achievements are as follows:(1)The mechanical properties and microstructural changes of AA2024 sheet at different temperatures were systematically studied,and the constitutive relationship of AA2024-T4 at different temperatures was constructed.The results show that the yield strength and tensile strength of AA2024-O increase with the decrease of strain rate at room temperature(25℃);the grain size of AA2024-T4 increases with the increase of test temperature,and the dimple size and depth on tensile fracture become larger and deeper.The yield strength,tensile strength and strain hardening index of AA2024-T4 decrease with the increase of test temperature.However,the uniform elongation increases with the increase of temperature.During warm-hot drawing,the recovery of AA2024-T4 occurs at 210℃ and recrystallization occurs at 240℃.(2)The deformation of sheet metal during incremental forming process was analyzed theoretically.The incremental forming limits of AA2024-O and AA2024-T4 under different experimental conditions were systematically studied.Analysised the effects of different factors on the limit angle of incremental forming.The results show that the forming temperature and the generatrix shape of the part have great influence on the forming limit angle of the material,while the shape of the part and the forming process have little influence on the forming limit angle of the material.At the same forming temperature,the forming limit angle of AA2024-T4 increases with the increase of the feed rate of the tool head or the decrease of the step down.Therefore,the optimum combination of process parameters for warm incremental forming of AA2024-T4 is the feed rate of 2000 mm/min and the step down of 0.1 mm.(3)The metallographic observation and mechanical properties of the side wall materials of the formed incremental forming parts were studied,and the appropriate forming temperature was determined to obtain better forming limit and higher strength of the materials.The results show that increasing the strain of the material can promote the dynamic recovery and recrystallization of the material,and achieve grain refinement.In the incremental forming process,the dynamic recovery behavior of AA2024-T4 occurs at 180℃,and the dynamic recrystallization behavior of AA2024-T4 occurs at 210℃.With the increase of incremental forming temperature,the strength of materials on the side wall of formed parts decreases gradually.In order to improve the plastic forming ability of AA2024-T4 and ensure the high strength of the parts after forming,the forming temperature should not be too high,not exceeding 180℃.