Study On Formability Improvement Of The Aluminum Alloy Sheet By Short Time Heat Treatment Under High Temperature

Aluminum alloy has high specific strength and low density,which makes aluminum alloy widely used in all walks of life.The low strain rate sensitivity of the aluminum alloy itself results in poor stamping formability of the sheet,which makes the usage rate of complex aluminum alloy sheet metal parts very low.Therefore,the research on how to improve the formability of aluminum alloy sheet has very high practical significance.In this paper,improve the formability of 5250 aluminum alloy sheet by using short-term high temperature heat treatment made in-depth study.Orthogonal test method is used.Using resistance furnace heating and laser heating to explore the influence of two main parameters include maximum heating temperature T_maxand holding time at the highest temperature t_holdon tensile mechanical properties and work-hardening index of H-state 5250 aluminum alloy sheet with a thickness of 1mm.The forming limit of the 5250 aluminum alloy plate with the initial H state and the short-time high temperature heat treatment of the 5250 aluminum alloy plate with the maximum temperature of 500℃are predicted theoretically through the Swift model and Hill model.The common plate thermoforming test machine is used to make rigid-shaped bulging experiment on aluminum alloy plate to obtain accurate short-term high-temperature heat treatment before and after the actual forming limit sheet of aluminum alloy sheet.The results show that the maximum heating temperature is the most important factor affecting the softening effect of aluminum alloy plate with a thickness of 1mm.The effect of holding time on softening of aluminum alloy plate is related to the maximum heating temperature.When using the box-type resistance furnace heat treatment at a maximum temperature of 500℃,the aluminum plate softening effect is significant,and the softening effect is close to that of H-state aluminum alloy after complete annealing.By observing the uncorroded metallograph of 5250 aluminum alloy before and after short-time high-temperature heat treatment with a metallurgical microscope,it can be seen that the short-time high-temperature heat treatment basically does not change the quantity and volume of Al-Mg mesophases in Al matrix of 5250 aluminum alloy sheet.The research shows that the short-time high-temperature heat treatment by laser heating can soften the H-state 5250 aluminum alloy sheet.However,its softening effect is obviously weaker than the resistance furnace short-time high temperature heat treatment.The results show that the initial bulge of 5250 aluminum alloy plate in the single tensile strain state bulge height increase rate of 111.76%.The rate of increase of bulging height of the initial H-shaped aluminum alloy sheet was 46.17%in the same twin-strain state.It can be seen that the H-shape 5250 aluminum alloy plate with a thickness of 1 mm can significantly increase the forming limit after short-time high temperature heat treatment,According to the prediction of the forming limit before and after the short-time high temperature heat treatment using the Swift-Hill model.