Experimental And Numerical Investigation On Warm Formability Of Aluminum Alloy 5083 Sheet

Aluminum alloy has been widely used due to its high strength to weight ratio,high specific stiffness,low density and good corrosion resistance.The lightweight aluminum and magnesium material have been increasingly used to substitute the traditional steel and cast iron,as the result of the increasing requirement in the economic efficiency and environmental protection.Al-Mg alloys(5000 series aluminum alloy)are relatively mature alloys in China which have been widely used in the traditional industry.However,the Al-Mg alloys have poor formability under the room temperature,and thus can not be used to produce profile with complex shape,while warm forming process can greatly improve the formability and surface quality of the products.In this study,numerical simulation and experiment of AA5083 sheet were conducted to study its flow behavior and formability under worm forming conditions.The tensile tests were conducted under different temperatures(20 ?,100 ?,150 ? 200 ? and 250 ?),strain rates(0.001s-1,0.01s-1 and 0.1s-1)and directions which were 0,45 and 90 degrees to the rolling direction to analyze the flow behavior of AA5083.It is found that the flow stress shows negative temperature sensitivity and positive strain rate sensitivity and its mechanical properties are isotropic.Finally,three type of constitutive equations(modified Swift model,modified Ludwigson model and H/V model)that coupled temperature and strain rate were constructed.All three models show good accuracy in the prediction of flow stress for AA5083.The experimental and numerical Nakajima forming process were conducted in order to obtain the forming limit curve(FLC)of AA5083.In the experimental process,the setup and the samples were designed according to the ISO-12004-1:2008.The Nakajima experiments were conducted based on the EC600 experiment platform,at the same time,the deformation strain field of the sheet was acquired by the ARAMIS non-contact strain measurement system of GOM.For obtaining the limit strain,judging the moment of necking is an indispensable step which directly affects the precision of the forming limit curve.Some scholars have proposed different criteria for necking determination,and in this paper three widely used necking criteria were selected.Ultimately the maximum value of punch counterforce and the cross-section method were used to obtain the forming limit.By comparing the result of simulation and experiment,it was found that they were in good agreement with each other.Finally,the established modified Swift and modified Ludwigson constitutive equation were introduced in the finite element simulation of the Nakajima forming process,and the FLCs under different deformation conditions were obtained.It was found that the forming limit of AA5083 sheet was significantly improved under evaluated temperature compared with that under room temperature.Under high temperature its forming limit were slightly enhanced with the increase of temperature at low strain rates while it has no significant changes with the increase of temperature at high strain rates.Moreover,under the evaluated temperature,the forming limit of AA5083 shows negative strain rate sensitivity,and the influence of strain rate increased with the increasing of temperature.