Study On Hot Formability And Forming Of 7050 High Strength Aluminum Alloy Forgings

Aluminum alloy plays an extremely important role in aerospace,aviation,and navigation industries.7050 aluminum alloy,which belongs to Al-Zn-Mg-Cu alloy(super hard aluminum),possesses excellent mechanical properties and anode reaction.It is widely employed in aerospace,mold processing,machinery and equipment,especially for aircraft manufacturing structures and other requirements of high strength,strong corrosion resistance of high stress structures.In this paper,the rheological behaviors of aluminum alloy are investigated by a series of hot compression tests.The constitutive equation and processing maps are established according to stress-strain curves which are obtained by those hot compression tests.After that,the constitutive model of this new material is written into DEFORM software.By simulating the forming process in DEFORM,hot working process parameters of 7050 aluminum alloy can be optimized to obtain forgings with excellent deformation uniformity and no defects as far as possible.At last,the simulation results are verified in practical production.The conclusion is as follows:In the process of hot compression deformation,the stress-strain curves 7050 aluminum alloy exhibit three features:(1)in the initial stage of deformation,the stress rises rapidly with the increase of strain due to the surging of dislocation density;(2)afterwards the slope of curves gradually decreases owing to the enhancement of softening mechanism;(3)finally,the stress shows a steady state with the increase of strain,which indicates that work hardening and dynamic softening achieve a dynamic balance.The flow stress of 7050 aluminum alloy is expressed in terms of the hyperbolic law in an Arrhenius-type equation.Four strains of 0.2,0.4,0.6 and 0.8 are selected under different deformation conditions to construct thermal working maps.The instability zone and the safety zone are obtained through the thermal working maps,and the differences between the instability zone and the safety zone are discussed.The most suitable processing area is obtained by analyzing the thermal processing maps above,which is able to provide accurate guidance for the subsequent simulation.The forming process of die forging is simulated,and the optimal process parameters are obtained through continuous optimization.In addition,the strain field,folding and mold stress in the simulation results are analyzed after processing to judge whether there is uneven deformation,surface defects and mold deformation.The simulation results show that 7050 aluminum alloy,which is deformed under the optimal parameters,displays excellent forming property and can be forged into products with uniform deformation and no folding.At last,in order to verify the accuracy of simulation result,7050 aluminum alloy is forged on 800 MN press under the obtained optimal process parameters.Meanwhile a series of heat preservation and heat insulation measures are taken.The forges obtained by the practical production do not appear folding,filling,wrinkling and rupture and other defects.Moreover,physical and chemical tests were carried out on the forgings and the results were in line with the required standards.