Optimized Deformation Processes And Related Mechanisms For Improving The Strength,Toughness And Formability Of AA7050 Aluminum Alloy

With increasing demands of energy-saving,emission-reduction and safe life in transportation industry,it puts forward higher requirements for the weight-reduction and damage-tolerance of engineering materials.The 7xxx series A1 alloys with higher strength-to-weight ratio,higher toughness and excellent corrosion resistance could be as the potential candidate materials to realize the lightweight in transportation industry.However,the formability is relative poor,which has become a bottleneck and restricted the development of its application.At present,the researches of high-strength 7xxx series Al alloy are mainly concentrated on the plate,so it is lack of systematic study on the mechanical properties of sheet,such as formability,strength and toughness.Under this background,different rolling processes have been conducted to optimize the microstructural evolution and mechanical properties in this paper,and the effects of different rolling temperatures and particle sizes on the microstructure and properties were studied systematically.Moreover,in order to meet the formation ability of complex workpiece and reduce the cost during manufacturing process,a kind of processing technology for sheet metal has been developed,which could obtain the high-strain-rate superplastic forming of AA7050 aluminum alloy.On the base of the study on the relationship between deformation,microstructure and property,it could provide a theoretical basis and technical support for the application of high-strength 7xxx series Al alloy in lightweight industry.The main conclusions could be summarized as follows:By the analyses of the hot workability of AA7050 A1 alloy,the results show that good workability could be obtained at the temperature ranges 380-420 ? and strain rate ranges 0.001-0.18 s-1,while flow instability occur at the temperature ranges 360-420 ? and strain rate ranges 0.1-10 s-1.The good hot workability could be attributed to the occurrence of continuous dynamic recrystallization,which is more likely to occur at lower or higher strain rates,higher deformation temperatures and larger deformations.Large size particles(>1 ?m)can produce particle stimulated nucleation effect,which could effectively refine the recrystallization grains and weaken the rolling and recrystallization textures.So it is helpful to improve the fracture toughness and formability.With the decrease of the deformation temperature,it is beneficial to the increase of the deformation energy storage and the grain refinement after recrystallization.Cryogenic rolling can promote the formation of shear bands,which could increase the recrystallization nucleation sites and reduce Cube texture component that is bad for formability.In addition,cryogenic rolling can effectively suppress the dynamic strain aging,so it is helpful to improve the cold workability and reduce the critical particle size of the occurrence of the particle stimulated nucleation effect.The subgrains could be transformed into fine recrystallization grains with fully-formed large angle grain boundaries by the continuous dynamic recrystallization during hot deformation.Meanwhile,grain boundary sliding could easily occur among these new recrystallization gains.The synthetic effect of these two mechanisms could achieve the high-strain-rate superplasticity.