Effect Of Multi Direction Strong Strain And Aging Treatment On Strength Ductility And Corrosion Resistance Of Al-Zn-Mg-Cu Alloys

Ultra high strength Al-Zn-Mg-Cu alloys have been widely used in many fields because of its advantages such as high strength,low density and excellent processing performance.With the rapid development of science and technology,Al-Zn-Mg-Cu aluminum alloys are more and more used in aerospace,military industry and other high-tech fields,which puts forward higher requirements for the comprehensive properties of the alloy.However,it is difficult to achieve high strength,good ductility and excellent intergranular corrosion resistance of Al-Zn-Mg-Cu alloys simultaneously by conventional process,which hinders the development and application of Al-Zn-Mg-Cu alloys.In this work,7075 aluminium alloy was processed by multi-directional forging and aging treatment.The alloy wiil have high strength,high ductility and high corrosion resistance.In this experiment,the microstructures of the samples were characterized by optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM).Moreover,The hardness,strength,ductility,intergranular corrosion and salt spray corrosion were tested.On this basis,the effect of the multi-directional forging and aging tratement on the microstructure,strength,ductility and corrosion resistance of Al-Zn-Mg-Cu alloys were discussed in detail.After multi-directional forging,the additional dislocations were generated,the microstructure of alloy was refined obviously and the ultrafine-grained structure was formed.The strength and hardness of the alloy were improved significantly,but the ductility was decreased clearly.After aging treatment,the strength of the material was further improved,and the ductility was enhanced by the improvement of the grain inhomogeneity and reduction of the residual stress.The hardness and tensile strength of 7075 aluminum alloy after multi-directional forging and aging treatment were 191.4 HV and 644.4 MPa respectively,which were increased by 18.2 % and 19.6 % compared with the T6 state.Meanwhile,the ductility was 16.8 %,without decreased ductility much compared with the T6 state.After multi-directional forging and aging treatment,the grain boundaries were decorated with the coarser and discontinuously distributed precipitates,which hindered the formation of corrosion channels,and the intergranular corrosion resistance of the alloy was significantly improved.The coarse precipitates in the alloy grains have reduced,which inhibited the pitting corrosion.Therefore,The alloy showed better corrosion resistance in neutral salt spray corrosion test after multi-directional forging and aging treatment.