Influence Of Hot Rolling On Microstructure,Texture And Mechanical Properties Of Al-Zn-Mg-Cu Alloy

With the rapid development in the fields of aviation,aerospace,naval vessels and weaponry,the requirements for the comprehensive performance of ultra-high strength Al-Zn-Mg-Cu alloy plate which is a key lightweight structural material are increasing.Hot rolling is the most basic and important manufacturing process for the plate.The resulting microstructure is a decisive factor in the final properties and uniformity of the plate.Mastering the influence of hot rolling on microstructure,texture and mechanical properties of ultra-high strength Al-Zn-Mg-Cu alloy plate is key to develop process control technology of microstructure and properties to effectively improve the overall performance of ultra-high strength Al-Zn-Mg-Cu alloy plate.In this study,the microstructure,texture and mechanical properties of ultra-high strength Al-6.4Zn-2.3Mg-2.1Cu alloy plate with thickness of 60 mm produced by the factory were revealed by means of microstructure,texture and mechanical property analysis.The influence of hot-rolling deformation on grain structure,orientation and mechanical properties of ultra-high strength Al-Zn-Mg-Cu alloy plate was studied systematically.The main results are shown as follows:1)The strength of Al-6.4Zn-2.3Mg-2.1Cu ultra-high strength aluminum alloy plate with thickness of 60 mm gradually increases from surface layer to center layer of plate thickness,while the elongation rate decreases gradually.The longitudinal strength of center layer of plate thickness is higher than that in the transverse direction while the transverse strength near the surface is higher than that in the longitudinal direction.The longitudinal elongation is all higher than the transverse direction.The recrystallized grains and the shear texture gradually decrease from the surface layer to center layer of plate thickness,while the deformation texture gradually increases and the fibrous structure gradually becomes thicker.The difference of recrystallized texture is not obvious.The difference of the microstructure and mechanical properties except the cooling conditions of the ingot is mainly controlled.by the rolling process because the composition of the thickness direction is uniform.2)The hot rolling at 390? and 420? has obvious effect on the texture and hot-rolled microstructure of the plate.The deformation of center layer of plate thickness is more serious than that of surface layer under the lower temperature(390?)rolling,While the whole thickness direction of the plate is more uniform under higher temperature(420?)rolling.After the solution treatment,the difference of recrystallization degree of plate under two different temperatures rolling is not obvious,but it decreases gradually from the surface to the center layer of plate thickness.After hot rolling,the strong Goss{011}<100>texture and weak copper-type texture is mainly formed at the center layer of plate thickness while the a fiber texture of center layer of plate thickness under lower temperature(390?)rolling is weaker than that under higher temperature(420?).After the solution treatment,the ? fiber texture is significantly enhanced and stronger under lower temperature(390?)rolling.3)In the case of single-pass hot rolling,the grain lengthening in the center layer of plate thickness is more obvious than that in the surface layer with the increase of single-pass reduction rate(in the range of 25%to 50%).After the solution treatment,the grain structure still inherits the morphological characteristics of deformed hot-rolled plate grain and recrystallization mainly occurs in the ingot original large grain boundary with enrichment of coarse second phase which forms the characteristics of small recrystallized grain delineating the original large grain.The intensity of a fiber texture increases significantly whle the copper-type texture decreases significantly with the increase of single pass reduction.After solution treatment,the ? fiber texture increase significantly in the low reduction rate,but decrease significantly in the large reduction rate.The copper-type texture decreases after solution treatment.4)In the case of multi-pass hot rolling,the total reduction rate is larger and the fiber characteristics of plate are more obvious.When the pass reduction rate is large,the center layer of the plate thickness deforms more serious than the surface layer.With the total reduction rate larger(86.7%),there is no obvious difference in the thickness direction of the plate.After the solution treatment,the recrystallization of plate is adequate,but the recrystallized grain size of the center layer of the plate thickness is relatively smaller than the surface layer.When the pass reduction rate is small,the deformation of the surface layer of plate is more serious than that of the center layer of plate thickness.When the total reduction rate is larger(86.7%),the fiber structure of surface layer of the plate is thinner than the center of plate thickness,and the recrystallized grain of surface layer of the plate is more equiaxial than the center layer of plate thickness.For the hot-rolled plate,the deformation texture of the center layer of the plate thickness is smaller when the thickness reduction per pass is higher.After the solution treatment,when the total reduction rate is 46.7%,the deformation texture of the center layer the plate thickness is stronger as the thickness reduction per pass is lower.When the total reduction rate is 86.7%,the deformation texture of the center layer of the plate thickness is weaker as the thickness reduction per pass is lower.5)The ingots were multi-passes hot-rolled into 3 mm thickness sheet with different total reduction rate from 62.5%to 90.6%.After solution and T77 treatment,the recrystallization degree gradually decreases from the surface layer to the center layer of sheet thickness,while grain size and its aspect ratio increases gradually.When the thickness reduction per pass is high,the aspect ratio of grains in the center layer of the sheet thickness obviously increases when the total reduction ratio is 83.3%,while the difference of grain size at other total reduction ratio is not obvious and the recrystallization fraction of them are all about 84%.When the thickness reduction per pass is low,with the increase of the total reduction rate,the change of the grain size is not obvious and the recrystallization fraction gradually increases especially reaching 98.5%when the total reduction ratio is 90.6%.Furthermore,the recrystallization fraction is obviously greater when the thickness reduction per pass is lower.With the increase of the total reduction rate,the a and 0 fiber texture increase while the copper-type texture decreases.Generally speaking,the deformation texture and ? fiber texture of the center layer of sheet thickness after the solution treatment is weaker when the thickness reduction per pass is lower.With the increase of the total reduction rate,the strength and elongation of sheet with high thickness reduction per pass shows a decreasing trend.While the strength and elongation of sheet with low thickness reduction per pass undergo first decrease and then increase.The lowest point exits when the total reduction rate is 72.7%.When the total reduction rate is over 83.3%,the strength and elongation of sheet are larger when the thickness reduction per pass is lower.