| Because of its low production cost,high specific strength,good formability,corrosion resistance,weldability and conductivity,aluminum alloy plays an important role in the fields of household appliances,automobile manufacturing,mechanical equipment and building consumables,and has become one of the lightweight non-ferrous metal materials widely used in modern industrial production.However,following the developing quickly of the modern industry,the existing Al-Mg alloys can not meet the higher requirements of the manufacturing industry.It is still difficult to realize the idea that Al-Mg alloys have both high strength and high plasticity.For Al-Mg alloy,the common large plastic deformation(SPD)method is difficult to be widely used in industrial production.At present,the vast majority of manufacturers still use conventional rolling methods to produce large quantities of industrial aluminum alloy sheets.They can only produce the aluminum alloy sheets which are difficult to deform at room temperature by the complex process of reducing reduction and intermediate annealing.The process of producing aluminum alloy by this method is not only complicated,but also the shear stress along the rolling direction is easy to crack the hard deformed aluminum alloy.It is an important task for material workers to develop a low-cost and suitable preparation method for large-scale industrial production of high strength and toughness Al-Mg alloys.Al-Mg alloy sheet is easy to crack,and its strength and plasticity are difficult to improve at the same time.In view of the above characteristics,a new process of liquid nitrogen hard-plate rolling was developed to improve the formability of Al-Mg alloy with high solid solution Mg content,and to prepare high solid solution Al-Mg alloy rolled sheet with high strength and high plasticity.The effects of Mg element and deformation temperature on the hard-plate rolling were studied,and the materials with high solid solution Mg content and high plasticity were analyzed The annealing thermodynamics of the microstructure evolution of Al-Mg alloy with high solid solution Mg content during high temperature deformation is discussed.The main conclusions are as follows:(1)It is found that extrusion pre deformation process can effectively eliminate as-cast defects and improve the microstructure of the alloy,which is beneficial to improve the mechanical properties of the deformed alloy in subsequent deformation.The extrusion process parameters of as-cast Al-x Mg alloy were optimized: the extrusion heat preservation parameters of as-cast Al-1Mg and Al-5Mg alloy were 380℃ for 1h,and that of Al-9Mg alloy was 400℃ for 1h.(2)The microstructure and mechanical properties of extruded Al-Mg alloy change obviously with Mg content.With the increase of Mg content by 1 wt%,the average grain size of extruded Al-Mg alloy decreases by about 30 μm.The extruded Al-1Mg alloy is mainly columnar crystal.With the increase of Mg content,the columnar crystal of Al-Mg alloy gradually transforms into columnar crystal with secondary dendrite.With the increase of Mg content,the secondary dendrite is more developed and gradually transforms into equiaxed dendrite.With the increase of Mg content,the tensile strength of extruded AlMg alloy is 135 MPa,280 MPa and 380 MPa respectively,and the elongation at break is 25%,40% and 55%.The Mg element in extruded Al-Mg alloy can refine the deformation structure and improve the strength and plasticity at the same time.(3)An improved method for preparing Al Mg alloy with high solid solution Mg content by hard-plate rolling was proposed.The results show that the liquid nitrogen hard-plate rolling can effectively prevent the sample from cracking,improve the surface quality of the sample,and make it easier to realize single pass rolling with large reduction.The results show that the strength of Al Mg alloy increases while the plasticity remains high.The tensile strength of Al-9Mg alloy prepared by controlled rolling with liquid nitrogen liner is up to 565 MPa and the elongation is up to 8%.Mg element can refine the microstructure of Al Mg alloy prepared by LNT-HPR,and improve the strength and plasticity simultaneouly.(4)The mechanism of low temperature deformation inhibiting dynamic recovery and dynamic recrystallization during rolling process is revealed,which is more conducive to the formation of deformation band and the increase of dislocation density of deformation structure,so that the deformation alloy has higher work hardening ability.In addition,high solid solution Mg content can not only refine grains,but also pin dislocations during deformation,which is conducive to the accumulation of dislocations during deformation.Lower deformation temperature and higher Mg content promote the formation of mixed crystal structure,which improves the strength and plasticity of Al-Mg alloy.(5)The Al-9Mg alloy prepared by LNT-HPR has the highest thermal stability.The recrystallization temperature of al-1mg alloy is 300℃-350℃,that of Al-5Mg alloy is275℃-300℃,and that of Al-9Mg alloy is 300℃-350℃.Because the annealing structure is affected by both recrystallization driving force and Mg pinning,the recrystallization temperature of deformed Al-Mg alloy is not linear with Mg content,and the dominant position of these two factors changes obviously with Mg content.(6)The results show that the recrystallization kinetics of(001)and(111)oriented deformed zones and the whole grains are different from that of(101)oriented grains.The(001)and(111)orientation regions have higher dislocation density,leading to the formation of recrystallization core,and the recrystallization structure has obvious preferred orientation during the expansion process. |
