Study On Microstructure,properties And Thermal Stability Of Nanostructured Al-Cu-Mn Alloy

Al alloy is currently mainly used in aerospace,transportation and some building materials.Its advantages are high specific strength,low density,low cost and good processing performance.In the aviation and aerospace fields,the use temperature of many machine parts is above 150?.Titanium alloys and composite materials have high density and high manufacturing costs.In order to save energy and reduce costs,many domestic and foreign researchers are currently committed to developing research heat-resistant Al alloy to improve aircraft performance.Nanostructured materials obtained by severe plastic deformation have high strength and poor plasticity;aging heat treatment can be used to improve the plasticity of nanostructured materials.At the same time,many heat-resistant Al alloys used aging heat treatment to introduce dispersed nano-scale precipitates to improve the material grain boundary stability and resistance to recrystallization,thereby improving the thermal stability of the material.The experimental material of the paper is Al-Cu-Mn alloy.The Al-Cu-Mn alloy after solution treatment is cold-rolled with a deformation of 90%in order to obtain nanostructured materials.The mechanical properties,microstructure and thermal stability of the nano-structured material Al-Cu-Mn alloy were explored by annealing at two temperatures of 200°C and 300°C at different times.The thesis experiment uses scanning electron microscope(SEM),electron backscatter diffraction technique(EBSD),electron channel contrast(ECC)and transmission electron microscope(TEM)to explore the micro-crystals,particle size,morphology of second phase particles,number per unit volume,average particle size of Al-Cu-Mn alloy in cold rolled and annealed states,The mechanical properties of Al-Cu-Mn alloy in various states were tested using a micro hardness tester and experimental tensile machine.Finally got the following conclusions:(1)After 90%cold rolling,the tensile strength of the Al-Cu-Mn alloy is 514 MPa,the yield strength is 477 MPa,the elongation is 5.8%,and the microhardness is 159 HV.Most of the Al-Cu-Mn alloy grains are distributed between 40 nm-80 nm,and the average layer spacing is about 75 nm,indicating that the Al-Cu-Mn alloy is a typical nano-layered structure material.(2)There are many primary phases with different shapes in the Al-Cu-Mn alloy,and most of them are distributed along the rolling direction at the grain boundary,and a small amount of fine particles are distributed inside the grain.The average size does not change much.The primary phase particles contain Al and Cu elements,and some primary phases contain Mn elements.(3)After annealing at 200?,the nanostructured Al-Cu-Mn alloy is annealed from200?-24h to 200?-120h.The tensile strength of 300 MPa is stable for 4 days,and there is no obvious change in the size of the equiaxed crystal.Better thermal stability.(4)After annealing at 300?for nanostructured Al-Cu-Mn alloy,its tensile strength showed a small peak at 300?-4h;During the subsequent annealing process,the tensile strength of Al-Cu-Mn alloy decreased greatly,this is related to the coarsening of the internal microstructure.(5)The precipitation position of Al₂Cu annealed at 200?is different in different periods.The first period is the precipitation at the grain boundary,along the grain boundary in discontinuous points,the second period is the precipitation and formation inside the grain.With the extension of annealing time,the size is increasing,but the density increases first and then does not change;After annealing at 300?for a long time,some phases were found to be dissolved.(6)In the 200°C annealed structure,precipitation has an impeding effect on grain boundary migration,and the grain size does not change much,ensuring stable mechanical properties.Annealing at 300?,the structure appears uneven recrystallization behavior,the coarsening of grains and particles has an important impact on the performance of the alloy.