Study On The Microstructure Optimization And Properties Of 2219 Aluminum Alloy Ring With Large Dimensions

The large-scale 2219 aluminum alloy ring is an important workpiece required in the aerospace field.The manufacture of large rings usually requires multiple processes such as smelting,homogenization annealing,multi-directional forging,ring rolling,and heat treatment of finished products.Each process will affect the subsequent processing,microstructure and properties;and during the manufacturing process of large rings,the microstructure changes in different positions are uneven.Therefore,by analyzing and studying the different positions of the workpiece in different processes,it is possible to better understand the evolution of the microstructure during the ring manufacturing process,which can provide suggestions and references for the improvement of the forming process of the large ring,the improvement of the forming ability and the optimization of the final mechanical properties.In this paper,the homogenized 2219 aluminum alloy ingot,the forging billet and the T8 solution-aged ring in the ring manufacturing process are used as experimental materials.Through the observation of the microstructure and the test of mechanical properties in specific areas and different directions,the influence of each process on the microstructure and mechanical properties is analyzed,and the evolution of microstructure and the change of the mechanical properties during the manufacturing process is analyzed,too.The main conclusions are as follows:(1)From the edge to the center of the homogenized 2219 aluminum alloy ingot,the microstructure gradually coarsens and the mechanical properties gradually decrease.The average size of grains increases from 116?m to 132?m,and there are more chain-like or network-like large-size Al₂Cu in the center area,which is detrimental to the mechanical properties.Affected by the grain size and the second phase,UTS(ultimate tensile strength)decreased from 202 MPa to 180 MPa from edge to center;EL(elongation)decreased from 11.5%to 5.3%.(2)The homogenized 2219 aluminum alloy ingot after multi-directional forging process,the microstructure is refined and the EL is improved.Due to the dynamic recrystallization during the multi-directional forging process,the grain size is refined from 116-132?m(±60-77 um)to 5.3-8.4?m(±2.8-5.4?m);the coarse Al₂Cu in the homogenized structure is reduced by broken and distributed more evenly;the changes in YS(yield strength),UTS and hardness are not obvious.The refinement of the microstructure caused by multi-directional forging makes the EL increase from 5.3%-11.5%to 12.2%-19.0%.(3)From the center area of the forging billet to the edge,the structure becomes coarser and the EL decreases.There are many coarse Al₂Cu and grains remaining in the edge area of the forging billet,and the grains in the center area of the forging billet are fine and Al₂Cu is evenly distributed.The EL(19.0%)of the center area of the forging billet is higher than that of the edge area(12.2%).(4)After ring rolling and T8 solution-aged,the grains of the forging billet grow up compared with the forged state,and the grain size on the cross-section(axis-radius plane)of the ring is 165-237?m(±94-202?m).The primary Al₂Cu dissolves significantly and precipitates small strengthening phase.The YS in each area and direction of the ring reaches 266-313 MPa,UTS reaches 378-448 MPa,the hardness is103-114 HV.It has the largest EL along the circumferential direction of the ring,reaching 16.0%-21.1%;followed by the radial direction,?11.6%;the axial EL is in the range of 8.2%-11.8%.(5)The grains and Al₂Cu particles in the T8 solution-aged ring microstructure are elongated along the circumferential direction.Compared with the circumference-axis plane and the circumference-radius plane,the size of Al₂Cu and grains on the cross-section of the ring is smaller;in terms of the maximum size of Al₂Cu on different observation planes,circumference-radius plane(34-54?m)>circumference-axis plane(31-47?m)>axis-radius plane(30-34?m).From the inner diameter to the outer diameter of the ring,the degree of solid solution is first reduced and then increased;the grain size is first reduced and then increased,and the grain size at the inner diameter is larger than that at the outer diameter.From the center of the ring to the end face,the degree of solid solution is enhanced.In terms of the average value of the mechanical properties in the axial and circumferential directions,from the inner diameter to the outer diameter,YS and UTS first decrease and then increase,the YS and UTS at the inner diameter are slightly lower than the outer diameter;the EL first increases and then decreases,and the EL at the inner diameter is lower than the outer diameter.From the center of the ring to the end face,YS and UTS increase,and the anisotropy of YS,UTS and EL is also enhanced,especially the EL anisotropy is more obvious.The changes in the mechanical properties of the different areas of the ring are the result of the combined effect of the aging precipitation phase and the grain size.