Research On Microstructure Evolution And Properties For2024Aluminium Alloy During Thermomechanical Treatment

The paper mainly aims to obtain the strengthening process of large and thin-walledbearing made of2024aluminum alloy. Deformation was adopted combined with heattreatment process and12kinds of thermomechanical processes were designed. EBSD,TEM, Vickers hardness, friction and wear test, ring opening test and other methods wereapplied to investigate the relationship between the evolution of the microstructure andthe mechanical properties of the2024aluminum. The optimal thermomechanicalprocess was obtained finally.The effect of different deformations on the microstructure and properties of2024aluminum alloy. With the increase of the deformation of the surface strain strengthening,the surface grain size of the original extruded rods get refined which leads to thetransition fromt the axis subgrains of the extrusion direction to the axis subgrains of therolling direction. Textures changes from muti-component <111> turns to <100>. Thedislocation density increases and leads to the formation of slip bands. The thickness ofthe surface hardened layer decreases with the increase of the deformation. The processwith the unilateral deformation of0.8mm is the optimal. The surface hardness reaches91MPa that is34%higher than that of the untreated one. The thickness of the hardenedlayer under four kinds of deformations could reach about2.5mm.The effect of deformation on aging behavior of2024aluminum alloy was studied.Rolling-quenching-aging(R+T6), quenching-aging-rollin(T6+R), quenching-rolling-aging(Q+R+A) were carried out. It is found that deformation could promote theprecipitation of the S′phase in2024aluminum alloy at lower temperature. Dislocationsgenerated from the deformation could provide nucleation sites for the precipitation ofthe S′phase, which makes the size of the S′phase precipitated during the aging processsmall and dispersive and increase the number at the same time. Therefore, thedeformation strengthening before aging could make a more significant strengtheningeffect. By contrast, Q+R+A process gives the best strengthening effect. The hardness ofthe hardened layer within1.5mm reaches108Mpa, which improves20%compared withthat of the untreated specimen. The friction coefficients and wear rates of2024aluminum alloy bars could be reduced and the wear resistance could be improved afterthermomechanical process. The Q+R+A process gives the optimal wear resistance. Thefriction coefficient decreases to0.378under the load of200g and the wear rates are alsothe lowest among different loads.The radial ring opening test shows that surface deformation process wouldintroduce large number of macroscopic residual stress, reducing the dimensionalstability of the material. The dimensional stability of the alloy improves after T6process. A follow-up thermal cycling treatment could further improve the dimensional stabilityof the alloy. The process that gives the alloy best dimensional stability is Q+R+A+TCC.According the results discussed in this paper, the process that has the best surfacedeformation strengthening effect on the alloy is Q+R+A.