Research On Anisotropy Of Dimensional Stability For2024Alluminium Alloy Sheet

2024aluminum alloy has been widely used in the precision instrument industry.High-precision apparatus demand that materials should be of high dimensional stability.However, the dimensional stability anisotropy of2024aluminum alloy sheet does notgain the concern from the academia and the engineering, and there are few reportedresearches about it. It will lead to the hidden danger of long-term stability of high-precision apparatus. So the study about dimensional stability of2024aluminum alloysheet has a high practical value. In this paper, the microstructure and the dimensionalstability anisotropy of2024aluminum alloy sheet were researched by TEM, EBSD andsmall deformation resistance test. The influence of the microstructure and deformationresistance and dimensional change behavior in different directions by differentstabilization process were analyzed. And the stabilization treatment process which wasconducive to the isotropic was selected.The effect of annealing treatment on the anisotropic of dimensional stability wasstudied. From the TEM observation, it can be seen that after annealing treatment, thereare a great amount of undissolved rodlike phase s in the alloy. And small reformationresistance tests indicates that the small reformation resistance anisotropic index is0.95,which is pretty close to1, which means that annealing treatment is capable ofeliminating the anisotropy of small reformation resistance in the sheet. The dimensionalchange real-time detection testing results appears that sheet’s size diminishes with theincreasing of cycle numbers, and the anisotropic index D of dimensional change is1.68.So it can be seen that under alternating temperature conditions, the annealing treatmentmakes no contribution to reducing the anisotropy of dimensional change.Aging treatment of sheet was carried out and the effect of aging time on theanisotropy of dimensional stability was studied. It can be seen from TEM result thatwith the increasing of aging time, the lamellar phase is precipitated more fully, anddistributes with directionality. Small deformation resistance test shows that with theincrease of aging time, the gap betweenσ_0.01^T.D/σ_0.01^R.D and1increases (σ_0.01^T.D/σ_0.01^R.D fortwo-stage aging is0.97, for4h is0.92, for10h is1.18). The isotropy effect on smalldeformation resistance decreases. Dimensional changes in real-time detectiondemonstrate that size increases with the increasing of cycles. In addition, with the agingtime increases, the anisotropic index D of dimensional change becomes bigger. Theisotropic effect for two-stage aging is the best with the D value of0.46, while the agingtime with10h shows the worst with the D value of0.83. After two kinds of thermal-cycling treatment （TCC and A+TCC） are processed for2024sheet, TEM observations indicate that precipitations is facilitated by thermalcycling treatment. The results of micro-yield strength indicate that the thermal-cyclingtreatment improves the micro-yield strength of sheet material. The best technologies forthe micro-yield strength isotropic are TCC（-196℃） and A+TCC（-196℃）(σ_0.01^T.D/σ_0.01^R.D are1.16and1.07respectively). The results for dimension change real-time detectionsindicate that the dimension of sheet material decreases with cycling times increasing.The best technologies for the dimensional isotropic are TCC（-196℃） andA+TCC（-196℃）（D are0.87and0.63respectively）. According to all kinds of treatment,the best process for dimensional stability is A+TCC（-196℃）.In this paper, influence factors on anisotropy of dimensional stability for2024include: the change of morphology and distribution for precipitated phase S’ andanisotropy of residual stress relaxation. If S’ are precipitated fully and have the samesize, also distribute uniformly, the dimensional stability anisotropy will be eliminated.Besides, that the degree of anisotropy of residual stress relaxation reducing also caneliminate the dimensional stability anisotropy.