| Dimensional stability is the ability of materials to resist micro-deformation.High-precision instruments such as gyroscopes,star sensors,optical sights,and precision bearings are extremely dimensionally stable.The factors affecting dimensional stability are very complicated.At present,foreign countries mainly study the stability of tissues through means of tissue regulation.However,the stress stability of residual stress is mainly studied in China,but the research on dimensional stability mechanism is not clear,especially The influence of the precipitation effect of the phase on the dimensional stability is not deep,and thus the research on the optimization of the alloy composition based on dimensional stability is scarce.In this paper,the dimensional stability of the raw material 2024 aluminum alloy during constant temperature aging process is analyzed,the mechanism of phase stability is studied,and the relationship between the microscopic lattice constant and the macroscopic dimensional stability is established.Real-time detection of dimensional change was carried out by using a thermal dilatometer,and the evolution of the precipitated phase was observed by TEM,and the lattice constant was detected by XRD.The composition of aluminum alloy was optimized based on dimensional stability.The influence of silicon content on component stability,precipitation phase and dimensional stability was simulated by Jmat.Pro software.Finally,according to the calculation results,a new alloy was prepared,and the relationship between the Si element content and the dimensional change amount was found,and the aluminum alloy with the best dimensional stability was obtained,and the internal relationship between the microstructure and the macroscopic performance was established.The dimensional change of the aging process of the raw material 2024Al alloy,the change of the precipitated phase and the change of the lattice constant:the as-cast process of the as-cast 2024 aluminum alloy at 190°C,the size decreased,and the relative change of the aging time of 72 hours was-7.86×10-5,010h is the rapid reduction stage,1036h is the slow stage,and 3672h is the stable stage.Compared with pure Al,the size change of the as-cast 2024Al alloy is due to the precipitation effect of the precipitated phase.The formation of the GPB zone and the S?(Al2CuMg)phase 10 hours before aging is the main reason for the dimensional stability.After aging,the diffraction peak shifts to the right,the lattice constant decreases,and the dimensional stability caused by the variation of the lattice constant can be used to characterize the dimensional stability in the macroscopic sense.The simulation results of Jmat.Pro software show that the main elements in the raw material 2024 aluminum alloy have the partial molar Gibbs free energy and activity at the aging temperature of 190°C:Mg>Si>Cu.It is explained that Cu,Mg,and Si easily form a solid solution with the matrix Al element.The partial molar Mobs free energy and activity of Cu element are less affected by Si element,Mg element is greatly affected by Si element content,and the molar Mobius free energy of Mg decreases with the increase of Si content at the same temperature.When the Si content reaches a certain value,the Mg2Si phase or the AlxCuxMgxSix quaternary alloy phase is easily formed.In the case where the Cu and Mg contents are not changed,changing the Si content can minimize the dimensional change of the sample.When the Mg element is 1.5%,the relative volume change is closer to zero,and the experiment verifies that 4.53 wt.%Cu,1.5 wt.%Mg matrix is selected.The new alloy study found that the Si element mass fraction ranged from 0.43%to 2.3%,and the size of the alloy increased.The higher the Si content,the more obvious the size increase.The aluminum alloy having a Si content of between 0.08%and 0.36%has a decreasing tendency.The 0.32wt.%Si new aluminum alloy has the best dimensional stability performance,and the final deformation is-4.12×10-6,which has reached the performance requirements of inertial instrumentation.The law of dimensional stability changes consistent with the law of strains caused by lattice constants,and the strains caused by lattice constants can characterize macroscopic dimensional stability.The precipitation phase of the 0.43 wt.%Si new alloy at 190°C was mainly S'phase(34 vol.%)and Q'phase(57 vol.%).The precipitated phase of the 0.32 wt.%Si new alloy at 190°C was also S'phase(47 vol.%)and Q'phase(44vol.%).The Q'phase is a size increasing phase,and the S'phase is a size decreasing phase. |
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