Residual stress regulation and control method and rapid evaluation method for optical aluminum mirror blank

Abstract

The invention relates to the technical field of metal material heat treatment, in particular to a residual stress regulation and control method and a rapid evaluation method for an optical aluminum mirror blank. According to the residual stress regulation and control method provided by the invention, the residual stress of the mirror blank is gradually released and homogenized through the synergistic effect of a composite process combining warm water quenching, thermal shock treatment and medium-temperature heat preservation, so that subsequent processing deformation is effectively inhibited. Besides, according to the rapid evaluation method for the residual stress of the mirror blank, a correlation model of the surface stress and the overall stress of the mirror blank is established based on finite element simulation data, and the overall stress state (mean value and distribution uniformity) of the mirror blank can be rapidly predicted according to the actual measurement result of the surface stress of the mirror blank; and establishing a stress grading standard of the mirror blank according to the simulated processing deformation data, and further performing stress grading evaluation on the mirror blank. According to the method, the residual stress of the mirror blank can be efficiently reduced, the problem of rapid stress evaluation during batch manufacturing is solved, and the manufacturing quality and the quality consistency of the optical aluminum mirror can be improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal material heat treatment, and particularly relates to a residual stress regulation method and a rapid evaluation method for an optical aluminum mirror blank. BACKGROUND

[0002] As a core component of optical equipment, the surface accuracy of a mirror directly determines the performance of an optical system. Aluminum alloy has become a commonly used material for manufacturing mirrors due to its high reflectivity, wide waveband, lightweight, high strength, and optical-mechanical thermal integration. However, residual stress is introduced during the manufacturing stage of an aluminum alloy mirror blank. If an effective stress relief procedure is not performed, the removal of material during the preparation and processing stage will cause the release of residual stress and deformation, which can easily induce size out-of-tolerance phenomena, making it difficult to ensure the surface accuracy of the mirror.

[0003] Currently, there are two major difficulties in the field of mirror blank residual stress control: ① The traditional stress reduction process has limited effectiveness, and stress is difficult to completely eliminate and uniformly distribute. Specifically, mechanical stress relief methods (tension / compression method) have poor stress uniformity, and thermal treatment methods (thermal aging method) can damage mechanical properties. ② The stress distribution of the mirror blank is complex, and traditional detection and evaluation methods are cumbersome. Specifically, detailed understanding of the stress field of a certain mirror blank requires a large number of tests. The commonly used X-ray diffraction method and contour method have limitations and can only measure points on the surface or perform destructive testing, which is time-consuming and labor-intensive, and cannot meet the needs of mass production.

[0004] Taking the existing technology as an example, patent CN118563232A mentions that relying on low-temperature annealing to reduce the residual stress of the mirror blank can cause loss of mechanical properties. In document 1, a composite heat treatment method of ethylene glycol quenching + boiling water uphill quenching + conventional aging + cold and hot cycling is used, which has the disadvantage of insufficient residual stress reduction effect. Patent CN117906812A proposes to release the stress of the mirror blank through high-temperature treatment and evaluate the stress through deformation. However, the high-temperature treatment mentioned in this method can severely weaken the mechanical properties of the mirror blank, making it impossible to continue using the evaluated mirror blank. SUMMARY

[0005] The present application provides a residual stress regulation method for an optical aluminum mirror blank, which can achieve significant reduction and uniformization of the residual stress of the mirror blank without losing mechanical properties.

[0006] To achieve the above-mentioned purpose, the present application provides a residual stress regulation method for an optical aluminum mirror blank, comprising the following steps:

[0007] Step S1, solution quenching: the aluminum alloy mirror blank is subjected to solution treatment at a temperature of 510-530℃ for 2-3h, and then quenched with warm water at a temperature of 50-60℃;

[0008] Step S2, heat shock treatment: the mirror blank after quenching is cooled completely in liquid nitrogen at-180℃ to-196℃, and then quickly put into a heat exchange medium at 200-210℃ for heating, and after the mirror blank is hot, it is air-cooled to room temperature;

[0009] Step S3, medium temperature holding to release and homogenize stress: the mirror blank after air cooling is heated from room temperature to 200-210℃, and after holding for 4-10h, it is cooled, and finally an aluminum alloy mirror blank with further released and homogenized residual stress is obtained.

[0010] Further, in step S2, the heat shock treatment is performed on the mirror blank within 2h after quenching; the transfer time of the mirror blank cooled by liquid nitrogen from the liquid nitrogen to the heat exchange medium is limited within 30s; the heat exchange medium uses low viscosity dimethyl silicone oil with viscosity of 50-100cSt.

[0011] Further, in step S3, the holding time is determined according to the following empirical formula (1): (1);

[0012] In formula (1), is the holding time, is the holding temperature.

[0013] In order to solve the problem of complicated residual stress evaluation of optical aluminum mirror blanks in the prior art, the present application also provides a rapid evaluation method for the residual stress of an optical aluminum mirror blank, which is prepared by the above-mentioned residual stress regulation method; the rapid evaluation method specifically comprises the following steps:

[0014] Step I, obtaining residual stress field simulation data of the mirror blank: based on the established finite element model of the aluminum mirror blank heat treatment and its simulation results, obtaining the residual stress field data of the mirror blank after heat treatment;

[0015] Step II, determining the surface and overall stress characterization area of the mirror blank: based on the simulation obtained residual stress field distribution law of the mirror blank, m height layers are determined in the axial direction of the mirror blank, and n concentric circles are set in each height layer, and s measuring points are arranged on each circle for evaluating the stress state of the surface and the whole of the mirror blank;

[0016] Step III, establishing a surface stress-global stress correlation model (including a peak correlation model and a distribution uniformity correlation model): based on the characterization area determined in step II, the stress simulation data of the surface and the whole of the mirror blank are extracted, and by analyzing the correlation between the peak value and the distribution uniformity, a peak correlation model and a distribution uniformity correlation model of the surface stress-global stress are established;

[0017] Step IV, establishing the stress grading standard of mirror blank: establishing the finite element model of material removal of aluminum mirror blank, obtaining the simulation results of machining deformation of mirror blank with different levels of residual stress under typical machining conditions; extracting the surface stress and machining deformation data of mirror blank, establishing the surface stress-machining deformation curve; based on the relationship curve, establishing the stress grading standard of mirror blank according to the allowable deformation threshold;

[0018] Step V, obtaining the measured data of surface stress of mirror blank: based on the surface stress characterization area determined in step II, further selecting representative test points, using X-ray diffraction method to measure, obtaining the measured data of surface stress of mirror blank;

[0019] Step VI, predicting the stress state (peak value, stress distribution uniformity) of mirror blank and performing grading evaluation: inputting the measured data of surface stress of mirror blank obtained in step V into the peak value correlation model and distribution uniformity correlation model of surface stress-global stress established in step III, obtaining the prediction results of global stress peak value and distribution uniformity of mirror blank; then, according to the stress grading standard established in step IV, evaluating the stress grade of mirror blank.

[0020] Further, in step II, the number of height layers m ranges from 2 to 4, the number of concentric circles n in each height layer ranges from 2 to 4, and the number of test points s arranged on each circle ranges from 4 to 12.

[0021] Further, in step II, the stress of the test point is radial.

[0022] Further, in step III, the calculation method of the global and surface stress level of the mirror blank is formula (2): (2);

[0023] In formula (2), is the i-th test point when all test points are arranged in descending order of stress value, is the integer part of 30% of the total number of test points, is the stress level value of the mirror blank, which actually represents the average value of the top 30% stress values in all test points arranged in descending order.

[0024] The calculation method of the global and surface stress distribution uniformity of the mirror blank is formula (3): (3);

[0025] In formula (3), is the stress uniformity value of the mirror blank, is the stress value of all test points, is the average value of the stress values of all test points, is the total number of test points.

[0026] Further, the correlation analysis on the peak value and the uniformity of distribution of the stress simulation data of the mirror blank surface and the whole in step III is a Pearson correlation analysis.

[0027] Further, in step IV, the surface stress-amount of processing deformation curve is established by drawing a surface stress-amount of processing deformation scatter plot and performing polynomial fitting, and the goodness of fit R² is greater than 0.9.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) The residual stress regulation method for optical aluminum mirror blanks in the present application can release and homogenize the residual stress of the mirror blank step by step through the combined process of warm water quenching, thermal shock treatment and medium temperature holding, thereby effectively inhibiting subsequent processing deformation. The regulation method is reasonable in design, effectively solves the problems existing in the prior art, and has high practicability and ease of use.

[0030] (2) The mirror blank residual stress rapid evaluation method for optical aluminum mirror blanks in the present application can quickly predict the overall stress state (mean value and distribution uniformity) of the mirror blank through the measured surface stress of the mirror blank based on the establishment of the correlation model between the surface stress of the mirror blank and the overall stress of the mirror blank based on finite element simulation data, and further evaluate the stress classification of the mirror blank according to the simulated processing deformation data. The present application can efficiently reduce the residual stress of the mirror blank and solve the difficulty of rapid stress evaluation in batch manufacturing, which is helpful to improve the manufacturing quality and quality consistency of optical aluminum mirrors.

[0031] In addition to the purposes, features and advantages described above, the present application has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings are used to provide further understanding of the embodiments of the present application, and constitute a part of the specification, and are used to explain the embodiments of the present application together with the following specific embodiments, but do not constitute a limitation on the embodiments of the present application. In the drawings:

[0033] Figure 1 is the flow chart of the establishment of the mirror blank stress classification standard of the present application;

[0034] Figure 2 is the cross-sectional stress distribution obtained by numerical simulation of example 1 and comparative example 1 and comparative example 2 of the present application; wherein (a) is the cross-sectional stress distribution obtained by numerical simulation of example 1, (b) is the cross-sectional stress distribution obtained by numerical simulation of comparative example 1, and (c) is the cross-sectional stress distribution obtained by numerical simulation of comparative example 2;

[0035] Figure 3 is the stress uniformity distribution obtained by experiment of the embodiment 1 of the present application and the comparative example 1, the comparative example 2;

[0036] Figure 4 is the cross-section characteristic path stress distribution obtained by numerical simulation of the embodiment 2 of the present application;

[0037] Figure 5 is the measuring point layout of the whole residual stress evaluation model in the embodiment 2 of the present application; wherein, (a) is a schematic diagram of the stress characterization area of the mirror blank; (b) is a schematic diagram of the axial distribution of the stress characterization area of the mirror blank; (c) is a schematic diagram of the end surface distribution of the stress characterization area of the mirror blank;

[0038] Figure 6 is the stress of the measuring point of the whole residual stress evaluation model in the embodiment 2 of the present application;

[0039] Figure 7 is the stress characterization area and the stress measuring point in the embodiment 2 of the present application;

[0040] Figure 8 is the stress characterization area and the stress measuring point in the embodiment 2 of the present application;

[0041] Figure 9 is a schematic diagram of a typical forming structure of the mirror blank in the embodiment 2 of the present application; wherein, (a) is a perspective view of the mirror blank; (b) is a front view of the mirror blank; (c) is a side view of the mirror blank;

[0042] Figure 10 is the "surface stress-amount of processing deformation" curve in the embodiment 2 of the present application. DETAILED DESCRIPTION

[0043] The present application will be described in detail below with reference to the embodiments shown in the drawings, but it should be noted that these embodiments are not a limitation on the present application, and equivalent transformations or substitutions of function, method or structure made by those skilled in the art according to these embodiments are within the scope of protection of the present application.

[0044] The present application provides a residual stress regulation method for an optical aluminum mirror blank, specifically comprising the following steps:

[0045] Step S1, solution quenching: after solution treatment of the aluminum alloy mirror blank at a temperature of 510-530℃ for 2-3h, quenching is performed with warm water at a temperature of 50-60℃. In this step, the quenching water temperature is 50-60℃, which reduces the residual stress generated during quenching; if the water temperature is too high, it is difficult to obtain a supersaturated solid solution, resulting in a decrease in mechanical properties, and the water is easy to vaporize on the surface of the workpiece and produce a large amount of bubbles, resulting in uneven cooling; if the water temperature is too low, the reduction of the initial residual stress is limited.

[0046] Step S2, thermal shock treatment: the mirror blank after quenching is cooled completely in -180℃ to -196℃ liquid nitrogen, and then quickly placed in 200 to 210℃ heat transfer medium for heating, and the mirror blank is air cooled to room temperature after thermal penetration; wherein the thermal shock treatment is performed on the mirror blank within 2h after quenching to avoid natural aging to increase the yield strength of the material, thereby weakening the stress release effect; the transfer time of the mirror blank cooled by liquid nitrogen from liquid nitrogen to the heat transfer medium is limited within 30s to avoid the workpiece heating in room temperature environment; the heat transfer medium uses low viscosity dimethyl silicone oil with viscosity of 50-100cSt, and the flow rate of the heat transfer medium is increased to improve the heat transfer effect and increase the thermal shock amplitude; the heat transfer medium temperature is 200-210℃ to avoid overaging of the material caused by high temperature, which leads to serious mechanical property degradation.

[0047] Step S3, stress release and stress homogenization at medium temperature: the mirror blank is reheated from room temperature to 200-210℃ and is kept for 4-10h before cooling, and finally an aluminum alloy mirror blank with further released and homogenized residual stress is obtained; wherein the holding time can be determined according to the following empirical formula: (1);

[0048] In the above formula (1), is the holding time, is the holding temperature.

[0049] The aluminum alloy in the regulation method of the application is 6061 aluminum alloy. The innovation of the regulation method of the application is that a step-by-step stress release method of "warm water quenching to reduce initial stress-thermal oil shock to reduce stress-medium and high temperature holding to release and homogenize stress" is proposed, which realizes the net reduction of residual stress of the mirror blank and the maintenance of mechanical properties, and by precisely constraining the range of each process parameter, the significant and stability of the reduction effect are ensured.

[0050] Example 1

[0051] The embodiment provides a residual stress regulation method for an optical aluminum mirror blank, and the aluminum alloy mirror blank is 6061 aluminum alloy. The method comprises the following specific steps:

[0052] (1) Warm water quenching to reduce initial stress:

[0053] Take the rough machined 6061 aluminum alloy disc mirror blank (φ160*40mm) and heat it to 525℃ in a high temperature resistance furnace and keep it for 2h for solid solution treatment, heat the water in the quenching tank to 60℃, then quickly take out the mirror blank from the resistance furnace and quench it, and continuously stir the liquid in the quenching tank to break the bubbles during quenching, and cool the workpiece to room temperature after quenching.

[0054] (2) Thermal oil thermal shock stress reduction:

[0055] The workpiece after quenching for 2h was directly placed into liquid nitrogen for 15min to cool completely, then it was quickly transferred into dimethyl silicone oil medium heated to 200°C within 30s, the flow rate was increased by stirring the dimethyl silicone oil to fully exchange heat, heated for 10min to thermal penetration, then the workpiece was moved into the air to cool slowly.

[0056] (3) Medium-high temperature holding to release and homogenize stress:

[0057] According to the formula of step (3), when the heating temperature is 200°C, the heating time is 4.3-10.2h, the workpiece is heated to 200°C and held for 10h in a high-temperature resistance furnace, then removed from the air and slowly cooled.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that the quenching condition in step (1) is water quenching at 25°C, the thermal shock treatment in step (2) is changed to plastic deformation treatment, and the heating condition in step (3) is different, which is 175°C x 12h. The steps (1)(2)(3) of the comparative example mainly rely on strong deformation to release stress, and there is a phenomenon of uneven stress distribution.

[0060] (1) Conventional quenching:

[0061] A rough machined 6061 aluminum alloy disc-shaped mirror blank (φ160x40mm) was heated to 525°C and held for 2h in a high-temperature resistance furnace for solid solution treatment, then the mirror blank was quickly taken out of the resistance furnace and quenched, the initial water temperature of the quenching pool was 25°C, and the liquid in the quenching pool was continuously stirred to break the bubbles during quenching, and the workpiece was cooled to room temperature after quenching.

[0062] (2) 2%-3% plastic deformation:

[0063] The workpiece after quenching for 2h was deformed by 2%-3% of the thickness of the workpiece under a forging press.

[0064] (3) Aging temperature holding treatment:

[0065] The workpiece after plastic deformation was heated to 175°C and held for 12h in a high-temperature resistance furnace, then removed from the air and slowly cooled.

[0066] Comparative Example 2

[0067] The difference between the present comparative example and Example 1 is that, in the present comparative example, the quenching condition in step (1) is water quenching at 25℃, the heating condition in step (2) is at 175℃, which is lower than the temperature range of about 30℃ in the example, and the heating condition in step (3) is at 175℃, and the heating time is 3-4h longer than in the example. The process conditions in steps (1), (2) and (3) in Comparative Example 2 have no effect of stress release step by step, and the overall stress reduction is not large, and the temperature range in step (3) cannot fully activate the diffusion and rearrangement of atoms in the material, resulting in poor stress release and homogenization effect.

[0068] (1) Water quenching:

[0069] The rough machined 6061 aluminum alloy disc-shaped mirror blank (φ160x40mm) was heated to 525℃ in a high temperature resistance furnace and held for 2h for solid solution treatment, then the mirror blank was quickly taken out from the resistance furnace and quenched, the initial water temperature of the quenching pool was 25℃, the liquid in the quenching pool was continuously stirred to break the bubbles during quenching, and the workpiece was cooled to room temperature after quenching.

[0070] (2) Hot oil thermal shock stress reduction:

[0071] The workpiece placed for 2h after quenching was directly placed in liquid nitrogen for 15min to cool completely, then it was quickly transferred to dimethyl silicone oil medium heated to 175℃ within 30s, the flow rate was increased by stirring the dimethyl silicone oil to fully exchange heat, heated for 10min to heat penetration, then the workpiece was moved into the air and slowly cooled.

[0072] (3) Aging temperature holding treatment:

[0073] The workpiece after thermal shock was heated to 175℃ in a high temperature resistance furnace and held for 12h, then removed from the air and slowly cooled.

[0074] Implementation results

[0075] Figure 2 The cross-sectional stress distribution of Example 1 and Comparative Examples 1 and 2 obtained by numerical simulation, Figure 3 The stress distribution uniformity of Example 1 and Comparative Examples 1 and 2 obtained by experiment, Table 1 is the stress evaluation index and mechanical property of Example 1 and Comparative Examples 1 and 2 based on the experimental results and the stress evaluation method of the present application.

[0076] It can be seen from Figure 2 that the present example has the effects of low stress level and no stress concentration. From Figure 3It can be seen that the stress distribution of the embodiment is more uniform. As can be seen from Table 1, the comprehensive stress level of the embodiment is controlled below 30 MPa, the stress distribution uniformity is 3.47, and the yield strength reaches 256 MPa. Under the condition of equivalent mechanical properties, the stress state indexes are better than those of the comparative examples.

[0077] Table 1 Overall stress and mechanical properties of Example 1 of the application and Comparative Examples 1 and 2 obtained by experiments

[0078] As Figure 1 shown, the application also provides a method for rapid evaluation of residual stress of an optical aluminum mirror blank, wherein the aluminum mirror blank is prepared by the regulation method in Example 1. The rapid evaluation method comprises the following steps:

[0079] Step I, obtaining simulation data of residual stress field of the mirror blank: based on the established finite element model of heat treatment of the aluminum mirror blank and the simulation results thereof, obtaining the residual stress field data of the mirror blank after heat treatment;

[0080] Step II, determining the surface and overall stress characterization region of the mirror blank: based on the simulation obtained residual stress field distribution law of the mirror blank, determining m height layers in the axial direction of the mirror blank, and setting n concentric circles in each height layer, and arranging s measuring points on each circle for evaluating the stress state of the surface and the overall of the mirror blank; specifically, the number of height layers is 2-4 layers, the number of concentric circles in each height layer is 2-4, and the number of measuring points arranged on each circle is 4-12; the stress of the measuring point is radial.

[0081] Step III, establishing a surface stress-global stress correlation model of the mirror blank: based on the characterization region determined in Step II, extracting the stress simulation data of the surface and the overall of the mirror blank, respectively, and establishing a peak correlation model and a distribution uniformity correlation model of the surface stress-global stress by analyzing the correlation therebetween in terms of peak value and distribution uniformity; the correlation analysis of the stress simulation data of the surface and the overall of the mirror blank in terms of peak value and distribution uniformity is Pearson correlation analysis. In this step:

[0082] The calculation method of the overall and surface stress level of the mirror blank is as follows: (2) ;

[0083] In the above formula (2), is the i-th measuring point when all the measuring points are arranged in descending order of stress value, is the integer part of 30% of the total number of measuring points, is the stress level value of the mirror blank, which actually represents the average value of the stress values of the top 30% in descending order of stress value among all the measuring points.

[0084] The calculation method of the uniformity of the stress distribution of the mirror blank as a whole and on the surface is: (3).

[0085] In the above formula (3), is the stress uniformity value of the mirror blank, is the stress value of all measuring points, is the average value of the stress values of all measuring points, is the total number of measuring points.

[0086] Step IV, establishing a stress grading standard for the mirror blank: a finite element model of material removal of the aluminum mirror blank is established, and simulation results of machining deformation of the mirror blank with different levels of residual stress under typical machining conditions are obtained; the surface stress and machining deformation data of the mirror blank are extracted, and a surface stress-machining deformation curve is established; based on the relationship curve, the stress grading standard for the mirror blank is established according to the allowable deformation threshold; the surface stress-machining deformation curve is: a scatter plot of surface stress-machining deformation is drawn, and polynomial fitting is performed, and the goodness of fit R² is greater than 0.9.

[0087] Step V, obtaining the measured data of the surface stress of the mirror blank: based on the surface stress characterization region determined in step II, further selecting representative test points, and using the X-ray diffraction method to measure, obtaining the measured data of the surface stress of the mirror blank.

[0088] Step VI, predicting the stress state (peak value, stress distribution uniformity) of the mirror blank and performing grading evaluation: inputting the measured data of the surface stress of the mirror blank obtained in step V into the peak correlation model and the distribution uniformity correlation model of the surface stress-whole stress established in step III, obtaining the prediction results of the whole stress peak value and the distribution uniformity of the mirror blank; and then according to the stress grading standard established in step IV, evaluating the stress grade of the mirror blank.

[0089] Example 2

[0090] This example is based on an aluminum alloy mirror blank with a specification of φ160x40mm, which is subjected to warm water quenching at 60°C, hot oil impact at 200°C, and holding treatment at 200°C, and the residual stress is evaluated by the evaluation method of Example 2. Based on the finite element model and simulation results of the mirror blank heat treatment established in the previous research, the specific evaluation method includes the following steps:

[0091] Step (1), according to the stress distribution basic law of the mirror blank obtained by finite element simulation, the stress distribution nephogram is as shown in Figure 2 (a), the path on the cross section is extracted, and the stress distribution law is observed as shown in Figure 4 .

[0092] Step (2): Based on the obtained stress distribution of the mirror blank, an overall residual stress evaluation model for the mirror blank is established. Three height layers—0 / 4H (surface), 1 / 4H, and 2 / 4H—are used. Within each height layer, three concentric circles (1 / 4D, 2 / 4D, and 3 / 4D) are set up, with an average of 6 measuring points on each circle, for a total of 54 measuring points, to evaluate the residual stress of the mirror blank. Specifically, the distribution of the 54 measuring points in the model is as follows: Figure 5 As shown, the stress measured at each measuring point is as follows: Figure 6 As shown.

[0093] In step (3), by Figure 6 It is known that the stress on the surface and the overall structure of a mirror blank are correlated in terms of both horizontality and uniformity of distribution. Therefore, a correlation model between surface stress and overall stress in a mirror blank is established. Based on mirror blanks with the same process but different process parameters, the surface stress and overall stress are measured, and correlation analysis is performed. Figure 7 As shown.

[0094] from Figure 7 It can be seen that the surface stress level of the workpiece has a linear relationship with the overall stress level, and the correlation coefficient R is... 2 The value is 0.99, which satisfies equation (4): (4);

[0095] The surface stress distribution uniformity of the workpiece is linearly related to the overall stress distribution uniformity, with a correlation coefficient of [missing value]. The value is 0.90, which satisfies equation (5): (5);

[0096] according to Figure 4 The stress distribution is determined, and the area with uniform stress distribution on the surface of the mirror blank is identified as the characterization area of ​​the stress on the mirror blank surface.

[0097] like Figure 8 As shown, a region with a radius R = 42.5 mm on the circle was determined to have a uniform stress distribution, which was designated as the stress characterization area. For ease of positioning, stress characterization points were arranged on the circle with a radius R = 40 mm and radially. Six points A1~A6 were evenly spaced at equal angles on the circle, and four points B1~B4 were evenly spaced at equal intervals along the radial path, serving as characterization points for stress level and stress uniformity, respectively. Points A1 and A4 overlapped with points B1 and B4, reducing the actual number of measurement points; a total of eight measurement points were used.

[0098] In step (4), the removal process of mirror blank material at different stress levels was simulated using finite element method. The initial surface stress value of the mirror blank and the deformation during the service stage were extracted. Polynomial fitting was used to establish the "surface stress-processing deformation" curve, as shown in the figure. Figure 10 As shown.

[0099] It needs to be particularly pointed out that: in the embodiment, the mirror blank with a surface stress of 0~110MPa and a size of φ160*40mm is selected. In the material removal stage, the removed material includes: mirror surface processing layer A, the removed material thickness is H1=10mm; lightweight structure layer B, the removed material thickness is H2=15mm, the reinforcing rib width d=5mm, the process fillet radius r=4mm, and the specific structure is shown in Figure 9 .

[0100] According to actual needs, the mirror blank is taken as an index for grading screening with a deformation of 0~30μm, a deformation of 30~80μm and a deformation of 80μm or more, so the surface initial stress corresponding to the workpiece when the deformation is 30μm and 80μm is found on the curve, which is 38MPa and 71MPa, the stress value is rounded to 10MPa, and the stress grading standard of the mirror blank is established.

[0101] Table 2 Stress grading standard established by the embodiment 2 of the application

[0102] In step (5), the stress test is performed on the surface of the mirror blank according to the planning of Figure 8 , and the prediction is performed in combination with the overall stress level prediction formula (4) and the overall stress distribution uniformity prediction formula (5), so it can be known that the stress condition of the embodiment 2 is =24.6MPa, =3.4MPa, and according to the grading standard in Table 2, the stress level of the mirror blank belongs to grade I.

[0103] The above only describes the preferred embodiments of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for controlling residual stress in an optical aluminum mirror blank, characterized in that, Includes the following steps: Step S1, Solution quenching: After solution treatment at 510℃~530℃ for 2~3 hours, the aluminum alloy mirror blank is quenched with warm water at 50~60℃. Step S2, thermal shock treatment: The quenched mirror blank is placed in liquid nitrogen at -180℃~-196℃ for complete cooling, and then quickly placed in a heat exchange medium at 200~210℃ for heating. After the mirror blank is thoroughly heated, it is air-cooled to room temperature. Step S3, medium-temperature heat preservation for stress release and homogenization: The air-cooled mirror blank is reheated from room temperature to 200~210℃, held for 4~10h and then cooled to obtain an aluminum alloy mirror blank with further release and homogenization of residual stress.

2. The control method according to claim 1, characterized in that, In step S2, the mirror blank is subjected to thermal shock treatment within 2 hours after quenching; the transfer time of the mirror blank after being cooled by liquid nitrogen from liquid nitrogen to the heat exchange medium is limited to within 30 seconds; the heat exchange medium is a low viscosity dimethyl silicone oil of 50-100 cSt.

3. The control method according to claim 1, characterized in that, In step S3, the heat preservation time is specifically determined according to the following empirical formula (1): (1)； In formula (1), For heat preservation time, This is the insulation temperature.

4. A method for rapid assessment of residual stress in optical aluminum mirror blanks, characterized in that, Includes the following steps: Step 1: Obtain simulation data of residual stress field of mirror blank: Based on the established finite element model of heat treatment of aluminum mirror blank and its simulation results, obtain the residual stress field data of mirror blank after heat treatment; Step II: Determine the stress characterization area of ​​the mirror blank surface and the whole: Based on the distribution law of the residual stress field of the mirror blank obtained by simulation, m height layers are determined in the axial direction of the mirror blank, and n concentric circles are set in each height layer. S measuring points are arranged on each circle to evaluate the stress state of the mirror blank surface and the whole. Step III: Establish the surface stress-overall stress correlation model of the mirror blank: Based on the characterization region determined in Step II, extract the stress simulation data of the mirror blank surface and the whole, respectively. By analyzing the correlation between the peak value and the distribution uniformity, establish the peak value correlation model and the distribution uniformity correlation model of the surface stress-overall stress. Step IV: Establish stress grading standards for mirror blanks: Establish a finite element model for removing aluminum mirror blank material, and obtain simulation results of machining deformation of mirror blanks with different levels of residual stress under typical machining conditions; extract surface stress and machining deformation data of mirror blanks, and establish a surface stress-machining deformation curve; based on this relationship curve, establish stress grading standards for mirror blanks according to allowable deformation thresholds. Step V: Obtain measured data of surface stress on mirror blank: Based on the surface stress characterization area of ​​mirror blank determined in Step II, further select representative test points and use X-ray diffraction to measure and obtain measured data of surface stress on mirror blank. Step VI: Predict the stress state (peak value, stress distribution uniformity) of the mirror blank and perform a graded evaluation: Input the measured surface stress data of the mirror blank obtained in Step V into the peak value correlation model and distribution uniformity correlation model of surface stress-overall stress established in Step III to obtain the predicted results of the peak value and distribution uniformity of the overall stress of the mirror blank; then evaluate the stress level of the mirror blank according to the stress grading standard established in Step IV.

5. The rapid evaluation method according to claim 4, characterized in that, The aluminum mirror blank is prepared by the control method described in any one of claims 1-3.

6. The rapid evaluation method according to claim 4, characterized in that, In step II, the number of height layers m ranges from 2 to 4, the number of concentric circles n in each height layer ranges from 2 to 4, and the number of measuring points s arranged on each circle ranges from 4 to 12.

7. The rapid evaluation method according to claim 4, characterized in that, In step II, the stress at the measuring point is radial.

8. The rapid evaluation method according to claim 4, characterized in that, In step III, the calculation method for the overall and surface stress level of the mirror blank is formula (2): (2)； In formula (2), For all measuring points arranged in descending order of stress value, the i-th measuring point is... Rounded down to 30% of the total number of measurement points. The stress level value of the mirror blank represents the average of the top 30% stress values ​​from all measuring points, arranged from largest to smallest. The calculation method for the uniformity of stress distribution on the whole and surface of the mirror blank is formula (3): (3)； In formula (3), The stress uniformity value of the mirror blank. For stress values ​​at all measuring points, The average stress value at all measuring points. This represents the total number of measurement points.

9. The rapid evaluation method according to claim 4, characterized in that, In step III, the correlation analysis of the stress simulation data of the mirror blank surface and the whole in terms of peak value and distribution uniformity is Pearson correlation analysis.

10. The rapid evaluation method according to claim 4, characterized in that, In step IV, the surface stress-processing deformation curve is established by plotting a scatter plot of surface stress-processing deformation and performing polynomial fitting, with a goodness of fit R² greater than 0.9.

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