Method for measuring and analyzing precipitation processes in aluminum alloys at ultrafast cooling rates

Abstract

The present application relates to a kind of methods for measuring and analyzing the precipitation process of aluminum alloy under the condition of ultrafast cooling rate, comprising the following steps: (1) material preparation;(2) solution treatment;(3) ultrafast quenching (5~4×10 5 K / s);(4) artificial aging;(5) two-step reheating method and thermal analysis: S1: first reheating: each test sample after artificial aging in step (4) is heated to solution treatment temperature at 10 3 K / s~10 4 K / s rate, record heat flow curve;S2: re-solution treatment and ultrafast cooling;S3: second reheating: test sample is reheated to solution treatment temperature at the same heating rate in S1, record baseline heat flow curve;S4: differential analysis: by the difference of two heat flow curves, obtain the total enthalpy change of precipitation reaction in cooling and aging process, realize the quantitative measurement and analysis of quenching vacancy to precipitation behavior.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal material analysis testing, and particularly relates to a method for measuring and analyzing an aluminum alloy precipitation process under an ultrafast cooling rate condition. BACKGROUND

[0002] Aluminum alloys, especially 7xxx (Al-Zn-Mg(-Cu)) series, are widely used in aerospace and automotive industries due to their excellent mechanical properties and corrosion resistance. The strengthening mechanism of this kind of alloy is mainly precipitation strengthening, and the formation of precipitates such as η' phase depends on the diffusion behavior of solute atoms and quenching vacancies. Traditional analysis and testing methods are difficult to systematically study the influence of quenching vacancies on subsequent precipitation reactions during quenching process due to the limited cooling rate, and the concentration of quenching vacancies as important defects in the diffusion process directly affects the subsequent aging precipitation process and material properties.

[0003] In the prior art, such as Differential Scanning Calorimetry (DSC), Positron Annihilation Lifetime Spectroscopy (PALS), etc., the maximum cooling rate of the equipment is limited, and it is impossible to accurately measure the influence of quenching vacancies on precipitation reactions under an ultrafast cooling rate condition. Therefore, it is of great significance to develop a method for measuring and analyzing the aluminum alloy precipitation process under an ultrafast cooling rate condition. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for measuring and analyzing the aluminum alloy precipitation process under an ultrafast cooling rate condition, which is suitable for measuring and analyzing the influence of quenching vacancies on precipitation reactions under an ultrafast cooling rate condition.

[0005] The technical solution adopted by the present application to solve the above technical problem is: a method for measuring and analyzing the aluminum alloy precipitation process under an ultrafast cooling rate condition, characterized by comprising the following steps:

[0006] (1) Material preparation: preparing an aluminum alloy, and performing surface treatment on the aluminum alloy, and then cutting the aluminum alloy into a plurality of test samples;

[0007] (2) Solution treatment: heating each test sample of step (1) to a solution treatment temperature, and performing heat preservation treatment for a set time to make alloy elements fully dissolve;

[0008] (3) Ultrafast quenching: dividing the plurality of test samples of step (2) into a plurality of groups, each group including at least one test sample, the cooling rate of the test samples in each group being different, and the cooling rate of the test samples in the same group being the same, and using a device capable of achieving a cooling rate of 5~4×105 K / s cooling rate, each test sample from step (2) is rapidly cooled from the solution treatment temperature to a specified temperature (room temperature ~ -196℃) to obtain different concentrations of quenched vacancies;

[0009] (4) Artificial aging: each test sample quenched in step (3) is placed at an aging temperature for a set time for artificial aging treatment to promote the formation of precipitates;

[0010] (5) Two-step reheating method and thermal analysis:

[0011] S1: first reheating:

[0012] Each test sample after artificial aging in step (4) is heated to the solution treatment temperature at a rate of 10 4 K / s, and the heat flow curve is recorded to obtain the total endothermic peak including the dissolution of precipitates during cooling and aging;

[0013] S2: re-solution treatment and ultrafast cooling:

[0014] Each test sample after heating in S1 is solution treated at the solution treatment temperature and holding time in step (2), and then cooled to the specified temperature in step (3) at an ultrafast cooling rate of 10 4 K / s ~ 10 5 K / s, which is sufficient to completely suppress the precipitation reaction during cooling;

[0015] S3: second reheating:

[0016] The test sample after cooling in S2 is reheated to the solution treatment temperature at the same heating rate as in S1, and the baseline heat flow curve is recorded;

[0017] S4: differential analysis:

[0018] By differentiating the two heat flow curves, the total enthalpy change of the precipitation reaction during cooling and aging is obtained, and the quantitative measurement and analysis of the effect of quenched vacancies on precipitation behavior are realized.

[0019] In order to further study the effect of quenched vacancies on the precipitation reaction, the method further comprises step (6), comparing the enthalpy changes obtained in steps (2) ~ (5) at different cooling rates, determining the critical cooling rate to reach the saturation of quenched vacancies, and determining the influence law of quenched vacancies on the precipitation reaction.

[0020] For further studying the influence of quenched vacancies on the precipitation reaction, in the step (4), each group includes at least two test samples, and the test samples in the same group are subjected to artificial aging at different temperatures respectively, in the step (6), the critical cooling rate (such as 10 K / s) reaching the saturation of quenched vacancies is determined by comparing the enthalpy changes at different cooling rates and different artificial aging temperatures, and the influence law of quenched vacancies on the precipitation reaction is determined. 4 K / s), determine the influence law of quenched vacancies on the precipitation reaction.

[0021] In the above scheme, in the steps (2)-(5), the equipment for heating and cooling the test samples is a differential fast scanning calorimeter (DFSC).

[0022] Preferably, in the step (1), the surface treatment method of the aluminum alloy is that the aluminum alloy is polished to a thickness of 5-70 microns by using SiC sandpaper with different mesh numbers, and surface polishing is performed by using SiC sandpaper.

[0023] Preferably, in the step (3), the specified temperature is room temperature-196℃.

[0024] Compared with the prior art, the method of the present application has the advantages that the method of the present application can systematically control the concentration of quenched vacancies in the aluminum alloy under the quenching condition of ultrafast cooling rate, and through the two-step reheating method, the enthalpy change of the precipitation reaction and the content of the precipitated phase after ultrafast quenching are measured with high precision, and the influence law of quenched vacancies on the precipitation reaction is determined. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is an AA7150 aluminum alloy sample placed in the center of the heating zone of the differential fast scanning calorimeter (DFSC), which is just above the center of the heating zone, which is conducive to the detection of temperature change signals;

[0026] Figure 2 It is a temperature and time program diagram in the differential fast scanning calorimetry measurement process in Example 1 of the present application;

[0027] Figure 3 It is a differential graph of the heat flow curve of AA7150 aluminum alloy after two-step reheating treatment at different cooling rates in Example 1 of the present application;

[0028] Figure 4 It is a relationship curve of the enthalpy change with different artificial aging temperatures after the AA7150 aluminum alloy is subjected to solid solution treatment, ultrafast quenching, artificial aging and two-step heating treatment in Example 1 of the present application;

[0029] Figure 5The enthalpy change of the AA7068 aluminum alloy in Example 2 of the present application after solid solution treatment, ultra-fast quenching, artificial aging and two-step heating treatment at an artificial aging temperature of 130℃ varies with different cooling rates. DETAILED DESCRIPTION

[0030] The present application is further described in detail below with reference to the accompanying drawings. Example 1

[0031] The method for measuring and analyzing the precipitation process of the aluminum alloy under the ultra-fast cooling rate condition of the present example includes the following steps:

[0032] (1) Material preparation: prepare the aluminum alloy, and perform surface treatment on the aluminum alloy: specifically, polish the aluminum alloy to a thickness of 30 microns using SiC sandpaper of different mesh, and then polish the surface using 1200-mesh or 2500-mesh SiC sandpaper, and then cut the aluminum alloy into multiple 800-nanogram cubes or flakes under an optical microscope as test samples for subsequent testing; the aluminum alloy of the present example is AA7150 aluminum alloy, and the AA7150 aluminum alloy is placed on the heating zone of a differential fast scanning calorimeter under an optical microscope, as shown in FIG. 1. Figure 1 ;

[0033] (2) Solid solution treatment: heat each test sample of step (1) to a solid solution treatment temperature, and perform heat preservation treatment for a set time to fully solid-solution the test sample; specifically, use a differential fast scanning calorimeter (DFSC) device to heat each test sample to 480℃ and preserve for 5 minutes;

[0034] (3) Ultra-fast quenching: use equipment capable of achieving a cooling rate of 5~4×10 5 K / s to rapidly cool and quench each test sample of step (2) from the solid solution treatment temperature to -196℃; the specific operation mode is as follows: divide the multiple test samples of step (2) into multiple groups, each group including three test samples, the cooling rate of the test samples in each group is different, and the cooling rate of the test samples in the same group is the same to obtain different concentrations of quenched vacancies; in the present example, the multiple test samples are rapidly cooled and quenched from the solid solution treatment temperature to -196℃ at cooling rates of 5, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 200000, 300000, 400000 K / s, and the equipment for cooling the test samples is a differential fast scanning calorimeter (DFSC);

[0035] (4) Artificial aging: the test samples quenched in step (3) are placed at different aging temperatures for a set time for artificial aging treatment to promote the formation of precipitates; specifically, the three test samples in the same group are subjected to artificial aging at aging temperatures of 70°C, 90°C and 110°C respectively, and the set time is 10 minutes, and the equipment for artificial aging is differential fast scanning calorimeter (DFSC);

[0036] (5) Two-step reheating method and thermal analysis to obtain the endothermic peak of precipitate dissolution and calculate the enthalpy change:

[0037] S1: first reheating:

[0038] Each test sample subjected to artificial aging in step (4) is heated to the solution treatment temperature at a rate of 10³ K / s, the heat flow curve is recorded, the total endothermic peak of precipitate dissolution during cooling and aging is obtained, and the integral enthalpy change is calculated;

[0039] S2: re-solution treatment and ultrafast cooling:

[0040] Each test sample heated in S1 is subjected to solution treatment at the solution treatment temperature and the set holding time in step (2), i.e. each test sample heated in S1 is held at the solution treatment temperature of 480°C for 5 minutes, and then cooled to a lower temperature of -196°C at a rate of 10 5 K / s, which is sufficient to completely suppress the precipitation reaction during cooling (i.e. the enthalpy change of the precipitation reaction is zero);

[0041] S3: second reheating:

[0042] Each test sample cooled in S2 is reheated to the solution treatment temperature at the same heating rate as in S1, and the baseline heat flow curve (without precipitation reaction endothermic peak) is recorded to obtain the baseline;

[0043] S4: differential analysis:

[0044] By the difference between the two heat flow curves, the total enthalpy change of the precipitation reaction during cooling and aging is obtained, and the quantitative measurement and analysis of the quenching vacancy on the precipitation behavior are realized;

[0045] The equipment for heating and cooling the test samples in this step (5) is differential fast scanning calorimeter (DFSC).

[0046] (6) result analysis:

[0047] By comparing the enthalpy changes of the test samples at different cooling rates and different aging temperatures in steps (2) to (5), the critical cooling rate (such as 10 4 K / s) to reach the quenching vacancy saturation is determined, and the influence of the quenching vacancy on the precipitation reaction is determined.

[0048] The temperature and time profile of the test procedure used in Example 1 is shown in the attached Figure 2 , in Figure 2 , the horizontal axis is time and the vertical axis is temperature. The curve first shows the sample being held at the solutionizing temperature (480°C), then rapidly cooled at a set ultrafast cooling rate (e.g. 5-4x10 5 K / s) to a lower temperature. Subsequently, the sample is held at a different artificial aging temperature (e.g. 70°C, 90°C or 110°C) for a period of time (e.g. 10 minutes) to promote the formation of precipitates. After artificial aging, the sample is subjected to a first reheating at a high heating rate (10 3 K / s) and the heat flow curve of precipitate dissolution is recorded. Immediately after, the sample is held at the solutionizing temperature and rapidly cooled at an ultrafast cooling rate (10 5 K / s) to a lower temperature, during which the precipitation reaction is completely suppressed. Subsequently, a second reheating is performed at the same rate and the baseline heat flow curve is recorded.

[0049] The heat flow curve of step S4 in Example 1 is shown in the attached Figure 3 , Figure 3 The vertical axis of the curve is heat flow signal (mW) and the horizontal axis is temperature (°C). The change in the curve peak value indicates that the amount and type of precipitates in the alloy change with the increase of cooling rate. This figure is an important experimental basis for quantitatively analyzing the relationship between quenching vacancies and precipitation behavior and revealing the influencing mechanism in the present application.

[0050] The attached Figure 4 The enthalpy change of Comparative Example 1 at different cooling rates in step (3) is compared, and the enthalpy change of Comparative Example 1 at different aging temperatures in step (4) is also compared.

[0051] Figure 4 The horizontal axis of the curve is cooling rate (K / s) and the vertical axis is enthalpy change (J / g), which represents the heat released by the precipitation reaction. The curve reflects the effect of cooling rate on the total amount of precipitates under different artificial aging temperatures (70°C, 90°C, 110°C). The curve shows that the precipitation enthalpy gradually increases with the increase of cooling rate, indicating that the number of quenching vacancies in the material increases at a higher cooling rate, thereby forming more precipitates in the subsequent artificial aging stage. When the cooling rate is higher than a certain threshold (e.g. 10 4 K / s), the curve tends to be flat, indicating that the quenching vacancies are saturated and the number of precipitates no longer increases significantly. This figure clearly shows that the present application method can precisely control and measure the amount of precipitates in aluminum alloy by adjusting the cooling rate, and verifies the effectiveness of the ultrafast quenching combined with the two-step reheating method. Example 2

[0052] The method for measuring and analyzing the precipitation process of an aluminum alloy under the condition of the ultrafast cooling rate of the present embodiment comprises the following steps:

[0053] (1) Material preparation: prepare an aluminum alloy, polish the metal sample to a thickness of 45 microns using SiC sandpaper of different mesh, and polish the surface using 1200-mesh or 2500-mesh SiC sandpaper, and then cut the sample into multiple 500-nanogram cubes or flakes under an optical microscope as test samples; the aluminum alloy of the present embodiment is AA7068 aluminum alloy, and the AA7068 alloy is placed on the heating zone of a differential fast scanning calorimeter under an optical microscope;

[0054] (2) Solution treatment: heat each test sample of step (1) to a solution treatment temperature, and perform heat preservation treatment for a set time to allow the alloying elements to be fully dissolved; specifically, use a differential fast scanning calorimeter (DFSC) device to heat the AA7068 alloy to 480℃ and preserve it for 10 minutes;

[0055] (3) Ultrafast quenching:

[0056] An apparatus capable of achieving a cooling rate of 5~4×10 5 K / s is used to rapidly cool and quench each test sample of step (2) from the solution treatment temperature to room temperature at different cooling rates; the specific operation mode is as follows: multiple test samples are divided into multiple groups, and each group includes one test sample; in the present embodiment, the multiple groups of test samples are rapidly cooled and quenched from the solution treatment temperature to room temperature at cooling rates of 5, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, and 100000 K / s, respectively; the apparatus for cooling the test sample is a differential fast scanning calorimeter (DFSC);

[0057] (4) Artificial aging: place each test sample quenched in step (3) at an aging temperature and perform artificial aging treatment for a set time to promote the formation of precipitates; specifically, perform 10-minute artificial aging of each quenched test sample at 130℃, and the apparatus for artificial aging is a differential fast scanning calorimeter (DFSC);

[0058] (5) Two-step reheating method and thermal analysis to obtain the endothermic peak of precipitate dissolution and calculate the enthalpy change:

[0059] S1: first reheating:

[0060] The test samples in step (4) were heated to 480℃ at a rate of 10 3 K / s, and the heat flow curve was recorded to obtain the total endothermic peak including the dissolution of precipitated phase during cooling and aging, and the integral enthalpy change was calculated;

[0061] S2: Re-solution treatment and ultra-fast cooling:

[0062] The heated test samples in S1 were solution treated according to the solution treatment temperature and holding time in step (2), that is, the heated test samples in S1 were held at the solution treatment temperature of 480℃ for 10 minutes, and then cooled to room temperature at a rate of 10 5 K / s, which is sufficient to completely suppress the precipitation reaction during cooling (i.e. the enthalpy change of precipitation reaction is zero);

[0063] S3: Second reheating:

[0064] The cooled samples in S2 were reheated to the solution treatment temperature at the same heating rate as in S1, and the baseline heat flow curve (without precipitation reaction endothermic peak) was recorded to obtain the baseline;

[0065] S4: Differential analysis:

[0066] By the difference between the two heat flow curves, the total enthalpy change of the precipitation reaction during cooling and aging was obtained, and the quantitative measurement and analysis of quenching vacancies on the precipitation behavior were realized;

[0067] The equipment for heating and cooling the test samples in this step (5) is differential fast scanning calorimeter (DFSC).

[0068] (6) Result analysis:

[0069] By comparing the enthalpy change of the test samples in steps (2)-(5) at different cooling rates, see the attached Figure 5 , the influence of quenching vacancies on the precipitation reaction was determined.

[0070] Figure 5 The abscissa is the cooling rate (K / s), and the ordinate is the enthalpy change (mJ), which represents the heat released by the precipitation reaction. The curve reflects the influence of cooling rate on the total amount of precipitated phase at the artificial aging temperature of 130℃. The curve shows that as the cooling rate increases, the precipitation enthalpy gradually increases, indicating that the number of quenching vacancies in the material increases at a higher cooling rate, thereby forming more precipitated phase in the subsequent artificial aging stage.

[0071] The differential fast scanning calorimeter (DFSC) used in the present application is Spark III differential fast scanning calorimeter of FMR e.V. company.

Claims

1. A method for measuring and analyzing the precipitation process of aluminum alloys under ultrafast cooling rates, characterized in that: Includes the following steps: (1) Material preparation: Prepare aluminum alloy, perform surface treatment on the aluminum alloy, and then cut it into multiple test samples; (2) Solution treatment: Heat each test sample from step (1) to the solution treatment temperature and hold it for a set time to allow the alloying elements to dissolve completely. (3) Ultrafast quenching: The multiple test samples from step (2) are divided into multiple groups, each group including at least two test samples. The cooling rates of the test samples in each group are different, while the cooling rates of the test samples in the same group are the same. A cooling rate of 5~4×10 is used. 5 The device with a cooling rate of K / s rapidly cools each test sample from the solution treatment temperature to the specified temperature in step (2) to obtain quenching vacancies of different concentrations. (4) Artificial aging: Place each test sample after quenching in step (3) at an aging temperature, and perform artificial aging on the test samples in the same group at different temperatures for a set time to promote the formation of precipitates; (5) Two-step reheating method and thermal analysis: S1: Reheating once: Each test sample that underwent artificial aging in step (4) was subjected to 10... 3 K / s ~10 4 Heating to the solution treatment temperature at a rate of K / s, recording the heat flow curve, and obtaining the total endothermic peak including the dissolution of the precipitated phase during cooling and aging processes; S2: Resolution treatment and ultrafast cooling: After heating each test sample in S1, perform solution treatment according to the solution treatment temperature and holding time set in step (2), and then use 10 4 K / s ~10 5 Cooling to the specified temperature in step (3) at an ultrafast cooling rate of K / s, which is sufficient to completely suppress the precipitation reaction during cooling; S3: Second reheating: The test sample cooled in S2 was reheated to the solution treatment temperature at the same heating rate as in S1, and the baseline heat flow curve was recorded. S4: Difference Analysis: By differentiating the two heat flow curves, the total enthalpy change of the precipitation reaction during the cooling and aging process is obtained, enabling quantitative measurement and analysis of the precipitation behavior of quenching vacancies. (6) By comparing the different cooling rates and enthalpy changes at different aging temperatures obtained in steps (2) to (5), the critical cooling rate at which quenching vacancies are saturated is determined, and the influence of quenching vacancies on the precipitation reaction is determined.

2. The method for measuring and analyzing the precipitation process of aluminum alloys under ultrafast cooling rate conditions according to claim 1, characterized in that: In steps (2) to (5), the equipment used for heating and cooling the test samples is a differential rapid scanning calorimeter.

3. The method for measuring and analyzing the precipitation process of aluminum alloys under ultrafast cooling rate conditions according to claim 1, characterized in that: In step (1), the surface treatment method of aluminum alloy is as follows: polish the aluminum alloy with SiC sandpaper of different mesh sizes until the thickness is 5~70 micrometers, and then polish the surface with SiC sandpaper.

4. The method for measuring and analyzing the precipitation process of aluminum alloys under ultrafast cooling rate conditions according to claim 1, characterized in that: In step (3), the specified temperature is room temperature to -196°C.

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