Method for determining the upper limit of electrical conductivity of an aluminium alloy after ageing heat treatment

Abstract

The present application belongs to the field of heat treatment special processing and manufacturing, and relates to a method for determining the upper limit value of the electric conductivity of aluminum alloy after aging heat treatment. The present application collects, collates and analyzes the electric conductivity data of aluminum alloy after aging heat treatment, adopts 3σ criterion to quickly calculate the normal distribution data of known average and standard deviation, combines the electric conductivity data to obtain the expected value and standard deviation of the electric conductivity, further analyzes and calculates the confidence interval of the electric conductivity, and preliminarily obtains the upper limit value range of the electric conductivity. Then, the tensile strength value of aluminum alloy after aging heat treatment is used for secondary confirmation and checking, and finally the upper limit value of the electric conductivity is obtained, so as to facilitate the quality control of aluminum alloy products.

Description

Technical Field

[0001] The present invention belongs to the field of special heat treatment manufacturing, and relates to a method for determining the upper limit value of the conductivity of aluminum alloy after age heat treatment. Background Art

[0002] The 7-series alloy has high specific strength and hardness, good corrosion resistance and high toughness, and is widely used in the aviation field. The 7B04 aluminum alloy is one of the important aviation structural aluminum alloys in the 7-series aluminum alloys, belonging to typical ultra-high strength aluminum alloys. Usually, the conductivity is used to judge the precipitation of strengthening phases during the age treatment of aluminum alloys, and the conductivity is used as a rapid acceptance criterion for aluminum alloy heat treatment products. At present, in the actual production process, the hardness inspection of various types of wrought aluminum alloy parts can be replaced by conductivity inspection. The conductivity of the 7B04 aluminum alloy plate is 100% inspected in the aged state. When the conductivity is qualified, it is determined that the aluminum alloy plate (or part) after final heat treatment is qualified. When the conductivity is unqualified, supplementary aging should be carried out. After supplementary aging, the conductivity is still inspected according to the regulations. At present, the detection determination value is conductivity ≥ 21 MS / m. However, in the actual production process, extreme situations occur, resulting in parts of the 7B04 aluminum alloy with too high conductivity and unqualified mechanical properties, but they can pass the conductivity determination method, mistakenly believing that the parts meet the requirements, thus increasing the risk of quality problems of 7B04 aluminum alloy parts. The conductivity determination values of some grades of the 7-series alloy after heat treatment are in a certain determined interval, that is, there are both lower limit values and upper limit values, while the conductivity determination value of the 7B04 aluminum alloy after T74 state heat treatment only has a lower limit value of 21 MS / s and no requirement for the upper limit value of conductivity. Therefore, stipulating the upper limit value of conductivity is conducive to production implementation, convenient for quality control, and avoids the misjudgment of unqualified parts in extreme situations. At present, there is no relevant literature reporting the method for determining the upper limit value of conductivity. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for determining the upper limit value of the conductivity of aluminum alloy after age heat treatment, and through scientific analysis methods and calculations, the upper limit value of the conductivity of the 7B04 aluminum alloy material after age heat treatment can be obtained.

[0004] In order to achieve the above invention purpose, by collecting, sorting and analyzing the conductivity data of aluminum alloy after age heat treatment, the 3σ criterion is used to quickly calculate the normal distribution data with known mean and standard deviation, and the expected value and standard deviation of the conductivity are obtained by combining the conductivity data. Further analysis and calculation are carried out to obtain the confidence interval of the conductivity, and the upper limit value range of the conductivity is initially obtained. Then, the upper limit value of the conductivity is finally obtained through secondary confirmation and verification by the tensile strength value after the age heat treatment of the aluminum alloy, so as to facilitate the quality control of aluminum alloy products.

[0005] The specific technical solution of the present invention is as follows:

[0006] A method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment, the specific steps of which are as follows:

[0007] The first step is to collect measured data.

[0008] Collect measured electrical conductivity data of aluminum alloy materials of corresponding grades and heat treatment states after aging heat treatment.

[0009] Specifically, data on aluminum alloy materials after aging heat treatment of corresponding grades and heat treatment states over the past 5 years will be collected, including no less than 5 material specifications and no less than 5,000 measured data on the electrical conductivity of the parts.

[0010] The second step is to perform discrete normal distribution partitioning.

[0011] Using statistical methods, the measured conductivity data are divided into n intervals, and the conductivity range Δ = A is determined for each interval. i -A i-1 , where A i-1 Let A be the minimum value of the measured conductivity data for the i-th interval. i X represents the maximum value of the measured conductivity data in the i-th interval; X represents the median value of the measured conductivity data in the i-th interval. i The number of measured conductivity data in the i-th interval is Y. i The proportion of the measured conductivity data in the i-th interval to the total data is P. i With i = 1 to n, we obtain normally distributed data.

[0012] The third step is to calculate the mean and standard deviation.

[0013] The mean μ and standard deviation σ of the measured conductivity data are obtained by calculating the normally distributed data.

[0014]

[0015] The fourth step is to determine the upper limit of conductivity based on the 3σ criterion.

[0016] The upper limit of conductivity is determined based on the 3σ criterion to assess and control the stability and reliability of the process.

[0017] The confidence interval for conductivity is (μ-3σ, μ+3σ) MS / m. If a conductivity measurement in a set of data is not within the (μ-3σ, μ+3σ) interval, i.e., the absolute value of the residual error is greater than 3σ, then that measurement value should be discarded. The upper limit of conductivity for the corresponding grade and condition of aluminum alloy is initially set at (μ+3σ) MS / m.

[0018] Because, usually, an error equal to ±3σ is taken as the limiting error, and for a normally distributed random error, the probability of it falling outside ±3σ in a finite number of measurements is very small.

[0019] Step 5: Verify the upper limit of conductivity.

[0020] Collect over 500 tensile strength data points for aluminum alloys of corresponding grades and heat treatment states after aging heat treatment, and determine the tensile strength σ when the upper limit of electrical conductivity is (μ+3σ) MS / m. b MPa. The tensile strength value (σ) in the corresponding aluminum alloy grade and temper material standard is found to be... b1 ~σ b2 ) MPa, for comparison, if σ b1 ≤σ b ≤σ b2 If the upper limit of the electrical conductivity of the aluminum alloy after aging heat treatment is determined to be (μ+3σ)MS / m, then the requirements of the qualified verification index of the part are met.

[0021] The beneficial effects of this invention are: This invention determines the upper limit of the conductivity of aluminum alloys by using the normal distribution and 3σ criterion method of big data statistics, which is beneficial to production execution and facilitates product quality control. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method for analyzing the upper limit of electrical conductivity of aluminum alloys.

[0023] Figure 2 This is a discrete normal distribution diagram of the electrical conductivity of 7B04-T74 aluminum alloy. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0025] like Figure 1 As shown in this embodiment, the method for determining the upper limit of the electrical conductivity of 7B04-T74 aluminum alloy after aging heat treatment includes the following steps:

[0026] The first step is to collect measured data.

[0027] A total of 10,921 measured electrical conductivity data were collected for 7B04-T74 aluminum alloy parts with diameters of 11 sizes (δ1.0mm, δ1.2mm, δ1.5mm, δ1.8mm, δ2.0mm, δ2.5mm, δ3.0mm, 3.5mm, 4.0mm, 5.0mm, and 8.0mm) after five years of aging heat treatment.

[0028] The second step is to perform discrete normal distribution partitioning.

[0029] Using statistical methods, a conductivity range of 0.4 MS / m was determined. The measured conductivity data were divided into 9 intervals, and the normal distribution of the measured conductivity values ​​is shown in Table 1. Figure 2 As shown.

[0030] Table 17 Calculation Table of Normal Distribution Intervals After Aging Heat Treatment of B04-T74 Aluminum Alloy

[0031]

[0032] The third step is to calculate the mean and standard deviation.

[0033] The mean and standard deviation of the electrical conductivity data of 7B04-T74 aluminum alloy after aging heat treatment are as follows:

[0034] average value

[0035] Standard deviation

[0036] The fourth step is to determine the upper limit of conductivity based on the 3σ criterion.

[0037] Based on the formula and conductivity data, the expected value of conductivity and the standard deviation of conductivity are obtained, as shown in Table 2.

[0038] Table 2. Range of Expected Conductivity Values ​​and Standard Deviation

[0039]

[0040]

[0041] According to the 3σ criterion, conductivity values ​​exceeding the μ+3σ range are considered to be gross errors rather than random errors. Therefore, data above 24.2 MS / m should be discarded. The upper limit of conductivity for 7B04 aluminum alloy is initially set at 24.2 MS / m.

[0042] Step 5: Verify the upper limit of conductivity.

[0043] More than 962 tensile strength data points of 7B04-T74 aluminum alloy after aging heat treatment were collected. From these, parts with a δ1.8mm thick sheet metal exhibited an electrical conductivity of 24.2 MS / m. The tensile strength details are shown in Table 3. Referring to the 7B0-T74 aluminum alloy material standard, the tensile strength values ​​are (440~520) MPa. Comparison revealed that the tensile strengths corresponding to the electrical conductivity of 24.2 MS / m for the extracted δ1.8mm thick 7B04-T74 sheet metal parts after aging heat treatment all fell within the (440~520) MPa range. Therefore, it can be verified that when the upper limit of the electrical conductivity of 7B04-T74 aluminum alloy after aging heat treatment is 24.2 MS / m, it meets the requirements for part qualification verification.

[0044] Table 3. Statistical Table of Electrical Conductivity and Tensile Strength Values ​​of 7B04-T74 Parts

[0045] System order number Material thickness (mm) Conductivity MS / m Tensile strength value (MPa) 1 Plate δ1.8 24.2 473 2 Plate δ1.8 24.2 476 3 Plate δ1.8 24.2 478 4 Plate δ1.8 24.2 482 5 Plate δ1.8 24.2 486 6 Plate δ1.8 24.2 495 7 Plate δ1.8 24.2 496 8 Plate δ1.8 24.2 498 9 Plate δ1.8 24.2 502 10 Plate δ1.8 24.2 506 11 Plate δ1.8 24.2 508 12 Plate δ1.8 24.2 511 13 Plate δ1.8 24.2 512 14 Plate δ1.8 24.2 513 15 Plate δ1.8 24.2 515 16 Plate δ1.8 24.2 517 17 Plate δ1.8 24.2 518

Claims

1. A method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment, characterized in that, The specific steps are as follows: The first step is to collect measured data. Collect measured electrical conductivity data of aluminum alloy materials of corresponding grades and heat treatment states after aging heat treatment; The second step is to perform discrete normal distribution partitioning. Using statistical methods, the measured conductivity data are divided into n intervals, and the conductivity range Δ = A is determined for each interval. i -A i-1 , where A i-1 Let A be the minimum value of the measured conductivity data for the i-th interval. i X represents the maximum value of the measured conductivity data in the i-th interval; X represents the median value of the measured conductivity data in the i-th interval. i The number of measured conductivity data in the i-th interval is Y. i The proportion of the measured conductivity data in the i-th interval to the total data is P. i , i = 1 to n, to obtain normally distributed data; The third step is to calculate the mean and standard deviation. The mean μ and standard deviation σ of the measured conductivity data are obtained by calculating the normally distributed data. The fourth step is to determine the upper limit of conductivity based on the 3σ criterion. The upper limit of conductivity (μ+3σ) MS / m is determined based on the 3σ criterion to evaluate and control the stability and reliability of the process. Step 5: Verify the upper limit of conductivity. Collect tensile strength data of aluminum alloys of corresponding grades and heat treatment states after aging heat treatment. The tensile strength σ is the maximum conductivity value when the upper limit is (μ+3σ) MS / m. b MPa; The tensile strength value (σ) in the corresponding aluminum alloy grade and temper material standard is found to be... b1 ~σ b2 ) MPa, for comparison, if σ b1 ≤σ b ≤σ b2 If the upper limit of the electrical conductivity of the aluminum alloy after aging heat treatment is determined to be (μ+3σ)MS / m, then the requirements of the qualified verification index of the part are met.

2. The method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment according to claim 1, characterized in that, In the first step, data on aluminum alloy materials of corresponding grades and heat treatment states after aging heat treatment were collected over the past 5 years.

3. The method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment according to claim 2, characterized in that, The data includes no fewer than 5 material specifications and no fewer than 5,000 measured data points on the electrical conductivity of the parts.

4. The method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment according to claim 1, 2, or 3, characterized in that, In the third step, the formulas for calculating the mean μ and the standard deviation σ are as follows:

5. A method for determining the upper limit of electrical conductivity of an aluminum alloy after aging heat treatment according to claim 1, 2, or 3, characterized in that, In the fourth step, the confidence interval for conductivity is (μ-3σ, μ+3σ) MS / m. If a conductivity measurement value in a set of measurement data is not within the (μ-3σ, μ+3σ) interval, that is, the absolute value of the residual error is >3σ, then the measurement value should be discarded. The upper limit of conductivity for aluminum alloys of the corresponding grade and condition is set as (μ+3σ) MS / m.

6. The method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment according to claim 4, characterized in that, In the fourth step, the confidence interval for conductivity is (μ-3σ, μ+3σ) MS / m. If a conductivity measurement value in a set of measurement data is not within the (μ-3σ, μ+3σ) interval, that is, the absolute value of the residual error is >3σ, then the measurement value should be discarded. The upper limit of conductivity for aluminum alloys of the corresponding grade and condition is set as (μ+3σ) MS / m.

7. A method for determining the upper limit of electrical conductivity of an aluminum alloy after aging heat treatment according to claim 1, 2, 3, or 6, characterized in that, In the fifth step, collect more than 500 tensile strength data points of aluminum alloy materials after aging heat treatment for corresponding grades and heat treatment states.

8. The method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment according to claim 4, characterized in that, In the fifth step, collect more than 500 tensile strength data points of aluminum alloy materials after aging heat treatment for corresponding grades and heat treatment states.

9. The method for determining the upper limit of electrical conductivity of aluminum alloy after aging heat treatment according to claim 5, characterized in that, In the fifth step, collect more than 500 tensile strength data points of aluminum alloy materials after aging heat treatment for corresponding grades and heat treatment states.

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