A non-isothermal solid solution heat treatment method for improving corrosion resistance of 7075 aluminum alloy

Abstract

This invention relates to a non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy, belonging to the field of aluminum alloy heat treatment technology. Addressing the problems of the poor solubility of the coarse, iron-rich phase (Al7Cu2Fe) in existing 7075 aluminum alloys, which induces severe localized corrosion, and the tendency for overheating in traditional isothermal solution treatment processes, this invention proposes a non-isothermal solution control method. A mathematical model is constructed between the peak temperature and the heating rate. Based on thermodynamic driving forces and non-isothermal diffusion kinetics, the 7075 aluminum alloy billet is heated non-isothermally from room temperature to the target peak temperature of 510-570°C at a preset slow heating rate, immediately followed by water quenching to room temperature and then artificial aging treatment. This invention utilizes the solute diffusion effect during the non-isothermal process to dynamically increase the overheating threshold (i.e., solidus line) in localized micro-regions of the alloy, thereby achieving the fragmentation, refinement, and resolubilization of the poorly soluble iron-rich phase under conditions far exceeding conventional solution temperatures.

Description

Technical Field

[0001] This invention relates to a non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy, belonging to the field of aluminum alloy heat treatment technology. Background Technology

[0002] The presence of Fe, an impurity element, in 7075 aluminum alloy inevitably leads to the formation of coarse, iron-rich phases. These coarse iron-rich phases exhibit high electrochemical inertness, with their electrode potential significantly higher than that of the aluminum matrix. This causes the iron-rich phase to act as the cathode, while the aluminum matrix acts as the anode. This potential difference creates micro-galvanic corrosion between the iron-rich phase and the surrounding aluminum matrix, accelerating the dissolution of the surrounding matrix. Existing solid solution techniques for eliminating the iron-rich phase face the challenge of reconciling solubility with the risk of overheating.

[0003] Currently, the standard solution treatment process for 7075 alloy in industry typically involves isothermal holding at temperatures between 460°C and 480°C. While this temperature range is sufficient to dissolve the main strengthening phase, η (MgZn2), it is far below the dissolution temperature of the iron-rich phase, Al7Cu2Fe (>540°C). Even after conventional treatment, 7075 alloy still retains a large number of coarse, undissolved Al7Cu2Fe particles in its microstructure. These residual phases not only fail to contribute to strength but also become sources of corrosion sensitivity. The existing heat treatment technology system is trapped in a vicious cycle: to avoid overheating, the solution temperature must be limited (<490°C); however, limiting the temperature prevents the elimination of the harmful iron-rich phase, resulting in a persistent bottleneck in the corrosion resistance of 7075 aluminum alloy.

[0004] Therefore, there is an urgent need for a completely new heat treatment approach that can safely raise the heating temperature to 500℃ or even 550℃ or higher without overheating. This would allow for the utilization of high atomic diffusion kinetics at high temperatures to completely crush, dissolve, or spheroidize those stubborn, coarse, iron-rich phases, thus cutting off the corrosion pathway at the source of the microstructure. Summary of the Invention

[0005] To address the shortcomings of existing 7075 aluminum alloys, such as poor corrosion resistance due to residual insoluble iron-rich phases, the inability of traditional isothermal solution treatment to simultaneously dissolve coarse second phases and prevent overheating, and severe intergranular corrosion caused by large grain boundary potential differences, this invention proposes a non-isothermal solution heat treatment method to improve the corrosion resistance of 7075 aluminum alloys. By constructing a mathematical model between the peak temperature and a preset heating rate, and based on thermodynamic driving forces and non-isothermal diffusion kinetics, the 7075 aluminum alloy billet is non-isothermally heated from room temperature to the target peak temperature of 510-570°C at a slow, preset heating rate, immediately followed by water quenching to room temperature and then artificial aging treatment. This invention utilizes the solute diffusion effect during the non-isothermal process to dynamically increase the overheating threshold (i.e., solidus line) in local micro-regions of the alloy, thereby achieving the fragmentation, refinement, and re-dissolution of the insoluble iron-rich phase under conditions far exceeding conventional solution temperatures.

[0006] A non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy, the specific steps of which are as follows: The 7075 aluminum alloy is heated to the target peak temperature of 510~570℃ at a preset heating rate, immediately cooled to room temperature by water quenching, and then subjected to artificial aging treatment; the preset heating rate satisfies the formula for preventing overheating. ; In the formula, T0 is the initial temperature of the 7075 aluminum alloy, β is the preset heating rate, and T pure Where C is the melting point of pure aluminum, m is the positive slope of the liquidus and solidus lines, and C is the solidus. GB C represents the local solute concentration in the low-melting-point eutectic phase micro-region at the grain boundary at heating time t. GB It decreases dynamically as the heating time t increases.

[0007] The local solute concentration C GB The rate of decrease of the heating time t is defined by a diffusion kinetics model: ; In the formula, δ is the thickness of the diffusion layer. This represents the actual solute concentration in the current matrix. The dynamic diffusion coefficient of the low-melting-point eutectic element. Satisfies the Arrhenius equation: ; In the formula, It is the diffusion constant. β is the diffusion activation energy of solute atoms at the grain boundary, R is the gas constant, T0 is the initial temperature of the 7075 aluminum alloy, β is the preset heating rate, and t is the heating time.

[0008] By mass percentage, 7075 aluminum alloy contains 5.1-6.1% Zn, 2.1-2.9% Mg, 1.2-2.0% Cu, as well as unavoidable impurity elements Fe and Si, with the remainder being Al.

[0009] The mechanism by which this invention improves the corrosion resistance of 7075 aluminum alloy: This invention utilizes a non-isothermal heating path to keep the system in a dynamic quasi-equilibrium state. The extremely high peak temperature (510-570℃) provides a chemical potential difference far exceeding that of traditional processes, significantly breaking the chemical stability of the refractory iron-rich phase as a phase transformation driving force, and providing the prerequisite thermodynamic conditions for its diffusion and dissolution into the matrix. During the non-isothermal heating process, the dynamic solidus temperature of local micro-regions of the alloy... The overheating threshold of the material is determined, and the overheating prevention formula constructed according to this invention is used. It can be seen that in order to achieve the instantaneous external heating temperature To consistently and safely approach or even exceed the upper limit of conventional solid solution temperature, it is necessary to increase the local solute concentration at the grain boundaries. With heating time The dynamic descent is essentially governed by diffusion kinetics models. Strict control is required. This invention abandons the traditional method of rapidly heating to a high temperature and holding it there, instead adopting a slow heating strategy. From the perspective of kinetic integral effects, the extremely small heating rate β significantly extends the time window of the non-isothermal process, making the dynamic diffusion coefficient following the Arrhenius equation more stable. The effective diffusion length increases significantly with time integration. Before the temperature reaches the initial melting point of the low-melting-point phase, solute atoms at the grain boundaries, under the influence of the huge concentration difference, have ample time to diffuse long-range into the α-Al matrix.

[0010] The beneficial effects of this invention are: (1) The method of the present invention breaks through the technical bottleneck of the treatment of refractory phases of 7075 alloy: the existing technology is difficult to eliminate iron-rich phases by isothermal solid solution and is prone to overheating. The present invention constructs a mathematical model between the peak temperature and the preset heating rate. Starting from the thermodynamic driving force and non-isothermal diffusion kinetics mechanism, the 7075 aluminum alloy billet is heated from room temperature at a preset slow heating rate. By using the strategy of heating and diffusion at the same time, the Al7Cu2Fe phase is effectively dissolved and refined at the target peak temperature of 510~570℃, which solves the contradiction between temperature and phase solubility in the traditional process. (2) The method of the present invention achieves a significant leap in corrosion resistance: Unlike the case where the intergranular corrosion depth is relatively deep (about 124 μm) after traditional process treatment, the maximum intergranular corrosion depth of the 7075 alloy material treated by the non-isothermal solution heat treatment of the present invention is greatly reduced (can be reduced to below 75 μm) due to the elimination of coarse second phase and the discontinuous distribution of grain boundary precipitates, which significantly improves the structural safety of the alloy in the service environment. (3) The method of the present invention does not require complex equipment modification or the addition of expensive microalloying elements. It can achieve the control of microstructure and properties by simply optimizing the heat treatment process curve. It has a wide process window, strong controllability, and significant prospects for industrial application and economic benefits. Attached Figure Description

[0011] Figure 1 Diagrams showing different heat treatment processes for 7075 aluminum alloy; Figure 2 SEM image of solution-treated 7075 aluminum alloy (Comparative Example 1). Figure 3 Here is a SEM image of the solution-heat-treated 7075 aluminum alloy from Example 1; Figure 4 The graph shows the area analysis of the coarse Al7Cu2Fe phase in the solution-heat-treated 7075 aluminum alloy of Example 1 and Comparative Example 1. Figure 5 This is a diagram showing the maximum intergranular corrosion depth of the solution-treated 7075 aluminum alloy in Comparative Example 1. Figure 6 This is a diagram showing the maximum intergranular corrosion depth of the 7075 aluminum alloy subjected to solution heat treatment in Example 1. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0013] In both the embodiments and comparative examples of this invention, rolled 7075 aluminum alloy sheet was used, with the following chemical composition (mass percentage): 5.76% Zn, 2.68% Mg, 1.54% Cu, 0.21% Cr, 0.20% Fe, 0.07% Si, 0.06% Mn, and the balance being Al. The aluminum alloy sheet was cut into samples with dimensions of 10mm × 10mm × 10mm and subjected to surface polishing pretreatment. In this embodiment of the invention, the preset heating rate of the 7075 aluminum alloy satisfies the overheating prevention temperature formula: ; In the formula, T0 is the initial temperature of the 7075 aluminum alloy, β is the preset heating rate, and T pure Where C is the melting point of pure aluminum, m is the positive slope of the liquidus and solidus lines, and C is the solidus. GBC represents the local solute concentration in the low-melting-point eutectic phase micro-region at the grain boundary at heating time t. GB It decreases dynamically with increasing heating time t; The local solute concentration C GB The rate of decrease of the heating time t is defined by a diffusion kinetics model: ; In the formula, δ is the thickness of the diffusion layer. This represents the actual solute concentration in the current matrix. The dynamic diffusion coefficient of the low-melting-point eutectic element. Satisfies the Arrhenius equation: ; In the formula, It is the diffusion constant. β is the diffusion activation energy of solute atoms at the grain boundary, R is the gas constant, T0 is the initial temperature of 7075 aluminum alloy, β is the preset heating rate, and t is the heating time. To solve for the maximum safe heating rate allowed under limiting conditions This inequality can be expressed under a critical equality condition, whereby the external heating curve is exactly tangent to the time-dependent rise curve of the local solidus line at the grain boundary. Differentiating both sides of the equation with respect to time t yields the dynamic coupling relationship between the heating rate and the rate of decrease in grain boundary solute concentration:

[0014] The local solute concentration proposed in this invention Diffusion kinetics model that decreases over time Substituting into the above equation, we obtain the equation for the instantaneous heating rate:

[0015] The Arrhenius equation, which characterizes dynamic diffusion capability, will be further applied. By substituting the values, we can construct a model for the heating rate. equation

[0016] A conservative estimate is made using the boundary conditions at the initial stage of heating: at this point, the local concentration difference is at its maximum (taking...). ), and include the dangerous temperature item Approximate substitution with the initial eutectic melting temperature of the alloy This allows us to deduce the formula for the preset safe heating rate applicable throughout the entire heating phase:

[0017] Substitute the specific material parameters of the rolled 7075 aluminum alloy sheet selected in this embodiment into the following: melting point of pure aluminum Approximately 660℃; for the Zn-rich, Mg-rich, low-melting-point eutectic phase that plays a dominant role in alloy 7075, its initial eutectic melting temperature is... Approximately 475℃ (i.e., 748K); the liquid / solid line slope constant m, based on the Al-Zn-Mg ternary phase diagram, is empirically taken as approximately 3.5℃ / wt.%; the effective diffusion activation energy of the dominant solute in the aluminum matrix. The diffusion pre-factor is 70~110 kJ / mol. 1.0×10 -4 Ideal gas constant Initial grain boundary segregation concentration difference Based on the composition (Zn 5.76%, Mg 2.68%) and the as-cast segregation, the effective diffusion layer thickness is estimated to be approximately 10~25 wt.%. The microregion of the rolled grain boundary is approximately 1.0 × 10⁻⁶. -7 ~5.0×10 -7 m.

[0018] Due to different target peak temperatures T peak There are significant differences in the driving force for the dissolution of the second phase in the high-temperature region and the requirements for high-temperature liquefaction safety margin. According to the kinetic coupling model of the present invention, for different T... peak It is necessary to introduce a dynamically varying effective diffusion layer thickness ( ) and initial safe concentration difference ( Stepped boundary estimation is performed.

[0019] Example 1: According to the formula of the preset heating rate And for the target peak temperatures of 510℃, 530℃, 550℃, and 570℃, the range of preset heating rates was calculated as follows: when the target peak temperature is 510℃, the range of preset heating rate is β≤45.2℃ / h; when the target peak temperature is 530℃, the range of preset heating rate is β≤42.6℃ / h; when the target peak temperature is 550℃, the range of preset heating rate is β≤38.5℃ / h; and when the target peak temperature is 570℃, the range of preset heating rate is β≤35.1℃ / h. In this embodiment, the preset heating rate for the 7075 aluminum alloy is 30℃ / h. A non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy, the specific steps of which are as follows: 7075 aluminum alloy was heated to the target peak temperatures of 510℃, 530℃, 550℃, and 570℃ at a preset heating rate (30℃ / h), immediately cooled to room temperature by water quenching, and then subjected to artificial aging treatment. The specific method of artificial aging treatment was as follows: the temperature was heated to 150℃ at a rate of 10℃ / min and held for 24 hours, and then naturally cooled to room temperature in air. 7075 aluminum alloy samples with target peak temperatures of 510℃, 530℃, 550℃, and 570℃ after non-isothermal solution heat treatment were obtained, and are denoted as (a), (b), (c), and (d). According to the national standard GB / T7998-2023, artificially aged 7075 aluminum alloy samples (a), (b), (c), and (d) were placed in a sodium chloride-hydrogen peroxide solution and immersed in a water bath at 30±3℃ for 6 hours. The maximum corrosion depth of the 7075 aluminum alloy was then observed. The sodium chloride concentration in the sodium chloride-hydrogen peroxide solution was 1 mol / L, and the hydrogen peroxide concentration was 0.1 mol / L. In this embodiment, the area fractions of the Al7Cu2Fe phase in the 7075 aluminum alloy samples (a), (b), (c) and (d) after non-isothermal solution heat treatment were as low as 1.35%, 1.15%, 0.70% and 0.50%, respectively, and their maximum intergranular corrosion depths were 108 μm, 85 μm, 77 μm and 61 μm, respectively, and their performance was good. SEM images of the 7075 aluminum alloy samples (a), (b), (c), and (d) after non-isothermal solution heat treatment in this embodiment are shown below. Figure 3 The quantity and morphology of the second phase changed significantly with increasing temperature. In the SEM image of the 7075 aluminum alloy sample (a) after non-isothermal solution heat treatment at a target peak temperature of 510℃, a large number of fine second phase particles were observed to be discontinuously distributed, and some particles had irregular morphologies, indicating that the solution process was not yet complete and solute diffusion was limited. In the SEM image of the 7075 aluminum alloy sample (b) after non-isothermal solution heat treatment at a target peak temperature of 530℃, the quantity of the second phase was significantly reduced, the particle morphology tended to be round, and the surface outline was blurred, indicating that the soluble phase further dissolved into the matrix. In the SEM image of the 7075 aluminum alloy sample (c) after non-isothermal solution heat treatment at a target peak temperature of 550℃, only a small number of fine and dispersed particles were visible, indicating that the non-isothermal heating process effectively promoted the dissolution and refinement of the second phase. In the SEM image of the 7075 aluminum alloy sample (d) after non-isothermal solution heat treatment at a target peak temperature of 570℃, there were very few coarse second phases in the 7075 aluminum alloy microstructure, and the overall microstructure was relatively clean. The area analysis statistics of the coarse Al7Cu2Fe phase in samples (a), (b), (c), and (d) of the 7075 aluminum alloy samples subjected to non-isothermal solution heat treatment in this embodiment are shown in the figure. Figure 4The area fraction of the second phase gradually decreases. In the 7075 aluminum alloy sample (a) after non-isothermal solution heat treatment at a target peak temperature of 510℃, some coarse gray Al7Cu2Fe particles appear. As the target peak temperature gradually increases from 510℃ to 570℃, the coarse gray second phase particles gradually decrease in size and basically disappear at the target peak temperature of 570℃. Figure 3 The SEM images also show that after non-isothermal solution treatment, the alloy microstructure exhibits many diffusely distributed white second phases, which are small in size and uniformly distributed in the matrix. As the target peak temperature gradually increases from 510℃ to 570℃, the area fraction of the coarse Al7Cu2Fe phase gradually decreases. The enhanced diffusion ability, increased phase equilibrium solubility, and decreased Gibbs free energy at high temperatures jointly promote the dissolution of the second phase. Under non-isothermal solution treatment at the target peak temperature of 570℃, the diffusion rate exceeds the solid solution line of most equilibrium phases, and the dissolution is basically completed. The maximum intergranular corrosion depth diagrams for the non-isothermal solution heat-treated 7075 aluminum alloy samples (a), (b), (c), and (d) in this embodiment are shown below. Figure 6 ,from Figure 6 It is evident that under solution heat treatment at target peak temperatures of 510℃ and 530℃, the coarse Al7Cu2Fe phase does not dissolve sufficiently due to the limited solute diffusion rate during heating. Continuous or semi-continuous η(MgZn2) and S(Al2CuMg) phase precipitation zones remain near the grain boundaries. These phases have more negative electrode potentials than the matrix, creating a continuous anodic pathway at the grain boundaries. Consequently, corrosion propagates rapidly along the grain boundaries, resulting in a significant intergranular corrosion depth. When the target peak temperature rises to 550℃, the dissolution of the second phase accelerates significantly, the coarse Fe phase gradually fractures and partially dissolves, the solute concentration in the matrix increases, and the grain boundary precipitation exhibits a discontinuous distribution. This discontinuous corrosion path significantly reduces intergranular corrosion susceptibility. When the target peak temperature reaches 570℃, the non-isothermal heating process provides higher diffusion motive force, and most of the soluble second phase in the alloy is fully dissolved. The Fe phase size is significantly refined and transformed into dispersed particles, and the grain boundary precipitates are basically broken or significantly reduced. This microstructure significantly reduces the potential difference between the grain boundary and the matrix, blocking the continuous propagation of corrosion along the grain boundary, thereby achieving the minimum intergranular corrosion depth. Therefore, high-temperature non-isothermal solid solution effectively weakens grain boundary electrochemistry by promoting the dissolution, refinement, and homogenization of the second phase, which is the main mechanism for improving intergranular corrosion performance.

[0020] Comparative Example 1: This comparative example uses isothermal solution heat treatment to heat-treat rolled 7075 aluminum alloy, specifically including: 7075 aluminum alloy was heated to target temperatures of 510℃, 530℃, 550℃, and 570℃ at a heating rate of 10°C / min and held for 1 hour. It was then immediately water-quenched to room temperature and subjected to artificial aging treatment. The specific method of artificial aging treatment was as follows: the temperature was heated to 150℃ at a rate of 10℃ / min and held for 24 hours. It was then naturally cooled to room temperature in air. 7075 aluminum alloy samples with target temperatures of 510℃, 530℃, 550℃, and 570℃ were obtained and denoted as (a1), (b1), (c1), and (d1). According to the national standard GB / T7998-2023, artificially aged 7075 aluminum alloy samples (a1), (b1), (c1), and (d1) were placed in a sodium chloride-hydrogen peroxide solution and immersed in a water bath at 30±3℃ for 6 hours. The maximum corrosion depth of the 7075 aluminum alloy was then observed. The sodium chloride concentration in the sodium chloride-hydrogen peroxide solution was 1 mol / L, and the hydrogen peroxide concentration was 0.1 mol / L. In this comparative example, the area fractions of the Al7Cu2Fe phase in the 7075 aluminum alloy samples (a1), (b1), (c1), and (d1) after isothermal solution heat treatment were as low as 1.41%, 1.37%, 1.19%, and 1.01%, respectively. The maximum intergranular corrosion depth of 7075 aluminum alloy sample (a1) was 124 μm, and that of 7075 aluminum alloy sample (b1) was 120 μm. 7075 aluminum alloy sample (c1) exhibited severe grain boundary overburning, and its intergranular corrosion performance was not measured. 7075 aluminum alloy sample (d1) also exhibited very severe grain boundary overburning, and its intergranular corrosion performance was not measured. SEM images of the 7075 aluminum alloy samples (a1), (b1), (c1), and (d1) after isothermal solution heat treatment in this comparative example are shown below. Figure 2 The secondary phase in 7075 aluminum alloy samples (a1) and (b1) is mainly composed of white, coarse, irregularly shaped blocky or strip-shaped phases and black, fine secondary phases. These coarse secondary phases are mainly formed during the alloy casting process and are difficult to remove during subsequent heat treatment. They are mainly intermetallic compounds generated by the reaction of elements such as Fe and Si. It can also be seen that when the solid solution temperature reaches 550°C and 570°C, obvious overheating phenomenon occurs at the grain boundaries of 7075 aluminum alloy samples (c1) and (d1). The statistical graph of the area analysis of the coarse Al7Cu2Fe phase in the isothermal solution heat-treated 7075 aluminum alloy samples (a1), (b1), (c1), and (d1) of this comparative example is shown in the figure. Figure 4At solution temperatures of 510°C and 530°C, the Al7Cu2Fe phase in 7075 aluminum alloy samples (a1) and (b1) did not show significant dissolution. Compared with non-isothermal solution, the increased solution temperature improved the diffusion coefficient of solute atoms, making it easier for elements such as Cu, Mg, and Zn to diffuse from the second phase to the matrix, thereby promoting the dissolution of low-melting-point eutectic and part of the Al7Cu2Fe phase. The maximum intergranular corrosion depth diagrams of isothermal solution heat-treated 7075 aluminum alloy samples (a1) and (b1) in this comparative example are shown below. Figure 5 ,from Figure 5 It can be seen that as the solid solution temperature increases, the dissolution of the η phase and S phase and the diffusion of elements are accelerated, which promotes the redistribution of strengthening elements such as Cu, Zn, and Mg to the matrix, thereby reducing the number and size of continuous precipitates at grain boundaries.

[0021] Example 2: According to the formula of the preset heating rate The target peak temperatures are 510℃, 530℃, 550℃, and 570℃. The ranges of the preset heating rates are calculated as follows: β ≤ 45.2℃ / h for a target peak temperature of 510℃, β ≤ 42.6℃ / h for a target peak temperature of 530℃, β ≤ 38.5℃ / h for a target peak temperature of 550℃, and β ≤ 35.1℃ / h for a target peak temperature of 570℃. In this embodiment, the preset heating rate for the 7075 aluminum alloy is 25℃ / h. A non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy, the specific steps of which are as follows: 7075 aluminum alloy was heated to the target peak temperatures of 510℃, 530℃, 550℃, and 570℃ at a preset heating rate (25℃ / h), immediately cooled to room temperature by water quenching, and then subjected to artificial aging treatment. The specific method of artificial aging treatment was as follows: the temperature was heated to 160℃ at a rate of 15℃ / min and held for 18h, and then naturally cooled to room temperature in air. 7075 aluminum alloy samples with target peak temperatures of 510℃, 530℃, 550℃, and 570℃ after non-isothermal solution heat treatment were obtained, and were denoted as (a2), (b2), (c2), and (d2). According to the national standard GB / T7998-2023, artificially aged 7075 aluminum alloy samples (a2), (b2), (c2), and (d2) were placed in a sodium chloride-hydrogen peroxide solution and immersed in a water bath at 30±3℃ for 6 hours. The maximum corrosion depth of the 7075 aluminum alloy was then observed. The sodium chloride concentration in the sodium chloride-hydrogen peroxide solution was 1 mol / L, and the hydrogen peroxide concentration was 0.1 mol / L. In this embodiment, the area fractions of the Al7Cu2Fe phase in the 7075 aluminum alloy samples (a2), (b2), (c2) and (d2) after non-isothermal solution heat treatment were as low as 1.38%, 1.31%, 0.65% and 0.52%, respectively, and their maximum intergranular corrosion depths were 102 μm, 81 μm, 76 μm and 57 μm, respectively, all of which showed good performance.

[0022] Example 3: According to the formula of the preset heating rate And for the target peak temperatures of 510℃, 530℃, 550℃, and 570℃, the range of preset heating rates was calculated as follows: when the target peak temperature is 510℃, the range of preset heating rate β is ≤ 45.2℃ / h; when the target peak temperature is 530℃, the range of preset heating rate β is ≤ 42.6℃ / h; when the target peak temperature is 550℃, the range of preset heating rate β is ≤ 38.5℃ / h; when the target peak temperature is 570℃, the range of preset heating rate β is ≤ 35.1℃ / h. In this embodiment, the preset heating rate for the 7075 aluminum alloy is 20℃ / h. A non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy, the specific steps of which are as follows: 7075 aluminum alloy was heated to the target peak temperatures of 510℃, 530℃, 550℃, and 570℃ at a preset heating rate (20℃ / h), immediately cooled to room temperature by water quenching, and then subjected to artificial aging treatment. The specific method of artificial aging treatment was as follows: the temperature was heated to 120℃ at a rate of 5℃ / min and held for 36h, and then naturally cooled to room temperature in air. 7075 aluminum alloy samples with target peak temperatures of 510℃, 530℃, 550℃, and 570℃ after non-isothermal solution heat treatment were obtained, and were denoted as (a3), (b3), (c3), and (d3). According to the national standard GB / T7998-2023, artificially aged 7075 aluminum alloy samples (a3), (b3), (c3), and (d3) were placed in a sodium chloride-hydrogen peroxide solution and immersed in a water bath at 30±3℃ for 6 hours. The maximum corrosion depth of the 7075 aluminum alloy was then observed. The sodium chloride concentration in the sodium chloride-hydrogen peroxide solution was 1 mol / L, and the hydrogen peroxide concentration was 0.1 mol / L. In this embodiment, the area fractions of the Al7Cu2Fe phase in the 7075 aluminum alloy samples (a3), (b3), (c3) and (d3) after non-isothermal solution heat treatment were as low as 1.36%, 1.29%, 0.62% and 0.47%, respectively, and their maximum intergranular corrosion depths were 112 μm, 88 μm, 72 μm and 54 μm, respectively, all of which showed good performance.

[0023] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy, characterized in that, The specific steps are as follows: The 7075 aluminum alloy is heated to the target peak temperature of 510~570℃ at a preset heating rate, immediately cooled to room temperature by water quenching, and then subjected to artificial aging treatment; the preset heating rate satisfies the formula for preventing overheating. ； wherein T0 is the initial temperature of the 7075 aluminum alloy, β is a preset temperature increase rate, T pure is the melting point of pure aluminum, m is a positive value of the slope of the liquidus and the solidus, C GB is the local solute concentration of the low melting point eutectic phase microzone at the grain boundary at the heating and temperature increase time t, C GB dynamically decreases with the increase of the heating and temperature increase time t.

2. The non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy according to claim 1, characterized in that: Local solute concentration C GB The rate of decrease of the heating time t with respect to the heating rate is defined by a diffusion kinetics model: ； In the formula, δ is the thickness of the diffusion layer. This represents the actual solute concentration in the current matrix. The dynamic diffusion coefficient of the low-melting-point eutectic element. Satisfies the Arrhenius equation: ； In the formula, The diffusion constant is β is the diffusion activation energy of solute atoms in the aluminum matrix, R is the gas constant, T0 is the initial temperature of the 7075 aluminum alloy, β is the preset heating rate, and t is the heating time.

3. The non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy according to claim 1, characterized in that: By mass percentage, 7075 aluminum alloy contains 5.1-6.1% Zn, 2.1-2.9% Mg, 1.2-2.0% Cu, as well as unavoidable impurity elements Fe and Si, with the remainder being Al.

4. The non-isothermal solution heat treatment method for improving the corrosion resistance of 7075 aluminum alloy according to claim 1, characterized in that: The specific method for artificial aging treatment is as follows: heat the temperature to 120-160℃ at a rate of 2-15℃ / min and keep it at that temperature for 12-36 hours.

Images