A method for simultaneously improving the strength and intergranular corrosion resistance of age hardening Al-Mg-Zn-Cu(-Ag) alloys

Abstract

This invention relates to a method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys. It belongs to the field of aluminum alloy heat treatment technology, and specifically relates to a method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys. This invention aims to solve the problem that the re-aging process is complex and cannot significantly improve the alloy strength. The method involves sequentially subjecting the Al-Mg-Zn-Cu(-Ag) alloy to solution treatment and non-isothermal aging treatment. This invention simultaneously improves the alloy's strength and intergranular corrosion resistance by increasing the number density of intragranular precipitates and controlling the discontinuous distribution of grain boundary precipitates. This invention also significantly accelerates the age-hardening response speed, greatly shortens the process flow, and is more conducive to industrial production.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy heat treatment technology, and particularly relates to a method for simultaneously improving the strength and resistance to intergranular corrosion of age-hardening Al-Mg-Zn-Cu(-Ag) alloys. Background Technology

[0002] 5-series Al-Mg alloys possess advantages such as excellent formability, corrosion resistance, and weldability, making them the preferred material for aluminum alloy plates used in shipbuilding. However, this alloy system is not heat-treatable and can only improve its strength through cold work hardening and solid solution strengthening with Mg. Adding Zn, Cu(Ag), and other elements to Al-Mg alloys transforms the traditional strengthening method of 5-series aluminum alloys from solid solution strengthening and work hardening to precipitation strengthening, significantly improving the alloy's strength, but at the cost of reduced resistance to intergranular corrosion.

[0003] Researchers have proposed a re-aging heat treatment process for 7-series aluminum alloys to address their poor corrosion resistance. This process allows precipitates to be uniformly dispersed within the grains and discontinuously distributed at grain boundaries, thereby improving the alloy's resistance to intergranular corrosion.

[0004] The re-aging heat treatment process is also applicable to age-hardened Al-Mg-Zn-Cu(-Ag) alloys; however, this process is relatively complex and does not significantly improve the alloy's strength. Therefore, developing a heat treatment process that simultaneously improves the strength and intergranular corrosion resistance of age-hardened Al-Mg-Zn-Cu(-Ag) alloys is of great significance. Summary of the Invention

[0005] The present invention aims to solve the problem that the re-aging process is complex and cannot significantly improve the strength of alloys, and provides a method to simultaneously improve the strength and resistance to intergranular corrosion of age-strengthened Al-Mg-Zn-Cu(-Ag) alloys.

[0006] The present invention provides a method for simultaneously improving the strength and intergranular corrosion resistance of age-hardened Al-Mg-Zn-Cu(-Ag) alloys by subjecting the Al-Mg-Zn-Cu(-Ag) alloys to solution treatment and non-isothermal aging treatment in sequence.

[0007] The beneficial effects of this invention are:

[0008] The heat treatment process provided by this invention can significantly improve the microstructure of Al-Mg-Zn-Cu(-Ag) alloy. The high number density and finely dispersed precipitates within the grains can improve the alloy strength to a certain extent. The discontinuous distribution of precipitates at grain boundaries and the narrow width of the non-precipitated bands at grain boundaries greatly improve the alloy's resistance to intergranular corrosion.

[0009] The heat treatment process provided by this invention offers a new approach for developing high-strength, corrosion-resistant, age-strengthened Al-Mg-Zn-Cu(-Ag) alloys, and has high research and application prospects. Detailed Implementation

[0010] Specific Implementation Method 1: One method of simultaneously improving the strength and intergranular corrosion resistance of age-hardened Al-Mg-Zn-Cu(-Ag) alloys is to sequentially subject the Al-Mg-Zn-Cu(-Ag) alloys to solution treatment and non-isothermal aging treatment.

[0011] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the age-hardening Al-Mg-Zn-Cu(-Ag) alloy is composed of 4.0–7.0% Mg, 1.5–6.0% Zn, 0.2–1.0% Cu, 0–0.7% Ag, 0.1–1.0% Mn, 0–0.3% Zr, 0–0.1% Ti, 0–0.3% Fe, 0–0.3% Si, and the balance being Al by mass percentage. Everything else is the same as in Specific Implementation Method One.

[0012] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method Two in that the age-hardening Al-Mg-Zn-Cu(-Ag) alloy is composed of 4.0–7.0% Mg, 1.5–6.0% Zn, 0.2–1.0% Cu, 0.3–0.7% Ag, 0.1–1.0% Mn, 0.1–0.3% Zr, 0.05–0.1% Ti, 0.1–0.3% Fe, 0.1–0.3% Si, and the balance being Al by mass percentage. Everything else is the same as in Specific Implementation Method Two.

[0013] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Two in that the age-hardening Al-Mg-Zn-Cu(-Ag) alloy is composed of 4.4% Mg, 1.9% Zn, 0.2% Cu, 0.3% Ag, 0.5% Mn, 0.1% Zr, 0.05% Ti, 0.1% Fe, 0.1% Si, and the balance being Al by mass percentage. Everything else is the same as in Specific Implementation Method Two.

[0014] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method One in that the solution treatment process involves holding the solution at 450–530°C for 10 minutes to 2 hours, followed by rapid water quenching to room temperature. Everything else is the same as in Specific Implementation Method One.

[0015] This embodiment first involves holding the solution in a salt bath furnace (or air furnace) at 450℃~530℃ for 10 minutes to 2 hours. If the solution temperature is too low or the solution time is too short, the solute atoms will not completely dissolve into the matrix, reducing the precipitation strengthening effect of the alloy. If the solution temperature is too high, the alloy will overheat, also reducing its mechanical properties. If the solution time is too long, the grain size will significantly increase and coarsen. High-temperature, short-time solution treatment in a salt bath furnace and low-temperature, long-time solution treatment in an air furnace can both achieve the goal of complete re-dissolution of solute atoms into the matrix. After solution treatment, the solution is quickly quenched in water to room temperature to form a supersaturated solid solution, providing thermodynamic impetus for subsequent precipitation.

[0016] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the heating device is a salt bath furnace or an air furnace. Everything else is the same as in Specific Implementation Method Five.

[0017] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Five in that it is kept at 475°C for 2 hours. Everything else is the same as Specific Implementation Method Five.

[0018] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method One in that the non-isothermal aging process is as follows: The temperature is increased to 280℃~350℃ at a rate of 5℃~12℃, and then removed and cooled to room temperature after reaching the set temperature. Everything else is the same as in Specific Implementation Method One.

[0019] In this embodiment, the temperature is increased to 280°C to 350°C at a heating rate of 5°C to 12°C, and then removed and cooled to room temperature after reaching the set temperature. On the one hand, in the low-temperature stage of non-isothermal aging, the nucleation driving force is relatively large, and the critical nucleation radius is small, which is conducive to the nucleation and precipitation of GP zones, resulting in a higher proportion of GP zones. As the aging temperature increases, the critical nucleation radius increases, the nucleation driving force decreases, and the formation of T'-Mg is promoted. 32 (Al,Zn,Cu) 49 The nucleation and precipitation of the GP phase, and the dynamic evolution of the aging temperature, also promote the dynamic transformation of the GP zone to the T' and T phases. On the other hand, the low-temperature stage of non-isothermal aging can effectively suppress the nucleation and precipitation of grain boundary precipitates. As the aging temperature increases, small-sized grain boundary precipitates dissolve, while large-sized grain boundary precipitates coarsen at defect nucleation sites, resulting in a more discontinuous distribution of grain boundary precipitates. At the same time, the faster aging rate of non-isothermal aging treatment can suppress the diffusion of Ag atoms to grain boundaries, making the non-precipitate zone at the grain boundaries narrower. In addition, non-isothermal aging can also accelerate atomic diffusion and the dynamic evolution of age-induced precipitates, thereby accelerating the age-hardening response of the alloy.

[0020] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that it heats to 300°C at a heating rate of 5.8°C. Everything else is the same as in Specific Implementation Method Eight.

[0021] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Eight in that it heats to 300°C at a heating rate of 11.6°C. Everything else is the same as in Specific Implementation Method Eight.

[0022] The beneficial effects of the present invention are verified using the following embodiments:

[0023] Cold-rolled alloy sheets with the alloy composition shown in Table 1 were solution-treated in an air furnace at 475℃ for 2 hours, then quenched with water to room temperature. Immediately after solution treatment, the samples underwent different aging treatments, as shown in Table 2. Vickers hardness, tensile properties, and intergranular corrosion resistance were tested on the peak-aged samples, and the results are shown in Table 3. Tensile property testing was performed according to national standard (GB / T228.1-2021), and intergranular corrosion resistance testing was performed according to national standard (GB / T26491-2011).

[0024] Table 1. Composition of Al-Mg-Zn-Cu(-Ag) alloy used in implementing this invention (mass percentage, wt%)

[0025]

[0026] Table 2. Aging heat treatment processes used in the examples and comparative examples.

[0027]

[0028] Table 3. Performance test results of the examples and comparative examples at peak efficiency.

[0029]

[0030] As shown in Table 3, compared with the comparative example (conventional T6 process), the heat treatment process described in this invention shortens the peak aging time of the alloy by 58.3%–77.8%, increases the tensile strength by 2.9%–5.1%, increases the yield strength by 4.2%–12.4%, and reduces the mass loss after intergranular corrosion testing by 38.9%–46.3%. These experimental results demonstrate that the heat treatment process mentioned in this invention for age-strengthened Al-Mg-Zn-Cu(-Ag) alloys significantly accelerates the age hardening response of the alloy while improving its strength, and also significantly enhances its resistance to intergranular corrosion.

Claims

1. A method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys, characterized in that... A method to simultaneously improve the strength and intergranular corrosion resistance of age-hardened Al-Mg-Zn-Cu(-Ag) alloys involves sequentially subjecting the Al-Mg-Zn-Cu(-Ag) alloy to solution treatment and non-isothermal aging treatment. The age-hardened Al-Mg-Zn-Cu(-Ag) alloy is composed of 4.0~7.0% Mg, 1.5~6.0% Zn, 0.2~1.0% Cu, 0.3~0.7% Ag, 0.1~1.0% Mn, 0.1~0.3% Zr, 0.05~0.1% Ti, 0.1~0.3% Fe, 0.1~0.3% Si, and the balance being Al. The solution treatment process involves holding the solution at 450-530°C for 10 minutes to 2 hours, followed by rapid water quenching to room temperature. The non-isothermal aging process is as follows: heat to 280℃~350℃ at a heating rate of 5℃~12℃, and then remove and cool to room temperature after reaching the set temperature.

2. The method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys according to claim 1, characterized in that... The age-hardening Al-Mg-Zn-Cu(-Ag) alloy is composed of 4.4% Mg, 1.9% Zn, 0.2% Cu, 0.3% Ag, 0.5% Mn, 0.1% Zr, 0.05% Ti, 0.1% Fe, 0.1% Si and the balance being Al by mass percentage.

3. The method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys according to claim 1, characterized in that... The heating equipment is a salt bath furnace or an air furnace.

4. The method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys according to claim 1, characterized in that... Keep warm in a heating device at 475℃ for 2 hours.

5. The method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys according to claim 1, characterized in that... Heat to 300°C at a heating rate of 5.8°C.

6. The method for simultaneously improving the strength and intergranular corrosion resistance of age-hardening Al-Mg-Zn-Cu(-Ag) alloys according to claim 1, characterized in that... Heated to 300°C at a heating rate of 11.6°C.

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