Heat treatment method for pre-low-temperature aging before deformation of Al-Zn-Mg-Cu aluminum alloy

Abstract

The invention discloses a heat treatment method for pre-low-temperature aging before deformation of an Al-Zn-Mg-Cu aluminum alloy. The pre-low-temperature aging treatment is carried out after solution treatment and before rolling. A heat treatment method of solution treatment, low-temperature aging before rolling, rolling deformation and subsequent aging is adopted, and the solution treatment enables a previous precipitated phase to be completely dissolved, dislocated and restored to the initial state of crystal grains. And then low-temperature aging treatment before rolling is conducted for different times, so that different precipitated phases are generated, the low-temperature aging times are different, structures, components, number densities, volume fractions and the like of solute atomic clusters in different alloy segregation states are different, the work hardening effects caused in the subsequent rolling process are completely different, and therefore the purpose of strengthening is achieved. The yield strength of the Al-Zn-Mg-Cu aluminum alloy subjected to the low-temperature aging heat treatment before deformation is 350 to 413 MPa, and the tensile strength of the Al-Zn-Mg-Cu aluminum alloy is 384 to 449 MPa. And the uniform elongation is 4%, the percentage elongation after fracture is 12-20%, and application and development of the Al-Zn-Mg-Cu aluminum alloy in civil industries such as civil large airplanes and high-speed trains are promoted.

Description

Technical Field

[0001] The invention relates to the field of material preparation, in particular to a heat treatment process for pre-low temperature aging of an aluminum alloy with a grade of 7N01 in Al-Zn-Mg-Cu before deformation. Background Art

[0002] Al-Zn-Mg-Cu alloy is a typical heat-treatable aluminum alloy with ultra-high specific strength. Therefore, it is widely used as a structural material in civil industries such as large civil aircraft and high-speed trains, as well as defense equipment such as bulletproof armor and tanks. With the increasing requirements of modern industry for structural materials, in addition to the basic strength and weight requirements, it is more inclined to pursue excellent comprehensive performance and service performance, such as pursuing high strength while taking into account good toughness, fatigue performance, corrosion resistance, etc.

[0003] For Al-Zn-Mg-Cu alloy, the commonly used single-stage aging heat treatment process, such as T6 peak aging, makes the alloy have peak strength, but at the same time the alloy's stress corrosion resistance is poor and the fracture toughness deteriorates. In 1961, in order to solve the problem of low plasticity and poor corrosion resistance of Al-Zn-Mg-Cu alloy under the peak aging state, Alcoa invented the T73 double-stage aging heat treatment based on the single-stage aging. In 1974, the three-stage aging process system and concept were proposed, which made the Al-Zn-Mg-Cu alloy not only have the same strength as the peak T6 alloy, but also have excellent stress corrosion resistance and fracture toughness.

[0004] The development of modern industry has put forward higher strength and good comprehensive performance requirements for aluminum alloys. Single strengthening method can no longer meet the requirements of modern industry. At this time, deformation heat treatment process came into being. In recent years, a method combining deformation and heat treatment has been developed to simultaneously improve tensile strength and ductility. The method of "solid solution → rolling deformation → aging" is used to produce nano-precipitation, so that aluminum alloys can obtain higher strength and mechanical properties such as plasticity and toughness, and achieve excellent comprehensive performance that single work hardening and precipitation strengthening cannot achieve.

[0005] The patent "A deformation-solution heat treatment process of Al-Zn-Mg-Cu aluminum alloy" with the search application number 201110183388.X, Al-Zn-Mg-Cu aluminum alloy undergoes the process of pre-deformation, pre-solid solution, re-deformation, short-time solution and quenching, that is, deformation-solid solution is repeated alternately to avoid the matrix recrystallization caused by excessive dislocation density caused by deformation in a single deformation-solid solution process. After quenching and aging, the strength, plasticity and fracture toughness of the alloy are significantly improved, which is of great significance to the development of aerospace and transportation fields. However, it has disadvantages such as complex process, long time-consuming repeated heating and insulation, high energy consumption and high processing cost. Summary of the invention

[0006] In order to overcome the shortcomings of conventional methods in the prior art, such as insufficient strength, complex process, high energy consumption and high processing cost, the present invention proposes a heat treatment method for Al-Zn-Mg-Cu aluminum alloy pre-low temperature aging before deformation.

[0007] The specific process of the present invention is:

[0008] Step 1, solution treatment:

[0009] The Al-Zn-Mg-Cu aluminum alloy is subjected to a solid solution treatment to obtain a test piece subjected to the solid solution treatment.

[0010] The solution treatment is to heat the heat treatment furnace to 460-500°C, put the test piece in, and keep it warm for 1.5-2.5 hours. After the end of the heat preservation, put it in water to cool, and the transfer time is ≤10s.

[0011] Step 2, early aging treatment:

[0012] The solution treated specimen is subjected to a preliminary aging treatment to obtain a preliminary aging treated specimen.

[0013] The preliminary aging treatment is to heat the heat treatment furnace to 60-110° C., put the solution treated specimen into the furnace, and keep the temperature for 18-33 hours.

[0014] Step 3, rolling deformation treatment:

[0015] The obtained specimens after the preliminary aging treatment are placed in a reversible cold rolling mill for multiple passes of room temperature rolling; the rolling speed is 35-40 mm / s. During the rolling, the reduction amount of each pass is 5%-10%, and the total reduction amount is 80%, so as to obtain a rolled plate.

[0016] Step 4, subsequent aging treatment:

[0017] The rolled plate is subsequently subjected to aging treatment in an oil bath furnace.

[0018] The oil bath is a primary oil bath or a secondary oil bath. When a primary oil bath is used, the oil bath temperature is 110-130° C., and the oil bath time is 29-31.

[0019] When using a secondary oil bath, the first oil bath temperature is 110-130°C, and the oil bath time is 110-130°C; the second oil bath temperature is 140-160°C, and the oil bath time is 1.5-2.5

[0020] At this point, the pre-low temperature aging heat treatment of the Al-Zn-Mg-Cu aluminum alloy before deformation is completed.

[0021] The purpose of the present invention is to overcome the shortcomings of the prior art and optimize the deformation heat treatment process. The yield strength of the Al-Zn-Mg-Cu aluminum alloy after the pre-low temperature aging heat treatment before deformation is 350-413MPa, the tensile strength is 384-449Mpa, the uniform elongation is 4%, and the elongation after fracture is 12-20%.

[0022] The present invention targets Al-Zn-Mg-Cu aluminum alloy, performs a pre-low-temperature aging treatment after solution treatment and before rolling, that is, innovatively designs the precipitation phase before deformation, thereby optimizing the deformation heat treatment process, and optimizing the coupling effect between dislocations and nano-precipitated phases, in order to achieve a strengthening effect that exceeds the superposition of the mixed law of different strengthening methods, filling the gap in aluminum alloys in this regard.

[0023] The present invention first performs a solution treatment to completely dissolve the previous precipitation phase, and the dislocation and grain return to the initial state. Then, different low-temperature aging treatments are performed before rolling to produce different precipitation phases. The low-temperature aging time is different, and the structure, composition, number density, volume fraction, etc. of the solute atom clusters in different alloy segregation states are different, and the work hardening effect caused in the subsequent rolling process is also completely different. Then, it is subjected to rolling deformation treatment to introduce dislocations and refine grains. The rolled alloy grain structure presents a discontinuous lamellar morphology, and the solute atom clusters in the dislocation line and its vicinity are slightly larger than the cluster size of the dislocation area. The dislocation density of the rolled alloy of pre-low-temperature aging is slightly improved, and the grain refinement effect is very obvious. Finally, the deformed sample is subjected to subsequent aging treatment, and the size of the precipitation phase in the alloy is obviously increased, and the number density of the precipitation phase is reduced, but the volume fraction is reduced more significantly. This is because in the subsequent aging process, many solute atom clusters are redissolved into the matrix, and only part of them evolve into precipitation phases. During the subsequent aging process, the degree of lattice distortion decreases, recovery recrystallization occurs, the dislocation density of the alloy decreases slightly, and the grain size increases slightly.

[0024] Compared with the conventional deformation-heat treatment method, the heat treatment method of solution treatment → low-temperature aging before rolling → rolling deformation → subsequent aging is adopted in the present invention. The low-temperature aging precipitation phase can effectively refine the grains and increase dislocations. The precipitation phase before deformation is innovatively designed to optimize the coupling effect between dislocations and nano-precipitation phases, thereby achieving the purpose of strengthening.

[0025] Experiments show that the heat treatment method of the present invention of solution treatment → low temperature aging before rolling → rolling deformation → subsequent aging in Al-Zn-Mg-Cu aluminum alloy significantly improves the strength of the alloy after subsequent aging compared with the conventional deformation-heat treatment method.

[0026] In summary, the process of the present invention is simple and easy to operate. The heat treatment method of solution treatment → low temperature aging before rolling → rolling deformation → subsequent aging is adopted. The low temperature aging is used to design the precipitation phase before deformation, and then the deformation heat treatment process is optimized, which can effectively play a strengthening role. It provides an effective basis for the optimization of Al-Zn-Mg-Cu aluminum alloy and promotes the application and development of Al-Zn-Mg-Cu aluminum alloy in civil large aircraft, high-speed trains and other civil industries. DETAILED DESCRIPTION

[0027] The present invention is a heat treatment method for pre-low temperature aging of Al-Zn-Mg-Cu aluminum alloy before deformation, and its technical scheme will be described in detail through six embodiments.

[0028] The Al-Zn-Mg-Cu aluminum alloy is 7N01Al-Zn-Mg-Cu aluminum alloy, which is composed of 4.35% Zn, 1.34% Mg, 0.03% Mn, 0.07% Cu, and the balance is Al; the percentages are mass percentages; the total mass is 100%.

[0029] The Al-Zn-Mg-Cu aluminum alloy is cut into a rectangular aluminum block of 50*25*10 mm.

[0030] The specific process of the present invention is:

[0031] Step 1, solution treatment:

[0032] The Al-Zn-Mg-Cu aluminum alloy is subjected to a solid solution treatment. Specifically, a heat treatment furnace is heated to 460-500° C., a test piece is placed therein, and the test piece is kept at this temperature for 1.5-2.5 hours. After the heat preservation is completed, the test piece is placed in water for cooling, and the transfer time is ≤10 seconds. A test piece subjected to the solid solution treatment is obtained.

[0033] Table 1 Process parameters of each embodiment in step 1

[0034]

[0035] Step 2, early aging treatment:

[0036] Heat the heat treatment furnace to 60-110°C; put the solution treated specimens in and keep them warm for 18-33 hours.

[0037] The specimens obtained after preliminary aging treatment.

[0038] Table 2 Process parameters of each embodiment in step 2

[0039]

[0040] Step 3, rolling deformation treatment:

[0041] The obtained specimens after the preliminary aging treatment are placed in a reversible cold rolling mill for multiple passes of room temperature rolling; the rolling speed is 35-40 mm / s. During the rolling, the reduction amount of each pass is 5%-10%, and the total reduction amount is 80%, so as to obtain a rolled plate.

[0042] In this embodiment, an aluminum alloy sheet with a thickness of 10 mm is cold rolled into a rolled plate with a thickness of 2 mm.

[0043] Table 3 Process parameters of each embodiment in step 3

[0044]

[0045] Step 4, subsequent aging treatment:

[0046] The rolled plate is subsequently subjected to aging treatment in an oil bath furnace.

[0047] The oil bath is a primary oil bath or a secondary oil bath. When a primary oil bath is used, the oil bath temperature is 110-130° C., and the oil bath time is 29-31.

[0048] When using a secondary oil bath, the first oil bath temperature is 110-130°C, and the oil bath time is 110-130°C; the second oil bath temperature is 140-160°C, and the oil bath time is 1.5-2.5

[0049] Table 4 Process parameters of each embodiment in step 4

[0050]

[0051] At this point, the pre-low temperature aging heat treatment of the Al-Zn-Mg-Cu aluminum alloy before deformation is completed.

[0052] Table 5 Comparison of mechanical properties of the aluminum alloy obtained by the present invention with that of the aluminum alloy obtained without pre-low temperature aging

[0053]

Claims

1. A heat treatment method for Al-Zn-Mg-Cu aluminum alloy pre-aging before deformation, characterized in that: The specific process is: Step 1, solution treatment: Performing a solid solution treatment on the Al-Zn-Mg-Cu aluminum alloy to obtain a test piece subjected to the solid solution treatment; Step 2, early aging treatment: Performing preliminary aging treatment on the solution treated specimen; The obtained specimens after preliminary aging treatment; Step 3, rolling deformation treatment: The obtained specimens after the preliminary aging treatment are placed in a reversible cold rolling mill for multiple passes of room temperature rolling; the rolling speed is 35-40 mm / s; during the rolling, the reduction amount of each pass is 5%-10%, and the total reduction amount is 80%; and the rolled plate is obtained; Step 4, subsequent aging treatment: Performing subsequent aging treatment on the rolled plate in an oil bath furnace; The oil bath is a primary oil bath or a secondary oil bath; when a primary oil bath is used, the oil bath temperature is 110-130°C, and the oil bath time is 29-31; When using a secondary oil bath, the first oil bath temperature is 110-130°C, and the oil bath time is 110-130°C; the second oil bath temperature is 140-160°C, and the oil bath time is 1.5-2.5 At this point, the pre-low temperature aging heat treatment of the Al-Zn-Mg-Cu aluminum alloy before deformation is completed.

2. The heat treatment method for Al-Zn-Mg-Cu aluminum alloy pre-aging before deformation according to claim 1, characterized in that: The solution treatment described in step 1 is to heat the heat treatment furnace to 460-500° C.; place the test piece and keep it warm for 1.5-2.5 hours; after the insulation is completed, place it in water to cool, and the transfer time is ≤10 seconds.

3. The heat treatment method for Al-Zn-Mg-Cu aluminum alloy pre-aging before deformation according to claim 1, characterized in that: The preliminary aging treatment described in step 2 is to heat the heat treatment furnace to 60-110° C.; place the solution treated specimen in the furnace and keep the temperature for 18-33 hours.

4. The heat treatment method for Al-Zn-Mg-Cu aluminum alloy pre-deformation low temperature aging according to claim 1, characterized in that: The yield strength of the Al-Zn-Mg-Cu aluminum alloy subjected to the pre-low temperature aging heat treatment before deformation is 350-413 MPa, the tensile strength is 384-449 MPa, the uniform elongation is 4%, and the elongation after fracture is 12-20%.

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