Soaking annealing treatment method for large-size 7xxx series aluminum alloy slab ingot

Abstract

The invention discloses a soaking annealing treatment method for a large-size 7xxx series aluminum alloy slab ingot, and relates to the technical field of aluminum alloy heat treatment, and the soaking annealing treatment method is characterized in that the soaking annealing method is two-stage soaking annealing treatment and specifically comprises the following steps that S1, first-stage soaking annealing is conducted, specifically, a cast ingot is heated to 400-460 DEG C, the heating rate is 5-8 DEG C / min, and heat preservation is conducted for 5-20 h; s2, second-stage soaking annealing is conducted, specifically, the temperature of the cast ingot continues to rise to 460-480 DEG C, the heating rate is 0.5-3 DEG C / min, and the heat preservation time is 20-50 h; and S3, cooling treatment is conducted, specifically, the cast ingot obtained after second-stage soaking annealing treatment is cooled to the room temperature, and the cooling rate is 2-8 DEG C / min. The large-size aluminum alloy slab ingot treated through the method is uniform in component, has high plasticity, facilitates subsequent rolling and extrusion deformation and can be suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy heat treatment, and more specifically, to a soaking annealing treatment method for large-size 7xxx series aluminum alloy flat ingots. Background Art

[0002] With the increasing demand for lightweight structures in aerospace, transportation and other equipment, the market demand for wide-width 7075, 7050 and other 7xxx series deformed aluminum alloy plates and strips is increasing, and wide-width plates and strips need to be processed through large-sized slabs. The quality of the slabs directly determines the organizational properties of the wide-width plates. However, the total content of alloying elements in 7xxx series aluminum alloys is high (more than 9%), the composition is complex, the crystallization temperature range is wide, the casting solidification structure and composition are seriously non-uniform, and it has a high tendency to crack. The larger the slab specifications and width-to-thickness ratio, the greater the tendency to crack. Therefore, it is very difficult to cast 7xxx series aluminum alloy slabs. Moreover, the large-sized aluminum alloy slabs produced in my country have problems such as serious uneven composition and organization, coarse grains, and high impurity content, resulting in the quality of large-sized slabs being at a medium and low-end level, which cannot meet the demand for large-sized slabs of high-comprehensive performance wide-width aluminum alloy plates. As a result, the comprehensive properties of 7xxx series deformed aluminum alloys such as strength, toughness, corrosion resistance, and fatigue resistance are significantly lower than those of advanced developed countries such as the United States. High-end wide-width deformed aluminum alloys are heavily dependent on imports, which restricts the development of my country's aerospace, transportation and other industries.

[0003] Large-sized 7xxx series aluminum alloy slabs are usually prepared by water-cooled semi-continuous casting, which leads to serious segregation of the ingot structure and large residual stress. High-temperature soaking annealing is required for subsequent treatment to eliminate the segregation and non-equilibrium solidification phase in the dendrites of the ingot structure and improve the toughness and mechanical processing properties of the ingot. However, the soaking annealing process involves factors such as heating rate, heating temperature, holding time, cooling rate, etc. The process is relatively complicated. Only a suitable soaking annealing process can ensure that the ingot does not crack during the subsequent rolling process. The currently commonly used soaking annealing process is a single-stage annealing treatment, which makes it difficult to eliminate the segregation and non-equilibrium solidification phase in the dendrites of the ingot structure, and cannot effectively improve the toughness and rolling and other mechanical processing properties of large-sized slabs.

[0004] The object of the present invention is to provide a soaking annealing method for large-size 7xxx series aluminum alloy slabs in view of the deficiencies in the prior art. Summary of the invention

[0005] The purpose of the present invention is to provide a method for soaking annealing large-size 7xxx series aluminum alloy slabs, which adopts a two-stage soaking annealing system, and obtains annealed large-size aluminum alloy slabs with high homogeneity and high plasticity by regulating the soaking annealing process and optimizing the process conditions. The slabs have good rolling and forging properties.

[0006] 3. The above technical objectives of the present invention are achieved through the following technical solutions: A method for soaking annealing a large-size 7xxx series aluminum alloy flat ingot, wherein the soaking annealing method is a two-stage soaking annealing treatment, specifically comprising the following steps:

[0007] S1. First stage soaking annealing: first heat the ingot to 400-460°C, heating rate is 5-8°C / min, keep warm for 5-20h;

[0008] S2. Second stage soaking annealing: continue heating the ingot to 460-480°C, heating rate 0.5-3°C / min, holding time 20-50h;

[0009] S3. Cooling treatment: Cool the ingot after the second stage soaking annealing treatment to room temperature at a cooling rate of 2 to 8°C / min.

[0010] The present invention is further configured as follows: the 7xxx series aluminum alloys include 7075, 7175, 7050, 7B50, 7A04, 7150, 7055, and 7085.

[0011] The present invention is further configured as follows: in step S1, the heating rate is 5-8°C / min.

[0012] The present invention is further configured as follows: in step S2, the heating rate is 0.5-3°C / min.

[0013] In summary, the present invention has the following beneficial effects:

[0014] The present invention adopts a two-stage soaking annealing treatment method, and by controlling the heating rate, holding temperature, holding time, cooling rate and other process parameters in the soaking annealing process, the dendrite segregation and grain boundary non-equilibrium solidification phase in the large-size flat ingot are greatly reduced. The large-size aluminum alloy flat ingot treated by the present invention has a relatively uniform composition, high plasticity, is conducive to subsequent rolling and extrusion deformation, and is suitable for industrial production. The purpose of the first stage soaking annealing is to eliminate the low-melting point non-equilibrium phase such as T (Al ZnMgCu) phase in the ingot and reduce the dendrite segregation. The purpose of the second stage soaking annealing is to further reduce the number of high-melting point non-equilibrium phases such as MgZn2, Al2Cu, Al2CuMg on the grain boundary in the ingot, and accelerate the diffusion of solute elements such as Zn, Mg, Cu in the dendrite, and then control the cooling rate to prevent the dispersion and precipitation of η (MgZn2) phase in the ingot, and finally obtain a high-homogeneity ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of a method for soaking annealing a large-size 7xxx series aluminum alloy flat ingot in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] The embodiments and comparative examples of the present invention both use large-size 7075 aluminum alloy flat ingots as blanks, and process them through different soaking annealing processes.

[0018] Comparative Example 1

[0019] A single-stage soaking annealing process was adopted: directly heating from 25°C to 470°C, with an acceleration rate of 5°C / min, a holding time of 24h, and then cooling to room temperature at a cooling rate of 4°C / min. The room temperature tensile properties test was then carried out. The properties of the material are shown in Table 1.

[0020] Comparative Example 2

[0021] A single-stage soaking annealing process was adopted: directly heating from 25°C to 450°C, with an acceleration rate of 10°C / min, a holding time of 48h, and then cooling to room temperature at a cooling rate of 1°C / min. The room temperature tensile properties test was then carried out. The material properties are shown in Table 1.

[0022] Comparative Example 3

[0023] A single-stage soaking annealing process was adopted: directly heating from 25°C to 480°C, with an acceleration rate of 3°C / min, a holding time of 36h, and then cooling to room temperature at a cooling rate of 10°C / min. The room temperature tensile properties test was then carried out. The properties of the material are shown in Table 1.

[0024] Example 1

[0025] A double soaking annealing process was adopted: the ingot was first heated to 400°C at a heating rate of 5°C / min and kept warm for 20h; then the ingot was further heated to 460°C at a heating rate of 3°C / min and kept warm for 50h; the ingot after the second soaking annealing was cooled to room temperature at a cooling rate of 2°C / min, and then the room temperature tensile properties test was carried out. The properties of the material are shown in Table 1.

[0026] Example 2

[0027] A double soaking annealing process was adopted: the ingot was first heated to 460°C at a heating rate of 8°C / min and kept warm for 5h; then the ingot was further heated to 470°C at a heating rate of 0.5°C / min and kept warm for 20h; the ingot after the second soaking annealing was cooled to room temperature at a cooling rate of 8°C / min, and then a room temperature tensile performance test was carried out. The material properties are shown in Table 1.

[0028] Example 3

[0029] A double soaking annealing process was adopted: the ingot was first heated to 430°C at a heating rate of 6.5°C / min and kept warm for 12h; then the ingot was further heated to 480°C at a heating rate of 1.5°C / min and kept warm for 36h; the ingot after the second soaking annealing was cooled to room temperature at a cooling rate of 5°C / min, and then the room temperature tensile properties test was carried out. The properties of the material are shown in Table 1.

[0030] Example 4

[0031] A double soaking annealing process was adopted: the ingot was first heated to 450°C at a heating rate of 6°C / min and kept warm for 15h; then the ingot was further heated to 470°C at a heating rate of 2°C / min and kept warm for 40h; the ingot after the second soaking annealing was cooled to room temperature at a cooling rate of 6°C / min, and then the room temperature tensile properties test was carried out. The properties of the material are shown in Table 1.

[0032] Table 1 Room temperature properties of the alloy of the present invention

[0033] Example <![CDATA[R m (MPa)]]> <![CDATA[R 0.2 (MPa)]]> A(％) Comparative Example 1 309 202 3.4 Comparative Example 2 298 198 2.1 Comparative Example 3 305 212 3.2 Example 1 313 141 13.4 Example 2 307 144 12.8 Example 3 303 137 15.3 Example 4 308 145 11.3

[0034] By comparing the performance parameter values ​​of the embodiment and the comparative example, it can be seen that the elongation (A) of the large-sized flat ingot treated by the double-stage soaking annealing of the present invention is significantly higher than that of the alloy of the comparative example.

[0035] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A soaking annealing method for large-size 7xxx series aluminum alloy flat ingots, characterized by: The soaking annealing method is a two-stage soaking annealing process, which specifically includes the following steps: S1. First stage soaking annealing: heat the ingot to 400-460℃ and keep it at this temperature for 5-20h; S2. Second stage soaking annealing: continue heating the ingot to 460-480°C for 20-50h; S3. Cooling treatment: Cool the ingot after the second stage soaking annealing treatment to room temperature at a cooling rate of 2 to 8°C / min.

2. The soaking annealing method for a large-size 7xxx series aluminum alloy slab according to claim 1, characterized in that: The 7xxx series aluminum alloys include 7075, 7175, 7050, 7B50, 7A04, 7150, 7055 and 7085.

3. The soaking annealing method for a large-size 7xxx series aluminum alloy slab according to claim 1, characterized in that: In step S1, the heating rate is 5-8°C / min.

4. The soaking annealing method for a large-size 7xxx series aluminum alloy slab according to claim 1, characterized in that: In step S2, the heating rate is 0.5-3°C / min.

Images