CN111485187A - A kind of non-isothermal overaging treatment method of large diameter AlZnMgCu alloy extruded rod - Google Patents

Abstract

The invention discloses a non-isothermal overaging treatment method of a larger-diameter AlZnMgCu alloy extrusion rod, which comprises the steps of firstly carrying out solution quenching treatment on the larger-diameter AlZnMgCu alloy extrusion rod to be treated, then carrying out first-stage preaging treatment according to underaging below the highest aging temperature point strengthening effect, secondly, the large-diameter AlZnMgCu alloy extrusion bar which is subjected to the pre-aging treatment in the first stage is heated to the highest aging temperature point at a certain heating rate, and then is immediately cooled to room temperature at a certain cooling rate, the method reasonably utilizes the difference of the heating and cooling rates of the surface layer and the core part of the extrusion bar to balance the actual aging effects of different layers by the heating and cooling aging technology, the strength and the stress corrosion resistance of the material are improved, the radial structure uniformity and the performance uniformity of the AlZnMgCu alloy extrusion bar with larger diameter can be improved, and the method is suitable for aging heat treatment of the AlZnMgCu alloy extrusion bar with larger diameter.

Description

A kind of non-isothermal overaging treatment method of large diameter AlZnMgCu alloy extruded rod

technical field

The invention relates to a non-isothermal overaging treatment method for a larger-diameter AlZnMgCu alloy extruded rod, and belongs to the technical field of heat treatment strengthening of aluminum alloys.

Background technique

The use of high-strength AlZnMgCu alloy extruded rods to directly manufacture or cooperate with machining to prepare load-bearing structural parts is one of the important ways to realize the lightweight of fast rail vehicles and aircraft structures. With the continuous advancement of China's high-speed train and "large aircraft" plan, the continuous improvement of the carrying capacity and performance of vehicles has put forward more stringent requirements for the comprehensive performance of structural weight reduction and extruded bars.

As a typical precipitation-strengthened alloy, the comprehensive properties of high-quality AlZnMgCu alloy extruded rods strongly depend on aging technology. However, single-stage aging can only maximize the strength of AlZnMgCu alloys. The result of isothermal double-stage overaging to improve the stress corrosion resistance of the alloy is based on the premise of sacrificing the mechanical properties of the alloy. Regression and reaging only theoretically solves the possibility that the strength and corrosion resistance of AlZnMgCu alloys can be synergistically improved, but its process window is narrow and industrial application is extremely difficult. Therefore, the synergistic improvement of the mechanical properties and stress corrosion resistance of AlZnMgCu alloys is the key technical difficulty to be solved in the aging heat treatment of this series of alloys.

In addition, with the increasing emphasis on near-net-shape and overall manufacturing concepts, the aging heat treatment of large-sized AlZnMgCu alloy structural parts also has the problem of microstructure and performance inhomogeneity caused by the difference in the aging degree of the core and surface layers of thick-section components. , such as high-performance light-weight extruded bars used in high-speed railways and large aerospace equipment, the breakthrough in the level of mechanical and corrosion properties of such products and their uniformity is very important to meet the urgent needs of my country's high-speed rail transit and aerospace fields. Structural parts play a key role. Therefore, the heat treatment strengthening treatment of AlZnMgCu alloy extruded rods with larger diameter should achieve the following two purposes: (1) have high mechanical properties and stress corrosion resistance at the same time; (2) have low radial inhomogeneity of properties.

SUMMARY OF THE INVENTION

Aiming at the defects and deficiencies of the existing conventional double-stage aging heat treatment, the present invention provides a non-isothermal over-aging treatment method of a larger diameter AlZnMgCu alloy extruded rod, which has solved the above-mentioned problems in the background technology.

The present invention starts from the optimal matching of four factors: the first-stage pre-aging, the heating rate of the second-stage heating-up aging, the maximum aging temperature point, and the cooling rate of the cooling-aging aging. The proportion of GP region, η' phase and grain boundary η phase; through the matching of the heating rate of the second stage heating and aging and the maximum aging temperature point, while suppressing the coarsening of the intragranular semi-coherent phase, the grain boundary η phase is promoted. Coarse and intermittent; then cool down to room temperature at a certain cooling rate, use the supersaturated solid solution to re-desolubilize the matrix to strengthen the matrix, and use the larger diameter extruded bar surface layer and core heating and cooling rates. Compensation effect, to control the size of intragranular and grain boundary precipitation phase and its optimal distribution in the radial direction of the rod, and effectively improve the radial performance uniformity of the larger diameter AlZnMgCu alloy extruded rod.

A non-isothermal overaging treatment method for a larger diameter AlZnMgCu alloy extruded rod of the present invention comprises the following steps:

(1) Under the condition of extrusion ratio of 15 to 18, an AlZnMgCu alloy extruded rod with a diameter of 60 to 80 mm is obtained. Solution treatment of extruded bars. The solution temperature is 470～480℃, the solution time is 1～2h, and the quenching transfer time is less than or equal to 10s;

(2) The first-stage pre-aging treatment is performed on the large-diameter AlZnMgCu alloy extruded rod in the solid solution state according to the under-aging that is lower than the strengthening effect at the maximum aging temperature point. The pre-aging temperature of the first stage is less than or equal to 120℃, and the pre-aging time of the first stage is less than or equal to 24h;

(3) The heating rate of the second-stage heating and aging is 60℃～300℃/h, and the temperature is heated to the preset maximum aging temperature of 215～250℃. The isothermal heat preservation platform of the second-stage aging is cancelled, and the temperature is increased to the preset temperature. Immediately after the maximum aging temperature point, the cooling and aging shall be carried out at a cooling rate of 60°C to 120°C/h.

The beneficial effects of the present invention are:

In the research, the inventor found that through the first stage of pre-aging, a certain proportion of GP region and η' phase was precipitated in the alloy, and η equilibrium phase was precipitated at the grain boundary; in the second stage of heating and aging, the intragranular precipitated phase. From GP region and η' phase to η' and η phase, the grain boundary phase η completes the coarsening and discontinuous process. During the cooling and aging stage, the hardness of the alloy increases with the re-precipitation of the intragranular non-equilibrium phase, while the grain boundary η phase continues to coarsen and discontinuously at the high temperature stage of cooling, resulting in a continuous increase in the electrical conductivity of the alloy. Among them, the aging organization state in the first stage will have an important influence on the aging behavior at temperature. The direct heating and aging of the solution quenched or severely underaged samples is not conducive to the discontinuity and coarsening of the grain boundary precipitates, and restricts the improvement of the alloy's stress corrosion resistance; and if peak aging or overaging is used in the first stage The treatment will lead to severe coarsening of the intragranular phase during the non-isothermal heating and aging process, which is not conducive to the improvement of the alloy strength. The heating rate and the maximum ageing temperature point of the second-stage heating-aging of non-isothermal overaging determine the properties of the alloy. The higher the heating rate and the higher the maximum aging temperature, the higher the stress corrosion resistance of the alloy. In addition, the elimination of the isothermal holding stage enables a short flow operation of the heat treatment process. By adopting the non-isothermal overaging treatment of the present invention, the mechanical properties of the larger diameter AlZnMgCu alloy extruded bars are much higher than the results of the traditional two-stage heat treatment treatment, but the electrical conductivity (%IACS) level is similar to the traditional two-stage heat treatment treatment results. quite.

Description of drawings

Fig. 1 is the process flow schematic diagram of the present invention.

Detailed ways

The preferred embodiments of the present invention are described in detail below, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, so as to make clearer and clearer boundaries of the protection scope of the present invention.

The comparative example and the embodiment of the present invention all use a hot extrusion Al8Zn2Mg2Cu aluminum alloy bar with an extrusion ratio of 15 and a diameter of 60mm. The solution heat treatment process is 470°C, 1h+480°C, 1h. Transfer time <10s. Then, the samples of the examples and the examples were subjected to different aging treatments respectively. After the treatment, all the samples of the examples and the comparative examples were tested for electrical conductivity, hardness and tensile mechanical properties. The performance test results are shown in Table 1 and Table 2.

Comparative Example 1:

The extruded rod was aged by a single-stage (120°C/24) peak aging method. After the aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. The room temperature tensile properties were then tested on the peak aging samples, and the test results are shown in Table 2.

Comparative Example 2:

The samples were aged by isothermal two-stage (120℃/12h+160℃/18h) over-aging method. After the aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. Subsequently, the room temperature tensile properties were tested on the double-aged samples, and the test results are shown in Table 2.

Example 1:

For the pre-aged samples treated by natural aging (room temperature/24h), the temperature was raised to 215°C at a heating rate of 60°C/h, and the furnace cooling and cooling aging was started immediately after reaching the temperature, and the cooling rate was 80°C/h. After aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. The samples were tested for tensile properties at room temperature, and the test results are shown in Table 2.

Example 2:

For the pre-aged samples treated by natural aging (room temperature/24h), the heating rate was raised to 225°C at a heating rate of 180°C/h, and the furnace cooling and cooling aging started immediately after reaching the temperature, and the cooling rate was 80°C/h. After aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. The samples were tested for tensile properties at room temperature, and the test results are shown in Table 2.

Example 3:

For the pre-aged samples treated at 105°C/24h, the temperature was raised to 215°C at a heating rate of 60°C/h, and the furnace cooling and cooling aging was started immediately after reaching the temperature, and the cooling rate was 80°C/h. After aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. The samples were tested for tensile properties at room temperature, and the test results are shown in Table 2.

Example 4:

For the pre-aged samples treated at 105°C/24h, the temperature was raised to 225°C at a heating rate of 180°C/h, and the furnace cooling and cooling aging was started immediately after reaching the temperature, and the cooling rate was 80°C/h. After aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. The samples were tested for tensile properties at room temperature, and the test results are shown in Table 2.

Example 5:

For the pre-aged samples treated at 120°C/24h, the temperature was raised to 215°C at a heating rate of 60°C/h, and the furnace cooling and cooling aging was started immediately after reaching the temperature, and the cooling rate was 80°C/h. After aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. The samples were tested for tensile properties at room temperature, and the test results are shown in Table 2.

Example 6:

For the pre-aged samples treated at 120°C/24h, the temperature was raised to 225°C at a heating rate of 180°C/h, and the furnace cooling and cooling aging started immediately after reaching the temperature, and the cooling rate was 80°C/h. After aging, the hardness and electrical conductivity were tested, and the experimental results are shown in Table 1. The samples were tested for tensile properties at room temperature, and the test results are shown in Table 2.

The microstructures of AlZnMgCu alloys under different non-isothermal overaging conditions were detected by TecnaiG ² 20 high-resolution transmission electron microscope. The results show that the intragranular precipitation phase is dominated by η' phase, including a certain amount of GP region and a small amount of η phase, while there are coarse and intermittent η phase on the grain boundary. Effectively cut off the stress corrosion channel and improve the corrosion resistance of the extruded rod. The tensile strength of the extruded rod obtained by the non-isothermal overaging in the example is about 650MPa, and the electrical conductivity is higher than 38%IACS.

To sum up, after the non-isothermal overaging treatment provided by the present invention, the larger diameter AlZnMgCu alloy extruded bar can obtain excellent mechanical and stress corrosion resistance properties, and has broad application prospects in the fields of high-speed rail transit and aerospace. .

The above disclosures are only specific embodiments of the present application, and any changes in process parameters that fall within the scope of the present application should fall within the protection scope of the present application.

Table 1 Comparison of electrical conductivity and hardness of samples with different heat treatment regimes

Table 2 Comparison of mechanical properties at room temperature of samples with different heat treatment regimes

Claims (8)

1. a non-isothermal over-aging treatment method of a larger diameter AlZnMgCu alloy extruded rod, is characterized in that, comprises the following steps: (1) After the solution quenching treatment of the larger diameter AlZnMgCu alloy extruded rod to be treated, the first stage pre-aging treatment is carried out according to the under-ageing effect lower than the maximum aging temperature; (2) The larger diameter AlZnMgCu alloy extruded rod after the first-stage pre-aging treatment is heated to the maximum aging temperature point at a certain heating rate, and then immediately cooled to room temperature at a certain cooling rate. 2. the non-isothermal overaging treatment method of a kind of larger diameter AlZnMgCu alloy extruded rod according to claim 1, is characterized in that: the extrusion ratio of described AlZnMgCu alloy extruded rod is 15～18, and the diameter is 60mm～80mm. 3. The non-isothermal overaging treatment method of a larger diameter AlZnMgCu alloy extruded rod according to claim 1, characterized in that: the solution temperature is 470 ℃～480 ℃, and the solution time is 1h～ 2h. 4 . The non-isothermal overaging treatment method for a larger diameter AlZnMgCu alloy extruded rod according to claim 1 , wherein the quenching transfer time is less than or equal to 10s. 5 . 5. The non-isothermal overaging treatment method of a larger diameter AlZnMgCu alloy extruded rod according to claim 1, characterized in that: the first-stage pre-aging temperature≤120°C, the first-stage pre-aging time ≤24h. 6 . The non-isothermal over-aging treatment method for a larger diameter AlZnMgCu alloy extruded rod according to claim 1 , wherein the heating rate in the heating stage is 60° C. to 300° C./h. 7 . 7 . The non-isothermal overaging treatment method of a larger diameter AlZnMgCu alloy extruded rod according to claim 1 , wherein the maximum aging temperature point is 210-250° C. 8 . 8 . The non-isothermal overaging treatment method for a larger diameter AlZnMgCu alloy extruded rod according to claim 1 , wherein the cooling rate in the cooling stage is 60° C. to 120° C./h. 9 .

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