CN115094277B - Mixed crystal structure aluminum alloy and preparation method and application thereof - Google Patents
Mixed crystal structure aluminum alloy and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses an aluminum alloy with a mixed crystal structure and a preparation method and application thereof, and relates to the technical field of heterogeneous materials. The mixed crystal structure aluminum alloy is a 7-series aluminum alloy containing a rare earth element Er, and the microstructure of the mixed crystal structure aluminum alloy has the following characteristics: in the rolling direction vertical to the mixed crystal structure aluminum alloy, the grain size is in periodic gradient distribution change, and in any period, the grain size is continuously increased from fine grains with nanometer scale to coarse grains with micrometer scale; the crystal grains are isometric crystals with different scales; the inside of the crystal grains contains nanometer precipitated phases with different sizes, and the dislocation inside the crystal grains is 10 15 m ‑2 The above. The aluminum alloy with the mixed crystal structure has excellent mechanical property, and can be widely applied to the fields of aviation plates or automobile plates and the like. In addition, the preparation method provided by the application enables the finally formed material to have a special microstructure through component design and variable temperature rolling control process, and the plasticity and mechanical property of the metal material are obviously improved.
Description
Technical Field
The invention relates to the technical field of heterogeneous materials, in particular to an aluminum alloy with a mixed crystal structure and a preparation method and application thereof.
Background
The heterogeneous material is widely applied to the high-tech fields such as aviation, aerospace, national defense and emerging technologies as a common advanced material, and the excellent mechanical properties of macroscopical structures such as toughness and the like of the heterogeneous material closely depend on the micro-structural characteristics of nano-scale and micro-scale, namely, the heterogeneous material has cross-scale mechanical behavior. The heterogeneous material means that a great mechanical property difference exists between one area and other areas in the material, and the mechanical property difference can reach 100%.
Typical isomerism includes: such as a gradient structure (the grain size is in gradient distribution change), a bimodal structure (consisting of grains with two-stage sizes), a lamellar structure (large and small grains are arranged alternately layer by layer), a dual-phase structure (soft-hard phase grains are arranged alternately), a nanometer twin structure (high-density twin boundaries are introduced into the grains) and a multilayer plate structure (materials with different properties are combined through chemical bonds to form the nanometer twin structure, and the layer thickness is within hundreds of microns). Wherein, twin crystal means that two areas in the crystal grain are distributed in mirror symmetry. This plane of symmetry is called a twin boundary, which can interact with dislocations, thereby affecting the properties of the material.
One common feature of these heterostructures is that the material contains units of different strengths within the material. "heterogeneous" metal means a material having a microstructure unit with a large difference in strength. These microstructure units may be due to differences in strength (hardness or softness) due to differences in grain size, crystal structure, or material composition. The heterogeneous material can have the capacity of high strength and high plasticity, so that the strength and the plasticity are perfectly matched.
However, the existing aluminum alloy is more uniform in structure, and the aluminum alloy structure with specific mechanical property difference is difficult to obtain.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide an aluminum alloy with a mixed crystal structure and a preparation method and application thereof.
The invention is realized by the following steps:
in a first aspect, the present invention provides a mixed crystal structure aluminum alloy, wherein the mixed crystal structure aluminum alloy is a 7-series aluminum alloy containing a rare earth element Er, and a microstructure of the mixed crystal structure aluminum alloy has the following characteristics: in the rolling direction vertical to the mixed crystal structure aluminum alloy, the grain size is in periodic gradient distribution change, and in any period, the grain size is continuously increased from fine grains with nanometer scale to coarse grains with micrometer scale; the crystal grains are isometric crystals with different sizes; the above-mentionedThe inside of the crystal grains contains nanometer precipitated phases with different sizes, and the dislocation inside the crystal grains is 10 DEG 15 m -2 As described above.
In a second aspect, the present invention provides a method for producing a mixed crystal structure aluminum alloy as described in any one of the preceding embodiments, comprising casting a melt into a billet, followed by subjecting the billet to a homogenization treatment, a temperature-changing rolling treatment, a cold rolling treatment, a solution quenching treatment, and an aging treatment; when the melt is cast into the blank, the rare earth element Er is added into the prepared 7-series aluminum alloy melt by Al-10Er alloy, and the variable-temperature rolling treatment comprises the step of carrying out variable-temperature rolling on the blank for multiple passes, wherein the rolling reduction of each pass is 10-30%.
In a third aspect, the invention provides a mixed crystal structure aluminum alloy as described in any one of the preceding embodiments or a mixed crystal structure aluminum alloy obtained by the preparation method of the mixed crystal structure aluminum alloy as described in any one of the preceding embodiments, and the application of the mixed crystal structure aluminum alloy in preparing aviation plates or automobile plates.
The invention has the following beneficial effects:
the application provides a mixed crystal structure aluminum alloy, because of it has the crystalline grain size to be the change of periodic gradient distribution, in arbitrary one cycle, the crystalline grain size all increases the microstructure to the coarse grain of micron scale from the fine grain of nanometer scale in succession, and this mixed crystal structure aluminum alloy can obtain higher tensile properties and excellent percentage elongation simultaneously, has enlarged aluminum alloy material's application, makes mixed crystal structure aluminum alloy can the wide application at aviation panel or automobile panel. In addition, the preparation method provided by the application enables the finally formed material to have a special microstructure by controlling the variable temperature rolling process, and the plasticity and mechanical property of the metal material are obviously improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a graph showing the temperature change from the core to the surface during the variable temperature rolling treatment of the mixed crystal aluminum alloy provided in example 1 of the present application;
FIG. 2 is a three-dimensional view of a microstructure of an aluminum alloy of a mixed crystal structure provided in example 1 of the present application;
FIG. 3 is a schematic view of a microstructure of an aluminum alloy of mixed crystal structure provided in example 1 of the present application in the RD-ND direction;
FIG. 4 is a TEM image of a local region of an aluminum alloy with a mixed crystal structure provided in example 1 of the present application;
FIG. 5 is a performance curve diagram of T6 and T4 states of the mixed-crystal aluminum alloy provided in example 1 of the present application;
FIG. 6 is a schematic diagram illustrating an internal precipitated phase of grains of an aluminum alloy with a mixed crystal structure provided in example 1 of the present application;
fig. 7 is a schematic view of internal dislocation of crystal grains of the mixed crystal aluminum alloy provided in example 1 of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The invention provides an aluminum alloy with a mixed crystal structure, which is a 7-series aluminum alloy containing a rare earth element Er, and the microstructure of the aluminum alloy has the following characteristics:
in the rolling direction vertical to the mixed crystal structure aluminum alloy, the grain size is in periodic gradient distribution change, and in any period, the grain size is continuously increased from fine grains with nanometer scale to coarse grains with micrometer scale; the mixed crystal structure aluminum alloy comprises 60-70% of fine crystal grains and 30-40% of coarse crystal grains by mass percent; the crystal grains are isometric crystals with different scales; the fine grains have an average grain size of 80 to 400nm and the coarse grains have an average grain size of 1 to 10 μm.
Referring to fig. 6, the crystal grains contain nano precipitated phases with different sizes; the size of precipitated phase in the crystal grain is 1-50nm, and the precipitated phase includes GP zone, eta' phase, eta phase, and Al 3 Zr and Al 3 One or more of Er;
referring to FIG. 7, dislocations are present within the grains at 10 15 m -2 The above.
The addition amount of the rare earth element Er is 0.1-0.6%; preferably, the addition amount of the rare earth element Er is 0.2-0.3%; preferably, the chemical components of the mixed crystal structure aluminum alloy comprise, by mass, less than 0.06% of Si, less than 0.08% of Fe, 2.2-2.4% of Cu, less than 0.1% of Mn, 2.0-2.2% of Mg, less than 0.01% of Cr, 7.8-8.2% of Zn, less than 0.02% of Ti, 0.10-0.15% of Zr, 0.2-0.3% of Er and the balance of Al. As can be seen from the graphs in FIGS. 2-4, the rare earth element Er is distributed in the fine grain region, and because the rare earth aluminum alloy has higher Dynamic Recrystallization (DRX) temperature and usually has a large amount of fine dispersed precipitated phases, the grain boundary can be pinned, and the growth of DRX grains is inhibited, so that a mixed crystal structure is easily formed in the rare earth aluminum alloy. By adding rare earth element Er in the application, al generated by the rare earth element Er 3 The Er phase can promote the DRX crystal grain nucleation, so that the volume fraction of a fine crystal area is improved, and the purpose of regulating and controlling a mixed crystal structure is achieved, thereby forming the mixed crystal structure aluminum alloy with 60-70% of fine crystal grains and 30-40% of coarse crystal grains.
At present, the rare earth element Er is added into the aluminum alloy to mainly play a role in refining grains so as to improve the performance of the aluminum alloy. However, the present application has found that, by adding rare earth element Er to an aluminum alloy, there exists uneven and regular distribution in the casting solidification process, specifically, rare earth element Er tends to be distributed near secondary dendrite (i.e. fine grain region), and during the subsequent hot rolling, the secondary dendrite is prone to fracture at the position to form fine crystals, that is, the crystal grains at the position containing rare earth element Er are small and easy to form fine grains, while the crystal grains at the position not containing rare earth element Er are large and easy to form coarse grains. Therefore, the mass percentage of the Er content in the fine grains to the total Er content is more than 80%.
As can be seen from figures 4 and 5, the T6-state tensile strength, the yield strength and the elongation of the mixed crystal structure aluminum alloy provided by the application are 690-710MPa, 650-690MPa and more than or equal to 15%; the tensile strength of the T4 state is 580-640MPa, the yield strength is 480-540MPa, and the elongation is more than or equal to 29 percent. The mixed crystal structure aluminum alloy has good tensile strength and yield strength, high elongation and excellent mechanical property, the mechanical property of the mixed crystal structure aluminum alloy has close relation with the integral number of fine crystals, and the contribution of crystal boundary strengthening to the strength can be expressed by a Hall-Petch formula after the following correction:
wherein:
f fine and d f -fine crystal volume fraction and fine crystal average grain size;
f coarse and d c -coarse crystal volume fraction and coarse crystal average grain size;
σ 0,f and k f -a constant associated with the fine crystalline region and the fine crystalline material;
σ 0,c and k c -a constant associated with the macrocrystalline region and the macrocrystalline material.
The above shows that the increase of the volume fraction of the fine crystalline region in the mixed crystal structure has a significant effect on the improvement of the alloy yield strength.
Further, according to the research of the deformation characteristics of the related coarse and fine crystals, the coarse crystals with the characteristics of the independent and mosaic structure have the effect of facilitating the HDI strengthening to be exerted compared with the continuous and interconnected coarse crystals, and further more dislocations can be accumulated in the coarse crystals; meanwhile, due to the existence of the coarse-fine crystal interface, a higher stress gradient exists in the coarse crystal of the mosaic structure, and the higher stress can block the speed of dislocation sliding, so that the work hardening is lower. Although the dislocation slip is hindered, the work hardening rate is low, the total quantity of the accumulated dislocation in the coarse crystal is not influenced, and the material can still obtain high plasticity on the whole. Therefore, the method for improving the volume fraction of the fine grain region can fully exert the advantages of the mixed crystal structure, obtain high strength and realize high plasticity. According to the method, the rare earth element Er is added, and the specific variable temperature rolling process is combined, so that the volume fraction of the fine crystal area is remarkably improved, the mixed crystal aluminum alloy with 60-70% of fine crystal grains and 30-40% of coarse crystal grains is obtained, and the mixed crystal aluminum alloy has excellent properties of high strength and high plasticity.
In addition, the invention provides a preparation method of the mixed crystal structure aluminum alloy, which comprises the following steps:
(1) The melt is cast into a billet.
When the melt is cast into a blank, the rare earth element Er is added into the prepared 7-series aluminum alloy melt by Al-10Er alloy, the cast blank is used for obtaining an uneven solidification structure containing Er, the solidification structure is a crystal grain containing secondary dendrite, and the rare earth element Er is distributed in a fine crystal grain region.
(2) And carrying out homogenization treatment on the blank.
Homogenization treatment comprises 420 ℃ multiplied by 5h +465 ℃ multiplied by 10h +478 ℃ multiplied by 24h.
(3) And (5) carrying out variable temperature rolling treatment.
The rough crystal and the fine crystal with nonuniform Er content can be obtained after the variable temperature rolling treatment, the variable temperature rolling treatment comprises the steps of carrying out variable temperature rolling on the blank for multiple passes, wherein the reduction of each pass is 10-30%, reheating the blank after each pass of rolling to enable the temperature of the surface and the core of the blank to be uniform, then cooling in the transfer process, because the surface heat dissipation is fast, the core heat dissipation is slow, the temperature from the surface to the core is gradually increased, and the reheating heating temperature is reduced along with the increase of the rolling passes.
In the application, the blank is reheated after each pass of rolling, and there are various reheating modes including but not limited to directly returning the blank to the furnace for heating, and the blank can also be directly heated by using a roller, and the blank is heated according to a specific heating temperature by regulating and controlling the furnace temperature for returning to the furnace for heating or the heating temperature of the roller. Because the alloy is easy to recrystallize at high temperature, and the alloy is not easy to recrystallize at low temperature. The reheating temperature is controlled to be reduced along with the increase of rolling passes, so that the temperature difference between the core part of the blank and the surface of the blank is gradually reduced, the recrystallization degree of the blank is different due to the fact that the temperature of the blank from the core part to the surface of the blank is different, and the aim of regulating and controlling a mixed crystal structure is achieved by combining the uneven distribution of rare earth elements.
Further, in the application, the reduction range of the reheating heating temperature is firstly increased and then reduced, the reheating heating temperature is 445-450 ℃ at most, and the reheating heating temperature is 420-422 ℃ at least; the reheating temperature is the same as the surface temperature of the blank of the corresponding pass; preferably, the temperature of the core is 420-445 ℃ and the temperature of the surface is 385-390 ℃; by controlling the reduction range of the heating temperature, the temperature change of different cross-section areas is not uniform, and the recrystallization degree of the alloy is promoted to be different.
Preferably, and in particular to the present application, which lists a typical but non-limiting example, the temperature-swing rolling comprises 6 passes of rolling, wherein the temperature at the first pass is the heating temperature at which the rolling is carried out; the core temperature of the blank is 445-450 ℃ and the surface temperature is 385-386 ℃ during the second pass rolling; the core temperature of the blank in the third rolling is 442-444 ℃, and the surface temperature is 386-387 ℃; the core temperature of the blank in the fourth rolling is 435-449 ℃, and the surface temperature is 387-388 ℃; the core temperature of the blank in the fifth rolling is 425-429 ℃ and the surface temperature is 388-389 ℃; the core temperature of the blank in the sixth rolling is 420-424 ℃, and the surface temperature is 389-390 ℃. By adopting the variable temperature rolling process, the temperature difference of different cross section areas can be regulated and controlled, so that the recrystallization degree of the alloy is different, the alloy with high temperature is easy to recrystallize, and the alloy with low temperature is not easy to recrystallize. And the purpose of regulating and controlling the mixed crystal structure is achieved by combining the uneven distribution of the rare earth elements.
According to the method, the cast structure is converted into the processed structure through variable temperature rolling, and the plasticity of the material is greatly improved through the conversion of the structure. During the variable temperature rolling treatment, the method simultaneously monitors the pressing amount, the reheating temperature change and the temperature difference between the surface temperature and the core temperature, so that the generation of recrystallized grains is promoted through a particle excited nucleation (PSN) mechanism during the hot rolling of the alloy, and the grains are refined; more fine grains are obtained. The surface temperature of the blank can be rapidly increased and the core temperature is gradually increased in the process of remelting and heating, and the tempering time is short (30-45 min), so that the surface temperature and the core temperature are not uniform and have a certain temperature difference, the surface temperature is higher than the core temperature, the surface is easier to recrystallize during hot rolling, crystal grains are easy to grow, the core temperature is lower, the recrystallization is not easy to occur, and the crystal grains are smaller. After the gradient structure of the casting structure is rolled and deformed, because of the deformation and recrystallization of metal, the original coarse dendrite and columnar crystal grains are changed into equiaxial recrystallization structures with finer crystal grains and uniform sizes, the original segregation, looseness, pores, slag inclusion and the like in the alloy are compacted and welded, the structures are tighter, and the plasticity and mechanical property of the metal material are improved.
(4) And (5) cold rolling treatment.
And (3) pickling the hot rolled coil subjected to the temperature-changing rolling treatment to remove oxide skins, and then carrying out cold continuous rolling.
(5) And (5) solution quenching treatment.
The solution treatment and quenching treatment comprises the steps of carrying out solution treatment for 30-90min at 450-500 ℃;
(6) And (5) aging treatment.
The aging treatment comprises primary aging treatment at 120-125 deg.C for 3-6 hr, and secondary aging treatment at 160-165 deg.C for 12-15 hr.
The solid solution quenching treatment and the aging treatment can strengthen the interaction of precipitated phases and dislocation and other defects, and further obtain coarse-grain and fine-grain structures with stable structures.
The mixed crystal structure aluminum alloy with the specific microstructure can be obtained by the preparation method of the mixed crystal structure aluminum alloy, and the mixed crystal structure aluminum alloy can simultaneously obtain higher tensile property and excellent elongation, so that the application field of aluminum alloy materials is expanded, and the mixed crystal structure aluminum alloy can be widely applied to aviation plates or automobile plates.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a mixed crystal structure aluminum alloy, and the preparation method comprises the following steps:
the raw materials are mixed according to the following chemical components: less than 0.06 percent of Si, less than 0.08 percent of Fe, 2.2 to 2.4 percent of Cu, less than 0.1 percent of Mn, 2.0 to 2.2 percent of Mg, less than 0.01 percent of Cr, 7.8 to 8.2 percent of Zn, less than 0.02 percent of Ti, 0.10 to 0.15 percent of Zr, 0.2 to 0.3 percent of Er and the balance of Al. The components are smelted to form a melt, and the melt is cast to form a blank.
Homogenizing the blank at 420 ℃ multiplied by 5h +465 ℃ multiplied by 10h +478 ℃ multiplied by 24h. Then the blank is subjected to a variable temperature rolling process, as can be seen from fig. 1, the depth from the core part to the surface layer in fig. 1 is the depth from the core part to the upper surface of the blank, that is, the thickness of the blank is 2 times of the depth of the corresponding pass, wherein the position with the depth of 0mm in fig. 1 represents the surface layer, and the position close to the depth of 32mm represents the core part.
Wherein, the first pass is to roll the blank with the thickness of 100mm to the thickness of 80mm;
then reheating, wherein the reheating temperature is 445 ℃, the heating is stopped when the surface temperature and the core temperature are both 445 ℃, and then cooling is carried out until the temperature of the core of the blank is 445 ℃ and the surface temperature is 385 ℃, and the second-pass rolling is carried out until the thickness is 62mm;
then reheating at 443 deg.C, stopping heating when the surface temperature and the core temperature are both 443 deg.C, cooling to 443 deg.C and 386 deg.C, and rolling to 50mm thickness in the third pass;
reheating at 437 deg.C, stopping heating when the surface temperature and the core temperature are both 437 deg.C, cooling to 437 deg.C and 387 deg.C, and rolling to 40mm thickness in the fourth pass;
reheating at 427 deg.C, stopping heating when the surface temperature and the core temperature are 427 deg.C, cooling to 427 deg.C, and performing fifth-pass rolling to 28mm thickness when the core temperature and the surface temperature are 388 deg.C;
then reheating at 422 deg.C, stopping heating when the surface temperature and the core temperature are both 422 deg.C, cooling to 422 deg.C and 389 deg.C, and rolling to 14mm thickness in sixth pass;
and (3) pickling the hot rolled coil subjected to the variable temperature rolling treatment to remove oxide skins, carrying out cold continuous rolling to 2mm, then carrying out solid solution treatment at 480 ℃ for 60min, then carrying out primary aging treatment at 121 ℃ for 5h, and then carrying out secondary aging treatment at 163 ℃ for 13h to obtain the mixed crystal structure aluminum alloy.
Referring to fig. 2-4, it can be seen from fig. 2-4 that the grain size of the mixed-crystal aluminum alloy obtained in this embodiment is periodically distributed in a gradient manner in a direction perpendicular to the rolling direction of the mixed-crystal aluminum alloy, and in any period, the grain size of the mixed-crystal aluminum alloy obtained in this embodiment is continuously increased from fine grains of nanometer scale to coarse grains of micrometer scale, wherein the average grain size of the fine grains is 80-400nm, the average grain size of the coarse grains is 1-10 μm, and the proportion of the fine grains is greater than that of the coarse grains, wherein the fine grains account for 60-70% and the coarse grains account for 30-40%. The crystal grains have different sizes and comprise fine crystal grains and coarse crystal grains, and basically all the crystal grains are equiaxed grains; the crystal grain contains nanometer precipitated phases with different sizes of 1-50nm, and the precipitated phases include GP zone, eta' phase, eta phase and Al 3 Zr and Al 3 One or more of Er; in addition, the internal dislocations of the crystal grains of the present application are 10 15 m -2 The above.
Through detection, referring to fig. 5, the T6-state tensile strength of the aluminum alloy with the mixed crystal structure provided in this embodiment is 709MPa, the yield strength is 686MPa, and the elongation is 15%; the tensile strength in the T4 state is 600MPa, the yield strength is 485MPa, and the elongation is 29 percent.
Example 2
This example is substantially the same as example 1, except that the parameters of the variable temperature rolling are different:
rolling a blank with the thickness of 100mm to the thickness of 80mm in a first pass;
then reheating at 450 ℃, stopping heating when the surface temperature and the core temperature are both 450 ℃, and then cooling to 450 ℃ and 386 ℃ when the core temperature of the blank is at 386 ℃, and performing second-pass rolling to 60mm thickness;
then reheating at 444 ℃ until the surface temperature and the core temperature are both 444 ℃, stopping heating, then cooling to 444 ℃ until the core temperature and the surface temperature are 387 ℃, and rolling to the thickness of 45mm for the third time;
then reheating, wherein the reheating temperature is 439 ℃, heating is stopped when the surface temperature and the core temperature are both 439 ℃, and then cooling is carried out until the temperature of the core of the blank is 439 ℃ and the surface temperature is 388 ℃, and rolling is carried out to the thickness of 35mm in a fourth pass;
reheating at 429 deg.C, stopping heating when the surface temperature and the core temperature are both 429 deg.C, cooling to 429 deg.C and 389 deg.C, and rolling to 20mm thickness in the fifth step;
then reheating is carried out, the reheating temperature is 424 ℃, heating is stopped when the surface temperature and the core temperature are both 424 ℃, and then cooling is carried out until the temperature of the core of the blank is 424 ℃ and the surface temperature is 390 ℃, and the sixth-pass rolling is carried out until the thickness is 10mm.
And (3) pickling the hot rolled coil subjected to variable temperature rolling treatment to remove oxide skin, carrying out cold continuous rolling to 3mm, then carrying out solid solution treatment at 480 ℃ for 60min, then carrying out primary aging treatment at 121 ℃ for 5h, and then carrying out secondary aging treatment at 163 ℃ for 13h to obtain the mixed crystal structure aluminum alloy.
Through detection, please refer to fig. 5, the material provided by the comparative example has a tensile strength of 694MPa in T6 state, a yield strength of 657MPa, and an elongation of 15%; the tensile strength in the T4 state is 594MPa, the yield strength is 480MPa, and the elongation is 29%.
Example 3
This example is essentially the same as example 1, except that the aging parameters are different: this example was subjected to a first stage ageing treatment at 125 ℃ for 4h followed by a second stage ageing treatment at 160 ℃ for 15h.
The microstructure analysis of the material obtained in this example revealed a gradient structure.
Through detection, the tensile strength of the material in the T6 state provided by the comparative example is 705MPa, the yield strength is 681MPa, and the elongation is 14%; the tensile strength in the T4 state is 585MPa, the yield strength is 500MPa, and the elongation is 27%.
Comparative example 1
Comparative example 1 is substantially the same as example 1 except that the hot rolling treatment was carried out by a conventional hot rolling technique in this comparative example.
Specifically, the hot rolling treatment in this comparative example includes: when the thickness of each pass is reduced to the thickness corresponding to the embodiment 1, the melting furnace is returned and heated, and the temperature of each time of the melting furnace is kept consistent and is 450 ℃.
The material obtained in this comparative example was subjected to microstructure analysis and found to have a coarse-grained structure.
Through detection, the tensile strength of the material in the T6 state provided by the comparative example is 580MPa, the yield strength is 535MPa, and the elongation is 10%; the tensile strength in the T4 state is 480MPa, the yield strength is 350MPa, and the elongation is 15%.
To sum up, the mixed crystal structure aluminum alloy that this application provided is because of it has the crystalline grain size and is the change of periodic gradient distribution, and in arbitrary one cycle, the crystalline grain size all increases the microstructure to the coarse grain of micron yardstick from the fine grain of nanometer yardstick in succession, and this mixed crystal structure aluminum alloy can obtain higher tensile properties and excellent percentage elongation simultaneously, has enlarged the application field of aluminum alloy material, makes mixed crystal structure aluminum alloy can the wide application in aviation panel or car panel. In addition, the preparation method provided by the application enables the finally formed material to have a special microstructure by controlling a hot rolling process, and the plasticity and mechanical property of the metal material are obviously improved.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The mixed crystal structure aluminum alloy is characterized in that the mixed crystal structure aluminum alloy is a 7-series aluminum alloy containing a rare earth element Er, and the microstructure of the mixed crystal structure aluminum alloy has the following characteristics: in the rolling direction vertical to the mixed crystal structure aluminum alloy, the grain size is in periodic gradient distribution change, and in any period, the grain size is continuously increased from fine grains with nanometer scale to coarse grains with micrometer scale; the crystal grains are isometric crystals with different scales; the crystal grains contain nanometer precipitated phases with different sizes, and the dislocation inside the crystal grains is 10 DEG 15 m -2 The above;
the mixed crystal structure aluminum alloy comprises, by mass, 60-70% of fine crystal grains and 30-40% of coarse crystal grains; the average grain size of the fine grains is 80-400nm, and the average grain size of the coarse grains is 1-10 mu m;
the rare earth element Er is distributed in a fine grain region; the content of the rare earth element Er in the fine grains accounts for more than 80 percent of the total weight of the rare earth element Er;
the chemical components of the mixed crystal structure aluminum alloy comprise, by mass, less than 0.06% of Si, less than 0.08% of Fe, 2.2-2.4% of Cu, less than 0.1% of Mn, 2.0-2.2% of Mg, less than 0.01% of Cr, 7.8-8.2% of Zn, less than 0.02% of Ti, 0.10-0.15% of Zr, 0.2-0.3% of Er and the balance of Al.
2. The mixed-crystal aluminum alloy according to claim 1, wherein the size of the precipitated phases within the grains is 1 to 50nm, and the species of the precipitated phases include GP zones, η' phase, η phase, al 3 Zr and Al 3 One or more Er.
3. A method for producing the mixed crystal structural aluminum alloy as recited in any one of claims 1 to 2, which comprises casting a melt into a billet, and subsequently subjecting the billet to a homogenization treatment, a temperature-changing rolling treatment, a cold rolling treatment, a solution quenching treatment and an aging treatment; when the melt is cast into the blank, the rare earth element Er is added into the prepared 7-series aluminum alloy melt by Al-10Er alloy, and the variable-temperature rolling treatment comprises the step of carrying out variable-temperature rolling on the blank for multiple passes, wherein the rolling reduction of each pass is 10-30%; the temperature-varying rolling comprises reheating the blank after each rolling pass to make the temperature of the surface and the core of the blank uniform, and then cooling to gradually increase the temperature from the surface to the core, wherein the reheating heating temperature is reduced along with the increase of the rolling pass.
4. The method for producing the mixed crystal structure aluminum alloy as claimed in claim 3, wherein the reheating heating temperature is decreased after being increased, the reheating heating temperature is 445 to 450 ℃ at the maximum, and the reheating heating temperature is 420 to 422 ℃ at the minimum; the reheating temperature is the same as the surface temperature of the blank in the corresponding pass.
5. The method of producing a mixed crystal structure aluminum alloy as recited in claim 4, wherein the temperature of said core portion is 420 to 445 ℃ and the temperature of said surface is 385 to 390 ℃.
6. The method for preparing the mixed crystal structure aluminum alloy as claimed in claim 4, wherein the reheating mode comprises a return heating or a roll heating.
7. The method for preparing an aluminum alloy with a mixed crystal structure according to claim 4, wherein the temperature-varying rolling comprises 6-pass rolling,
the temperature at the first pass rolling, i.e. the temperature at which the billet is cast;
the core temperature of the billet during the second pass rolling is 445-450 ℃, and the surface temperature is 385-386 ℃;
the core temperature of the blank in the third rolling is 442-444 ℃, and the surface temperature is 386-387 ℃;
the core temperature of the blank in the fourth pass of rolling is 435-449 ℃, and the surface temperature is 387-388 ℃;
the core temperature of the blank in the fifth rolling is 425-429 ℃ and the surface temperature is 388-389 ℃;
the core temperature of the blank in the sixth rolling is 420-424 ℃, and the surface temperature of the blank is 389-390 ℃.
8. The method for producing the mixed-crystal aluminum alloy according to claim 4, wherein the solution quenching treatment includes solution treatment at 450 to 500 ℃ for 30 to 90min.
9. Method for producing an aluminium alloy with a mixed crystal structure according to claim 4, characterised in that the ageing treatment comprises a first stage ageing treatment at 120-125 ℃ for 3-6h, followed by a second stage ageing treatment at 160-165 ℃ for 12-15h.
10. Use of the mixed-crystal aluminum alloy as defined in any one of claims 1 to 2 or the mixed-crystal aluminum alloy obtained by the method for producing the mixed-crystal aluminum alloy as defined in any one of claims 3 to 9 for producing aviation or automotive panels.
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