CN113403514A

CN113403514A - High-strength cast aluminum alloy and preparation method thereof

Info

Publication number: CN113403514A
Application number: CN202110650926.5A
Authority: CN
Inventors: 郭洪民; 孙铁铁
Original assignee: Nanchang University
Current assignee: Nanchang University
Priority date: 2021-06-11
Filing date: 2021-06-11
Publication date: 2021-09-17
Anticipated expiration: 2041-06-11
Also published as: CN113403514B

Abstract

A high-strength cast aluminum alloy and a preparation method thereof are disclosed, which comprises the following alloy elements: copper: 4.0-5.5%, silicon: 0.2-3.0%, manganese: 0.05-1.0%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum. The invention designs an alloy component formula aiming at a smelting and casting method, and can obtain a qualified alloy material for the lightweight structural part of the automobile by assisting a tilting casting process and a heat treatment process. Compared with the traditional material: the alloy is a heat-treatable alloy, and the strength and toughness of the alloy are obviously improved before and after heat treatment; the alloy has the advantages of easily obtained raw materials, low cost, less required metal types, no addition of strengthening metal similar to magnesium element, further development and research potential, and obvious advantages in mechanical property compared with the alloy containing the same element types; the alloy casting adopts a tilting casting mode, so that the pores similar to pore shrinkage in the alloy are reduced as much as possible, and the material strength is improved.

Description

High-strength cast aluminum alloy and preparation method thereof

Technical Field

The invention is suitable for the components of the high-strength cast aluminum-copper alloy.

Background

In recent years, with the development of economy, the requirements of the public on automobiles in families are more generalized and privatized, and new energy automobiles are gradually promoted in the domestic development. On the material selection layer, aluminum is used for replacing steel, so that the light weight of the automobile is realized, the energy consumption of the automobile can be greatly reduced, and the requirements of emission reduction and environmental protection are met. The automobile structural part serves as a framework and a stressed part of an automobile, plays a role in supporting and protecting, and has great influence on the safety performance and the service life of the automobile.

The aluminum-copper alloy is a common alloy for aerospace as a mature 2-grade series alloy, is favored by various industries all the time due to the advantages of small density, high strength and good electric and thermal conductivity, and has very bright prospect and development potential.

Disclosure of Invention

The invention aims to provide a high-strength cast aluminum alloy which is suitable for gravity casting, tilting casting and rheocasting methods. The invention adopts the tilting casting, which can reduce the casting defects of pores and the like, thereby obtaining the high-quality billet.

Because the crystallization temperature of the aluminum-copper alloy is wide, the casting performance and the fluidity are poor, other elements are often added to improve the performance of the alloy, and a certain proportion of silicon and manganese are added in the invention. The silicon element is used for improving the fluidity and the casting performance of the alloy, and experiments show that the fluidity of the alloy can be greatly improved by adding the silicon element, but when the silicon element is increased again, the fluidity is not obviously improved any more. Manganese mainly serves to neutralize iron impurity. Iron is a harmful element in the aluminum alloy, and the addition of manganese can change the appearance of a microstructure formed by iron, so that the iron is transformed from a harmful phase into a harmless phase.

The whole preparation process does not use the traditional gravity casting any more, but uses the tilting casting instead, and in the casting forming process, the alloy liquid is basically in a stable state, so that the alloy liquid can be disturbed to the minimum extent, gas involved in the air in the alloy is reduced, and the occurrence of air holes is avoided. The tilting casting pressure head is larger than gravity casting, and defects such as shrinkage cavity can be further reduced.

The invention is realized by the following technical scheme.

The invention relates to a high-strength cast aluminum alloy which comprises the following alloy elements in percentage by mass: copper: 4.0-5.5%, silicon: 0.2-3.0%, manganese: 0.05-1.0%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum.

The invention has the components of silicon and manganese besides two alloy elements of aluminum and copper, and avoids the harm of impurity iron. Silicon mainly plays a role in enhancing the fluidity, resisting heat cracking and increasing the casting performance, and also plays a role in increasing the tensile strength; the silicon element is not suitable to be increased too much, otherwise, the toughness of the alloy is reduced, and the elongation is reduced; the manganese element can neutralize the harmful effect of iron in the raw material and play a certain role in inhibiting the growth of silicon phase.

The sources of the elements will now be further described. The aluminum element of the alloy finished product comes from four aspects: 1. pure aluminum ingot (purity > 99.9%); 2. aluminum composition in Al-10Si (90% aluminum, 10% silicon) master alloy; 3. aluminum composition in Al-10Mn (90% aluminum, 10% manganese) master alloy; 4. the aluminum foil used in the alloy preparation process is used for wrapping small raw materials and metal refining agents. The source of silicon element in the alloy finished product is as follows: si element in Al-10 Si. The source of manganese element in the alloy finished product is as follows: manganese element in Al-10 Mn. The source of copper element in the alloy finished product is as follows: a pure copper block.

The invention relates to a preparation method of a high-strength cast aluminum alloy, which comprises the following steps:

(1) adding part of pure aluminum, and smelting at the temperature of 720-750 ℃. The smelting temperature is not suitable to be too high or too low. When the temperature is too high, the burning loss phenomenon of the alloy in a short time is serious, and when the temperature is too low, the oxidization is also serious due to too long smelting time, meanwhile, the working efficiency is low, and the smelting time is too long. The smelting temperature is controlled between 720 ℃ and 750 ℃ considering both the smelting work efficiency and the oxidation prevention.

(2) Adding Al-10Mn, Al-10Si intermediate alloy blocks and pure aluminum. Respectively adding large intermediate alloy blocks of Al-10Mn and Al-10Si, and then adding pure aluminum blocks, ensuring that all raw materials are immersed in the aluminum liquid in the feeding process, if the raw materials are added again, exposing the raw materials in the air, stopping adding the raw materials, and after all the added raw materials are melted, continuously adding the raw materials until all the raw materials with larger volume are melted. The added pure aluminum uses blocks with larger volume as much as possible, and the Al-10Mn and Al-10Si master alloy blocks use larger blocks (the specific surface area of the ball body is the smallest, if the raw materials can be processed into the ball body and then smelted) instead of small fragments so as to reduce the specific surface area. Therefore, the contact area between the added pure aluminum and the intermediate alloy of Al-10Mn and Al-10Si and the air is as small as possible, and a large amount of oxidation is avoided. Pure aluminum and Al-10Mn and Al-10Si intermediate alloy are immersed in molten aluminum, so that the manganese and the silicon are in contact with air as little as possible, and oxidation is avoided.

(3) And (3) after the large Al-10Mn intermediate alloy and the Al-10Si intermediate alloy added in the step (2) and pure are completely melted, covering pure copper and small broken pieces of Al-10Mn intermediate alloy and Al-10Si intermediate alloy which are small in weighing and difficult to be added individually by individuals by using aluminum foils, and adding the pure copper and the small broken pieces of Al-10Mn intermediate alloy and Al-10Si intermediate alloy. The aluminum foil and Al-10Mn and Al-10Si intermediate alloy blocks wrapped by the aluminum foil are sunk into molten aluminum by utilizing the higher density of pure copper, so that the alloy wrapped by the aluminum foil is prevented from floating and contacting with air.

(4) After the alloy is completely melted, hexachloroethane is added for refining and dehydrogenation, the addition amount of hexachloroethane is 0.3-0.8 percent, preferably 0.5 percent, based on the total mass of the melt, and the hexachloroethane is added in two times, so that the reaction is more sufficient and thorough, and a better deslagging effect is achieved.

(5) Under the laboratory condition, the crucible used for smelting is a large crucible capable of containing at least 5kg of raw materials, the larger the batch production is, the better the batch production is (the larger the crucible is, the better the slag removal effect is), after hexachloroethane is added, argon can be added to be introduced for further dehydrogenation and slag removal. After the air is introduced, the scum in the alloy liquid floats on the surface of the alloy liquid along with the introduced gas, after the scum is removed, the alloy liquid in the large crucible is transferred to a small crucible for casting, and before the small crucible is used, the alloy liquid is preheated to 720 ℃ in a furnace to prevent the alloy liquid from being condensed too fast. And (3) fixing the small crucible on the tilting casting equipment, matching with the tilting casting mold, and performing tilting casting to obtain an alloy ingot.

(6) And (3) carrying out heat treatment on the obtained alloy ingot, and carrying out solid solution at 520 ℃ for 12h + aging at 140 ℃ for 12h according to the experiment result, wherein the obtained alloy has the highest tensile strength and the highest elongation.

In the smelting process, silicon and manganese are added in a mode of intermediate alloy, and copper is added in a mode of pure copper. Because the specific surface area of powder and the like is too large, the oxidation and deterioration are serious in the adding process, and the adding of the intermediate alloy requires a large block. And because the melting points of pure manganese and pure silicon are too high, in order to avoid the problems of segregation caused by too much low-temperature phase, serious burning loss under high-temperature condition and the like, Al-10Mn is a better alloy by observing Al-Mn and Al-Si phase diagrams. The low-temperature phase variety of the Al-Si phase diagram is few, the problem caused by excessive low-temperature phase variety does not need to be considered, experiments show that pure copper can be melted in aluminum liquid at about 720 ℃, and large burning loss can not be caused, so in order to avoid the problems of difficult component determination and segregation caused by secondary forming, the copper element directly uses pure copper, and does not use industrially produced Al-20Cu, Al-50Cu and the like. Hexachloroethane is added in the later stage of the smelting process as a metal refining agent to play a role in removing slag and dehydrogenating.

The invention designs the formula of the component alloy aiming at a smelting casting method, and the component alloy is assisted with a forming process of tilting casting, so that the qualified automobile structural part material can be obtained. Compared with the existing method, the alloy has the greatest advantages of easy obtaining mode of alloy raw materials, few raw material types, low cost and high strength, belongs to heat-treatable alloys, and has further potential of excavation and development. And the forming mode of the alloy billet can ensure the alloy quality and is easy to form.

Pure aluminum is added into the alloy for melting in the casting process, and after the aluminum liquid is completely melted, the intermediate alloy and the pure copper are added to be completely immersed into the aluminum liquid, so that the problems of oxidation and the like caused by contact between the intermediate alloy and the air are avoided. After the alloy is completely melted, hexachloroethane is added for refining and dehydrogenation, and oxidation slag generated after hexachloroethane is added is stripped. Then argon is introduced by a graphite carbon rod which is infusible at 730 ℃, and slag is further removed. And (5) removing slag, preserving heat and forming.

Drawings

FIG. 1 is a microstructure view of an alloy that has not been heat treated.

FIG. 2 is a microstructure diagram of an alloy subjected to only solution heat treatment, under the conditions: keeping the temperature at 520 ℃ for 12 h.

FIG. 3 is a microstructure of an alloy after solution and aging, with the following conditions: keeping the temperature at 520 ℃ for 12 h. After the quenching is finished, artificial aging is immediately carried out at 140 ℃ for 12 h.

Detailed Description

The technical solution of the present invention is further described below with reference to the alloy microstructure diagram of the drawings, including but not limited to, the technical solution of the present invention is covered by the scope of the present invention, and all equivalent substitutions, modifications and alterations to the alloy composition and the forming solution of the present invention can be made without departing from the spirit and scope of the present invention.

The present embodiment provides an alloy composition formula. The alloy is characterized in that no refiner is added, no magnesium element is added, and the cast state and the heat treatment state are compared only under the condition of the aluminum-copper-manganese-silicon four components, so that the potential energy of the alloy is excavated and developed as much as possible, and the alloy becomes the maximum mechanical property developed on the basis of adding the refiner, magnesium and other reinforcers.

The function of each component is as follows: the aluminum copper is a basic component of the cast aluminum copper alloy, and the manganese and the silicon are used for neutralizing the inevitable doping of iron in the industrial pure aluminum, so that the harm caused by the existence of the needle-shaped iron-rich phase is avoided. The addition of silicon reduces or avoids heat cracking, improves casting performance, and plays a role in improving tensile strength. Because the manganese mainly neutralizes impurity iron, the actual amount is not excessive, and the amount of the manganese element is mainly determined according to the source of the aluminum ingot. If the quality of the aluminum ingot is poor, the manganese content is properly increased, and if the quality of the prepared aluminum ingot is good and the purity is high, the manganese content can be reduced to 0.1 percent or below. According to the prediction of experience, the manganese content is not more than 1%, and the composition proportion is considered that the manganese element can not be added under the ideal condition, namely the condition that the amount of iron impurities in the raw materials is 0, but the manganese element can hardly be added under the actual condition, so that the amount of the manganese element is 0.05-1.0%.

Example 1.

A high-strength cast aluminum alloy comprises the following alloy elements in percentage by mass: copper: 5.0%, silicon: 1.0%, manganese: 1.0%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum.

The preparation method of the alloy comprises the following steps.

(1) Part of the pure aluminum was added and the pure aluminum melted at 740 ℃.

(2) Firstly adding large intermediate alloy blocks of Al-10Mn and Al-10Si, and then adding pure aluminum blocks; the pure aluminum block body should be used in a larger volume as much as possible, and the intermediate alloy block body should be used in a larger volume but in a flatter shape, so that the aluminum ingot can press the intermediate alloy in the liquid more easily, and the intermediate alloy is prevented from floating on the surface of the liquid and contacting with the air to cause oxidation.

(3) Cutting pure copper into 0.5-1cm³Square blocks, small fragments of Al-10Mn and Al-Si intermediate alloy are wrapped by aluminum foil (calculated in the mass of pure aluminum) and put into aluminum liquid.

(4) After the alloy is completely melted, hexachloroethane is added for refining and dehydrogenation, the addition amount of hexachloroethane is 0.5 percent based on the total mass of the melt, and the hexachloroethane is added twice, so that the reaction is more sufficient and thorough, and a better slag removal effect is achieved.

(5) The raw materials are put into a crucible for smelting, argon is introduced into the smelted alloy liquid for 20 minutes, and further deslagging and dehydrogenation are carried out. After argon gas is introduced, purified alloy liquid is transferred to a small tilting casting crucible from a large melting crucible for smelting, the liquid level of the metal liquid flows as stably as possible in the transfer process, transition flow and turbulence are avoided as far as possible, and after the transfer, the small melting crucible containing the metal liquid is placed on a tilting casting device and matched with a corresponding die, so that an alloy ingot can be cast.

And (3) comparing the mechanical properties of the gravity casting alloy with that of the tilting casting alloy: the tensile strength of the alloy in the gravity casting cast state can reach 180Mpa, and the tensile strength of the tilt casting alloy can reach 200 Mpa. The elongation of the alloy obtained by the two casting modes is not greatly different, and the elongation is about 5.5 percent.

(6) The alloy is subjected to solid solution at 520 ℃ for 12h, the tensile strength of the alloy can reach 380MPa to the maximum after aging at 140 ℃ for 12h, and the elongation can reach 12.5%.

Example 2.

The alloy was prepared in the same manner as in example 1, and the alloy components were copper 5.0%, silicon: 1.0%, manganese: 0.05%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum.

And (3) comparing the mechanical properties of the gravity casting alloy with that of the tilting casting alloy: the tensile strength of the alloy in a gravity casting state can reach 175MPa, and the tensile strength of the tilt casting alloy can reach 203 MPa. The elongation of the alloy obtained by the two casting modes is not greatly different, and the elongation is about 5.8 percent.

The alloy is subjected to solid solution at 520 ℃ for 12h, the tensile strength of the alloy can reach 388Mpa at the highest after aging at 140 ℃ for 12h, and the elongation can reach 13.3%.

Example 3.

The alloy was prepared in the same manner as in example 1, and the alloy components were copper 5.0%, silicon: 3.0%, manganese: 0.3%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum.

And (3) comparing the mechanical properties of the gravity casting alloy with that of the tilting casting alloy: the tensile strength of the alloy in a gravity casting state can reach 188Mpa, and the tensile strength of the tilt casting alloy can reach 205 Mpa. The elongation of the alloy obtained by the two casting modes is not greatly different, and the elongation is about 3.2%.

The alloy is subjected to solid solution at 520 ℃ for 12h, the tensile strength of the alloy can reach 350MPa to the maximum after aging at 140 ℃ for 12h, and the elongation can reach 9.2%.

Example 4.

The alloy was prepared in the same manner as in example 1, and the alloy components were 4.6% copper, silicon: 1.0%, manganese: 0.3%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum.

And (3) comparing the mechanical properties of the gravity casting alloy with that of the tilting casting alloy: the tensile strength of the alloy in a gravity casting state can reach 187Mpa, and the tensile strength of the tilt casting alloy can reach 208 Mpa. The elongation of the alloy obtained by the two casting modes is not greatly different, and the elongation is about 6.3%.

The alloy is subjected to solid solution at 520 ℃ for 12h, the tensile strength of the alloy can reach 375Mpa at most after aging at 140 ℃ for 12h, and the elongation can reach 12.7%.

Example 5.

The alloy was prepared in the same manner as in example 1, and the alloy components were 4.0% copper, silicon: 0.2%, manganese: 0.05%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum.

And (3) comparing the mechanical properties of the gravity casting alloy with that of the tilting casting alloy: the tensile strength of the alloy in a gravity casting state can reach 166Mpa, and the tensile strength of the tilt casting alloy can reach 192 Mpa. The elongation of the alloy obtained by the two casting modes is not greatly different, and the elongation is about 6.7%.

The alloy is subjected to solid solution at 520 ℃ for 12h, the tensile strength of the alloy can reach 355Mpa at most after aging at 140 ℃ for 12h, and the elongation can reach 14.2%.

Example 6.

The alloy was prepared in the same manner as in example 1, and the alloy components were 5.5% copper, silicon: 3.0%, manganese: 1.0%, impurity iron: less than or equal to 0.1 percent and the balance of aluminum.

And (3) comparing the mechanical properties of the gravity casting alloy with that of the tilting casting alloy: the tensile strength of the alloy in a gravity casting state can reach 189Mpa, and the tensile strength of the tilt casting alloy can reach 215 Mpa. The elongation of the alloy obtained by the two casting modes is not greatly different, and the elongation is about 3.3%.

The alloy is subjected to solid solution at 520 ℃ for 12h, the tensile strength of the alloy can reach 395MPa to the maximum after aging at 140 ℃ for 12h, and the elongation can reach 11.3%.

The above examples are only partial examples, and from the overall experimental tests of the present invention, the tensile strength of the alloy increases with the increase of the silicon content, and the elongation rate decreases with the increase of the silicon content. The tensile strength and the elongation are not necessarily related to manganese, the manganese is mainly determined according to the source of the aluminum ingot, and is not more than 1.0 percent at most, the high-purity aluminum ingot is recommended to be maintained at about 0.3 percent, and if the quality of the aluminum ingot is not good, the manganese content is properly increased and can be maintained at about 0.8 percent. The mechanical property of the alloy is optimal when the copper element is between 4.6 and 5.0 percent, the alloy shows certain brittleness compared with the recommended composition (4.6 to 5.0 percent) when the nominal composition of the alloy is between 5.0 and 5.5 percent, and the alloy is slightly softer than the recommended composition and the elongation is increased when the nominal composition of the alloy is between 4.0 and 4.5 percent.

The microstructure of the alloy under the metallographic microscope does not change much in the above range, and the analysis is as follows.

(1) Before the heat treatment, the solution aging was not performed, and the microstructure of the alloy was shown by using aluminum as a base, 5.0% of Cu, 0.8% of Mn, 0Si (FIG. 1a, hereinafter referred to as 0 Si) as alloying elements, and 5.0% of Cu, 0.8% of Mn, and 1.0% of Si (FIG. 1b, hereinafter referred to as 1 Si) as alloying elements.

As shown in the microstructure diagram of the alloy of fig. 1. In which, in FIG. 1a, no silicon element is added, and in FIG. 1b, 1% of silicon element is added. It can be clearly observed in the figure that the grain boundary of the alloy microstructure has more cullet-like structures, and the front and rear components of the alloy are only silicon different, so that silicon is enriched at the grain boundary, a certain filling effect is provided for the pores of the alloy, and the tensile strength is increased, that is, the alloy containing silicon element (the figure only takes 1Si alloy as an example, the content of silicon is within the range stated in the invention, and the structure diagram is basically consistent) has higher mechanical properties. Under an electron microscope, it can be observed that white bright spots in 1Si substantially disappear and are converted into a network structure, especially beta-Al formed by impurity iron having a large influence on the alloy performance, compared with a white bright spot-shaped structure in 0Si_nFe forms alpha-Al (Mn, Fe) Si with small influence on the alloy, thereby improving the mechanical property of the alloy. FIGS. 1c and 1d are electron microscopic structural views of 0Si and 1Si alloys, respectively. Therefore, the alloy added with the silicon element has higher development potential.

(2) The microstructure diagrams of the alloy samples obtained by subjecting an aluminum base alloy to solution treatment and aging after solution treatment are shown in FIGS. 2a and 2b, respectively, by taking an alloy containing 5.0% Cu, 0.8% Mn and 1.0% Si as alloying elements as an example.

FIG. 2a shows the microstructure of the alloy after solution heat treatment but without ageing, it being observed that the grain boundaries in FIG. 1b have disappeared and the alloy has essentially formed one piece. Since the grain boundaries of the alloy disappear, the alloy is no longer suitable for the addition of grain refiners. However, the river-like speckles in the tissue and the matrix are distributed in a mutually spaced manner, and after aging, as shown in FIG. 2b, the microstructure layout is substantially the same, but the white microstructure distribution is more uniform and the single microstructure is finer. The strength of the alloy is further improved.

(3) Taking an alloy with an alloy composition of an aluminum matrix, alloy elements of 5.0% of Cu, 0.8% of Mn and 1.0% of Si as an example, a tensile fracture pattern of a sample in an as-cast state and a sample subjected to solid solution and aging is shown in a figure 3a, which is a tensile fracture pattern of the as-cast alloy without heat treatment, and a figure 3b, which is a tensile fracture pattern of the alloy subjected to solid solution at 520 ℃ for 12h and aging at 140 ℃ for 12 h.

From FIG. 3a, it can be seen that the alloy is not heat-treated, and the tensile fracture shows complete crystal grains and lamellar tearing edges, so that it can be judged that the fracture mechanism of the alloy is mainly fracture along the crystal (brittle fracture), and the elongation and tensile strength of the alloy are poor. In fig. 3b, the small grains and lamellar tearing edges are no longer visible, but are dominated by honeycomb dimples, which shows that the alloys after heat treatment are dominated by ductile fracture. Because the grain boundary disappears, the situation that the alloy mainly has brittle fracture does not occur any more, and the performance of the alloy is improved.

Claims

1. The high-strength cast aluminum alloy is characterized by comprising the following alloy elements in percentage by mass: 4.0 to 5.5 percent of copper, 0.2 to 3.0 percent of silicon, 0.05 to 1.0 percent of manganese, less than or equal to 0.1 percent of impurity iron and the balance of aluminum.

2. The method of producing a high strength cast aluminum alloy according to claim 1, comprising the steps of:

(1) adding part of pure aluminum, and smelting at the temperature of 720-750 ℃;

(2) respectively adding large intermediate alloy blocks of Al-10Mn and Al-10Si, and then adding pure aluminum blocks to ensure that all raw materials are immersed in the aluminum liquid;

(3) after the large raw materials Al-10Mn, Al-10Si alloy and pure aluminum blocks in the step (2) are completely melted, wrapping pure copper and small broken pieces Al-10Mn and Al-10Si intermediate alloy which are small in weighing and difficult to be added individually by using aluminum foil for adding;

(4) after all the alloys in the step (3) are completely melted, adding hexachloroethane according to the total mass of the melt of 0.3-0.8% for refining, dehydrogenating, slagging off and performing tilting casting to obtain alloy ingots;

(5) solid solution is carried out for 12h at 520 ℃ and aging is carried out for 12h at 140 ℃.

3. The method of claim 2, wherein the hexachloroethane is added in an amount of 0.5% by weight based on the total mass of the melt in the step (4).