A high-strength foam aluminum alloy casting method

Abstract

The invention discloses a high-strength foam aluminum alloy casting method, comprising the following steps: S1, degreasing and sensitizing graphene, then placing the graphene in a chemical nickel plating solution for chemical nickel plating, and drying to obtain chemical nickel-plated graphene nanosheets; S2, heating and melting pure aluminum and Al-20Si in a furnace, and continuously keeping the aluminum melt warm and stirring at a temperature of 750-780°C for 30-40 minutes; S3, cooling the aluminum melt in step S2 to 700-710°C, adding the chemical nickel-plated graphene nanosheets, a tackifier, and a foaming agent, stirring, and water-cooling to obtain a foam aluminum alloy blank; and S4, mechanically processing the foam aluminum alloy blank, and then performing a solid solution treatment at a high temperature of 560-573°C, and furnace cooling to obtain the high-strength foam aluminum alloy. In this method, graphene needs to be surface-plated with Ni in advance, which can effectively pin dislocations and grain boundaries and hinder their movement; the graphene-enhanced foam Al-Si alloy is directly subjected to high-temperature solid solution treatment and furnace cooling without rapid quenching, which can reduce the damage to the pore structure caused by the shrinkage stress caused by quenching.

Description

Technical Field

[0001] The invention relates to the technical field of metal alloy materials, and in particular to a high-strength foam aluminum alloy casting method. Background Art

[0002] Aluminum foam is a lightweight, porous material composed of pores and an aluminum skeleton. Its numerous voids provide it with numerous excellent functional properties, such as lightness, sound insulation, heat insulation, and impact energy absorption. However, the presence of numerous voids in the foam results in a generally low strength (typically less than 10 MPa), significantly limiting its expanded applications.

[0003] At present, there are two main ways to enhance aluminum foam. One is to improve the overall strength by compounding materials with higher density, such as compounding aluminum alloy plates on the surface of aluminum foam. However, this will result in a significant overall weight increase and fail to meet the requirements of light weight. The other is to further improve the mechanical properties of the aluminum foam alloy matrix through matrix alloying and heat treatment. However, due to the presence of pores, the thermal conductivity of aluminum foam is low. Simply replacing the matrix with traditional high-strength aluminum alloy and combining it with solid solution and aging treatment is difficult to achieve an effective improvement in the performance of large-scale aluminum foam alloys, and will lead to uneven performance of the foam material. Therefore, it is necessary to develop a reinforced casting method and heat treatment process for aluminum foam materials, so as to further uniformly improve the strength of aluminum foam while ensuring the porosity of aluminum foam alloys and expand its application range. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high-strength foam aluminum alloy casting method. By adding nickel-plated nanographene sheets during the foam aluminum alloy casting production process, the porosity of the foam aluminum alloy is ensured while avoiding the negative impact of the introduction of metallic nickel on the cast foam aluminum alloy, thereby achieving a significant improvement in the strength of the foam aluminum alloy.

[0005] To achieve the above object, the present invention provides a high-strength foam aluminum alloy casting method, comprising the following steps:

[0006] S1, after degreasing and sensitizing the graphene, placing it in a chemical nickel plating solution for chemical nickel plating, and obtaining chemical nickel-plated graphene nanosheets after drying;

[0007] S2. Heat and melt pure aluminum and Al-20Si in a furnace, and continue to stir the aluminum melt at a temperature of 750-780°C for 30-40 minutes;

[0008] S3, cooling the aluminum melt of step S2 to 700-710° C., adding a tackifier, stirring, then adding chemically nickel-plated graphene nanosheets and a foaming agent, stirring, and water-cooling to obtain a foamed aluminum alloy billet;

[0009] S4, machining the foamed aluminum alloy blank, performing a solution treatment at a temperature of 560-573° C., keeping the temperature for 12-15 hours, and cooling with the furnace to obtain a high-strength foamed aluminum alloy;

[0010] The mass proportion of silicon in the high-strength foamed aluminum alloy is 8.5% to 10.5%, and the mass proportion of graphene is 0.3% to 0.5%.

[0011] Preferably, in step S1, the graphene is kept at 400-480° C. and burned for 35-45 minutes for degreasing, and then the graphene is immersed in a chemical nickel plating activator and ultrasonically stirred for 5-10 minutes; the treated graphene is then placed in a chemical nickel plating solution, the plating solution is heated to 40-50° C., ultrasonically stirred for 15-20 minutes, and dried for use.

[0012] Nickel plating on the surface of graphene nanosheets can effectively prevent the oxidation loss of graphene nanosheets caused by high-temperature aluminum liquid; at the same time, surface nickel plating increases the wettability of graphene nanosheets and aluminum liquid, which is conducive to the uniform dispersion of graphene nanosheets.

[0013] Preferably, in step S3, the viscosity enhancer is fly ash, and the foaming agent is titanium hydride or calcium carbonate.

[0014] Preferably, in step S3, the chemically nickel-plated graphene nanosheets, the tackifier and the foaming agent are all wrapped in aluminum foil and then added to the aluminum melt, wherein the chemically nickel-plated graphene nanosheets and the foaming agent are added to the aluminum melt together.

[0015] The chemically nickel-plated graphene nanosheets and foaming agent are wrapped with aluminum foil and then put into the aluminum liquid, and are stirred at high speed at the same time, which is conducive to the graphene nanosheets and foaming agent quickly sinking below the liquid surface of the aluminum liquid and being fully dispersed in the aluminum melt; the graphene nanosheets evenly dispersed in the aluminum melt matrix can effectively pin grain boundaries and dislocations during subsequent deformation, hinder grain boundary slip and dislocation movement, and effectively improve the matrix strength.

[0016] Preferably, in step S3, the mass ratio of the chemically nickel-plated graphene nanosheets, the tackifier and the foaming agent is 1-1.1:2-2.2:0.5-0.7.

[0017] Preferably, in step S3, the stirring speed is 100-120 r / min, the stirring time after adding the viscosity enhancer is 100-150 s, and the stirring time after adding the chemically nickel-plated graphene nanosheets and the foaming agent is 10-15 s.

[0018] In the high-strength foam aluminum alloy casting method provided by the present invention, graphene nickel plating is of great significance for the protection, uniform dispersion and mechanical property improvement of graphene, but the nickel metal element introduced therein may still have an adverse effect on the performance of the foam aluminum alloy: the interface between the Ni-plated layer on the graphene surface and the aluminum substrate mainly includes Ni, Al interface diffusion and Al, Ni reaction to form Al3Ni intermetallic compounds, among which the Ni, Al bonding interface formed by the diffusion reaction has high strength, while the Al3Ni intermetallic compounds generated by the reaction have an adverse effect on the interface bonding strength, and excessive Al3Ni intermetallic compounds will significantly reduce the strength of the foam aluminum alloy. The method of the present invention adopts 560-573 ℃ high temperature solution treatment. The higher temperature heating treatment is conducive to the diffusion of Ni atoms in the Ni-plated layer on the surface of the graphene into the aluminum matrix, prompting more Ni atoms to be dissolved in the aluminum matrix and improving the Ni-Al interface bonding strength; while performing a long time (12-15h) of high temperature insulation treatment can effectively spheroidize eutectic silicon, and is also conducive to the diffusion and dissolution of Al3Ni intermetallic compounds. Compared with short-term insulation, Al3Ni at the interface junction is less and more discontinuous. Therefore, the long-term high temperature solution treatment combined with the Ni-plated graphene layer can effectively improve the compressive strength of the overall foam aluminum alloy. In addition, although the solubility of C in Ni is extremely low, under specific environments, such as high temperature environment, ultrasonic vibration, etc., C and Ni atoms can also undergo appropriate interface diffusion, further improving the bonding strength of the graphene layer and the Ni layer. Compared with the solid solution treatment temperature of 535°C for ZL1xxx alloy specified in the current standard GB / T1173-2013, the solid solution treatment in the method of the present invention is higher. During the high-temperature heat preservation treatment process, it is more conducive to the diffusion and dissolution of silicon atoms into the aluminum matrix. At the same time, silicon atoms are continuously precipitated from the aluminum matrix and reach equilibrium at a certain temperature. Through the reciprocating process of dissolution and precipitation, silicon particles gradually become smaller and spheroidized, and the rod-shaped eutectic silicon becomes discontinuous, which has the effect of refining and spheroidizing the eutectic silicon, and further enhances the comprehensive performance of the foam aluminum alloy.

[0019] The above solution of the present invention has the following beneficial effects:

[0020] The high-strength aluminum foam alloy preparation method provided by the present invention achieves a significant improvement in strength by adding nano-graphene sheets to a matrix of an Al-Si foam alloy and performing subsequent heat treatment: the nano-graphene is surface-plated with Ni in advance to avoid oxidation loss caused by contact between the graphene and high-temperature aluminum liquid; at the same time, the wettability of the graphene surface and the aluminum liquid is increased, which is more conducive to the uniform distribution of the graphene in the aluminum melt, effectively pinning dislocations and grain boundaries and hindering their movement, thereby significantly improving the strength of the aluminum foam alloy.

[0021] The method of the present invention performs high-temperature solution treatment on a graphene-enhanced foamed Al-Si alloy blank, and performs furnace cooling without rapid quenching, thereby minimizing the damage to the pore structure caused by shrinkage stress caused by quenching and preventing destructive damage to the pore wall. The method adopts a solution treatment temperature of 535°C for the ZL1xxx alloy, which is higher than that specified in GB / T 1173-2013, to promote the diffusion of Ni atoms in the Ni plating layer into the aluminum matrix, thereby further improving the interface bonding strength between Ni and Al, reducing the generation of brittle Al3Ni intermetallic compounds by the reaction of Al and Ni, and minimizing the problem of reduced strength of the foamed aluminum alloy caused by the introduction of nickel elements by nickel plating. At the same time, the method performs a long-term (12 to 15 hours) high-temperature heat preservation treatment, which, while spheroidizing eutectic silicon, is also conducive to the dissolution and diffusion of the Al3Ni intermetallic compound, thereby reducing the adverse effect on interface bonding.

[0022] In summary, the present invention, through surface-coated Ni-graphene reinforcement and subsequent high-temperature solution treatment, can produce a high-strength aluminum foam alloy while maintaining lightweight properties. When the porosity of the aluminum foam alloy is controlled at 80%, the compressive strength can reach 22.3 MPa, compared to only 10 MPa for conventional aluminum foam with the same porosity. This 120% increase in strength significantly expands the application range of aluminum foam alloys and has great potential for promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is a microstructure diagram of the high-strength aluminum foam alloy Ni-plated graphene sheet prepared in Example 1 of the present invention;

[0025] Figure 2 This is a microstructure diagram of the high-strength aluminum alloy foam graphene distributed in the Al-Si matrix prepared in Example 1 of the present invention;

[0026] Figure 3 This is a microstructure diagram of the eutectic silicon of the high-strength foam aluminum alloy prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0028] The following examples are provided to illustrate the present invention but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0029] The nanographene sheets used in the present invention are produced by Nanjing Xianfeng Nanomaterial Technology Co., Ltd., model number XF021 7440-44-0;

[0030] The chemical nickel plating activator was produced by Guangzhou Yishun Chemical Co., Ltd., model number Q / YS.602-2;

[0031] The chemical nickel plating solution was produced by Guangdong Bigley Technology Co., Ltd., model number Ni-809.

[0032] Example 1

[0033] In this embodiment, the mass percentage of silicon in the foam aluminum alloy is 10%, and the mass percentage of graphene nanosheets in the foam aluminum alloy is 0.35%. The specific preparation method is as follows:

[0034] (1) The graphene nanosheets were kept at 450°C for 35 minutes, then degreased and air-cooled; the degreased graphene was immersed in a chemical nickel plating activator and ultrasonically vibrated for 5 minutes; the treated graphene was placed in a chemical nickel plating solution, the plating solution was heated to 40°C, ultrasonically vibrated and stirred for 15 minutes, and then taken out and dried to obtain chemical nickel-plated graphene nanosheets.

[0035] (2) Pure aluminum and Al-20Si were heated and melted in a furnace in a mass percentage of 1:1, and the aluminum melt was kept warm and melted at 760°C and stirred for 30 minutes. When the aluminum melt was cooled to 705°C, 0.7% fly ash was added to the aluminum melt and stirred at a stirring speed of 100 r / min for 120 seconds. Then, 0.35% graphene nanosheets and 0.25% calcium carbonate were mixed evenly, wrapped with aluminum foil, and added to the aluminum melt while stirring at a stirring speed of 100 r / min for 11 seconds. The mixture was then water-cooled to obtain a foamed aluminum alloy blank.

[0036] (3) The foamed aluminum alloy blank was machined, solution treated at 570° C., kept warm for 12 h, and then furnace cooled to obtain a high-strength foamed aluminum alloy with a porosity of 80±2%.

[0037] Figure 1 This is a microstructure image of the Ni-plated graphene sheets in the high-strength aluminum foam alloy produced in this example. As can be seen, the graphene sheets are approximately 4-5 nm wide. Although the solubility of carbon in nickel is extremely low, some atomic diffusion still occurs at the interface between the carbon and nickel layers at high temperatures. There are no obvious cracks between the Ni-plated layer and the graphene, indicating good bonding between the two layers. Figure 2 The microstructure of the high-strength aluminum foam alloy graphene-reinforced matrix distributed in the Al-Si matrix prepared in this embodiment. Figure 2 The black arrows in the middle indicate Ni-plated graphene sheets. It can be seen that most of the graphene is distributed at grain boundaries or subgrain boundaries. There are no obvious cracks, holes or intermetallic compounds between the graphene sheets and the aluminum matrix, indicating that the Ni element diffuses well into the aluminum matrix. In the subsequent load-bearing process, these graphene can effectively hinder dislocations and grain boundary slip, greatly improving the strength of the foam aluminum alloy. Figure 3 This is a microstructure diagram of eutectic silicon in a high-strength aluminum foam alloy. It can be seen that the eutectic silicon is spherical in shape and very small, approximately 5 to 8 μm in size. No large rod-shaped eutectic silicon particles are found in the matrix. This demonstrates that high-temperature solution treatment has a positive effect on the C / Ni and Ni / Al diffusion layers and the spheroidization of the eutectic silicon.

[0038] Example 2

[0039] In this embodiment, the mass percentage of silicon in the foam aluminum alloy is 8.5%, and the mass percentage of graphene nanosheets in the foam aluminum alloy is 0.3%. The specific preparation method is as follows:

[0040] (1) The graphene nanosheets were kept at 400°C for 35 minutes, then degreased and air-cooled; the degreased graphene was immersed in a chemical nickel plating activator and ultrasonically vibrated for 5 minutes; the treated graphene was placed in a chemical nickel plating solution, the plating solution was heated to 40°C, ultrasonically vibrated and stirred for 20 minutes, and then taken out and dried to obtain chemical nickel-plated graphene nanosheets.

[0041] (2) Pure aluminum and Al-20Si were heated and melted in a furnace at a mass percentage of 2.3:1.7, and the aluminum melt was kept warm and melted at 780°C and stirred for 30 minutes. When the aluminum melt was cooled to 710°C, 0.62% fly ash was added to the aluminum melt and stirred at a stirring speed of 100 r / min for 130 seconds. Then, 0.3% graphene nanosheets and 0.18% calcium carbonate were mixed evenly, wrapped with aluminum foil, and added to the aluminum melt while stirring at a stirring speed of 100 r / min for 11 seconds. The mixture was then water-cooled to obtain a foamed aluminum alloy blank.

[0042] (3) The foamed aluminum alloy billet is machined, solution treated at 560° C., kept warm for 15 h, and then furnace cooled to obtain a high-strength foamed aluminum alloy with a porosity of 78%±2.

[0043] Comparative Example 1

[0044] Preparation of conventional aluminum foam

[0045] The specific preparation method of the comparative example foam aluminum is:

[0046] 99.98% pure aluminum was melted in a furnace at 715°C and stirred for 30 minutes. 1.1% fly ash was added to the aluminum melt and stirred at a speed of 100 r / min for 120 seconds. 0.25% titanium hydride was then added to the aluminum melt and stirred at a speed of 100 r / min for 12 seconds. The mixture was then water-cooled to produce a foamed aluminum billet. The foamed aluminum alloy billet was then machined to obtain a foamed aluminum with a porosity of 80±2%.

[0047] Comparative Example 2

[0048] The specific preparation method is the same as that of Example 1, except that the solution treatment temperature is set to 535° C., which is the solution treatment temperature of the ZL1xxx alloy specified in GB / T 1173-2013, to prepare a foamed aluminum alloy material with a porosity of 80%.

[0049] Comparative Example 3

[0050] According to prior art reports (Compression properties of cellular AlCu5Mn alloy foams with wide range of porosity. J. Mater. Sci., 2009, 44: 5552-5556.), a foamed AlCu5Mn alloy with a porosity of about 80% was prepared.

[0051] Experimental Example 1

[0052] Compression specimens were cut from the foamed aluminum alloy products obtained in Examples 1 to 2 and Comparative Examples 1 to 3 by wire cutting, and their compressive strength was tested according to GB / T 7314-2017 standard, and their neutral salt spray corrosion performance was tested according to GB / T 10125-2012 standard. The results are shown in Table 1.

[0053] Table 1 Compressive strength test results of different foam aluminum alloy products

[0054]

[0055] *Prepare the samples according to the preparation method in the literature and conduct a uniform comparison of salt spray corrosion performance.

[0056] It can be seen from the results in Table 1 that when the porosity is about 80%, the compressive strength of the foamed aluminum alloy prepared by the method of the present invention reaches more than 22 MPa, and its strength is more than twice the strength of the foamed aluminum prepared by the conventional method (Comparative Example 1). The foamed aluminum alloy prepared by the method of the present invention has significantly improved the compressive strength and salt spray corrosion resistance while ensuring the porosity.

[0057] Comparative Example 2, which uses a ZL1xxx alloy solution treatment temperature of 535°C as specified in GB / T 1173-2013, produces an aluminum foam with a strength that is more than 10% lower than that of Examples 1 and 2. This is primarily due to the high-temperature solution treatment used in the present invention, which allows the Ni atoms in the Ni layer to diffuse into the aluminum matrix, promoting the solution of Ni atoms in the aluminum matrix, further enhancing the Ni-Al interface bonding strength, preventing the Al-Ni reaction from forming Al3Ni intermetallic compounds at the interface layer, and minimizing the problem of reduced aluminum foam strength caused by the introduction of nickel elements during nickel plating.

[0058] The AlCu5Mn aluminum foam alloy prepared in comparative example 3 has a large number of element types and a complex composition, and the Cu-rich phase in the matrix also leads to relatively poor corrosion resistance. Moreover, the strength of the aluminum foam alloy prepared therefrom is still significantly lower than that of the aluminum foam alloys prepared in Examples 1 to 2 of the present invention. This also proves that the high-strength aluminum foam alloy prepared by the method of the present invention can achieve a significant improvement in strength at the same porosity without significantly sacrificing environmental adaptability, and can well expand the application range of the aluminum foam alloy.

[0059] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A high-strength foam aluminum alloy casting method, characterized in that: The steps are: S1, degreasing and sensitizing the graphene and then placing it in a chemical nickel plating solution for chemical nickel plating, and drying to obtain chemical nickel-plated graphene nanosheets; in the step S1, the graphene is kept at 400-480° C. and calcined for 35-45 minutes to degrease, and then the graphene is immersed in a chemical nickel plating activator and ultrasonically stirred for 5-10 minutes; then the treated graphene is placed in a chemical nickel plating solution, the plating solution is heated to 40-50° C., ultrasonically stirred for 15-20 minutes, and dried for standby use; S2. Heat and melt pure aluminum and Al-20Si in a furnace, and continue to stir the aluminum melt at 750-780°C for 30-40 minutes; S3, cooling the aluminum melt of step S2 to 700-710°C, adding a tackifier, stirring, then adding chemically nickel-plated graphene nanosheets and a foaming agent, stirring, and water-cooling to obtain a foamed aluminum alloy billet; in the step S3, the chemically nickel-plated graphene nanosheets, the tackifier, and the foaming agent are all wrapped in aluminum foil and then added to the aluminum melt, wherein the chemically nickel-plated graphene nanosheets and the foaming agent are put into the aluminum melt together; S4, machining the foamed aluminum alloy blank, performing a solution treatment at a temperature of 560-573° C. for 12-15 hours, and cooling the blank in the furnace to obtain a high-strength foamed aluminum alloy; The mass proportion of silicon in the high-strength aluminum foam alloy is 8.5% to 10.5%, and the mass proportion of graphene is 0.3% to 0.5%.

2. The casting method according to claim 1, characterized in that In step S3, the viscosity enhancer is fly ash, and the foaming agent is titanium hydride or calcium carbonate.

3. The casting method according to claim 1, characterized in that In step S3, the mass ratio of the chemically nickel-plated graphene nanosheets, the tackifier, and the foaming agent is 1-1.1:2-2.2:0.5-0.

7.

4. The casting method according to claim 1, wherein: In step S3, the stirring speed is 100-120 r / min, and the stirring time after adding the tackifier is 100-150 s; the stirring time after adding the chemically nickel-plated graphene nanosheets and the foaming agent is 10-15 s.

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