Low temperature aging method to obtain excellent combination of properties of the aluminum matrix and the aluminum / steel interface

Abstract

The application provides a low-temperature aging method for obtaining excellent performance combination of aluminum matrix and aluminum / steel interface, and belongs to the technical field of metal material heat treatment. The method comprises the following steps: firstly, heating a heat treatment furnace to 60-100 DEG C; then, putting aluminum / steel bimetal in a solid solution state into the heat treatment furnace, and keeping heat for 14-20 hours; finally, taking out and air cooling to room temperature to obtain low-temperature aging aluminum / steel bimetal. In the method, the low-temperature condition can slow down the deterioration of the aluminum / steel bimetal interface bonding quality in the aging process, and can induce the precipitation of the second phase in the supersaturated solid solution matrix of the bimetal aluminum alloy side, produce the precipitation strengthening effect, and improve the mechanical properties of the aluminum alloy side. The application has the advantages of simple and stable process, convenient operation, low energy consumption and strong applicability, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for metallic materials, and in particular to a low-temperature aging method for obtaining an excellent combination of properties of an aluminum matrix and an aluminum / steel interface. Background Technology

[0002] Aluminum / steel bimetallic composites combine the low specific gravity, good corrosion resistance, and good castability of aluminum alloys with the high strength and wear resistance of steel, showing great promise for lightweighting automotive engine cylinder liners. [Article 1: Ma Jingbo. Study on the microstructure and properties of the liquid-solid composite interface of aluminum / steel bimetals. Henan University of Science and Technology, 2022.]. Solid-liquid forming (composite casting method) is a simple and economical method for preparing aluminum / steel bimetals. For aluminum / steel bimetals after solid-liquid forming, it is necessary to ensure the bonding quality of the aluminum / steel interface and to release the age hardening potential of the aluminum matrix through heat treatment to optimize the mechanical properties of the aluminum matrix. Heat treatment processes affect the morphology and size of eutectic silicon and Al2Cu intermetallic compounds in aluminum-silicon alloys, thereby altering their mechanical properties [Article 2: Costa AT, Dias M, Gomes GL, et al. Effect of solution time in T6 heat treatment on microstructure and hardness of a directionally solidified Al–Si–Cu alloy[J]. Journal of Alloys and Compounds, 2016, 683.]. Different heat treatment processes can break lath-like eutectic Si particles into smaller segments, and with prolonged heat treatment, the eutectic Si particles become more rounded. [Article 3: Li K, Zhang J, Chen X, et al. Microstructure evolution of eutectic Si in Al-7Si binary alloy by heat treatment and its effect on enhancing thermal conductivity[J]. Journal of Materials Research and Technology, 2020, 9(4).]. During the solution treatment process, coarse Al₂Cu dissolves into the aluminum matrix, resulting in a supersaturated solid solution after quenching. In the subsequent aging process, Al₂Cu precipitates as fine particles, improving the mechanical strength of the aluminum matrix through precipitation hardening. Existing research typically employs medium-to-high temperature heat treatment of bimetallic materials. The commonly used process involves solution treatment at 500°C, water quenching at 80°C, and aging at 160°C. However, because Al atoms diffuse faster than Fe atoms in the intermetallic phase, vacancies form at the bimetallic interface. Furthermore, excessively high aging temperatures lead to elemental segregation in the Al matrix, causing a localized decrease in the hardness of the aluminum matrix.[Article 4: Cong W, Zhaojie W, Hong X, et al. Microstructure and age hardening behavior of Al / Fe bimetal prepared by one-step compound casting[J]. Journal of Alloys and Compounds, 2022, 905.]. Jiang et al. applied aging at 165℃ after solution treatment at 500℃, resulting in an increase in the thickness of the interfacial reaction layer. The brittle compounds led to a decrease in the bonding performance of the bimetallic interface. [Article 5: Wenming J, Guangyu L, Yao W, et al. Effect of heat treatment on bonding strength of aluminum / steel bimetal produced by a compound casting[J]. Journal of Materials Processing Tech., 2018, 258.]. Furthermore, excessive heat treatment not only alters the interfacial microstructure but also causes the oxide layer to extend at the interfacial transition layer, significantly weakening the bonding strength of the aluminum / steel bimetal. Therefore, while conventional aging heat treatment methods induce precipitation strengthening of the aluminum matrix, they inevitably lead to a decline in the bonding quality of the aluminum / steel interface. There is an urgent need to find new heat treatment methods that can improve the mechanical properties of the aluminum matrix while ensuring the bonding performance of the aluminum / steel interface. Summary of the Invention

[0003] This invention provides a low-temperature aging method for obtaining a combination of excellent properties between an aluminum matrix and an aluminum / steel interface. The aluminum / steel bimetal treated by this method not only improves the mechanical properties of the aluminum matrix but also ensures good interfacial bonding strength, guaranteeing the excellent overall performance of the bimetal.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] A heat treatment method for improving the hardness of aluminum / steel bimetallic aluminum matrix and ensuring interfacial bonding performance through low-temperature aging involves performing aging heat treatment on the aluminum / steel bimetallic matrix at low temperatures using heat treatment furnaces such as oil bath furnaces and salt bath furnaces. The low-temperature aging process promotes the precipitation and spheroidization of the Si phase in the aluminum matrix, as well as the precipitation strengthening of the Al2Cu phase, thereby increasing the hardness of the aluminum matrix. Simultaneously, the low temperature slows down atomic diffusion in the aluminum / steel interface region, hindering the formation of vacancies; it also slows down the increase in the thickness of the interfacial reaction layer, reducing the decline in interfacial bonding performance caused by brittle compounds; and it effectively slows down the formation of the oxide layer, preventing the oxide layer from deteriorating the interfacial bonding performance, thus ensuring the interfacial bonding performance of the bimetallic matrix.

[0006] The method specifically includes the following steps:

[0007] S1. Heat the heat treatment furnace to 60-100℃;

[0008] S2. After the heat treatment furnace is heated up, the solution-treated aluminum / steel bimetallic material is placed in the heat treatment furnace for single-stage low-temperature aging treatment, and the aging holding time is 14-20 hours.

[0009] S3. Remove and air-cool to room temperature to obtain a low-temperature aged aluminum / steel bimetal.

[0010] The heat treatment furnace in step S1 is an oil bath furnace or a salt bath furnace.

[0011] The aluminum / steel bimetal in the solution-treated state in step S2 is a solid-liquid formed aluminum / steel bimetal.

[0012] The aluminum / steel bimetallic material is ZL702A aluminum alloy / SUS304 stainless steel.

[0013] Preferably, the heating temperature in step S1 is 80°C, and the holding time in step S2 is 16 hours.

[0014] In step S2, the aluminum alloy side of the aluminum / steel bimetallic alloy is one of aluminum alloys with precipitation strengthening effect, such as aluminum-silicon alloy, aluminum-copper alloy, aluminum-zinc alloy, and aluminum-magnesium alloy, while the steel side material is any type of steel, such as structural steel, high-chromium steel, carbon steel, and high-speed steel.

[0015] This method utilizes a heat treatment furnace to perform low-temperature aging heat treatment on aluminum / steel bimetallic materials. Low-temperature aging promotes the precipitation of the second phase and precipitation strengthening in the aluminum matrix, thereby improving the mechanical properties of the aluminum matrix. At the same time, the low-temperature treatment slows down atomic diffusion in the aluminum / steel interface region, thus hindering the formation of vacancies and even voids in the interface region, slowing down the increase in the thickness of the interface reaction layer, thereby reducing the decline in interfacial bonding performance caused by brittle compounds, and slowing down the formation of the oxide layer, thus preventing the oxide layer from deteriorating the interfacial bonding performance, ensuring good interfacial bonding performance of the bimetallic materials.

[0016] The above technical solution has at least the following advantages compared with the existing technology:

[0017] The above scheme involves solid-liquid forming of an aluminum / steel bimetallic alloy followed by solution quenching and then low-temperature aging at 60–100℃. This low-temperature aging process changes the silicon phase morphology of the aluminum-silicon alloy matrix from lath-like to spherical, increasing eutectic Si precipitation. Simultaneously, the supersaturated solution-treated aluminum matrix obtained through solution quenching precipitates a large number of fine Al₂Cu particles during subsequent low-temperature aging, resulting in precipitation strengthening. The combined effect leads to an increase in the hardness and mechanical properties of the aluminum-silicon alloy matrix, and the precipitation strengthening effect produced by low-temperature aging at 60–100℃ is comparable to that of medium-high temperature aging at 120℃ and 160℃. Furthermore, compared to medium-high temperature aging at 120℃ and 160℃, low-temperature aging effectively slows atomic diffusion at the aluminum / steel interface, hindering vacancy formation; reduces the increase in the thickness of the interface reaction layer, minimizing the decline in interfacial bonding performance caused by brittle compounds; and slows the formation of an oxide layer at the interface, preventing the oxide layer from deteriorating interfacial bonding performance. The combined effect ensures good interfacial bonding quality in the aluminum / steel bimetallic alloy and reduces the decrease in interfacial bonding strength. Specifically, in the solid-liquid forming aluminum / steel bimetallic alloy, the aluminum-silicon alloy has a hardness of 63.13 HV and an aluminum / steel interfacial shear strength of 50.31 MPa. After aging at 80℃, the peak hardness of the aluminum-silicon alloy increases to 77.93 HV, while the aluminum / steel interfacial shear strength decreases to 38.17 MPa. After aging at 120℃, the peak hardness of the aluminum-silicon alloy increases to 79.38 HV, while the aluminum / steel interfacial shear strength decreases to 28.59 MPa. After aging at 160℃, the peak hardness increases to 77.52 HV, while the bimetallic shear strength decreases to 28.54 MPa. Low-temperature aging produces an excellent combination of properties in the aluminum matrix and the interface. The final aluminum / steel bimetallic alloy has a hardness value higher than 77 HV and an aluminum / steel interfacial shear strength higher than 38 MPa.

[0018] This method is simple, stable, and easy to operate, with low aging temperature and low energy consumption, making it suitable for industrial production and reducing production costs. Using this method, low-temperature treatment in heat treatment furnaces such as oil bath furnaces and salt bath furnaces can strengthen the aluminum matrix while maintaining higher interfacial bonding strength, showing great application potential in improving the overall performance of aluminum / steel bimetallic materials. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 These are the hardness variation curves of the aluminum substrate under different process conditions in the embodiments of the present invention;

[0021] Figure 2These are bimetallic photographs under different heat treatment processes in the embodiments of the present invention, wherein (a) is in the as-cast state, (b) is in the solution-quenched state, (c) is in the state of aging at 80℃ for 16h, (d) is in the state of aging at 120℃ for 6h, and (e) is in the state of aging at 160℃ for 2h.

[0022] Figure 3 The figures show the curves of the bimetallic interface bonding strength under different states in the embodiments of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a low-temperature aging method for obtaining a combination of excellent properties of the aluminum matrix and the aluminum / steel interface. The method includes the following steps:

[0025] S1. Heat the heat treatment furnace to 60-100℃;

[0026] S2. After the heat treatment furnace is heated up, the solution-treated aluminum / steel bimetallic material is placed in the heat treatment furnace for single-stage low-temperature aging treatment, and the aging holding time is 14-20 hours.

[0027] S3. Remove and air-cool to room temperature to obtain a low-temperature aged aluminum / steel bimetal.

[0028] The following description, in conjunction with specific embodiments, illustrates this point.

[0029] Taking aluminum / steel bimetal as an example (material composition is shown in Table 1), the evolution of mechanical properties of aluminum / steel bimetal under different aging temperatures and aging times was studied.

[0030] Table 1 Chemical composition (wt%) of each experimental material

[0031]

[0032] After solid-liquid formed aluminum / steel bimetallic materials were solution-treated at 500℃ for 2 hours, they were then quenched in water at 80℃. A DV-20 digital display constant-temperature oil bath was heated to 80℃, 120℃, and 160℃ respectively. The solution-treated aluminum / steel bimetallic materials were then placed in the oil bath for aging treatment with timed holding for 2–20 hours, followed by air cooling. Aging-state aluminum / steel bimetallic samples with different holding temperatures and times were obtained. The aluminum-silicon alloy side of the aging-state aluminum / steel bimetallic materials was ground and polished, and the hardness was measured at 10 random locations on the aluminum-silicon alloy. The peak hardness values ​​at each temperature are shown below. Figure 1 As shown.

[0033] The hardness of the aluminum matrix improved after aging heat treatment. During the solution treatment process, coarse Al₂Cu dissolved in the aluminum matrix, and quenching yielded a supersaturated solid solution. In the subsequent aging process, Al₂Cu precipitated as fine particles, causing precipitation strengthening. Furthermore, eutectic silicon precipitated near the grain boundaries and spheroidized, all of which contributed to the improvement of the aluminum matrix hardness. When the aluminum matrix was aged at 80℃, 120℃, and 160℃, it reached its peak hardness at 16h, 6h, and 2h, respectively, with peak hardness values ​​of 77.93HV, 79.38HV, and 77.52HV, respectively. Figure 1 The precipitation strengthening effect produced by aging at 80℃ is comparable to that of aging at 120℃ and 160℃.

[0034] Comparison of aluminum / steel interface microstructure at peak aging temperatures of 80℃, 120℃, and 160℃ (e.g.) Figure 2 ) and interfacial bonding strength (e.g. Figure 3 It was found that during the aging process at 80℃ for 16 hours, due to the low aging temperature, no obvious oxide layer or voids were observed on the aluminum side of the aluminum / steel bimetallic interface transition layer. Figure 2 As shown in (c), the interfacial bonding strength of the aluminum / steel bimetallic substrate aged at 80℃ (38.17 MPa) remains essentially the same as that of the solution-quenched state (36.21 MPa). However, the oxygen layer thickness and void area at the aluminum / steel interface significantly increase after aging at 120℃ for 6 hours and 160℃ for 2 hours, respectively, resulting in a decrease in the interfacial bonding strength to 28.59 MPa and 28.54 MPa. These results indicate that low-temperature aging not only strengthens the aluminum matrix but also ensures high interfacial bonding performance, thus producing an excellent combination of properties between the aluminum matrix and the interface.

[0035] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low temperature aging method to obtain a combination of excellent properties of the aluminum matrix and the aluminum / steel interface, characterized in that, The steps include the following: S1. Heat the heat treatment furnace to 60~100℃; S2. After the heat treatment furnace is heated up, the solution-treated aluminum / steel bimetallic material is placed in the heat treatment furnace for single-stage low-temperature aging treatment, and the aging holding time is 14~20h. S3. Remove and air-cool to room temperature to obtain a low-temperature aged aluminum / steel bimetallic product; The aluminum / steel bimetal in the solution-treated state in step S2 is a solid-liquid formed aluminum / steel bimetal. The final aluminum / steel bimetal has a hardness value of over 77 HV for aluminum and a shear strength of over 38 MPa for the aluminum / steel interface.

2. The low temperature aging method to obtain a combination of excellent properties of the aluminum matrix and aluminum / steel interface according to claim 1, characterized in that, The heat treatment furnace in step S1 is an oil bath furnace or a salt bath furnace.

3. The low temperature aging method to obtain a combination of excellent properties of the aluminum matrix and aluminum / steel interface according to claim 1, characterized in that, The aluminum / steel bimetallic material is ZL702A aluminum alloy / SUS304 stainless steel.

4. The low temperature aging method to obtain a combination of excellent properties of the aluminum matrix and aluminum / steel interface according to claim 1, characterized in that, In step S1, the heating temperature is 80℃, and in step S2, the holding time is 16h.

5. The low temperature aging method to obtain a combination of excellent properties of the aluminum matrix and aluminum / steel interface according to claim 1, characterized in that, In step S2, the aluminum alloy side of the aluminum / steel bimetallic alloy is one of aluminum-silicon alloy, aluminum-copper alloy, aluminum-zinc alloy, and aluminum-magnesium alloy, while the steel side is one of structural steel, high-chromium steel, carbon steel, and high-speed steel.

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