Aluminum / steel bimetallic composite having a discontinuous intermetallic compound interface and method of making same

Abstract

The application provides an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface and a preparation method thereof. After the surface of a steel base is subjected to alkali washing, acid washing and plating assisting treatment, a Zn-Al alloy coating is plated on the steel base through hot dipping treatment, then the steel base is placed into a mold, and aluminum-silicon alloy melt is poured into the mold for compounding, so that the aluminum / steel bimetallic composite material is obtained. The interface of the castings formed through the method is well metallurgically combined, and a discontinuous intermetallic compound layer is formed at the interface, so that the interface bonding strength of the aluminum / steel bimetallic composite material can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of bimetallic liquid-solid composite casting, specifically to an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface and its preparation method. Background Technology

[0002] Aluminum / steel bimetallic composites combine the high-temperature strength and wear resistance of steel with the low density, high thermal conductivity, and corrosion resistance of aluminum, thus achieving lightweighting. Bimetallic composite casting has attracted widespread attention due to its simple process and minimal structural limitations. Currently, the main challenge in aluminum / steel liquid-solid bimetallic composite casting is the formation of continuous hard and brittle intermetallic compounds at the interface, leading to less than ideal bimetallic bonding performance.

[0003] Existing aluminum / steel bimetallic composites often involve electroplating the steel substrate with nickel or copper before liquid-solid bonding, or hot-dip immersion of the steel substrate in molten aluminum or zinc to improve wettability and inhibit oxidation of the steel substrate surface, thereby enhancing the interfacial bonding strength between aluminum and steel. However, these methods all result in the formation of a continuous, hard, and brittle intermetallic compound layer at the interface, leading to lower interfacial bonding strength in the bimetallic composite. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface and its preparation method. This invention involves hot-dip treatment of a steel substrate by immersing it in a zinc-aluminum alloy molten solution to prevent high-temperature oxidation of the steel substrate surface. The zinc-aluminum alloy molten solution exhibits excellent wettability with the steel. Through interfacial diffusion and reaction, a discontinuous intermetallic compound layer is formed at the aluminum-steel bimetallic composite interface, thereby improving the interfacial bonding strength of the composite material.

[0005] To achieve the above objectives, the specific solution adopted by the present invention is as follows: On one hand, this invention discloses a method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface, which mainly includes the following steps: Step 1: Clean the steel substrate to remove oil and rust from its surface. Step 2: Perform fluxing treatment on the cleaned steel substrate; Step 3: Immerse the steel substrate in molten zinc-aluminum alloy for hot dipping treatment; Step 4: Cast molten aluminum-silicon alloy onto the surface of the hot-dip treated steel substrate and allow it to solidify to obtain an aluminum / steel bimetallic composite material.

[0006] Furthermore, in step one, the method for cleaning the steel substrate is as follows: first, use a 15wt.% NaOH solution for alkaline washing to remove oil, and then use 10% hydrochloric acid for acid washing to remove rust.

[0007] Furthermore, in step two, the fluxing solution used in the fluxing treatment is a mixed solution composed of NH4Cl, ZnCl2, and SnCl2 in a volume ratio of 4:3:2.

[0008] Furthermore, in step two, the temperature of the fluxing treatment is 80-90℃, and the time is 3-5 minutes.

[0009] Furthermore, in step three, during the hot-dip treatment, the temperature of the zinc-aluminum alloy melt is maintained at 500-600℃.

[0010] Furthermore, in step three, the zinc-aluminum alloy melt comprises the following components by weight fraction: Al 10-20%, Ni 0-1%, Bi 0-1%, with the balance being Zn.

[0011] Furthermore, in step four, the aluminum-silicon alloy melt comprises the following components by weight fraction: 6-8% Si, with the balance being Al.

[0012] On the other hand, the present invention discloses an aluminum / steel bimetallic composite material prepared by the above-described preparation method.

[0013] Furthermore, at the interface between the transition layer and the steel matrix of the aluminum / steel bimetallic composite material, a discontinuous intermetallic compound layer composed of iron-aluminum compounds and tough solid solution phases is formed.

[0014] Furthermore, the bonding strength of the liquid-solid composite interface in the aluminum / steel bimetallic composite material can reach 35 MPa.

[0015] Beneficial effects: 1) This invention utilizes hot-dip zinc-aluminum melt to prevent high-temperature oxidation of the steel substrate surface. The zinc-aluminum melt has good wettability with steel. Through interfacial diffusion and reaction during hot dipping and subsequent casting processes, a discontinuous intermetallic compound layer composed of iron-aluminum compounds and a tough solid solution phase (Zn) is formed at the interface. The tough solid solution phase (Zn) effectively hinders crack propagation. The castings formed by this method have good metallurgical bonding at the interface, thereby effectively improving the interfacial bonding strength of aluminum / steel bimetallic composite materials.

[0016] 2) In this invention, zinc-aluminum alloy melt is selected for hot dipping. Zinc can significantly improve the wettability of aluminum-steel, and Al can improve the fluidity of zinc. Compared with the iron-zinc compound formed by hot dipping galvanizing, which forms a continuous iron-aluminum compound at the interface after remelting during composite casting, the addition of Al can form iron-aluminum compound (such as Al5Fe2) on the surface of the steel substrate through hot dipping instead of iron-zinc compound. During composite casting, a large amount of Zn exists in the form of a tough solid solution phase at the interface, forming a discontinuous intermetallic compound layer at the interface, thereby ensuring a good metallurgical bond between aluminum and steel. Bi and Ni can both improve the wettability of aluminum-silicon alloy melt with the steel substrate.

[0017] 3) During the bimetallic liquid-solid composite process, the composite interface is affected by the types of elements in the matrix material. In this invention, the aluminum-silicon alloy Al-Si alloy is selected during casting, which has good casting performance, can effectively reduce the tendency of hot cracking, reduce shrinkage porosity, and improve air tightness; on the other hand, Si can effectively reduce the thickness of the intermetallic compound layer at the interface.

[0018] 4) The interfacial bonding strength of the aluminum / steel bimetallic composite material prepared by casting using the method provided by this invention can reach 35 MPa, which is more than 75% higher than that of the aluminum / steel bimetallic composite material prepared by hot-dip pure zinc. Attached Figure Description

[0019] Figure 1 This is a microstructure diagram of the interface of the aluminum / steel bimetallic composite material prepared in Example 1.

[0020] Figure 2 for Figure 1 Enlarged view of point A in the middle.

[0021] Figure 3 for Figure 1 Enlarged view of point B in the middle.

[0022] Figure 4 for Figure 1 A magnified view of point C in the middle. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0024] This invention provides an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface. At the interface between the transition layer and the steel matrix, a discontinuous intermetallic compound layer composed of an aluminum-iron compound and a toughening solid solution phase (Zn) is formed. The toughening solid solution phase (Zn) effectively hinders crack propagation, thereby effectively improving the bonding strength of the aluminum / steel bimetallic composite material. The preparation method of this composite material mainly includes the following steps: Step 1: The oxidation of the steel substrate includes a naturally formed oxide layer in the air and secondary oxidation generated at high temperatures during the experiment. To remove the oxide layer and oil stains from the steel substrate surface and protect the steel substrate under high temperatures, the steel substrate is subjected to alkaline washing (15wt.% NaOH solution alkaline washing for degreasing for 20 min) and acid washing (10% hydrochloric acid acid washing for rust removal for 3 min) to remove oil stains and rust from the steel substrate surface; Step 2: Prepare a mixed solution of NH4Cl, ZnCl2, and SnCl2 as a fluxing solution in a ratio of 4:3:2; immerse the steel substrate in the fluxing solution at a constant temperature of 80-90℃ for 3-5 minutes; remove and dry, ensuring the fluxing solution adheres evenly to the surface of the steel substrate to be laminated; the main purpose of the fluxing treatment is to remove iron salts and oxide scale that were not completely removed from the steel substrate surface; to form a protective film on the steel substrate surface to prevent secondary oxidation; and to activate the substrate surface and improve the wettability of the aluminum liquid to the steel substrate. Step 3: Melt the zinc-aluminum alloy to obtain a zinc-aluminum alloy melt, and keep its temperature at 500℃~600℃. Then, immerse the steel substrate in the zinc-aluminum alloy melt for hot dipping treatment. Step 4: After hot dipping, remove the steel substrate and place it in the casting mold. Immediately pour the molten aluminum-silicon alloy onto the substrate. Once solidified, the aluminum / steel bimetallic composite material is obtained.

[0025] It should be noted that in step three, the zinc-aluminum alloy melt comprises the following components by weight fraction: Al 10-20%, Ni 0-1%, Bi 0-1%, with the balance being Zn. In step four, the aluminum-silicon alloy melt comprises the following components by weight fraction: Si 6-8%, with the balance being Al. The technical solution of the present invention will be described in detail below with reference to specific embodiments. It should be noted that all raw materials used in the present invention are commercially available.

[0026] Example 1

[0027] This embodiment provides an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface. The preparation method of this composite material mainly includes the following steps: Step 1: Alkaline washing (15wt.% NaOH solution for 20 min to remove oil) and acid washing (10% hydrochloric acid for 3 min to remove rust) are performed on the steel substrate to remove oil and rust from the surface of the steel substrate. Step 2: Prepare a mixed aqueous solution of NH4Cl, ZnCl2 and SnCl2 as a fluxing solution in a ratio of 4:3:2; immerse the steel substrate in the fluxing solution at a constant temperature of 85℃ for 3 minutes; remove and dry it, and then allow the fluxing solution to adhere evenly to the surface of the steel substrate to be laminated. Step 3: Melt the zinc-aluminum alloy to obtain a zinc-aluminum alloy melt (Zn12Al, Al 12%, balance Zn), and keep its temperature at 500℃. Then, immerse the steel substrate in the zinc-aluminum alloy melt for 5 minutes for hot dipping treatment. Step 4: After hot dipping, remove the steel substrate and place it in the casting mold. Immediately pour the molten aluminum-silicon alloy (Si 7%, balance Al) onto the substrate. Once solidified, the aluminum / steel bimetallic composite material is obtained.

[0028] Figures 1 to 4 This is a microstructure diagram of the interface of the aluminum / steel bimetallic composite material prepared in this embodiment. Figure 1 This is a SEM image of the bimetallic interface, with aluminum alloy on the upper side and steel on the lower side. The thickness of the intermediate transition layer is approximately 400 μm, and four distinct diffusion layers are observed. Viewed from the steel side towards the aluminum side, the first layer is the interface between the steel substrate and the transition layer, mainly composed of the gray phase Al5Fe2. Within the gray phase, FeAl phase and a white, highly resilient solid solution phase (Zn) are dispersed. Figure 2 As shown. Layer II is a transition layer close to the steel matrix, mainly consisting of a large amount of gray α-Al and a small amount of light gray (Al+Zn) eutectoid structure with blocky dark gray phase τ5 and black phase (Si) distributed on it, such as... Figure 3 As shown. Layer III is a transition layer close to the Al matrix, mainly composed of light gray (Al+Zn) eutectoid structure and gray α-Al structure. A small amount of white phase is found within the light gray (Al+Zn) eutectoid structure, which is residual (Zn), while blocky black phase (Si) is found near the gray α-Al structure. Layer IV is mainly composed of gray α-Al phase. The structures of layers III and IV are as follows. Figure 4 As shown.

[0029] Example 2

[0030] The difference between Example 2 and Example 1 is that in step 3, the ratio of zinc-aluminum alloy melt is: Al 12%, Bi 1%, and the balance is Zn.

[0031] Example 3

[0032] The difference between Example 3 and Example 1 is that in step three, the ratio of the zinc-aluminum alloy melt is: Al 12%, Ni 1%, Bi 1%, with the balance being Zn.

[0033] Example 4

[0034] The difference between Example 4 and Example 1 is that in step three, the ratio of zinc-aluminum alloy melt is: Al 12%, Ni 1%, and the balance is Zn.

[0035] Example 5

[0036] The only difference between Example 5 and Example 1 is that in step three, the temperature of the zinc-aluminum alloy melt is maintained at 600°C.

[0037] Example 6

[0038] The only difference between Example 6 and Example 5 is that in step 3, the hot soaking time is 10 minutes.

[0039] Comparative Example 1

[0040] The difference between Comparative Example 1 and Example 1 is that in step three, pure zinc is melted to obtain pure zinc melt, and its temperature is maintained at 500°C. The steel substrate is then immersed in the pure zinc melt for 5 minutes for hot dipping treatment.

[0041] The interfacial bonding strength of the composite materials prepared in Examples 1-5 and Comparative Example 1 was tested, and the test results are shown in Table 1.

[0042] Table 1. Interfacial bonding strength test results of the composite materials prepared in Examples 1-6 and Comparative Example 1. Shear strength / MPa Example 1 26.83 Example 2 30.56 Example 3 34.46 Example 4 31.48 Example 5 36.37 Example 6 40.92 Comparative Example 1 20.3

[0043] As shown in Example 1 and Comparative Example 1, compared with hot-dip galvanizing, hot-dip galvanized aluminum alloy melt can significantly improve the bonding strength of aluminum / steel bimetallic alloys. As shown in Examples 1 and 5, by appropriately increasing the temperature and time during hot-dip treatment, the bonding strength of the bimetallic liquid-solid composite interface can be improved. Furthermore, as shown in Examples 1-4, adding Bi and / or Ni elements to the zinc-aluminum alloy melt can also improve the bonding strength of the bimetallic liquid-solid composite interface.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface, characterized in that, The preparation method of the aluminum / steel bimetallic composite material includes the following steps: Step 1: Clean the steel substrate to remove oil and rust from its surface. Step 2: Perform fluxing treatment on the cleaned steel substrate; Step 3: Immerse the steel substrate in molten zinc-aluminum alloy for hot dipping treatment; Step 4: Cast molten aluminum-silicon alloy onto the surface of the hot-dip treated steel substrate and allow it to solidify to obtain an aluminum / steel bimetallic composite material. The transition layer of the aluminum / steel bimetallic composite material has a discontinuous intermetallic compound layer composed of iron-aluminum compounds and tough solid solution phases at the interface with the steel substrate; the transition layer is located between the aluminum substrate and the steel substrate and is obtained by the interfacial diffusion and reaction of the zinc-aluminum alloy coating during the subsequent casting and solidification process.

2. The method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface according to claim 1, characterized in that, In step one, the method for cleaning the steel substrate is as follows: first, use a 15 wt.% NaOH solution for alkaline washing to remove oil, and then use 10% hydrochloric acid for acid washing to remove rust.

3. The method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface according to claim 1, characterized in that, In step two, the fluxing solution used in the fluxing treatment is a mixed solution composed of NH4Cl, ZnCl2, and SnCl2 in a volume ratio of 4:3:

2.

4. The method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface according to claim 1, characterized in that, In step two, the temperature for the fluxing treatment is 80-90℃, and the time is 3-5 minutes.

5. The method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface according to claim 1, characterized in that, In step three, during the hot-dip treatment, the temperature of the zinc-aluminum alloy melt is maintained at 500-600℃.

6. The method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface according to claim 1, characterized in that, In step three, the zinc-aluminum alloy melt comprises the following components by weight fraction: Al 10-20%, Ni 0-1%, Bi 0-1%, with the balance being Zn.

7. The method for preparing an aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface according to claim 1, characterized in that, In step four, the aluminum-silicon alloy melt comprises the following components by weight fraction: Si 6-8%, with the balance being Al.

8. An aluminum / steel bimetallic composite material prepared by the method for preparing an aluminum / steel bimetallic composite material having a discontinuous intermetallic compound interface as described in any one of claims 1 to 7.

9. An aluminum / steel bimetallic composite material with a discontinuous intermetallic compound interface according to claim 8, characterized in that, The bonding strength of the liquid-solid composite interface in the aluminum / steel bimetallic composite material can reach 35 MPa.

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