A casting with a hollow pipe and a preparation method thereof

Abstract

The present invention relates to the technical field of investment casting, and particularly relates to a casting containing a hollow pipe and a preparation method thereof. The preparation method is simple to operate, easy to implement, and has a relatively high success rate. In particular, it is convenient to prepare a casting with a special-shaped and complex hollow pipe inside. Moreover, the preparation process is not affected by the shape, size, and complexity of the internal pipe.

Description

Technical Field

[0001] The present invention relates to the technical field of investment casting, and particularly to a casting containing a hollow pipe and a preparation method thereof. Background Art

[0002] When producing a casting with a hollow pipe inside by investment casting, it is mainly achieved by using a ceramic core or metal forming inside it and then removing the above-mentioned core after pouring, so as to form a hollow and slender pipe inside the casting. For a casting with a curved and slender pipe. However, as disclosed in the background art of the invention patent with the document number CN 102806311B, the defects of the above method include: it is not easy to remove the slender and complex-shaped pipe core, and the inner wall of the pipe is easily damaged during the removal process. Therefore, the above patent provides a complex pipe forming process for titanium alloy investment castings. In this process, a material of the same grade as the casting is prepared into a hollow pipe of the required shape, and then the above hollow pipe is inlaid in the wax pattern to prepare a mold shell, and then the mold shell is prepared and poured after high-temperature roasting, so that the above hollow pipe and the casting form an integral body. Although the above process solves the defect of difficult removal of the core in the traditional method, as mentioned in the background art of the Chinese invention patent with the document number CN105234353B, the defect of adopting the above process is that: after the mold shell is roasted at high temperature, the metal pipe body inlaid in the mold shell is prone to problems such as oxidation, deformation, and cracking under the action of high temperature, still resulting in unqualified castings. Especially for the titanium material metal pipe body of titanium alloy castings, it is more prone to oxidation and cracking. Aiming at the problems of oxidation, deformation, cracking, etc. of the metal pipe body after high-temperature roasting, the invention patent with the document number CN 102806311 B further fills graphite powder in the hollow pipe to reduce the oxidation of the titanium pipe at the high temperature of roasting and pouring through the graphite powder, and the graphite powder has a certain chilling effect. However, even so, this process still has certain defects, resulting in it being difficult to meet the requirements in actual application. For example, the inventor found that when preparing a pipe with a small inner diameter, even if materials such as graphite powder are filled inside it, due to the small filling amount of graphite powder and limited chilling effect, the titanium alloy hollow pipe is still prone to oxidation, deformation, and extremely easy to crack. At the same time, when preparing some complex pipes with a small inner diameter, a complex bending structure, and a large length, the graphite powder is not easily evenly dispersed into the hollow pipe, and it is extremely easy to appear filling gaps. Furthermore, the quality of the casting is easily affected.

[0003] Micro-arc oxidation, also known as micro-plasma oxidation and anodic spark deposition, is a process that, through the combination of an electrolyte and corresponding electrical parameters, relies on the instantaneous high temperature and high pressure generated by arc discharge on the surfaces of metals such as aluminum, magnesium, and titanium and their alloys to in-situ grow a ceramic film layer mainly composed of the matrix metal oxide (i.e., the micro-arc oxidation layer) on the workpiece surface to achieve the purpose of surface strengthening of the workpiece. The above-mentioned micro-arc oxidation layer has a dense structure, high toughness, and good wear resistance and high-temperature impact resistance. Currently, the research on the micro-arc oxidation layer mainly focuses on improving its wear resistance, and there is less research and application on its high-temperature resistance.

[0004] Method content

[0005] To solve the above technical problems, the purpose of the present invention is to provide a casting containing a hollow pipe and a preparation method thereof. The preparation method is simple to operate, easy to implement, and has a high success rate, especially facilitating the preparation of castings with special-shaped and complex hollow pipes inside.

[0006] To achieve the above technical effects, the present invention adopts the following technical solutions:

[0007] In the first aspect, a casting containing a hollow pipe provided by the present invention includes a hollow channel provided inside the casting and a layered structure formed on one side of the hollow channel. The layered structure includes a first metal layer, an outer oxidation layer, and a second metal layer distributed in sequence. The first metal layer is closely arranged against the hollow channel, and the first metal layer and the second metal layer are made of the same matrix material.

[0008] Preferably, the matrix material is any one of aluminum and its alloys, magnesium and its alloys, titanium and its alloys, zirconium and its alloys, and beryllium and its alloys, and preferably titanium and its alloys.

[0009] Further, the outer oxidation layer is prepared by the micro-arc oxidation method.

[0010] Further, the outer oxidation layer is prepared from the first metal layer by the micro-arc oxidation method, and the second metal layer is combined with the outer oxidation layer by the molten casting method.

[0011] Further, the thickness of the outer oxidation layer is 5 - 1000 um. Preferably, the outer oxidation layer is prepared with a titanium alloy as the matrix material and has a thickness of 5 - 100 um.

[0012] Preferably, it further includes an inner oxidation layer, and the inner oxidation layer is arranged on the side of the first metal layer close to the hollow channel.

[0013] Preferably, the outer oxidation layer includes a dense layer and a porous layer. The porosity of the porous layer is greater than that of the dense layer, and a part of the matrix material in the second metal layer penetrates into the pores of the porous layer to form a doped layer, thereby improving the bonding strength between the first metal layer and the second metal layer.

[0014] Furthermore, the porosity of the dense layer is 0.5% - 10%, and the porosity of the porous layer is 5% - 50%.

[0015] In a second aspect, a method for preparing a casting containing a hollow pipe provided by the present invention includes the steps of:

[0016] S1: Preparing a matrix material into an elongated pipe fitting with a hollow channel as required;

[0017] S2: Treating the elongated pipe fitting by micro-arc oxidation, and the treated part at least includes the outer surface of the elongated pipe fitting to form an outer oxide layer on the outer surface of the elongated pipe fitting so as to prepare it into an oxidation core mold;

[0018] S3: Embedding the oxidation core mold in a mold shell and then pouring molten metal liquid to obtain a casting with a hollow channel inside.

[0019] Furthermore, the matrix material is any one of aluminum and its alloys, magnesium and its alloys, titanium and its alloys, zirconium and its alloys, and beryllium and its alloys, and preferably titanium and its alloys.

[0020] Preferably, the treated part further includes the inner surface of the elongated pipe fitting to form an inner oxide layer on the inner surface of the elongated pipe fitting.

[0021] Furthermore, the parameters of the micro-arc oxidation method are controlled as follows: voltage 220 - 450V, current density 3 - 7A / dm 2 , duty cycle 15% - 30%, and micro-arc oxidation time 5 - 120 min.

[0022] Preferably, the mold shell is prepared by the investment casting method or other methods. Specifically, when the investment casting method is used, S3 includes:

[0023] S301: Preparing a wax mold by a wax pressing machine and pre-embedding the oxidation core mold in the wax mold;

[0024] S302: Making a shell with the wax mold obtained in S301 and obtaining a mold shell after dewaxing;

[0025] S303: Pouring molten metal liquid into the mold shell to obtain a casting with a hollow channel inside. Preferably, the hollow channel is a special-shaped structure.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] A casting containing a hollow pipe and a preparation method thereof provided by the present invention. The casting is prepared by forming an outer oxidation layer on a first metal layer through a micro-arc oxidation method. The outer oxidation layer obtained through the micro-arc oxidation method has good high-temperature resistance to protect the first metal layer. Then, a second metal layer is prepared through a melting and casting method and the second metal layer is combined with the outer oxidation layer, so that the first metal layer, the outer oxidation layer, and the second metal layer form an integral body. The preparation method is simple to operate, easy to implement, and has a high success rate, effectively avoiding cracking and oxidation of the first metal layer. It is particularly suitable for preparing castings with irregular and complex hollow pipes inside. Moreover, the preparation process is not affected by the shape, inner diameter, and complexity of the hollow channels. After preparation, a hollow channel can be naturally formed inside the casting without further post-treatment. For the preparation of castings that require prefabricated hollow channels inside, especially those with complex, curved, and slender hollow channels, the success rate and preparation efficiency of the preparation can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FIG. 6 is a schematic diagram of the overall structure of a casting containing a hollow pipe provided in the first embodiment of the present invention;

[0029] Figure 2 FIG. 10 is a schematic diagram of the transverse sectional structure of a casting containing a hollow pipe provided in the first embodiment of the present invention;

[0030] Figure 3 FIG. 14 is a schematic diagram of a partially enlarged structure at A of a casting containing a hollow pipe provided in the first embodiment of the present invention;

[0031] Figure 4 FIG. 18 is a schematic diagram of the layered structure of a casting containing a hollow pipe provided in the second embodiment of the present invention;

[0032] Figure 5 FIG. 22 is a schematic diagram of the layered structure of a casting containing a hollow pipe provided in the third embodiment of the present invention;

[0033] Reference numerals are: 11, slender pipe fitting; 11a, hollow channel; 21, first metal layer; 22, outer oxidation layer; 221, dense layer; 222, porous layer; 23, second metal layer; 24, inner oxidation layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The embodiments of the technical solution of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, so they are only examples and cannot be used to limit the protection scope of the present invention. The embodiments are only used to explain the present invention and are not used to limit the scope of the present invention. The test methods used in the following embodiments are all conventional methods unless otherwise specified; the materials, reagents or instruments used without indicating the manufacturer are, unless otherwise specified, reagents and materials that can be obtained from commercial channels, and those not indicating specific conditions in the embodiments are all carried out according to conventional conditions or conditions recommended by the manufacturer.

[0035] Embodiment 1

[0036] Please refer to Figures 1 to 3 , the following is the first embodiment of the present invention. This embodiment provides a casting containing a hollow pipe and a preparation method thereof. The casting containing the hollow pipe is internally provided with a plurality of curved hollow channels 11a, and a layered structure is formed on one side of the hollow channels 11a of the casting containing the hollow pipe. The layered structure includes a first metal layer 21, an outer oxide layer 22, and a second metal layer 23 that are sequentially distributed. The first metal layer 21 is disposed closely to the hollow channel 11a, and the first metal layer 21 and the second metal layer 23 are made of the same base material, and the base material is a titanium alloy material. The outer oxide layer 22 is prepared from the first metal layer 21 by micro-arc oxidation. Therefore, an outer oxide layer 22 is formed on the outer surface of the first metal layer 21. The outer oxide layer 22 is a titanium alloy ceramic layer formed by titanium alloy matrix metal oxides or a modified titanium alloy ceramic layer mainly composed of titanium alloy matrix metal oxides and supplemented with micro-arc oxidation electrolyte components. The second metal layer 23 is combined with the outer oxide layer 22 by a melting casting method so that the first metal layer 21, the outer oxide layer 22, and the second metal layer 23 form an integral structure.

[0037] In this embodiment, the preparation method adopted to prepare the above structure is as follows:

[0038] S1: Prepare the base material into an elongated pipe fitting 11 containing a hollow channel 11a as required;

[0039] S2: Treat the outer surface of the elongated pipe fitting 11 by micro-arc oxidation to form an outer oxide layer 22 on the outer surface of the elongated pipe fitting 11 to prepare it into an oxidation core mold. Specifically:

[0040] When performing micro-arc oxidation treatment, the port parts at both ends of the above-mentioned slender pipe fitting 11 are pre-blocked. The blocking material is preferably a non-metallic material and is easy to be separated from the slender pipe fitting, such as low-temperature wax material or resin material. After blocking the port parts, they are then put into the micro-arc oxidation electrolyte for micro-arc oxidation treatment to obtain an outer oxidation layer 22 on the outer surface of the slender pipe fitting 11. The above-mentioned micro-arc oxidation electrolyte and treatment conditions can be arbitrarily selected from the prior art. The ultimate goal is to make the thickness of the prepared outer oxidation layer 22 between 5um and 100um, and the outer oxidation layer 22 can withstand at least an instantaneous high temperature of more than 1500°C, preferably can withstand an instantaneous high temperature of 1650°C and above, so as to effectively protect the first metal layer 21. This is easy to achieve and reach in the prior art, so this application will not elaborate on it here.

[0041] S3: Embed the oxidation core in the mold shell and then pour the molten metal liquid. After the above-mentioned molten metal liquid cools, a casting with a hollow channel 11a inside can be obtained, specifically including:

[0042] S301: Use a wax press to prepare a wax mold and embed the oxidation core in the wax mold;

[0043] S302: Make a shell with the wax mold obtained in S301 and obtain the mold shell after dewaxing;

[0044] S303: Pour the molten metal liquid into the mold shell to obtain a casting with a hollow channel 11a inside. Preferably, the hollow channel 11a is a special-shaped structure.

[0045] In the above step S3, the specific operation process of preparing the mold shell can refer to the method in the reference number CN 102806311B, or other methods in the prior art can also be selected.

[0046] Embodiment 2

[0047] Please refer to Figure 4 , the following is the second embodiment of the present invention. This embodiment provides a casting with a hollow pipe and a preparation method thereof. The casting with a hollow pipe has a hollow channel 11a and forms a layered structure on one side of the hollow channel 11a. The layered structure includes a first metal layer 21, an outer oxidation layer 22, and a second metal layer 23 distributed in sequence. The first metal layer 21 is arranged closely to the hollow channel 11a, and both the first metal layer 21 and the second metal layer 23 are made of titanium alloy material. The difference between the casting with a hollow pipe and the preparation method provided in this embodiment and those in Embodiment 1 is:

[0048] In this embodiment, the outer oxide layer 22 is prepared from the first metal layer 21 by micro-arc oxidation, so as to form the outer oxide layer 22 on the outer surface of the first metal layer 21. The second metal layer 23 is combined with the outer oxide layer 22 by a melting casting method, so that the first metal layer 21, the outer oxide layer 22 and the second metal layer 23 form an integral structure. Specifically, to improve the bonding energy between the second metal layer 23 and the outer oxide layer 22 and the first metal layer 21, the outer oxide layer 22 is prepared in a form including a dense layer 221 and a porous layer 222. The porosity of the porous layer 222 is greater than that of the dense layer 221, so that when molten metal is poured, part of the matrix material of the second metal layer 23 can penetrate into the pores of the porous layer 222 to form a doped layer, thereby improving the bonding strength between the first metal layer 21 and the second metal layer 23, and making the first metal layer 21 and the outer oxide layer 22 not easily fall off during use. It should be particularly noted that the preparation method of the outer oxide layer 22 including the dense layer 221 and the porous layer 222 is prior art, for example, obtained by adjusting electrolysis parameters.

[0049] Embodiment 3

[0050] Please refer to Figure 5 , the following is the third embodiment of the present invention. This embodiment provides a casting with a hollow pipe and a preparation method thereof. The casting with a hollow pipe has a hollow channel 11a and forms a layered structure on one side of the hollow channel 11a. The layered structure includes an inner oxide layer 24, a first metal layer 21, an outer oxide layer 22, and a second metal layer 23 distributed in sequence. The first metal layer 21 and the second metal layer 23 are made of the same matrix material. The preparation method of the casting with a hollow pipe is slightly different from that in Embodiment 1. Specifically:

[0051] When the slender pipe fitting 11 is treated by micro-arc oxidation in step S2, it is not necessary to seal the port part of the slender pipe fitting 11, and the whole slender pipe fitting 11 is immersed in the micro-arc oxidation electrolyte for micro-arc oxidation treatment, so as to form the inner oxide layer 24 and the outer oxide layer 22 on the inner and outer surfaces of the slender pipe fitting 11 respectively. Specifically, through the above micro-arc oxidation method, depending on the different micro-arc oxidation electrolytes selected, the inner oxide layer 24 and the outer oxide layer 22 can be titanium alloy ceramic layers formed by titanium alloy matrix metal oxides, or modified titanium alloy ceramic layers mainly composed of titanium alloy matrix metal oxides and supplemented by components of the micro-arc oxidation electrolyte.

[0052] The remaining operation steps can refer to Embodiment 1.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention. The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A casting with a hollow pipe, characterized in that: It includes a hollow channel (11a) provided inside the casting and a layered structure formed on one side of the hollow channel (11a). The layered structure includes a first metal layer (21), an outer oxide layer (22), and a second metal layer (23) that are sequentially distributed. The first metal layer (21) is disposed closely to the hollow channel (11a), and the first metal layer (21) and the second metal layer (23) are made of the same base material; the outer oxide layer (22) is prepared by a micro-arc oxidation method; the outer oxide layer (22) is obtained by preparing the first metal layer (21) through the micro-arc oxidation method, and the second metal layer (23) is combined with the outer oxide layer (22) by a melting and casting method; the outer oxide layer (22) includes a dense layer (221) and a porous layer (222). The dense layer (221) is disposed closely to the first metal layer (21), and the porosity of the porous layer (222) is greater than that of the dense layer (221). Part of the base material in the second metal layer (23) penetrates into the pores of the porous layer (222) to form a doped layer; it also includes an inner oxide layer (24), and the inner oxide layer (24) is disposed on the side of the first metal layer (21) close to the hollow channel (11a).

2. The casting with a hollow pipe according to claim 1, characterized in that: The thickness of the outer oxide layer (22) is 5 - 1000 um.

3. A method for preparing the casting with a hollow pipe according to claim 1 or 2, characterized in that, It includes steps: S1: Prepare the base material as a slender pipe fitting (11) containing a hollow channel (11a) as required; S2: Process the slender pipe fitting (11) by a micro-arc oxidation method. The processed part at least includes the outer surface of the slender pipe fitting (11) to form an outer oxide layer (22) on the outer surface of the slender pipe fitting (11) to prepare it as an oxidation core; S3: Embed the oxidation core in a mold shell and then pour molten metal to obtain a casting with a hollow channel (11a) inside.

4. The method for preparing the casting with a hollow pipe according to claim 3, characterized in that: The base material is any one of aluminum and its alloys, magnesium and its alloys, titanium and its alloys, zirconium and its alloys, and beryllium and its alloys.

5. The method for preparing the casting with a hollow pipe according to claim 3, characterized in that, The parameter control of the micro-arc oxidation method is as follows: voltage 220 - 450V, current density 3 - 7A / dm 2 , duty cycle 15% - 30%, and micro-arc oxidation time 5 - 120 min.

6. The method for preparing the casting with a hollow pipe according to claim 3, characterized in that, The S3 includes: S301: Prepare a wax pattern and embed the oxidation core in the wax pattern; S302: Make a shell with the wax pattern prepared in S301 and obtain a mold shell after dewaxing; S303: Cast the mold shell to obtain a casting with a hollow channel (11a) inside.

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