Mgal laminated composite filler metal, method for preparing same, and brazing method

Abstract

The application discloses MgAl laminated composite brazing filler metal and a preparation method and a brazing method thereof, belongs to the technical field of magnesium alloy welding materials, and solves the technical problems of insufficient welding strength of magnesium alloy brazing filler metal prepared by a melting method and difficulty in reducing the thickness of the brazing filler metal through secondary processing before welding, and the solution is as follows: Mg rolling plates and Al rolling plates are staggered and laminated according to the sandwich structure of Al rolling plate-Mg rolling plate-Al rolling plate, and then hot rolling is adopted to obtain the MgAl laminated composite brazing filler metal, the length and width of the Mg rolling plate and the Al rolling plate are the same, the thickness of the Mg rolling plate and the Al rolling plate is 0.4-0.6 mm, the thickness of the MgAl laminated composite brazing filler metal is not more than 500 microns, the melting temperature is 437-455 DEG C, and the brazing temperature is 460-500 DEG C. The preparation process is simple, the low-melting-point eutectic structure of the MgAl laminated composite brazing filler metal can be diffused and generated in the brazing process, and the brazing filler metal preparation and brazing process are realized in one step.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloy welding materials, and particularly relates to a MgAl rolled composite solder and a preparation method and a brazing method thereof. Background Art

[0002] Magnesium alloy is the lightest metal material currently used in structural metal materials. It has the advantages of low specific gravity, high specific strength, easy cutting and processing, and easy recycling. It has significant advantages in achieving lightweight, reducing energy consumption, and reducing environmental pollution. It is known as the "green" engineering material of the 21st century and has therefore received increasing attention. In particular, it has extremely important application value and broad application prospects in the fields of electronics, transportation, automobiles, aviation, aerospace, and national defense and military. Therefore, research on the metallurgical bonding of magnesium alloys has also received increasing attention.

[0003] Magnesium alloys need to be brazed and formed in some applications in radar and electronics fields. The brazing flux is an important factor affecting brazing forming. Currently, most magnesium alloy brazing materials are mainly prepared by smelting alloys. The main component of the magnesium alloy brazing materials prepared by smelting is eutectic structure. The brazing materials prepared by smelting method usually need to be reprocessed to obtain the required brazing material size. However, the eutectic structure of magnesium alloys is very brittle and difficult to reprocess. In addition, the method of obtaining magnesium alloy brazing materials by smelting alloys is difficult to prepare in batches. Summary of the Invention

[0004] The main purpose of the present invention is to overcome the deficiencies in the prior art and solve the technical problems of insufficient welding strength of magnesium alloy brazing filler metals prepared by smelting method and difficulty in reducing the thickness of the brazing filler metals by secondary processing before welding. The present invention provides a MgAl rolled composite brazing filler metal and its preparation method and brazing method.

[0005] The design concept of the present invention is: through the method of composite rolling of Mg rolled plate and Al rolled plate, a MgAl rolled composite solder with a thickness of less than 500μm is directly prepared. The solder is "formed first and then formed into properties", and the low-melting-point eutectic structure will diffuse and generate during the brazing process, and the solder preparation and brazing process can be realized in "one step". The advantage of this method is that it can conveniently and efficiently prepare composite solders with a large area and a thickness of less than 500μm in batches, without the need for reprocessing the solder, and the generation of the eutectic structure and the brazing process are integrated. In addition, the brazing temperature of the solder is suitable, the process is simple, the brazing formability is excellent, and the joint shear strength is high. While ensuring the welding connection performance requirements of magnesium alloy structural parts, it can realize the industrial production of magnesium alloy solders.

[0006] The present invention is achieved through the following technical solutions:

[0007] A MgAl rolled composite solder is prepared by hot rolling after Mg rolled plates and Al rolled plates are alternately stacked in a sandwich structure of Al rolled plates-Mg rolled plates-Al rolled plates. The Mg rolled plates and Al rolled plates have the same length and width, and both have a thickness of 0.4-0.6 mm. The thickness of the MgAl rolled composite solder does not exceed 500 μm.

[0008] A method for preparing the MgAl rolled composite solder as described above comprises the following steps:

[0009] S1. Raw material preparation: First, pure Mg ingots and pure Al ingots were cut to obtain cast plates with dimensions of 70 mm in length, 30 mm in width, and 1.5 mm in height. Then, the cast Mg plates and Al plates were rolled at 350°C to 400°C, with a reduction of 15% to 20% per pass, respectively, to obtain Mg rolled plates and Al rolled plates with thicknesses of 0.4 to 0.6 mm. Finally, one Mg rolled plate and two Al rolled plates were alternately stacked in a sandwich structure of Al rolled plate-Mg rolled plate-Al rolled plate to obtain a brazing filler metal.

[0010] S2. Place the solder blank prepared in step S1 into a heating furnace, set the heating temperature to 280-400°C, and keep it warm for 2-10 minutes after reaching the set temperature;

[0011] S3. The solder blank heated in step S2 is fed into a rolling device for multiple rolling passes, with a reduction of 15% to 30% in each pass and a total reduction of 50% to 70%, to obtain a MgAl laminated composite solder.

[0012] A brazing method using the MgAl rolled composite brazing filler metal as described above comprises the following steps:

[0013] S1. First, clean the surface of the magnesium alloy to be brazed to remove impurities, oil stains and oxide film on the surface; then use 80 and 600 mesh metallographic sandpaper to polish the surface to be brazed smooth; finally, rinse the magnesium alloy to be brazed and the MgAl laminated brazing material with alcohol and blow dry with cold air, leaving them for later use;

[0014] S2. Place the cleaned MgAl rolled composite brazing filler metal between the surfaces of the magnesium alloy to be brazed, and then place it in a brazing mold. To improve the efficiency of the filler metal diffusion to form the eutectic structure and the connection accuracy, the brazing mold applies a constant vertical pressure of 0.5-5 MPa.

[0015] S3. Place the brazing mold assembled in step S2 as a whole in a vacuum hot pressing welding furnace. First, evacuate the vacuum hot pressing welding furnace to a vacuum degree of 0-10 Pa; then, fill the vacuum hot pressing welding furnace with argon gas for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, set the heating rate of the vacuum hot pressing welding furnace to 1°C / min-10°C / min, and keep the temperature for 5-10 minutes every time the temperature rises by 30-50°C. The final brazing temperature is 460-500°C, and the holding time is 30-120 minutes. Cool to room temperature to complete the brazing of the magnesium alloy material.

[0016] Preferably, in step S2, the constant vertical pressure applied by the brazing mold is 2-3 MPa.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) The MgAl rolled composite brazing filler metal prepared by the present invention has a melting temperature of 437-455°C, a brazing temperature of 460-500°C, and a thickness of less than 500 μm, eliminating the need for secondary thinning before brazing. The filler metal is prepared using a mature rolling method, facilitating industrial transformation for enterprises without the need to purchase new equipment, enabling simple and convenient mass production.

[0019] 2) This invention utilizes a brazing process to simultaneously control the conversion of the MgAl rolled composite filler metal to a eutectic structure and component welding. During the brazing process, the filler metal first transforms into a eutectic structure with a lower melting point, which then melts to achieve component welding. This process promotes micro-diffusion between the welded components and the filler metal, reducing defects such as cracks, pores, and inclusions in the weld. It also exhibits excellent surface wettability, ensuring sufficient fill in the braze joint. When using the furnace brazing process to weld magnesium and aluminum alloys, no flux is required, and the shear strength of the welded joint ranges from 43 to 96 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a DSC curve of the MgAl rolled composite solder prepared in Example 1;

[0021] Figure 2 This is a low-magnification OM photograph of the MgAl rolled composite solder prepared in Example 1. DETAILED DESCRIPTION

[0022] The present invention will be described in further detail below with reference to the accompanying drawings and examples. Example 1

[0023] A method for preparing a MgAl rolled composite solder comprises the following steps:

[0024] S1. Raw material preparation: First, pure Mg ingots and pure Al ingots (with a purity of 99.9% or higher) were cut to obtain cast plates with dimensions of 70 mm in length, 30 mm in width, and 1.5 mm in height. Then, the cast Mg plates and Al plates were rolled at 350°C, with a reduction of 16% per pass, to obtain 0.45 mm thick Mg rolled plates and 0.42 mm thick Al rolled plates. Finally, one Mg rolled plate and two Al rolled plates were alternately stacked in a sandwich structure of Al rolled plate-Mg rolled plate-Al rolled plate to obtain a brazing filler metal.

[0025] S2. Place the solder blank prepared in step S1 into a heating furnace, set the heating temperature to 300°C, and heat it to the set temperature and keep it warm for 10 minutes;

[0026] S3, the solder blank heated in step S2 is sent to a rolling equipment for multiple rolling processes, with a reduction of 25% in each process and a total reduction of 64%, to obtain a MgAl laminated composite solder. The thickness of the MgAl laminated composite solder is 457 μm. The DSC curve of the MgAl laminated composite solder is shown in FIG. Figure 1 As shown, it can be known that the melting point of the composite solder is 452°C.

[0027] A brazing method using the MgAl rolled composite brazing filler metal as described above comprises the following steps:

[0028] S1. In Example 1, the size of the magnesium alloy to be brazed is 30 mm × 50 mm × 5.7 mm. First, the surface to be brazed of the magnesium alloy is cleaned to remove impurities, oil stains, and oxide films on the surface; then, the surface to be brazed is polished smooth using 80-grit and 600-grit metallographic sandpapers, respectively; finally, the magnesium alloy to be brazed and the MgAl rolled composite brazing filler metal are rinsed with alcohol and blown dry with cold air for subsequent use;

[0029] S2. Place the cleaned MgAl rolled composite brazing filler metal between the surfaces of the magnesium alloy to be brazed, and then place it in a brazing mold. The brazing mold applies a constant vertical pressure of 2 MPa.

[0030] S3. Place the brazing mold assembled in step S2 in a vacuum hot pressing welding furnace. First, evacuate the vacuum hot pressing welding furnace to a vacuum degree of 10Pa. Then, fill the vacuum hot pressing welding furnace with argon gas for protection, and the argon gas pressure is not less than the standard atmospheric pressure. Finally, set the vacuum hot pressing welding furnace to a heating rate of 10°C / min, and hold the temperature for 5 minutes each time the temperature rises by 50°C. The final brazing temperature is 480°C, the holding time is 60 minutes, and the temperature is cooled to room temperature to complete the brazing of the magnesium alloy material. The low-magnification OM photograph of the weld position is as follows: Figure 2The MgAl alloy joints obtained by brazing are well connected, with no obvious defects such as cracks and pores in metallographic observation. The metallurgical bonding of the welding interface is tight, and the room temperature shear strength is 84.3 MPa. Example 2

[0031] A method for preparing a MgAl rolled composite solder comprises the following steps:

[0032] S1. Raw material preparation: First, pure Mg ingots and pure Al ingots (with a purity of 99.9% or higher) were cut to obtain cast plates with dimensions of 70 mm in length, 30 mm in width, and 1.5 mm in height. Then, the cast Mg plates and Al plates were rolled at 380°C with a reduction of 18% per pass to obtain 0.45 mm thick Mg rolled plates and 0.5 mm thick Al rolled plates. Finally, one Mg rolled plate and two Al rolled plates were alternately stacked in a sandwich structure of Al rolled plate-Mg rolled plate-Al rolled plate to obtain a brazing filler metal.

[0033] S2. Place the solder blank prepared in step S1 into a heating furnace, set the heating temperature to 310°C, and heat it to the set temperature and keep it warm for 8 minutes;

[0034] S3. The solder blank heated in step S2 is fed into a rolling device for multiple rolling passes, with a reduction of 25% in each pass and a total reduction of 68%, to obtain a MgAl laminated composite solder having a thickness of 464 μm.

[0035] A brazing method using the MgAl rolled composite brazing filler metal as described above comprises the following steps:

[0036] S1. In Example 2, the size of the magnesium alloy to be brazed is 30 mm × 50 mm × 5.7 mm. First, the surface to be brazed of the magnesium alloy is cleaned to remove impurities, oil stains, and oxide films on the surface. Then, the surface to be brazed is polished smooth using 80-grit and 600-grit metallographic sandpapers. Finally, the magnesium alloy to be brazed and the MgAl rolled composite brazing filler metal are rinsed with alcohol and dried with cold air for later use.

[0037] S2. Place the cleaned MgAl rolled composite brazing filler metal between the surfaces of the magnesium alloy to be brazed, and then place it in a brazing mold. The brazing mold applies a constant vertical pressure of 3 MPa.

[0038] S3. The brazing mold assembled in step S2 is placed as a whole in a vacuum hot pressing welding furnace. First, the vacuum hot pressing welding furnace is evacuated to a vacuum degree of 8 Pa; then, argon gas is filled into the vacuum hot pressing welding furnace for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, the vacuum hot pressing welding furnace is set to a heating rate of 8°C / min, and the temperature is kept for 6 minutes every time the temperature is increased by 50°C. The final brazing temperature is 480°C, the temperature is kept for 60 minutes, and the brazing is completed to room temperature. The brazing of the magnesium alloy material is completed. The MgAl alloy joint obtained by brazing is well connected, and no obvious defects such as cracks and pores are observed by metallographic observation. The metallographic bonding of the welding interface is tight, and the room temperature shear strength is 79.9 MPa. Example 3

[0039] A method for preparing a MgAl rolled composite solder comprises the following steps:

[0040] S1. Raw material preparation: First, pure Mg ingots and pure Al ingots (with a purity of 99.9% or higher) were cut to obtain cast plates with dimensions of 70 mm in length, 30 mm in width, and 1.5 mm in height. Then, the cast Mg plates and Al plates were rolled at 400°C, with a reduction of 20% per pass, to obtain Mg rolled plates with a thickness of 0.51 mm and Al rolled plates with a thickness of 0.42 mm. Finally, one Mg rolled plate and two Al rolled plates were alternately stacked in a sandwich structure of Al rolled plate-Mg rolled plate-Al rolled plate to obtain a brazing filler metal.

[0041] S2. Place the solder blank prepared in step S1 into a heating furnace, set the heating temperature to 320°C, and heat it to the set temperature and keep it warm for 10 minutes;

[0042] S3. The solder blank heated in step S2 is fed into a rolling device for multiple rolling passes, with a reduction of 20% in each pass and a total reduction of 64%, to obtain a MgAl laminated composite solder having a thickness of 486 μm.

[0043] A brazing method using the MgAl rolled composite brazing filler metal as described above comprises the following steps:

[0044] S1. In Example 3, the size of the magnesium alloy to be brazed is 30 mm × 50 mm × 5.7 mm. First, the surface to be brazed of the magnesium alloy is cleaned to remove impurities, oil stains, and oxide films on the surface. Then, the surface to be brazed is polished smooth using 80-grit and 600-grit metallographic sandpapers. Finally, the magnesium alloy to be brazed and the MgAl rolled composite brazing filler metal are rinsed with alcohol and dried with cold air for later use.

[0045] S2. Place the cleaned MgAl rolled composite brazing filler metal between the surfaces of the magnesium alloy to be brazed, and then place it in a brazing mold. The brazing mold applies a constant vertical pressure of 5 MPa.

[0046] S3. The brazing mold assembled in step S2 is placed as a whole in a vacuum hot pressing welding furnace. First, the vacuum hot pressing welding furnace is evacuated to a vacuum degree of 5 Pa; then, argon gas is filled into the vacuum hot pressing welding furnace for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, the vacuum hot pressing welding furnace is set to a heating rate of 6°C / min, and the temperature is kept for 5 minutes every time the temperature is increased by 50°C. The final brazing temperature is 480°C, the temperature is kept for 60 minutes, and the brazing is completed to room temperature. The brazing of the magnesium alloy material is completed. The MgAl alloy joint obtained by brazing is well connected, and no obvious defects such as cracks and pores are observed by metallographic observation. The metallographic bonding of the welding interface is tight, and the room temperature shear strength is 80.1 MPa.

[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a MgAl rolled composite solder, characterized in that: The following steps are involved: S1. Raw material preparation: First, pure Mg ingots and pure Al ingots were cut to obtain cast plates with dimensions of 70 mm in length, 30 mm in width, and 1.5 mm in height. Then, the cast Mg plates and Al plates were rolled at 350°C to 400°C, with a reduction of 15% to 20% per pass, respectively, to obtain Mg rolled plates and Al rolled plates with thicknesses of 0.4 to 0.6 mm. Finally, one Mg rolled plate and two Al rolled plates were alternately stacked in a sandwich structure of Al rolled plate-Mg rolled plate-Al rolled plate to obtain a brazing filler metal. S2. Place the solder blank prepared in step S1 into a heating furnace, set the heating temperature to 280-400°C, and keep it warm for 2-10 minutes after reaching the set temperature; S3. The solder blank heated in step S2 is fed into a rolling device for multiple rolling passes, with a reduction of 15% to 30% in each pass and a total reduction of 50% to 70%, to obtain a MgAl laminated composite solder.

2. A brazing method using the MgAl rolled composite brazing filler metal prepared by the preparation method according to claim 1, characterized in that: The following steps are involved: S1. First, clean the surface of the magnesium alloy to be brazed to remove impurities, oil stains and oxide film on the surface; then use 80 and 600 mesh metallographic sandpaper to polish the surface to be brazed smooth; finally, rinse the magnesium alloy to be brazed and the MgAl laminated brazing material with alcohol and blow dry with cold air, leaving them for later use; S2. Place the cleaned MgAl rolled composite brazing filler metal between the surfaces of the magnesium alloy to be brazed, and then place it in a brazing mold. The brazing mold applies a constant vertical pressure of 0.5-5 MPa. S3. Place the brazing mold assembled in step S2 as a whole in a vacuum hot pressing welding furnace. First, evacuate the vacuum hot pressing welding furnace to a vacuum degree of 0-10 Pa; then, fill the vacuum hot pressing welding furnace with argon gas for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, set the heating rate of the vacuum hot pressing welding furnace to 1°C / min-10°C / min, and keep the temperature for 5-10 minutes every time the temperature rises by 30-50°C. The final brazing temperature is 460-500°C, and the holding time is 30-120 minutes. Cool to room temperature to complete the brazing of the magnesium alloy material.

3. The brazing method according to claim 2, wherein: In step S2, the constant vertical pressure applied by the brazing mold is 2-3 MPa.

Images