Ultrathin magnesium-zinc brazing filler metal and preparation method and brazing method thereof

Abstract

The invention discloses ultrathin magnesium-zinc 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 that the magnesium alloy brazing filler metal prepared through a smelting method is insufficient in welding strength, and the thickness of the brazing filler metal is difficult to reduce through secondary machining before welding. The outermost layer of the ultrathin magnesium-zinc brazing filler metal is zinc foil; the preparation method of the ultrathin magnesium-zinc brazing filler metal comprises the steps that clean magnesium foils and zinc foils are sequentially staggered and stacked from bottom to top in the mode that one layer of zinc foil and one layer of magnesium foil are arranged, the zinc foil is arranged on the outermost layer, then the magnesium-zinc brazing filler metal blank is put into a resistance furnace to be heated, a magnesium-zinc brazing filler metal blank is prepared and then fed into a cold rolling unit to be rolled, and the ultrathin magnesium-zinc brazing filler metal with the thickness not larger than 500 micrometers is prepared. The magnesium alloy brazing filler metal is used for magnesium alloy material brazing, the final brazing temperature ranges from 380 DEG C to 420 DEG C, and the heat preservation time ranges from 30 min to 120 min. The preparation technology is simple, the low-melting-point eutectic structure of the ultrathin magnesium-zinc brazing filler metal can be generated in a diffusion mode in the brazing process, and brazing filler metal preparation and brazing processes are achieved in one step.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloy welding materials, and particularly relates to an ultra-thin magnesium-zinc solder and a preparation method and a brazing method thereof. Background Art

[0002] Magnesium alloys have the advantages of low density, high specific strength and stiffness, good electrical and thermal conductivity, excellent damping and shock absorption performance, good electromagnetic shielding effect, good mechanical processing performance, and easy recycling. As the lightest metal structural material applicable in industry, it has important application value and broad application prospects in the fields of aerospace, national defense, automobile manufacturing, and electronic products. Due to the demand for lightweight products, there is an urgent need to braze some widely used magnesium alloys, which requires research and development of the brazing filler metals required for magnesium alloy brazing.

[0003] The currently reported methods for preparing magnesium alloy brazing filler metals are mainly based on smelting. In order to lower the brazing melting point of magnesium alloy brazing filler metals, the main component of the magnesium alloy brazing filler metals prepared by smelting is eutectic structure. The presence of excessive eutectic structure in the brazing seam will significantly reduce the welding strength. Moreover, the brazing filler metals prepared by smelting often require secondary processing to thin the filler metal thickness before welding. However, the eutectic structure of magnesium alloys is very brittle, which makes the processing of magnesium alloy brazing filler metals difficult and difficult to achieve mass production and application. 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 solder prepared by smelting method and difficulty in thinning the solder thickness by secondary processing before welding. The present invention provides an ultra-thin magnesium-zinc solder and a preparation method and a brazing method thereof.

[0005] The design concept of the present invention is: a magnesium-zinc composite solder with a thickness of less than 500 μm is directly prepared by a method of composite rolling of magnesium foil and zinc foil. The solder is "formed first and then formed into properties", and a low-melting-point eutectic structure will diffuse and generate during the brazing process, and the solder preparation and brazing process are realized in "one step". The method is simple in process and can prepare magnesium-zinc composite solder with a thickness of less than 500 μm in batches without secondary processing. In addition, the solder has a suitable brazing temperature, a simple process, excellent brazing performance, and good comprehensive joint performance. While ensuring the welding connection performance requirements of magnesium alloy structural parts, the industrial production of magnesium alloy solder is realized.

[0006] The present invention is achieved through the following technical solutions: An ultra-thin magnesium-zinc solder comprises 6 to 10 layers of cross-rolled magnesium foil and 7 to 11 layers of zinc foil, each layer of magnesium foil has a thickness of 0.03 to 0.1 mm, each layer of zinc foil has a thickness of 0.03 to 0.07 mm, and the outermost layer of the ultra-thin magnesium-zinc solder is zinc foil.

[0007] Preferably, the number of cross-laminated magnesium foil layers is 8 to 10, the number of zinc foil layers is 9 to 11, the thickness of each magnesium foil layer is 0.05 to 0.1 mm, and the thickness of each zinc foil layer is 0.03 to 0.05 mm.

[0008] A method for preparing an ultra-thin magnesium-zinc solder comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.03-0.1 mm into 6-10 pieces, and cut the zinc foil with a thickness of 0.03-0.07 mm into 7-11 pieces, clean them with ultrasonic wave, blow dry them with cold wind, and keep them for later use; S2, taking the magnesium foil and zinc foil prepared in step S1 and stacking them alternately from bottom to top in a manner of one layer of zinc foil and one layer of magnesium foil, with the outermost layer being zinc foil, and then putting them into a resistance furnace for heating at a temperature of 280° C. to 350° C. for a holding time of 2 to 10 minutes, to obtain a magnesium-zinc solder blank; S3, rolling forming: the Mg-Zn solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 15% to 30% per pass and a total reduction of 50% to 70%, to obtain an ultra-thin Mg-Zn solder with a thickness of no more than 500 μm.

[0009] Preferably, the prepared ultra-thin Mg-Zn solder has a melting temperature range of 340-370°C and a welding temperature range of 380-420°C, and is used for brazing Mg-Zn alloys with a solidus temperature above 420°C.

[0010] A brazing method for ultra-thin magnesium-zinc brazing filler metal comprises the following steps: 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 grind the surface to be brazed smooth; finally, rinse the magnesium alloy to be brazed and the ultra-thin magnesium-zinc brazing material with alcohol and blow dry with cold air for later use; S2, placing the cleaned ultra-thin magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold. In order to improve the efficiency of the ultra-thin magnesium-zinc brazing filler metal in diffusing to form a eutectic structure and the connection accuracy, a constant vertical pressure of 0.5-5 MPa is applied to the brazing mold; 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 0-10Pa. 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, a step-by-step heating method is used to promote the formation of eutectic structure. The heating rate of the vacuum hot pressing welding furnace is set to 1°C / min-10°C / min, and the temperature is kept for 5-10 minutes every time the temperature is increased by 30°C-50°C. The final brazing temperature is 380-420°C, and the insulation time is 30-120 minutes. Cool to room temperature to complete the brazing of magnesium alloy materials.

[0011] Preferably, in step S2, the brazing mold applies a constant vertical pressure of 2-3 MPa.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. The melting temperature of the ultra-thin magnesium-zinc solder provided by the present invention is 340°C-370°C, the brazing temperature is 380°C-420°C, the thickness of the ultra-thin magnesium-zinc solder is less than 500 μm, and no secondary processing and thinning is required before brazing; the solder is prepared by a rolling method with mature technology, which is convenient for the industrial transformation of enterprises, and there is no need to purchase new equipment, and batch production can be realized simply and conveniently; 2. The present invention uses the brazing process to control the transformation of the ultra-thin magnesium-zinc brazing filler metal (converted into eutectic structure) and the welding of components simultaneously. The ultra-thin magnesium-zinc brazing filler metal is first converted into a eutectic structure with a lower melting point during the brazing process, and then the eutectic structure melts to achieve component welding. This process promotes the micro-diffusion of welding components and brazing fillers, reduces defects such as cracks, pores and inclusions at the weld, has good surface wettability, and fully fills the brazing seam; when the brazing process is used to weld magnesium-zinc alloys, no brazing flux is required, and the shear strength of the welded joint after brazing is between 42 and 55 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a low-magnification OM photograph of the ultra-thin magnesium-zinc solder prepared in Example 1; Figure 2 The DSC curve of the ultra-thin magnesium-zinc solder prepared in Example 1; Figure 3 This is a low-magnification OM photograph of magnesium alloy brazing using the ultra-thin magnesium-zinc brazing filler metal prepared in Example 1. DETAILED DESCRIPTION

[0014] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Example 1

[0015] A method for preparing an ultra-thin magnesium-zinc solder comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.1 mm into 10 pieces, and cut the zinc foil with a thickness of 0.03 mm into 11 pieces, clean them by ultrasonic wave, blow dry them with cold wind and keep them for later use; wherein the purity of the magnesium foil and the zinc foil are both above 99.9%; S2, taking the magnesium foil and zinc foil prepared in step S1 and stacking them alternately from bottom to top in the manner of one layer of zinc foil and one layer of magnesium foil, with the outermost layer being zinc foil, and then putting them into a resistance furnace for heating at a heating temperature of 290° C. for a holding time of 10 min, to obtain a magnesium-zinc solder blank; S3, rolling forming: the Mg-Zn solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 25% per pass and a total reduction of 64%, to obtain an ultra-thin Mg-Zn solder with a thickness of 490 μm. The microstructure and DSC curve are shown in FIG. Figure 1 and Figure 2 shown.

[0016] A brazing method using the ultra-thin magnesium-zinc brazing filler metal prepared in Example 1 comprises the following steps: S1. In this embodiment 1, the size of the magnesium alloy to be brazed is 50 mm in length × 30 mm in width × 5.7 mm in thickness. First, the surface to be brazed of the magnesium alloy to be brazed is cleaned to remove impurities, oil stains and oxide films on the surface; then, 80 and 600 mesh metallographic sandpapers are used to grind the surface to be brazed smooth; finally, the magnesium alloy to be brazed and the ultra-thin magnesium-zinc brazing material are rinsed with alcohol and dried with cold air for later use; S2, placing the cleaned ultra-thin magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold, and applying a constant vertical pressure of 2 MPa to the brazing mold; S3, the brazing mold assembled in step S2 is placed in a vacuum hot pressing welding furnace. First, the vacuum hot pressing welding furnace is evacuated to a vacuum degree of 10Pa; 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 have a heating rate of 10°C / min, and the temperature is kept for 5 minutes every time the temperature is increased by 50°C. The final brazing temperature is 400°C, the temperature is kept for 90 minutes, and the brazing is completed after cooling to room temperature. The brazing of the magnesium alloy material is completed, and the microstructure of the brazing seam is as follows: Figure 3 As shown, it can be seen that the magnesium-zinc alloy joint obtained by brazing is well connected, there are no obvious defects such as cracks and pores in metallographic observation, the welding interface is metallurgically bonded tightly, and the room temperature shear strength is 42.2MPa. Example 2

[0017] A method for preparing an ultra-thin magnesium-zinc solder comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.1 mm into 10 pieces, and cut the zinc foil with a thickness of 0.05 mm into 11 pieces, clean them by ultrasonic wave, blow dry them with cold wind and keep them for later use; wherein the purity of the magnesium foil and the zinc foil are both above 99.9%; S2, taking the magnesium foil and zinc foil prepared in step S1, stacking them alternately from bottom to top in the manner of one layer of zinc foil and one layer of magnesium foil, with the outermost layer being zinc foil, and then putting them into a resistance furnace for heating at a heating temperature of 300° C. for a holding time of 8 minutes, to obtain a magnesium-zinc solder blank; S3, rolling forming: the Mg-Zn solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 25% per pass and a total reduction of 68%, to obtain an ultra-thin Mg-Zn solder with a thickness of 495 μm.

[0018] A brazing method using the ultra-thin magnesium-zinc brazing filler metal prepared in Example 2 comprises the following steps: S1. In this embodiment 2, the size of the magnesium alloy to be brazed is 50 mm in length × 30 mm in width × 5.7 mm in thickness. First, the surface to be brazed of the magnesium alloy to be brazed is cleaned to remove impurities, oil stains and oxide films on the surface; then, 80 and 600 mesh metallographic sandpapers are used to grind the surface to be brazed smooth; finally, the magnesium alloy to be brazed and the ultra-thin magnesium-zinc brazing material are rinsed with alcohol and blown dry with cold air for later use; S2, placing the cleaned ultra-thin magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold, and applying a constant vertical pressure of 3 MPa to the brazing mold; 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 8Pa; 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 8°C / min, keep warm for 6 minutes every time the temperature rises by 50°C, the final brazing temperature is 400°C, the insulation time is 90 minutes, and the brazing is completed to room temperature. The brazing of the magnesium alloy material is completed, and the brazing of the magnesium-zinc alloy joint is well connected, and the room temperature shear strength is 45.5MPa. Example 3

[0019] A method for preparing an ultra-thin magnesium-zinc solder comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.05 mm into 10 pieces, and cut the zinc foil with a thickness of 0.05 mm into 11 pieces, clean them by ultrasonic wave, blow dry them with cold wind and keep them for later use; wherein the purity of the magnesium foil and the zinc foil are both above 99.9%; S2, taking the magnesium foil and zinc foil prepared in step S1 and stacking them alternately from bottom to top in the manner of one layer of zinc foil and one layer of magnesium foil, with the outermost layer being zinc foil, and then putting them into a resistance furnace for heating at a heating temperature of 310° C. for a holding time of 10 min, to obtain a magnesium-zinc solder blank; S3, rolling forming: the Mg-Zn solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 20% per pass and a total reduction of 54%, to obtain an ultra-thin Mg-Zn solder with a thickness of 480 μm.

[0020] A brazing method using the ultra-thin magnesium-zinc brazing filler metal prepared in Example 3 comprises the following steps: S1. In this embodiment 3, the size of the magnesium alloy to be brazed is 50 mm in length × 30 mm in width × 5.7 mm in thickness. First, the surface to be brazed of the magnesium alloy to be brazed is cleaned to remove impurities, oil stains and oxide films on the surface; then, 80 and 600 mesh metallographic sandpapers are used to grind the surface to be brazed smooth; finally, the magnesium alloy to be brazed and the ultra-thin magnesium-zinc brazing material are rinsed with alcohol and blown dry with cold air for later use; S2, placing the cleaned ultra-thin magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold, and applying a constant vertical pressure of 5 MPa to the brazing mold; 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 5Pa; 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 6°C / min, keep warm for 5 minutes every time the temperature rises by 50°C, the final brazing temperature is 400°C, the insulation time is 90 minutes, and the brazing is completed to room temperature. The brazing of the magnesium alloy material is completed, and the brazing of the magnesium-zinc alloy joint is well connected, and the room temperature shear strength is 54.6MPa.

[0021] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An ultra-thin magnesium-zinc solder, characterized in that: The ultra-thin magnesium-zinc solder includes 6 to 10 layers of cross-rolled magnesium foil and 7 to 11 layers of zinc foil, each layer of magnesium foil has a thickness of 0.03 to 0.1 mm, each layer of zinc foil has a thickness of 0.03 to 0.07 mm, and the outermost layer of the ultra-thin magnesium-zinc solder is zinc foil.

2. The ultra-thin magnesium-zinc solder according to claim 1, characterized in that: The number of layers of the cross-laminated magnesium foil is 8 to 10, and the number of layers of the zinc foil is 9 to 11. The thickness of each layer of the magnesium foil is 0.05 to 0.1 mm, and the thickness of each layer of the zinc foil is 0.03 to 0.05 mm.

3. A method for preparing the ultra-thin magnesium-zinc solder according to claim 1, characterized in that: The following steps are involved: S1. Cut the magnesium foil with a thickness of 0.03-0.1 mm into 6-10 pieces, and cut the zinc foil with a thickness of 0.03-0.07 mm into 7-11 pieces, clean them with ultrasonic wave, blow dry them with cold wind, and keep them for later use; S2, taking the magnesium foil and zinc foil prepared in step S1 and stacking them alternately from bottom to top in a manner of one layer of zinc foil and one layer of magnesium foil, with the outermost layer being zinc foil, and then putting them into a resistance furnace for heating at a temperature of 280° C. to 350° C. for a holding time of 2 to 10 minutes, to obtain a magnesium-zinc solder blank; S3, rolling forming: the Mg-Zn solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 15% to 30% per pass and a total reduction of 50% to 70%, to obtain an ultra-thin Mg-Zn solder with a thickness of no more than 500 μm.

4. The method for preparing an ultra-thin magnesium-zinc solder according to claim 3, characterized in that: The prepared ultra-thin magnesium-zinc brazing filler metal has a melting temperature range of 340-370°C and a welding temperature range of 380-420°C, and is used for brazing magnesium-zinc alloys with a solidus temperature above 420°C.

5. A brazing method using the ultra-thin magnesium-zinc brazing filler metal as claimed in 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 grind the surface to be brazed smooth; finally, rinse the magnesium alloy to be brazed and the ultra-thin magnesium-zinc brazing material with alcohol and blow dry with cold air for later use; S2, placing the cleaned ultra-thin magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold, and applying a constant vertical pressure of 0.5-5MPa to the brazing mold; 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 0-10Pa; 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 heating rate of the vacuum hot pressing welding furnace to 1°C / min-10°C / min, and keep warm for 5-10 minutes every time the temperature rises by 30°C-50°C. The final brazing temperature is 380-420°C, and the insulation time is 30-120 minutes. Cool to room temperature to complete the brazing of the magnesium alloy material.

6. A brazing method for ultra-thin magnesium-zinc brazing filler metal according to claim 5, characterized in that: In step S2, the brazing mold applies a constant vertical pressure of 2-3 MPa.

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