An ultra-thin magnesium-zinc brazing filler metal, a preparation method thereof and a brazing method

Abstract

The application discloses an ultrathin magnesium-zinc filler metal, a preparation method thereof and a brazing method, belongs to the technical field of magnesium alloy welding materials, and solves the technical problems of insufficient welding strength of magnesium alloy filler metal prepared by a melting method and difficulty in reducing the thickness of the filler metal before welding. The solution is as follows: the ultrathin magnesium-zinc filler metal comprises 6-10 layers of magnesium foils and 7-11 layers of zinc foils which are cross-laminated, and the outermost layer of the ultrathin magnesium-zinc filler metal is a zinc foil; the preparation method of the ultrathin magnesium-zinc filler metal is as follows: clean magnesium foils and zinc foils are cross-laminated in the mode of one layer of zinc foil and one layer of magnesium foil from bottom to top, and the outermost layer is a zinc foil; then the magnesium-zinc filler metal blank is prepared by heating in a resistance furnace; and then the ultrathin magnesium-zinc filler metal with a thickness of not more than 500 mu m is prepared by feeding into a cold rolling mill, and is used for brazing of magnesium alloy materials; and the final brazing temperature is 380-420 DEG C, and the holding time is 30-120 min. The preparation process is simple, the low-melting-point eutectic structure of the ultrathin magnesium-zinc filler metal can be diffused and generated in the brazing process, and the filler metal preparation and brazing process are realized in one step.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of magnesium alloy welding material, and particularly relates to an ultrathin magnesium-zinc filler metal and a preparation method and a brazing method thereof. BACKGROUND

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

[0003] At present, the preparation method of magnesium alloy filler metal mainly adopts smelting. In order to reduce the brazing melting point of magnesium alloy filler metal, the main component of the magnesium alloy filler metal prepared by smelting is eutectic structure, and the excessive eutectic structure at the brazing seam can significantly reduce the welding strength. Moreover, the filler metal prepared by smelting often needs secondary processing to reduce the thickness of the filler metal before welding. However, the magnesium alloy eutectic structure is very brittle, which makes the magnesium alloy filler metal difficult to process and difficult to realize mass production and application. SUMMARY

[0004] The main purpose of the present application is to overcome the deficiencies in the prior art, solve the technical problems of insufficient welding strength of the magnesium alloy filler metal prepared by smelting and difficulty in secondary processing to reduce the thickness of the filler metal before welding, and provide an ultrathin magnesium-zinc filler metal and a preparation method and a brazing method thereof.

[0005] The design concept of the present application is to directly prepare a magnesium-zinc composite filler metal with a thickness of less than 500 microns by the method of composite rolling of magnesium foil and zinc foil. The low-melting-point eutectic structure will diffuse and generate during the brazing process, and the filler metal preparation and brazing process are realized in one step. This method is simple and can batch produce magnesium-zinc composite filler metal with a thickness of less than 500 microns without the need for secondary processing. The brazing temperature of the filler metal is appropriate, the process is simple, the brazing performance is excellent, and the joint comprehensive performance is good. While ensuring the welding connection performance requirements of magnesium alloy structural parts, the industrial production of magnesium alloy filler metal is realized.

[0006] The present application is realized by the following technical solutions:

[0007] An ultrathin magnesium-zinc filler metal, comprising 6-10 layers of magnesium foil and 7-11 layers of zinc foil which are cross-rolled, the thickness of each layer of magnesium foil is 0.03-0.1 mm, the thickness of each layer of zinc foil is 0.03-0.07 mm, and the outermost layer of the ultrathin magnesium-zinc filler metal is zinc foil.

[0008] Preferably, the cross-laminated magnesium foil has 8-10 layers, the zinc foil has 9-11 layers, each layer of magnesium foil has a thickness of 0.05-0.1 mm, and each layer of zinc foil has a thickness of 0.03-0.05 mm.

[0009] A preparation method of the super-thin magnesium-zinc filler metal comprises the following steps:

[0010] S1, cut the magnesium foil with a thickness of 0.03-0.1 mm into 6-10 pieces, cut the zinc foil with a thickness of 0.03-0.07 mm into 7-11 pieces, and then ultrasonic clean and dry with cold air for later use;

[0011] S2, take the magnesium foil and zinc foil prepared in step S1, and stack them in an alternating manner from bottom to top, with one layer of zinc foil and one layer of magnesium foil, and the outermost layer being the zinc foil, and then place them in a resistance furnace for heating, with a heating temperature of 280-350°C and a holding time of 2-10 min, to obtain a magnesium-zinc filler metal blank;

[0012] S3, rolling forming: send the magnesium-zinc filler metal blank prepared in step S2 into a cold rolling mill, with a pass reduction of 15-30% and a total reduction of 50-70%, to obtain a super-thin magnesium-zinc filler metal with a thickness of not more than 500 μm.

[0013] Preferably, the prepared super-thin magnesium-zinc 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 alloy with a solidus temperature above 420°C.

[0014] A brazing method of a super-thin magnesium-zinc filler metal comprises the following steps:

[0015] S1, first, clean the welding surface of the magnesium alloy to be brazed to remove impurities, oil stains and oxide films on the surface; then polish the welding surface with 80 and 600 mesh metallographic sandpaper in sequence; finally, rinse the magnesium alloy to be brazed and the super-thin magnesium-zinc filler metal with alcohol and dry them with cold air for later use;

[0016] S2, place the cleaned super-thin magnesium-zinc filler metal between the welding surfaces of the magnesium alloy to be brazed, and then place it in a brazing mold; to improve the efficiency of the super-thin magnesium-zinc filler metal in generating eutectic structure and the precision of the connection, the brazing mold applies a constant vertical pressure of 0.5-5 MPa;

[0017] S3, the whole of the brazing mold assembled in step S2 is placed in a vacuum hot-pressing welding furnace, first, the vacuum hot-pressing welding furnace is vacuumized to a vacuum degree of 0-10 Pa; then, the vacuum hot-pressing welding furnace is filled with argon for protection, the argon pressure is not less than the standard atmospheric pressure; finally, a stepwise multi-step heating mode is adopted to promote the generation of eutectic structure, the heating rate of the vacuum hot-pressing welding furnace is set to 1-10 ℃ / min, and the temperature is increased by 30-50 ℃ every time, and the temperature is kept for 5-10 min, the final brazing temperature is 380-420 ℃, the holding time is 30-120 min, and the temperature is cooled to room temperature, and the magnesium alloy material brazing is completed.

[0018] Preferably, in step S2, the brazing mold is applied with a constant vertical pressure of 2-3 MPa.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1. The melting temperature of the ultra-thin magnesium-zinc filler metal provided by the present application is 340-370 ℃, the brazing temperature is 380-420 ℃, the thickness of the ultra-thin magnesium-zinc filler metal is less than 500 μm, and no secondary processing is required before brazing. The filler metal is prepared by a mature rolling method, which is convenient for industrial transformation of enterprises, does not require the purchase of new equipment, and realizes batch production simply and conveniently.

[0021] 2. The present application controls the microstructure transformation (transformation into eutectic structure) of the ultra-thin magnesium-zinc filler metal and the welding of the component synchronously by using the brazing process. The ultra-thin magnesium-zinc filler metal is first transformed into eutectic structure with a lower melting point during the brazing process, and then the eutectic structure melts to realize the welding of the component. The process promotes the micro-diffusion of the welded component and the filler metal, reduces the defects such as cracks, pores and inclusions at the weld, has good surface wettability, and fully fills the brazing seam. When the magnesium-zinc alloy is welded by using the brazing process, no flux is required, and the shear strength of the welded joint after brazing is between 42-55 MPa. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The low-magnification OM photograph of the ultra-thin magnesium-zinc filler metal prepared for Example 1;

[0023] Figure 2 The DSC curve diagram of the ultra-thin magnesium-zinc filler metal prepared for Example 1;

[0024] Figure 3 The low-magnification OM photograph of the magnesium alloy brazing after the ultra-thin magnesium-zinc filler metal prepared by using Example 1. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with the drawings and examples. Example 1

[0026] A preparation method of an ultrathin magnesium-zinc filler metal, comprising the following steps:

[0027] S1, cut magnesium foils with a thickness of 0.1 mm into 10 pieces, cut zinc foils with a thickness of 0.03 mm into 11 pieces, ultrasonic cleaning and drying with cold air, and then wait for use in the next step; wherein the purity of the magnesium foils and the zinc foils is more than 99.9%;

[0028] S2, stack the magnesium foils and the zinc foils prepared in step S1 in an alternating manner from bottom to top, with one zinc foil and one magnesium foil, and the outermost layer being a zinc foil, and then heat in a resistance furnace, the heating temperature being 290℃, and the holding time being 10 min, to obtain a magnesium-zinc filler metal blank;

[0029] S3, roll forming: send the magnesium-zinc filler metal blank prepared in step S2 into a cold rolling mill, the reduction per pass being 25%, and the total reduction being 64%, to obtain an ultrathin magnesium-zinc filler metal with a thickness of 490μm, the microstructure and the DSC curve diagram thereof being shown in Figure 1 and Figure 2 .

[0030] A brazing method using the ultrathin magnesium-zinc filler metal prepared in the embodiment 1, comprising the following steps:

[0031] S1, in the embodiment 1, the size of the magnesium alloy to be brazed is 50*30*5.7mm, first, clean the welding surface of the magnesium alloy to be brazed, remove the impurities, oil stains and oxide film on the surface; then polish the welding surface with 80 and 600 mesh metallographic sandpaper in turn; finally, rinse the magnesium alloy to be brazed and the ultrathin magnesium-zinc filler metal with alcohol and dry them with cold air, and wait for use in the next step;

[0032] S2, place the cleaned ultrathin magnesium-zinc filler metal between the welding surfaces of the magnesium alloy to be brazed, and then put it into a brazing mold, the brazing mold applies a constant vertical pressure of 2MPa;

[0033] S3, place the assembled brazing mold of step S2 into a vacuum hot pressing welding furnace, first, vacuumize the vacuum hot pressing welding furnace to a vacuum degree of 10Pa; then, fill argon gas in the vacuum hot pressing welding furnace for protection, 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 10℃ / min, and hold for 5min every 50℃, the final brazing temperature is 400℃, the holding time is 90min, and cool to room temperature, complete the brazing of the magnesium alloy material, the microstructure of the brazing seam is shown in Figure 3 , it can be seen that the magnesium-zinc alloy joint obtained by brazing is well connected, there is no obvious crack and pore defect in the metallographic observation, the welding interface is tightly combined, and the room temperature shear strength is 42.2MPa. Embodiment 2

[0034] A preparation method of an ultrathin magnesium-zinc filler metal, comprising the following steps:

[0035] S1, cut magnesium foils with a thickness of 0.1 mm into 10 pieces, cut zinc foils with a thickness of 0.05 mm into 11 pieces, ultrasonic cleaning and drying with cold air, and then wait for use in the next step; wherein the purity of the magnesium foils and the zinc foils is more than 99.9%;

[0036] S2, stack the magnesium foils and the zinc foils prepared in step S1 in an alternating manner from bottom to top, with one zinc foil and one magnesium foil, and the outermost layer being a zinc foil, and then heat in a resistance furnace, the heating temperature being 300 DEG C, and the holding time being 8 min, to obtain a magnesium-zinc filler metal blank;

[0037] S3, roll forming: send the magnesium-zinc filler metal blank prepared in step S2 into a cold rolling mill, the reduction per pass being 25%, and the total reduction being 68%, to obtain an ultrathin magnesium-zinc filler metal with a thickness of 495 μm.

[0038] A brazing method using the ultrathin magnesium-zinc filler metal prepared in the embodiment 2, comprising the following steps:

[0039] S1, in the embodiment 2, the size of the magnesium alloy to be brazed is 50*30*5.7 mm, first, clean the welding surface of the magnesium alloy to be brazed, remove the impurities, dirt and oxide film on the surface, then polish the welding surface with 80 and 600 mesh metallographic sandpaper in turn, and finally wash the magnesium alloy to be brazed and the ultrathin magnesium-zinc filler metal with alcohol and dry them with cold air, and wait for use in the next step;

[0040] S2, place the cleaned ultrathin magnesium-zinc filler metal between the welding surfaces of the magnesium alloy to be brazed, and then put it into a brazing mold, the brazing mold applies a constant vertical pressure of 3 MPa;

[0041] S3, place the assembled brazing mold of step S2 in a vacuum hot pressing welding furnace, first, vacuumize the vacuum hot pressing welding furnace to a vacuum degree of 8 Pa, then fill argon gas in the vacuum hot pressing welding furnace for protection, 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 DEG C / min, and hold for 6 min every 50 DEG C, the final brazing temperature is 400 DEG C, the holding time is 90 min, and the magnesium alloy material brazing is completed after cooling to room temperature, the magnesium-zinc alloy joint is connected well by brazing, and the room temperature shear strength is 45.5 MPa. Embodiment 3

[0042] A preparation method of an ultrathin magnesium-zinc filler metal, comprising the following steps:

[0043] S1, cut the magnesium foil with a thickness of 0.05mm into 10 pieces, cut the zinc foil with a thickness of 0.05mm into 11 pieces, ultrasonic cleaning and blowing dry with cold air, then wait for later use; wherein, the purity of magnesium foil and zinc foil is more than 99.9%;

[0044] S2, take the magnesium foil and zinc foil prepared in step S1, and stack them alternately from bottom to top in the manner of one layer of zinc foil and one layer of magnesium foil, and the outermost layer is zinc foil, then put them into a resistance furnace, the heating temperature is 310℃, and the holding time is 10min, to obtain a magnesium-zinc solder blank;

[0045] S3, rolling forming: put the magnesium-zinc solder blank prepared in step S2 into a cold rolling mill, the reduction per pass is 20%, and the total reduction is 54%, to obtain an ultra-thin magnesium-zinc solder with a thickness of 480μm.

[0046] A brazing method using the ultra-thin magnesium-zinc solder prepared in this embodiment 3, comprising the following steps:

[0047] S1, in this embodiment 3, the size of the magnesium alloy to be brazed is 50mm in length, 30mm in width and 5.7mm in thickness, first, clean the welding surface of the magnesium alloy to be brazed, remove the impurities, dirt and oxide film on the surface, then polish the welding surface with 80 and 600 mesh metallographic sandpaper in turn, finally, rinse the magnesium alloy to be brazed and the ultra-thin magnesium-zinc solder with alcohol and dry them with cold air, and wait for later use;

[0048] S2, place the cleaned ultra-thin magnesium-zinc solder between the welding surfaces of the magnesium alloy to be brazed, then put it into the brazing mold, and the brazing mold applies a constant vertical pressure of 5MPa;

[0049] S3, put the assembled brazing mold of step S2 into a vacuum hot pressing welding furnace, first, vacuumize the vacuum hot pressing welding furnace to a vacuum degree of 5Pa, then fill argon gas in the vacuum hot pressing welding furnace for protection, the argon gas pressure is not less than standard atmospheric pressure, finally, set the heating rate of the vacuum hot pressing welding furnace to 6℃ / min, and keep the temperature for 5min every 50℃, the final brazing temperature is 400℃, the holding time is 90min, and the magnesium alloy material brazing is completed after cooling to room temperature, the magnesium-zinc alloy joint is connected well by brazing, and the room temperature shear strength is 54.6MPa.

[0050] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing an ultrathin magnesium-zinc solder, characterized by, It comprises the following steps: S1, cut the magnesium foil with a thickness of 0.05-0.1 mm into 8-10 pieces, cut the zinc foil with a thickness of 0.03-0.05 mm into 9-11 pieces, ultrasonic cleaning and dry with cold air, and then wait for use in the next step; S2, take the magnesium foil and zinc foil prepared in step S1, and stack them alternately from bottom to top in the manner of one layer of zinc foil and one layer of magnesium foil, and the outermost layer is zinc foil, then put them into a resistance furnace, heat at a temperature of 280-350℃, and keep the temperature for 2-10 min to obtain a magnesium-zinc solder blank; S3, rolling forming: put the magnesium-zinc solder blank prepared in step S2 into a cold rolling mill, the reduction per pass is 15-30%, and the total reduction is 50-70%, to obtain an ultra-thin magnesium-zinc solder with a thickness of not more than 500μm.

2. The method for preparing an ultrathin magnesium-zinc brazing filler metal according to claim 1, characterized in that, The melting temperature range of the prepared ultra-thin magnesium-zinc solder is 340-370℃, the welding temperature range is 380-420℃, and it is used for magnesium-zinc alloy brazing with a solidus temperature above 420℃.

3. A brazing method using the ultra-thin magnesium-zinc filler metal prepared by the method of claim 1, characterized in that, It comprises the following steps: S1, first, clean the welding surface of the magnesium alloy to be brazed, remove the impurities, oil stains and oxide film on the surface, then polish the welding surface smooth with 80 and 600 mesh metallographic sandpaper in turn, and finally rinse the magnesium alloy to be brazed and the ultra-thin magnesium-zinc solder with alcohol and dry them with cold air, and wait for use in the next step; S2, place the cleaned ultra-thin magnesium-zinc solder between the welding surfaces of the magnesium alloy to be brazed, then put it into a brazing mold, and the brazing mold applies a constant vertical pressure of 0.5-5MPa; S3, place the assembled brazing mold of step S2 in a vacuum hot pressing welding furnace, first, vacuumize the vacuum hot pressing welding furnace to a vacuum degree of 0-10Pa, then fill it with argon for protection, the argon pressure is not less than standard atmospheric pressure, finally, set the heating rate of the vacuum hot pressing welding furnace to 1-10℃ / min, keep the temperature constant for 5-10 min every time the temperature rises by 30-50℃, the final brazing temperature is 380-420℃, the holding time is 30-120 min, and cool to room temperature to complete the brazing of the magnesium alloy material.

4. The brazing method of the ultrathin magnesium-zinc filler metal according to claim 3, characterized by: In step S2, the brazing mold applies a constant vertical pressure of 2-3MPa.

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