Aluminum alloy brazing filler metal and preparation method thereof

Abstract

The present invention belongs to the technical field of aluminum alloy brazing materials, and specifically relates to a brazing filler metal for aluminum alloy and a preparation method thereof. The preparation method of the brazing filler metal for aluminum alloy of the present invention uses fly ash as raw material, reduces aluminum oxide and silicon oxide to obtain a crude aluminum silicon alloy, then adds Ge, Zn, and Mn elements for smelting during the refining process, and produces Al-Si-Ge-Zn brazing filler metal after brazing processing. The present invention uses fly ash as Al source and Si source. Since Al and Si are evenly distributed in the natural fly ash structure, the composition segregation caused by the density difference between the two can be avoided during the smelting process, so that the brazing filler metal obtained after the crude aluminum silicon alloy and Ge and Zn metal are smelted is more uniform in composition, and the mechanical properties of the aluminum alloy joint obtained by welding are significantly improved. The shear strength of the brazed joint is as high as 149.3 to 186.4 MPa, which is suitable for aluminum alloy brazing applications.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy brazing materials, and particularly relates to a brazing filler metal for aluminum alloy and a preparation method thereof. Background Art

[0002] Brazing has the advantages of small deformation of brazed parts, high dimensional accuracy, and strong structural adaptability. It is an important method for connecting aluminum alloys. Al-Si brazing filler metal has good wettability, high strength, and excellent processing performance. It can be easily made into needle wire or box and is widely used in brazing of aluminum and aluminum alloys. However, in the brazing process of 6061 aluminum alloy, due to the low solidus temperature of 6061 aluminum alloy (582-595℃), when Al-Si eutectic brazing filler metal (melting point is about 577℃) is used for brazing, the brazing temperature is very close to the solidus temperature of 6061 aluminum alloy, which can easily cause overburning and softening of the base material.

[0003] Therefore, for the brazing of 6061 aluminum alloy, Mg, Cu, Ge, Zn and other elements are currently added to the Al-Si brazing filler metal to meet the requirements of process performance. After summarizing the production practice, several series of aluminum brazing filler metals have been formed, some of which can achieve satisfactory brazing results when combined with appropriate brazing processes, such as Al-Si-Cu series, Al-Si-Ge series and Al-Si-Zn series brazing filler metals.

[0004] At present, the existing technology for producing Al-Si solder mainly adopts the method of mixing other elements after smelting pure aluminum and pure silicon, that is, using metal aluminum and industrial silicon produced by electrolysis as raw materials, re-smelting, and mixing other elements in proportion to melt. Using the existing process, from ore to finished solder, it needs to go through multiple processes of multiple enterprises such as alumina plant, electrolytic aluminum plant, industrial silicon plant, solder plant, etc. to complete, which has a long production process, complex process, high energy consumption cost, and great impact on the environment. In addition, when the existing Al-Si solder production method is used to produce composite solder, since the composite solder is added with other elements on the basis of Al-Si eutectic solder alloy, the solder alloy inevitably contains needle-like Si phases that degrade the joint performance, thereby limiting the further improvement of the mechanical strength of the solder alloy and the brazed joint. Therefore, it has become a technical problem to be solved urgently to develop a new solder preparation process with simple process, low energy consumption cost and high joint strength.

[0005] Fly ash is the fine ash captured in the flue gas after coal combustion, and it mainly comes from pulverized coal boilers in thermal power plants and factories. When coal is burned in the boiler, the combustible part of the pulverized coal (volatile matter, fixed carbon) burns quickly to release heat, and the non-combustible part (ash) melts at high temperature. The molten residual material is discharged with the flue gas, and it cools rapidly during the rising process and condenses into particles of different sizes. The fine particles are collected by the dust removal device, which is fly ash. The fly ash discharged by power plants in my country has a high content of aluminum oxide and silicon oxide. Such high content of aluminum oxide and silicon oxide makes it a potential resource of aluminum and silicon.

[0006] However, there is no research on the effective use of fly ash in the preparation of aluminum alloy brazing filler metals. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing a brazing filler metal for aluminum alloy, which uses fly ash as an aluminum source and a silicon source for preparing the brazing filler metal, thereby realizing the recycling of solid waste and having a low process cost. Moreover, after the prepared brazing filler metal is used for brazing of aluminum alloy, the mechanical strength of the obtained brazed joint is relatively high.

[0008] The present invention also aims to provide a brazing filler metal for aluminum alloys, wherein the aluminum alloy joints obtained by brazing have high shear strength and are suitable for the brazing application of aluminum alloys.

[0009] In order to achieve the above objectives, the method for preparing the aluminum alloy brazing filler metal of the present invention adopts the following technical scheme:

[0010] A method for preparing a brazing filler metal for aluminum alloy comprises the following steps:

[0011] (1) Fly ash reduction: fly ash, collector, foaming agent and water are mixed evenly to obtain slurry, and then the slurry is filtered and the precipitate is collected to obtain a solid mixture;

[0012] The solid mixture, the carbon reducing agent, the binder and water are mixed to obtain pellets, and then the pellets are dried and reduced to obtain a crude aluminum-silicon alloy;

[0013] (2) Melting of solder alloy: placing crude aluminum-silicon alloy with Mn, Ge and Zn in a melting furnace for melting treatment, and then cooling to obtain Al-Si-Ge-Zn alloy and manganese-silicon-titanium-iron compound with a layered structure; wherein the manganese-silicon-titanium-iron compound is at the bottom of the melting furnace, and the Al-Si-Ge-Zn alloy is on the upper layer of the manganese-silicon-titanium-iron compound;

[0014] The layered Al-Si-Ge-Zn alloy and the manganese-silicon-titanium-iron compound are filtered to obtain the Al-Si-Ge-Zn alloy;

[0015] (3) Processing and molding of solder: melting and heat-insulating the Al-Si-Ge-Zn alloy obtained in step (2), and then processing the solder to obtain the aluminum alloy solder;

[0016] Wherein, in step (2), by weight, for every 10 parts of crude aluminum silicon alloy, the amount of Mn used is 2-2.5 parts, the amount of Ge used is 0.5-1 parts, and the amount of Zn used is 1.5-2.5 parts.

[0017] The preparation method of the aluminum alloy solder of the present invention uses fly ash as raw material, adopts a reduction method to reduce the fly ash to obtain a crude aluminum silicon alloy, then adds Ge, Zn, and Mn elements during the refining process for smelting, and produces Al-Si-Ge-Zn quaternary solder after solder processing. The present invention has found through experimental exploration that by using fly ash as the Al source and Si source, since Al and Si are evenly distributed in the natural fly ash structure, the component segregation caused by the density difference between the two can be avoided during the smelting process, and the appearance of needle-like Si phase can be reduced. Therefore, the solder composition obtained after the crude aluminum silicon alloy is smelted with Ge and Zn metals is more uniform, which is more conducive to the improvement of the mechanical strength of the solder.

[0018] In the present invention, Mn element is also added during smelting. The addition of Mn element can effectively combine Ti and Fe impurity elements in the fly ash reduction product to form manganese silicon titanium iron compound, which is convenient for filtering and separation with Al-Si-Ge-Zn alloy.

[0019] In addition, the present invention uses fly ash as the raw material source for producing brazing filler metal, and the price of fly ash is extremely low, which can save the cost of raw materials. Moreover, the preparation method of the present invention has a simple process, which eliminates the addition of pure aluminum and industrial silicon required in the previous brazing filler metal production process, and eliminates multiple processes of multiple enterprises such as alumina plants, electrolytic aluminum plants, industrial silicon plants, and aluminum alloy plants, which can simplify the production process, reduce construction investment, and further reduce production costs. Moreover, the preparation process of the present invention uses discarded fly ash as raw material, realizes the recycling of resources, reduces the cost of aluminum silicon alloy, and reduces environmental pollution.

[0020] In order to ensure the rationality of the solder ratio and the mechanical strength of the brazed joint, in step (1), the particle size of the fly ash is less than 0.1 mm; in the fly ash, the content of Al2O3 is ≥50wt.%, the content of SiO2 is 20wt.%~40wt.%, the content of Fe2O3 is <4wt.%, and the content of TiO2 is <2wt.%.

[0021] As a further preferred solution, the collector is kerosene; the foaming agent is cresol acid; the carbon reducing agent is carbon; and the binder is lignin sulfonate. By adding kerosene as a collector and cresol acid as a foaming agent, the unburned carbon in the fly ash can be removed, and the collector can change the surface properties of the unburned carbon from hydrophilic to oleophobic to oleophilic to hydrophobic, so that the unburned carbon is adsorbed on the oil film of the flotation foam and is separated from the pulp, thereby obtaining a solid mixture mainly composed of silicon oxide and aluminum oxide. Furthermore, the present invention uses carbon as a reducing agent and lignin sulfonate as a binder to perform bonding of pellets and reduction treatment of pellets, thereby obtaining a reduced crude aluminum silicon alloy.

[0022] Furthermore, in step (1), for every 100 parts of fly ash, the amount of the collector is 2-3 parts, the amount of the foaming agent is 0.5-1 parts, and the amount of water is 180-200 parts; for every 50 parts of the solid mixture, the amount of the carbon reducing agent is 10-12 parts, the amount of the binder is 10-12 parts, and the amount of water is 10-12 parts.

[0023] Preferably, in step (1), the temperature of the reduction treatment is 1000-1200° C., and the time of the reduction treatment is 1-1.5 h.

[0024] Furthermore, in step (2), the temperature of the smelting treatment is 1000-1100°C, the smelting treatment time is 50-80 min, and electromagnetic stirring is used during the smelting treatment; the cooling is specifically: cooling to 600-640°C at 30-50°C / min.

[0025] As a further preferred solution, the filtration is specifically as follows: the layered Al-Si-Ge-Zn alloy and manganese silicon titanium iron compound are transferred to a mineral heating furnace with a ceramic filter layer, and the Al-Si-Ge-Zn alloy and manganese silicon titanium iron compound are placed on the ceramic filter layer, the mineral heating furnace is heated to 600-700°C, the gas pressure in the inner cavity of the mineral heating furnace is adjusted to be lower than -950Pa, and the Al-Si-Ge-Zn alloy is obtained by filtration. Titanium and iron exist in the form of TiO2 and Fe2O3 in fly ash, and after the reduction process, they are combined with Mn and Si to form manganese silicon titanium iron compounds. Since the manganese silicon titanium iron compound has a large difference in surface tension compared with the Al-Si-Ge-Zn alloy, a layered structure can be formed. At this time, the Al-Si-Ge-Zn alloy is distributed on the upper layer of the manganese silicon titanium iron compound due to its low density, and the two can be effectively separated by filtration through the above filtration process.

[0026] Preferably, in step (3), the smelting temperature is 700-800° C., and the insulation time is 15-25 min.

[0027] Preferably, in step (3), during the heat preservation process, a covering agent is used to cover the melt after smelting; the covering agent consists of KCl and NaCl; and the mass ratio of KCl to NaCl is 1:1.

[0028] The aluminum alloy brazing filler metal of the present invention is prepared by the above-mentioned preparation method of the aluminum alloy brazing filler metal. The aluminum alloy brazing filler metal is composed of the following components in mass percentage: Si 8.5% to 13%, Ge 7% to 12%, Zn 21% to 30%, and the balance is Al.

[0029] Furthermore, the aluminum alloy is 6061 aluminum alloy.

[0030] The aluminum alloy brazing filler metal of the present invention utilizes discarded fly ash as raw material, thereby realizing the recycling of solid waste resources. In addition, the present invention uses fly ash as an aluminum source and a silicon source to prepare a composite brazing filler metal, which can make the composition of the brazing filler metal more uniform and can effectively improve the mechanical strength of the brazing filler metal. Experiments have confirmed that the mechanical properties of the aluminum alloy joint obtained by welding the Al-Si-Ge-Zn brazing filler metal prepared by the present invention are significantly improved, and the shear strength of the brazed joint is as high as 149.3-186.4 MPa, which has broad application prospects in the field of aluminum alloy brazing. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with specific embodiments. However, it should be understood by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0032] In the following examples, the raw materials involved are all conventional commercial products unless otherwise specified. In the following examples, the collector is kerosene; the foaming agent is cresol; the carbon reducing agent is carbon; and the binder is wood sulfonate. Kerosene, cresol, and carbon are all from Sinopharm Group; wood sulfonate is purchased from Shandong Huayunda New Materials Company.

[0033] In the following examples, the fly ash is from Nanjing Hongqian Environmental Protection Engineering Co., Ltd., and the particle size is less than 0.1 mm. After testing, the fly ash has the following mass percentage composition: Al2O3 63.94wt.%, SiO2 29.83wt.%, Fe2O33.21wt.%, TiO2 1.34wt.%, and the remainder is other impurities.

[0034] Example 1

[0035] The aluminum alloy brazing filler metal of this embodiment is composed of the following components in percentage by mass: Si 8.5%, Ge 12%, Zn 30%, and the balance is Al.

[0036] The method for preparing the above-mentioned brazing filler metal for aluminum alloy comprises the following steps:

[0037] (1) Reduction of fly ash

[0038] 100 kg of fly ash, 3 kg of collector (kerosene), and 1 kg of foaming agent (cresol) are put into 200 kg of water, put into a blender and mixed evenly to form a slurry, and the precipitate is collected by filtration to obtain a solid mixture of silicon oxide and aluminum oxide.

[0039] 50 kg of a solid mixture of silicon oxide and aluminum oxide, 12 kg of a carbon reducing agent (carbon), 12 kg of a binder (lignosulfonate), and 12 kg of water were mixed to prepare pellets, which were dried and added to a submerged arc furnace for reduction at 1200° C. for 1 hour to obtain a crude aluminum silicon alloy.

[0040] (2) Melting of solder alloy

[0041] 10 kg of crude aluminum-silicon alloy, 2.5 kg of Mn, 1 kg of Ge, and 2.5 kg of Zn were added into a smelting furnace, and electromagnetically stirred at 1000°C for 60 min, and then cooled to 620°C at a rate of 40°C / min to obtain Al-Si-Ge-Zn alloy and manganese-silicon-titanium-iron compound with a layered structure;

[0042] The Al-Si-Ge-Zn alloy and the manganese silicon titanium iron compound are transferred to a mineral arc furnace with a ceramic filter layer, and the Al-Si-Ge-Zn alloy and the manganese silicon titanium iron compound are placed on the ceramic filter layer. The mineral arc furnace is heated to 650°C, and the furnace cavity pressure is adjusted to a negative pressure of -950Pa, and the Al-Si-Ge-Zn alloy is filtered.

[0043] (3) Brazing material processing and forming

[0044] The Al-Si-Ge-Zn alloy was melted in a medium frequency furnace, heated to 750°C in the furnace, and the melt was completely covered with a KCl:NaCl covering agent with a mass ratio of 1:1. After keeping warm for 20 minutes, it was cooled and refined with argon gas. The refining time was 25 minutes. When the temperature was cooled to 700°C, the smelting was completed and the solution was injected into a mold to form an ingot. During the pouring process, the cooling system was turned on to cool the ingot rapidly to obtain a rod-shaped ingot with a diameter of 32 mm. The rod-shaped ingot was extruded, drawn and reduced to a filament-shaped brazing material with a diameter of 1.5 mm, thus obtaining the brazing material for the aluminum alloy of Example 1.

[0045] Example 2

[0046] In the preparation method of the aluminum alloy brazing filler metal of the present embodiment, in step (2), the addition amounts of Mn, Ge and Zn elements are changed, and 10 kg of crude aluminum silicon alloy is melted with 2 kg of Mn, 0.5 kg of Ge and 1.5 kg of Zn, and the rest of the steps are the same as those of Example 1.

[0047] The aluminum alloy brazing filler metal prepared in this embodiment has a mass percentage composition of Si 13%, Ge 7%, Zn 21%, and the balance is Al.

[0048] Example 3

[0049] The preparation method of the aluminum alloy brazing material of this embodiment comprises the following steps: 100 kg of fly ash, 2 kg of collector (kerosene), and 0.5 kg of foaming agent (cresol) are put into 200 kg of water, and mixed evenly in a blender to form a slurry, and the precipitate is collected by filtration to obtain a mixture of silicon oxide and aluminum oxide. 50 kg of the mixture of silicon oxide and aluminum oxide, 10 kg of carbon reducing agent (carbon), 10 kg of binder (lignosulfonate), and 10 kg of water are mixed to prepare pellets, which are dried and added to a submerged arc furnace for reduction at 1000°C for 1 hour to obtain a crude aluminum silicon alloy. The rest of the steps are the same as those of Example 1.

[0050] The aluminum alloy brazing filler metal prepared in this embodiment has a mass percentage composition of Si 10.2%, Ge 9.5%, Zn 24%, and the balance is Al.

[0051] Comparative Example 1

[0052] Comparative Example 1 is a brazing filler metal for aluminum alloy prepared by the existing method, and the specific brazing filler metal composition is: Si 8.5%, Ge 12%, Zn 30%, and the balance is Al. The preparation process is to take a certain amount of Al and Si metals according to a preset ratio and add them to a metal smelting furnace, heat it to 1000°C, and keep it warm for 30 minutes until Al and Si are completely melted, and then add Ge and Zn metals in a preset ratio to the smelting furnace to prepare an Al-Si-Ge-Zn brazing filler metal alloy. Then, the Al-Si-Ge-Zn brazing filler metal alloy is subjected to the same brazing filler metal processing process as step (3) of Example 1 to obtain a filamentary brazing filler metal with a diameter of 1.5 mm.

[0053] Test example

[0054] The performance of the joints brazed with the aluminum alloy brazing filler metal of Examples 1 to 3 and Comparative Example 1 was tested. The specific test process is as follows: During the brazing process, the base material is 6061 aluminum alloy with a size of 40mm×40mm×2mm. Before the experiment, the 6061 aluminum alloy base material is polished with 400-mesh sandpaper to remove surface oil stains. The 6061 aluminum alloy is overlapped with a lap length of 2mm, a gap of 0.3mm, a brazing temperature of 560°C, a heating rate of 40°C / min, and a brazing insulation time of 20min. The shear strength test of the brazed joint was prepared in accordance with the requirements of GB11363-89 "Test Method for Strength of Brazed Joints", and the brazed joint was tested using an MTS810 universal material tensile testing machine. The results are shown in Table 1.

[0055] Table 1 Shear strength of aluminum alloy joints brazed in Examples 1 to 3 and Comparative Example 1

[0056]

[0057] As can be seen from Table 1, the aluminum alloy brazing filler metal obtained by the preparation method of the present invention has a shear strength of the brazed joint of 149.3-186.4 MPa, which can significantly improve the shear strength of the joint compared with the brazing filler metal in the prior art.

[0058] In summary, the aluminum alloy brazing filler metal and the preparation method thereof of the present invention utilize waste fly ash as raw material, thereby realizing the recycling of solid waste resources. In addition, the present invention uses fly ash as aluminum source and silicon source to prepare composite brazing filler metal, which can make the brazing filler metal composition more uniform, and can significantly improve the mechanical properties of the aluminum alloy joint obtained by welding, and the shear strength of the brazed joint is as high as 149.3~186.4MPa, which has broad application prospects in the field of aluminum alloy brazing.

Claims

1. A method for preparing a brazing filler metal for aluminum alloy, characterized in that: The following steps are involved: (1) Fly ash reduction: fly ash, collector, foaming agent and water are mixed evenly to obtain slurry, and then the slurry is filtered and the precipitate is collected to obtain a solid mixture; The solid mixture, the carbon reducing agent, the binder and water are mixed to obtain pellets, and then the pellets are dried and subjected to reduction treatment to obtain a crude aluminum-silicon alloy; (2) Melting of solder alloy: placing crude aluminum-silicon alloy with Mn, Ge and Zn in a melting furnace for melting treatment, and then cooling to obtain Al-Si-Ge-Zn alloy and manganese-silicon-titanium-iron compound with a layered structure; wherein the manganese-silicon-titanium-iron compound is at the bottom of the melting furnace, and the Al-Si-Ge-Zn alloy is on the upper layer of the manganese-silicon-titanium-iron compound; The layered Al-Si-Ge-Zn alloy and the manganese-silicon-titanium-iron compound are filtered to obtain the Al-Si-Ge-Zn alloy; (3) Processing and molding of solder: melting and heat-insulating the Al-Si-Ge-Zn alloy obtained in step (2), and then processing the solder to obtain the aluminum alloy solder; Wherein, in step (1), the particle size of the fly ash is less than 0.1 mm; in the fly ash, the content of Al2O3 is ≥50wt.%, the content of SiO2 is 20wt.%~40wt.%, the content of Fe2O3 is <4wt.%, and the content of TiO2 is <2wt.%; in step (2), in terms of mass parts, for every 10 parts of crude aluminum silicon alloy, the corresponding amount of Mn is 2~2.5 parts, the corresponding amount of Ge is 0.5~1 part, and the corresponding amount of Zn is 1.5~2.5 parts.

2. The method for preparing the brazing filler metal for aluminum alloy according to claim 1, characterized in that: In step (1), the collector is kerosene; the foaming agent is cresol; the carbon reducing agent is carbon; and the binder is wood sulfonate.

3. The method for preparing the brazing filler metal for aluminum alloy according to claim 1, characterized in that: In step (1), by weight, for every 100 parts of fly ash, the amount of the collector is 2-3 parts, the amount of the foaming agent is 0.5-1 parts, and the amount of water is 180-200 parts; In terms of mass, for every 50 parts of the solid mixture, the amount of the carbon reducing agent is 10-12 parts, the amount of the binder is 10-12 parts, and the amount of water is 10-12 parts.

4. The method for preparing the brazing filler metal for aluminum alloy according to any one of claims 1 to 3, characterized in that: In step (1), the temperature of the reduction treatment is 1000-1200° C., and the time of the reduction treatment is 1-1.5 h.

5. The method for preparing the brazing filler metal for aluminum alloy according to any one of claims 1 to 3, characterized in that: In step (2), the smelting treatment temperature is 1000-1100°C, the smelting treatment time is 50-80 minutes, and electromagnetic stirring is used during the smelting treatment; The cooling process specifically includes: cooling to 600-640°C at a rate of 30-50°C / min; the filtering process specifically includes: transferring the layered Al-Si-Ge-Zn alloy and the manganese silicon titanium iron compound to a mineral arc furnace with a ceramic filter layer, and placing the Al-Si-Ge-Zn alloy and the manganese silicon titanium iron compound on the ceramic filter layer, heating the mineral arc furnace to 600-700°C, adjusting the gas pressure in the inner cavity of the mineral arc furnace to be lower than -950Pa, and filtering to obtain the Al-Si-Ge-Zn alloy.

6. The method for preparing the brazing filler metal for aluminum alloy according to any one of claims 1 to 3, characterized in that: In step (3), the smelting temperature is 700-800° C. and the insulation time is 15-25 min.

7. The method for preparing the brazing filler metal for aluminum alloy according to any one of claims 1 to 3, characterized in that: In step (3), during the heat preservation process, a covering agent is used to cover the melt after smelting; the covering agent is composed of KCl and NaCl; and the mass ratio of KCl to NaCl is 1:

1.

8. A brazing filler metal for aluminum alloy prepared by the method for preparing a brazing filler metal for aluminum alloy according to any one of claims 1 to 3, characterized in that: It is composed of the following components in mass percentage: Si 8.5%~13%, Ge 7%~12%, Zn 21%~30%, and the balance is Al.

9. The brazing filler metal for aluminum alloy according to claim 8, characterized in that: The aluminum alloy is 6061 aluminum alloy.

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