CN101856757B - Powder Diffusion Reaction Resistance Brazing Method of Aluminum Alloy - Google Patents

Abstract

The invention discloses a powder medium diffusion reaction resistance brazing method for aluminum and aluminum alloy materials, which is applied to the welding of aluminum and aluminum alloy materials. The method uses an aluminum-based alloy powder medium or a zinc-aluminum powder solder medium as a filling layer to improve the initial welding contact resistance of the difficult-to-weld aluminum alloy material. Using resistance heat as the welding heat source, under the action of resistance heat, the partial melting of the surface of the material to be welded and the rapid melting of the powder medium occur simultaneously to form an alloy solder. Under the action of an appropriate electrode pressure impact, the oxide film is broken, and the powder medium is promoted to produce a eutectic reaction at the interface of the material to be welded, and the eutectic is formed at the interface by virtue of the diffusion between different metals, so as to realize the reliability of the material. connect. The method can be welded in an atmosphere environment or an inert gas protection environment, has strong flexibility, and has relatively ideal engineering significance.

Description

Powder Diffusion Reaction Resistance Brazing Method of Aluminum Alloy

technical field

The invention relates to an aluminum alloy powder medium diffusion reaction resistance brazing method, which is suitable for welding aluminum and aluminum alloy plates and wires, especially difficult-to-weld aluminum alloy materials.

Background technique

Due to the physical and chemical properties of aluminum and aluminum alloys, a series of problems are prone to occur during the welding process, mainly as follows:

(1) Metal materials such as aluminum alloys have high thermal conductivity and low electrical resistivity. During the welding process, a large amount of welding heat is rapidly transferred to the metal substrate and the surrounding environment and lost. Therefore, a relatively higher welding energy action is required to achieve high-quality welding of such materials.

(2) Aluminum has a high affinity with oxygen. In the atmospheric environment, it is easy to form a dense oxide film with a high melting point with oxygen, which hinders the melting of the metal during the welding process, thereby forming slag inclusion defects, or generating pores in the weld.

(3) The linear expansion coefficient of aluminum alloy is about twice that of steel. When welding, it often deforms due to large internal stress, and even produces hot cracks in the brittle temperature range.

(4) Due to the high welding current required during resistance welding, alloying between the aluminum alloy material and the electrode material is prone to occur and pitting corrosion occurs on the electrode surface, which affects the improvement of welding quality and greatly reduces the life of the electrode.

A typical example of using powdered brazing material to connect aluminum and aluminum alloy materials with a brazing connection method is disclosed in CN1211484, wherein the powdered brazing material used is heated and melted before welding, so that it is pre-melted on the surface to be welded. On the surface of the material, a dense solid solder layer is formed, and then the solder layer is remelted by the brazing method, and the brazing of the material to be welded is realized. In addition, in the disclosed CN86102511, when welding the starter motor armatures of automobiles and tractors, the thermal spraying form of spray gun heating is used to pre-melt the powder brazing material on the welding surface of the workpiece before welding, and then the brazing material is heated by resistance. After remelting, the purpose of resistance brazing is achieved.

In the resistance welding process, the weldability of the material depends largely on the contact resistance of the material. For materials such as aluminum alloy, the contact resistance is small, so the weldability of resistance welding is poor, which affects the improvement of welding quality in industries that use a large number of aluminum alloy materials such as automobiles. For commonly used brazing processes, such as arc brazing to weld aluminum alloys, the brazing quality is also difficult to control because the melting point of the brazing material is not much different from that of aluminum and aluminum alloy materials. These problems have always affected the application of aluminum alloys in industrial production.

Compared with the existing brazing technology using powder brazing material, the powder medium diffusion reaction resistance brazing method proposed by the present invention reduces the pre-melting process of powder brazing material, and forms welding joints while the powder medium is melting. Moreover, in order to avoid the disadvantages of low contact resistance and poor weldability of materials such as aluminum alloys during resistance welding, an aluminum-based powder medium layer with a certain particle size is evenly sprayed or coated on the surface of the workpiece to be welded, and the powder medium and the to-be-welded workpiece are used. The local point contact formed on the surface of the workpiece to be welded is not only beneficial to improve the initial contact resistance of the workpiece to be welded, to increase the welding current density passing through the contact surface of the workpiece to be welded during welding, but also to make the powder medium filling layer under the action of resistance heat Rapid melting, and under the action of electrode pressure and its holding pressure, a diffusion reaction under eutectic conditions occurs between the base metal and the filler layer, thereby successfully achieving welding. To sum up, there is no report on the welding technology with the above characteristics at home and abroad.

Contents of the invention

The object of the present invention is to provide a kind of easy to implement, the powder medium diffusion reaction resistance brazing method that uses aluminum-based alloy powder medium or zinc-aluminum powder solder medium as filling layer, makes the poor weldability metal materials such as aluminum alloy The contact resistance at the initial stage of welding is changed. Under the action of a relatively small current, the welding current density passing through the workpiece to be welded is increased, supplemented by appropriate electrode pressure, so that the eutectic condition is formed between the base metal and the molten powder filling layer. Diffusion reaction to form a reliable connection.

In order to achieve the above object, the present invention takes the following technical measures:

A powder medium diffusion reaction resistance brazing method for aluminum and aluminum alloy, which is carried out according to the following steps:

(1) Mix the aluminum-based alloy powder medium or the zinc-aluminum powder medium with acetone solution;

(2) uniformly spraying or uniformly coating the powder medium on the welding surface of the workpiece to be welded, forming a powder medium filling layer with uniform thickness between the welding surfaces of the workpiece to be welded;

(3) After the acetone in the powder medium filling layer is volatilized, clamp the workpiece to be welded between the upper and lower electrodes, so that the welding surface of the workpiece to be welded with the powder medium is in close contact;

(4) Apply electrode pressure impact, and press the surface to be welded under the impact force, break the oxide film on the surface of the substrate through the impact of electrode pressure, and maintain the pressure in the subsequent process.

(5) Pass the welding current to produce a resistance heating effect, so that the powder medium is melted to form an alloy solder, and a eutectic reaction occurs under pressure, and diffusion occurs at the welding interface;

(6) Stop the action of welding current, keep the electrode pressure for a certain period of time, until the weldment cools down naturally;

(7) Stop the electrode pressure, remove the upper and lower electrodes, and complete the welding.

The welding environment is welding under the atmosphere, or under the protection of an inert gas such as argon.

The workpieces to be welded are plates or wires, and the welding joints are mainly lap joints.

The heating of the workpiece to be welded and the powder medium filling layer is the resistance heat effect generated under the action of the welding current, and the welding current is in the form of a single main welding current or a main welding current plus an auxiliary welding current.

The end surfaces of the upper and lower welding electrodes are spherical, and also can be truncated conical.

During the welding process, the welding surface of the workpiece to be welded is slightly or not melted, and the powder medium produces a eutectic reaction at the interface of the material to be welded, and relies on the diffusion between different metals to form a eutectic at the interface, thereby realizing the material. Reliable connection.

The innovation of the invention lies in that the application of the powder medium changes the welding forming mechanism and improves the weldability of the material. The schematic diagram of powder medium diffusion reaction resistance brazing of aluminum alloy is shown in Figure 1, and its welding forming mechanism is shown in Figure 2. Due to the granular shape of the powder medium 2, from a microscopic point of view, the contact area between the powder particles and between the powder particles and the workpiece 1 to be welded is greatly reduced, thereby increasing the initial contact resistance of the welding material. On the other hand, a number of relatively small conductive channels are also formed between the powder particles, so that the current density can be greatly increased during the welding process without increasing the absolute value of the welding current. Therefore, at the initial stage of welding, the application of the powder medium 2 increases the contact resistance of the material, thereby obtaining a large amount of resistance heat required for material melting. The resistance heat between the interfaces causes the powder medium filling layer 2 to melt, a liquid phase 8 is formed between the connection interfaces, and the oxide film 9 at the connection interface is broken under the action of the electrode pressure 5 . Due to the spherical or truncated cone shape of the electrode end surface, the broken oxide film 9 flows to the edge of the welded joint according to the relative flow direction 10 of the molten liquid, so that the amount of oxide film in the welded joint can be reduced, thereby improving the quality of the welded joint. In the middle stage of welding, the electrode pressure 5 produced by the upper and lower electrodes 3 and 4 forces the material to be welded to have a good interface contact, and is heated together with the powder medium filling layer 2 to above the eutectic temperature under the continuous action of the welding current. The prepared powder medium filling layer 2 takes advantage of the eutectic characteristics of dissimilar metals, and forms eutectics at the interface by mutual diffusion between metals, and connects the workpieces 1 to be welded together as solder. In the later stage of welding, the welding current stops working, but the role of electrode pressure 5 is continued to ensure reliable welding joints during the slow cooling process.

The powder medium diffusion reaction resistance brazing method of aluminum alloy proposed by the present invention can realize reliable welding of aluminum and aluminum alloy materials, is an enrichment and supplement to the aluminum alloy welding processing method, and has the following advantages and effects:

(1) The powder medium and the surface of the workpiece to be welded form several point contact interfaces, and the change of the contact surface between the powder particles and the material to be welded is used to increase the initial contact resistance of the welding part of the material to be welded, thereby improving the weldability of the difficult-to-weld material.

(2) A number of relatively small conductive channels are formed between the powder particles. Without increasing the absolute value of the welding current, the current density passing through the part of the material to be welded can be greatly increased, thereby obtaining a large amount of resistance heat required in the initial stage of welding.

(3) During the welding process, the welding surface of the workpiece to be welded is slightly melted or does not melt, and the powder medium filling layer is heated above the eutectic temperature under the action of resistance heat, and a eutectic reaction occurs on the interface to form a eutectic, relying on the intermetallic Diffusion effect to achieve a reliable connection.

(4) The oxide film filling the interface is broken by the action of electrode pressure.

(5) Utilize the extrusion effect of the spherical electrode, and discharge the broken oxide film under the convection action of the molten solder, thereby forming a reliable welded joint.

(6) The formulation of the powder filling medium is flexible, which can improve the metallurgical behavior of the weld metal.

(7) The welding of aluminum and aluminum alloy materials is realized under the atmosphere environment or under the protection of inert gas. The welding surface does not need special cleaning, the welding efficiency is high, the cost is low, and the joint is reliable, which has ideal engineering practical significance.

Description of drawings

Fig. 1 is a schematic diagram of powder medium diffusion reaction resistance brazing of aluminum alloy.

Fig. 2 is a schematic diagram of the formation mechanism of aluminum alloy powder medium diffusion reaction resistance brazing forming in area A in Fig. 1 .

Fig. 3 and Fig. 4 are respectively the schematic diagrams of the welding process of embodiment 1 and embodiment 2.

In the figure, 1 aluminum alloy workpiece, 2 powder medium filling layer, 3 upper electrode, 4 lower electrode, 5 upper and lower electrode pressure, 6 welding current, 7 welding power supply, 8 liquid phase, 9 broken oxide film, 10 liquid convective direction ;

F electrode pressure, I welding current, I ₁ main welding current, I ₂ auxiliary welding current, t ₁ electrode pressure duration, t ₂ welding current duration, t ₃ auxiliary welding current duration.

Detailed ways

Below in conjunction with specific embodiment, further illustrate the present invention.

Embodiment 1: The clamping of the material to be welded and the welding process flow are shown in Figure 1 and Figure 3 respectively, which is a welding process in the form of a single main welding current. The 2024 aluminum alloy workpiece 1 is the overlapping joint of two flat plates with a thickness of 1 mm. After the aluminum-based powder medium is uniformly mixed with acetone, the pressure sprayer is evenly sprayed on the surface of the aluminum alloy workpiece 1 to be welded to form a powder medium filling layer 2 . The main welding parameters are set as: welding current I=10000A, electrode pressure F=2350N, welding current duration t ₂ =2.0s. After the acetone in the powder filling layer is volatilized, the flat plate workpieces to be welded are overlapped and clamped between the upper and lower electrodes 3 and 4. Apply electrode pressure F to make the workpieces to be welded tightly. Maintain the role of electrode pressure F, apply welding current I, the duration is 2.0s. After the welding current is applied, keep the electrode pressure F for a certain period of time until the end of welding. Remove the upper and lower electrodes 3, 4, and take off the workpiece.

Embodiment 2: The clamping of materials to be welded and the welding process flow are shown in Figure 1 and Figure 4 respectively, the welding process in the form of main welding current plus auxiliary welding current. Compared with the process flow shown in Figure 3, the process flow shown in Figure 4 increases the auxiliary welding current I ₂ after the main welding current I ₁ to keep the filling layer of the welded joint at a higher temperature for a certain period of time to facilitate the diffusion of dissimilar metals conduct. The 2024 aluminum alloy workpiece 1 is the overlapping joint of two flat plates with a thickness of 1 mm. After the aluminum-based powder medium is uniformly mixed with acetone, it is evenly sprayed on the surface of the workpiece 1 to be welded by a pressure sprayer to form a filling layer 2 . The main welding parameters are set as: main welding current I ₁ =10000A, auxiliary welding current I ₂ =8000A, electrode pressure F=2350N, main welding current duration t ₂ =2.0s, auxiliary welding current duration t3=1.5s. After the acetone in the powder filling layer is volatilized, the flat plate workpieces to be welded are overlapped and clamped between the upper and lower electrodes 3 and 4. Apply electrode pressure F to make the workpieces to be welded tightly. Keep the electrode pressure F, and apply the main welding current I ₁ for 2.0s. After the main welding current I ₁ is finished, the auxiliary welding current I ₂ takes effect immediately, and the duration is 1.5s. After the welding current is applied, keep the electrode pressure F for a certain period of time until the end of welding. Remove the upper and lower electrodes 3, 4, and take off the workpiece.

Claims (5)

1. the powder medium diffusion reaction resistance brazing method of aluminium and aluminum alloy materials is characterized in that this welding method may further comprise the steps:

(1) acieral powder medium or zinc-aluminium powder medium are mixed with acetone soln;

(2) on the solder side of workpiece to be welded, evenly spray or evenly apply said powder medium, between the solder side of workpiece to be welded, form the uniform powder medium packed layer of thickness;

(3) treat the acetone volatilization of powder medium packed layer after, clamping workpiece to be welded closely contacts the workpiece solder side to be welded of attaching powder medium between upper/lower electrode;

(4) apply electrode pressure and impact, and under impact force action, compress to be welded, make the matrix surface oxide-film broken through the electrode pressure percussion, and the effect that in the subsequent technique process, keep-ups pressure;

(5) logical welding current, the heating effect that has a resistance makes the powder medium fusing form solder alloy, eutectic reaction takes place under pressure, and produce diffusion at weld interface;

(6) stop the welding current effect, keep electrode pressure, cool off naturally to weldment;

(7) stop the electrode pressure effect, remove upper/lower electrode, accomplish welding.

2. the powder medium diffusion reaction resistance brazing method of aluminium according to claim 1 and aluminum alloy materials is characterized in that: said workpiece to be welded is directly welding under atmospheric environment, or under logical inert gas shielding, realizes welding.

3. the powder medium diffusion reaction resistance brazing method of aluminium according to claim 1 and aluminum alloy materials is characterized in that: said workpiece to be welded is sheet material or wire rod.

4. the powder medium diffusion reaction resistance brazing method of aluminium according to claim 1 and aluminum alloy materials; It is characterized in that: treat the resistance heat effect that produces under the welding current effect that is heated to be of welder's part and powder medium packed layer, welding current is that single main welding current form or main welding current add auxiliary welding current form.

5. the powder medium diffusion reaction resistance brazing method of aluminium according to claim 1 and aluminum alloy materials is characterized in that: the described end face of welding electrode up and down is sphere shape or truncated cone.

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