HK1089721B - Method for inert gas welding or inert gas soldering workpieces comprising identical or different metals or metal alloys by means of an additional zn/al metal - Google Patents

Description

Method for inert gas welding or inert gas brazing of workpieces comprising identical or different metals or metal alloys with a Zn/Al additive material

Technical Field

The invention relates to a method for inert gas welding or inert gas brazing of workpieces made of the same or different metals or metal alloys by means of a Zn-based additive metal alloy. Workpieces made of steel, magnesium, aluminum, copper, and alloys thereof are welded or brazed, and the workpieces to be joined may be composed of the same or different metals or metal alloys. The invention also relates to a welding wire for use in said method.

Background

In the automobile industry, in particular in the car industry, it has become common to employ various light metal parts in the body structure in order to reduce the overall weight of the body, which has a positive effect on the overall fuel consumption. Components made of aluminum, aluminum alloys or magnesium alloys are generally used in this connection. In fact, in the automobiles currently on the market, these materials constitute more than half of their bodies.

Material changes used in vehicle body construction have also required corresponding adaptations of prior art joining processes. Although early vehicle body structures required primarily sheet steel welding, it was now necessary to provide the connections in different materials in such a way that they were used in industrial processes without major complications.

In order to join steel sheets, such as galvanized steel sheets, which are often used in vehicle body structures, the prior art uses, in particular, inert gas welding or inert gas brazing. These processes have been described in DIN 1910-2.

Inert gas welding of metals is a process in which a workpiece in the area to be welded is melted by the burning of an arc between a wire electrode and the workpiece in a stream of inert gas. The wire electrode may include welding additives and must be adapted to the material to be welded. In this way, the regions of the workpieces to be welded are connected to one another.

The steel and the nonferrous metal can be welded together by adopting the method.

An alternative method is metal inert gas brazing, which differs from metal inert gas welding mainly in that a flux with a melting point lower than that of the substrate material to be joined is used as the wire electrode, so that the entire process can be carried out at a lower temperature.

This method, also known as "MIG brazing", has been successful, in particular, in joining galvanized sheet metal in the automotive industry. The advantages of this welding method are higher process safety, better weld quality and high joining strength, and higher corrosion resistance of the joined metal parts, compared to corresponding welding methods. In this method, argon gas or a gas containing argon gas may be used as the inert gas for welding. These gas mixtures include reactive gases that can produce smoother welds and good weld transitions to the base material. For this purpose, for example, an argon mixture with a small amount of oxygen is used.

Hard solder or high temperature solder such as copper-based solder wire is used as the solder. They are composed primarily of copper including various alloying elements such as silicon, aluminum, tin, nickel, zinc, and manganese. The melting point of the solder is approximately 950 to 1400 ℃, and this is also the temperature region in which this brazing is performed. The brazing method also has the advantage, compared to the welding method, that the heat load on the components is rather low and that the zinc layer of the galvanized sheet metal does not change strongly due to the welding temperature, resulting in a reduced corrosion resistance thereof.

The invention described below is intended to provide an improvement to the welding or brazing process to enable joining together of metallic materials made of different metals and metal alloys, particularly those made of steel, aluminum, magnesium, copper or alloys thereof. Joining these materials by inert gas welding or inert gas brazing using a zinc-based solder has not been mentioned so far.

However, other methods of joining steel and aluminum are known in the art. DE10057180a1 describes a method of connecting steel pipes and aluminum ribs. Wherein a zinc-aluminum alloy having an aluminum content of 0.5 to 20 wt% is used as the solder. The joining method is carried out in such a manner that a solder layer is first applied to the steel pipe or the aluminum rib by a flame spraying or arc method. Only then are the aluminum ribs brought into contact with the steel pipe and coated with a flux in the form of cesium aluminum tetrafluoride at room temperature. Thereafter, the steel pipe provided with the aluminum ribs was brazed in a furnace at a brazing temperature of 370 to 470 ℃. The above method comprises two process steps. In a first step, solder is applied to the individual components. Subsequently, the solder is allowed to cool. In a second process step, the components are brought into contact and flux is applied at room temperature and the components are brazed in a furnace. It is clear that this method cannot be carried out in an industrial continuous process, in particular in the case of vehicle body structures.

The technical object of the present invention is therefore to improve the inert gas welding or brazing methods known from the prior art in such a way that, in addition to joining the same metals, the method is also suitable for joining different metals, in particular steel, aluminum, magnesium, copper or alloys thereof.

Disclosure of Invention

The above technical aim is achieved by a method for inert gas welding or inert gas brazing a workpiece (a) made of steel, aluminium, magnesium, copper or alloys thereof and a workpiece (B) made of steel, aluminium, magnesium, copper or alloys thereof, wherein said workpieces (a) and (B) may consist of the same or different metals or metal alloys, characterized in that it comprises the following steps: a method for joining a workpiece made of steel and a workpiece made of other metallic material with an additive metal alloy, characterized by comprising the steps of:

a) butting or lapping workpieces to be connected;

b) melting an additive metal alloy comprising a Zn/Al alloy;

c) applying a molten additive metal alloy to a contact surface or a localized area of a contact surface that contacts a workpiece;

d) cooling the joined workpieces;

wherein steps b) and c) are carried out directly one after the other and at least steps b) and c) are carried out using an inert gas.

What is considered as inert gas in the sense of the present invention is a gas or gas mixture which does not undergo any reaction with the additive metal alloy or with the workpiece material during this process. In a preferred manner, an inert gas, in particular argon, is used for this purpose. Alternatively, gas mixtures comprising inert gases and reactive gases that affect the process or alloy formation may also be used. These include, for example, gas mixtures consisting of argon and small amounts of oxygen or carbon dioxide.

By using the zinc-based alloy as the additional metal alloy and using an inert gas, it is possible to interconnect workpieces made of different metal materials in a single step process, which can also be done in a continuous and automated manner. Because the zinc-based alloy has a lower melting temperature of 350 ℃ to 450 ℃, the entire process can be performed at a lower temperature than previous inert gas brazing processes performed at about 1000 ℃. Therefore, since the entire operation can be performed at a lower temperature, deformation of the constituent parts is significantly less. This therefore also allows the connection of very thin materials, such as metal strips or plates with a thickness of less than 1 MM. In addition, lower temperatures are beneficial for the brazing process to save considerable energy consumption. A further advantage is that the steel component, if used in the form of galvanized steel sheet, is not damaged in its zinc coating due to the lower temperature, so that corrosion protection is maintained in the region of the weld seam or braze seam, and therefore no cumbersome secondary operations have to be carried out to maintain corrosion protection.

The melting point of zinc is 419 ℃ and the boiling point is 908 ℃. Therefore, at brazing temperatures around 1000 ℃, most of the zinc coating of the steel sheet will evaporate. This affects on the one hand the joining process and the joint strength and on the other hand results in a reduction of the corrosion resistance of the steel sheet, which is achieved by the zinc coating and will be destroyed during the joining process. By the method according to the invention, the connection can be made at substantially lower temperatures, thereby avoiding the above problems.

In addition, it was found that the brazed joints thus produced have high strength and good corrosion resistance.

In a preferred embodiment, the method employs a workpiece made of a galvanized or non-galvanized steel material. Currently, thin galvanized metal sheets are commonly used in the automotive industry to extend the useful life of automobiles. The average percentage of these metal sheets in the vehicle body structure currently exceeds 70%. Therefore, most automobile manufacturers guarantee a rust-proof shelf life of about 12 years.

In a preferred embodiment, the metallic material is composed of steel, aluminum alloys, magnesium alloys, copper, and copper alloys. Particularly preferred are aluminum and aluminum alloys and magnesium aluminum alloys which are currently used in the automobile industry. They have good mechanical properties and, due to their low specific gravity, lead to a reduction in the overall weight of the vehicle body and therefore to a reduction in fuel consumption. In a particularly preferred embodiment, a material made of steel, in particular galvanized steel, is joined to a material made of aluminum, an aluminum alloy, magnesium, a magnesium alloy. For this purpose, zinc-based alloys with aluminum are preferably used.

In a particularly preferred embodiment, an inert gas welding/brazing process is used to join the workpieces.

The above method is a method in which the solder is melted by arc or plasma or laser, and the liquid solder is applied to the position to be soldered/brazed. These methods are known as arc welding methods, plasma welding methods or WIG welding methods and are distinguished according to the method according to the invention in that zinc-based solders are used for carrying out the method.

Particularly preferred is an arc welding/brazing process. The arc burns between the wire electrode and the workpiece. The wire electrode is surrounded by an inert gas nozzle from which inert gas is passed to the location to be joined. The wire electrode is composed of the additive metal alloy, thus providing a solder for joining the workpieces. The method allows for continuous joining of metallic materials in a single step continuous process. The melting of the additive metal alloy is preferably performed using an electric arc that burns between the wire electrode and the workpiece. When joining steel and light metals, such as aluminum or magnesium and alloys thereof, the light metals are partially melted in the method according to the invention. In addition, such a solder is used, so that the method is a combined solder-brazing method.

Detailed Description

The process of the invention may be carried out with or without fluxing agents. In general, fluxing agents are used to facilitate melting of the solder during brazing, to promote deposition of particulate matter, or to prevent oxidation. In the case of aluminum in particular, a flux is generally used in order to remove the interfering oxide layer. However, the use of fluxes has the disadvantage that most fluxes are very aggressive, causing corrosion of the aluminum after joining with other metals. An additional step is therefore required to remove these fluxes after the thermal bonding. Surprisingly, it has been found that the method of the invention can be carried out without the use of any fluxing agent and still produce a strong and durable connection between the materials to be joined. Even more surprising is that the joining of precisely such dissimilar metals, for example metals made of steel, aluminium or magnesium alloys, may form very brittle intermetallic phases, resulting in insufficient strength of the joined parts. It is clear that the substantially lower temperatures required in the process of the invention just avoid the formation of said intermetallic phases, thereby achieving a stronger connection.

As additional metal alloys, preference is given to those zinc-based alloys which, in addition to the normal impurities, comprise from 1 to 25% by weight of aluminum. Especially preferred are zinc alloys comprising 5 to 15 wt% aluminium, and most preferred are zinc based alloys comprising 4 wt% aluminium. More specifically, the following zinc alloys may be employed: ZnAl₅、ZnAl₁₅、ZnAl₂、ZnAl₂₀、ZnAl₂₂And ZnAl₄。

In addition to normal impurities, the zinc-based alloy may include one or more alloying additives, specifically up to 500ppmMg, up to 500ppmCr, up to 2000ppmMn, up to 300ppmLi, up to 4% Cu, up to 50ppmB, up to 500ppmTi, and up to 1000 ppmSi.

In the method according to the invention, an additional metal alloy in the form of a solid wire or a cored wire is used. If a cored wire is used, the core of such a cored wire may include suitable additives required for brazing. For example, the additive may be a flux (e.g., Cs-based), a metal powder selected from the group consisting of aluminum, chromium, titanium, manganese, and nickel.

In a preferred manner, the method according to the invention is carried out in such a way that a wire electrode made of a zinc-based alloy surrounded by a flow of inert gas is melted in an arc, plasma or laser and the molten additional metal alloy is applied on the respective contact surface or on a partial region of the contact surface of the contacting workpieces. This is performed immediately after melting the additive metal alloy.

The invention also relates to a welding wire with a diameter of 0.8 to 3.2mm for use in a method for inert gas welding or inert gas brazing a workpiece a made of steel, aluminum, magnesium, copper or an alloy thereof and a workpiece B made of steel, aluminum, magnesium, copper or an alloy thereof with a molten additive metal alloy consisting of a zinc-based alloy with an aluminum content of 1 to 25 wt.%, wherein the workpieces a and B may consist of the same or different metals or metal alloys.

In another preferred embodiment, the zinc-aluminum alloy may include one or more of the following alloying additives, alone or in combination: up to 500ppmMg, up to 500ppmCr, up to 2000ppmMn, up to 300ppmLi, up to 4% Cu, up to 50ppmB, up to 500ppmTi and up to 1000 ppmSi. In a preferred form, the wire may be a solid wire or a cored wire.

The present invention will be described in more detail below with reference to the following examples.

Examples

Tests were conducted to produce brazed joints using inert gas welding and zinc-aluminum solder, which were joined together and were composed of galvanized steel components and aluminum components. Welding devices from various manufacturers were used.

As the base material, a galvanized steel member having a thickness of 0.7 to 2mm and an aluminum member having a thickness of 0.8 to 2.5mm were used. By using a tube with a diameter of 1.6mmZnAl in the form of a solid wire₄The brazing wire acts as a solder material. Argon was used as the inert gas. An overlapping connection portion and an adjoining connection portion are produced between the steel members and between the steel member and the aluminum member.

The device angle is 45 to 80 ° and the inclination of the torch (arc at the torch) is 60 to 90 °. The spacing between the welding torch and the workpieces to be joined is 10 to 25mm at the inert gas nozzle and the channel feed speed during brazing is 0.3 to 1.3 m/min.

It was found that with the above parameters it is possible to produce reproducible connections between steel components and between steel and aluminium components individually and with uniform weld/braze welds. Subsequent observations of the mechanical-technical properties show that the aluminium material breaks outside the heated zone in the tensile test in all the brazed specimens (Rm ≧ 205 MPa).

This shows that, when using the method according to the invention, it is possible to produce, for example, a strong and corrosion-resistant connection between a material made of steel and a material made of aluminum.

Claims (11)

1. A method of inert gas welding or inert gas brazing a workpiece a made of steel, aluminum, magnesium, copper or alloys thereof to a workpiece B made of steel, aluminum, magnesium, copper or alloys thereof using a molten additive metal alloy, wherein the workpieces a and B may be composed of the same or different metals or metal alloys, characterized by the steps of:

a) butting or lapping workpieces to be connected;

b) melting an additive metal alloy comprising a Zn-based alloy;

c) applying a molten additive metal alloy to a contact surface or a localized area of a contact surface that contacts a workpiece;

d) cooling the joined workpieces;

wherein steps b) and c) are carried out directly one after the other and at least steps b) and c) are carried out using an inert gas.

2. The method of claim 1, wherein the steel workpiece is comprised of galvanized or non-galvanized steel.

3. The method according to claim 1 or 2, wherein said melting of the additive metal alloy is performed in an electric arc or by a plasma method or by a laser.

4. The method of claim 1, wherein the joining of the work pieces is performed with or without the use of flux.

5. The method of claim 1, wherein the Zn-based alloy comprises 1 to 25 wt% Al.

6. The method of claim 5, wherein the Zn/Al alloy may include one or more of the following alloying additives, alone or in combination: up to 500ppmMg, up to 500ppmCr, up to 2000ppmMn, up to 300ppmLi, up to 4% Cu, up to 50ppmB, up to 500ppmTi and up to 1000 ppmSi.

7. The method of claim 1, wherein joining the workpieces is performed with an additive metal alloy having a melting temperature of 370 to 600 ℃.

8. The method of claim 1, wherein the additional metal alloy is used in the form of a solid wire or a cored wire.

9. Use of a welding wire with a diameter of 0.8 to 3.2mm consisting of a zinc-based alloy with an aluminium content of 1 to 25 wt.%, in a method for inert gas welding or inert gas brazing of a workpiece a made of steel, aluminium, magnesium, copper or an alloy thereof and a workpiece B made of steel, aluminium, magnesium, copper or an alloy thereof, wherein the workpieces a and B may consist of the same or different metals or metal alloys.

10. Use according to claim 9, wherein the Zn/Al alloy may comprise one or more of the following alloying additions, alone or in combination: up to 500ppmMg, up to 500ppmCr, up to 2000ppmMn, up to 300ppmLi, up to 4% Cu, up to 50ppmB, up to 500ppmTi and up to 1000 ppmSi.

11. Use according to claim 9 or 10, wherein the welding wire is a solid wire or a cored wire.