DE102019215050A1 - Process for producing a laser soldered connection between coated sheet steel components - Google Patents

Abstract

The invention relates to a method for producing a laser soldered connection (3) between coated sheet steel components (1, 2) comprising the steps: - providing a first coated sheet steel component (1) and a second coated sheet steel component (2), - connecting the two sheet steel components (1) 2) by laser soldering using an additional material (5) along at least one solder joint (4). The invention also relates to a laser-soldered connection (3) between a first coated sheet steel component (1) and a second coated sheet steel component (2).

Description

• - Bereitstellen eines ersten beschichteten Stahlblechbauteils und eines zweiten beschichteten Stahlblechbauteils, - Verbinden der beiden Stahlblechbauteile durch Laserlöten mittels eines Zusatzmaterials entlang mindestens einer Lötfuge. Die Erfindung betrifft ferner eine lasergelötete Verbindung zwischen einem ersten beschichteten Stahlblechbauteil und einem zweiten beschichteten Stahlblechbauteil.

The invention relates to a method for producing a laser soldered connection between coated sheet steel components, comprising the steps:

• Providing a first coated sheet steel component and a second coated sheet steel component, connecting the two sheet steel components by laser soldering by means of an additional material along at least one solder joint. The invention also relates to a laser-soldered connection between a first coated sheet steel component and a second coated sheet steel component.

It is known from the prior art to use coated steel sheets with zinc-based coatings in automobile body construction, which have good corrosion resistance. In order to improve the corrosion resistance and optimize the forming behavior in the press shop, coating systems based on zinc with the addition of magnesium and aluminum have been developed, cf. EP 1 851 352 B1 . The laser soldering or laser beam soldering of zinc-based coated steel sheets is, for example, from the German Offenlegungsschrift DE 10 2018 120 523 A1 known.

The advantage of (laser) soldering compared to (laser) welding is that the base material (sheet metal) does not melt, which would otherwise lead to a higher susceptibility to corrosion. Coating systems based on zinc with additions of magnesium and aluminum are, like coating systems based purely on zinc, easy to weld, but have the disadvantage with laser soldering that the additives (Mg and Al) in the coating make diffusion more difficult during the formation of a laser soldered seam when joining two sheets this can lead to a reduced connection cross-section, in particular no complete connection of the laser solder seam root can be guaranteed. A reduced connection cross-section can mean that the strength desired in individual cases or required by the customer is not achieved. This effect does not occur when laser soldering sheet steel components coated purely on a zinc basis, so that the desired level of strength in the laser soldered connection can be ensured, in particular an essentially complete connection of the laser solder seam root can be guaranteed.

In order to achieve a level of strength comparable to that of coating systems based purely on zinc, this effect could be compensated for by constructive measures in the design and the joint situation of the coated sheet steel components, for example by additional joining points, relocation of the laser soldered connection in less stressed areas, etc.

However, if these constructive measures are not possible for the customer due to technical, e.g. package restrictions, or optical reasons, there is a need for optimization with regard to the laser soldering suitability of zinc-based coating systems with the addition of magnesium and optionally aluminum.

The invention is thus based on the object of specifying a method for producing a laser soldered connection between coated sheet steel components, with which a sufficient strength can be provided in the laser soldered connection.

This object is achieved by a method with the features of claim 1.

The inventors have found that the energy (laser power) required for the connection and / or diffusion processes in the standard laser soldering process used, as in FIG DE 10 2018 120 523 A1 is not sufficient, as the zinc-based coating with magnesium and optionally aluminum does not allow a secure connection of the laser solder seam root or a complete connection of the laser solder seam cross-section and would have to be increased in order to improve the soldered connection. The laser beam is shaded by the additional material used in laser soldering in the critical area (in the fused area of the additional material) of the soldered connection, so that simply increasing the laser power would not make sense and would result in the surface of the base material melting, which is by no means desirable in the laser soldering process is.

According to the invention, it is provided that the first and / or the second sheet steel component is coated with a zinc-based coating, with the coating, in addition to zinc and unavoidable impurities, additional elements such as magnesium with a content of 0.3 to 5% by weight and optionally aluminum a content of up to 5% by weight, and that during laser soldering, the soldering joint is thermally applied at least in advance of the introduction and melting of the additional material.

A comparable method is exemplified in the article "Two-beam laser brazing of thin sheet steel for automotive industry using Cu-base filler material", C. Mittelstadt et al. known. This article aims at a laser soldered connection of press-hardened manganese-boron steels provided with an AlSi coating in order to provide a joint connection between press-hardened components, which does not adversely affect the properties of the components, which are set by press hardening.

The first and / or second sheet steel component is coated with a zinc-based coating, which is preferably applied by hot-dip coating, with the coating, in addition to zinc and unavoidable impurities, additional elements such as magnesium with a content of 0.3 to 5% by weight and optionally aluminum a content up to 5 wt .-% contains. Steel sheets with a zinc-based coating have very good cathodic corrosion protection, which has been used in automotive engineering for years. Improved protection against corrosion is ensured if the coating contains magnesium with a content of at least 0.3% by weight, in particular at least 0.6% by weight, preferably at least 0.9% by weight. Aluminum can be added in addition to magnesium with a content of at least 0.3% by weight, in particular to improve the bonding of the coating to the steel sheet and in particular a diffusion of iron from the steel sheet into the coating during a heat treatment of the coated steel sheet in the Essential to avoid. Both magnesium and aluminum can each be restricted in particular to a maximum content of 4% by weight, preferably to 3% by weight. The total content of magnesium and aluminum can particularly preferably be at least 1% by weight and at most 5% by weight.

The thickness of the coating can be between 1.5 and 15 μm, in particular between 2 and 12 μm, preferably between 3 and 10 μm. Below the minimum limit, adequate cathodic corrosion protection cannot be guaranteed and above the maximum limit, joining problems can occur when connecting the sheet steel or a sheet steel component made from it to another component.

The first and second sheet steel components are connected to one another by means of laser soldering. Before the connection, the sheet steel components are aligned according to needs and requirements and positioned with respect to one another so that they form at least one solder joint between them in the area to be connected, in which a soldered connection and thus a material connection between the sheet steel components is established through the action of energy and the addition of an additional material.

Under "thermally applied" in the sense of the invention is to be understood that the solder joint is applied to the actual laser soldering process with an energy (preheating energy) that corresponds to at least 15% of the energy (connection energy) required to melt the additional material and form a soldered connection is. To improve and / or stabilize the laser soldering process, the preheating energy can in particular be at least 20%, preferably at least 30%, preferably at least 40% of the connection energy.

Due to the thermal exposure of the solder joint in advance, the additives contained in the zinc-based coating, such as magnesium and optionally aluminum, can be influenced in the structure of the coating so that these additives do not negatively influence the diffusion processes in the subsequent laser soldering process and thus a complete connection of the laser soldering seam cross-section can be ensured.

The additional material is preferably supplied as an additional wire and consists of a copper-based composition. The feed of the additional wire is set in particular between 2 and 10 m / min, preferably between 3 and 9 m / min, preferably between 3.5 and 8.5 m / min. The filler wire can have a diameter between 1.0 and 1.6 mm.

The laser power for forming a soldered connection is set in particular between 1.8 and 10 kW, preferably between 2 and 7 kW, preferably between 2.1 and 5 kW.

The speed for forming a soldered connection is set in particular between 1.5 and 10 m / min, preferably between 2 and 8 m / min, preferably between 2.1 and 7 m / min.

Further advantageous configurations and developments emerge from the following description. One or more features from the claims, the description as well as the drawing can be combined with one or more other features therefrom to further refinements of the invention linked. One or more features from the independent claims can also be linked by one or more other features.

According to one embodiment, a laser is used, a laser radiation emanating from the laser being directed onto the additional material in such a way that part of the radiation (connection energy) is absorbed by the additional material for melting the additional material and forming the soldered connection and part of the radiation (preheating energy) is absorbed by the additional material is reflected in advance on the solder joint to preheat the solder joint. With the help of simulations and / or “trial and error” tests, the required laser power and the required angle that fulfills the two subtasks can be determined.

According to an alternative embodiment, a laser is used, by means of which laser radiation is directed onto the additional material, thereby causing the additional material to melt and the soldered joint to be formed, and at least one further heat source, which acts on the soldering joint in advance to preheat the soldering joint . The further heat source can be a laser (see, for example, the above-mentioned article), a diode or another suitable heat source which can only locally apply heat to the solder joint in a targeted manner. With this approach, the laser for soldering as well as the additional heat source for preheating can be controlled and / or aligned individually and independently of one another.

According to one embodiment, the first coated sheet steel component is positioned with a height offset to the second coated sheet steel component.

According to one embodiment, the first and / or the second sheet steel component consists of a carbon steel with a tensile strength Rm up to a maximum of 600 MPa, in particular up to a maximum of 500 MPa, preferably up to a maximum of 400 MPa. The tensile strength of the first and / or second sheet steel component relates to the final state or installed state of the sheet steel components. Carbon steel is a cold-formable steel, in particular deep-drawing steel, BH steel (bake-hardening) or IF steel (interstitial free). The first and / or second sheet steel component can have a thickness of up to a maximum of 2 mm, in particular up to a maximum of 1.5 mm, preferably up to a maximum of 1 mm, preferably up to a maximum of 0.8 mm.

According to a second teaching, the invention relates to a laser-soldered connection between a first coated sheet steel component and a second coated sheet steel component, the first and / or the second sheet steel component being coated with a zinc-based coating, the coating having additional elements such as magnesium in addition to zinc and unavoidable impurities a content of 0.3 to 5% by weight and optionally aluminum with a content of up to 5% by weight, the laser-soldered connection between the sheet steel components having a complete connection of the laser seam cross-section.

“Complete connection” of the laser seam cross-section in the context of the invention is to be understood as meaning that a laser soldered seam, viewed in cross-section, is essentially free of voids and / or pores to the adjoining surface of the at least one sheet steel component, preferably to the adjoining surfaces of the sheet steel components. In particular, deviations within the scope of the tolerance are permitted.

According to a preferred embodiment, the laser-soldered connection is designed as a flanged seam or fillet weld. A flanged seam is used, for example, in the area of a roof structure in the automotive body area. A fillet weld is used, for example, in the area of a moving, in particular large-area, body part in the automobile body area, preferably on a door, engine hood or tailgate.

• 1: eine schematische Darstellung eines ersten Ausführungsbeispiels der Erfindung,
• 2: eine schematische Darstellung eines zweiten Ausführungsbeispiels der Erfindung,
• 3 eine schematische Darstellung eines dritten Ausführungsbeispiels der Erfindung,
• 4 eine schematische Darstellung eines vierten Ausführungsbeispiels der Erfindung und
• 5a, b: jeweils einen Ausschnitt eines Schliffbildes einer lasergelöteten Verbindung gemäß dem Stand der Technik (a) und einer lasergelöteten Verbindung gemäß einer erfindungsgemäßen Ausführungsform (b).

The invention is explained in more detail below with reference to drawings. The same parts are always provided with the same reference symbols. Show in detail:

• 1 : a schematic representation of a first embodiment of the invention,
• 2 : a schematic representation of a second embodiment of the invention,
• 3 a schematic representation of a third embodiment of the invention,
• 4th a schematic representation of a fourth embodiment of the invention and
• 5a, b : each a section of a micrograph of a laser-soldered connection according to the prior art (a) and a laser-soldered connection according to an embodiment of the invention (b).

1 shows a schematic representation of a first embodiment of the invention. Two coated sheet steel components ( 1 , 2 ), where the first sheet steel component ( 1.1 ) and the second sheet steel component ( 2.1 ) each consist of a carbon steel with a tensile strength Rm up to a maximum of 600 MPa, each have a thickness of up to a maximum of 2 mm and each with a zinc-based coating ( 1.2 , 2.2 ) are coated, the coating ( 1.2 , 2.2 ) in addition to zinc and unavoidable impurities, contains additional elements such as magnesium with a content of 0.3 to 5% by weight and optionally aluminum with a content of up to 5% by weight, are welded via a fillet weld connection by means of laser soldering using an additional material ( 5 ), preferably in the form of a copper-based filler wire, connected to one another. To ensure sufficient strength in the laser soldered joint ( 3 ) and a complete connection of the laser solder seam cross-section ( 3.1 ), see. 3b) to be able to ensure, is with laser soldering at least in advance of the introduction and melting of the additional material ( 5 ) the solder joint ( 4th ) thermally applied. For example, a laser (not shown) can be used, whereby a laser radiation ( 6th ) starting from the laser on the additional material ( 5 ) is directed that part of the radiation from the additional material ( 5 ) to melt the additional material ( 5 ) and forming the soldered connection ( 3 ) is absorbed and part of the radiation ( 6.1 ) of the additional material ( 5 ) leading to the solder joint ( 4th ) to preheat the solder joint ( 4th ) is reflected.

2 shows a schematic representation of a second embodiment of the invention. In contrast to the first exemplary embodiment, a laser (not shown) through which laser radiation ( 6th ) on the additional material ( 5 ) and thereby a melting of the additional material ( 5 ) and forming the soldered connection ( 3 ) is effected, and at least one other heat source, not shown, which is from the additional material ( 5 ) leading to the solder joint ( 4th ) to preheat the solder joint ( 4th ) acts, symbolically by the arrow ( 7th ) shown can be used.

The ones in the 1 and 2 shown laser-soldered connection ( 3 ) in the form of a fillet weld is used, for example, in the area of a moving body part, in particular a door, bonnet or tailgate, in the automobile body area.

3 shows a schematic representation of a third embodiment of the invention. In contrast to the first exemplary embodiment, two coated sheet steel components ( 1 , 2 ) via a flanged seam connection by means of laser soldering using an additional material ( 5 ) connected with each other.

4th shows a schematic representation of a fourth embodiment of the invention. In contrast to the second exemplary embodiment, two coated sheet steel components ( 1 , 2 ) via a flanged seam connection by means of laser soldering using an additional material ( 5 ) connected with each other. Furthermore, the first coated sheet steel component ( 1 ) with a height offset (H) to the second coated sheet steel component ( 2 ) positioned.

The ones in the 3 and 4th shown laser-soldered connection ( 3 ) in the form of a flanged seam is used, for example, in the area of a roof structure in the automotive body area.

5 each shows a section of a micrograph, the micrographs being polished for a light microscopic examination and etched with 3% HNO3 acid, photos being taken with 25x magnification, of a laser-soldered connection in the form of a flanged seam according to the prior art 5a) and a laser-soldered connection according to an embodiment of the invention 5b) .

The difference between the embodiment according to the prior art and the embodiment according to the invention can be clearly seen in the micrograph. 5a) shows imperfections within the laser seam cross-section ( 3.1 ), each circled with dashed lines, whereby a reduced connection cross-section is formed, which cannot have the desired or required strength and therefore also early in the laser soldered connection with corresponding load ( 3 ) can fail. 5b) however, shows a complete connection of the laser seam cross-section ( 3.1 ), means that the laser solder joint ( 3 ) viewed in cross section essentially free of voids and / or pores to the adjacent surface of the first coated sheet steel component ( 1 ) as well as to the adjacent surface of the second sheet steel component ( 2 ) is trained. The procedure for making the laser solder joint ( 3 ) in 5b) can also according to the arrangement shown as in FIG 1 or 2 are executed.

In an investigation, several samples of differently coated sheet steel components were made using different laser soldering methods with additional material, each using a laser soldered connection in the form of a flanged seam according to the 5a) and 5b) connected with each other. The sheet steel components consisted of a carbon steel with tensile strengths of up to a maximum of 600 MPa and a thickness of up to a maximum of 2 mm. Some of the steel sheet components examined were provided with a pure zinc-based coating (Z), the other part of the steel sheet components examined were provided with a zinc-based coating with additional elements such as magnesium (Mg) with a content of 0.3 to 5% by weight and optionally provided aluminum (AI) with a content of up to 5% by weight. The standard process (S) and the one in the 1 , 3 and 2 , 4th shown arrangements (A1, A2) of the laser are used, with the arrangement (A2) according to 2 , 4th Another laser was used as a heat source. The laser-soldered samples were subjected to a tensile test according to DVS 2614-1. Two identical sheet steel components with the same coating were used for each sample. A copper-based additional wire was used as additional material, an additional wire of quality CuSi31Mn1. The results of the investigations are shown in Table 1 below. Table 1 sample Coating [wt.%] arrangement Laser power [kW] Soldering speed [m / min] Wire feed [m / min] to fail 1 Z S. 4th 4.5 2.6 + 2 Mg1, Al1 S. 4th 4.5 2.6 - 3 Mg2, AI2 S. 4th 4.5 2.6 - 4th Mg1, Al1 A1 4.75 6th 8th + 5 Mg2, Al1 A2 4/1 5 2.8 + 6th Mg1, AI2 A1 4.75 6th 8th + 7th Mg2, AI2 A2 4/1 5 2.8 +

Because rehearsals 1 to 7th were stressed until failure (tearing), + means that the sample failed in one of the sheet steel components and not in the laser soldered joint, so that sufficient strength could be achieved in the laser soldered seam. - means a failure in the laser soldered connection, which was unsatisfactory, see samples 2 and 3 . At the rehearsals 5 and 7th the first laser power relates to the connection energy and the second laser power to the preheating energy.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 1851352 B1 [0002]
• DE 102018120523 A1 [0002, 0008]

Claims (10)

A method for producing a laser soldered connection (3) between coated sheet steel components (1, 2) comprising the steps: - providing a first coated sheet steel component (1) and a second coated sheet steel component (2), - connecting the two sheet steel components (1, 2) by laser soldering by means of an additional material (5) along at least one solder joint (4), characterized in that the first and / or the second sheet steel component (1.1, 2.1) is coated with a zinc-based coating (1.2, 2.2), the coating (1.2, 2.2 ) in addition to zinc and unavoidable impurities, contains additional elements such as magnesium with a content of 0.3 to 5% by weight and optionally aluminum with a content of up to 5% by weight, and that with laser soldering, at least in advance of the introduction and melting of the additional material (5) the solder joint (4) is thermally applied. Procedure according to Claim 1 , a laser being used, a laser radiation (6) starting from the laser being directed onto the additional material (5) in such a way that part of the radiation (6) from the additional material is used to melt the additional material (5) and form the soldered connection (3) is absorbed and part of the radiation (6.1) is reflected by the additional material (5) leading to the solder joint (4) to preheat the solder joint (4). Procedure according to Claim 1 , whereby a laser, by which a laser radiation (6) is directed onto the additional material (5) and thereby a melting of the additional material (5) and formation of the soldered connection (3) is effected, and at least one further heat source, which from the additional material (5 ) acts in advance on the solder joint (4) to preheat the solder joint (4). Method according to one of the preceding claims, wherein the first coated sheet steel component (1) is positioned with a height offset (H) to the second coated sheet steel component (2). Method according to one of the preceding claims, wherein the first and / or the second sheet steel component (1.1, 2.1) consists of a carbon steel with a tensile strength Rm up to a maximum of 600 MPa. Method according to one of the preceding claims, wherein the first and / or second sheet steel component (1.1, 2.1) has a thickness of up to a maximum of 2 mm. Laser-soldered connection (3) between a first coated sheet steel component (1) and a second coated sheet steel component (2), characterized in that the first and / or the second sheet steel component (1.1, 2.1) is coated with a zinc-based coating (1.2, 2.2) , wherein the coating (1.2, 2.2) in addition to zinc and unavoidable impurities, additional elements such as magnesium with a content of 0.3 to 5 wt .-% and optionally aluminum with a content of up to 5 wt .-%, the laser-soldered connection (3) between the coated sheet steel components (1, 2) has a complete connection of the seam cross-section (3.1). Laser soldered connection after Claim 7 , wherein the laser-soldered connection (3) is designed as a flanged seam or fillet weld. Laser soldered connection after Claim 8 , whereby a flanged seam is used in the area of a roof structure in the automotive body area. Laser soldered connection after Claim 8 , wherein a fillet weld in the area of a moving body part, in particular a door, bonnet or tailgate, is used in the automobile body area.

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