METHODS FOR JOINING TWO BLANKS AND BLANKS AND PRODUCTS OBTAINED

Abstract

Methods for joining a first blank and a second blank, at least one of the first and second blanks comprising at least a layer of aluminum or of an aluminum alloy or a layer of zinc or of a zinc alloy. The method comprises selecting a first portion of the first blank to be joined to the second blank, and selecting a second portion of the second blank to be joined to the first portion, and welding the first portion to the second portion. The welding comprises using a filler metal laser beam and a welding laser beam, and displacing both laser beams in a welding direction to melt and mix a filler wire material with the melted portions of the two blanks. The present disclosure further relates to blanks obtained by any of these methods and to products obtained from such blanks.

Claims

1.-13. (canceled)

14. A method for joining a first blank and a second blank, the method comprising: selecting a first portion of the first blank to be joined to the second blank, and selecting a second portion of the second blank to be joined to the first portion; wherein the first blank, the second blank, or both the first blank and the second blank comprise a steel substrate with a coating of aluminum or aluminum alloy, and wherein the first and the second blanks are square butt-jointed, the first portion being an edge of the first blank and the second portion being an edge of the second blank; melting the first portion and the second portion, while supplying a filler wire to a weld zone using a first laser beam and a second laser beam, wherein the first laser beam melts the filler wire in the weld zone during welding, the first portion and the second portion of the blanks are melted and mixed with the melted filler wire using the second laser beam, and the filler wire comprises iron, 0%-0.3% by weight carbon, 0%-1.3% by weight silicon, 0.5%-7% by weight manganese, 5%-22% by weight chromium, 6%-20% by weight nickel, 0%-0.4% by weight molybdenum, and 0%-0.7% by weight niobium, 70%-80% by weight iron, 10%-20% by weight chromium, 1.0%-9.99% by weight nickel, 1%-10% by weight silicon, and 1%-10% by weight manganese, or iron, 2.1% by weight carbon, 1.2% by weight silicon, 28% by weight chromium, 11.5% by weight nickel, 5.5% molybdenum, and 1% by weight manganese.

15. The method according to claim 14, wherein using the second laser beam comprises displacing the second laser beam in an oscillating manner to mix the first portion and the second portion of the blanks with the melted filler wire.

16. The method according to claim 14, wherein using the second laser beam comprises using a twin-spot laser beam to melt the first portion and the second portion and to mix the first portion and the second portion of the blanks with the melted filler wire.

17. The method according to claim 14, wherein the first laser beam generates a spot having a size equal to a diameter of the filler wire.

18. The method according to claim 14, wherein the first and second laser beams are generated by a single laser head.

19. The method according to claim 14, wherein the first laser beam is generated by a first laser head and the second laser beam is generated by a second laser head.

20. The method according to claim 14, wherein the first laser beam generates one spot and the second laser beam generates one or more spots and the first and second laser beams generate spots arranged substantially in line with a welding direction.

21. The method according to claim 14, wherein using the second laser beam comprises generating a twin-spot comprising spots, and wherein the spots of the twin-spot are arranged substantially perpendicularly to a welding direction.

22. The method according to claim 21, wherein the spots of the twin-spot either precede or follow a spot of the first laser beam in the welding direction.

23. The method according to claim 14, wherein the first laser beam generates one spot and using the second laser beam comprises generating a twin-spot comprising spots, wherein the spots of the twin-spot and the spot of the first laser beam are arranged collinearly in a welding direction, and wherein the spot of the first laser beam is arranged between the spots of the twin-spot.

24. The method according to claim 14, wherein the steel substrate of the first blank, the second blank, or both the first blank and the second blank is an ultra-high strength steel.

25. A method for forming a product, the method comprising: forming a blank according to the method of claim 14 by joining the first blank and the second blank, heating the blank, and hot deforming and subsequently quenching the heated blank.

26. The method according to claim 14, wherein the filler wire comprises iron, 0%-0.3% by weight carbon, 0%-1.3% by weight silicon, 0.5%-7% by weight manganese, 5%-22% by weight chromium, 6%-20% by weight nickel, 0%-0.4% by weight molybdenum, and 0%-0.7% by weight niobium.

27. The method according to claim 14, wherein the filler wire comprises 70%-80% by weight iron, 10%-20% by weight chromium, 1.0%-9.99% by weight nickel, 1%-10% by weight silicon, and 1%-10% by weight manganese.

28. The method according to claim 14, wherein the filler wire comprises iron, 2.1% by weight carbon, 1.2% by weight silicon, 28% by weight chromium, 11.5% by weight nickel, 5.5% molybdenum, and 1% by weight manganese.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Non-limiting examples of the present disclosure will be described in the following, with reference to the appended drawings, in which:

[0052] FIGS. 1a-1d schematically illustrate examples of joining two blanks;

[0053] FIGS. 2a-2c schematically illustrate example arrangements for a welding laser beam and a filler wire melting beam according to various implementations; and

[0054] FIGS. 3a-3f schematically illustrate relative positions of welding laser beams and filler wire melting beams.

[0055] FIG. 4 is a flow diagram of a method of joining blanks.

DETAILED DESCRIPTION OF EXAMPLES

[0056] FIGS. 1a-1d schematically illustrate examples of methods of joining blanks.

[0057] In FIG. 1a a first portion or region A1 of a first blank A is to be joined to a second portion or region B2 of a second blank B. In this example, the two blanks are to be butt-joined, i.e. an edge-to-edge welding, specifically with straight edges (without special shaping/beveling of the edges).

[0058] In this example, both blanks A and B may be of coated steel, such as e.g. Usibor® 1500P. Both blanks may comprise a steel substrate 1 upon which a coating 2 may be provided. The coating applied in this example is aluminum-silicon (Al87Si10Fe3). Due to the process of application of the coating, the resulting coating may have a metal alloy layer 4 and an intermetallic layer 3 as illustrated in FIG. 1b-1d.

[0059] FIGS. 1b-1d schematically illustrate a cross-sectional view along the plane defined by the line x-y and the corresponding top view according to some examples of dual laser welding. Such plane defined by the line x-y corresponds to the welding beam C, i.e. the line where the edge of blank A contacts the edge of blank B. In these examples, blanks A and B may comprise a steel substrate 1 with a coating 2, which may have a metal alloy layer 4 as the outermost layer and an intermetallic layer 3 arranged between the steel substrate 1 and the metal alloy layer 4. When blanks A and B are welded, the coating layer and the steel substrate of the welded portions of blanks A and B, and the filler are mixed in the welding beam. Thus, after welding, the welding beam does not comprise a defined coating layer. In these examples, the arrow WD indicates the welding direction in the top view.

[0060] FIG. 1b further illustrates a cross-sectional view along the plane defined by the line x-y and the corresponding top view of the method of joining according to an example of dual laser welding. Schematically illustrated is a cross-sectional and top view of a filler metal melting laser 20 having a laser head 21 from which a first laser beam L1 exits. A filler wire 25 may be used as welding material. Also schematically illustrated is a laser welder 30 having a laser head 31 from which a second laser beam L2 exits.

[0061] In a dual laser welding process, two laser beams collaborate to form a weld zone 40. In this example, the first laser beam L1 (directly) melts the filler wire. The second laser beam L2 melts portions of the blanks in a weld pool substantially where the two blanks are to be welded. The melted filler wire is directed in the—common—weld pool and at the same time the melted filler wire mixes with the melted portions of the blanks. As the filler wire melts, any gap between the blanks may be filled and a weld may be created.

[0062] FIG. 1b further illustrates a top view of the weld zone 40 created in the zones to be welded of the blanks A and B. Laser beam spot S1 corresponds to the spot created by the first laser beam L1, while laser beam spot S2 corresponds to the spot created by the second laser beam L2.

[0063] In the example of FIG. 1b, the second laser beam L2, the laser welder beam, may be moveable in a wobbling manner to mix the material in the weld pool as a consequence of the Marangoni effect. As the melted portion of the blanks comprises steel substrate material as well as coating material, mixing the weld pool ingredients may avoid any harmful effects attributable to the Al alloy coating and, therefore, mechanical properties of the welded zone may not be affected.

[0064] It may be seen that in this case, there is no need for removing the coating of the steel substrates prior to welding, as the homogeneous mixing of the materials along the whole thickness of the blanks mitigates any harmful effects of the coating thus simplifying and speeding up manufacture. This may bring about a substantial cost reduction. At the same time, a filler wire of suitable composition may ensure that good mechanical properties are obtained after the standard heat treatment for Usibor® and after hot deformation processes such as hot stamping.

[0065] A standard treatment for Usibor® blanks would be to heat the obtained blank in e.g. a furnace to bring about (among others) austenization of the base steel. Then the blank may be hot stamped to form e.g. a bumper beam or a pillar. During rapid cooling after a hot deformation, martensite which gives satisfactory mechanical characteristics may thus be obtained. The standard treatment is not affected in any manner by the methods of joining proposed herein. In particular, thanks to the elements of a suitable filler wire (i.e. filler wire with gammagenic elements) that are supplied into the weld zone, a martensite structure can also be obtained in the area of the weld, in spite of the presence of aluminum.

[0066] FIG. 1c further illustrates a cross-sectional view along the plane defined by the line x-y and the corresponding top view of a method of joining two blanks according to another example of dual laser welding. Schematically illustrated is a filler metal melting laser 20 having a laser head 21 from which a first laser beam L1 exits. A filler wire 25 may be used as welding material. Also schematically illustrated is a laser welder 30 having a laser head 31 from which two sub-beams L2a and L2b exit. The laser head 31 may comprise twin-spot laser optics.

[0067] In this example of dual laser welding process, the laser beams also collaborate to form a weld zone 40. The first laser beam L1 melts the filler wire 25 similarly as in the example discussed with reference to FIG. 1b. The two sub-beams, L2a and L2b, generate a twin-spot that melts portions of the blanks in a weld pool substantially where the two blanks are to be welded. The melted filler wire is directed in the—common—weld pool and at the same time the melted filler wire mixes with the melted portions of the blanks. The twin-spot may warrant the mixing of the melted filler wire material with the melted portions of the blanks without any wobbling of any of the sub-beams L2a and L2b to be required.

[0068] FIG. 1c further illustrates a top view of the weld zone 40 created in the zones to be welded of the blanks A and B. Laser beam spot S1 corresponds to the spot created by the first laser beam L1, while laser beam spot S2a and S2b corresponds to the spots created by the sub-beams L2a and L2b respectively.

[0069] FIG. 1d represents a variation of the example of FIG. 1b, having a single laser head 51 and a single laser melting the wire and welding. In this example the melting and welding laser 50 has a single laser head 51 from which a first laser beam L1 and a second laser beam L2 exit.

[0070] FIG. 2a schematically illustrates a top view of a method of joining two blanks according to an example. A first blank A is to be joined to a second blank B along a weld seam C, wherein a first laser beam spot S1 may be responsible for melting a filler wire 25 material in the weld seam C zone and a second laser beam spot S2 may be responsible for melting a portion of the first blank A and a portion of the second blank B as well as mix the melted filler wire material with the melted portions of the blanks. The perforated line circles indicate the circular movement of the second laser beam in order to homogeneously mix the melted materials. FIG. 2b schematically illustrates a weaving movement of the laser beam spot S2 while FIG. 2c schematically illustrates a wobbling movement of the laser beam spot S2. The selection of movement may depend on weld zone characteristics.

[0071] In all the examples illustrated herein so far, blanks in the shape of flat plates are joined together. It should be clear that examples of the methods herein disclosed may also be applied to blanks of different shapes.

[0072] FIGS. 3a-3f schematically illustrate the relative positions of the spots generated from the first and second laser beams when a twin-spot laser beam is used for melting the portions of the blanks and for mixing the melted portions of the blanks with the melted filler wire. The arrow indicates the welding direction. In FIGS. 3a-3c the three spots are arranged collinearly along the welding direction. In FIG. 3a the spots S2a and S2b of the twin-spot precede the spot of the filler wire melting beam. In FIG. 3b the spot of the filler wire melting beam S1 precedes the spots S2a and S2b of the twin-spot. In FIG. 3c the spot S1 of the filler wire melting beam is interpolated between the two spots S2a and S2b of the twin-spot. In FIG. 3d the spots S2a and S2b of the twin-spot precede the spot S1 of the filler wire melting beam. However, in this case, the two spots of the twin-spot are arranged perpendicularly to the welding direction. In FIG. 3e, the two spots S2a and S2b of the twin-spot are arranged also perpendicularly to the welding direction, but, contrary to the arrangement of FIG. 3d, they follow the spot S1 of the filler wire melting beam. Finally, in FIG. 3f, the three spots are arranged along a direction perpendicular to the welding direction where the spot S1 of the filler wire melting beam is interpolated between the two spots S2a and S2b of the twin-spot.

[0073] When a twin-spot is used, the two spots may also induce or improve a similar Marangoni effect and the elements of the welding zone may again be homogeneously distributed with the austenite stabilizing elements in the filler reaching the bottom part of the weld. Therefore, the aluminum may not lead to worse mechanical properties in the welding zone after hot deformation processes such as hot stamping.

[0074] The percentage of ferrite and austenite depends on the amount of aluminum. Adding these austenite stabilizing stainless filler materials may increase the mass content of aluminum necessary for starting the ferrite phase. In other words, thanks to the filler, more aluminum may be allowed in the weld area while still maintaining the desired mechanical properties, i.e. while still ensuring the presence of austenite. Thus, the influence of the aluminum in the welding area may be minimized and a weld joint with good mechanical properties may be obtained.

[0075] FIG. 4 is a flow diagram of a method of joining blanks according to an example. In box 105, a first portion of a first blank to be joined to a second blank may be selected. The first blank may comprise at least a layer of aluminum or of an aluminum alloy or a layer of zinc or of a zinc alloy. In some examples, the first blank might comprise a steel substrate with a coating comprising the layer of aluminum or of an aluminum alloy or the layer of zinc or of a zinc alloy. In some examples, the steel substrate may be an ultra-high strength steel, in particular the steel may be a boron steel.

[0076] In box 110, a second portion of a second blank to be joined to the first portion may be selected. The second blank may also comprise at least a layer of aluminum or of an aluminum alloy or a layer of zinc or of a zinc alloy. In some examples, the second blank might comprise a steel substrate with a coating comprising the layer of aluminum or of an aluminum alloy or the layer of zinc or of a zinc alloy. In some examples, the steel substrate may be an ultra-high strength steel and in particular a boron steel.

[0077] In box 115, using a laser welding beam, the first portion and the second portion of the blanks may be melted in a weld zone. In box 120, a filler wire may be supplied and melted to the weld zone using a filler wire melting laser beam. The filler wire melting laser beam corresponds to a first laser beam. Such first laser beam is arranged to melt the filler wire in the weld zone. The laser welding beam may correspond to a second laser beam. Using such second laser beam may comprise displacing the second laser beam in an oscillating manner or using a twin-spot laser.

[0078] In box 125, the melted portions of the blanks and the melted filler wire are mixed in the weld zone to produce a weld. By mixing the filler along the whole weld zone, i.e. along the whole thickness of the blanks, mechanical properties of the weld can be improved.

[0079] Good mechanical properties are obtained, where two Usibor® 1500P blanks were welded by dual laser welding with the use of a filler wire melting laser beam and a welding laser beam. Particularly, a high tensile strength is obtained when fillers containing austenite stabilizing materials are used. The tensile strength obtained could be compared with an unwelded Usibor® products and a welded 22MnB5 uncoated boron products.

[0080] These good mechanical properties may be obtained using a relatively high welding speed, improving the manufacturing processes and reducing the welding time. Welding speed from 5-12 m/min may be achieved in various examples.

[0081] Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and/or equivalents thereof are possible. Furthermore, all possible combinations of the described examples are also covered. Thus, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow.