Method for improving the friction stir weld strength between a steel plate and an aluminum plate
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- GM GLOBAL TECHNOLOGY OPERATIONS LLC
- Filing Date
- 2016-06-29
- Publication Date
- 2026-07-02
Smart Images
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Abstract
Description
TECHNICAL AREA This invention relates to improvements in friction stir weld strength in general. In particular, the invention relates to a method for improving the friction stir weld strength between aluminum and steel, which has a surface coating, by forming a local texture of points with increased height and mechanically mixing the steel and aluminum to form the weld. Friction stir welding processes are described, for example, in documents EP 1 749 614 A1 and US 2005 / 0 035 180 A1. Furthermore, it is known from documents JP 2014-108 450 A and US 2002 / 0 166 843 A1 to emboss raised areas in plates to be welded together, at which the plates are welded. BACKGROUND Joining dissimilar metals is desirable to create products with improved properties due to the combined aspects of each metal. However, large differences in physical and metallurgical properties between alloy systems, poor metallurgical bonding, high residual stresses, and poor weld strength have limited such applications. Combining alloys such as aluminum and magnesium with iron- and nickel-based alloys would be desirable to potentially create products with improved and customizable properties, such as reduced and targeted weights. However, problems with weldability and poor weld strength have not been overcome. There has long been a need in engineering for improved methods and devices for joining dissimilar metals. This document provides descriptions of such methods and devices that improve the friction stir weld strength between steel and aluminum with a surface coating and pre-formed local texture. SUMMARY According to the invention, a method with the features of claim 1 for improving the friction stir weld strength between a steel plate and an aluminum plate is presented. In certain embodiments, an aluminum plate and a steel plate are provided. Methods may include coating a surface of the steel plate with a layer containing at least one zinc, aluminum, and silicon. The layer may be provided, for example, by hot-dip coating the steel plate to form a surface coating. Such methods may include punching at least a portion of the surface of the steel plate. The surface punching may be performed to create a pre-formed local texture with raised points in at least one section of the steel plate. The raised height may range from approximately 0.010 millimeters to approximately 0.500 millimeters.Subsequently, friction stir welding can be performed to form the weld, with exemplary methods including arranging the steel plate in contact with the aluminum plate and generating heat between a friction stir welding tool and both the steel and aluminum plates to soften each of the metal plates near the friction stir welding tool. Methods may include applying mechanical pressure to the softened metals via the friction stir welding tool and metallurgically and mechanically mixing the steel and aluminum plates to form the weld between the steel plate and / or coating and the aluminum plate. In certain methods, the pre-formed local texture of the steel plate is located within the weld. In certain embodiments, the speed of the friction stir welding tool tip ranges from approximately 1700 to approximately 2000 revolutions per minute.In certain embodiments, the speed ranges from about 1800 revolutions to about 2000 revolutions. Additional embodiments described herein provide a method for improving the friction stir weld strength between a steel plate and an aluminum plate. In certain embodiments, the steel plate has a surface coating at the beginning of the method, and in others, the coating is added before each of the following steps described herein. Methods may include providing an aluminum plate and a steel plate, and punching at least one section of a surface of the steel plate. The punching may produce a preformed local texture consisting of points of increased height on the surface of the steel plate.Friction stir welding can involve arranging the steel plate in contact with the aluminum plate and generating heat between the friction stir welding tool and both the steel and aluminum plates, resulting in softening of each metal plate in the vicinity of the welding tool. Subsequently, the process may involve applying mechanical pressure to the softened metals via the friction stir welding tool and metallurgically and mechanically mixing the steel plate, the steel surface coating, and the aluminum plate to form the weld between them. In certain processes, the pre-formed local texture of the steel plate is retained within the weld. Further embodiments described herein provide a method for improving the friction stir weld strength between a steel plate and an aluminum plate. The method may include providing an aluminum plate and a steel plate, coating the surface of at least one of the plates with a layer of zinc, aluminum, and silicon by hot-dip coating the at least one of the plates to form the surface coating, and punching at least one section of the at least one of the plates, which includes the surface coating, to produce the pre-formed local texture consisting of points of raised protrusion in at least that section of the at least one of the plates.The method can also include friction stir welding to form the weld, wherein the friction stir welding comprises arranging the steel plate in contact with the aluminum plate and generating heat between a friction stir welding tool and the steel plate and the aluminum plate to soften each of the metal plates near the friction stir welding tool. The method can also include applying mechanical pressure to the softened metals via the friction stir welding tool and mechanically mixing the steel plate, the aluminum plate, and the surface coating to form the weld between the steel plate and the aluminum plate, wherein the preformed local texture of at least one of the plates is contained therein. BRIEF DESCRIPTION OF THE DRAWING Fig. 1A illustrates an improved friction stir weld between steel and aluminum with a pre-formed local texture; Fig. 1B illustrates an embodiment of a steel plate with a pre-formed local texture near an aluminum plate, before welding has been performed; Fig. 2 illustrates another embodiment of a steel plate with a pre-formed local texture near an aluminum plate, before welding has been performed; Fig. 3A illustrates a method for forming a coating on a steel plate; Fig. 3B illustrates a cross-section of a steel plate showing a coating formed by an immersion process; Fig. 3C illustrates a cross-section of a steel plate showing a coating formed substantially on one side of the steel plate; Fig. 4A and Fig.Figures 4B show the steel plate (4A) and a heating device (4B) for preparing the steel plate for punching; Figure 5A illustrates a female stand tool used according to the invention above the steel plate, which is held in a forming container; Figure 5B illustrates the steel plate of Figure 5A after punching by the female punching tool; Figure 6A illustrates a male punching tool used contrary to the invention above the steel plate; Figure 6B illustrates the steel plate of Figure 6A after punching by the male punching tool; Figure 7A illustrates a friction steel tool over adjacent steel and aluminum plates to form an overlap weld; Figure 7B illustrates a continuous weld of the steel plate and the aluminum plate; FigureFigure 8A illustrates a friction steel tool over adjacent steel and aluminum plates, with arrows indicating an exemplary embodiment where spot welding can be performed; Figure 8B illustrates an embodiment of an end-to-end weld of the steel plate and the aluminum plate, the indicated pre-formed local texture being able to be formed at one end or the ends of the plates; Figure 9 illustrates an engine mount manufactured according to the method described herein. The embodiments shown in the drawings are for illustrative purposes only and are not intended to limit the embodiments defined by the claims. Furthermore, certain aspects of the drawings and the embodiments become more fully apparent and understandable in light of the detailed description that follows. DETAILED DESCRIPTION Specific embodiments of the present invention will now be described. However, the invention can be implemented in various forms and should not be interpreted as being limited to the embodiments presented here. Exemplary embodiments are provided to ensure that this disclosure is thorough and fully conveys its scope to those skilled in the art. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as they would normally be understood by a person skilled in the art in the field to which the embodiments of this invention belong. The terminology used herein serves solely to describe certain exemplary embodiments and is not intended to be restrictive in any way. As used herein, the singular forms "a" and "the" include the plural forms where appropriate, unless the context clearly excludes this. Unless otherwise specified, all numbers expressing quantities of components, properties such as molecular weight, reaction conditions, and so forth, as used in the description and claims, shall be understood in all cases as being modified by the term "approximately," which is intended to mean up to ±10% of a given value. Furthermore, the disclosure of ranges in the description and claims shall be understood to include the range itself, everything subsumed therein, and endpoints. Unless otherwise specified, the numerical properties set forth in the description and claims are approximate values that may vary depending on the desired properties sought in embodiments of the present invention.Notwithstanding the fact that the numerical ranges and parameters illustrating the broad scope of embodiments of the invention are approximations, the numerical values presented in the specific examples are illustrated as accurately as possible. However, each numerical value inherently contains certain errors that necessarily result from errors found in their respective measurements. Parts of the procedure described herein, such as mathematical determinations, calculations, input of data for calculations or determinations of equations or parts thereof, may be performed on parts thereof or on one or more computers or computer systems, which may include one or more processors, as well as software to run or execute programs and to perform calculations or computations. The methods and systems and parts thereof described herein can be combined to implement embodiments of the invention. Word forms used herein may have variations: for example, when a word such as "bilden" is used, this means that variations such as "bildung" and "Bilden" are understood and have been taken into account. As used herein, "plate" refers to a sheet of aluminum or steel. The plate may be thin and essentially a square, rectangular, triangular, semicircular, or circular piece of metal, as viewed from one side, although it may also be formed in a shape required to encompass at least one section of a vehicle chassis. The plate may be flat or formed from a flat piece into a shaped piece with angles. The plate may be malleable and / or formed such that one or more pieces can be combined to form a curved section of a chassis. Fig. 1A illustrates an improved friction stir weld 103 between a steel plate 102 and an aluminum plate 101 with a pre-formed local texture comprising one or more points of raised protrusion 104 and intervening smooth sections 105. The formation of these one or more points of raised protrusion 104 increases the weld surface area, allowing for the formation of a stronger friction stir weld 103. Such a weld improves the metallurgical and mechanical bond integrity and strength between the steel plate 102 and the aluminum plate 101, minimizing springback and reducing residual stress at the welds. Additionally, it reduces friction stir welding tool wear due to the reduction of the contact area between the tool and the steel plate and the increased energy concentration on the pre-formed textured surfaces. A joined product 100 made of aluminum plate 101 and steel plate 102 may have one or more raised protrusions 104, which are at an angle to a longitudinal axis of the steel plate. In certain embodiments, the angle between the one or more raised protrusions 104 and the longitudinal axis of the steel plate 102 is ninety degrees, and in certain embodiments, after welding, the one or more raised protrusions 104 are bent to an angle of less than ninety degrees. In certain embodiments, the angle of less than ninety degrees may be formed before welding, and in other cases, the welding process causes the angling or deformation of the raised protrusions 104. Fig. 1B illustrates an embodiment of the steel plate 102 with a pre-formed local texture near an aluminum plate 101, before welding has been performed. The steel plate 102 has ends 109, 209, an outer side 107, and an inner side 207, the inner side being the side to be joined to the aluminum plate 101. The local pre-formed texture, consisting of one or more points of raised protrusion 104 and smooth sections 105, is also illustrated on the inner side 207 of the steel plate 102. The aluminum plate 101 has ends 108, 208, an outer side 106, and an inner side 206, the inner side 206 being the side to be joined to the steel plate 102. Fig. 2 illustrates another embodiment of a steel plate 102 with the pre-formed local texture near the aluminum plate 101, and before welding has been carried out. As illustrated in Fig. 1B, the steel plate 102 is shown with ends 109, 209, an outer side 107, and an inner side 207, the inner side being the side to be joined to the aluminum plate 101. Also shown on the inner side 207 of the steel plate is the local pre-formed texture, which is formed from one or more points of raised protrusion 104 and smooth sections 105. The aluminum plate 101 has ends 108, 208, an outer side 106, and an inner side 206, the inner side being the side to be joined to the steel plate 102.In this embodiment, each of the raised protrusion points 104 abuts another raised protrusion point 104, and raised protrusion points are arranged equidistant from opposite ends 109, 209 of the steel plate 102, with the smooth sections 105 extending outwards from both sides of the ends 109, 209 of the steel plate 102. The methods described herein result in points with reduced residual stresses 210, 211 due to a reduction in springback caused by the raised protrusion point 104. Fig. 3A illustrates a method for forming a coating 114 on the steel plate 102, such as hot-dip galvanizing, with the steps illustrated at 115. The methods and apparatus of the embodiments described herein may use one or more parts of the method. Specific embodiments have four immersions 110, 111, 112, 113, of the steel plate 102, each in containers A, B, C, and D, respectively. Container A shows a container with sodium hydroxide solution for removing oils, paint, and markings; container B shows a container with an acid solution for removing rust or mill scale; container C shows a container with a flax solution to prevent oxidation; and container D shows a container with a zinc solution. In certain embodiments, directly galvanized steel plates are used (the plates are provided in a first process step).In certain embodiments, the aluminium plate 101 or parts thereof is coated in addition to the coating of the steel plate 102. In certain embodiments, rinsing steps are performed between one or more of the provided immersions. In certain embodiments, the flux zinc ammonium chloride is applied to the steel plate 102 to prevent oxidation of the cleaned surface upon contact with air; the flux is allowed to dry on the steel plate 102 and can aid in a process of liquid zinc wetting and adhesion to the steel. In certain embodiments, the steel plate 102 is immersed in a molten zinc bath and held there until the temperature of the steel is equilibrated with that of the bath. Fig. 3B illustrates a cross-section of the steel plate 102 from Fig. 3A, showing a coating 114 formed by an immersion process, which can be seen on all four sides of the steel plate 102. In certain embodiments, the coating 114 can be provided substantially or completely on a single side of the steel plate 102, as shown in Fig. 3C, which shows the cross-section of another embodiment of the steel plate 102 from Fig. 3A. The steel plate 102 can be immersed just enough to create a surface coating 114 substantially on one side; alternatively, the coating 114 could be applied by another method, such as spraying. Figures 4A and 4B show the steel plate 102 (Figure 4A) and a heating device 116 (Figure 4B) for preparing the steel plate 102 for punching. Figure 4B illustrates the heating device 116, with an upper structural section 117 and a lower structural section 118, each structural section 117 and 118 having a heating element 119 and 120, respectively. The heating device 116 can hold the steel plate 102 between the heating elements 119 and 120. Heat can be supplied to one side of the steel plate 102 via the heating element 119, as shown by arrows E, F, and G, and heat can be supplied to the other side of the steel plate via the heating element 120, as shown by arrows H, I, and J. In certain embodiments, the steel plate can be arranged in the heating device so that each side or both ends point directly towards heating element 119 or heating element 120.In certain embodiments, cold forming is used and heat is not applied to the plate(s) during the production of the pre-formed local texture. Fig. 5A illustrates a female punching tool 121 used according to the invention above the steel plate 102, which is held in a mold container 126. The female punching tool 121 has an upper structural section 122 which is coupled to a female die 123 having at least one recessed section 124. The mold container 126 has a receiving area 127 for holding the steel plate 102. The upper structural section 122 can be pressed towards the receiving area 127 in the direction 125 to punch the steel plate 102 with the die 123. Arrows K, L, M illustrate the direction of movement of the at least one recessed section 124; the number of which can vary (for example, from about one to about ten, or about ten to about fifty, or about twenty-five to about fifty). Fig. 5B illustrates the steel plate 102 from Fig. 5A after punching by the female die 123. The steel plate 102 is shown with ends 109, 209 and sides 107, 207. Although Fig. 5A illustrates the steel plate 102 with completely smooth surfaces, Fig. 5B illustrates the raised points 104 formed by the female die 123. In certain embodiments, the raised points 104 are formed so densely as to form a line either longitudinally or laterally across the steel plate 102. In certain embodiments, the raised points 104 have a height of about 0.010 millimeters to about 0.200 millimeters. In certain embodiments, the raised points 104 are spaced about 0.5 millimeters to about 1 millimeter apart. Fig. 6A illustrates a male punching tool 138 used contrary to the invention above the steel plate 102. The male punching tool 138 has an upper structural section 128 coupled to a male die 129, which has at least one protruding section 130. The upper structural section 128 can be pressed towards the steel plate 102 in the direction 131. Fig. 6B shows the results of the punching, showing the steel plate 102 and the smooth surface 105, as well as points of raised protrusion 104 formed by the male die 129. The points of raised protrusion 104 point in the opposite direction to those shown in Fig. 5B, although the steel plate 102 can be turned over and used in a similar way to the finished steel plate 102 shown in Fig. 5B with respect to welding to the aluminum plate 101.For punching with one of the dies provided herein, the steel plate can be placed on a conveyor belt 139, as shown in Fig. 6A. The steel plate 102 can be placed on a conveyor belt 139 resting on springs 132, 133. As the belt moves laterally, a steel plate can be positioned under the male die, and punching can occur to form the points of raised protrusion 104. The springs 132, 133 yield to absorb some of the impact of the punching, allowing the conveyor belt 139 to continue operating. After punching, the steel plate 102 can be moved, and the process can be repeated with new, unpunched steel plates. In another embodiment, the steel plate 102 is held in place for punching and is not on a conveyor belt 139. Fig. 7A illustrates a friction stir steel tool 134 over adjacent steel and aluminum plates (102 and 101, respectively) to form an overlap weld. The friction stir steel tool 134 is shown with a conical upper section 135, a middle section 136 with a smaller diameter than the conical upper section, and a tip 137. Fig. 7B illustrates the friction stir weld 103 between the steel plate 102 and the aluminum plate 101. In certain embodiments, as shown in Fig. 7B, the weld 103 is a continuous weld. Another example of friction stir welding can be found in jointly owned U.S. Patent 7,997,472, which is hereby incorporated by reference in its entirety.The weld interface where the two plates are formed is shown in 103a, where the aluminum plate 101, the steel plate 102, and any surface coating are mixed together during welding. This is where the intermetallic compound of steel and aluminum (Fe4Al13) is formed, which in certain embodiments has a thickness that is substantially at or below the height of the raised points 104 (from about 0.010 millimeters to about 0.200 millimeters, or in certain embodiments from about 0.010 millimeters to about 0.10 millimeters). The thickness of the intermetallic compound would not be made substantially greater than the height of the raised points. Fig. 8A illustrates the friction steel tool 134 over adjacent steel and aluminum plates (102 and 101, respectively). The friction steel tool 134 is shown with the conical upper section 135, the middle section 136 with a smaller diameter than the conical upper section, and the tip 137. In certain embodiments, the radius of the tip 137 is from about 20 mm to about 100 mm in diameter; in other embodiments, the tip 137 is at least 20 mm in diameter. In still other embodiments, a weld width of about 4 mm to about 10 mm is produced. The friction steel tool 134 can form spot welds at points N, O, P to form three exemplary spot welds corresponding to the points of raised protrusion 104 and forming the friction stir weld seam 103 between the steel plate 102 and the aluminum plate 101.In certain embodiments, spot welding is performed only at the points of raised protrusion 104. In certain embodiments, spot welding is also performed on smooth sections 105, as indicated at point S. For the sake of completeness, the outer side 107 of the steel plate 102 is indicated. Fig. 8B illustrates an embodiment of an end-to-end (109, 108) weld of the steel plate 102 or the aluminum plate 101, respectively; the indicated pre-formed local texture can be formed at one end or the ends (109, 209) of the steel plate. Fig. 9 illustrates an engine mount according to the methods described herein. The mount can be formed from at least one aluminum plate 101 and at least one steel plate 102. In certain embodiments, the mount has no bolts. In certain embodiments, an aluminum-steel weld is formed on the engine mount, with at least one weld being approximately 30 to 40 millimeters long and approximately 2 to 6 mm wide. In certain embodiments, there are two welds forming the mount, one on each opposite side of the engine mount, each approximately 30 to 40 millimeters long and approximately 2 to 6 mm wide. In other embodiments, part of a chassis is formed using the methods described herein. In certain embodiments, the methods provided herein include producing, by punching, raised points 104 to a height of about one hundred to about two hundred micrometers from at least the section of the steel plate 102. In certain embodiments, the height is from about 0.010 millimeters to about 0.200 millimeters. In certain embodiments, the height is from about one hundred and twenty-five to about one hundred and seventy-five micrometers. The methods provided herein may include the production, by punching, of raised points 104 such that each raised point 104 comprises a dome shape. In certain embodiments, one or more of the raised points 104 comprise a dome shape. In certain embodiments, the methods provided herein include the production, by punching, of raised points 104 in a series of rows. In certain embodiments, the surface coating 114 is provided over the entire surface of the steel plate 102, and the mechanical mixing of the steel plate 102 and the aluminum plate 101 comprises forming the seam by applying the friction stir welding tool 134 to several coated surfaces of the steel plate 102. The methods provided herein may further include arranging the steel plate 102 in a forming container 126 prior to punching. This can be done to maintain the shape of the steel plate 102, so that its shape is the same before and after punching, except for the points of raised protrusion 104 formed. In such an example, compression will increase the density of the steel plate 102 by changing the thickness of the steel plate in the direction of the punching 125. In certain embodiments, the steel plate may remain essentially flat, except for the points of raised protrusion 104. As previously stated, the methods provided herein may include punching with a female die 123. In certain embodiments, the methods provided herein may further include punching with a male die 129 such that raised points of the protrusion 104 extend from the steel plate 102 in the direction away from the punching operation. In certain embodiments, the methods provided herein further include punching at least one second steel plate. The methods provided herein may further include the surface coating 114 on the steel plate 102 with a layer of zinc, aluminum, and silicon. In certain embodiments, the layers of zinc, aluminum, and silicon are applied by immersion. In certain embodiments, the methods provided herein further include the formation of the friction stir weld seam 103 by spot welding. The methods provided herein may further comprise the formation of the points of raised protrusion 104 only in predetermined sections of the steel plate 102, which are separated from one another by substantially smooth sections 105. The methods may also comprise the formation of the friction stir weld 103 by spot welding only at each of the locations of the predetermined sections. In certain embodiments, the predetermined sections may be provided by calculations on a computer associated with an automated welding system. In certain embodiments, the points to be welded are determined prior to welding. The methods provided herein further comprise the formation of the friction stir weld 103 by substantially continuous welding, thereby forming a single weld seam. In certain embodiments, the methods provided herein further comprise forming the points of raised protrusion 104 in at least the portion of the surface of the steel plate 102 at an angle of about ten to about seventy-five degrees from a longitudinal plane of the steel. In certain embodiments, the angle may be from about thirty-five to about sixty-five degrees or from about forty-five to about fifty-five degrees from the longitudinal plane of the steel plate 102. The longitudinal plane of the steel plate 102 lies, in certain embodiments, in the same direction as the friction stir weld 103, as shown in Fig. 1A. In certain embodiments, the methods provided herein further comprise a second punching of at least the portion of the surface of the steel plate 102 to form a second set of points of raised elevation 104, which are of a different height than those formed by the first punching. For example, one set could be from about one hundred micrometers to about one hundred and fifty micrometers in height, and the other could be from about one hundred and fifty to about two hundred micrometers in height. Having described the invention in detail with reference to specific embodiments thereof, it will be obvious that modifications and variations are possible. More precisely, it is considered that the present invention is not necessarily limited to the preferred aspects of the invention, even though some aspects are described here as preferred or particularly advantageous. The methods and apparatus provided herein can also include determining the position and size (length and width) of the pre-formed local texture, forming the texture before, during, or after the parts are formed, clamping the aluminum to the steel, locating the weld points either manually or with pre-programmed robots, and friction stir welding of the aluminum to the steel to form overlap welds.
Claims
Method for improving the friction stir weld strength between a steel plate (102) and an aluminum plate (101) comprising: providing an aluminum plate (101) and a steel plate (102); coating a surface of the steel plate (102) with a layer (114) of zinc, aluminum and silicon; punching out at least one section of the surface of the steel plate (102) comprising the surface coating (114) to produce a preformed local texture formed from points of raised protrusion (104) in at least the area of the steel plate (102); and friction stir welding to form the weld (103), wherein the friction stir welding comprises: arranging the steel plate (102) in contact with the aluminium plate (101); generating heat between a friction stir welding tool (134) and the steel plate (102) and the aluminium plate (101) to soften each of the metal plates near the friction stir welding tool (134);Application, via the friction stir welding tool (134), of a mechanical pressure on the softened metals; and mechanical mixing of the steel plate (102) and the aluminum plate (101) to form the weld (103) between them, wherein the surface coating and the preformed local texture of the steel plate (102) are contained therein; wherein the steel plate (102) is positioned in a receiving area (127) of a mold container (126) prior to punching to hold the steel plate (102) in a mold such that the shape of the plate is the same before and after punching, except for the points of raised protrusion (104) formed, and compression increases the density of the steel plate thickness in the direction of punching, wherein the at least one punched section of the surface of the steel plate (102) is substantially flat, except for the points of raised protrusion (104).; Method according to claim 1, wherein the punching further comprises the production of the points of increased elevation (104) to a height of one hundred to two hundred micrometers. Method according to claim 2, wherein the punching further comprises the production of the points of raised elevation (104) such that each of the raised points comprises a dome shape. Method according to claim 3, wherein the punching further comprises the production of the points of raised elevation (104) in a series of lines. Method according to claim 1, further comprising punching with a female die (123). The method according to claim 1, further comprising forming the points of increased elevation (104) at an angle of about ten to about seventy-five degrees from a longitudinal plane of the steel. Method according to claim 1, further comprising punching at least one second steel plate (102).