DK201670472A1 - Metal Sheets Spot Welding with inoculation agents - Google Patents

Abstract

The present invention relates to a method of spot welding of two sheets mainly formed of aluminum alloys, including the steps of: predetermining the location area of the two sheets in contact with each other in which a weld spot is to be formed; applying materials comprising inoculant particles onto the surface of at least one of the two sheets at said location area; spot welding said two sheets by passing electrical current through the sheets via a pair of electrodes, wherein the particles comprise at least one material selected from the group consisting of:(a) Al+Ti,(b) Al+C.

Description

(19) DANMARK (1°) DK 2016 70472 A1

<¹²> PATENTANSØGNING

Patent- og

Varemærkestyrelsen (51)

Int.CI.: B 23 K 11/10 (2006.01)

C 22 F 1/04(2006.01) (21) Ansøgningsnummer: PA 2016 70472 (22) Indleveringsdato: 2016-06-30 (24) Løbedag: 2016-06-30 (41) Aim. tilgængelig: 2017-12-31 (71) Ansøger: Hebei Lixin Technology Co., Ltd., Suite 404, Tower 7, Hexie Street 19, Handan Hebei, Kina (72) Opfinder: Lixin Zhou, Suite 404, Tower 7, Hexie Street 19, Handan Hebei, Kina (74) Fuldmægtig: GUARDIAN IP CONSULTING l/S, Diplomvej, Bygning 381, 2800 Kongens Lyngby, Danmark (54) Benævnelse: Metal Sheets Spot Welding with inoculation agents (56) Fremdragne publikationer:

US 2005/0103406 A1 US 5552573 A (57) Sammendrag:

The present invention relates to a method of spot welding of two sheets mainly formed of aluminum alloys, including the steps of: predetermining the location area of the two sheets in contact with each other in which a weld spot is to be formed; applying materials comprising inoculant particles onto the surface of at least one of the two sheets at said location area; spot welding said two sheets by passing electrical current through the sheets via a pair of electrodes, wherein the particles comprise at least one material selected from the group consisting of:(a)

Al+Ti,(b) Al+C.

DK 2016 70472 A1

DK 2016 70472 A1 i

Metal Sheets Spot Welding with inoculation agents

FIELD OF THE INVENTION

The present invention generally relates to spot welding area and metal inoculation area, and more particularly to a method of spot welding combined with nugget inoculating in metal sheets in order to refine the weld grain structure, and thus to obtain metal welds with enhanced mechanical properties.

BACKGROUND OF THE INVENTION

Resistance spot welding (RSW) is a process in which contacting metal surfaces are joined by the heat obtained from resistance. Work-pieces are held together under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020 to 0.118 in) thickness range. The process uses two shaped copper alloy electrodes to concentrate welding current into a small spot and to simultaneously clamp the sheets together. Forcing a large current through the spot will melt the metal and form the weld. The attractive feature of spot welding is that a lot of energy can be delivered to the spot in a very short time (approximately 10-100 milliseconds). That permits the welding to occur without excessive heating of the remainder of the sheet.

The amount of heat (energy) delivered to the spot is determined by the resistance between the electrodes and the magnitude and duration of the current. The amount of energy is chosen to match the sheet's material properties, its thickness, and type of electrodes. Applying too little energy will not melt the metal or will make a poor weld. Applying too much energy will melt too much metal, eject molten material, and make a hole rather than a weld. Another feature of spot welding is that the energy delivered to the spot can be controlled to produce reliable welds.

The most common application of spot welding is in the automobile and airplane manufacturing industry, where it is used almost universally to weld the sheet

DK 2016 70472 A1 metal to form a car and aircraft. Spot welding is also used in the orthodontist's clinic, where small-scale spot welding equipment is used when resizing metal molar bands used in orthodontics.

Another application is spot welding straps to nickel-cadmium or nickel-metal hydride cells to make batteries. The cells are joined by spot welding thin nickel straps to the battery terminals. Spot welding can keep the battery from getting too hot, as might happen if conventional soldering were done.

Good design practice must always allow for adequate accessibility. Connecting surfaces should be free of contaminants such as scale, oil, and dirt, to ensure quality welds. Metal thickness is generally not a factor in determining good welds.

Because vehicle applications impose cyclic stresses on the body components over a long period of time, it is important that the metal welds possess adequate mechanical strength and resistance to fatigue.

In order to form resistance type spot welds between sheets of an metal, the sheets are clamped together under pressure between a pair of welding electrodes, typically copper, and an electrical current is passed between the electrodes so as to flow through an area or spot on the sheets. This current flow heats the metal material at the spot to its melting temperature, producing a molten weld nugget in which metal from the two sheets migrate toward each other to form a fusion weld when the molten nugget has cooled and solidified. The solidification process results from nucleation and growth of a new phase (a solid) at an advancing solid/liquid interface within the weld nugget. The solid phase within a molten weld nugget generally initiates by epitaxial growth from the surfaces of the material being welded, and proceeds by competitive growth toward the centerline of the weld. That is, grains with their easy growth direction oriented most preferentially along the heat flow direction gradient, tend to crowd out those grains whose easy growth directions are not as suitably oriented. The grain structure of the resulting weld is determined by the type of nucleation and growth of the solid phase. As the weld nugget cools, the solidification that begins at the

DK 2016 70472 A1 walls of the substrate result the formation of grains that grow against the heat flux; these grains are known as columnar grains. Eventually, and depending upon the solidification conditions, equiaxed grains form in the central region the weld nugget. The columnar grain structures, i.e. structures in which the grains tend to be elongate and run parallel to each other, result in a weld that possesses less mechanical strength compared to a weld having an equiaxed grain structure where the grains are uniform in size and are arranged in a random orientation. Furthermore, the mechanical strength of the weld would degrade even more if the columnar grain structure is in the proximity of the high stress regions formed at the intersection of the weld nugget and the opening of the sheets. A solidified weld normally possesses both columnar and equiaxed grains, with the equiaxed grains being disposed in the center of the weld and surrounded by an outer boundary layer of columnar grains. In order to increase the mechanical strength of the weld as well as its resistance to fatigue, it would be desirable to maximize the volume of equiaxed grains, compared to the volume of the columnar grains. The present invention is directed toward achieving this objective.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a method of spot welding of two sheets mainly formed of aluminum alloys, including the steps of: predetermining the location area of the two sheets in contact with each other in which a weld spot is to be formed; applying materials comprising inoculant particles onto the surface of at least one of the two sheets at said location area; spot welding said two sheets by passing electrical current through the sheets via a pair of electrodes, wherein the particles comprise at least one material selected from the group consisting of:(a) Al+Ti,(b) Al+C.

A significant advantage of the invention resides in its ability to not only increase the mechanical properties of an metal weld, but also improve the consistency of weld quality by introducing an relatively inexpensive inoculant to the weld

DK 2016 70472 A1 nugget.

Another advantage of the invention is conventional resistance welding equipment may be used to practice the inventive method without increasing weld cycle time.

These and other advantages and features of the invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves a fusion bond such as a weld between two workpieces formed of metal. The weld is commonly referred to as a spot weld that may be produced using conventional resistance welding equipment well-known in the art. Such equipment typically includes a power supply, and a pair of electrodes between which the sheets are clamped with a pre-determined force. With the sheets in face-to-face contact under pressure, the power supply delivers an electrical current to the electrodes which flows through the facing, contacting surfaces of the sheets to produce a molten weld nugget. This weld nugget solidifies and cools to form a weld which ideally possesses a mechanical strength approaching that of the metal sheet material itself

As weld nugget cools, the molten metal crystallizes as it changes state from a liquid to a solid. During the cooling process, crystallization of the outer boundary layers occurs first, and solidification proceeds inwardly toward the center of the weld until the weld has completely crystallized. Crystallization of an outer boundary layer in the weld nugget results in a columnar grain structure in which the individual grains tend to be elongate with their longitudinal axes extending parallel to each other and oriented in the direction of the heat flow. The outer boundary transitions into a central area where the grain structure is equiaxed, i.e.

DK 2016 70472 A1 the individual grains have equal dimensions, rather than being elongate, and have their axes randomly oriented relative to each other. As will be later discussed, the equiaxed grain structure of the central area tends to provide the weld with superior mechanical strength and fatigue resistance compared to a weld where columnar grain structure are predominate within the weld nugget.

In accordance with the present invention, it has been found that the strength of a weld formed between workpieces can be improved by inoculating the molten weld nugget with certain materials which tend to be particularly effective in promoting the nucleation of equiaxed grains as the nugget solidifies.

The inoculant is applied to one or both if the facing surfaces of the workpieces to be welded. The inoculant may be in the form of a liquid or paste that is sprayed or brushed onto the workpiece surface, or the inoculant may be incorporated into a carrier formed into a film or foil which is interposed between the workpiece surfaces before they are clamped and welded.

The workpieces of metal sheets can be formed of various material suitable for spot welding, including at least mild steel, galvanized steel, quenched steel, stainless steel, Aluminium-plated Steel, copper alloy, titanium alloy and aluminum alloys. The present invention can also be applied to other metal sheets spot welding.

In an example, the location area of the two sheets in contact with each other in which a weld spot is to be formed is predetermined. A small hole can be formed at the center of the location area of at least one of the two sheets. The inoculant particles can be put into the hole. The two sheets are joined by passing electrical current through the sheets via a pair of electrodes. The particles comprise at least one material selected from the group consisting of:

DK 2016 70472 A1 (a) Al+Ti,(b) Al+C,(c) Ti+C(d)Ti-B alloy+Al,(e) C+Ti-B alloy,(f) Al-Ti-B-Re alloy +C, (h) Al+Ca,(i)Sr+Zr,(j)Ba+Zr,(k)Si+C,(l)Zr+Al,(m) Na+Al, (n)Si+Na,(o)Al+Ba,(p)Al+Si,(q) Si+Ba,

The diameter of the hole can be 0.1-lmm.The depth of the hole can be 1/20-1/5 of the sheet. The particles can be in the form of powder. The two sheets can have the same or different depths.

The inoculant particles can be applied onto the surface of at least one of the two 10 sheets at the location area. The materials can be applied in a form of a film onto the surface. The materials can be applied in a form of a paste onto the surface. The thickness of the film can be in the range of 0.01-0.1mm. The two sheets can have the same or different depths.

The method of the invention can use any of above listed inoculant particles, though the claimed ones are preferable.

A series of tests were performed to compare the properties of welds produced with and without inoculation according to the inventive method. These test results clearly show that the mechanical properties of the inoculated welds were superior to those which did not receive inoculants.

Sheets material	sheet thickness (mm)	electrode pressure (KN)	current (KA)	Time (cycle)	inoculatio n agents	shear strength (KN)
aluminum alloys	1	3	30	2	no	1.2
Al+Ti,	1.8
Al+C,	1.6

DK 2016 70472 A1

mild steels	1	2.25	8.8	8	no	5.7
Ti+C	6.5
Ti-B alloy+Al	6.6
galvanized steels	1	3	11	9	no	5.9
C+Ti-B alloy	6.7
Al-Ti-BRe alloy +C	6.8
quenched steels	1	1.5	6	25	no	6
Al+Ca	6.5
Sr+Zr	6.4
Aluminiumplated Steels	1	2.5	10.5	11	no	3.9
Ba+Zr	4.6
Si+C	4.5
stainless steels	1	4	6	7	no	5.2
Zr+Al	5.9
Na+Al,	6
copper alloys	1	3	23	6	no	1.4
Si+Na	1.75
Al+Ba	1.8
Titanium alloys	1	5	5.5	7	no	7
				Al+Si	7.8
				Si+Ba	7.9

DK 2016 70472 A1

Table 1 Mechanical property of various metal sheets with or without the inoculation agents.

The results of these tests are represented in the table 1 which clearly show that the 5 mechanical properties of inoculated welds according to the method of the present invention are markedly superior to those welds not having inoculation. Again, it can be seen that welds provided with inoculation in accordance with the present invention exhibited superior shear strength compared to welds without inoculation.

From the foregoing, it may be appreciated that the weld nugget inoculation described above not only provides advantages over the prior welding methods, but does so in a particularly effective and economical manner. It is recognized, of course, that those skilled in the art may make various modifications or additions chosen to illustrate the invention without departing from the spirit or scope of the present contribution to the art. Accordingly, it is to be understood that the protection sought and to be afforded hereby should be deemed to extend to the subject matter claimed and all equivalents thereof fairly within the scope of the invention.

DK 2016 70472 A1

Claims (5)

1. What is claimed is:

   1. A method of spot welding of two sheets mainly formed of aluminum alloys, including the steps of:

   5 predetermining the location area of the two sheets in contact with each other in which a weld spot is to be formed;

   applying materials comprising inoculant particles onto the surface of at least one of the two sheets at said location area;

   spot welding said two sheets by passing electrical current through the sheets via a 10 pair of electrodes, wherein the particles comprise at least one material selected from the group consisting of:

   (a) Al+Ti, (b) Al+C.
2. 2. The method according to claim 1, wherein the materials are applied in a form of a film onto said surface.
3. 3. The method according to claim 1, wherein the materials are applied in a form of 20 a paste onto said surface.
4. 4. The method according to claim 2, wherein the thickness of the film is in the range of 0.01-0.1mm.

   DK 2016 70472 A1
5. 5. The method according to claim 1, wherein the two sheets have the same or different depths.

   Fato? Asm Ornes

   SEARCH REPORT - PATENT Application No. PA 2016 70472 1.1 1 Certain claims were found unsearchable (See Box No. I). 2, 1 1 Unity of invention is lacking prior to search (See Box No. II). A. CLASSIFICATION OF SUBJECT MATTER B23K 11/10 (2006.01); C 22 F 1/04(2006.01) According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) IPC & CPC: B23K, C22F Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched DK, NO, SE, FI: IPC-classes as above. Electronic database consulted during the search (name of database and, where practicable, search terms used) EPODOC, WPI, FULL TEXT: ENGLISH C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant for claim No. X US 2005/0103406 Al (ZHAO et al.) 19.05.2005, see paragraph (0001) - (0007), 1-5 (0020), (0022), (0024), claims 1-22 A US 5552573 A (OKITA et al.) 03.09.1996, see whole document 1 1 Further documents are listed in the continuation of Box C. * Special categories of cited documents: P Document published prior to the filing date but later than the A Document defining the general state of the art which is not priority date claimed. considered to be of particular relevance. T Document not in conflict with the application but cited to D Document cited in the application. understand the principle or theory underlying the invention. E Earlier application or patent but published on or after the filing date. X Document of particular relevance; the claimed invention cannot be considered novel or cannot be considered to involve an inventive L Document which may throw doubt on priority claim(s) or which is sten when the document is taken alone. cited to establish the publication date of another citation or other special reason (as specified). Y Document of particular relevance; the claimed invention cannot be considered to involve an inventive step when the document is O Document referring to an oral disclosure, use, exhibition or other combined with one or more other such documents, such means. combination being obvious to a person skilled in the art. Document member of the same patent family. Danish Patent and Trademark Office Date of completion of the search report Helgeshøj Allé 81 DK-2630 Taastrun 20 January 2017 Denmark Authorized officer Peter Simonsen Telephone No. +45 4350 8000 Facsimile No. +45 4350 8001 Telephone No. +45 4350 8325

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   SEARCH REPORT - PATENT Application No. PA 2016 70472 C (Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant for claim No.

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   SEARCH REPORT - PATENT Application No. PA 2016 70472 Box No. I Observations where certain claims were found unsearchable This search report has not been established in respect of certain claims for the following reasons: 1. 1 1 Claims Nos.: because they relate to subject matter not required to be searched, namely: 2. □ Claims Nos.: because they relate to parts of the patent application that do not comply with the prescribed requirements to such an extent that no meaningful search can be carried out, specifically: 3. 1 1 Claims Nos.: because of other matters. Box No, II Observations where unity of invention is Sacking prior to the search The Danish Patent and Trademark Office found multiple inventions in this patent application, as follows:

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   SEARCH REPORT - PATENT Application No. PA 2016 70472 SUPPLEMENTAL BOX Continuation of Box [.]

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