TECHNICAL FIELD
[001] Present disclosure generally relates to the field of manufacturing. Particularly, but not exclusively, the present disclosure relates to welding of galvanized steel components. Further, embodiments of the disclosure disclose a method for welding galvanized steel components by providing a metallic barrier to prevent liquid metal embrittlement.
BACKGROUND OF THE DISCLOSURE
[002] Steel is one of the important alloys of iron which finds extensive application in the fields of construction, automotive, ship building, machineries, manufacturing, aerospace industry and so on. Steels that have yield strengths above 550 MPa are said to be advanced high strength steels (HSS). HSS parts are widely used as structural elements in automotive vehicles for anti-intrusion or energy absorption functions. In such type of applications, it is desirable to produce steel parts that combine high mechanical strength, high impact resistance, good corrosion resistance and dimensional accuracy. Generally, high-strength steels are coated with zinc to derive certain properties. Zinc based coatings are used because they allow for a protection against corrosion, which can be either through barrier protection or cathodic protection. The barrier effect is obtained by the application of a metallic or non-metallic coating on the steel surface, thereby preventing the contact between steel and corrosive atmosphere. The barrier effect is independent of the nature of the coating and the substrate. On the contrary, sacrificial cathodic protection is based on the fact that zinc is an active metal as compared to steel as per the EMF series. Thus, if corrosion occurs, zinc is consumed preferentially as compared to steel. Cathodic protection is essential in areas where steel is directly exposed to corrosive atmosphere, like cut-edges where surrounding zinc is consumed before the steel. Hot-dip galvanizing process is the best-known commercial method to coat the steels with zinc.
[003] Automotive sectors and other industries which employ steel as a raw material often perform joining of steel components that are usually in the form of thin sheets, bars, pipes, and so on. Resistance spot welding (RSW) is one form of the welding process employed to join thin sheets of steel by application of pressure and temperature. In RSW, steel sheets are clamped between the electrodes (usually the copper electrodes because of their high conductivity). Upon application of

potential difference, electric current flows through the steel sheets, and due to the high resistance at the interface between the sheets, heat is generated (joule heating), thereby causing localized melting and formation of weld nugget. Joints are established after the cooling of the sheets. During RSW of high-strength steels, Zinc coating on the steel is melted because more heat is generated by resistance. Zinc melts at 419℃, which is much below the melting temperature of steel (1450℃). During the progress of welding, there is high probability that liquid Zinc enters into the steel matrix (grain boundaries), resulting in formation of cracks in the steel which initiates from the steel/coating interface. Formation and propagation of cracks is dominant in the heat affected zone (HAZ) of the weld. In addition, due to the stresses from the RSW process, cracks propagate and often result in liquid metal embrittlement (LME). LME, alternatively referred to as “liquid metal assisted cracking (LMAC)”, is a phenomenon where ductile materials like steel experience drastic loss in tensile ductility or undergo brittle fracture under the influence of specific liquid metals, which is zinc in case of steels. Apart from reducing tensile ductility and rendering the steel brittle, LME tends to suppress hardenability of steel. Several solutions of have been proposed in the past to address the LME issues, such as adding Titanium and Boron as alloying elements to the galvanized steel, annealing the steel between 600-1200OC before galvanizing with zinc, performing alloying heat treatments post galvanizing, and so on. These techniques not only require additional alloying elements and heat treatment/alloying steps to mitigate the LME, but also tend to alter certain properties of steel which is not desirable. Moreover, said alloying procedures and heat treatment steps add to manufacturing costs, as well as man and machine hours, at the same time necessitate the need for comprehensive research and investigations to ensure that they are feasible enough to avoid LME and its effects.
[004] Present disclosure is directed to overcome one or more limitations stated above or any other limitations associated with the prior arts.
SUMMARY OF THE DISCLOSURE
[005] One or more shortcomings of the prior arts are overcome by the method as disclosed in the present disclosure and additional advantages are provided through the method. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments

and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
[006] In a non-limiting embodiment of the present disclosure, a method for joining galvanized steel components is disclosed. The method includes positioning the galvanized steel components to be joined between a pair of electrodes of a resistance welding system, such that at least a portion of a first major surface of each of the galvanized steel components to be joined overlaps. Further, the method includes positioning a metallic barrier between a second major surface of each of the galvanized steel components and a corresponding electrode of the pair of electrodes. Then, the method includes supplying electric current to the pair of electrodes to perform resistance welding of the galvanized steel components. The metallic barrier is configured to inhibit infusion of zinc into phases of steel in the galvanized steel components during the resistance welding.
[007] In an embodiment, the metallic barrier is configured to contact at least a portion of the second major surface of each galvanized steel component on one side, and the corresponding electrode of the pair of electrodes on another side opposite to the one side.
[008] In an embodiment, the metallic barrier is a nickel coated copper substrate. Further, the nickel coated copper substrate is fabricated by electro-deposition of nickel on a copper substrate, where the electro-deposition is performed in a Watts bath
[009] In an embodiment, the resistance welding is performed by supplying the electric current ranging from of 8.5 kilo ampere (kA) to 9.5 kilo ampere (kA) for a time ranging between 200-300 milliseconds, and at a load ranging between 3.25 kN to 3.75 kN. Further, the resistance welding is performed at 10% of expulsion current at 16 weld cycles.
[0010] In an embodiment, nickel of the metallic barrier has a higher melting point than the zinc, and a lower melting point than the steel in the galvanized steel components.
[0011] In an embodiment, the zinc of the galvanized steel components diffuses into one or more phases of the nickel in the metallic barrier to form at least one inter-metallic nickel-zinc layer.

[0012] In an embodiment, the at least one inter-metallic nickel-zinc layer comprises β1-NiZn, γ-Ni2Zn5 and δ-NiZn8 at 450°C , and β1-NiZn, γ-Ni2Zn5 at 550°C and 650°C.
[0013] In an embodiment, the pair of electrodes are copper electrodes.
[0014] In an embodiment, the zinc vaporizes at a weld interface of the galvanized steel components during the resistance welding. Further, the resistance welding is a spot welding.
[0015] In an embodiment, maximum temperature attained by the metallic barrier during the resistance welding ranges from 800°C to 850°C, and the maximum temperature range is lesser than boiling point of the zinc.
[0016] In an embodiment, thickness of the copper substrate ranges from 0.20 mm to 0.30 mm. Further, the galvanized steel components are GI DP 780 steel sheets, each having a thickness of 1 mm to 1.3 mm.
[0017] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.
[0018] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
[0019] The novel features and characteristics of the disclosure are set forth in the appended description. The disclosure itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

[0020] FIG. 1 illustrates a schematic view of a resistance welding system having the metallic barrier placed between the electrodes and the steel components, according to an embodiment of the present disclosure;
[0021] FIG. 2 illustrates a schematic view of a Watts bath used to perform electro-deposition of nickel on a copper substrate to form the metallic barrier, according to some embodiments of the disclosure;
[0022] FIG. 3 is a micrograph illustrating nickel deposited on the copper substrate by electro-deposition set-up shown in FIG. 2;
[0023] FIG. 4 is a graph illustrating the variation of weld time as a function of weld current for a weld lobe established for steel grade GI DP 780, according to an embodiment of the present disclosure;
[0024] FIG. 5 is a graph illustrating the dynamic contact resistance varying with time during the spot-welding operation, with and without the metallic barrier;
[0025] FIGS. 6A and 6B are photographs illustrating macro-images of surfaces of the steel components showing the cracks developed during welding due to liquid metal embrittlement (LME) in the absence of metallic barrier;
[0026] FIGS. 7A and 7B are photographs illustrating macro-images of surfaces of the steel components without any cracks due to presence of the metallic barrier during welding;
[0027] FIGS. 8 is an SEM micrograph showing cracks developed in the steel components welded in the absence of metallic barrier;
[0028] FIGS. 9 is an SEM micrograph showing cracks developed in the steel components welded in the presence of metallic barrier;
[0029] FIG. 10 is a graph depicting variations of crack lengths as observed on the steel components welded with and without the metallic barrier, according to an embodiment of the present disclosure;

[0030] FIGS. 11 and 12 are graphs depicting variations of cross-tensile loads of the steel components welded with and without the metallic barrier at two different weld currents, according to an embodiment of the present disclosure; and
[0031] FIG. 13 is a spectrograph illustrating the distribution of temperatures in the heat affected zone (HAZ) when the steel components are welded using the resistance welding system shown in FIG. 1.
[0032] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the device and the system illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION
[0033] The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent methods do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.
[0034] In the present disclosure, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
[0035] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described

in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0036] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover non-exclusive inclusions, such that a method or a system that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such a method or a system. In other words, one or more acts in method or a system proceeded by “comprises… a” does not, without more constraints, preclude the existence of other acts or additional acts in the method or the system.
[0037] Embodiments of the present disclosure disclose a method for joining galvanized steel components by a joining process, such as resistance welding. Zinc [coating or layer] present in galvanized steel components may melt and react with steel matrix upon application of heat, leading to the effect of liquid metal embrittlement (LME). LME hampers mechanical and structural properties of steel. The method of the present disclosure is intended to mitigate the effects of LME and development of cracks due to LME in the steel components. The method includes positioning the galvanized steel components that are required to be joined between a pair of electrodes of a resistance welding system. The galvanized steel components are positioned such that that at least a portion of a first major surface of each of the galvanized steel components to be joined overlaps, as to form a lap joint. Further, the method includes positioning a metallic barrier between a second major surface [surface facing the electrode] of each of the galvanized steel components and a corresponding electrode of the pair of electrodes. Then, the method includes supplying electric current to the pair of electrodes to perform resistance welding of the galvanized steel components. The metallic barrier is configured to inhibit infusion of zinc into phases of steel in the galvanized steel components during the resistance welding.
[0038] When the metallic barrier is placed, the metallic barrier is configured to contact at least a portion of the second major surface of each galvanized steel component on one side, and the corresponding electrode of the pair of electrodes on another side opposite to the one side. In an embodiment, the metallic barrier is a nickel coated copper substrate that is fabricated by electro-deposition of nickel on a copper substrate which is performed in a Watts bath. Further, nickel of

the metallic barrier is selected such that it has a higher melting point than the zinc [galvanizing element], and a lower melting point than the steel [base element] in the galvanized steel components. When the resistance welding is performed after placing the metallic barrier being in intended position, the zinc of the galvanized steel components diffuses into one or more phases of the nickel in the metallic barrier to form at least one inter-metallic nickel-zinc layer. In an embodiment, the at least one inter-metallic nickel-zinc layer comprises β1-NiZn, γ-Ni2Zn5 and δ-NiZn8 at 450 °C, and β1-NiZn, γ-Ni2Zn5 at 550 °C and 650°C. Also, the zinc vaporizes at a weld interface of the galvanized steel components during the resistance welding.
[0039] In an embodiment, the resistance welding is a spot welding. The resistance welding is performed by supplying the electric current ranging from of 8.5 kilo ampere (kA) to 9.5 kilo ampere (kA) for a time ranging between 200-300 milliseconds, and at a load ranging between 3.25 kN to 3.75 kN. Further, the resistance welding is performed at 10% of expulsion current at 16 weld cycles. Further, the pair of electrodes employed to perform the resistance welding are copper electrodes. Upon welding, the maximum temperature attained by the metallic barrier during the resistance welding ranges from 800°C to 850°C, and the maximum temperature range is lesser than boiling point of the zinc. In an embodiment, thickness of the copper substrate ranges from 0.20 mm to 0.30 mm on which the layer of nickel is deposited by electro-deposition. Further, the galvanized steel components are GI DP 780 steel sheets, each having a thickness of 1 mm to 1.3 mm on which the metallic barrier is positioned.
[0040] The present disclosure is explained with the help of figures. However, such exemplary embodiments should not be construed as limitations of the present disclosure since the method and the system disclosed may be used or employed in any manufacturing facility. A person skilled in the art may envisage various such embodiments without deviating from scope of the present disclosure.
[0041] FIG. 1 is an exemplary embodiment of the present disclosure illustrating a schematic view of a resistance welding system (100) employed to perform resistance welding of galvanized steel components (10, 20). The method embodiments of the present disclosure are described with reference to FIG. 1. In galvanized steel components, the galvanizing element i.e., Zinc has a lower melting point in comparison to base component i.e., steel. Upon application of heat to perform

thermal joining processes such as welding, hot forming, etc., Zinc has the tendency to melt and infuse/penetrate into the steel matrix [grains] leading to the effect of liquid metal embrittlement [referred to as LME throughout]. Method embodiments of the present disclosure are intended to prevent infusion/penetration of liquid zinc into the steel matrix to mitigate the LME effects, and therefore, to minimize the possibility of development and propagation of cracks in the steel components. Method embodiments of the present disclosure are discussed with reference to a resistance welding system (100) [or set-up] which may be employed to perform resistance spot welding of galvanized steel components (10, 20), as shown in FIG. 1. The galvanized steel components (10, 20) are referred to as “components (10, 20)” throughout the specification for simplicity. In an embodiment, the galvanized steel components (10, 20) may be GI DP 780 steel sheets, each having a thickness ranging from about 1 mm to about 1.3 mm. Other grades of galvanized steel having different geometrical configurations like plates, bars, etc., may also be employed. The galvanized steel components (10, 20) as shown, may be placed between a pair of electrodes (E1, E2) of the resistance welding system (100). In an embodiment, the pair of electrodes (E1, E2) may be copper electrodes selected owing to their high thermal and electrical conductivity. The positioning of the galvanized steel components (10, 20) may be such that that at least a portion of a first major surface (10A, 20A) of each of the galvanized steel components (10, 20) to be joined overlaps. In alternate terms, a superficial portion of first major surface (10A, 20A) of both the galvanized steel components (10, 20) overlap so as to form a lap joint as shown. Upon welding, the overlapping portions get fused and joined to form a weld nugget (WN) or a weld bead.
[0042] Once the components (10, 20) are placed to overlap relative to each other, the flip sides of the first major surface (10A, 20A), i.e., the second major surface (10B, 20B) of the components (10, 20) face the electrodes (E1, E2). A metallic barrier (25) is placed on the second major surfaces (10B, 20B) of both the components (10, 20) such that the metallic barrier (25) partially or fully conceals the second major surface (10B, 20B) of both the components (10, 20). In an embodiment, the metallic barrier (25) may conceal only a portion of the second major surface (10B, 20B) of the components (10, 20) corresponding to [equal or substantially equal] the area of overlap at the first major surface (10A, 20A) of the components (10, 20). The composition and structure of the metallic barrier (25) will be explained in detail with reference to FIG. 2. Once the metallic barrier

(25) is placed on the second major surfaces (10B, 20B), the electrodes (E1, E2) may be pressed onto the metallic barrier (25) and in turn onto the respective components (10, 20) so as to introduce pressure at the first major surface (10A, 20A). The reason being that the resistance welding is performed by application of pressure on components to be welded so as to form a sturdy joint. The electrodes (E1, E2) may be then supplied with electric current by applying potential difference from a power source (30) at the leads (L1, L2). The electric current passes through the components (10, 20) and generates resistance at the interface i.e., the overlapping region of first major surface (10A, 20A) to cause localized heating (joule heating). The localized heating combined with the pressure applied by the electrodes (E1, E2) results in localized melting [fusion] of the steel at the interface, resulting in formation of the weld nugget (WN) as shown. Upon cooling, the welded joint will be established at the weld nugget (WN). Due to the presence of the metallic barrier (25) between the second major surface (10B, 20B) and the respective electrodes (E1, E2), the zinc [galvanizing element] present in the components (10, 20) is inhibited from entering the steel matrix at weld temperatures. The mode by which zinc infusion/penetration into the steel matrix is inhibited will be explained in detail in the forthcoming paragraphs.
[0043] FIG. 2 is an exemplary embodiment of the present disclosure illustrating a schematic of a Watts bath (200) employed to perform electro-deposition of nickel from a nickel strip (201) on a copper strip (202) to produce the metallic barrier (25). The exemplary Watts bath (200) shown in FIG. 2 contains a solution (203) of nickel sulphate (NiSO4.5H2O), nickel chloride (NiCl2.6H2O) and boric acid (H3BO3) taken in a beaker or a container (206). To perform the electro-deposition through electrolysis, pure copper strip (202) [also referred to as copper substrate (202)] is selected as the cathode, and two pure nickel strips (201) are selected as anodes. In an embodiment, the cross-sectional area of the copper strip (202) and each of the nickel strips (201) may be more or less equal. In another embodiment, the copper substrate (202) was polished using a 1200 grit size SiC polishing paper to remove any surface impurities and imperfections. Further, the thickness of the copper substrate may range from 0.20 mm to 0.30 mm. The two nickel anodes (201) were placed on both sides of the copper cathode (202) at an equal distance, for example, at 3 cm for electro-deposition. Table 1 shown below lists the exemplary concentrations of each of the compositions constituting the solution present in the Watts bath (200).

Bath constituent Concentration (g/l)
Nickel sulphate hexahydrate 250
Nickel chloride 50
Boric acid 30
pH = 2.4
Table 1
[0044] Electroplating was carried out in a 1 litre beaker (206) with the anode (201) and the cathode (202) dipped in the plating bath i.e., the solution (203). The anode (201) and the cathode (202) were connected to a PARSTAT 4000A potentiostat through respective leads (AL, CL) which is used to supply electric current for electroplating. Direct current (DC) electrodeposition is performed at a constant current density of 15 mA cm-2 for a duration of 50 minutes. The temperature of deposition is maintained at 50ºC (323 K). Magnetic stirring using a stirrer (204) and equipment (205) are employed at a constant stirring rate of 300 rpm. Table 2 below lists exemplary process parameters involved in the above-described electro-deposition process performed on the Watts bath (200).

Plating parameter Value
Plating current density 15 mA cm-2
Anode Pure nickel
Cathode Pure copper
Distance between anode and cathode 3 cm
Stirring rate 300 rpm
Temperature 323 K
Plating time 50 min

Table 2 [0045] After plating, the substrate may be washed with distilled water and dried. FIG. 3 shows the SEM micrograph of the electroplated copper substrate (301) having 98.5 wt.% nickel layer deposition to a thickness of (302T). The copper substrate (301) electro-deposited with the nickel layer to a thickness (302T) constitutes the metallic barrier (25) described in the above paragraphs.
[0046] Reference is now made to FIG. 4 which is a graph illustrating the variation of weld time with weld current for a weld lobe established for steel grade GI DP 780. In order to study the effect of LME on galvanized steel components (10, 20), resistance spot welding was performed using the welding parameters listed in Table 3 below.

Thickness Load Tip a b c d
Material (mm) (kN) diameter (mm) Hold (cycles) Upslope (cycles) Weld (cycles) Cool (cycles)
GI DP 1.2 3.6 6 71 1.2 16, 5
780 25%increment, 50%increment
Table 3
[0047] The components (10, 20) were welded at 10% of the expulsion current at 16 cycles for a weld time of 256 ms. According to exemplary investigations conducted in accordance with embodiments of the present disclosure, the LME crack analysis were conducted at two different weld current values i.e., 8.9kA and 9kA [with and without metallic barrier (25)] among the plurality of current values shown in FIG. 4.
[0048] When the resistance welding is performed on components (10, 20) using the above-mentioned weld parameters in the absence of metallic barrier (25), there is heat generation which is crucial at three critical points (P1, P2, P3 shown in FIG. 1). First point (P1) is at the interface of the components (10, 20) i.e., the contact point of first major surface (10A, 20A) of both the components. Second (P2) and third points (P3) are the interfaces of each of the electrodes (E1, E2) and the respective second major surface (10B, 20B) of the components (10, 20), in the absence of

metallic barrier (25). At the first point (steel-steel interface) the temperature at the heat affected zone (HAZ) is around 1400 degrees where the zinc vaporizes (melting point of zinc is around 419.5 deg C). Vaporization of zinc ensures that there is no penetration of molten [liquid] zinc into the steel matrix at point (P1) [interface of steel-steel]. However, at the electrode-steel interface [in the absence of metallic barrier (25)], i.e., points (P2) and (P3), the temperature due to welding may be around 500 deg C which easily melts the zinc, resulting in penetration/infusion of liquid zinc into the steel matrix. To alleviate the infusion/penetration of zinc into the steel matrix, the metallic barrier (25) i.e., nickel deposited copper substrate is placed at the interface points (P2) and (P3). The nickel present in the metallic barrier (25) [around 98.5 wt. %] serves as a barrier to prevent infusion/penetration of zinc into the steel matrix. The nickel layer in the metallic barrier (25), having a higher melting point [around 1455 deg C] compared to that of zinc, does not react with the copper electrodes (E1, E2), and thereby does not enhance the LME effect. Additionally, the molten Zinc layer formed at weld temperatures comes in contact with the nickel [in solid phase] present in the metallic barrier (25), and forms Ni-Zn inter-metallic layers due to mutual diffusion. In other words, the zinc in molten phase has higher affinity to the nickel atoms in comparison to the steel phases, which results in the molten zinc diffusing into the nickel [solid phase] instead of the steel matrix in the components (10, 20). Hence, due to the diffusion of molten zinc into the nickel, the effect of LME in the steel matrix of the components (10, 20) is reduced. Zinc may also not come in contact with copper due to metallic barrier restricting their movement.
[0049] FIG. 5 is a graph illustrating the dynamic contact resistance (DCR) curve varying with time during the spot-welding operation, with and without the metallic barrier (25). The spot-welding characteristics with and without metallic barrier (25) has been analysed at two different weld currents i.e., 8.9 kA and 9.0 kA as shown in FIG. 5. As apparent from FIG. 5, presence of a small hump in case of 8.9 kA weld current and in the absence of the metallic barrier (25) as compared to the case where the metallic barrier (25) was present suggests the enhanced melting of zinc layer. In case of the situation where metallic barrier (25) was absent (curve corresponding to current of 8.9 kA), a hump (H) at ~50 ms was observed that signifies the melting of the zinc layer in contact with the electrodes (E1, E2). During the initial stage of the hump (H), with the melting of the zinc layer, resistivity increases in proportion to the temperature increment. But, as the melting of zinc layer progresses with time, the area of contact with the electrodes (E1, E2) also

increases. Hence, the net result is decrease in resistance. The hump (H) which signifies the melting of zinc is followed by stages where the base material (i.e., galvanized steel components 10, 20) starts to melt. In contrast to this observation, the DCR curve where nickel deposited metallic barrier (25) was used (curve corresponding to higher current of 9 kA), the DCR curve was devoid of any hump, as observed in the former case due to melting of zinc at about 50 ms. This observation can be explained by the fact that nickel has a melting point of 1455˚C and at no point during the welding operation the temperature of this nickel layer reached its melting point.
[0050] FIGS. 6A and 6B are photographs illustrating macro-images of surfaces of the steel components (10, 20 respectively) showing the cracks developed during welding due to liquid metal embrittlement (LME) in the absence of metallic barrier (25). It is evident from FIGS. 6A and 6B that in case of the welding operation where the metallic barrier (25) is not used has led to the formation and propagation of cracks which were substantially noticeable. In order to analyze the influence of metallic barrier (25) on surface cracking due to possible LME effect, the steel components (10, 20) are welded with the metallic barrier (25) positioned as explained before. FIGS. 7A and 7B illustrate macro-images of surfaces of the steel components (10, 20 respectively) welded in the presence of the metallic barrier (25) showing no cracks on the surfaces. This confirms that the presence of the metallic barrier (25) at the electrode-steel component interface minimizes the effect of LME and crack formation to significant extent. FIGS. 8 and 9 are SEM micrographs showing the extents of cracks formed on the surfaces of components (10, 20) welded with and without the nickel deposited metallic barrier (25), respectively. It is clearly evident that even if cracks are formed during welding of steel components (10, 20) in the presence of the metallic barrier (25) [as shown in FIG. 9], the extent of crack is significantly minute in comparison to the crack formed on steels welded without the metallic barrier (25) shown in FIG. 8.
[0051] FIG. 10 is a graph depicting variations of crack lengths as observed on the steel components (10, 20) welded with and without the metallic barrier (25), according to an exemplary embodiment of the present disclosure. Bar graphs indicated by (10X) and (10Y) represent the extent of crack length (in mm) observed in steel components (10, 20) welded without the nickel deposited metallic barrier (25). On the other hand, bar graphs indicated by (10P) and (10Q) represent the extent of crack length (in mm) observed in steel components (10, 20) welded in the presence of nickel deposited metallic barrier (25). Graphs (10P) and (10Q) depict the considerable

reduction in extent of crack lengths due to the presence of metallic barrier (25) at the time of welding, as compared to the counterparts (10X, 10Y) welded without the metallic barrier (25). As shown in FIG. 10, the average crack length in the steel component (10) welded without using the metallic barrier (25) was 43μm [10X], and for the other steel component (20), the average crack length without the metallic barrier (25) was found to be 55μm [10Y]. Comparatively, in case of welding the steel components (10, 20) in the presence of metallic barrier (25), the crack length was reduced to 5.7μm and 13.2μm, respectively, for each of component (10) and component (20) [10P and 10Q].
[0052] To elucidate the effect of LME and inherent crack on the mechanical properties of the welded steel components (10, 20), tensile shear test and cross tensile test (as per AWS D8.9 standard) was carried out on the welded components (10, 20). FIG. 11 is a graph depicting variations of cross-tensile loads of the steel components (10, 20) welded with and without the metallic barrier (25) at two different weld currents i.e., 8.9 kA and 9.0 kA. FIG. 11 shows the cross tensile load variation of the steels welded with and without using the Ni inter layers. Graph (11 A) represents cross tensile load variation of components (10, 20) welded at a weld current of 8.9kA in the absence of the metallic barrier (25). Graph (11B) represents cross tensile load variation of components (10, 20) welded at a weld current of 8.9 kA in the presence of the metallic barrier (25), while graph (11C) represents the tensile load variation of components (10, 20) welded at a weld current of 9.0 kA in the presence of the metallic barrier (25). It can be concluded from the graphs (11A-11C) that ~19 % improvement in cross tensile load can be attained in case of steel components (10, 20) welded in the presence of metallic barrier (25) at weld currents 8.9kA and 9kA as compared to welding without the metallic barrier (25).
[0053] FIG. 12 shows the tensile load variation of the steels welded with and without using the Ni inter layers. Graph (12A) represents cross tensile load variation of components (10, 20) welded at a weld current of 8.9kA in the absence of the metallic barrier (25). Graph (12B) represents tensile load variation of components (10, 20) welded at a weld current of 8.9 kA in the presence of the metallic barrier (25), while graph (12C) represents the tensile load variation of components (10, 20) welded at a weld current of 9.0 kA in the presence of the metallic barrier (25). It can be concluded from the graphs (12A-12C) that there is significant improvement in tensile load capacity

of the steel components (10, 20) welded in the presence of metallic barrier (25) as compared to the steel components (10, 20) welded without the metallic barrier (25).
[0054] FIG. 13 is a spectrograph illustrating the distribution of temperatures in the heat affected zone (HAZ) when the steel components are welded using the resistance welding system (100) shown in FIG. 1. The temperature distribution corresponds to HAZ at various interfaces of welded of components (10, 20) welded in the presence of metallic barrier (25) at 8.9kA current and 698 ms weld time. FIG. 13 shows that the maximum temperature experienced by the nickel deposited metallic barrier (25) [indicated as Ni coated Cu strip in FIG. 13] ranges from 800-850 ˚C, specifically at about 810 ˚C [far lesser than melting point of nickel which is 1455 ˚C] for the layer facing the Cu electrode. The maximum temperature range 800-850 ˚C attained by nickel deposited metallic barrier (25) is less compared to the boiling point of zinc, which is about 907 ˚C. Even if minute quantity of nickel gets melted, it may react with copper in the Cu electrode to form a Cu-Ni isomorphous system which does not have any detrimental effect of inter-metallic formation on the steel matrix. Further, in the presence of the nickel deposited metallic barrier (25), zinc has the tendency to form the following inter-metallic phases with nickel: β1-NiZn, γ-Ni2Zn5 and δ-NiZn8 at 450 ℃, and only β1-NiZn and γ-Ni2Zn5 at 550°C and 650°C. The dissolution of nickel atoms into these inter-metallic phases is enhanced with rise in temperature. Hence, due to this Ni-Zn inter-metallic formation in the presence of nickel deposited metallic barrier (25), the availability of molten zinc to lead to LME and inherent crack formation is considerably reduced.
[0055] The method of the present disclosure has some inherent advantages.
[0056] One advantage is that the metallic barrier (25) can be produced in a simple, convenient, and economical manner using a Watts bath. The metallic barrier (25) so produced may be positioned between the electrodes and the steel components during the resistance welding without a need for significant constructional or design changes in the resistance welding system/set-up. Another advantage is that the metallic barrier minimizes the LME crack length to up to ~ 80% by hindering the penetration liquid into the steel matrix. The crack length reduction in turn resulted in an increased tensile strength of the welded joints by ~20% as compared to the steel components welded without the metallic barrier. Yet another advantage is that the presence of nickel in the

metallic barrier does not react with the copper present in the copper electrode, and therefore, does not alter the performance and intended function of the copper electrodes with respect to welding.
Equivalents:
[0057] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
[0058] It will be understood by those within the art that, in general, terms used herein, and
especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone,

C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."
[0059] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.

Table of reference numerals
Component/Step Numeral
Resistance welding System 100
Steel components 10, 20
First major surface 10A, 20A
Second major surface 10B, 20B
Metallic barrier 25
Electrodes E1, E2
Leads of electrodes L1, L2
Interfaces/points P1, P2, P3
Weld nugget WN
Power source 30
Watts bath set-up 200

Anodes (Ni strip) 201
Cathode (Cu strip) 202
Solution 203
Magnetic stirrer 204
Magnetic stirring equipment 205
Beaker/Container 206
Leads of anode and cathode AL, CL
Copper substrate 301
Deposited Nickel thickness 302T
Crack length graphs 10X, 10Y, 10P, 10Q
Cross-tensile load variation graphs 11A-11C
Tensile load variation graphs 12A-12C

We Claim:
1. A method for joining galvanized steel components (10, 20), the method comprising:
positioning the galvanized steel components (10, 20) to be joined between a pair of electrodes (E1, E2) of a resistance welding system (100), such that at least a portion of a first major surface (10A, 20A) of each of the galvanized steel components (10, 20) to be joined overlaps;
positioning a metallic barrier (25) between a second major surface (10B, 20B) of each of the galvanized steel components (10, 20) and a corresponding electrode of the pair of electrodes (E1, E2); and
supplying electric current to the pair of electrodes (E1, E2) to perform resistance welding of the galvanized steel components (10, 20);
wherein, the metallic barrier (25) being configured to inhibit infusion of zinc into phases of steel in the galvanized steel components (10, 20) during the resistance welding.
2. The method as claimed in claim 1, wherein the metallic barrier (25) is configured to contact at least a portion of the second major surface (10B, 20B) of each galvanized steel component on one side, and the corresponding electrode of the pair of electrodes (E1, E2) on another side opposite to the one side.
3. The method as claimed in claim 1, wherein the metallic barrier (25) is a nickel coated copper substrate.
4. The method as claimed in claim 3, wherein the nickel coated copper substrate is fabricated by electro-deposition of nickel (201) on a copper substrate (202), and wherein the electro-deposition is performed in a Watts bath (200).
5. The method as claimed in claim 1, wherein the resistance welding is performed by supplying the electric current ranging from of 8.5 kilo ampere (kA) to 9.5 kilo ampere (kA) for a time ranging between 200-300 milliseconds, and at a load ranging between 3.25 kN to 3.75 kN.

6. The method as claimed in claim 5, wherein the resistance welding is performed at 10% of expulsion current at 16 weld cycles.
7. The method as claimed in claim 3, wherein nickel of the metallic barrier (25) has a higher melting point than the zinc, and a lower melting point than the steel in the galvanized steel components (10, 20).
8. The method as claimed in claims 1 and 3, wherein the zinc of the galvanized steel components (10, 20) diffuses into one or more phases of the nickel in the metallic barrier (25) to form at least one inter-metallic nickel-zinc layer.
9. The method as claimed in claim 8, wherein the at least one inter-metallic nickel-zinc layer comprises β1-NiZn, γ-Ni2Zn5 and δ-NiZn8 at 450 °C, and β1-NiZn, γ-Ni2Zn5 at 550 °C and 650°C
10. The method as claimed in claim 1, wherein the pair of electrodes (E1, E2) are copper
electrodes.
11. The method as claimed in 1, wherein the zinc vaporizes at a weld interface (WN) of the galvanized steel components (10, 20) during the resistance welding.
12. The method as claimed in claim 1, wherein maximum temperature attained by the metallic barrier (25) during the resistance welding ranges from 800°C to 850°C, and wherein the maximum temperature range is lesser than boiling point of the zinc.
13. The method as claimed in claim 3, wherein thickness of the copper substrate (202) ranges from 0.20 mm to 0.30 mm.
14. The method as claimed in claim 1, wherein the galvanized steel components (10, 20) are GI DP 780 steel sheets, each having a thickness of 1 mm to 1.3 mm.

15. The method as claimed in claim 1, wherein the resistance welding is a spot welding.