CN115106633A - Resistance spot welding method for hot-dip galvanized hot-formed steel - Google Patents
Resistance spot welding method for hot-dip galvanized hot-formed steel Download PDFInfo
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- 238000003466 welding Methods 0.000 title claims abstract description 188
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- 239000010959 steel Substances 0.000 title claims abstract description 67
- 238000000034 method Methods 0.000 title claims abstract description 55
- 239000000463 material Substances 0.000 claims abstract description 9
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- 230000000052 comparative effect Effects 0.000 description 5
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/10—Spot welding; Stitch welding
- B23K11/11—Spot welding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/30—Features relating to electrodes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/36—Auxiliary equipment
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- Resistance Welding (AREA)
Abstract
The invention discloses a resistance spot welding method for hot galvanizing hot forming steel, which comprises the following steps: (1) the welding material is a hot-dip galvanized hot-formed steel plate, and a flat-head electrode is selected as a welding tool; (2) spot welding prepressing is carried out on two sides of the lap joint area simultaneously, the prepressing time is controlled to be 10-20 ms, and the electrode pressure is 3.2-3.6 kN; (3) performing double-pulse welding, wherein the welding current of two pulses is controlled to be 6-8.8 kA and 6-8.8 kA respectively, the welding time of the two pulses is controlled to be 100-150 ms, a preheating current is applied for 15-20 ms before each pulse current, and a slow-falling current is applied for 15-20 ms after each pulse current; (4) and maintaining the pressure, wherein the pressure maintaining time is controlled to be 10-20 ms. The resistance spot welding quality of the hot-dip galvanized hot-formed steel is obviously improved, and high mechanical properties are kept; the invention has simple process, does not introduce other processes, can effectively reduce the generation of splashing and cracks, and improves the mechanical property and prolongs the service life of the electrode tip.
Description
Technical Field
The invention relates to a welding method, in particular to a resistance spot welding method for hot-dip galvanized hot-formed steel.
Background
The high-strength steel and the ultrahigh-strength steel are widely applied to automobile bodies at present due to the characteristic of high toughness, but when the high-strength steel and the ultrahigh-strength steel are stamped by adopting traditional processes such as cold forming and the like, the problems of serious rebound deformation, poor precision and poor formability and the service life of a die are easily caused, the problems are solved by a hot stamping forming technology without rebound during high-temperature forming, the required forming resistance is small, the energy consumption is reduced, and the cost is reduced. The earliest hot forming steels were bare plates without plating, and the iron scale on the surface of the bare plates reduced the heat transfer efficiency, quenching performance and friction coefficient during hot stamping, ultimately affecting the accuracy. The prior solution is to coat the surface with oil to form a liquid film for protection, but the subsequent pickling increases the possibility of hydrogen embrittlement of the steel sheet. In order to solve the problems of oxidation and decarburization, the surface is often galvanized to have excellent corrosion resistance and to reduce oxidation.
At present, hot dip galvanized hot formed steel is usually subjected to resistance spot welding and is also the most connection mode for connecting white body parts in a main engine plant. Resistance spot welding is accomplished primarily by the application of electrical current through the contact surfaces of the weld joint, as well as the resistive heat generated by the interior regions. Resistance spot welding can be understood as pressure welding, the forging and pressing characteristic is good, the filler is not needed usually, the cost of a host factory can be controlled, the heating time is short, the part deformation and the residual stress are small, the welding operation is simple, the automation is easy to realize, and the production efficiency is high. But different materials, thicknesses, coating compositions and structures can affect welding points, the problems of cold welding and splashing of a molten core of a galvanized plate are included, and the liquid metal can be cracked more seriously; the spot welding process window of the hot galvanizing hot forming steel is narrow, and the spot welding joint quality is poor. Therefore, the resistance spot welding technology of the hot-dip galvanized hot-formed steel needs to be further researched to overcome the welding problem of the existing hot-dip galvanized hot-formed steel and improve the application range of the hot-dip galvanized hot-formed steel in automobiles.
Because the existence of the liquid metal brittle cracks greatly restricts the application of the hot forming steel in the industrial field, the defects are widely concerned in the industry in recent years and become a hotspot problem of research, and experts and scholars at home and abroad make a lot of research for solving the problems.
Through retrieval, The existing Spot Welding mainly relates to hot forming Steel, for example, The document of 'The effective of Silicon Content on Liquid-metal-electroplated coating sensitivity in Resistance Spot Welding of Galvanized Dual-phase Steel' researches The influence of Silicon Content on The embrittlement sensitivity of Liquid metal in The Resistance Spot Welding of The Galvanized Dual-phase Steel, and The Silicon Content in The Dual-phase Steel is increased from 0.7% to 1.8%, so that The embrittlement sensitivity of The Liquid metal is improved; during resistance spot welding, as the silicon content increases, the heat input strength of the material increases and the material is prematurely expelled, which is related to the higher resistivity of the material.
The Chinese patent application No. 202110804943.X discloses a spot welding process for inhibiting the brittle cracks of liquid metal of a galvanized high-strength steel resistance spot welding joint, which is characterized in that compared with the traditional spot welding process, a part of leading current with constant numerical value is added before pulse current to change the surface temperature and stress state of a welding spot in the thermal cycle process, so that the coating and a substrate generate alloying reaction, and the brittle cracks of the liquid metal are inhibited. However, the pilot current is applied for a long time, and does not participate in the formation of the spot welding nugget during the application of the pilot current, so that the nugget is easily enlarged, and spatter is easily generated.
The Chinese patent application No. 202011457615.9 discloses a 1800MPa grade double-sided non-equal-thickness aluminum-silicon coating hot forming steel and a resistance spot welding method thereof, which is characterized in that the 1800MPa grade double-sided non-equal-thickness aluminum-silicon coating hot forming steel and the resistance spot welding method thereof are provided, the cold bending performance can be enhanced, and the weldability is good; however, the Al-Si coating cannot play a role in cathodic protection, and corrosion easily occurs at cracks, so that the failure tendency of parts is increased.
The Chinese patent application No. 201811080299.0 discloses a resistance spot welding method of a three-layer plate suitable for intermediate aluminum-silicon coating hot forming steel, wherein the welding material is intermediate aluminum-silicon coating hot forming steel, one side of the intermediate layer is respectively a cold-rolled plate with the tensile strength not lower than 500MPa and the other side is a galvanized plate with the tensile strength not higher than 450 MPa; spot welding prepressing is carried out on two sides simultaneously; welding; and maintaining the pressure. The electrodes with different end face diameters are used on the two sides, so that the current density of the galvanized plate side is increased, the welding current window at least reaches 9.6-11.2 kA, and the size of the window is 1.6kA, the problems of uneven current density and the phenomena of insufficient solder and splashing when three layers of high-strength steel and galvanized plates are respectively matched on the two sides of aluminum-silicon coating hot forming steel for spot welding due to different strength, thickness and plating conditions of a steel plate are solved, the qualification rate of resistance spot welding is improved to more than 90%, and the requirements of automobile manufacturers for production and manufacturing are basically met. However, the welding process is complicated, and the welding cost and the vehicle body weight are increased, which is contrary to the light weight concept.
Disclosure of Invention
The invention aims to provide a resistance spot welding method for hot-dip galvanized hot-formed steel, which can effectively inhibit splashing.
In order to solve the technical problem, the method provided by the invention comprises the following steps: (1) the welding material is a hot-dip galvanized hot-formed steel plate, and a flat-head electrode is selected as a welding tool;
(2) spot welding prepressing is carried out on two sides of the lap joint area simultaneously, the prepressing time is controlled to be 10-20 ms, and the electrode pressure is 3.2-3.6 kN;
(3) performing double-pulse welding, wherein the welding current of two pulses is controlled to be 6-8.8 kA, the welding time of the two pulses is controlled to be 100-150 ms, a preheating current is applied for 15-20 ms before each pulse current, and a slow-decreasing current is applied for 15-20 ms after each pulse current;
(4) and maintaining the pressure, wherein the pressure maintaining time is controlled to be 10-20 ms.
In the step (3), the interval between two pulses is 15-20 ms.
The diameter of the front end of the electrode tip of the flat-head electrode is 6-10 mm. The end face of the electrode head is an arc face, and the curvature radius of the arc face is 150-180%.
The thickness of the hot galvanizing hot forming steel plate is 1.4-2.0 mm. The yield strength of the hot-dip galvanized hot-formed steel plate after hot forming is not lower than 400MPa, and the tensile strength of the hot-dip galvanized hot-formed steel plate is not lower than 600 MPa.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: according to the invention, through observation of metallographic phase and scanning electron microscope of the spot-welded joint, preheating and slow-falling current before and after pulse current is increased, so that splashing and crack generation can be effectively reduced; the nugget forming process is analyzed, preheating and slow descending are beneficial to forming of a plastic ring, the nugget growth is promoted, and the comprehensive mechanical property of a welding spot is improved; the element scanning is carried out on the welding spots after the stretching experiment, the element segregation phenomenon can be relieved by comparing the samples without preheating and slow drop current, the process window range is increased, the phenomena of insufficient solder and splashing generated when the hot formed steel with the zinc-aluminum coating is subjected to spot welding in the automobile manufacturing process are solved, the qualification rate of resistance spot welding is greatly improved, the requirement of a host factory is met, and the further popularization of the hot formed steel by hot galvanizing is facilitated.
According to the invention, a slowly rising current (preheating) and a slowly falling current are added before and after a single-pulse welding current of a traditional spot welding process, and a pulse current is added to a double pulse; the problems of difficult welding, serious splashing and liquid metal brittle cracks caused by the damage of surface oxides and coatings of hot-dip galvanized steel after hot-dip galvanized steel is subjected to hot forming can be inhibited, so that the resistance spot welding quality of the hot-dip galvanized hot-formed steel is obviously improved, and high mechanical property is kept; the invention has simple process, does not introduce other processes, can effectively reduce the generation of splashing and cracks, and improves the mechanical property and prolongs the service life of the electrode tip.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a schematic view of the welding process of the present invention;
FIG. 2 is a morphology of a resistance spot welding fracture of example 1 of the present invention and a comparative example.
Detailed Description
The resistance spot welding method for hot-dip galvanized hot-formed steel comprises the following steps: (1) the welding material is a hot-dip galvanized hot-formed steel plate with the thickness of 1.4-2.0 mm, the yield strength after hot forming is not lower than 400MPa, the tensile strength is not lower than 600MPa, the single-side thickness of the coating is not lower than 10 mu m, and the weight of the single-side coating is not lower than 50g/m 2 (ii) a Before resistance spot welding, oil stains on the surface of a sample are cleaned by alcohol so as to avoid influencing metallurgical connection of the thin plates in the resistance spot welding process.
(2) A resistance spot welding machine is used, a flat-head electrode is selected as a welding tool, the diameter of the front end of the electrode tip is 6-10 mm, the end face of the electrode tip is arranged to be a cambered surface, the curvature radius of the cambered surface is 150-180, the height of the electrode tip is 18-23 mm, preferably 23mm, and the electrode tip is made of chromium-zirconium-copper; because alloying diffusion exists between the electrode material copper and the hot-formed steel plate, in order to avoid abrasion of the electrode tip, the electrode tip with a certain curvature radius of 150-180 is selected, so that the surface composition of the electrode tip is uniformly changed, the surface of the electrode is uneven, the current density of spot welding is increased, the current distribution is regular, and the qualified rate of spot welding is increased. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted; cooling water flow rate is 10-14L/min, upper and lower electrodes are 4-5L/min, and transformer cooling water is 6-9L/min, preferably cooling water flow rate is 11L/min, upper and lower electrodes are 5L/min, and transformer cooling water is 6L/min.
(3) And spot welding prepressing is carried out on two sides of the lap joint area simultaneously, the prepressing time is controlled to be 10-20 ms, and the electrode pressure F = 3.2-3.6 kN.
(4) As shown in figure 1, a double-pulse welding is carried out by adopting an inverter resistance welding machine, and the welding current of two pulses is respectively controlled at I 1 =6 ~ 8.8kA and I 2 = 6-8.8 kA, and the welding time of two pulses is controlled at t 1 =100 ms-150 ms and t 3 =100ms to 150ms, preferably t 1 =t 2 =100ms，Both pulses are complete welding current cycles; in which the interval between two pulses is t 2 = 15-20 ms, and a preheating current t is applied before each pulse current S = 15-20 ms, i.e. at t S Linearly increasing the current from 0 to the welding current over time; applying a ramp-down current t after each pulse current F = 15-20 ms, i.e. at t F Linearly reducing the current from the welding current to 0 over time; the two pulses have the same waveform, i.e. I 1 =I 2 、t 1 =t 3 Etc.; in the double-pulse welding process, the electrode pressure F = 3.2-3.6 kN. The method controls the preheating current time and the slow reduction current time to be between 15ms and 20ms, can slowly increase and reduce the current before spot welding pulse current, ensures that molten pool metal flows fully, ensures that the electrode pressure at the center promotes the metal to flow to the periphery, ensures that nuggets are formed more fully and uniformly, and avoids the abrupt temperature gradient caused by sudden change to cause the stress concentration and the generation of cracks near a welding spot heat affected zone.
(5) And maintaining the pressure, wherein the pressure maintaining time is controlled to be 10-20 ms. According to the method, the steel plate can be restrained to a certain extent before nucleation by setting the prepressing in the step (3) and the pressure maintaining time in the step, and the plastic ring wraps the nugget for a certain time after the nucleation is finished, so that the situations of gasification splashing and impurity flying-out formed between the nuggets due to the low melting point of Zn element in the coating are avoided, and the completeness and the mechanical property of the nugget are ensured.
Example 1: the resistance spot welding method for hot-dip galvanized hot-formed steel adopts the following specific process.
S1, before resistance spot welding, the surface of the sample was cleaned with alcohol to remove oil stains. A hot-dip galvanized steel sheet having a thickness of 1.4mm was welded by a resistance spot welding machine. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted.
S2, the electrode tip is made of chromium zirconium copper, the diameter of the end face is 6mm, the curvature radius of the cambered surface is 150, and the height is 23 mm; the flow rate of cooling water is 11L/min, the upper and lower electrodes are 5L/min, and the cooling water of the transformer is 6L/min.
And S3, spot welding and prepressing are carried out on two sides simultaneously, the prepressing time is controlled to be 20ms, and the welding electrode pressure is controlled to be F =3.6 kN.
S4, welding by using an inverse resistance welder, wherein the welding current is controlled to be I 1 =I 2 =8kA, the welding time adopting double pulses is controlled at t 1 =t 3 =100 ms; and applying preheating and slow-down current for time t before and after pulse current S =t F =15ms, interval t between two pulses 2 =15ms。
S5, pressure maintaining is carried out, and the pressure maintaining time is controlled to be t 0 =20ms。
The properties of the weld nugget region of the hot dip galvanized hot formed steel obtained are shown in Table 1 below.
Example 2: the resistance spot welding method for hot-dip galvanized hot-formed steel adopts the following specific process.
S1, before resistance spot welding, the surface of the sample was cleaned with alcohol to remove oil stains. A hot-dip galvanized hot-formed steel sheet of 1.6mm thickness was welded using a resistance spot welder. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted.
S2, the electrode tip is made of chromium zirconium copper, the diameter of the end face is 6mm, the curvature radius of the cambered surface is 150, and the height is 23 mm; the flow rate of cooling water is 11L/min, the upper and lower electrodes are 5L/min, and the cooling water of the transformer is 6L/min.
And S3, spot welding and prepressing are carried out on two sides simultaneously, the prepressing time is controlled to be 20ms, and the welding electrode pressure is controlled to be F =3.5 kN.
S4, welding by using an inverse resistance welder, wherein the welding current is controlled to be I 1 =I 2 =8kA, the welding time adopting double pulses is controlled at t 1 =t 3 =100 ms; and applying preheating and slow-down current for time t before and after pulse current S =t F =15ms, interval t between two pulses 2 =20ms。
S5, pressure maintaining is carried out, and the pressure maintaining time is controlled to be t 0 =20ms。
The properties of the weld nugget region of the hot dip galvanized hot formed steel obtained are shown in Table 1 below.
Example 3: the resistance spot welding method for hot-dip galvanized hot-formed steel adopts the following specific process.
S1, before resistance spot welding, the surface of the sample was cleaned with alcohol to remove oil stains. A hot-dip galvanized steel sheet having a thickness of 1.8mm was welded by a resistance spot welding machine. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted.
S2, the electrode tip is made of chromium zirconium copper, the diameter of the end face is 8mm, the curvature radius of the cambered surface is 150, and the height is 23 mm; the flow rate of cooling water is 11L/min, the upper and lower electrodes are 5L/min, and the cooling water of the transformer is 6L/min.
And S3, spot welding and prepressing are carried out on two sides simultaneously, the prepressing time is controlled to be 20ms, and the welding electrode pressure is controlled to be F =3.4 kN.
And S4, welding: welding with an inverter resistance welder with welding current controlled at I 1 =I 2 =8kA, the welding time adopting double pulses is controlled at t 1 =t 3 =100 ms; and applying preheating and slow-down current for time t before and after pulse current S =t F =20ms, interval t between two pulses 2 =18ms。
S5, pressure maintaining is carried out, and the pressure maintaining time is controlled to be t 0 =20ms。
The properties of the weld nugget region of the hot dip galvanized hot formed steel obtained are shown in Table 1 below.
Example 4: the resistance spot welding method for hot-dip galvanized hot-formed steel adopts the following specific process.
S1, before resistance spot welding, the surface of the sample was cleaned with alcohol to remove oil stains. A hot-dip galvanized steel sheet having a thickness of 2mm was welded by a resistance spot welding machine. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted.
S2, the electrode tip is made of chromium zirconium copper, the diameter of the end face is 8mm, the curvature radius of the cambered surface is 150, and the height is 23 mm; the flow rate of cooling water is 11L/min, the upper and lower electrodes are 5L/min, and the cooling water of the transformer is 6L/min.
And S3, spot welding and prepressing are carried out on two sides simultaneously, the prepressing time is controlled to be 20ms, and the welding electrode pressure is controlled to be F =3.2 kN.
And S4, welding: welding with an inverter resistance welder with welding current controlled at I 1 =I 2 =8kA, the welding time adopting double pulses is controlled at t 1 =t 3 =100 ms; and preheating and slow descending are applied before and after the pulse currentTime t of current S =t F =20ms, interval t between two pulses 2 =20ms。
S5, pressure maintaining is carried out, and the pressure maintaining time is controlled to be t 0 =20ms。
The properties of the weld nugget region of the hot dip galvanized hot formed steel obtained are shown in Table 1 below.
Example 5: the resistance spot welding method for hot-dip galvanized hot-formed steel adopts the following specific process.
S1, before resistance spot welding, the surface of the sample was cleaned with alcohol to remove oil stains. A hot-dip galvanized steel sheet having a thickness of 1.5mm was welded by a resistance spot welding machine. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted.
S2, the electrode tip is made of chromium zirconium copper, the diameter of the end face is 10mm, the curvature radius of the cambered surface is 160 mm, and the height is 20 mm; the cooling water flow is 10L/min, the upper and lower electrodes are 4.5L/min, and the transformer cooling water is 8L/min.
And S3, spot welding and prepressing are carried out on two sides simultaneously, the prepressing time is controlled to be 18ms, and the welding electrode pressure is controlled to be F =3.5 kN.
S4, welding by using an inverse resistance welder, wherein the welding current is controlled to be I 1 =I 2 =6kA, the welding time using double pulses is controlled at t 1 =t 3 =120 ms; and applying preheating and slow-down current for time t before and after pulse current S =t F =17ms, interval t between two pulses 2 =17ms。
S5, pressure maintaining is carried out, and the pressure maintaining time is controlled to be t 0 =17ms。
The properties of the weld nugget region of the hot dip galvanized hot formed steel obtained are shown in Table 1 below.
Example 6: the resistance spot welding method for hot-dip galvanized hot-formed steel adopts the following specific process.
S1, before resistance spot welding, the surface of the sample was cleaned with alcohol to remove oil stains. A hot-dip galvanized steel sheet having a thickness of 1.8mm was welded by a resistance spot welding machine. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted.
S2, the electrode tip is made of chromium zirconium copper, the diameter of the end face is 8mm, the curvature radius of the cambered surface is 180 mm, and the height is 18 mm; the flow rate of cooling water is 14L/min, the upper and lower electrodes are 5L/min, and the cooling water of the transformer is 7L/min.
And S3, spot welding and prepressing are carried out on two sides simultaneously, the prepressing time is controlled to be 10ms, and the welding electrode pressure is controlled to be F =3.3 kN.
S4, welding by using an inverse resistance welder, wherein the welding current is controlled to be I 1 =I 2 =8.8kA, the welding time using double pulses is controlled at t 1 =t 3 =130 ms; and applying preheating and slow-down current for time t before and after pulse current S =t F =18ms, interval t between two pulses 2 =16ms。
S5, pressure maintaining is carried out, and the pressure maintaining time is controlled to be t 0 =10ms。
The properties of the weld nugget region of the hot dip galvanized hot formed steel obtained are shown in Table 1 below.
Example 7: the resistance spot welding method for hot-dip galvanized hot-formed steel adopts the following specific process.
S1, before resistance spot welding, the surface of the sample was cleaned with alcohol to remove oil stains. A hot-dip galvanized steel sheet having a thickness of 1.6mm was welded by a resistance spot welding machine. The resistance spot welding adopts a direct current mode, the welding frequency is 1000hz, and an X-shaped welding tongs is adopted.
S2, the electrode tip is made of chromium zirconium copper, the diameter of the end face is 8mm, the curvature radius of the cambered surface is 170, and the height is 20 mm; the cooling water flow is 12L/min, the upper and lower electrodes are 4L/min, and the transformer cooling water is 9L/min.
And S3, spot welding and prepressing are carried out on two sides simultaneously, the prepressing time is controlled to be 15ms, and the welding electrode pressure is controlled to be F =3.4 kN.
And S4, welding: welding with an inverter resistance welder with welding current controlled at I 1 =I 2 =7kA, the welding time adopting double pulses is controlled at t 1 =t 3 =150 ms; and applying preheating and slow-down current for time t before and after pulse current S =15、t F =20ms, interval t between two pulses 2 =17ms。
S5, pressure maintaining is carried out, and the pressure maintaining time is controlled to be t 0 =15ms。
The properties of the weld nugget region of the hot dip galvanized hot formed steel obtained are shown in Table 1 below.
Statistics of the results of the micro vickers hardness values, the tensile and shear strengths, the spatters and the cracks of the nugget zones of the steel welds of examples 1 to 7 are shown in table 1; the comparative example in table 1 is the performance of the weld nugget region when welding was performed using a conventional resistance spot welding process;
table 1: properties of the weld nugget region of the various examples
Through comparative analysis of the examples shown in Table 1, the double-pulse belt preheating and cooling time current adopted by the method can improve the tensile and shearing force performance of the hot-dip galvanized hot-formed steel spot-welded joint; the method preheats the base metal and the area to be welded before welding through the preheating pulse current, can reduce the temperature gradient between a welding core of a welding spot and a heat affected zone, and reduces the generation of splashing and cracks. In FIG. 2, (a) shows the appearance of the welded joint resistance spot welding fracture formed in example 1, and (b) and (c) show EDS pictures of Zn element and Fe element at the fracture of example 1, wherein neither element is obviously enriched. (d) Resistance spot welding fracture morphology of the welded joint formed for the comparative example; (e) the figure is an EDS diagram of Zn element at the fracture of the spot-welded joint of the comparative example, wherein no obvious Zn element enrichment occurs; however, in the comparative example (f), Fe element is obviously enriched at the fracture, so that the mechanical property of the welding spot is reduced. Therefore, the method can reduce the element segregation near the welding point by slowly increasing the welding current before and after welding, effectively reduce the stress concentration generated during the spot welding of the hot-dip galvanized hot-formed steel and effectively improve the comprehensive mechanical property of the steel spot welding joint; the spot welding process has simple procedures, can effectively reduce energy consumption and cost, and can be popularized and applied to the field of welding hot-dip galvanized hot-formed steel.
Claims (6)
1. A resistance spot welding method for hot galvanizing hot forming steel is characterized by comprising the following steps:
(1) the welding material is a hot-dip galvanized hot-formed steel plate, and a flat-head electrode is selected as a welding tool;
(2) spot welding prepressing is carried out on two sides of the lap joint area simultaneously, the prepressing time is controlled to be 10-20 ms, and the electrode pressure is 3.2-3.6 kN;
(3) performing double-pulse welding, wherein the welding current of two pulses is controlled to be 6-8.8 kA, the welding time of the two pulses is controlled to be 100-150 ms, a preheating current is applied for 15-20 ms before each pulse current, and a slow-decreasing current is applied for 15-20 ms after each pulse current;
(4) and maintaining the pressure, wherein the pressure maintaining time is controlled to be 10-20 ms.
2. The resistance spot welding method for hot-dip galvanized hot-formed steel according to claim 1, characterized in that: in the step (3), the interval between the two pulses is 15-20 ms.
3. The resistance spot welding method for hot-dip galvanized hot-formed steel according to claim 1, characterized in that: the diameter of the front end of the electrode tip of the flat-head electrode is 6-10 mm.
4. The resistance spot welding method for hot-dip galvanized hot-formed steel according to claim 3, characterized in that: the end face of the electrode head is an arc face, and the curvature radius of the arc face is 150-180%.
5. The resistance spot welding method for hot-dip galvanized hot-formed steel according to any one of claims 1 to 4, characterized in that: the thickness of the hot galvanizing hot forming steel plate is 1.4-2.0 mm.
6. The resistance spot welding method for hot-dip galvanized hot-formed steel according to claim 5, characterized in that: the yield strength of the hot-dip galvanized hot-formed steel plate after hot forming is not lower than 400MPa, and the tensile strength of the hot-dip galvanized hot-formed steel plate is not lower than 600 MPa.
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