CN112620906B

CN112620906B - Method for improving corrosion resistance of resistance spot welding spot of 1500 MPa-grade hot forming steel

Info

Publication number: CN112620906B
Application number: CN202011457575.8A
Authority: CN
Inventors: 计遥遥; 刘永刚; 詹华; 崔磊; 张军; 刘东亚; 王伟峰; 成昌晶; 李子涛; 代朋虎; 王辉; 晋家春
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2020-12-11
Filing date: 2020-12-11
Publication date: 2022-08-16
Anticipated expiration: 2040-12-11
Also published as: CN112620906A

Abstract

The invention discloses a method for improving corrosion resistance of a resistance spot welding spot of 1500 MPa-grade hot forming steel, which is characterized in that a zinc or zinc alloy metal sheet is manually preset or a zinc or zinc alloy coating is prepared at the lap joint of positions to be welded of at least two workpieces to be welded in a chemical or spraying mode, and the like. The method is applied to resistance spot welding of 1500 MPa-level hot forming parts with or without coatings, can improve the corrosion resistance of welding spots, reduces the risk of failure of the hot forming parts due to welding spot corrosion in service, and improves the service performance of the hot forming parts.

Description

Method for improving corrosion resistance of resistance spot welding spot of 1500 MPa-grade hot forming steel

Technical Field

The invention belongs to the technical field of welding, and particularly relates to a method for improving corrosion resistance of a resistance spot welding spot of 1500 MPa-grade hot forming steel.

Background

In recent years, along with the enforcement of more stringent automobile emission laws and regulations, automobile manufacturers need to develop and produce automobile products with more energy conservation and emission reduction. The light weight of the automobile is one of the most effective ways for realizing energy conservation and emission reduction, and the emission of the fuel oil vehicle can be correspondingly reduced by 5-10% when the weight of the whole automobile is reduced by 10% in general. In order to realize the light weight of the automobile body and simultaneously not reduce the safety of the automobile, advanced high-strength automobile parts are widely applied to the manufacture of the automobile body at present. The cold-forming ultrahigh-strength steel with the tensile strength of over 1000MPa is limited in application to automobile body safety parts due to the problems of high resilience, insufficient forming size precision, serious abrasion to a stamping die and the like in the stamping process. The hot stamping forming technology has the advantages of high part size precision, good forming performance, high strength level, small tonnage required by stamping and the like. According to the material selection scheme of the current mainstream vehicle enterprises, a bare plate and an aluminum-silicon coating hot forming part which are designed based on a 22MnB5 component system and have the strength reaching 1500MPa after hot forming and stamping are widely applied to a vehicle body, such as safety parts of an A column, a B column, a C column, a door frame stiffening beam, a front wall cross beam, a left longitudinal beam, a right longitudinal beam, a vehicle door bumper and the like.

Resistance spot welding has been widely used in the automotive industry due to its advantages of high production efficiency, easy automation, etc., and is also a major welding method in welding hot-formed parts.

After loading, a hot forming part with a higher strength level is usually positioned in a cavity of a vehicle body, the risk of poor electrophoresis is easy to occur, a gap at a welding point connecting interface of the hot forming part after welding is very small, electrophoretic paint cannot reach the connecting surface of a welding point in the electrophoresis process, and secondly, as a material at the welding point position of the hot forming steel part is subjected to heating-melting-solidifying-cooling thermal cycle in the welding process, compared with a non-welding area, a welding core area is uneven in structure and components, gradient in hardness, and large welding internal stress exists around the welding core, a vehicle body is exposed in a corrosion environment in the service process of the whole vehicle, the position of a combining surface of the welding point of the hot forming part is the position which is most prone to corrosion, and then the risk of causing a safety problem exists

Disclosure of Invention

In view of the above situation, the present invention provides a method for improving corrosion resistance of a 1500MPa grade hot forming steel resistance spot welding spot, which can obviously improve corrosion resistance of the spot under the same conditions.

The specific technical scheme of the invention is as follows: a method for improving the corrosion resistance of a resistance spot welding spot of 1500 MPa-grade hot forming steel is implemented by the following steps, and the specific steps are described:

1) preparation stage of the workpiece to be welded:

and cleaning the area to be welded of the hot formed workpiece. The main chemical components of the hot forming workpiece base material are as follows in percentage by weight: c: 0.10 to 0.25, Si: 0.10 to 0.50, Mn: 0.80-1.50, P: less than or equal to 0.03, S: less than or equal to 0.03, Al: less than or equal to 0.10, Cr: 0.10 to 0.50, Mo: less than or equal to 0.03, B: 0.004-0.01, N: less than or equal to 0.01. The balance being Fe and unavoidable impurities. The thickness of the base material of the hot-formed workpiece is 0.5mm-3.0 mm. The base material of the further hot forming workpiece is not coated or is coated with an aluminum-based coating, and the main chemical components of the coating in percentage by weight are respectively Si: 8-12, and the balance of Al and inevitable impurities. The tensile strength of the hot formed workpiece ranges from 1300MPa to 1700 MPa.

2) Electrode preparation phase

The position and direction of the upper electrode and the lower electrode are adjusted to center the upper electrode and the lower electrode, and the main purpose of the step is to ensure that the area of the workpiece to be welded, which is in contact with the cross section of the electrode, is uniformly stressed in the pressure loading stage in the welding process and obtain uniform current in the current loading stage in the welding process. The diameter of the end face of the further electrode is 5mm-7 mm.

3) Preset layer addition

A prefabricated layer of zinc or zinc alloy is placed in the lap joint area of the workpieces to be welded. The preset layer is pure zinc or zinc alloy, and further comprises the following main chemical components in percentage by weight: zn: 75-99.9, and the balance of elements such as Mg, Al and the like and inevitable impurities. The main chemical components of the zinc alloy prefabricated layer are as follows by weight percent: zn: 79-98, Al: 0.5-15, Mg: 0.5 to 6; the main chemical components of the zinc alloy prefabricated layer are as follows by weight percent: zn: 96-99, Al: 0.5-2, Mg: 0.5 to 2. The thickness of the prefabricated layer is 0.01mm-0.5mm, and when the thickness is smaller than 0.01mm, the temperature of a nugget area in the welding process is far higher than the melting point of the prefabricated layer, the prefabricated layer cannot play a role in protection due to evaporation when being too thin, and when the thickness is larger than 0.5mm, the distribution and heat generation quantity of welding current in the welding process can be changed due to the existence of the prefabricated layer, so that the final welding quality is greatly influenced.

A layer of zinc or zinc alloy metal sheet is manually preset or a zinc or zinc alloy coating is prefabricated at the lap joint in a chemical or spraying mode, and further a layer of Zn or Zn alloy is prefabricated at the lap joint of the position to be welded in an electroplating, hot-dipping, vapor deposition, thermal spraying and other modes to achieve the same effect as the effect achieved by manually adding the zinc or zinc alloy layer.

4) And (3) welding:

by adjusting main parameters such as welding current, welding time, electrode pressure and the like in the welding process, effective nugget size is formed between the workpieces to be welded. In the main welding process in the welding process, the welding current range is 5.0kA-12.0kA, the electrode pressure range is 3.0kN-8.0kN, and the welding time is 100ms-500 ms.

Further, when the hot formed work piece has a thickness of 0.7 to 1.4mm, the preferred welding parameters are as follows: welding time: 150ms-300 ms; welding current: 5.0kA to 9.0kA, welding pressure: 3.0-5.0 kN;

when the hot formed workpiece thickness is between 1.5 and 2.0mm, the preferred welding parameters are as follows: welding time: 180ms-400 ms; welding current: 6.0kA-10.0kA, welding pressure: 3.5-5.5 kN;

when the hot formed workpiece has a thickness of 2.1-2.5mm, the preferred welding parameters are as follows: welding time: 200ms-500 ms; welding current: 7.0kA to 11.0kA, welding pressure: 4.0-6.0 kN.

Furthermore, in the welding stage, the Zn or Zn alloy preset layer reaches the melting point firstly at the initial stage of electrification, and the molten Zn and Zn alloy are extruded out of the welding core area under the action of the upper electrode and the lower electrode and are gathered around the welding core.

5) Pressure maintaining cooling stage

And after the welding current is electrified, the recommended pressure maintaining time is 200-500 ms.

Compared with the prior art, the invention has the beneficial effects that: the technical scheme of the invention can improve the corrosion resistance of the resistance spot welding spot of the 1500 MPa-grade hot forming steel. A zinc or zinc alloy metal sheet is manually preset or a zinc or zinc alloy coating is preset at the lap joint of the positions to be welded of at least two workpieces to be welded in a chemical or spraying mode and the like. In the electrified welding stage of resistance spot welding, a zinc or zinc alloy layer in a welding area is firstly melted, the melted zinc or zinc alloy layer is extruded out of a welding spot area under the action of electrode pressure, after welding is finished, a specific continuous or discontinuous zinc or zinc alloy area is formed at the joint of a spot welding workpiece outside a welding core, and the melted zinc or zinc alloy and the welding core of the welding workpiece are metallurgically combined, wherein the zinc or zinc alloy area can provide physical isolation between the welding core and an external corrosion medium, further the zinc or zinc alloy has a sacrificial anode protection effect relative to Fe and an alloy taking Fe as a matrix, can provide better electrochemical protection in the corrosion medium, and based on the physical isolation and the electrochemical corrosion protection effect, the method can obviously improve the corrosion resistance of the welding spot under the same condition.

Drawings

FIG. 1 is a schematic view of the welding of the present invention;

in the figure: 1. the device comprises an upper electrode, 12, an upper electrode end face, 2, a lower electrode, 21, a lower electrode end face, 3, a first workpiece, 4, a second workpiece, 5 and a preset layer.

Detailed Description

The invention is further described with reference to figure 1 of the specification and the specific embodiments.

Example 1

A method for improving corrosion resistance of a resistance spot welding spot of 1500 MPa-grade hot forming steel comprises the following steps:

1) preparation stage of the workpiece to be welded:

and cleaning the area to be welded of the hot formed workpiece. The first workpiece 3 and the second workpiece 4 to be welded are made of non-coating hot forming steel, the thicknesses of the steel are 1.2mm, and the chemical components in percentage by weight are respectively as follows: c: 0.10 to 0.25, Si: 0.10 to 0.50, Mn: 0.80-1.50, P: less than or equal to 0.03, S: less than or equal to 0.03, Al: less than or equal to 0.10, Cr: 0.10 to 0.50, Mo: less than or equal to 0.03, B: 0.004-0.01, N: less than or equal to 0.01, and the balance of Fe and inevitable impurities.

2) Electrode preparation phase

The positions and the directions of an upper electrode 1 and a lower electrode 2 of a welding gun of the resistance spot welding machine are adjusted to center the upper electrode and the lower electrode, the diameters of an end face 12 of the upper electrode and an end face 21 of the lower electrode are 6mm, the uniform stress of a contact area of a workpiece to be welded and an electrode section is ensured in a pressure loading stage in the welding process, and uniform current is obtained in a current loading stage in the welding process.

3) Preset layer addition

And placing the prefabricated layer 5 in the overlapping area of the first workpiece 3 and the second workpiece 4 to be welded. The preset layer 5 is pure zinc, and the main chemical components in percentage by weight are as follows: zn: 99.9 and the balance unavoidable impurities, preferably a thickness of 0.2 mm. 4) And (3) welding:

by adjusting main parameters such as welding current, welding time, electrode pressure and the like in the welding process, effective nugget size is formed between the workpieces to be welded. The main welding process parameters of this embodiment are as follows: welding time: 180 ms-220 ms; welding current: 6.2 kA-8 kA, welding pressure: 3.5 to 4.5 kN.

5) Pressure maintaining cooling stage

And after the welding current is electrified, the recommended pressure maintaining time is 300 ms.

Through the implementation of the steps, after the workpieces are welded, a specific continuous or discontinuous zinc or zinc alloy area is formed at the joint of the spot welding workpieces outside the welding nuggets, the molten zinc or zinc alloy and the nuggets of the welding workpieces are metallurgically bonded, the zinc or zinc alloy area can provide physical isolation between the welding nuggets of the workpieces and an external corrosion medium, and further Zn and the alloy taking Zn as a matrix have a sacrificial anode and cathode protection effect relative to Fe and the alloy taking Fe as the matrix, so that better electrochemical protection can be provided in the corrosion medium.

Example 2

A method for improving the corrosion resistance of a resistance spot welding spot of 1500 MPa-grade hot forming steel comprises the following steps:

1) preparation stage of the workpiece to be welded:

and cleaning the area to be welded of the hot formed workpiece. The first workpiece 3 and the second workpiece 4 to be welded are made of non-coating hot forming steel, the thickness of the steel is 1.2mm, and the chemical components in percentage by weight are as follows: c: 0.10 to 0.25, Si: 0.10 to 0.50, Mn: 0.80-1.50, P: less than or equal to 0.03, S: less than or equal to 0.03, Al: less than or equal to 0.10, Cr: 0.10 to 0.50, Mo: less than or equal to 0.03, B: 0.004-0.01, N: less than or equal to 0.01, and the balance of Fe and inevitable impurities.

2) Electrode preparation phase

The positions and the directions of an upper electrode 1 and a lower electrode 2 of a welding gun of the resistance spot welding machine are adjusted to center the upper electrode and the lower electrode, the diameters of a further upper electrode end face 12 and a further lower electrode end face 21 are 6mm, the uniform stress of a contact area of a workpiece to be welded and an electrode section is ensured in a pressure loading stage in the welding process, and uniform current is obtained in a current loading stage in the welding process.

3) Preset layer addition

And placing the prefabricated layer 5 in the overlapping area of the first workpiece 3 and the second workpiece 4 to be welded. The preset layer 5 comprises the following main chemical components in percentage by weight: zn: 98, Al: 1.4, Mg: 0.6 and the balance unavoidable impurities, the thickness of the pre-layer preferably being 0.2 mm.

4) And (3) a welding stage:

by adjusting main parameters such as welding current, welding time, electrode pressure and the like in the welding process, effective nugget size is formed between the workpieces to be welded. The main welding process parameters of this embodiment are as follows: welding time: 180 ms-220 ms; welding current: 6.2 kA-8 kA, welding pressure: 3.5-4.5 kN;

5) pressure maintaining cooling stage

Example 3

1) preparation stage of the workpiece to be welded:

and cleaning the area to be welded of the hot formed workpiece. The first workpiece 3 and the second workpiece 4 to be welded are aluminum-silicon plated hot forming steel, the thickness of each workpiece is 1.2mm, and the chemical components in percentage by weight are respectively as follows: c: 0.10 to 0.25, Si: 0.10 to 0.50, Mn: 0.80-1.50, P: less than or equal to 0.03, S: less than or equal to 0.03, Al: less than or equal to 0.10, Cr: 0.10 to 0.50, Mo: less than or equal to 0.03, B: 0.004-0.01, N: less than or equal to 0.01. The balance of Fe and inevitable impurities, and the main chemical components of the plating layer in weight percent are respectively Si: 9.0, the balance being Al and unavoidable impurities

2) Electrode preparation phase

3) Preset layer addition

And placing the prefabricated layer 5 in the overlapping area of the first workpiece 3 and the second workpiece 4 to be welded. The preset layer 5 is pure zinc, and the main chemical components in percentage by weight are as follows: zn: 81, Al: 14, Mg: 5; the balance being unavoidable impurities, the preferred predetermined layer thickness being 0.2 mm.

4) And (3) welding:

5) Pressure maintaining cooling stage

The above embodiments have been described in detail to illustrate the object and practice of the invention, it should be understood that the above embodiments are only specific embodiments of the invention, and the invention is not limited by the above embodiments, and various modifications, equivalent substitutions, improvements and the like within the spirit and principle of the invention or by using the technical concept and technical scheme of the invention are within the protection scope of the invention.

Claims

1. A method for improving the corrosion resistance of a resistance spot welding spot of 1500 MPa-grade hot forming steel is characterized by comprising the following steps:

1) preparation stage of the workpiece to be welded:

cleaning the area to be welded of the hot forming workpiece, wherein the main chemical components of the base material of the hot forming workpiece are as follows in percentage by weight: c: 0.10 to 0.25, Si: 0.10 to 0.50, Mn: 0.80-1.50, P: less than or equal to 0.03, S: less than or equal to 0.03, Al: less than or equal to 0.10, Cr: 0.10 to 0.50, Mo: less than or equal to 0.03, B: 0.004-0.01, N: less than or equal to 0.01, and the balance of Fe and inevitable impurities; the thickness of the base material of the thermal forming workpiece is 0.5mm-3.0 mm;

the base material of the hot forming workpiece is not coated, and the tensile strength range of the hot forming workpiece is 1300MPa-1700 MPa;

2) electrode preparation phase

Adjusting the positions and the directions of the upper electrode and the lower electrode to enable the upper electrode and the lower electrode to be centered, ensuring that the contact area of the workpiece to be welded and the end face of the electrode is uniformly stressed in the pressure loading stage in the welding process, and obtaining uniform current in the current loading stage in the welding process, wherein the diameter of the end face of the electrode is 5mm-7 mm;

3) addition of prefabricated layers

Manually prefabricating a layer of zinc or zinc alloy metal sheet to be placed in the lap joint area of the workpiece to be welded; or a layer of zinc or zinc alloy is prefabricated at the lap joint of the position to be welded in an electroplating, hot-dip, vapor deposition or hot spraying mode to achieve the same effect as the effect achieved by manually adding the zinc or zinc alloy layer, the prefabricated layer is pure zinc or zinc alloy, and the main chemical components of the zinc alloy prefabricated layer are as follows in percentage by weight: zn: 96-99, Al: 0.5-2, Mg: 0.5 to 2;

4) and (3) welding:

the method comprises the following steps of forming an effective nugget size between workpieces to be welded by adjusting main parameters of welding current, welding time and welding pressure in a welding process, wherein the welding current range in the main welding process in the welding process is 5.0kA-12.0kA, the welding pressure range is 3.0kN-8.0kN, and the welding time is 100ms-500 ms;

in the welding stage, the zinc or zinc alloy prefabricated layer reaches a melting point at first in the initial stage of electrifying, and the molten zinc or zinc alloy is extruded out of a nugget area under the action of the upper electrode and the lower electrode and is gathered around the nugget;

5) pressure maintaining cooling stage

And after the welding current is electrified, the pressure maintaining time is 200-500 ms.

2. The method of improving corrosion resistance of a 1500MPa grade hot formed steel resistance spot weld according to claim 1, wherein the thickness of the preform is 0.01mm to 0.5 mm.

3. The method for improving the corrosion resistance of the resistance spot welding spot of the hot forming steel with the pressure of 1500MPa according to the claim 1, wherein in the step 4), when the thickness of the hot forming workpiece is 0.7-1.4mm, the welding parameters are as follows: welding time: 150ms-300 ms; welding current: 5.0kA to 9.0kA, welding pressure: 3.0-5.0 kN;

when the thickness of the hot forming workpiece is 1.5-2.0mm, the welding parameters are as follows: welding time: 180ms-400 ms; welding current: 6.0kA-10.0kA, welding pressure: 3.5-5.5 kN;

when the thickness of the hot formed workpiece is 2.1-2.5mm, the welding parameters are as follows: welding time: 200ms-500 ms; welding current: 7.0kA to 11.0kA, welding pressure: 4.0-6.0 kN.