阅读说明：本技术 过渡层辅助的高强钢-铝合金异种金属等离子弧焊接方法 (Plasma arc welding method for high-strength steel-aluminum alloy dissimilar metal assisted by transition layer ) 是由 吴迪 李洪梅 孙大千 王蕾 郭红玲 于 2021-08-10 设计创作，主要内容包括：本发明涉及一种过渡层辅助的高强钢-铝合金异种金属等离子弧焊接方法,属于材料焊(连)接技术领域。工艺步骤为：试板表面处理→高强钢-过渡层-铝合金接触面预紧力调节→穿孔型等离子弧热源在高强钢-过渡层接触面施焊,实现高强钢-铝合金异种金属的连接。本发明针对高强钢-铝合金异种金属焊接接头的脆性问题,采用能量集中的穿孔型等离子弧作为焊接热源,选用铜作为过渡层,在单热源一次施焊的情况下形成包含钢-铜熔化连接和铜-铝瞬时液相扩散连接的复合接头。复合接头中存在的部分未熔化的铜过渡层可有效阻止铁、铝元素的混合及冶金反应,从而避免脆性Fe-Al金属间化合物的形成,降低接头脆性,改善其力学性能。(The invention relates to a transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals, belonging to the technical field of material welding (connection). The process comprises the following steps: surface treatment of a test plate → adjustment of pretightening force of a high-strength steel-transition layer-aluminum alloy contact surface → welding of a perforation type plasma arc heat source on the high-strength steel-transition layer contact surface to realize connection of high-strength steel-aluminum alloy dissimilar metals. Aiming at the brittleness problem of a high-strength steel-aluminum alloy dissimilar metal welding joint, the invention adopts a perforation type plasma arc with concentrated energy as a welding heat source, selects copper as a transition layer, and forms a composite joint comprising steel-copper fusion connection and copper-aluminum instantaneous liquid phase diffusion connection under the condition of one-time welding of a single heat source. The partial unmelted copper transition layer in the composite joint can effectively prevent the mixing and metallurgical reaction of iron and aluminum elements, thereby avoiding the formation of brittle Fe-Al intermetallic compounds, reducing the brittleness of the joint and improving the mechanical property of the joint.)

1. A plasma arc welding method for high-strength steel-aluminum alloy dissimilar metal assisted by a transition layer is characterized by comprising the following steps: adopting a metal material which can be respectively connected with steel and aluminum as a transition layer, and applying a single heat source on the high-strength steel-transition layer interface by adopting plasma arc welding to form a fusion welding seam on the high-strength steel-transition layer interface; meanwhile, due to the heating effect of the plasma arc, heat is conducted to the interface of the transition layer and the aluminum alloy through the transition layer, and an instantaneous liquid phase diffusion welding seam is formed.

2. The transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals according to claim 1, characterized in that: the plasma arc heat source is of a perforated type, in order to further reduce the diameter of an arc column of the plasma arc and further increase the energy density, the diameter of a selected tungsten electrode is 1.6mm, and the aperture of a compression nozzle is 1.5-2.0 mm; the transition layer is made of pure copper, and the thickness of the transition layer is 1.5-2.5 mm; the thickness range of the high-strength steel and the aluminum alloy base metal is 3-5 mm.

3. The transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals according to claim 1 or 2, characterized in that: the method comprises the following steps:

a) preparing before welding: respectively carrying out fine mechanical polishing on the high-strength steel, the aluminum alloy test plate and the copper transition layer, and carrying out alkali washing and acid washing for standby;

b) the joint form is as follows: the joint is in an I-shaped groove butt joint mode, and the pre-tightening force of 10N-30N is ensured to exist on the contact surface of the high-strength steel-copper transition layer-aluminum alloy during assembly welding and clamping;

c) the welding process comprises the following steps: welding by adopting plasma arc welding equipment, and welding by utilizing a plasma arc heat source with high energy density and good straightness; high-purity argon is selected as plasma gas and shielding gas, a keyhole effect is formed by optimizing welding parameters, perforation type plasma arc welding is realized on the steel-copper side, and instantaneous liquid phase diffusion welding is realized on the copper-aluminum alloy side;

d) the plasma arc heat source is controlled on the steel, and perforation type plasma arc welding is realized near the steel-copper contact surface to form a steel-copper fusion welding seam; because the linear expansion coefficients of steel and copper are different, the generated internal stress further promotes the close combination of copper and aluminum alloy and plays a role in crushing an oxide film on the surface of the aluminum alloy; meanwhile, in the process of implementing the perforation type plasma arc welding, heat is conducted to one side of the aluminum alloy through the copper transition layer, and the temperature near the contact surface of the copper and the aluminum alloy reaches the eutectic temperature of 548 ℃ lower than the melting points of the copper and the aluminum to form a liquid phase; in the continuous heating process, copper and aluminum elements are dissolved into a liquid phase from a parent metal to realize mutual diffusion of the copper and aluminum elements, and a diffusion reaction layer is formed after solidification, wherein the diffusion reaction layer is a copper-aluminum instantaneous liquid phase diffusion welding seam;

e) by accurately controlling welding parameters, an unmelted copper transition layer with the thickness of more than 0.5mm is always present between a steel-copper melting welding seam and a copper-aluminum instantaneous liquid phase diffusion welding seam in the composite joint, so that the mixing and metallurgical reaction of iron and aluminum elements can be effectively prevented, the formation of a brittle Fe-Al intermetallic compound is avoided, the brittleness of the joint is reduced, and the mechanical property of the joint is improved.

4. The transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals according to claim 3, wherein: and c) controlling the plasma arc heat source on the steel at a position 0.2-0.8 mm away from the steel-copper contact surface.

5. The transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals according to claim 3, wherein: the parameters for realizing the perforation type plasma arc welding in the steps c) and d) are as follows: the welding current is 70-100A, the welding speed is 200-280 mm/min, the flow of Ar plasma gas is 1.2-2.8L/min, the flow of Ar protective gas is 16-20L/min, and the distance between a nozzle and a workpiece is 3-4 mm.

6. The transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals according to claim 3, wherein: and simultaneously forming a composite joint comprising two connection modes of a steel-copper melting welding seam and a copper-aluminum instantaneous liquid phase diffusion welding seam by one-time welding.

7. The transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals according to claim 6, wherein: the partial unmelted copper transition layer in the composite joint can effectively prevent the mixing and metallurgical reaction of iron and aluminum elements, thereby avoiding the formation of brittle Fe-Al intermetallic compounds, reducing the brittleness of the joint and improving the mechanical property of the joint.

Technical Field

The invention relates to the technical fields of aerospace, transportation, mechanical manufacturing and the like, in particular to the technical field of material welding (connection), and particularly relates to a transition layer assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals. Aiming at the brittleness problem of a high-strength steel-aluminum alloy dissimilar metal welding joint, the invention adopts a perforation type plasma arc with concentrated energy as a welding heat source, selects copper as a transition layer, and forms a composite joint comprising steel-copper fusion connection and copper-aluminum instantaneous liquid phase diffusion connection under the condition of one-time welding of a single heat source. The partial unmelted copper transition layer in the composite joint can effectively prevent the mixing and metallurgical reaction of iron and aluminum elements, thereby avoiding the formation of brittle Fe-Al intermetallic compounds, reducing the brittleness of the joint and improving the mechanical property of the joint.

Background

Aluminum and aluminum alloy are light metals which are most widely applied at present, and have the advantages of small density, high specific strength, good corrosion resistance and the like, and high-strength steel has high tensile strength, good toughness, and higher specific strength and yield ratio. The purpose of light weight in the industrial field can be realized by increasing the using amount of the aluminum alloy and the high-strength steel, the reliable connection of the aluminum alloy and the high-strength steel plays an extremely important role in key components in the technical fields of aerospace, transportation, mechanical manufacturing and the like, but because the aluminum and the steel have obvious difference in physical and chemical properties and crystal structures and the solid solubility between Fe and Al is extremely low, a large amount of brittle Fe-Al intermetallic compounds are easily formed at a steel-aluminum welding joint in the fusion welding process, and the weldability and the mechanical properties of the joint are seriously deteriorated. Therefore, it is difficult to manufacture a joint having excellent mechanical properties when a high-strength steel-aluminum alloy dissimilar metal is directly welded by the fusion welding technique.

At present, the high-strength steel-aluminum alloy fusion-brazing connection can be realized by controlling the energy of a welding wire, the aluminum alloy and a filler wire are heated and melted in the welding process, liquid metal is spread to the surface of solid steel, a continuous interface layer is formed at the interface of the steel and the aluminum, the thickness of the interface layer is controlled to be less than 10 micrometers (CN 107824950B), the mechanical property of a steel-aluminum joint is improved to a certain extent, but the component of the interface layer in the joint is still a brittle Fe-Al intermetallic compound, and the risk of brittle fracture exists.

Disclosure of Invention

The invention aims to provide a plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals assisted by a transition layer, which solves the problems in the prior art. Aiming at the brittleness problem of the joint, the invention adopts a perforation type plasma arc with concentrated energy as a welding heat source, selects copper as a transition layer, and forms a composite joint comprising steel-copper fusion connection and copper-aluminum instantaneous liquid phase diffusion connection under the condition of one-time welding by a single heat source. The partial unmelted copper transition layer in the composite joint can effectively prevent the mixing and metallurgical reaction of iron and aluminum elements, thereby avoiding the formation of brittle Fe-Al intermetallic compounds, reducing the brittleness of the joint and improving the mechanical property of the joint.

The above object of the present invention is achieved by the following technical solutions:

the plasma arc welding method for the transition layer assisted dissimilar metal of the high-strength steel-aluminum alloy adopts a metal material which can be respectively connected with steel and aluminum as the transition layer, and adopts plasma arc welding to apply a single heat source on the interface of the high-strength steel-transition layer so as to form a fusion welding seam on the interface of the high-strength steel-transition layer; meanwhile, due to the heating effect of the plasma arc, heat is conducted to the interface of the transition layer and the aluminum alloy through the transition layer, and an instantaneous liquid phase diffusion welding seam is formed.

The plasma arc heat source is of a perforated type, in order to further reduce the diameter of an arc column of the plasma arc and further increase the energy density, the diameter of a selected tungsten electrode is 1.6mm, and the aperture of a compression nozzle is 1.5-2.0 mm; the transition layer is made of pure copper, and the thickness of the transition layer is 1.5-2.5 mm; the thickness range of the high-strength steel-aluminum alloy base metal is 3-5 mm.

The plasma arc welding method of the high-strength steel-aluminum alloy dissimilar metal assisted by the transition layer comprises the following steps:

a) preparing before welding: respectively carrying out fine mechanical polishing on the high-strength steel, the aluminum alloy test plate and the copper transition layer, and carrying out alkali washing and acid washing for standby;

b) the joint form is as follows: the joint is in an I-shaped groove butt joint mode, and the pre-tightening force of 10N-30N is ensured to exist on the contact surface of the high-strength steel-copper transition layer-aluminum alloy during assembly welding and clamping;

c) the welding process comprises the following steps: welding by adopting plasma arc welding equipment, and welding by utilizing a plasma arc heat source with high energy density and good straightness; high-purity argon is selected as plasma gas and shielding gas, a keyhole effect is formed by optimizing welding parameters, perforation type plasma arc welding is realized on the steel-copper side, and instantaneous liquid phase diffusion welding is realized on the copper-aluminum alloy side;

d) the plasma arc heat source is controlled on the steel, and perforation type plasma arc welding is realized near the steel-copper contact surface to form a steel-copper fusion welding seam; because the linear expansion coefficients of steel and copper are different, the generated internal stress further promotes the close combination of copper and aluminum alloy and plays a role in crushing an oxide film on the surface of the aluminum alloy; meanwhile, in the process of implementing the perforation type plasma arc welding, heat is conducted to one side of the aluminum alloy through the copper transition layer, and the temperature near the contact surface of the copper and the aluminum alloy reaches the eutectic temperature of 548 ℃ lower than the melting points of the copper and the aluminum to form a liquid phase; in the continuous heating process, copper and aluminum elements are dissolved into a liquid phase from a parent metal to realize mutual diffusion of the copper and aluminum elements, and a diffusion reaction layer is formed after solidification, wherein the diffusion reaction layer is a copper-aluminum instantaneous liquid phase diffusion welding seam;

e) by accurately controlling welding parameters, an unmelted copper transition layer with the thickness of more than 0.5mm is always present between a steel-copper melting welding seam and a copper-aluminum instantaneous liquid phase diffusion welding seam in the composite joint, so that the mixing and metallurgical reaction of iron and aluminum elements can be effectively prevented, the formation of a brittle Fe-Al intermetallic compound is avoided, the brittleness of the joint is reduced, and the mechanical property of the joint is improved.

And c) controlling the plasma arc heat source on the steel at a position 0.2-0.8 mm away from the steel-copper contact surface.

The parameters for realizing the perforation type plasma arc welding in the steps c) and d) are as follows: the welding current is 70-100A, the welding speed is 200-280 mm/min, the flow of Ar plasma gas is 1.2-2.8L/min, the flow of Ar protective gas is 16-20L/min, and the distance between a nozzle and a workpiece is 3-4 mm.

And simultaneously forming a composite joint comprising two connection modes of a steel-copper melting welding seam and a copper-aluminum instantaneous liquid phase diffusion welding seam by one-time welding. The partial unmelted copper transition layer in the composite joint can effectively prevent the mixing and metallurgical reaction of iron and aluminum elements, thereby avoiding the formation of brittle Fe-Al intermetallic compounds, reducing the brittleness of the joint and improving the mechanical property of the joint.

The invention has the beneficial effects that: the method of the invention is adopted to weld the dissimilar metals of high-strength steel-aluminum alloy, and the performance indexes are as follows:

(1) the energy of the perforation type plasma arc is concentrated, the arc column is straight, the welding process is stable, and the single-side welding and double-side forming are realized. The weld joint has beautiful formation, no welding defects such as cracks, pores, undercut, incomplete penetration, incomplete fusion and the like, and good welding process performance.

(2) Plasma arc welding of high-strength steel-aluminum alloy dissimilar metal with the plate thickness of 3-5mm is carried out, pure copper with the width of 1.5-2.5mm is selected as a transition layer, and the obtained welded composite joint does not contain brittle Fe-Al intermetallic compounds. In the tensile test, the joint is broken at the welding seam area of the liquid phase diffusion welding at one side of the copper-aluminum alloy, and the tensile strength is 110-150 MPa.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention.

FIG. 1 is a schematic view of a plasma arc welding process for high-strength steel-aluminum alloy dissimilar metals assisted by a transition layer according to the present invention;

FIG. 2 is a schematic view of a transition layer-assisted plasma arc welding method for high-strength steel-aluminum alloy dissimilar metals and a joint structure according to the present invention;

FIG. 3 is a microscopic structure (high magnification photograph of the interface of the high strength steel and the steel-copper fusion weld) inside the high strength steel-aluminum alloy composite joint of the present invention;

FIG. 4 is a microscopic structure (high magnification photograph of a fusion welding seam of a high strength steel-copper transition layer) inside the high strength steel-aluminum alloy composite joint of the present invention;

fig. 5 is a microstructure (high magnification photograph of a copper transition layer-aluminum alloy diffusion welding seam) inside the high-strength steel-aluminum alloy composite joint of the present invention.

Detailed Description

The details of the present invention and its embodiments are further described below with reference to the accompanying drawings.

Referring to fig. 1 to 5, the plasma arc welding method of the transition layer assisted high-strength steel-aluminum alloy dissimilar metal of the invention comprises the following process steps: surface treatment of a test plate → adjustment of pretightening force of a contact surface of high-strength steel-transition layer-aluminum alloy → welding of a perforation type plasma arc heat source on the contact surface of the high-strength steel-transition layer to realize connection of high-strength steel-aluminum alloy dissimilar metals. Aiming at the brittleness problem of a high-strength steel-aluminum alloy dissimilar metal welding joint, the invention adopts a perforation type plasma arc with concentrated energy as a welding heat source, selects copper as a transition layer, and forms a composite joint comprising steel-copper fusion connection and copper-aluminum instantaneous liquid phase diffusion connection under the condition of one-time welding of a single heat source. The partial unmelted copper transition layer in the composite joint can effectively prevent the mixing and metallurgical reaction of iron and aluminum elements, thereby avoiding the formation of brittle Fe-Al intermetallic compounds, reducing the brittleness of the joint and improving the mechanical property of the joint.

Example 1:

the plasma arc welding method for the transition layer assisted plasma arc welding of the dissimilar metals of the high-strength steel and the aluminum alloy is adopted to carry out the plasma arc welding of the dissimilar metals of the DP980 high-strength steel and the 6061 aluminum alloy assisted by the transition layer, and the specific steps are as follows:

1) the thickness of DP980 high-strength steel and 6061 aluminum alloy is 4mm, and the transition layer is made of pure copper with the thickness of 2.5 mm. And (4) finely and mechanically polishing the base material, and performing alkali washing and acid washing for later use.

2) The high-strength steel and the aluminum alloy are in an I-shaped groove butt joint mode, copper is added between the high-strength steel and the aluminum alloy to serve as a transition layer, the steel plate and the aluminum plate are fixed through the pressing plate, and 10N-30N pressure is kept between steel-copper-aluminum alloy contact surfaces by adjusting pretightening force.

3) The plasma arc heat source is controlled on the steel at a position 0.2mm away from the steel-copper contact surface, and the diameter of the compression nozzle in the plasma welding gun is 2.0 mm. The technological parameters are as follows: the welding current is 90A, the welding speed is 270mm/min, the Ar plasma gas flow is 2.2L/min, the Ar protective gas flow is 18L/min, and the distance between a nozzle and a workpiece is 3.5 mm.

The welding process is stable, the weld joint is attractive in forming, and welding defects such as cracks, air holes, undercut, incomplete penetration, incomplete fusion and the like are avoided; the obtained composite joint comprises a steel-copper fusion welding seam, a partially unmelted copper transition layer and a copper-aluminum instantaneous liquid phase diffusion welding seam; in the tensile test, the joint is broken in the weld zone of the liquid phase diffusion welding on one side of the copper-aluminum alloy, and the average tensile strength is 130 MPa.

Example 2:

the plasma arc welding method for the transition layer assisted plasma arc welding of the dissimilar metals of the high-strength steel and the aluminum alloy is adopted to carry out the plasma arc welding of the dissimilar metals of the DP1180 high-strength steel and the aluminum alloy-5A 06 assisted plasma arc welding of the transition layer, and the method comprises the following specific steps:

1) the plate thickness of DP1180 high-strength steel and 5A06 aluminum alloy is 3mm, and the transition layer is pure copper with the thickness of 2 mm. And (4) finely and mechanically polishing the base material, and performing alkali washing and acid washing for later use.

2) The high-strength steel and the aluminum alloy are in an I-shaped groove butt joint mode, copper is added between the high-strength steel and the aluminum alloy to serve as a transition layer, the steel plate and the aluminum plate are fixed through the pressing plate, and 10N-30N pressure is kept between steel-copper-aluminum alloy contact surfaces by adjusting pretightening force.

3) The plasma arc heat source is controlled on the steel at a position 0.5mm away from the steel-copper contact surface, and the diameter of the compression nozzle in the plasma welding gun is 1.5 mm. The technological parameters are as follows: the welding current is 70A, the welding speed is 260mm/min, the flow of Ar plasma gas is 1.6L/min, the flow of Ar protective gas is 18L/min, and the distance between a nozzle and a workpiece is 4 mm.

The welding process is stable, the weld joint is attractive in forming, and welding defects such as cracks, air holes, undercut, incomplete penetration, incomplete fusion and the like are avoided; the obtained composite joint comprises a steel-copper fusion welding seam, a partially unmelted copper transition layer and a copper-aluminum instantaneous liquid phase diffusion welding seam; in the tensile test, the joint is broken in the weld zone of the liquid phase diffusion welding on one side of the copper-aluminum alloy, and the average tensile strength is 125 MPa.

The above description is only a preferred example of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like of the present invention shall be included in the protection scope of the present invention.