A magnesium alloy and steel dissimilar metal tube or bar welding interface with multi-layer multi-modal characteristics and its welding method and application

Abstract

The present invention discloses a magnesium alloy and steel dissimilar metal tube or bar welding interface with multi-layer multimodal characteristics and a welding method and application thereof, belonging to the technical field of magnesium alloy and steel dissimilar metal welding. A magnesium alloy and steel dissimilar metal tube or bar welding interface with multi-layer multimodal characteristics, the welding interface obtained from the magnesium alloy side to the steel side includes three layers, which are Mg-Zn layer, Zn layer and Fe-Zn layer, respectively, the average grain size of the Mg-Zn layer is less than 2μm, and contains MgZn precipitate phase, the size of the precipitate phase is less than 100nm; the average grain size of the Zn layer is less than 2μm; the Fe-Zn layer contains an iron-zinc compound transition phase. The present invention can dock magnesium alloy and steel dissimilar metal tubes or bars, expanding the scope of application of ultrasonic welding to magnesium alloy and steel dissimilar metal shapes and welding methods.

Description

Technical Field

[0001] The invention relates to a magnesium alloy and steel dissimilar metal pipe or bar welding interface with multi-layer and multi-modal characteristics and a welding method and application thereof, belonging to the technical field of magnesium alloy and steel dissimilar metal welding. Background Art

[0002] Magnesium alloy has the advantages of high specific strength, specific stiffness, excellent electromagnetic shielding ability, good thermal conductivity and shock absorption, as well as rich resource reserves and low density. It has good development prospects in the fields of aerospace, automobiles, electronic products, etc. Steel has high absolute strength and is still irreplaceable in the important load-bearing structure of the car body. Due to the cross-application of steel and magnesium alloys, the composite structure of the two can replace the steel structure in some occasions to achieve lightweight structural parts. Therefore, the connection of magnesium alloy and steel dissimilar metals has broad application prospects. At present, the connection between magnesium alloy and steel is mainly achieved by mechanical methods such as bolts and riveting, which has low production efficiency, high cost and additional weight of the joint. Therefore, it is necessary to develop efficient, low-cost, lightweight and high comprehensive cost-effective magnesium alloy and steel dissimilar metal welding technology. However, due to the large differences in the physical and chemical properties of magnesium alloy and steel, the liquid phases of the two cannot coexist and can hardly form a metallurgical bond, which makes direct melting welding of the two very difficult and unable to form an effective connection.

[0003] Ultrasonic welding is a typical solid-phase welding technology that does not cause material melting. It has the characteristics of short welding time, simple operation, stable process, good forming, and relative insensitivity to surface oxides and contaminants. It is a potential advantage and suitable for the connection of magnesium alloys and steel dissimilar metals. In addition, based on the difficulty of forming metallurgical bonds caused by the differences in the physical and chemical properties of magnesium alloys and steel dissimilar metals, adding an intermediate layer is a good solution. However, the welding effect of ultrasonic welding products currently used for metals needs to be further improved, and it is only limited to the overlap of plates, and the scope of use is greatly limited; and the added intermediate layer is relatively single, usually a Zn layer. A single metal intermediate layer is prone to produce a continuous hard and brittle Mg-Zn phase, resulting in a decrease in mechanical properties.

[0004] Therefore, based on the above problems, the present invention uses a rotary ultrasonic welding process to prepare a magnesium alloy and steel dissimilar metal tube or rod weldment with a multi-layer multi-modal characteristic welding interface, which improves the connection strength of the magnesium alloy and steel dissimilar metal ultrasonic welding weldment and realizes the butt connection of magnesium alloy and steel dissimilar metal tubes or rods. Summary of the invention

[0005] In view of the current poor ultrasonic welding effect, limited applicable material shapes and connection methods, and the single intermediate layer causing the ultrasonic welding connection interface of magnesium alloy and steel dissimilar metals to easily generate hard and brittle intermetallic compounds, thereby resulting in low connection interface strength, the purpose of the present invention is to provide a method for obtaining a magnesium alloy and steel dissimilar metal tube or bar weldment with a multi-layer multi-modal characteristic welding interface using rotary ultrasonic welding. Through rotary ultrasonic welding processing, the added Zn / Mg / Zn composite intermediate layer reacts with the magnesium alloy and the steel base material to obtain a multi-layer multi-modal characteristic welding interface, which is Mg-Zn layer, Zn layer and Fe-Zn layer from the magnesium alloy side to the steel side, wherein the average grain size of the Mg-Zn layer is less than 2μm, and contains MgZn precipitate phase, the size of the precipitate phase is less than 100nm, and the average grain size of the Zn layer is less than 2μm.

[0006] At the same time, the present invention provides a magnesium alloy and steel dissimilar metal tube or rod welding interface with multi-layer and multi-modal characteristics.

[0007] At the same time, the present invention provides a magnesium alloy and steel dissimilar metal tube or bar weldment obtained by adopting a welding method for a magnesium alloy and steel dissimilar metal tube or bar welding interface with multi-layer multi-modal characteristics.

[0008] At the same time, the present invention provides an application of magnesium alloy and steel dissimilar metal tube or bar weldments in automotive industry workpieces (such as door frames, engine brackets, etc.), aerospace workpieces (such as seat frames, aircraft wings and landing gear, etc.) and electronic products (such as laptop computer housings and brackets, mobile phone middle frames, etc.).

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A welding interface of a magnesium alloy and a steel dissimilar metal tube or bar having multi-layer multi-modal characteristics, wherein the welding interface obtained from the magnesium alloy side to the steel side comprises three layers, namely, a Mg-Zn layer, a Zn layer and a Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and contains a MgZn precipitate phase, the size of the precipitate phase being less than 100 nm; the average grain size of the Zn layer is less than 2 μm; the Fe-Zn layer contains an iron-zinc compound transition phase; the thicknesses of the Mg-Zn layer, the Zn layer and the Fe-Zn layer are 10 to 40 μm, 1 to 4 μm and 4 to 16 μm, respectively.

[0011] A method for welding a magnesium alloy and steel dissimilar metal tube or bar welding interface having multi-layer multi-modal characteristics, comprising the following steps:

[0012] S1, cleaning the base material: grinding and cleaning the cross section of the welded magnesium alloy, steel base material tube or rod;

[0013] S2, preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn;

[0014] S3, fixing the welded components: placing the cleaned base metal and the Zn-Mg composite intermediate layer on the workbench of the rotary ultrasonic welding machine, and forming a butt joint structure with magnesium alloy on the upper side and steel on the lower side, and placing the Zn-Mg composite intermediate layer at the center of the butt joint area of ​​the base metal;

[0015] S4, welding process: the fixed welded components are subjected to rotary ultrasonic welding, and the ultrasonic parameters are: output frequency 20kHz, working power 1000-5000W, amplitude 10-50μm, and the whole process is divided into three stages: the first stage: 0.5-2s, rotation speed 500-1000r / min; the second stage: 2-4s; rotation speed 1000-2000r / min; the third stage: 4-5s; rotation speed 100-500r / min, to obtain the butt weld of the tube or bar;

[0016] S5, short-time annealing: annealing the obtained tube or bar butt weld to obtain a magnesium alloy and steel dissimilar metal tube or bar welding interface with multi-layer multi-modal characteristics.

[0017] Preferably, the magnesium alloy is selected from any one of Mg-Al, Mg-Zn, Mg-Mn, Mg-Zr and Mg-RE series, and the steel is selected from any one of carbon steel, alloy steel and high alloy steel.

[0018] Preferably, in S1, the parent material magnesium alloy and steel are both in tubular or rod-shaped, the inner diameter of the tube is 4.5 mm to 28 mm, the outer diameter is 6 mm to 30 mm, the length is 10 to 40 mm, the difference between the inner and outer diameters is 1.5 to 5 mm, the diameter of the rod is 3 to 15 mm, and the length is 10 to 40 mm, and the inner and outer diameters or diameters of the magnesium alloy and steel are the same.

[0019] Preferably, in S2, the inner and outer diameters of the Zn-Mg composite intermediate layer are the same as those of the magnesium alloy and the steel.

[0020] Preferably, in S4, the triggering condition for rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4 MPa.

[0021] Preferably, in S5, the annealing temperature is 150-220° C., and the time is 20 min-1 h.

[0022] The magnesium alloy and steel dissimilar metal pipe or bar weldment obtained by the welding method of the present invention has a tensile strength of more than 120 MPa.

[0023] The magnesium alloy and steel dissimilar metal tube or bar weldment of the present invention is used in automobile industry workpieces, aerospace workpieces and electronic products.

[0024] Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

[0025] The rotary ultrasonic welding process adopted by the present invention and the obtained multi-layer multi-modal characteristic welding interface can improve the quality of the weld. The specific principles are as follows: (1) The rotary ultrasonic welding process adds a rotating function to the tool head on the basis of traditional ultrasonic welding. The rotation of the tool head is conducive to generating more friction heat in the welded material, so that it is fully softened. At the same time, the rotating tool head also provides a certain stirring effect, so that the softened parts of the two welded parts are fully in contact, achieving the purpose of effective combination, thereby improving the quality of the joint welding. (2) The multi-layer multi-modal interface "parent material magnesium alloy / MgZn layer (ultrafine grain + nano-MgZn precipitation phase) / Zn layer (ultrafine grain) / Fe-Zn layer (containing Fe-Zn compound) / parent material steel" obtained after rotary ultrasonic welding has a good interface transition compared to the discontinuity of the Mg-Zn single-layer interface formed by traditional welding, which reduces the problem of strength reduction caused by the brittleness of the single-layer Mg-Zn interface. At the same time, since the MgZn layer and the Zn layer have ultrafine grains, and the MgZn precipitate phase is a nano-precipitate phase, it has a better strengthening effect on the interface and can effectively hinder the initiation and propagation of cracks, thereby significantly improving the interface connection strength between magnesium alloy and steel dissimilar metals.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The multi-layer multi-modal magnesium alloy and steel dissimilar metal tube or bar welding interface obtained by the present invention has significantly improved strength, and the tensile strength can reach more than 120 MPa, which is higher than the interface strength of the magnesium alloy and steel dissimilar metal plate lap weld obtained by the currently used ultrasonic welding.

[0028] (2) The multi-layer multimodal characteristic welding interface between magnesium alloy and steel dissimilar metal tube or rod obtained by the present invention is a multi-layer interface (the welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely Mg-Zn layer, Zn layer and Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and it contains MgZn precipitate phase, the size of the precipitate phase is less than 100 nm, and the average grain size of the Zn layer is less than 2 μm). This multi-layer interface overcomes the problem of strength reduction caused by the brittleness of the single-layer Mg-Zn interface, and the ultrafine-grained MgZn layer and Zn layer and the nano-MgZn precipitate phase further strengthen the interface, thereby improving the connection strength of the magnesium alloy and steel dissimilar metal interface.

[0029] (3) The rotary ultrasonic welding method described in the present invention has the advantages of simple processing, high efficiency, low heat input, no pollution, and low cost. In addition, due to the introduction of the rotating function in the tool head, the obtained product has a better welding effect than the general ultrasonic welding method and has broad application prospects.

[0030] (4) The rotary ultrasonic welding method described in the present invention can be used to butt-join magnesium alloy and steel dissimilar metal tubes or bars, breaking through the current limitation that ultrasonic welding is only used for overlapping plates when welding magnesium alloy and steel dissimilar metals, and expanding the scope of application of ultrasonic welding to magnesium alloy and steel dissimilar metal shapes and welding methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a microstructure diagram of the Mg-Zn layer after rotary ultrasonic welding of the present invention;

[0032] Figure 2 It is a microstructure diagram of the MgZn precipitation phase in the Mg-Zn layer after rotary ultrasonic welding of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0034] Example 1

[0035] A magnesium alloy and steel dissimilar metal pipe welding interface with multi-layer multi-modal characteristics, wherein the welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely, a Mg-Zn layer, a Zn layer and a Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and contains a MgZn precipitate phase, the size of the precipitate phase is less than 100 nm, and the average grain size of the Zn layer is less than 2 μm.

[0036] The thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 20 μm, 2 μm, and 10 μm, respectively.

[0037] The Fe-Zn layer contains an iron-zinc compound transition phase.

[0038] That is, in the magnesium alloy and steel dissimilar metal pipe welded forgings, the cross-section has the following structure: base material magnesium alloy / MgZn layer (ultrafine grains + nano-MgZn precipitation phase) / Zn layer (ultrafine grains) / Fe-Zn layer (containing Fe-Zn compounds) / base material steel.

[0039] A method for welding magnesium alloy and steel dissimilar metal pipes capable of forming a multi-layer multi-modal characteristic welding interface comprises the following steps:

[0040] S1: Cleaning the parent material: Grind and clean the cross-section of the welded magnesium alloy and steel parent material tubes; the magnesium alloy material is Mg-Al alloy, and the steel material is carbon steel; the parent material magnesium alloy and steel are both in tubular shape, with an inner diameter of 15mm, an outer diameter of 20mm, and a length of 20mm. The difference between the inner and outer diameters is 5mm, and the inner and outer diameters of the magnesium alloy and steel are the same;

[0041] S2: preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn; the inner and outer diameters of the Zn-Mg composite intermediate layer are the same as those of the magnesium alloy and the steel base material;

[0042] S3: Fix the welded components: Place the cleaned parent metal and the intermediate layer on the workbench of the rotary ultrasonic welding machine, and form a butt joint structure with magnesium alloy on the upper side and steel on the lower side, with the intermediate layer placed in the center of the butt joint area of ​​the parent metal;

[0043] S4: Welding process: Rotary ultrasonic welding is performed on the fixed welded components. The ultrasonic parameters are: output frequency 20kHz, working power 2500W, amplitude 30μm, and the whole process is divided into three stages: the first stage: 0.5~2s, speed 800r / min; the second stage: 2~4s; speed 1500r / min; the third stage: 4~5s; speed 300r / min; the triggering condition of rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4MPa;

[0044] S5: short-time annealing: the obtained pipe butt weld is annealed at a temperature of 200°C for 30 minutes to obtain a magnesium alloy and steel dissimilar metal pipe welding interface with multi-layer multi-modal characteristics.

[0045] The magnesium alloy and steel dissimilar metal pipe weldments obtained by the welding method in this embodiment are used in automotive industry workpieces, aerospace workpieces and electronic products.

[0046] Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

[0047] like Figure 1 As shown, this figure is a microstructure diagram of the Mg-Zn layer, in which the maximum grain size is less than 2 μm, meeting the requirement that the average grain size of the Mg-Zn layer is less than 2 μm;

[0048] like Figure 2 As shown, this figure is a microstructure diagram of the MgZn precipitation phase in the Mg-Zn layer, wherein the dark dots are MgZn precipitation phases, and the maximum size is less than 80nm, which meets the requirement that the size of the MgZn precipitation phase is less than 100nm.

[0049] Example 2

[0050] A magnesium alloy and steel dissimilar metal pipe welding interface with multi-layer multi-modal characteristics, wherein the welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely, a Mg-Zn layer, a Zn layer and a Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and contains a MgZn precipitate phase, the size of the precipitate phase is less than 100 nm, and the average grain size of the Zn layer is less than 2 μm.

[0051] The thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 10 μm, 1 μm, and 4 μm, respectively.

[0052] The Fe-Zn layer contains an iron-zinc compound transition phase.

[0053] That is, in the magnesium alloy and steel dissimilar metal pipe welded forgings, the cross-section has the following structure: base material magnesium alloy / MgZn layer (ultrafine grains + nano-MgZn precipitation phase) / Zn layer (ultrafine grains) / Fe-Zn layer (containing Fe-Zn compounds) / base material steel.

[0054] A method for welding magnesium alloy and steel dissimilar metal pipes capable of forming a multi-layer multi-modal characteristic welding interface comprises the following steps:

[0055] S1: Cleaning the parent material: Grind and clean the cross-section of the welded magnesium alloy and steel parent material tubes; the magnesium alloy material is Mg-Zn alloy, and the steel material is alloy steel; the parent material magnesium alloy and steel are both in tubular shape, with an inner diameter of 4.5 mm, an outer diameter of 6 mm, a length of 10 mm, and a difference of 1.5 mm between the inner and outer diameters. The inner and outer diameters of the magnesium alloy and steel materials are the same;

[0056] S2: preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn; the inner and outer diameters of the Zn-Mg composite intermediate layer are the same as those of the magnesium alloy and the steel base material;

[0057] S3: Fix the welded components: Place the cleaned parent metal and the intermediate layer on the workbench of the rotary ultrasonic welding machine, and form a butt joint structure with magnesium alloy on the upper side and steel on the lower side, with the intermediate layer placed in the center of the butt joint area of ​​the parent metal;

[0058] S4: Welding process: Rotary ultrasonic welding is performed on the fixed welded components. The ultrasonic parameters are: output frequency 20kHz, working power 1000W, amplitude 10μm, and the whole process is divided into three stages: the first stage: 0.5~2s, speed 500r / min; the second stage: 2~4s; speed 1000r / min; the third stage: 4~5s; speed 100r / min; the triggering condition of rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4MPa;

[0059] S5: short-time annealing: the obtained pipe butt weld is annealed at a temperature of 150°C for 20 minutes to obtain a magnesium alloy and steel dissimilar metal pipe welding interface with multi-layer multi-modal characteristics.

[0060] The magnesium alloy and steel dissimilar metal pipe weldments obtained by the welding method in this embodiment are used in automotive industry workpieces, aerospace workpieces and electronic products.

[0061] Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

[0062] Example 3

[0063] A magnesium alloy and steel dissimilar metal pipe welding interface with multi-layer multi-modal characteristics, wherein the welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely, a Mg-Zn layer, a Zn layer and a Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and contains a MgZn precipitate phase, the size of the precipitate phase is less than 100 nm, and the average grain size of the Zn layer is less than 2 μm.

[0064] The thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 40 μm, 4 μm, and 16 μm, respectively.

[0065] The Fe-Zn layer contains an iron-zinc compound transition phase.

[0066] That is, in the magnesium alloy and steel dissimilar metal pipe welded forgings, the cross-section has the following structure: base material magnesium alloy / MgZn layer (ultrafine grains + nano-MgZn precipitation phase) / Zn layer (ultrafine grains) / Fe-Zn layer (containing Fe-Zn compounds) / base material steel.

[0067] A method for welding magnesium alloy and steel dissimilar metal pipes capable of forming a multi-layer multi-modal characteristic welding interface comprises the following steps:

[0068] S1: Cleaning the parent material: Grind and clean the cross-section of the welded magnesium alloy and steel parent material tubes; the magnesium alloy material is Mg-Mn alloy, and the steel material is high alloy steel; the parent material magnesium alloy and steel are both in tubular shape, with an inner diameter of 28mm, an outer diameter of 30mm, and a length of 40mm. The difference between the inner and outer diameters is 2mm, and the inner and outer diameters of the magnesium alloy and steel are the same;

[0069] S2: preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn; the inner and outer diameters of the Zn-Mg composite intermediate layer are the same as those of the magnesium alloy and the steel base material;

[0070] S3: Fix the welded components: Place the cleaned parent metal and the intermediate layer on the workbench of the rotary ultrasonic welding machine, and form a butt joint structure with magnesium alloy on the upper side and steel on the lower side, with the intermediate layer placed in the center of the butt joint area of ​​the parent metal;

[0071] S4: Welding process: Rotary ultrasonic welding is performed on the fixed welded components. The ultrasonic parameters are: output frequency 20kHz, working power 5000W, amplitude 50μm, and the whole process is divided into three stages: the first stage: 0.5~2s, rotation speed 1000r / min; the second stage: 2~4s; rotation speed 2000r / min; the third stage: 4~5s; rotation speed 500r / min; the triggering condition of rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4MPa;

[0072] S5: short-time annealing: the obtained pipe butt weld is annealed at a temperature of 220°C for 1 hour to obtain a magnesium alloy and steel dissimilar metal pipe welding interface with multi-layer multi-modal characteristics.

[0073] The magnesium alloy and steel dissimilar metal pipe weldments obtained by the welding method in this embodiment are used in automotive industry workpieces, aerospace workpieces and electronic products.

[0074] Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

[0075] Example 4

[0076] A welding interface of magnesium alloy and steel dissimilar metal bars with multi-layer and multi-modal characteristics, wherein the welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely, a Mg-Zn layer, a Zn layer and a Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and contains a MgZn precipitate phase, the size of the precipitate phase is less than 100 nm, and the average grain size of the Zn layer is less than 2 μm.

[0077] The thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 15 μm, 2 μm, and 15 μm, respectively.

[0078] The Fe-Zn layer contains an iron-zinc compound transition phase.

[0079] That is, in the welded forgings of magnesium alloy and steel dissimilar metal bars, the cross-section has the following structure: base material magnesium alloy / MgZn layer (ultrafine grains + nano-MgZn precipitation phase) / Zn layer (ultrafine grains) / Fe-Zn layer (containing Fe-Zn compounds) / base material steel.

[0080] A method for welding magnesium alloy and steel dissimilar metal bars capable of forming a multi-layer multi-modal characteristic welding interface comprises the following steps:

[0081] S1: Cleaning the parent material: Grind and clean the cross-section of the welded magnesium alloy and steel parent material rods; the magnesium alloy material is Mg-Zr alloy, and the steel material is high alloy steel; the parent material magnesium alloy and steel are both in the shape of rods, the diameter of the rod is 10mm, the length is 20mm, and the diameters of the magnesium alloy and steel are the same;

[0082] S2: preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn; the diameter of the Zn-Mg composite intermediate layer is the same as that of the magnesium alloy and the steel base material;

[0083] S3: Fix the welded components: Place the cleaned parent metal and the intermediate layer on the workbench of the rotary ultrasonic welding machine, and form a butt joint structure with magnesium alloy on the upper side and steel on the lower side, with the intermediate layer placed in the center of the butt joint area of ​​the parent metal;

[0084] S4: Welding process: Rotary ultrasonic welding is performed on the fixed welded components. The ultrasonic parameters are: output frequency 20kHz, working power 5000W, amplitude 50μm, and the whole process is divided into three stages: the first stage: 0.5~2s, rotation speed 1000r / min; the second stage: 2~4s; rotation speed 2000r / min; the third stage: 4~5s; rotation speed 500r / min; the triggering condition of rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4MPa;

[0085] S5: short-time annealing: the obtained bar butt weld is annealed at a temperature of 220°C for 1 h to obtain a magnesium alloy and steel dissimilar metal bar welding interface with multi-layer multi-modal characteristics.

[0086] The magnesium alloy and steel dissimilar metal bar weldments obtained by the welding method in this embodiment are used in automotive industry workpieces, aerospace workpieces and electronic products.

[0087] Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

[0088] Example 5

[0089] A welding interface of magnesium alloy and steel dissimilar metal bars with multi-layer and multi-modal characteristics, wherein the welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely, a Mg-Zn layer, a Zn layer and a Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and contains a MgZn precipitate phase, the size of the precipitate phase is less than 100 nm, and the average grain size of the Zn layer is less than 2 μm.

[0090] The thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 10 μm, 1 μm, and 4 μm, respectively.

[0091] The Fe-Zn layer contains an iron-zinc compound transition phase.

[0092] That is, in the welded forgings of magnesium alloy and steel dissimilar metal bars, the cross-section has the following structure: base material magnesium alloy / MgZn layer (ultrafine grains + nano-MgZn precipitation phase) / Zn layer (ultrafine grains) / Fe-Zn layer (containing Fe-Zn compounds) / base material steel.

[0093] A method for welding magnesium alloy and steel dissimilar metal bars capable of forming a multi-layer multi-modal characteristic welding interface comprises the following steps:

[0094] S1: Cleaning the parent material: Grind and clean the cross-section of the welded magnesium alloy and steel parent material rods; the magnesium alloy material is Mg-RE alloy, and the steel material is carbon steel; the parent material magnesium alloy and steel are both in the shape of rods, the diameter of the rod is 3mm, the length is 10mm, and the diameters of the magnesium alloy and steel are the same;

[0095] S2: preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn; the diameter of the Zn-Mg composite intermediate layer is the same as that of the magnesium alloy and the steel base material;

[0096] S3: Fix the welded components: Place the cleaned parent metal and the intermediate layer on the workbench of the rotary ultrasonic welding machine, and form a butt joint structure with magnesium alloy on the upper side and steel on the lower side, with the intermediate layer placed in the center of the butt joint area of ​​the parent metal;

[0097] S4: Welding process: Rotary ultrasonic welding is performed on the fixed welded components. The ultrasonic parameters are: output frequency 20kHz, working power 1000W, amplitude 10μm, and the whole process is divided into three stages: the first stage: 0.5~2s, speed 500r / min; the second stage: 2~4s; speed 1000r / min; the third stage: 4~5s; speed 100r / min; the triggering condition of rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4MPa;

[0098] S5: short-time annealing: the obtained bar butt weld is annealed at a temperature of 150°C for 20 min to obtain a magnesium alloy and steel dissimilar metal bar welding interface with multi-layer multi-modal characteristics.

[0099] The magnesium alloy and steel dissimilar metal bar weldments obtained by the welding method in this embodiment are used in automotive industry workpieces, aerospace workpieces and electronic products.

[0100] Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

[0101] Example 6

[0102] A welding interface of magnesium alloy and steel dissimilar metal bars with multi-layer and multi-modal characteristics, wherein the welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely, a Mg-Zn layer, a Zn layer and a Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2 μm, and contains a MgZn precipitate phase, the size of the precipitate phase is less than 100 nm, and the average grain size of the Zn layer is less than 2 μm.

[0103] The thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 40 μm, 4 μm, and 16 μm, respectively.

[0104] The Fe-Zn layer contains an iron-zinc compound transition phase.

[0105] That is, in the welded forgings of magnesium alloy and steel dissimilar metal bars, the cross-section has the following structure: base material magnesium alloy / MgZn layer (ultrafine grains + nano-MgZn precipitation phase) / Zn layer (ultrafine grains) / Fe-Zn layer (containing Fe-Zn compounds) / base material steel.

[0106] A method for welding magnesium alloy and steel dissimilar metal bars capable of forming a multi-layer multi-modal characteristic welding interface comprises the following steps:

[0107] S1: Cleaning the parent material: Grind and clean the cross-section of the welded magnesium alloy and steel parent material rods; the magnesium alloy material is Mg-Al alloy, and the steel material is carbon steel; the parent material magnesium alloy and steel are both in the shape of rods, the diameter of the rod is 15mm, the length is 40mm, and the diameters of the magnesium alloy and steel are the same;

[0108] S2: preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn; the diameter of the Zn-Mg composite intermediate layer is the same as that of the magnesium alloy and the steel base material;

[0109] S3: Fix the welded components: Place the cleaned parent metal and the intermediate layer on the workbench of the rotary ultrasonic welding machine, and form a butt joint structure with magnesium alloy on the upper side and steel on the lower side, with the intermediate layer placed in the center of the butt joint area of ​​the parent metal;

[0110] S4: Welding process: Rotary ultrasonic welding is performed on the fixed welded components. The ultrasonic parameters are: output frequency 20kHz, working power 2000W, amplitude 20μm. The whole process is divided into three stages: the first stage: 0.5~2s, speed 600r / min; the second stage: 2~4s; speed 1800r / min; the third stage: 4~5s; speed 400r / min; the triggering condition of rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4MPa;

[0111] S5: short-time annealing: the obtained bar butt weld is annealed at a temperature of 180°C for 40 min to obtain a magnesium alloy and steel dissimilar metal bar welding interface with multi-layer multi-modal characteristics.

[0112] The magnesium alloy and steel dissimilar metal bar weldments obtained by the welding method in this embodiment are used in automotive industry workpieces, aerospace workpieces and electronic products.

[0113] Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

[0114] Comparative Example 1

[0115] This comparative example records the tensile strength of ultrasonic welding of magnesium alloy and steel dissimilar materials in the prior art, as shown in Table 1 below.

[0116] Table 1 The tensile strength of currently available ultrasonic welding of alloy and steel dissimilar materials

[0117]

[0118] Tube or bar welding tensile test method test standard: GB / T 2651-2008 / ISO 4136:2001.

[0119] 【1】Meng Yu. Microstructure and mechanical properties of magnesium / steel dissimilar metal ultrasonic welding joints[D]. Jilin University, 2024.

[0120] 【2】Chen J, Lim YC, Leonard D, et al. In Situ and Post-MortemCharacterizations of Ultrasonic Spot Welded AZ31B and Coated Dual Phase590Steel Joints[J]. Metals(Basel).2020,10(7):899.

[0121] 【3】Rinker TJ, Pan J, Santella M, et al. Fatigue behavior of dissimilarultrasonic welds in lap-shear specimens of AZ31 and steel sheets[J]. Engineering Fracture Mechanics, 2018, 189(C): 405-426.

[0122] 【4】Santella M, Brown E, Pozuelo M, et al.Details of Mg-Zn reactions inAZ31 to galvanised mild steel ultrasonic spot welds[J].Science and Technology of Welding and Joining, 2012,17(3):219-224.

[0123] Comparative Example 2

[0124] The difference between this comparative example and Example 1 is that the thicknesses of the Mg-Zn layer, the Zn layer and the Fe-Zn layer are 5 μm, 2 μm and 10 μm respectively.

[0125] Comparative Example 3

[0126] The only difference between this comparative example and Example 1 is that the thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 45 μm, 2 μm, and 10 μm, respectively.

[0127] Comparative Example 4

[0128] The only difference between this comparative example and Example 1 is that the thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 20 μm, 5 μm, and 10 μm, respectively.

[0129] Comparative Example 5

[0130] The only difference between this comparative example and Example 1 is that the thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 20 μm, 0.5 μm, and 10 μm, respectively.

[0131] Comparative Example 6

[0132] The only difference between this comparative example and Example 1 is that the thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 20 μm, 2 μm, and 2 μm, respectively.

[0133] Comparative Example 7

[0134] The only difference between this comparative example and Example 1 is that the thicknesses of the Mg-Zn layer, the Zn layer, and the Fe-Zn layer are 20 μm, 2 μm, and 20 μm, respectively.

[0135] Comparative Example 8

[0136] The difference between this comparative example and Example 1 is that the entire process of rotary ultrasonic welding is one stage: that is, 0.5 to 5 s, and the rotation speed is 1000 r / min.

[0137] Comparative Example 9

[0138] The difference between this comparative example and Example 1 is that the entire process of rotary ultrasonic welding is divided into two stages: the first stage: 0.5 to 2 s, the rotation speed is 800 r / min; the second stage: 2 to 5 s, the rotation speed is 1000 r / min.

[0139] Comparative Example 10

[0140] The difference between this comparative example and Example 1 is that the entire process of rotary ultrasonic welding is divided into four stages: the first stage: 0.5-2s, rotation speed 800r / min; the second stage: 2-4s, rotation speed 1500r / min; the third stage: 4-5s, rotation speed 300r / min; the fourth stage: 5-6s, rotation speed 500r / min.

[0141] Comparative Example 11

[0142] The difference between this comparative example and Example 1 is that the entire process of rotary ultrasonic welding is divided into three stages: the first stage: 0.5 to 2 s, rotation speed 400 r / min; the second stage: 2 to 4 s, rotation speed 1500 r / min; the third stage: 4 to 5 s, rotation speed 300 r / min.

[0143] Comparative Example 12

[0144] The difference between this comparative example and Example 1 is that the entire process of rotary ultrasonic welding is divided into three stages: the first stage: 0.5 to 2 s, rotation speed 1200 r / min; the second stage: 2 to 4 s, rotation speed 1500 r / min; the third stage: 4 to 5 s, rotation speed 300 r / min.

[0145] The tensile strength data of the magnesium alloy and steel dissimilar metal tube or bar weldments obtained in Examples 1 to 6 of the present invention and Comparative Examples 2 to 12 are shown in Table 2 below.

[0146] Table 2 Tensile strength data

[0147] Tensile strength(MPa) Example 1 140.8 Example 2 128.6 Example 3 132.7 Example 4 146.9 Example 5 142.9 Example 6 159.2 Comparative Example 2 110.2 Comparative Example 3 106.1 Comparative Example 4 108.2 Comparative Example 5 112.2 Comparative Example 6 102.0 Comparative Example 7 104.1 Comparative Example 8 93.9 Comparative Example 9 98.0 Comparative Example 10 87.8 Comparative Example 11 110.2 Comparative Example 12 112.2

[0148] It should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting the intention that the claimed invention requires more features than those expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in less than all of the features of the previously disclosed embodiments. Therefore, the claims that follow the detailed description are hereby expressly incorporated into the detailed description, with each claim itself serving as a separate embodiment of the present invention.

[0149] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

[0150] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A magnesium alloy and steel dissimilar metal tube or bar welding interface with multi-layer and multi-modal characteristics, characterized in that: The welding interface obtained from the magnesium alloy side to the steel side includes three layers, namely, Mg-Zn layer, Zn layer and Fe-Zn layer, wherein the average grain size of the Mg-Zn layer is less than 2μm, and it contains MgZn precipitation phase, and the size of the precipitation phase is less than 100nm; the average grain size of the Zn layer is less than 2μm; the Fe-Zn layer contains an iron-zinc compound transition phase; the thicknesses of the Mg-Zn layer, Zn layer and Fe-Zn layer are 10~40μm, 1~4μm and 4~16μm, respectively.

2. A welding method for a magnesium alloy and steel dissimilar metal tube or bar welding interface having multi-layer and multi-modal characteristics according to claim 1, characterized in that: The following steps are involved: S1, cleaning the base material: grinding and cleaning the cross section of the welded magnesium alloy, steel base material tube or rod; S2, preparing an intermediate layer: forming a Zn-Mg composite intermediate layer by arranging pure Zn and pure Mg in the order of Zn / Mg / Zn; S3, fixing the welded components: placing the cleaned base metal and the Zn-Mg composite intermediate layer on the workbench of the rotary ultrasonic welding machine, and forming a butt joint structure with magnesium alloy on the upper side and steel on the lower side, and placing the Zn-Mg composite intermediate layer at the center of the butt joint area of ​​the base metal; S4, welding process: the fixed welded components are subjected to rotary ultrasonic welding, and the ultrasonic parameters are: output frequency 20kHz, working power 1000~5000W, amplitude 10~50μm, and the whole process is divided into three stages: the first stage: 0.5~2s, rotation speed 500~1000r / min; the second stage: 2~4s; rotation speed 1000~2000r / min; the third stage: 4~5s; rotation speed 100~500r / min, to obtain the butt weld of the tube or bar; S5, short-time annealing: annealing the obtained tube or bar butt weld to obtain a magnesium alloy and steel dissimilar metal tube or bar welding interface with multi-layer multi-modal characteristics.

3. The welding method according to claim 2, characterized in that: In S1, the magnesium alloy is selected from any one of the Mg-Al, Mg-Zn, Mg-Mn, Mg-Zr and Mg-RE series, and the steel is selected from any one of carbon steel, alloy steel and high alloy steel.

4. The welding method according to claim 2, characterized in that: In S1, the parent material magnesium alloy and steel are both in tubular or rod-like form, the inner diameter of the tube is 4.5 mm to 28 mm, the outer diameter is 6 mm to 30 mm, the length is 10 to 40 mm, and the difference between the inner and outer diameters is 1.5 to 5 mm. The diameter of the rod is 3 to 15 mm, and the length is 10 to 40 mm. The inner and outer diameters or diameters of the magnesium alloy and steel are the same.

5. The welding method according to claim 4, characterized in that: In S2, the inner and outer diameters of the Zn-Mg composite intermediate layer are the same as those of the magnesium alloy and steel.

6. The welding method according to claim 2, characterized in that: In S4, the triggering condition for the rotary ultrasonic welding is that the pressure of the pressure head on the base material to be welded reaches 0.4 MPa.

7. The welding method according to claim 2, characterized in that: In S5, the annealing temperature is 150~220℃ and the time is 20min~1h.

8. A magnesium alloy and steel dissimilar metal pipe or bar weldment obtained by the welding method according to any one of claims 2 to 7, characterized in that: The tensile strength of the weldment reaches over 120MPa.

9. Application of the magnesium alloy and steel dissimilar metal tube or bar weldment according to claim 8 in automotive industry workpieces, aerospace workpieces and electronic products.

10. The use according to claim 9, characterized in that: Automotive industry workpieces include door frames and engine brackets; aerospace workpieces include seat frames, aircraft wings, and landing gear; electronic products include laptop cases, brackets, and mobile phone middle frames.

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