CN116240485A - A Method for Improving the High Temperature Friction and Wear Resistance of Friction Stir Welding Stirring Head - Google Patents

Abstract

The invention discloses a method for improving high-temperature friction wear resistance of a friction stir welding stirring head, which comprises the following steps: pretreatment of a stirring head: cleaning and sand blasting; vacuum chamber preparation: vacuumizing and preheating a vacuum chamber; plasma etching: performing high-energy ion bombardment on a workpiece and pre-etching and cleaning a target; a metal bonding layer; a gradient transition layer; a nano-multilayer composite layer; and (5) performing atmosphere protection aging treatment. According to the invention, the high-wear-resistance hard coating is prepared on the surface of the stirring head, the coating structure of the metal bonding layer, the gradient transition layer and the nano multi-layer composite layer is adopted, the process design of aging treatment is matched, the bonding strength of the coating and the stirring head can be effectively improved, meanwhile, the Nb element in the CrN or TiN coating in the surface layer is added to form the nano multi-layer composite layer, the high-temperature wear resistance of the stirring head is obviously improved, and the adhesion problem of low-melting-point metal to the stirring pin in the process of stirring friction welding of dissimilar metal is effectively solved.

Description

A Method for Improving the High Temperature Friction and Wear Resistance of Friction Stir Welding Stirring Head

technical field

The invention relates to the field of material surface modification, in particular to a method for improving the high-temperature friction and wear resistance of a friction stir welding stirring head.

Background technique

As a new solid-phase joining technology, friction stir welding can be used for both ferrous and non-ferrous metals. Compared with the traditional welding method, on the one hand, friction stir welding does not need to add welding wire and shielding gas, and does not generate smoke and spatter during the welding process, which is a relatively environmentally friendly welding method; on the other hand, in the friction stir welding process, The frictional heat between the stirring head and the workpiece makes the metal in a thermoplastic state, which inevitably produces welding residual stress. Due to the low heat input in the friction stir welding process, the residual stress is lower than that of the melting welding joint, and the deformation is smaller.

Stirring head is the key structure of friction stir welding. During the welding process, the stirring head is in direct contact with the weld metal and bears high temperature and stress, which directly affects the weld shape and quality. The material selection and structural design of the stirring head are the key to determine whether the friction stir welding technology can be successfully applied. Especially for aluminum-magnesium alloy thick plates and high melting point alloys, higher requirements are put forward for the high temperature wear resistance of the stirring head. At present, the materials used to make stirring heads mainly include tool steel, superalloy, tungsten-based alloy, and cemented carbide. In recent years, there have been reports on the application of materials such as Si ₃ N ₄ ceramics and polycrystalline cubic boron nitride (PCBN). The application of superhard materials improves the service life of the mixing head, but also brings problems such as difficult processing and high manufacturing costs. In contrast, it is more advantageous to prepare a hard coating on the surface of the tool steel stirring head. In view of the high temperature wear resistance requirements of the stirring head in the friction stir welding process of high melting point metals, and the adhesion of low melting point metals to the stirring pins in the friction stir welding process of dissimilar metals, we propose a method to improve the high temperature resistance of the friction stir welding stirring head. method of friction and wear properties for better weld quality.

Contents of the invention

The invention provides a method for improving the high-temperature friction and wear resistance of a friction stir welding stirring head, with the purpose of improving the high-temperature wear resistance of the stirring head, prolonging the service life and improving the weld seam quality.

To achieve the above object, the inventive method comprises the following steps:

1) Stirring head pretreatment: cleaning, sandblasting

Cleaning: Use 1.5~2.5% volume concentration of HT1170 cleaning agent as the ultrasonic cleaning liquid, and ultrasonically clean the stirring head at a temperature of 55~70°C, a frequency of 70Hz, and a time of 15~30min. After taking it out, put it in a drying oven at 120~160°C Dry in the box for 10~30min.

Sandblasting: use a sandblasting machine to sandblast the mixing head, the medium is 320 mesh white corundum, the pressure is 0.15~0.35MPa, and the time is 60~120S.

2) Vacuum preheating

Fix the stirring head upside down on the workpiece frame, turn on the vacuum system, and when the pressure is lower than 10 ^-3 Pa, turn on the heating system to heat the vacuum chamber to 300~350°C, and continue vacuuming until the pressure is lower than 10 ^-4 Pa.

3) Plasma etching: target pre-etching cleaning, workpiece high-energy ion bombardment

Introduce argon gas, the flow rate is 100~200sccm, the substrate negative bias voltage is 500~1000V, the Cr target or Ti target current is 60~100A, and the target is pre-etched and cleaned and the workpiece is bombarded with high-energy ions.

4) Metal bonding layer

The argon gas flow rate is 400~800sccm, the vacuum chamber pressure is 0.8~1.5Pa, the vacuum chamber temperature is 300~350°C, the substrate negative bias voltage is 5~15V, and the Cr target or Ti target current is 100~200A to prepare the metal bonding layer.

5) Gradient transition layer

The flow rate of argon gas is 50~600sccm, the flow rate of nitrogen gas is 200~1500sccm, the pressure of the vacuum chamber is 1.0~2.0Pa, the temperature of the vacuum chamber is 300~350℃, the negative bias voltage of the substrate is 5~15V, the current of Cr target or Ti target is 100~200A, and the preparation of metal Nitride gradient transition layer.

6) Nano multi-layer composite layer

Nitrogen flow rate 1500~3000sccm, vacuum chamber pressure 5~15Pa, vacuum chamber temperature 300~350℃, substrate negative bias voltage 10~20V, Cr target or Ti target current 150~220A, Nb target current 100~150A, to prepare nano-multilayer composite layer.

7) Atmosphere protection aging treatment

Put the coated stirring head into the vacuum tube annealing furnace, and carry out aging treatment under the protection of nitrogen atmosphere for 3~6h, and the aging temperature is 300~650℃.

Compared with the prior art, the beneficial effects of the present invention are as follows:

Before preparing the coating, sandblasting and ion bombardment are carried out on the mixing head, which can effectively remove defects such as curling, burrs, and rust during mechanical processing, improve surface cleanliness, and generate activation, which helps to improve the coating’s durability. Adhesion. In the preparation of the coating, the metal bonding layer and the gradient transition layer are preferentially prepared on the surface of the workpiece, so as to realize the excessive gradient of hardness and plasticity between the substrate and the nano-multilayer composite layer, and play a better supporting role for the nano-multilayer composite layer; through CrN Or the TiN coating is doped with Nb elements to form a nano-multilayer composite layer, which significantly enhances the high temperature wear resistance of the stirring head. Head sticking problem. After the coating is prepared, the stirring head is subjected to aging treatment to improve the adhesion of the coating through diffusion.

Description of drawings

Fig. 1 is a schematic diagram of the coating structure of the present invention.

Fig. 2 Metallographic structure of the CrN/NbN nanometer multilayer composite layer of the present invention.

Fig. 3 Metallographic structure of CrN/NbN nanometer multilayer composite layer after aging treatment of the present invention.

Detailed ways

The present invention is described in detail below, but it should be pointed out that the implementation of the present invention is not limited to the following embodiments.

Example 1:

A method for improving the high-temperature friction and wear resistance of a friction stir welding stirring head, wherein the material of the stirring head is H13 die steel, and the specific steps are as follows:

1) Mixing head pretreatment

Cleaning: Add 100ml of HT1170 cleaning agent to 4900ml of tertiary pure water, configure it as an ultrasonic cleaning solution with a volume concentration of 2.0%, set the ultrasonic cleaning frequency to 70Hz, and the cleaning temperature to 65°C. Wash the head for 30 minutes. Take it out after cleaning, use argon to blow off the surface cleaning solution, put it in a blast drying oven at 150°C, and dry it for 10 minutes;

Sandblasting: Sandblasting is carried out on the surface of the stirring needle and the shaft shoulder, the medium is 320 mesh white corundum, the pressure is 0.3MPa, and the time is 120S. Before sandblasting, it is necessary to use aluminum foil to cover the assembly position of the mixing head, so as to avoid the decrease of assembly accuracy caused by sandblasting, and the problem of inconsistent rotation and stirring.

2) Vacuum chamber preparation

Use a wire brush and a vacuum cleaner to clean the residual coating and dust on the surface of the heater and lining board. After cleaning, spray a boron nitride release agent on the surface of the heater. According to the coating structure requirements, replace the No. 1 and No. 2 targets with Cr Targets, No. 3 and No. 4 targets were replaced with Nb targets, and No. 1 and No. 2 Cr targets and No. 3 and No. 4 Nb targets were located on the vacuum chamber door and placed oppositely.

3) Vacuum preheating

Insert the stirring head upside down into the base of the planetary structure workpiece holder, ensuring that the stirring needle and the shaft shoulder are higher than the edge of the base and are not blocked. Use a tooling trolley to send the workpiece rack into the vacuum chamber, wipe the sealing strip of the vacuum chamber with dust-free paper dipped in alcohol, close the vacuum chamber door, and turn on the vacuum system. When the pressure is lower than 10 ^-3 Pa, set the workpiece rack speed to 2r/ min, turn on the heating system, heat the vacuum chamber to 350°C, and continue to evacuate until the pressure is lower than 10 ^-4 Pa.

4) Plasma etching

The vacuum chamber is filled with argon gas, the flow rate is set to 180sccm, the vacuum chamber pressure is 0.4Pa, the substrate negative bias voltage is 900V, and the Cr target current is 80A, and the target material is pre-etched and cleaned and the workpiece is bombarded with high-energy ions. During the plasma etching process, in order to prevent the stirring head from being overheated by ion bombardment, the No. 1 and No. 2 Cr targets need to be carried out intermittently in sequence, the etching (bombardment) time is 40S, the intermittent time is 10S, and the cycle is 5 times.

5) Cr bonding layer

Set the argon gas flow rate to 600sccm, the vacuum chamber pressure to 1.2Pa, the vacuum chamber temperature to 350°C, the substrate negative bias voltage to 5V, the Cr target current in groups 1 and 2 to 200A, and the workpiece frame speed to 2r/min to prepare the metal Cr bonding layer for 20 minutes.

6) CrN gradient transition layer

Set the vacuum chamber pressure to 1.5Pa, the vacuum chamber temperature to 350°C, the No. 1 and No. 2 Cr target currents to 200A, and the workpiece rack speed to 2r/min to prepare the CrN gradient transition layer. The process includes:

① The flow rate of argon gas is 400, nitrogen gas is 300, the negative bias voltage of the substrate is 5V, and the time is 10min;

②Argon gas flow rate 200, nitrogen gas 800, substrate negative bias voltage 10V, time 10min;

③Argon gas flow rate is 50, nitrogen gas is 1500, substrate negative bias voltage is 15V, and time is 10 minutes.

7) CrN/NbN nanometer multilayer composite layer

Turn off the argon gas, set the nitrogen flow rate to 2600sccm, the vacuum chamber pressure to 8Pa, the vacuum chamber temperature to 350°C, the substrate negative bias voltage to 15V, the No. 1 and No. 2 Cr target currents to 200A, the No. 3 and No. 4 Nb target currents to 135A, and the workpiece holder speed to 4r/min , to prepare the CrN/NbN nanometer multilayer composite layer for 5 hours, the metallographic structure of the coating is shown in Figure 2, and the magnification is 500 times.

8) Atmosphere protection aging treatment

After the coating is finished, take out the stirring head, put it into a vacuum tube annealing furnace, and carry out aging treatment for 4 hours under the protection of a nitrogen atmosphere. The aging temperature is 550°C. The phase organization is shown in Figure 3 with a magnification of 200 times.

Through the above process, the coating structure is 0.8~1.0umCr bonding layer, 1.2~1.4umCrN gradient transition layer, 8.0~12umCrN/NbN nano-multilayer composite layer, the surface hardness reaches 1950~2100HV _0.2 , and the thickness is 6061-T6 at 8.0mm In the friction stir butt welding of aluminum alloy, the stirring pin has no obvious wear and coating peeling phenomenon.

Example 2:

A method for improving the high-temperature friction and wear resistance of a friction stir welding stirring head, wherein the material of the stirring head is 6542 high-speed tool steel, and the specific steps are as follows.

1) Mixing head pretreatment

Cleaning: Add 100ml of HT1170 cleaning agent to 4900ml of tertiary pure water, configure it as an ultrasonic cleaning solution with a volume concentration of 2.0%, set the ultrasonic cleaning frequency to 70Hz, and the cleaning temperature to 65°C. Wash the head for 30 minutes. Take it out after cleaning, use argon to blow off the surface cleaning solution, put it in a blast drying oven at 150°C, and dry it for 10 minutes;

Sandblasting: Sandblasting is carried out on the surface of the stirring needle and the shaft shoulder, the medium is 320 mesh white corundum, the pressure is 0.2MPa, and the time is 80S. Before sandblasting, it is necessary to use aluminum foil to cover the assembly position of the mixing head, so as to avoid the decrease of assembly accuracy caused by sandblasting, and the problem of inconsistent rotation and stirring.

2) Vacuum chamber preparation

Use a wire brush and a vacuum cleaner to clean the residual coating and dust on the surface of the heater and lining board. After cleaning, spray boron nitride release agent on the surface of the heater. According to the coating structure requirements, replace the No. 1 and No. 3 targets with Ti Targets, No. 2 and No. 4 targets are replaced by Nb targets, No. 1 and No. 3 Ti targets and No. 2 and No. 4 Nb targets are located on the vacuum chamber door and placed alternately.

3) Vacuum preheating

Insert the stirring head upside down into the base of the planetary structure workpiece holder, ensuring that the stirring needle and the shaft shoulder are higher than the edge of the base and are not blocked. Use a tooling trolley to send the workpiece rack into the vacuum chamber, wipe the sealing strip of the vacuum chamber with dust-free paper dipped in alcohol, close the vacuum chamber door, and turn on the vacuum system. When the pressure is lower than 10 ^-3 Pa, set the workpiece rack speed to 2r/ min, turn on the heating system, heat the vacuum chamber to 330°C, and continue to evacuate until the pressure is lower than 10 ^-4 Pa.

4) Plasma etching

The vacuum chamber is filled with argon gas, the flow rate is set to 150sccm, the vacuum chamber pressure is 0.3Pa, the substrate negative bias voltage is 700V, and the Ti target current is 70A. The target is pre-etched and cleaned and the workpiece is bombarded with high-energy ions. During the plasma etching process, in order to prevent the stirring head from being overheated by ion bombardment, Ti targets No. 1 and No. 2 should be carried out intermittently in sequence. The etching (bombardment) time is 30S, the intermittent time is 10S, and the cycle is 3 times.

5) Ti binding layer

Set the argon gas flow rate to 400sccm, the vacuum chamber pressure to 1.0Pa, the vacuum chamber temperature to 330°C, the substrate negative bias voltage to 5V, the Ti target current in groups 1 and 2 to 150A, and the workpiece frame speed to 2r/min to prepare the metal Ti bonding layer for 20 minutes. Layer thickness 0.6~0.8um.

6) TiN gradient transition layer

Set the vacuum chamber pressure to 1.2Pa, the vacuum chamber temperature to 330°C, the No. 1 and No. 2 Ti target currents to 150A, and the workpiece rack speed to 2r/min to prepare a TiN gradient transition layer. The process includes:

①Argon gas flow rate 300, nitrogen gas 300, substrate negative bias voltage 5V, time 10min;

②Argon gas flow rate 200, nitrogen gas 600, substrate negative bias voltage 10V, time 10min;

③Argon gas flow rate is 100, nitrogen gas is 1100, substrate negative bias voltage is 15V, and time is 10 minutes.

7) TiN/NbN nano-multilayer composite layer

Turn off the argon gas, set the nitrogen flow rate to 1700sccm, the vacuum chamber pressure to 5Pa, the vacuum chamber temperature to 330°C, the substrate negative bias voltage to 15V, the No. 1 and No. 2 Ti target currents to 180A, the No. 3 and No. 4 Nb target currents to 110A, and the workpiece holder speed to 4r/min , prepare TiN/NbN nanometer multi-layer composite layer, time 3h, coating thickness 7.0~9.0um.

8) Atmosphere protection aging treatment

After the coating is finished, take out the stirring head, put it into a vacuum tube annealing furnace, and carry out aging treatment for 4 hours under the protection of nitrogen atmosphere. The aging temperature is 450°C.

Through the above process, the coating structure is 0.6~0.8umTi bonding layer, 1.0~1.2umTiN gradient transition layer, 7.0~9.0umTiN/NbN nano-multilayer composite layer, the surface hardness reaches 1800HV _0.2 , aluminum steel dissimilar metal friction stir welding process The adhesion problem of medium aluminum alloy to the stirring pin has been significantly improved.

Claims (4)

1. A method for improving friction stir welding stirring head high temperature friction and wear resistance, characterized in that, comprising the following steps: 1) Stirring head pretreatment: cleaning, sandblasting Cleaning: Use 1.5~2.5% volume concentration of HT1170 cleaning agent as the ultrasonic cleaning liquid, and ultrasonically clean the stirring head at a temperature of 55~70°C, a frequency of 70Hz, and a time of 15~30min. After taking it out, put it in a drying oven at 120~160°C Dry in the box for 10~30min; Sandblasting: use a sandblasting machine to sandblast the mixing head, the medium is 320 mesh white corundum, the pressure is 0.15~0.35MPa, and the time is 60~120S; 2) Vacuum chamber preparation: vacuuming, chamber preheating Fix the stirring head upside down on the workpiece rack, turn on the vacuum system, and when the pressure is lower than 10 ^-3 Pa, turn on the heating system to heat the vacuum chamber to 300~350°C, and continue vacuuming until the pressure is lower than 10 ^-4 Pa; 3) Plasma etching: target pre-etching cleaning, workpiece high-energy ion bombardment Introduce argon gas, the flow rate is 100~200sccm, the vacuum chamber pressure is 0.2~0.8MPa, the substrate negative bias voltage is 500~1000V, the Cr target or Ti target current is 60~100A, and the target is pre-etched and cleaned and the workpiece is bombarded with high-energy ions; 4) Metal bonding layer The argon gas flow rate is 400~800sccm, the vacuum chamber pressure is 0.8~1.5Pa, the vacuum chamber temperature is 300~350°C, the substrate negative bias voltage is 5~15V, and the Cr target or Ti target current is 100~200A to prepare the metal bonding layer; 5) Gradient transition layer The flow rate of argon gas is 500~600sccm, the flow rate of nitrogen gas is 200~1500sccm, the pressure of the vacuum chamber is 1.0~2.0Pa, the temperature of the vacuum chamber is 300~350℃, the negative bias voltage of the substrate is 5~15V, the current of Cr target or Ti target is 100~200A, and the preparation of metal Nitride gradient transition layer; 6) Nano multi-layer composite layer Nitrogen flow rate 1500~3000sccm, vacuum chamber pressure 5~10Pa, vacuum chamber temperature 300~350℃, substrate negative bias voltage 10~20V, Cr target or Ti target current 150~220A, Nb target current 100~150A, to prepare nano-multilayer Composite layer; 7) Atmosphere protection aging treatment Put the coated stirring head into the vacuum tube annealing furnace, and carry out aging treatment under the protection of nitrogen atmosphere for 3~6h, and the aging temperature is 300~550℃. 2. A method for improving the high temperature friction and wear resistance of a friction stir welding stirring head according to claim 1, characterized in that: in the process 3) plasma etching, the Cr target or Ti target is carried out intermittently, and the etching (Bombardment) time 30~50S, intermittent time 10~20S, cycle 3~5 times. 3. A method for improving the high temperature friction and wear resistance of a friction stir welding stirring head according to claim 1, characterized in that: in the process 5) in the nanometer multilayer composite layer, the Cr target or Ti target and the Nb target are in the same Placed opposite or alternately. 4. A method for improving the high temperature friction and wear resistance of a friction stir welding stirring head according to claim 1, characterized in that: in the process 6) in the atmosphere protection aging treatment, the heating and cooling speed of the tubular annealing furnace is not greater than 10°C/min.

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