A method for improving the surface corrosion resistance of magnesium alloy components based on strong deformation in-situ powder metallurgy

Abstract

The present invention provides a method for improving the surface corrosion resistance of magnesium alloy components based on strong deformation in-situ powder metallurgy, comprising: cleaning the surface of the magnesium alloy component; adjusting the spindle inclination angle of the welding machine so that the spindle axis and the surface normal of the magnesium alloy component form a set inclination angle; starting a powder feeding device and a cooling device, the powder feeding device is used to press rare earth element powder into the processing part, and the cooling device is used to cool the processing part; starting a friction stir welding machine, controlling the processing tool to press into the magnesium alloy component at a set rotation speed and move along a preset trajectory; stopping and cooling. The present invention can make the surface structure of the component rare earth alloyed, the grains refined, that is, the structure homogenized, effectively improve the corrosion resistance of the surface of the magnesium alloy component, simplify the process flow, save the preparation cost, and at the same time, the method can flexibly adjust the size of the processing tool to realize the processing of magnesium alloy components of different sizes and thicknesses, and has strong feasibility and high flexibility.

Description

Technical Field

[0001] The invention belongs to the technical field of surface modification of magnesium alloy components, and in particular relates to a method for improving the surface corrosion resistance of magnesium alloy components based on strong deformation in-situ powder metallurgy. Background Art

[0002] Studies have shown that the corrosion resistance of magnesium alloys can be effectively improved by adding rare earth elements during smelting. However, the high smelting difficulty and cost also make it difficult to promote and apply this method. Therefore, how to improve the corrosion resistance of magnesium alloys at low cost is an important research direction.

[0003] Friction stir processing (FSP) is a technology for modifying the surface of materials derived from the development of friction stir welding (FSW). As a new type of solid-phase processing technology, friction stir processing uses a high-speed rotating friction stir tool to apply heat-force to the material. The material undergoes severe plastic deformation under high temperature and the organizational state changes. This processing method can achieve grain refinement in specific areas, improve the corrosion resistance and toughness of materials in specific areas, and obtain high-performance components at a lower cost. Therefore, this technology has broad application prospects in the fields of aerospace and engineering machinery, and can be used for surface modification of alloy materials such as aluminum, magnesium, steel, copper, and titanium. However, when conventional friction stir processing technology is applied to the surface of magnesium alloys for modification, although the surface corrosion resistance can be improved to a certain extent by refining the surface grains of the component, the surface organization uniformity of the obtained component is poor, and the effect of improving the surface corrosion resistance is very limited, which has great limitations.

[0004] Existing document CN104999175B discloses a method for adding polytetrafluoroethylene to improve the uniformity of composite materials prepared by stir friction processing, which stores the added powder by presetting blind holes on the surface of the plate, and evenly stirs and distributes the powder in the blind holes in the matrix through stir friction processing, thereby obtaining a uniform intermetallic compound reinforced metal matrix composite material. However, this method cannot achieve the precise distribution of powder on the surface of the plate, and is also limited by the size of the preset blind holes. If the size is too large, it is easy to cause serious thinning of the processing area, and even defects such as grooves may appear on the surface of the plate after processing; if the size is too small, the amount of powder added is limited, which has certain limitations. Existing document CN110052698A discloses a pre-set metal wire stir friction processing method, which opens an installation groove on the parent material, sets the metal wire in the installation groove, and stirs the metal wire and its internal powder into the parent material through stir friction processing, thereby realizing the processing modification of the parent material. This method still uses the slotting method, and the effect of processing modification is limited by the slotting size. In particular, the surface structure uniformity of the modified component is poor, and the process is cumbersome and cannot be realized in engineering applications. Summary of the invention

[0005] The purpose of the present invention is to at least solve the technical problems mentioned in the background technology and to provide a method for improving the surface corrosion resistance of magnesium alloy components based on strong deformation in-situ powder metallurgy.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solution.

[0007] A method for improving the surface corrosion resistance of a magnesium alloy component based on strong deformation in-situ powder metallurgy, comprising:

[0008] Step 1, cleaning the surface of the magnesium alloy component;

[0009] Step 2, fix the cleaned magnesium alloy component, assemble the processing tool on the main shaft of the friction stir welding machine, and adjust the main shaft inclination angle of the welding machine so that the main shaft axis and the surface normal of the magnesium alloy component form a set inclination angle, and the inclination direction is that the processing tool is inclined in the direction opposite to the travel direction;

[0010] Step 3, starting a powder feeding device and a cooling device, wherein the powder feeding device is used to press rare earth element powder into the processing part, and the cooling device is used to cool the processing part;

[0011] Step 4, starting the friction stir welding machine, controlling the processing tool to press into the magnesium alloy component at a set rotation speed, and moving along a preset trajectory;

[0012] Step 5, stop the friction stir welding equipment and turn off the cooling device and the powder feeding device, and place the processed magnesium alloy component in the air to cool to room temperature.

[0013] Furthermore, the processing tool includes a rotating body, a probe is coaxially arranged at the shoulder of the lower end of the rotating body, a worm is arranged in the inner cavity of the rotating body, a vortex groove is arranged at the shoulder, a thread and a discharge hole are arranged on the side wall of the probe, and the discharge hole is communicated with the inner cavity of the rotating body; when the rotating body and the worm rotate and move forward, the rare earth element powder entering the inner cavity continuously moves downward and is pressed into the processing part through the discharge hole.

[0014] In order to further improve the uniformity of the surface structure of the modified component, the probe is in a frustum-shaped structure.

[0015] In order to further improve the uniformity of the surface structure of the modified component, the vortex groove has a groove depth of 0.3-1.0 mm and a width of 1.0-3.0 mm. The vortex groove surrounds the axis of the processing tool and is distributed in a circular array.

[0016] Preferably, the pitch of the thread is 1.0-1.5 mm.

[0017] Preferably, the diameter of the discharge hole is 2.0-3.0 mm.

[0018] In order to further improve the uniformity of the surface structure of the modified component, the inclination angle is 1-3°; in step 4,

[0019] The rotation speed of the processing tool is 500-1000rpm, the forward speed is 200-500mm / min, and the downward pressure is 0.05-0.1mm; the cooling temperature in step 3 is -20℃~0℃.

[0020] Preferably, the particle size d90 of the rare earth element powder is less than 20 μm.

[0021] Preferably, the discharge hole is perpendicular to the main shaft axis.

[0022] In the present invention, the magnesium alloy component is a rolled magnesium alloy component or a magnesium alloy component.

[0023] 1. During the processing, the rare earth element powder is fed into the feeding hole cavity (the inner cavity of the spindle) of the processing tool through the worm. Under the extrusion of the worm, the rare earth element powder is continuously fed downward along the hole cavity, and finally squeezed into the processing area through the discharge hole on the probe; when the processing tool rotates, the thread on the side surface of the probe drives the rare earth element powder to flow to the surface of the component, and the vortex groove at the shoulder drives the surface powder to spread evenly, and metallurgically combines with the magnesium alloy matrix at high temperature, so that the surface structure is rare earth alloyed, the grains are refined, that is, the structure is homogenized, thereby effectively improving the corrosion resistance of the surface of the magnesium alloy component;

[0024] 2. Use processing tools to process and modify the surface of magnesium alloy components. Apply severe plastic deformation to the surface metal of the component to refine the surface grain structure of the component and improve the uniformity of the structure. The surface structure of the component is transformed from the original rolled state to equiaxed grains. Combined with air cooling, rapid cooling is achieved, the high temperature residence time is shortened, and the grain coarsening phenomenon at high temperature is inhibited;

[0025] 3. Compared with the traditional smelting method for preparing corrosion-resistant rare earth magnesium alloy, the present invention greatly reduces the difficulty of preparation, simplifies the process flow, and saves preparation costs. At the same time, the method can flexibly adjust the size of the processing tool to achieve the processing of magnesium alloy components of different sizes and thicknesses. It has strong feasibility, high flexibility, economy and environmental protection, and is suitable for large-scale production applications, which significantly improves the breadth and depth of the application of magnesium alloy stir friction processing;

[0026] 4. During the processing, it can not only effectively prevent the thinning of the processing area, but also greatly reduce the flash formed by the processing material directly squeezed out from under the shaft shoulder, which can ensure the beauty and uniformity of the processing area. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a processing tool in an embodiment;

[0028] Figure 2 Schematic diagram of processing state in the embodiment;

[0029] Figure 3 is a cross-sectional schematic diagram of the processing state in Example 1;

[0030] Figure 4 It is a cross-sectional schematic diagram of the processing state in Example 2. Implementation

[0031] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the description of the following embodiments is only used to help understand the principle and core idea of ​​the present invention, and is not intended to limit the scope of protection of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, improvements made to the present invention also fall within the scope of protection of the claims of the present invention. Example

[0032] First, the processing tool in this embodiment is described. Figure 1 and Figure 2As shown, it includes a rotating body 20, a probe 23 is coaxially arranged at the shoulder 21 at the lower end of the rotating body 20, a worm 3 is arranged in the inner cavity of the rotating body 20, a vortex groove 22 is arranged at the shoulder 21, and a thread 24 and a discharge hole 25 are arranged on the side wall of the probe 23, and the discharge hole 25 is communicated with the inner cavity of the rotating body 20; when the rotating body 20 and the worm 3 rotate and move forward, the rare earth element powder entering the inner cavity continuously moves downward and is pressed into the processing part through the discharge hole 25. Among them: the probe 23 is a frustum-shaped structure; the groove depth of the vortex groove 22 is 0.8mm, the width is 2mm, the vortex groove 22 surrounds the axis of the processing tool and is distributed in a circumferential array; the pitch of the thread 24 is 1.2mm; the diameter of the discharge hole 25 is 2.5mm, and the discharge hole 25 is perpendicular to the axis of the rotating body 20.

[0033] A method for improving the surface corrosion resistance of magnesium alloy components (AZ91, plate thickness 4mm) based on strong deformation in-situ powder metallurgy, combined with Figure 3 As shown, the steps include:

[0034] Step 1, cleaning the surface of the magnesium alloy component 1; specifically: preparing the magnesium alloy component 1, removing impurities and oxide film on the surface of the magnesium alloy component 1 by mechanical grinding with an angle grinder, and then wiping the magnesium alloy component 1 with an organic solvent such as anhydrous ethanol or acetone solution and a cleaning agent to remove oil stains and powder on the surface of the magnesium alloy component 1;

[0035] Step 2: fix the cleaned magnesium alloy component 1, assemble the processing tool on the main shaft of the friction stir welding machine, and adjust the main shaft inclination angle of the welding machine so that the main shaft axis and the surface normal of the magnesium alloy component 1 form a set inclination angle, and the inclination direction is the direction opposite to the moving direction of the processing tool (i.e. Figure 2 The rotating body 20 is tilted by 2° (in the opposite direction of the arrow in the middle), that is, the axis of the rotating body 20 and the surface normal of the magnesium alloy component 1 are tilted by 2°;

[0036] Step 3, start the powder feeding device and cooling device, the powder feeding device is used to press rare earth element powder into the processing part, the rare earth element powder is a mixed powder of zirconium, cerium, neodymium and lanthanum with a particle size d90 less than 20 μm (the weight ratio of zirconium, cerium, neodymium and lanthanum is 1:1:1:1 respectively), and the cooling device is used to cool the processing part, and the cooling temperature is -10°C;

[0037] Step 4, start the friction stir welding machine, control the processing tool to press into the magnesium alloy component 1 at a set rotation speed, the pressing amount is 0.08 mm, that is, the distance between the shoulder 21 and the surface of the magnesium alloy component 1 is 0.08 mm, and move along a preset trajectory; wherein the rotation speed of the processing tool is 600 rpm, and the forward speed is 300 mm / min;

[0038] Step 5, stopping the friction stir welding equipment and closing the cooling device and the powder feeding device, and placing the processed magnesium alloy component 1 in the air to cool to room temperature.

[0039] Referring to the steps in Example 1, the difference from the example is that the axis of the rotating body 20 and the surface normal of the magnesium alloy component 1 are inclined at an angle of 0°, that is, the rotating body 20 is completely perpendicular to the surface of the magnesium alloy component 1. During the processing, the processed material is directly extruded from below the shoulder to form a flash.

[0040] Referring to the steps in Example 1, the difference from the example is that the axis of the rotating body 20 and the surface normal of the magnesium alloy component 1 form an inclination angle of 8°, that is, the rotating body 20 is tilted backward by 8°. The processing area is concave downward, that is, thinning occurs.

[0041] Referring to the steps in Example 1, the difference from the example is that the side wall of the probe 23 has no thread 24. The surface structure uniformity of the processed component is poor, and the distribution of rare earth elements is uneven. Along the depth direction of the component, some areas have high rare earth element content (the rare earth elements are mainly concentrated inside the component and close to the depth of the discharge hole 25), and some areas have basically no rare earth elements (the rare earth elements are not distributed in the 0-1mm area of ​​the surface of the component).

[0042] Referring to the steps in Example 1, the difference between the embodiment 1 and the embodiment 1 is that there is no vortex groove 22 at the shoulder 21. The surface structure uniformity of the processed component is poor, and the rare earth element distribution is uneven. Along the horizontal direction of the surface of the component, some areas have high rare earth element content, some areas have basically no rare earth element, and the areas with high rare earth element content are arranged alternately with the areas with basically no rare earth element.

[0043] Referring to the steps in Example 1, the difference from the example is that the probe 23 is in a smooth cylindrical shape. During the processing, there is instability of the processing tool (such as drifting during rotation), the surface structure uniformity of the processed component is poor, and along the horizontal direction of the surface of the component, some areas have high rare earth element content, some areas have low rare earth element content, and the areas with high rare earth element content are arranged alternately with the areas with low rare earth element content. Example

[0044] First, the processing tool in this embodiment is described. Figure 1 , Figure 2 and Figure 4As shown, it includes a rotating body 20, a probe 23 is coaxially arranged at the shoulder 21 at the lower end of the rotating body 20, a worm 3 is arranged in the inner cavity of the rotating body 20, a vortex groove 22 is arranged at the shoulder 21, and a thread 24 and a discharge hole 25 are arranged on the side wall of the probe 23, and the discharge hole 25 is communicated with the inner cavity of the rotating body 20; when the rotating body 20 and the worm 3 rotate and move forward, the rare earth element powder entering the inner cavity continuously moves downward and is pressed into the processing part through the discharge hole 25. Among them: the probe 23 is a frustum-shaped structure; the groove depth of the vortex groove 22 is 1mm and the width is 3mm. The vortex groove 22 surrounds the axis of the processing tool and is distributed in a circular array; the pitch of the thread 24 is 1mm; the diameter of the discharge hole 25 is 2mm, and the angle between the axis of the discharge hole 25 and the axis of the rotating body 20 is 70°.

[0045] A method for improving the surface corrosion resistance of a magnesium alloy component (LAZ933, plate thickness 3 mm) based on strong deformation in-situ powder metallurgy, comprising the following steps:

[0046] Step 1, cleaning the surface of the magnesium alloy component 1; specifically: preparing the magnesium alloy component 1, removing impurities and oxide film on the surface of the magnesium alloy component 1 by mechanical grinding with an angle grinder, and then wiping the magnesium alloy component 1 with an organic solvent such as anhydrous ethanol or acetone solution and a cleaning agent to remove oil stains and powder on the surface of the magnesium alloy component 1;

[0047] Step 2: fix the cleaned magnesium alloy component 1, assemble the processing tool on the main shaft of the friction stir welding machine, and adjust the main shaft inclination angle of the welding machine so that the main shaft axis and the surface normal of the magnesium alloy component 1 form a set inclination angle, and the inclination direction is the direction opposite to the moving direction of the processing tool (i.e. Figure 2 The rotating body 20 is tilted by 2° (in the opposite direction of the arrow in the middle), that is, the axis of the rotating body 20 and the surface normal of the magnesium alloy component 1 are tilted by 2°;

[0048] Step 3, start the powder feeding device and cooling device, the powder feeding device is used to press rare earth element powder into the processing part, the rare earth element powder adopts a mixed powder of zirconium, cerium, neodymium and lanthanum with a particle size d90 less than 20 μm (the mass ratio of zirconium, cerium, neodymium and lanthanum is 1:1:1:1 respectively), and the cooling device is used to cool the processing part, and the cooling temperature is -5°C;

[0049] Step 4, start the friction stir welding machine, control the processing tool to press into the magnesium alloy component 1 at a set rotation speed, the pressing amount is 0.1 mm, that is, the distance between the shoulder 21 and the surface of the magnesium alloy component 1 is 0.1 mm, and move along a preset trajectory; wherein the rotation speed of the processing tool is 500 rpm, and the forward speed is 230 mm / min;

[0050] Step 5, stopping the friction stir welding equipment and closing the cooling device and the powder feeding device, and placing the processed magnesium alloy component 1 in the air to cool to room temperature.

[0051] During the processing, the rare earth element powder 5 is fed into the feeding hole cavity (the inner cavity of the main shaft) of the processing tool through the worm 3. Under the extrusion action of the worm 3, the rare earth element powder 5 is continuously fed downward along the hole cavity, and finally squeezed into the processing area through the discharge hole on the probe 23; when the processing tool rotates, the thread 24 on the side surface of the probe 23 drives the rare earth element powder 5 to flow to the surface of the component, and drives the surface powder to spread evenly with the help of the vortex groove 22 at the shoulder 21, and metallurgically combines with the magnesium alloy matrix at high temperature, so that the surface structure is rare earth alloyed, the grains are refined, that is, the structure is homogenized, thereby effectively improving the corrosion resistance of the surface of the magnesium alloy component.

[0052] The surface of the magnesium alloy component is processed and modified by processing tools. The surface metal of the component is subjected to severe plastic deformation to refine the surface grain structure of the component and improve the uniformity of the structure. The surface structure of the component is transformed from the original rolled state to equiaxed grains of 3-10μm. Air cooling is used to achieve rapid cooling, shorten the high temperature residence time, and inhibit grain coarsening at high temperature.

[0053] Compared with the traditional smelting method for preparing corrosion-resistant rare earth magnesium alloys, this scheme greatly reduces the preparation difficulty, simplifies the process flow, and saves preparation costs. At the same time, this method can flexibly adjust the size of processing tools to achieve the processing of magnesium alloy components of different sizes and thicknesses. It has strong feasibility, high flexibility, economy and environmental protection, and is suitable for large-scale production applications. It significantly improves the breadth and depth of the application of stir friction processing of magnesium alloys.

[0054] During the processing, it can not only effectively prevent the thinning of the processing area, but also greatly reduce the flash formed by the processing material directly squeezed out from under the shaft shoulder, which can ensure the beauty and uniformity of the processing area.

[0055] In other embodiments, specific parameters can be selected within the following ranges: the groove depth of the vortex groove 22 is 0.3-1.0 mm, the width is 1.0-3.0 mm, the pitch of the thread 24 is 1.0-1.5 mm, the diameter of the discharge hole 25 is 2.0-3.0 mm, and the inclination angle during processing is 1-3°; in step 4, the rotation speed of the processing tool is 500-1000 rpm, the forward speed is 200-500 mm / min, and the downward pressure is 0.05-0.1 mm; the cooling temperature in step 3 is -20°C~0°C.

Claims

1. A method for improving the surface corrosion resistance of magnesium alloy components based on strong deformation in-situ powder metallurgy, characterized in that the steps include: Step 1, cleaning the surface of the magnesium alloy component; Step 2, fix the cleaned magnesium alloy component, assemble the processing tool on the main shaft of the friction stir welding machine, and adjust the main shaft inclination angle of the welding machine so that the main shaft axis and the surface normal of the magnesium alloy component are inclined at a set angle, and the inclination direction is that the processing tool is inclined in the direction opposite to the moving direction, and the inclination angle is 2°; The processing tool comprises a rotating body (20), a probe (23) is coaxially arranged at a shoulder (21) at the lower end of the rotating body (20), a worm (3) is arranged in the inner cavity of the rotating body (20), a vortex groove (22) is arranged at the shoulder (21), the vortex groove (22) has a groove depth of 0.3-1.0 mm and a width of 1.0-3.0 mm, the vortex groove (22) surrounds the axis of the processing tool and is distributed in a circular array, and the side wall of the probe (23) is provided with a worm (3). A thread (24) and a discharge hole (25) are provided, the discharge hole (25) is communicated with the inner cavity of the rotating body (20), and the diameter of the discharge hole (25) is 2.0-3.0 mm; when the rotating body (20) and the worm (3) rotate and move forward, the rare earth element powder entering the inner cavity continuously moves downward and is pressed into the processing part through the discharge hole (25), and the angle between the axis of the discharge hole (25) and the axis of the rotating body (20) is 70°; the probe (23) has a frustum-shaped structure; Step 3, starting a powder feeding device and a cooling device, wherein the powder feeding device is used to press rare earth element powder into the processing part, and the particle size d90 of the rare earth element powder is less than 20 μm, and the cooling device is used to cool the processing part; Step 4, starting the friction stir welding machine, controlling the processing tool to press into the magnesium alloy component at a set rotation speed, and moving along a preset trajectory; In step 4, the rotation speed of the processing tool is 500-1000rpm, the forward speed is 200-500mm / min, and the downward pressure is 0.05-0.1mm; the cooling temperature in step 3 is -20℃~0℃; Step 5, stop the friction stir welding equipment and turn off the cooling device and the powder feeding device, and place the processed magnesium alloy component in the air to cool to room temperature.

2. The method according to claim 1, characterized in that: The pitch of the thread (24) is 1.0-1.5 mm.

3. The method according to claim 1, characterized in that: The magnesium alloy component is a rolled or extruded magnesium alloy component.

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