Magnesium alloy die casting and preparation method and application thereof

Abstract

The invention provides a magnesium alloy die casting and a preparation method and application thereof, and belongs to the technical field of alloys, the magnesium alloy die casting comprises a magnesium alloy matrix and a composite layer prepared on the surface of the magnesium alloy matrix by using a plasma spraying technology; the composite layer comprises nickel powder and modified titanium dioxide, and the mass ratio of the nickel powder to the modified titanium dioxide is (1.7-1.9): 1. The method can effectively improve the long-term corrosion resistance of the prepared magnesium alloy die casting.

Description

Technical Field

[0001] The invention belongs to the technical field of alloys, and in particular relates to a magnesium alloy die casting and a preparation method and application thereof. Background Art

[0002] Magnesium alloys are lightweight and recyclable, and are widely used in electronic equipment, automobiles, and other fields, gradually becoming an ideal material for modern industrial products. Magnesium alloys have excellent shock absorption properties, can efficiently absorb road vibration energy, and reduce the impact transmitted to the vehicle body. Due to the strong damping, vibration reduction, and dryness reduction capabilities of magnesium alloys, magnesium alloy die castings can be used as shock absorber bottom cylinders in shock absorbers of electric tricycles or electric two-wheelers.

[0003] Magnesium alloy itself has poor corrosion resistance and is easily corroded in humid / salt spray environments; the nickel layer can improve the corrosion resistance of magnesium alloy to a certain extent in the short term by physically isolating the corrosive medium and using the passivation properties of nickel to slow down the corrosion rate (for example, the corrosion resistance time can reach more than 72 hours in a standard salt spray test).

[0004] However, as the time in the humid / salt spray environment increases, the potential difference between nickel and magnesium is large, forming a strong galvanic pair, and the conventional nickel layer is prone to micropores / damage, which will form a local corrosion cell and accelerate the pitting / corrosion of the substrate. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a magnesium alloy die casting and a preparation method and application thereof, which can effectively improve the long-term corrosion resistance of the prepared magnesium alloy die casting.

[0006] In order to achieve the above-mentioned purpose, in a first aspect, the present invention provides a magnesium alloy die-casting, comprising a magnesium alloy substrate and a composite layer prepared on the surface of the magnesium alloy substrate using plasma spraying technology; the composite layer comprises nickel powder and modified titanium dioxide, and the mass ratio of the nickel powder to the modified titanium dioxide is (1.7-1.9):1.

[0007] Furthermore, the preparation method of the modified titanium dioxide is as follows: A1. Add 750-800 mL of 9-10 mol / L sodium hydroxide solution into a three-necked flask, then add 18-20 g of nano titanium dioxide, and stir to obtain a mixture; A2, heating the mixture obtained in A1 to reflux to obtain a reactant; A3. After centrifugation, the reactant obtained in A2 is washed with distilled water until it becomes neutral, and dried to obtain modified titanium dioxide.

[0008] Furthermore, in A1, the stirring speed is 300-360 r / min, and the stirring time is 15-20 min.

[0009] Further, in A2, the mixture is heated to 100°C, and refluxed at 100°C for 10-12 h.

[0010] Furthermore, in A3, the drying temperature is 96-100° C., and the drying time is 50-70 min.

[0011] Furthermore, the magnesium alloy matrix comprises the following components in mass percentage: the magnesium alloy matrix comprises the following components in mass percentage: 0.4%-0.42% Si, 0.05%-0.065% Al, 0.02-0.04% RE, 0.01%-0.012% Mn, 0.01%-0.015% Zn and 0.009%-0.011% Ca, the remainder being Mg and unavoidable impurities; the RE comprises La and / or Ce.

[0012] In a second aspect, the present invention provides a method for preparing the above-mentioned magnesium alloy die casting, comprising the following steps: S1. Weighing raw materials according to the proportion of components in the magnesium alloy matrix, smelting, and casting to obtain a magnesium alloy ingot, and then melting and die-casting the magnesium alloy ingot to obtain a magnesium alloy matrix; S2. Polishing and grinding the surface of the magnesium alloy substrate, ultrasonically cleaning, and drying to obtain a pretreated substrate; S3, mixing nickel powder with modified titanium dioxide, ball milling for 3.5-4.5 hours to achieve uniform dispersion, and then drying in a vacuum oven at 80±2℃ for 11-12 hours to obtain composite powder; S4. Using plasma spraying, the composite powder obtained in S3 is sprayed on the pre-treated substrate obtained in S2, and then placed in a sintering furnace for vacuum sintering to obtain a magnesium alloy die casting.

[0013] Furthermore, in S4, the plasma spraying power is controlled at 35-45 kW, the working gas is a mixture of argon and hydrogen, the spraying distance is 90-100 mm, the argon flow rate is 42-47 L / min, the hydrogen flow rate is 5-6 L / min, the powder feeding amount is 30-40 g / min, and the preheating temperature is 120-130 °C.

[0014] Further, in S4, the temperature in the sintering furnace is raised to 410-460°C at a rate of 10°C / min and kept at this temperature for 0.6-1h. The vacuum degree in the sintering furnace is less than 1×10 -2 Pa.

[0015] In a third aspect, the present invention provides an application of the above-mentioned magnesium alloy die-casting, which is used in a shock absorber of an electric tricycle or an electric two-wheeled vehicle.

[0016] This application has the following beneficial effects: The invention comprises a magnesium alloy substrate and a composite layer prepared on the surface of the magnesium alloy substrate by using a plasma spraying technology; the composite layer comprises nickel powder and modified titanium dioxide.

[0017] Nano-titanium dioxide fills the gaps in nickel powder and forms a "brick-mud" structure after plasma spraying, which reduces the porosity. The semiconductor properties of titanium dioxide are between those of nickel and magnesium, which can construct a step-type potential gradient and reduce the local current density, which is beneficial to the improvement of long-term corrosion resistance.

[0018] Nano-titanium dioxide is soaked in sodium hydroxide solution and refluxed to make modified titanium dioxide. On the one hand, the surface hydroxylation density increases, which enhances the chemical bonding with nickel powder; and the reflux treatment induces phase transformation, and the layered structure is more conducive to blocking the diffusion path of the corrosive medium. On the other hand, the excess -OH groups on the surface of modified titanium dioxide can form a hydrogen bond network with the corrosion products, prompting the corrosion area to form a dense complex salt layer, achieving a self-repairing effect, and then synergistically improving the long-term corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 , a comparison trend chart of average corrosion rate test data of the test pieces of Examples 1 to 3 and Comparative Examples 1 to 5 in the test examples of the present invention immersed in 3.5% sodium chloride solution at 25°C for 45 days. DETAILED DESCRIPTION

[0020] The present application is further described in detail below with reference to the embodiments.

[0021] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0022] Example 1: (1) Preparation of modified titanium dioxide, the preparation method is as follows: A1. Add 780 mL of 9.5 mol / L sodium hydroxide aqueous solution into a three-necked flask, then add 19 g of nano titanium dioxide, stir at a speed of 320 r / min, and stir for 18 min to obtain a mixture. Among them, nano titanium dioxide (AEROXIDE P25-2) has a purity of 99.5% and an average particle size of 21 nm, and is purchased from Borida (Dongguan) New Materials Co., Ltd.

[0023] A2. Heat the mixture obtained in A1 to 100°C, and reflux at 100°C for 11 h to obtain the reactant.

[0024] A3. After centrifuging the reactant obtained in A2 (8000 r / min), wash it with distilled water until it is neutral, and then place it in a drying oven for drying at a temperature of about 98°C and a drying time of 100 minutes to obtain modified titanium dioxide.

[0025] (2) Preparing a magnesium alloy die casting, the preparation method comprising the following steps: S1. Prepare a magnesium alloy matrix, which includes the following components by mass percentage: 99.45% Mg, 0.415% Si, 0.059% Al, 0.023% Ce, 0.012% La, 0.012% Mn, 0.015% Zn and 0.011% Ca, and the remainder is inevitable impurities. The specific preparation method is the existing technology, first weighing the raw materials according to the component ratio in the magnesium alloy matrix, then smelting, and then casting to obtain a magnesium alloy ingot, and then melting the magnesium alloy ingot and die-casting it to obtain a magnesium alloy matrix.

[0026] S2. The surface of the magnesium alloy substrate was polished and ground. Specifically, rough polishing was performed first: 400 mesh abrasive belt, linear speed 15 m / s, feed rate 0.1 mm / pass; then fine polishing was performed: 2000 mesh diamond grinding paste, pressure 0.2 MPa, Ra ≤ 0.8 μm. Ultrasonic cleaning was performed using a cleaning agent (acetone-ethanol volume ratio 1:1 mixture), ultrasonic frequency 40 kHz, and cleaning time 15 min. Drying was performed in a hot air circulation drying oven at 80°C for 30 min to obtain a pretreated substrate.

[0027] S3. Mix nickel powder and modified titanium dioxide in a mass ratio of 1.8:1, and use a planetary ball mill (zirconia jar and grinding balls) for ball milling, with a ball-to-material ratio of 10:1, a rotation speed of 240 rpm, and pause for 5 minutes every 30 minutes to prevent overheating. The ball milling is performed for a total of 8 hours to achieve uniform dispersion. Then dry in a vacuum oven at about 80°C for 11.5 hours to obtain a composite powder. Among them, the particle size of the nickel powder is 5-10μm, which was purchased from Zhuyu New Material Technology Co., Ltd.

[0028] S4, plasma spraying, the composite powder obtained in S3 is sprayed on the pre-treated substrate obtained in S2, the plasma spraying power is controlled at 40 kW, the working gas is a mixed gas of argon and hydrogen, the spraying distance is 100 mm, the flow rate of argon is 45 L / min, the flow rate of hydrogen is 5 L / min, the powder feeding amount is 35 g / min, and the preheating temperature of the pre-treated substrate is 125 ° C. Then put it into the sintering furnace for vacuum sintering, specifically, the temperature in the sintering furnace is raised to 420 ° C at 10 ° C / min, and the temperature is kept for 0.8 h. The vacuum degree in the sintering furnace is less than 1×10 -2 Pa, and finally cooled to 150 ° C in the furnace and filled with high-purity argon gas to eventually form a composite layer (about 52μm), thus obtaining a magnesium alloy die-casting.

[0029] Embodiment 2: The difference between this embodiment and embodiment 1 is that a magnesium alloy die casting is prepared, and the preparation method thereof comprises the following steps: S1. Prepare a magnesium alloy matrix, which includes the following components by mass percentage: 99.45% Mg, 0.415% Si, 0.059% Al, 0.023% Ce, 0.012% La, 0.012% Mn, 0.015% Zn and 0.011% Ca, and the remainder is inevitable impurities. The specific preparation method is the existing technology, first weighing the raw materials according to the component ratio in the magnesium alloy matrix, then smelting, and then casting to obtain a magnesium alloy ingot, and then melting the magnesium alloy ingot and die-casting it to obtain a magnesium alloy matrix.

[0030] S2. Polishing and grinding the surface of the magnesium alloy substrate, ultrasonic cleaning, and drying to obtain a pretreated substrate.

[0031] S3. Mix nickel powder and modified titanium dioxide in a mass ratio of 1.7:1, ball mill for 3.5 hours to achieve uniform dispersion, and then dry in a vacuum oven at about 80°C for 11 hours to obtain composite powder.

[0032] S4, plasma spraying, the composite powder obtained in S3 is sprayed on the pre-treated substrate obtained in S2, the plasma spraying power is controlled at 40 kW, the working gas is a mixed gas of argon and hydrogen, the spraying distance is 100 mm, the flow rate of argon is 45 L / min, the flow rate of hydrogen is 5 L / min, the powder feeding amount is 35 g / min, and the preheating temperature of the pre-treated substrate is 125 ° C. Then put it into the sintering furnace for vacuum sintering, specifically, the temperature in the sintering furnace is raised to 420 ° C at 10 ° C / min, and the temperature is kept for 0.8 h. The vacuum degree in the sintering furnace is less than 1×10 -2 Pa, and finally after cooling to 150°C in the furnace, high-purity argon gas is filled in to finally form a composite layer to obtain a magnesium alloy die-casting.

[0033] Embodiment 3: The difference between this embodiment and embodiment 1 is that: a magnesium alloy die casting is prepared, and the preparation method thereof comprises the following steps: S1. Prepare a magnesium alloy matrix, which includes the following components by mass percentage: 99.45% Mg, 0.415% Si, 0.059% Al, 0.023% Ce, 0.012% La, 0.012% Mn, 0.015% Zn and 0.011% Ca, and the remainder is inevitable impurities. The specific preparation method is the existing technology, first weighing the raw materials according to the component ratio in the magnesium alloy matrix, then smelting, and then casting to obtain a magnesium alloy ingot, and then melting the magnesium alloy ingot and die-casting it to obtain a magnesium alloy matrix.

[0034] S2. Polishing and grinding the surface of the magnesium alloy substrate, ultrasonic cleaning, and drying to obtain a pretreated substrate.

[0035] S3. Mix nickel powder and modified titanium dioxide in a mass ratio of 1.9:1, ball mill for 4.5 hours to achieve uniform dispersion, and then dry in a vacuum oven at about 80°C for 12 hours to obtain composite powder.

[0036] S4, plasma spraying, the composite powder obtained in S3 is sprayed on the pre-treated substrate obtained in S2, the plasma spraying power is controlled at 40 kW, the working gas is a mixed gas of argon and hydrogen, the spraying distance is 100 mm, the flow rate of argon is 45 L / min, the flow rate of hydrogen is 5 L / min, the powder feeding amount is 35 g / min, and the preheating temperature of the pre-treated substrate is 125 ° C. Then put it into the sintering furnace for vacuum sintering, specifically, the temperature in the sintering furnace is raised to 420 ° C at 10 ° C / min, and the temperature is kept for 0.8 h. The vacuum degree in the sintering furnace is less than 1×10 -2 Pa, and finally after cooling to 150°C in the furnace, high-purity argon gas is filled in to finally form a composite layer to obtain a magnesium alloy die-casting.

[0037] Comparative Example 1: The difference between this comparative example and Example 1 is that the composite layer is deleted (the composite powder is deleted, and the magnesium alloy matrix is ​​a magnesium alloy die-casting).

[0038] Comparative Example 2: This comparative example differs from Example 1 in that the modified titanium dioxide is deleted (the composite powder is replaced by nickel powder).

[0039] Comparative Example 3: The difference between this comparative example and Example 1 is that the composite powder includes nickel powder and nano-titanium dioxide, and the mass ratio of nickel powder to nano-titanium dioxide is 2.2:1.

[0040] Comparative Example 4: The difference between this comparative example and Example 1 is that the composite powder includes nickel powder and nano-titanium dioxide, and the mass ratio of nickel powder to nano-titanium dioxide is 1.8:1.

[0041] Comparative Example 5: The difference between this comparative example and Example 1 is that in the composite powder, the mass ratio of nickel powder to modified titanium dioxide is 2.2:1.

[0042] Test example: Test object: Test pieces were prepared from Example 1 to Example 3 and Comparative Example 1 to Comparative Example 5. Test method: Weight m1 in dry environment, weight m2 obtained by drying after soaking in 3.5% sodium chloride solution at 25°C for 45 days, average corrosion rate = (m1-m2) / 30 / surface area of ​​test piece. Test results: See Table 1.

[0043] Table 1. Test data of the experimental example

[0044] Result analysis: Analyze Example 1-Example 3 and combine the data in Table 1 and Figure 1It can be seen that the average corrosion rate test data of the magnesium alloy die castings (test pieces) prepared by the present invention (Example 1-Example 3) immersed in 3.5% sodium chloride solution at 25°C for 45 days is as low as 0.40 mg·cm -2 ·d -1 The following fully meets the application requirements on shock absorbers of electric tricycles or electric two-wheelers.

[0045] Analyze Example 1 and Comparative Examples 1-5 and combine the data in Table 1 and Figure 1 By comparing Comparative Example 1 with Comparative Example 2, it can be seen that compared with Comparative Example 1, Comparative Example 2 adds a nickel layer, and the average corrosion rate is 0.59 mg·cm -2 ·d -1 (Comparative Example 1) increased to 0.63 mg cm -2 ·d -1 (Comparative Example 2) shows that the preparation of the nickel layer by (nickel powder) plasma technology actually leads to an increase in the average corrosion rate of the magnesium alloy die-casting (specimen) immersed in a 3.5% sodium chloride solution at 25°C for 45 days; that is, simply adding a nickel layer will cause the long-term corrosion resistance of the magnesium alloy specimen to decrease instead of increase.

[0046] This is because the corrosion resistance of magnesium alloy itself is poor and it is easy to corrode in a humid / salt spray environment; the nickel layer can improve the corrosion resistance of magnesium alloy to a certain extent in the short term by physically isolating the corrosive medium. However, as the time in the humid / salt spray environment increases (increased to 45 days in this test case), the potential difference between nickel and magnesium is large, forming a strong galvanic pair, and the conventional nickel layer is prone to micropores / damage, which will form a local corrosion cell, and instead begin to accelerate the pitting / corrosion of the substrate, ultimately causing the long-term corrosion resistance of the magnesium alloy specimen to decrease instead of increase.

[0047] By comparing Comparative Example 3 with Comparative Example 4, it can be seen that the addition of nano-titanium dioxide to nickel powder to prepare composite powder and then using ion technology to prepare the composite layer can reduce the average corrosion rate of the magnesium alloy die casting (test piece) immersed in 3.5% sodium chloride solution at 25°C for 45 days; that is, the addition of nano-titanium dioxide to nickel powder can improve the long-term corrosion resistance of the magnesium alloy test piece. Moreover, the improvement effect of the mass ratio of nickel powder to nano-titanium dioxide of 2.2:1 (Comparative Example 3) is significantly greater than the mass ratio of the two of 1.8:1 (Comparative Example 4).

[0048] This is because nano-titanium dioxide fills the gaps in nickel powder, forming a "brick-mud" structure after plasma spraying, which reduces the porosity; and the semiconductor properties of titanium dioxide are between nickel and magnesium, which can construct a step-type potential gradient to reduce the local current density. Only when the proportion of nickel powder is high enough can the conductive network of the composite layer be complete enough to better avoid local charge accumulation; if the proportion of nickel powder is low, it will not be conducive to better improvement of corrosion resistance.

[0049] By comparing Comparative Example 5 with Example 1, it can be seen that the modified titanium dioxide made of nano-titanium dioxide can produce a synergistic effect with nickel powder to synergistically improve the long-term corrosion resistance of the magnesium alloy test piece. In addition, the synergistic improvement effect of the mass ratio of nickel powder to modified titanium dioxide of 1.8:1 (Example 1) is significantly greater than that of the mass ratio of the two of 2.2:1 (Comparative Example 5).

[0050] This is because when nano titanium dioxide is made into the modified titanium dioxide of the present invention, on the one hand, the surface hydroxylation density increases, which enhances the chemical bonding with the nickel powder; and the reflux treatment induces phase transformation, and the layered structure is more conducive to blocking the diffusion path of the corrosive medium. On the other hand, the excess -OH groups on the surface of the modified titanium dioxide can form a hydrogen bond network with the corrosion products, prompting the formation of a dense complex salt layer in the corrosion area to achieve a self-healing effect. Only when the proportion of modified titanium dioxide is high enough can it better play a synergistic role with nickel powder and better exert its self-healing ability; if the proportion of modified titanium dioxide is low, it will not be conducive to better improvement of long-term corrosion resistance.

[0051] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0052] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A magnesium alloy die casting, characterized in that: It comprises a magnesium alloy substrate and a composite layer prepared on the surface of the magnesium alloy substrate by using plasma spraying technology; the composite layer comprises nickel powder and modified titanium dioxide, and the mass ratio of the nickel powder to the modified titanium dioxide is (1.7-1.9):

1.

2. The magnesium alloy die casting according to claim 1, characterized in that: The preparation method of the modified titanium dioxide is as follows: A1. Add 750-800 mL of 9-10 mol / L sodium hydroxide solution into a three-necked flask, then add 18-20 g of nano titanium dioxide, and stir to obtain a mixture; A2, heating the mixture obtained in A1 to reflux to obtain a reactant; A3. After centrifugation, the reactant obtained in A2 is washed with distilled water until it becomes neutral, and dried to obtain modified titanium dioxide.

3. The magnesium alloy die casting according to claim 2, characterized in that: In A1, the stirring speed is 300-360 r / min, and the stirring time is 15-20 min.

4. The magnesium alloy die casting according to claim 2, characterized in that: In A2, the mixture was heated to 100°C and refluxed at 100°C for 10-12 h.

5. The magnesium alloy die casting according to claim 2, characterized in that: In A3, the drying temperature is 96-100°C and the drying time is 50-70 minutes.

6. The magnesium alloy die casting according to claim 1, characterized in that: The magnesium alloy matrix includes the following components by mass percentage: 0.4%-0.42% Si, 0.05%-0.065% Al, 0.02-0.04% RE, 0.01%-0.012% Mn, 0.01%-0.015% Zn and 0.009%-0.011% Ca, and the balance is Mg and unavoidable impurities; the RE includes La and / or Ce.

7. A method for preparing a magnesium alloy die casting according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, weighing raw materials, melting, casting, and melt die-casting to obtain a magnesium alloy matrix; S2. Polishing and grinding the surface of the magnesium alloy substrate, ultrasonically cleaning, and drying to obtain a pretreated substrate; S3, mixing nickel powder with modified titanium dioxide, ball milling for 3.5-4.5 hours to achieve uniform dispersion, and then drying in a vacuum oven at 80±2℃ for 11-12 hours to obtain composite powder; S4. Using plasma spraying, the composite powder obtained in S3 is sprayed on the pre-treated substrate obtained in S2, and then placed in a sintering furnace for vacuum sintering to obtain a magnesium alloy die casting.

8. The method for preparing a magnesium alloy die casting according to claim 7, characterized in that: In S4, the plasma spraying power is controlled at 35-45 kW, the working gas is a mixture of argon and hydrogen, the spraying distance is 90-100 mm, the argon flow rate is 42-47 L / min, the hydrogen flow rate is 5-6 L / min, the powder feeding amount is 30-40 g / min, and the preheating temperature is 120-140 °C.

9. The method for preparing a magnesium alloy die casting according to claim 7, characterized in that: In S4, the temperature in the sintering furnace is raised to 410-460°C at a rate of 10°C / min and kept at this temperature for 0.6-1h. The vacuum degree in the sintering furnace is less than 1×10 -2 Pa.

10. An application of the magnesium alloy die casting according to any one of claims 1 to 6, characterized in that: Used in shock absorbers of electric tricycles or electric two-wheelers.

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