Surface-modified rare earth magnesium alloy and preparation method thereof

Abstract

The invention provides a surface-modified rare earth magnesium alloy and a preparation method thereof. AlSi10Mg alloy powder and nano TiB2 ceramic particles are fully mixed to form alloy powder, and the alloy powder is used as laser to be cladded on the surface of a rare earth magnesium alloy base material. The structure of the obtained laser cladding layer is in a dendritic structure form, crystal grains are refined, the structure of a bonding area of the laser cladding layer and the rare earth magnesium alloy base material is directionally-growing dendrites, and the laser cladding layer and the rare earth magnesium alloy base material are in a co-production crystallization characteristic, so that good metallurgical bonding is formed between the cladding layer and the rare earth magnesium alloy base material; therefore, the hardness, wear resistance and corrosion resistance of the surface of the rare earth magnesium alloy are improved, and the application range of the rare earth magnesium alloy is widened.

Description

Technical Field

[0001] The invention relates to the technical field of alloys, in particular to a surface-modified rare earth magnesium alloy. Background Art

[0002] The density of magnesium alloy is about 1.74 g / cm 3 , only 2 / 3, 1 / 3 and 1 / 4 of aluminum, titanium and steel, and is the lightest structural material among engineering metals. In addition, magnesium alloys have many excellent properties such as good electrical and thermal conductivity, excellent electromagnetic shielding and damping and vibration reduction performance, and good biocompatibility, and are known as the "21st century green engineering materials". With the development of science and technology, magnesium alloys have shown significant application value in aerospace, national defense, military, and biomedicine.

[0003] In the field of aerospace and defense, magnesium alloys have been used in key mechanical parts such as satellites and spacecrafts due to their excellent electromagnetic shielding and elastic modulus, making them irreplaceable engineering materials in the aerospace and defense industries. However, the low absolute strength and room temperature plasticity of traditional magnesium alloys limit their wide application in the aerospace field. In recent years, rare earth magnesium alloys have attracted the attention of many researchers due to their superior physical and chemical properties, but their lower hardness and poor wear and corrosion resistance limit their wider application.

[0004] Common surface modification technologies for magnesium alloys include electroplating, anodizing, thermal spraying, ion implantation and laser cladding. Laser cladding technology achieves selective local strengthening of the workpiece surface by precisely controlling energy transfer. It is suitable for workpieces with complex shapes and can be automatically controlled. Compared with traditional methods, laser cladding technology has the characteristics of fine and dense organization, small heat-affected area, small deformation after treatment, and higher efficiency. Therefore, it is widely used in the field of surface modification.

[0005] At present, there are few studies on the surface modification of rare earth magnesium alloys at home and abroad, and they are mainly focused on using traditional metal powders as cladding materials, and the effect of improving surface properties has reached a bottleneck. Therefore, how to use better cladding materials for the surface modification of rare earth magnesium alloys has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to propose a rare earth magnesium alloy and a preparation method thereof, in which the alloy powder obtained by fully mixing AlSi10Mg alloy powder and nano-TiB2 ceramic particles is used as a coating to cover the surface of a rare earth magnesium alloy, so as to improve the surface hardness, wear resistance and corrosion resistance of the rare earth magnesium alloy.

[0007] To achieve the above object, the present invention proposes a surface-modified rare earth magnesium alloy, in which alloy powder obtained by fully mixing AlSi10Mg alloy powder and nano-TiB2 ceramic particles is laser clad on the surface of a rare earth magnesium alloy substrate.

[0008] The present invention also provides a method for preparing a surface-modified rare earth magnesium alloy, comprising the following steps: S1: weigh AlSi10Mg alloy powder and TiB2 nano-ceramic particles; S2: placing AlSi10Mg alloy powder and TiB2 nano-ceramic particles in a ball mill and stirring and mixing them thoroughly; S3: Drying the mixed alloy powder; S4: preheating the surface of the rare earth magnesium alloy substrate; S5: grinding, cleaning and drying the surface of the preheated rare earth magnesium alloy substrate in sequence; S6: removing the oxide film on the surface of the rare earth magnesium alloy substrate and performing surface passivation treatment; S7: using the alloy powder as a cladding material to perform laser cladding on the surface of the treated rare earth magnesium alloy substrate; The laser cladding conditions are as follows: laser output power is 1.2~1.5 kW, laser scanning speed is 8~12 mm / s, spot diameter is 1.3~1.8 mm, and powder feeding amount is 1.3~1.6 g / min; laser cladding is carried out in an inert atmosphere.

[0009] Furthermore, the particle size of the TiB2 nano-ceramic particles is 50 nm.

[0010] Furthermore, in S2, the mass ratio of nano-TiB2 ceramic particles was 0.3-0.5%, the ball mill speed was 150 r / min, the mixing time was 6 h, and the reverse rotation was performed every 30 min.

[0011] Furthermore, in S3, the drying temperature is 80-100°C and the time is 6-8 h.

[0012] Furthermore, in S4, the preheating temperature of the rare earth magnesium alloy substrate is 100-120°C.

[0013] Furthermore, in S5, polishing is performed using 220#, 400#, and 800# SiC metallographic sandpapers in sequence, and cleaning is performed using anhydrous ethanol.

[0014] Compared with the prior art, the advantages of the present invention are: 1. The present invention uses AlSi10Mg alloy powder and TiB2 nano-ceramic particles as the surface coating of rare earth magnesium alloy. Compared with the traditional coating, the alloy coating with TiB2 nano-ceramic particles is thicker and the types of intermetallic compounds are increased. No cracks are found at the interface between the covering layer and the transition layer and the transition layer and the magnesium matrix. In addition, due to the presence of the transition layer, the magnesium matrix can be effectively prevented from diluting the top covering layer, so the hardness and corrosion resistance of the coating can be further improved. At the same time, the laser cladding layer is more compact and the pores in the coating are significantly reduced.

[0015] 2. In the preparation method, the present invention preheats the rare earth magnesium alloy to effectively prevent the generation of cracks during the laser cladding process; low-power laser cladding is used to reduce the thermal stress between the laser cladding layer and the rare earth magnesium alloy substrate, avoid the formation of hard and brittle intermetallic compounds at the interface between the cladding layer and the substrate, and prevent the rare earth magnesium alloy substrate from collapsing, excessive melting and burning through due to excessive heating temperature; the laser cladding layer obtained has a dendritic structure morphology, and the grains are refined. The bonding area between the laser cladding layer and the rare earth magnesium alloy substrate is a dendrite that grows in a directional manner, and has a co-crystallization feature with the rare earth magnesium alloy substrate, so that a good metallurgical bond is formed between the cladding layer and the rare earth magnesium alloy substrate, thereby improving the hardness, wear resistance and corrosion resistance of the surface of the rare earth magnesium alloy, thereby expanding its application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the surface morphology of the AlSi10Mg powder reinforced with nano-TiB2 ceramic particles in Example 1; Figure 2 This is a cross-sectional morphology diagram of the laser cladding layer in Example 1; Figure 3 This is a comparison chart of the hardness of the laser cladding layer and the rare earth magnesium alloy substrate in Example 1; Figure 4 This is a comparison diagram of the wear resistance of the laser cladding layer and the rare earth magnesium alloy substrate in Example 1; Figure 5 This is a comparison diagram of the polarization curves of the laser cladding layer and the rare earth magnesium alloy substrate in Example 1. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be further described below.

[0018] Embodiment 1: The present invention provides a method for reinforcing aluminum-based coating on the surface of rare earth magnesium alloy with nano-ceramic particles, wherein alloy powder obtained by fully mixing commercial AlSi10Mg alloy powder with nano-TiB2 ceramic particles is used as cladding material to perform laser cladding on the surface of a pretreated magnesium rare earth alloy substrate, thereby obtaining a surface-modified rare earth magnesium alloy; The preparation method is as follows: S1: Weigh AlSi10Mg alloy powder and TiB2 nano-ceramic particles; in this embodiment, the AlSi10Mg alloy powder is AlSi10Mg alloy powder prepared by vacuum atomization protection method provided by Jiangxi Baohang New Materials Co., Ltd., and the powder particle size is 80 μm. The alloy powder includes 8.0% Si, 1% Mg and the balance Al.

[0019] The nano-ceramic particles are commercial TiB2 nano-scale ceramic particles with a particle size of 50 nm.

[0020] S2: Place AlSi10Mg alloy powder and TiB2 nano-ceramic particles into a ball mill and stir and mix them thoroughly. The ball mill speed is 150 r / min, the mixing time is 6 h, and the ball mill rotates in the opposite direction every 30 min. During the mixing process, the powder state in the ball mill should be checked regularly to avoid powder sticking.

[0021] S3: Drying the mixed alloy powder; the drying temperature is 100 °C and the time is 8 h.

[0022] S4: preheating the surface of the rare earth magnesium alloy substrate; the preheating temperature is 120°C, which can effectively prevent the generation of cracks during the laser cladding process. In this embodiment, the magnesium alloy substrate is VW94 magnesium alloy in the Mg-Gd-Y series of rare earth magnesium alloys; in terms of mass fraction, the magnesium alloy includes 7% Gd, 5.5% Y, 0.5% Zr, 2.5% Zn and the remainder Mg.

[0023] S5: The surface of the preheated rare earth magnesium alloy substrate is polished, cleaned and dried in sequence; the polishing is preferably performed by using 220#, 400# and 800# SiC metallographic sandpaper in sequence. In this embodiment, the cleaning is performed by using anhydrous ethanol; the drying is performed by using a hot air blower.

[0024] S6: By adopting a combination of physical and chemical methods to remove the oxide film and surface passivation treatment, the oxide film on the surface of the rare earth magnesium alloy substrate is completely removed, eliminating the harmful effects of the oxide film; S7: Laser cladding the alloy powder as cladding material on the treated rare earth alloy substrate surface; the laser output power is 1.2 kW, the laser scanning speed is 8 mm / s, the spot diameter is 1.8 mm, and the powder feeding amount is 1.6 g / min.

[0025] Laser cladding is preferably carried out in an inert atmosphere, and the inert atmosphere is preferably high-purity Ar gas; the flow rate of the high-purity Ar gas is preferably 15 L / min. In the present invention, by protecting the laser molten pool with high-purity argon gas and optimizing the laser cladding process parameters, the oxidation of the molten metal and the formation of defects such as pores are prevented, such as Figure 1 and Figure 2 As shown, a well-formed, pore-free, crack-free, and firmly bonded cladding layer can be obtained on the surface of the rare earth magnesium alloy substrate.

[0026] In order to further discuss the technical effect of the present invention, the laser cladding layer in this embodiment is compared with the substrate, and the cross-sectional microhardness distribution of the obtained sample is shown in FIG. Figure 3 As shown. The hardness value of the cladding layer is about 150 HV 0.1 It is worth noting that there is a hardness peak at the transition zone, reaching about 260 HV 0.1 , while the hardness of the matrix is ​​only about 85 HV 0.1 The friction coefficient (COF) curves of the two samples are shown in Figure 4 The results show that the average COF of the substrate is about 0.5, while the average COF of the cladding layer is about 0.3. This comparison highlights the different tribological behaviors exhibited by the two materials. The cladding layer exhibits a lower friction coefficient due to its more uniform and finer microstructure. Figure 5 The potentiodynamic polarization curves of the substrate and cladding layer exposed to 3.5 wt.% NaCl solution are shown. Polarization curve analysis shows that the corrosion potential of the cladding surface is -1.108 V, which is significantly higher than the -1.725 V of the substrate. These results indicate that the cladding layer is more stable in the corrosive medium and effectively inhibits the dissolution of magnesium. Therefore, the corrosion resistance of the substrate is significantly improved.

[0027] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the content of the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. A surface-modified rare earth magnesium alloy, characterized in that: The alloy powder obtained by fully mixing AlSi10Mg alloy powder and nano-TiB2 ceramic particles is laser clad on the surface of rare earth magnesium alloy substrate.

2. A method for preparing a surface-modified rare earth magnesium alloy, comprising preparing the surface-modified rare earth magnesium alloy according to claim 1, characterized in that: The following steps are involved: S1: weigh AlSi10Mg alloy powder and TiB2 nano-ceramic particles; S2: placing the AlSi10Mg alloy powder and the TiB2 nano-ceramic particles in a ball mill and stirring and mixing them thoroughly; S3: Drying the mixed alloy powder; S4: preheating the surface of the rare earth magnesium alloy substrate; S5: grinding, cleaning and drying the surface of the preheated rare earth magnesium alloy substrate in sequence; S6: removing the oxide film and performing surface passivation treatment on the surface of the rare earth magnesium alloy substrate; S7: using the alloy powder as a cladding material to perform laser cladding on the treated surface of the rare earth magnesium alloy substrate; The laser cladding conditions are as follows: laser output power of 1.2-1.5 kW, laser scanning speed of 8-12 mm / s, spot diameter of 1.3-1.8 mm, and powder feeding amount of 1.3-1.6 g / min; the laser cladding is carried out in an inert atmosphere.

3. The method for preparing a surface-modified rare earth magnesium alloy according to claim 2, characterized in that: The particle size of the TiB2 nano-ceramic particles is 50 nm.

4. The method for preparing a surface-modified rare earth magnesium alloy according to claim 2, characterized in that: In S2, the mass ratio of the nano-TiB2 ceramic particles is 0.3-0.5%, the ball mill speed is 150 r / min, the mixing time is 6 h, and the reverse rotation is performed every 30 min.

5. The method for preparing a surface-modified rare earth magnesium alloy according to claim 2, characterized in that: In S3, the drying process is carried out at a temperature of 80-100°C and for a time of 6-8 hours.

6. The method for preparing a surface-modified rare earth magnesium alloy according to claim 2, characterized in that: In S4, the preheating temperature of the rare earth magnesium alloy substrate is 100-120°C.

7. The method for preparing a surface-modified rare earth magnesium alloy according to claim 2, characterized in that: In S5, the grinding is performed using 220#, 400#, and 800# SiC metallographic sandpapers in sequence, and the cleaning is performed using anhydrous ethanol.

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