CN106893881A - A kind of method that zirconium oxide modified graphene strengthens magnesium base composite material - Google Patents

Abstract

A method for reinforcing magnesium-based composite materials with zirconia-modified graphene, comprising the following steps: adding zirconia-modified graphene to ethanol to obtain a ZrO ₂ @GN solution; adding magnesium alloy powder and stirring to obtain a uniformly dispersed mixed slurry, After filtration, vacuum drying, cold pressing and sintering, the ZrO ₂ @GN prefabricated block is obtained, and the ZrO ₂ @GN reinforcement magnesium chips are obtained after cutting; the magnesium alloy is melted, and the preheated reinforcement magnesium chips are added after the furnace charge is completely melted ; When the temperature was adjusted to 550-780°C, mechanical stirring (gas protection) was carried out to obtain a melt with uniform reinforcement dispersion, and finally a ZrO ₂ @GN reinforced magnesium-based composite material was obtained by vacuum suction casting. The invention has the advantages of low process cost, safety and reliability, simple operation, relatively uniform dispersion of modified graphene in the magnesium alloy, good quality of bonding with the interface, good grain refinement effect, excellent composite material performance, and is suitable for industrialized preparation of high-performance graphene / Magnesium-based composites.

Description

A method for zirconia-modified graphene reinforced magnesium-based composites

technical field

The invention belongs to the field of metal composite material preparation, in particular to a preparation method of magnesium-based composite material.

Background technique

In recent years, with the rapid development of aerospace, automotive, electronics, urban transportation and other fields, higher requirements have been put forward for lightweight structural materials. As the most promising lightweight structural material, magnesium alloy composites have received extensive attention and attention due to their high specific strength and specific stiffness, excellent wear resistance, and vibration reduction. Since Graphene (GN) was discovered in 2004, it has been considered to be Ideal reinforcement for magnesium alloys. At present, graphene-reinforced metal matrix composites are still in the initial stage. To prepare high-performance magnesium-based composites, the following three problems need to be solved: one is how to realize the uniformity of graphene in the magnesium matrix; The problem of poor interfacial bonding of the magnesium matrix; the third is how to make graphene maintain its structural integrity during the preparation of composite materials. Zirconia can react with the magnesium matrix at the interface, and the resulting interface product, magnesium oxide, can form a strong interface bond with the magnesium matrix and refine the grain structure of the magnesium matrix. Meanwhile, the interfacial reaction can improve the dispersion of graphene in the magnesium matrix. Therefore, using zirconia to modify the surface of graphene and coating its surface with a uniform layer of zirconia can effectively improve the dispersion of graphene in the magnesium matrix, refine the grain structure, and improve the relationship between graphene and Interfacial bond strength of magnesium matrix.

Contents of the invention

The purpose of the present invention is to provide a method for zirconia-modified graphene to reinforce magnesium-based composite materials.

A method for zirconia-modified graphene-reinforced magnesium-based composite materials according to the present invention comprises the following steps.

(1) Preparation of reinforcement prefabricated blocks.

(a) Add zirconia functionalized graphene (Zirconia functionalized graphene, ZrO ₂ @GN) to an appropriate amount of ethanol, and sonicate for 1-4 hours to obtain a uniformly dispersed zirconia-modified graphene dispersion.

(b) According to the mass ratio of AZ91 magnesium alloy and zirconia-modified graphene 50-100:1-10, add AZ91 magnesium alloy powder with a particle size of less than 325 mesh into the mixed solution obtained in step (a), and mechanically stir for 2-5 hours Finally, a more uniformly dispersed mixed slurry is obtained.

(c) Filter and vacuum-dry the mixed slurry obtained in step (b), transfer it to a mold, and press at room temperature with a pressure of 600-1000 MPa to form a ZrO ₂ @GN reinforcement prefabricated block green body.

(d) Sintering the prefabricated block green body obtained in step (c) at 550-650°C for 2-4h under the protection of argon to obtain a ZrO ₂ @GN reinforced prefabricated block.

(e) Cutting the prefabricated block obtained in step (d) to obtain magnesium chips containing ZrO ₂ @GN reinforcement.

(f) Preheating the magnesium chips obtained in step (e) to 100-150°C for later use.

(2) Melting of composite materials.

(g) When the temperature of the furnace body rises to 200°C, add a certain amount of AZ91 magnesium alloy into the crucible, and evenly sprinkle RJ2 melting covering agent accounting for 1-2% of the weight ratio of the magnesium alloy on the charge, and pass Inject CO ₂ and SF6 protective gas to prevent magnesium from being oxidized during the smelting process. Continue to heat up to 680-750°C. After the charge is completely melted, remove the slag on its surface. After standing for 10-30 minutes, add the preheated magnesium chips containing ZrO ₂ @GN reinforcement in step (1), and wait until it is completely melted Finally, remove the slag on the surface of the melt, and then let it stand for 5-20 minutes to obtain a composite material melt.

(h) After adjusting the melt temperature of the composite material obtained in step (g) to 550-780°C, in a protective atmosphere, perform mechanical stirring and dispersion (stirring speed is 50-300rpm, stirring time is 3-20min) to obtain a reinforced phase More evenly dispersed composite material melt.

(3) Vacuum suction: Adjust the temperature of the composite material melt obtained in step (2) to 580-650°C, and after standing for 5-10 minutes, remove the surface slag, and adopt vacuum suction casting process (vacuum pressure is less than 0.1×10 ^{- 3} MPa, and the holding time is 3-10min) to prepare zirconia-modified graphene-reinforced magnesium-based composites.

The invention has the advantages of low process cost, safety and reliability, simple operation, uniform dispersion of the modified graphene in the magnesium alloy, high bonding strength with the matrix interface, obvious grain refinement effect, excellent performance of the composite material, and is suitable for industrial production of high-performance graphite ene/magnesium based composites.

Description of drawings

Fig. 1 is the SEM morphology of the coated zirconia graphene (ZrO ₂ @GN) reinforcement used in the present invention.

Fig. 2 is the fracture morphology of the ZrO ₂ @GN/AZ91 magnesium alloy prefabricated block prepared under the conditions of Example 1 of the present invention.

Fig. 3 is the microstructure of the AZ91 alloy prepared by the present invention.

Fig. 4 is the microstructure of the 0.3wt.%ZrO ₂ @GN/AZ91 magnesium-based composite material prepared under the conditions of Example 1 of the present invention.

Fig. 5 is the microstructure of the 0.5wt.% ZrO ₂ @GN/AZ91 magnesium-based composite material prepared under the conditions of Example 2 of the present invention.

detailed description

The present invention will be further described through the following examples in conjunction with the accompanying drawings.

Example 1.

Follow the steps below.

(1) Reinforcement prefabricated block preparation: (a) Add 3g of zirconia-modified graphene to 1000ml of ethanol, and ultrasonicate for 2 hours to obtain a uniformly dispersed ZrO ₂ @GN dispersion; (b) 97g of AZ91 magnesium with a particle size of less than 325 mesh Add the alloy powder to the dispersion obtained in step (a), and mechanically stir for 2 hours to obtain a mixed slurry with a relatively uniform dispersion; (c) filter and vacuum-dry the mixed slurry obtained in step (b), then transfer it to a mold, and store it at room temperature The ZrO ₂ @GN reinforcement prefabricated block green body was pressed with a pressure of 600MPa. (d) Sinter the prefabricated block green body obtained in step (c) at 600°C for 3h under the protection of argon to obtain a ZrO ₂ @GN reinforced prefabricated block. (e) Cutting the prefabricated block obtained in step (d) to obtain magnesium chips containing ZrO ₂ @GN reinforcement. (f) Preheating the magnesium chips obtained in step (e) to 100°C for later use.

(2) Composite material smelting: (g) When the temperature of the furnace body rises to 200°C, add 900g of AZ91 alloy into the crucible, and evenly sprinkle 10g of RJ2 covering agent on the charge, and simultaneously pass in CO ₂ and SF6 protection Gas to prevent magnesium from being oxidized during the smelting process. Continue to raise the temperature to 720°C. After the charge is completely melted, remove the slag on its surface. After standing still for 15 minutes, add the preheated magnesium chips in step (1). After it is completely melted, remove the slag on the surface of the melt. Stand still for 10 minutes to obtain a composite material melt. (h) After adjusting the melt temperature of the composite material obtained in step (g) to 650°C, perform mechanical stirring and dispersion in a protective atmosphere (stirring speed is 100rpm, stirring time is 10min) to obtain a composite material with a relatively uniform dispersion of the reinforcing phase melt.

(3) Vacuum suction: adjust the temperature of the composite material melt obtained in step (2) to 620°C, let it stand for 5 minutes, remove the surface slag, and adopt vacuum suction casting process (vacuum pressure is less than 0.1×10 ^-3 MPa, The holding time is 3min) to prepare the zirconia-modified graphene-reinforced magnesium matrix composite (0.3wt.%ZrO ₂ @GN/AZ91).

The mechanical properties of the 0.3wt.%ZrO ₂ @GN/AZ91 composite material were tested. The tensile strength reached 250-270MPa, the elongation rate reached 10.5-13.8%, and the hardness was 70-84HV. It is a composite with excellent mechanical properties. Material.

Example 2.

Follow the steps below.

(1) Preparation of reinforced prefabricated blocks: (a) Add 5g of zirconia-modified graphene to 1500ml of ethanol solution and mix it with 1500ml of ethanol solution, and obtain a uniformly dispersed ZrO ₂ @GN dispersion for 2 hours; (b) Mix 95g of zirconia-modified graphene Add AZ91 magnesium alloy powder to the dispersion obtained in step (a), and mechanically stir for 3 hours to obtain a more uniformly dispersed mixed slurry; (c) filter and vacuum-dry the mixed slurry obtained in step (b) and transfer it to a mold at room temperature The ZrO ₂ @GN reinforcement prefabricated block green body was pressed under the condition of 600MPa. (d) Sinter the prefabricated block green body obtained in step (c) at 600°C for 3h under the protection of argon to obtain a ZrO ₂ @GN reinforced prefabricated block. (e) Cutting the prefabricated block obtained in step (d) to obtain magnesium chips containing ZrO ₂ @GN reinforcement. (f) Preheating the magnesium chips obtained in step (e) to 100°C for later use.

(2) Composite material smelting: (g) When the temperature of the furnace body rises to 200°C, add 900g of AZ91 magnesium alloy into the crucible, and evenly sprinkle RJ2 smelting covering agent with a proportion of 10g of magnesium alloy on the charge, At the same time, CO ₂ and SF6 protective gas are introduced to prevent the oxidation of magnesium during the smelting process. Continue to heat up to 720°C. After the charge is completely melted, remove the slag on its surface. After standing still for 15 minutes, add the preheated magnesium chips containing ZrO ₂ @GN reinforcement in step (1). After it is completely melted, remove The slag on the surface of the melt was left to stand for 5 minutes to obtain a composite material melt. (h) After adjusting the melt temperature of the composite material obtained in step (g) to 650°C, perform mechanical stirring and dispersion in a protective atmosphere (stirring speed is 100rpm, stirring time is 10min) to obtain a composite material with a relatively uniform dispersion of the reinforcing phase melt.

(3) Vacuum suction: adjust the temperature of the composite material melt obtained in step (2) to 620°C, let it stand for 5 minutes, remove the surface slag, and adopt vacuum suction casting process (vacuum pressure is less than 0.1×10 ^-3 MPa, keep Zirconia-modified graphene-reinforced magnesium-based composites (0.5wt.%ZrO ₂ @GN/AZ91) were prepared with a pressing time of 5min.

The mechanical properties of the 0.5wt.%ZrO ₂ @GN/AZ91 composite material were tested. The tensile strength reached 270-305MPa, the elongation rate reached 12-16%, and the hardness was 80-100HV. It is a composite with excellent mechanical properties. Material.

Fig. 1 is the SEM morphology of the coated zirconia graphene (ZrO ₂ @GN) reinforcement used in the present invention. It can be observed in the figure that many nano-ZrO ₂ particles are coated on the surface of flake graphene, and the distribution is relatively uniform, indicating that its modification effect is better.

Fig. 2 is the fracture morphology of the ZrO ₂ @GN/AZ91 magnesium alloy powder prefabricated block prepared under the conditions of Example 1 of the present invention. The figure shows that the graphene nanosheets with wrinkled morphology are clearly visible, indicating that the ZrO ₂ @GN reinforcement is well dispersed in the prefabricated block.

Fig. 3 is the microstructure of the AZ91 alloy prepared by the present invention. Coarse grain structure can be observed in the figure, and a small amount of secondary phase (Mg ₁₇ Al ₁₂ ) can be observed at the boundary.

Fig. 4 is the microstructure of the 0.3wt.%ZrO ₂ @GN/AZ91 magnesium-based composite material prepared under the conditions of Example 1 of the present invention. The figure shows that the grain structure is obviously thinner, and the secondary phase at the boundary is significantly increased (compared with Figure 3), which plays a better fine-grain strengthening. At the same time, the strong interface combination makes the graphene load transfer strengthening mechanism more effective. Composite materials have high mechanical properties.

Fig. 5 is the microstructure of the 0.5wt.% ZrO ₂ @GN/AZ91 magnesium-based composite material prepared under the conditions of Example 2 of the present invention. It can be observed in the figure that the secondary phase in the structure further increases, the grain size is finer, and the strengthening effect of graphene is better.

Claims (1)

1. a kind of method that zirconium oxide modified graphene strengthens magnesium base composite material, it is characterized in that comprising the following steps：

（1）It is prepared by reinforcement prefabricated section：

（a）Zirconium oxide modified graphene is added in appropriate ethanol, ultrasonic 1-4h obtains dispersed oxidation modified zirconia Graphene dispersing solution；

（b）By AZ91 magnesium alloys and the mass ratio 50-100 ﹕ 1-10 of zirconium oxide modified graphene, granularity is less than 325 purposes AZ91 magnesium alloy powders are added to step（a）The more uniform mixing slurry of dispersion is obtained in gained mixed liquor, after mechanical agitation 2-5h Liquid；

（c）To step（b）Gained mixed serum be transferred in mould after filtering+being vacuum dried, and 600- is used under room temperature condition 1000MPa pressure is pressed into the zirconium oxide prefabricated block green body of modified graphene reinforcement；

（d）By step（c）The prefabricated block green body of gained 550-650 DEG C of sintering 2-4h under argon gas protection obtains zirconium oxide modified graphite Alkene reinforcement prefabricated section；

（e）By step（d）Gained prefabricated section carries out machining and obtains the magnesium chips containing zirconium oxide modified graphene reinforcement；

（f）By step（e）Gained magnesium chips be preheated to 100-150 DEG C it is standby；

（2）Composite melting：

（g）When furnace body temperature is increased to 200 DEG C, a certain amount of AZ91 magnesium alloys are added in crucible, and on furnace charge equably Sprinkle and account for magnesium alloy weight than the RJ2 melting covertures for 1-2%, while being passed through CO₂Gas is protected to prevent fusion process with SF6 Middle magnesium is oxidized；680-750 DEG C is continuously heating to, after after furnace charge all fusing, its surface slag is removed, 10-30 min are stood Afterwards, step is added（1）Preheated contains ZrO₂The magnesium chips of@GN reinforcements, until completely melted, removes bath surface slag, 5-20min is stood again obtains Composite Melt；

（h）By step（g）After gained Composite Melt temperature is adjusted to 550-780 DEG C, under protective atmosphere environment, machinery is carried out Dispersed with stirring（Stir speed (S.S.) is 50-300rpm, and mixing time is 3-20min）Obtain the more uniform composite of Dispersion of Reinforcement Melt；

（3）Vacuum is inhaled：By step（2）Gained Composite Melt temperature is adjusted to 580-650 DEG C, after standing 5-10min, removes it Surface slag, using process for suction casting, condition：Vacuum pressure is less than 0.1 × 10^-3MPa, the dwell time is 3-10min, is obtained The enhanced magnesium base composite material of zirconium oxide modified graphene.