CN116005039B - A kind of foamed aluminum and preparation method thereof - Google Patents

Abstract

The invention discloses foamed aluminum and a preparation method thereof, and belongs to the technical field of foamed aluminum manufacture. The method mixes the reinforcing phase with the plastic metal powder before foaming to form the modified reinforcing phase with plastic metal wrapping on the surface, then mixes the modified reinforcing phase with the raw material matrix, and wraps the reinforcing phase with metal with better plasticity in a large range, so that the reinforcing phase can be combined with the metal powder compactly in the pressing process of preparing the foamed aluminum by a powder metallurgy method, the compactness is improved, and the subsequent foaming is facilitated. The prepared foam aluminum precursor has high density, and the foam aluminum has good compression performance due to improved wettability of the reinforcing phase and the matrix.

Description

A kind of foamed aluminum and preparation method thereof

Technical Field

The invention belongs to the technical field of foam aluminum manufacturing, and more specifically, relates to foam aluminum and a preparation method thereof.

Background Art

Foam aluminum is a porous structural functional integrated material that integrates multiple excellent functions such as light weight, energy absorption, shock absorption, cushioning, sound insulation, heat insulation, electromagnetic shielding, etc. It meets the system's weight reduction, structural load-bearing and multi-functional comprehensive needs, and has broad development and application prospects in the future aerospace, automobile manufacturing, rail transit and other fields.

Improving the compressive strength of aluminum foam is one of the important ways to expand the application of aluminum foam. The foaming time of aluminum foam prepared by powder metallurgy is generally short, and it is difficult to achieve in-situ self-generation of reinforcing phases in a short foaming process by controlling the composition of the matrix. Therefore, the mechanical properties of aluminum foam materials are currently mainly improved by adding reinforcing phases. The reinforcing phases mainly include ceramic particles, whiskers and short fibers. Compared with the reinforcing phases generated by in-situ reactions, the added reinforcing phases have worse chemical compatibility and wettability with the matrix, resulting in poor reinforcement effect. In the process of preparing aluminum foam by melt foaming, although the reinforcing phase is added as the second phase, the reinforcing phase and the matrix are combined through solid-liquid bonding, and the bonding interface has good wettability; in contrast, when preparing aluminum foam by powder metallurgy, the added reinforcing phase can only be physically combined with the matrix through solid-solid bonding, and the wettability is poor. However, the powder metallurgy method has outstanding advantages in the preparation of aluminum foam fillings and special-shaped parts. In order to expand the advantages, it is an important innovation point worthy of research to improve its mechanical properties by improving the wettability of the added reinforcing phase and the aluminum foam matrix. Although some studies have reported that the wetting performance between the reinforcement phase and the substrate can be improved by plating metal on the outer surface of the reinforcement phase, the operation process is relatively complicated.

After searching, the patent publication number is CN101798665A, and the invention name is a method for preparing an aluminum-based foam material. First, a layer of metal is plated on the surface of the carbon fiber, and the carbon fiber with the metal coating is added to the aluminum or aluminum alloy melt, and then titanium hydride is added and stirred evenly. After foaming, it is taken out and cooled to obtain a carbon fiber-reinforced aluminum-based foam material. The present invention introduces carbon fiber into the preparation of the foam aluminum material, and realizes the stability of the bubbles and the improvement of the material performance. Compared with the prior art, the compression strength of the foam aluminum material prepared by the present invention is higher than 6MPa, the impact toughness is increased by about 30%, and the energy absorption capacity is increased by more than 50%. However, the electroplating process is complicated, and a large amount of acid, alkali, heavy metals and flammable, explosive and dangerous chemicals are used in the electroplating process, and waste water, waste gas and waste residue that are harmful to human health and pollute the environment are generated; similarly, the chemical plating process is complicated, and the composition of the plating solution will also cause pollution to the environment. In addition, the coating thickness obtained by the two processes is relatively thin, which is not conducive to the formation of intermetallic compounds between the reinforcement phase and the foam aluminum.

In addition, the patent publication number is CN105624451A, and the invention name is a high-strength and high-toughness foamed aluminum and its preparation method. The density of the foamed aluminum is 0.4-1g/ ^cm3 , the average size of the pores is 2-5mm, and the pore wall is composed of an aluminum matrix and reinforced particles uniformly dispersed therein, and the reinforced particles and the aluminum matrix form a high-strength metallurgical interface. First, the aluminum matrix powder, the reinforced particles and the foaming agent particles are uniformly mixed and cold-pressed into a rough blank, and the rough blank is heat-degassed by vacuum heat and then heat-deformed to form a foamable preform, and the foamed aluminum is obtained by heating and foaming. The aluminum matrix powder and the reinforced particles are mixed according to a volume percentage of 3-25% of the reinforced particles. Large plastic deformation helps the aluminum matrix and the reinforced particles to achieve a high-strength metallurgical interface, thereby improving the wettability of the reinforced particles and the molten aluminum matrix during the foaming process, reducing particle segregation, and helping to obtain a foamed aluminum with uniform particle distribution. The patent publication number is CN109321787A, and the invention name is a method for preparing an aluminum-based composite material. Plastically deformable metal particles are used as carriers, and ball milling is performed together with _TiH2 and a reinforcing phase, so that _TiH2 and the reinforcing phase are embedded and adsorbed on the carrier to prepare a foamed mixture; aluminum or aluminum alloy melt is placed in a crucible, and at a specified temperature, an appropriate amount of the foamed mixture wrapped in aluminum foil is added, and high-speed stirring is performed; the stirring device is taken out, and the crucible is subjected to heat preservation deposition; after reaching the specified heat preservation deposition time, the crucible is taken out and cooled to obtain an aluminum-based composite material at the bottom of the foam. In the above scheme, the metal particles, the reinforcing phase and the foaming agent particles are first uniformly mixed to obtain a foamed mixture. The disadvantage is that the obtained reinforcement material has extremely uneven pore distribution, and the upper part is a foam layer and the lower part is an aluminum-based composite material without a foam layer; and the reinforcing phase is mixed with the metal particles together with the foaming agent, resulting in incomplete coating of the reinforcing phase, which is not conducive to the formation of intermetallic compounds between the reinforcing phase and the foamed metal.

Summary of the invention

1. Problem to be solved

In view of the problem of poor wettability between a reinforcing phase and a foamed aluminum matrix in the process of preparing foamed aluminum by the existing powder metallurgy method, the present invention provides a foamed aluminum and a preparation method thereof, wherein the reinforcing phase prepared by the method has good wettability with the foamed aluminum matrix.

2. Technical solution

In order to solve the above problems, the technical solution adopted by the present invention is as follows:

The present invention provides a method for preparing foamed aluminum, and the specific steps are as follows:

Step S1, pretreatment of the reinforcement phase: the reinforcement phase and the plastic metal powder are mixed uniformly in a certain mass ratio, and then briquetting is performed, crushing and sieving to obtain a reinforcement phase with a certain particle size and the outer surface of which is coated with the plastic metal, which is recorded as a modified reinforcement phase;

The reinforcing phase is one of ceramic particles, whiskers or short fibers. The ceramic particles are SiC or _Al2O3 particles with a particle size of _200-400 meshes; the whiskers are mullite or spinel whiskers with a diameter of 0.2-0.5 μm and an aspect ratio of 20-60; the short fibers are carbon fibers with a length of 20-80 μm. The particle reinforcing phase mainly plays a reinforcing role by being evenly dispersed in the matrix due to the high strength of the ceramic particles; the whiskers and fibers mainly utilize the high aspect ratio of the reinforcing phase to be evenly interwoven in the matrix to achieve a mesh reinforcing effect. The plastic metal powder is selected from one or more of aluminum, copper, magnesium or tin powder, and it forms an intermetallic compound with an aluminum alloy with a melting point of 400-550°C, so that before foaming, the intermetallic compound first melts to wet the reinforcing phase. The particle size of the plastic metal powder ranges from 500 to 800 meshes, which is smaller than the particle size of the reinforcing phase, and can ensure to the greatest extent that the outer surface of the reinforcing phase is completely wrapped by the plastic metal with a smaller particle size. The mass ratio of the reinforcing phase to the plastic metal powder is 1:(2-6). If there is too much reinforcing phase, the coating rate is low, resulting in a low performance improvement rate; if there is too much plastic metal powder, the amount of reinforcing phase added is relatively low, which also results in a low performance improvement rate. Compared with the prior art [Ma Youcao. Preparation of carbon nanotube reinforced aluminum foam composite material by rapid powder metallurgy foaming method and its compression performance [D]. Tianjin University.], in which carbon nanotubes are directly coated on the surface of aluminum foam matrix, the present invention uses ceramic phase as reinforcing phase, and the reinforcing effect is more significant.

Since the raw material matrix for preparing foamed aluminum by powder metallurgy is metal powder, it is necessary to press before foaming to obtain a foamed precursor with higher density; since the added reinforcing phase and the matrix can only be physically bonded to each other through solid-solid physical bonding when preparing foamed aluminum by powder metallurgy, the bonding force is poor, resulting in low density of the foamed precursor. Therefore, the present invention mixes the reinforcing phase with plastic metal powder before foaming to form a reinforcing phase with plastic metal wrapped on the surface, and then mixes it with the raw material matrix. The reinforcing phase is widely wrapped by the metal with better plasticity, and will be densely combined with the metal powder during the pressing process, thereby improving the density and facilitating subsequent foaming.

The briquetting process comprises briquetting under a pressure of 400-600 MPa to obtain a cylindrical briquette with a thickness of 1-2 mm and a diameter of 50 mm; the briquette is crushed and sieved to obtain a reinforcing phase wrapped by plastic metal with a particle size range of 100-300 meshes, which is recorded as a modified reinforcing phase;

Step S2, preparing foamed aluminum: taking a certain mass of the modified reinforcing phase obtained in step S1, adding it to the metal powder raw material and the foaming agent, and mixing it, preparing the foamed aluminum, so that the wettability of the reinforcing phase and the foamed aluminum matrix is improved, thereby obtaining a foamed aluminum material with enhanced performance. The raw materials for preparing foamed aluminum by powder metallurgy include metal powder raw materials, modified reinforcing phases and foaming agents. The amount of the modified reinforcing phase added is 3.0wt% to 9.0wt% of the raw materials for preparing foamed aluminum by powder metallurgy. Too much will increase the viscosity of the matrix during the foaming process, and the formed pore structure is poor. Too little will limit the yield strength improvement rate of the foamed aluminum. The higher the coverage rate of the modified reinforcing phase, the higher the yield strength. When the coverage rate is constant, the greater the amount of the modified reinforcing phase added, the higher the yield strength. As shown in Figure 3-4, when the coverage rate is constant, which is 95%, the yield strength increases first and then decreases within the range of 3wt%-9wt% of the modified reinforcing phase added. When the addition amount is 6wt%, the yield strength improvement effect is best. The metal powder raw material is selected from 200-400 mesh Al powder, Mg powder or AlMg50 alloy powder, Si powder or AlSi12 alloy powder, Cu powder and Sn powder; during the preparation process, the metal powder raw material is formed by combining Al with a mass fraction of 74-90%, Mg with a mass fraction of 3-6%, Si with a mass fraction of 3-8%, Cu with a mass fraction of 2-6%, and Sn with a mass fraction of 2-6%; the foaming agent is titanium hydride, and the amount of the foaming agent added is 0.5wt%-1.0wt% of the raw material for preparing foamed aluminum by powder metallurgy, and the remaining components are metal powder raw materials. The modified reinforcing phase is mixed with the metal powder raw material and the foaming agent to prepare a foaming precursor; the foaming precursor is kept at a foaming temperature of 580-620°C for 5-20 minutes and then cooled to obtain foamed aluminum with enhanced performance.

3. Beneficial effects

Compared with the prior art, the present invention has the following beneficial effects:

(1) In a method for preparing aluminum foam of the present invention, a plastic metal powder is used to modify the reinforcing phase, and the obtained aluminum foam precursor has a high density. The aluminum foam has good compression performance due to the improved wettability between the reinforcing phase and the matrix;

(2) The preparation process is simple and easy to operate. It can fully share equipment with the powder metallurgy process for preparing foamed aluminum, and does not require any additional equipment, which has obvious advantages in industrial production.

BRIEF DESCRIPTION OF THE DRAWINGS

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

FIG1 is a scanning electron microscope photograph of the modified enhanced phase of Example 3;

FIG2 is a comparison of the compression properties of aluminum foam before and after the improvement of wettability in Example 3;

FIG3 is an effect of the coverage of a modified reinforcing phase on the yield strength improvement rate of aluminum foam, wherein the modified reinforcing phase is mullite whiskers;

FIG4 shows the effect of the amount of modified reinforcing phase added on the yield strength improvement rate of foamed aluminum, wherein the modified reinforcing phase is mullite whiskers.

DETAILED DESCRIPTION

The following detailed description of exemplary embodiments of the present invention refers to the accompanying drawings, which form a part of the description, and in which exemplary embodiments of the present invention that can be implemented are shown as examples. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, it should be understood that other embodiments can be implemented and various changes can be made to the present invention without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is only for the purpose of illustrating and not limiting the description of the characteristics and features of the present invention, so as to propose the best mode for performing the present invention and to enable those skilled in the art to implement the present invention. Therefore, the scope of the present invention is limited only by the appended claims.

Table 1 Component parameters of Examples 1-5 of the present invention

Table 2 Process parameters of Examples 1-5 of the present invention

Example 1

Example 1 provides a method for preparing foamed aluminum, and the specific steps are as follows:

Step S1, reinforcement phase pretreatment: SiC particle reinforcement phase with a particle size of 400 mesh and aluminum powder with a particle size of 800 mesh are uniformly mixed in a mass ratio of 1:6, and then pressed into blocks at a pressure of 500 MPa to obtain a cylinder with a thickness of 1.5 mm and a diameter of 50 mm, which is then crushed and passed through a 200-mesh sieve to obtain a SiC reinforcement phase wrapped by metal aluminum, whose microstructure is similar to that shown in Figure 1;

Step S2, preparing foamed aluminum: taking 7% by mass of the SiC reinforcing phase pretreated as above and adding it to the powder raw material for preparing foamed aluminum by powder metallurgy method, mixing, and preparing a foaming precursor; the foaming precursor is kept at a foaming temperature of 620° C. for 5 minutes and then cooled to obtain foamed aluminum with enhanced performance.

The modified reinforcing phase has a high coverage rate of being wrapped by the plastic metal. The foamed aluminum prepared using the modified reinforcing phase has high compression performance. Compared with the foamed aluminum with unmodified reinforcing phase, the yield strength improvement rate reaches 95%.

Example 2

Embodiment 2 provides a method for preparing foamed aluminum, and the specific steps are as follows:

Step S1, reinforcement phase pretreatment: after uniformly mixing Al ₂ O ₃ particle reinforcement phase with a particle size of 200 mesh and aluminum powder with a particle size of 500 mesh at a mass ratio of 1:3.5, briquetting was performed at a pressure of 500 MPa to obtain a cylinder with a thickness of 1.5 mm and a diameter of 50 mm, and then crushing and passing through a 100 mesh sieve to obtain an Al ₂ O ₃ reinforcement phase wrapped by metal aluminum, whose microstructure is similar to that shown in FIG1 ;

Step S2, preparing foamed aluminum: adding 9% of the pretreated _{Al2O3 reinforcing} phase to the powder raw material for preparing foamed aluminum by powder metallurgy and mixing them evenly to prepare a foaming precursor; the foaming precursor is kept at a foaming temperature of 580°C for 20 minutes and then cooled to obtain foamed aluminum with enhanced performance.

Example 3

Example 3 provides a method for preparing foamed aluminum, and the specific steps are as follows:

Step S1, reinforcement phase pretreatment: a mullite whisker reinforcement phase with a diameter of 0.5 μm and an aspect ratio of 20 and a tin powder with a particle size of 600 mesh are uniformly mixed in a mass ratio of 1:4, and then pressed into blocks at a pressure of 400 MPa to obtain a cylinder with a thickness of 1 mm and a diameter of 50 mm, which is then crushed and passed through a 200-mesh sieve to obtain a mullite whisker reinforcement phase wrapped by metal copper, the microstructure of which is shown in FIG1 ;

Step S2, preparing foamed aluminum: taking 7.5% by mass of the mullite whisker reinforcement phase pretreated as above, adding it to the powder raw material for preparing foamed aluminum by powder metallurgy method and mixing it evenly to prepare a foaming precursor; the foaming precursor is foamed at a temperature of 600°C, kept warm for 15 minutes and then cooled to obtain foamed aluminum with enhanced performance. The mechanical properties of the foamed aluminum obtained before and after the improvement of the wettability are compared as shown in Figure 2.

Example 4

Example 4 provides a method for preparing foamed aluminum, and the specific steps are as follows:

Step S1, reinforcement phase pretreatment: a spinel whisker reinforcement phase with a diameter of 0.2 μm and an aspect ratio of 60 and a magnesium powder with a particle size of 500 mesh are uniformly mixed in a mass ratio of 1:4, and then pressed into blocks at a pressure of 400 MPa to obtain a cylinder with a thickness of 2 mm and a diameter of 50 mm, which is then crushed and passed through a 200-mesh sieve to obtain a spinel whisker reinforcement phase wrapped by metal magnesium, whose microstructure is similar to that shown in FIG1 ;

Step S2, preparing foamed aluminum: taking 5% by mass of the spinel whisker reinforcement phase pretreated as above and adding it to the powder raw material for preparing foamed aluminum by powder metallurgy method, mixing, and preparing a foaming precursor; the foaming precursor is kept at a foaming temperature of 610° C. for 10 minutes and then cooled to obtain foamed aluminum with enhanced performance.

Example 5

Example 5 provides a method for preparing foamed aluminum, and the specific steps are as follows:

Step S1, reinforcement phase pretreatment: a carbon fiber reinforcement phase with a length of 40 μm and a copper powder with a particle size of 500 mesh are uniformly mixed in a mass ratio of 1:2, and then pressed into blocks at a pressure of 600 MPa to obtain a cylinder with a thickness of 1 mm and a diameter of 50 mm, which is then crushed and passed through a 300-mesh sieve to obtain a carbon fiber reinforcement phase wrapped by metal tin, whose microstructure is similar to that shown in FIG1 ;

Step S2, preparing foamed aluminum: taking 3% by mass of the carbon fiber reinforcement phase pretreated as above and adding it to the powder raw material for preparing foamed aluminum by powder metallurgy method, mixing them evenly, to prepare a foaming precursor; the foaming precursor is kept at a foaming temperature of 590° C. for 15 minutes and then cooled to obtain foamed aluminum with enhanced performance.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (3)

1. A foam aluminum, characterized in that a reinforcing phase is mixed in the foam aluminum, an intermetallic compound is present between the reinforcing phase and the foam aluminum, the melting point of the intermetallic compound is 400-550°C, the reinforcing phase is one of ceramic particles, whiskers or short fibers, the ceramic particles are SiC or _Al2O3 particles, and the particle size is _200-400 meshes; the whiskers are mullite or spinel whiskers, with a diameter of 0.2-0.5 μm and an aspect ratio of 20-60; the short fibers are carbon fibers, with a length of 20-80 μm; the intermetallic compound is formed by a plastic metal and an aluminum alloy, the plastic metal is selected from one of aluminum, copper, magnesium or tin powder, and the mass ratio of the reinforcing phase to the plastic metal powder is 1:(2-6); The specific steps of the preparation method of the foamed aluminum are as follows: Step S1, preparing a modified reinforcing phase: mixing the reinforcing phase and the plastic metal powder in a certain mass ratio, briquetting, crushing and sieving to obtain a reinforcing phase whose outer surface is coated with the plastic metal powder, which is recorded as the modified reinforcing phase; Step S2, preparing foamed aluminum: taking a certain mass of the modified reinforcing phase obtained in step S1, adding it to the metal powder raw material and the foaming agent, mixing them evenly, preparing a foaming precursor, and foaming to prepare foamed aluminum. The foaming precursor is foamed at a temperature of 580-620° C., and is kept warm for 5-20 minutes and then cooled to obtain foamed aluminum with enhanced performance; The raw materials for preparing foamed aluminum by the powder metallurgy method include metal powder raw materials, modified reinforcing phase and foaming agent, wherein the modified reinforcing phase is added in an amount of 3.0 wt% to 9.0 wt% of the raw materials for preparing foamed aluminum by the powder metallurgy method, the foaming agent is added in an amount of 0.5 wt% to 1.0 wt% of the raw materials for preparing foamed aluminum by the powder metallurgy method, and the remaining components are metal powder raw materials; The metal powder raw material includes Al powder, Mg powder or AlMg50 alloy powder, Si powder or AlSi12 alloy powder, Cu powder and Sn powder, and the mass fraction of each element is Al: 74~90%, Mg: 3~6%, Si: 3~8%, Cu: 2~6%, Sn: 2~6%, and the particle size of the metal powder raw material is 200~400 mesh. 2. The foamed aluminum according to claim 1, characterized in that the plastic metal is plastic metal powder, and the particle size range of the plastic metal powder is 500~800 mesh. 3. The foamed aluminum according to claim 1, characterized in that the foaming agent is titanium hydride.