Disclosure of Invention
The invention aims to provide a preparation method of a low-cost powder metallurgy aluminum lithium alloy, which solves the problem of high cost of the aluminum lithium alloy prepared by the traditional casting method.
The technical scheme of the invention is as follows: lithium source compounds such as lithium oxide, lithium carbonate, lithium chloride and lithium oxide are dried in vacuum to remove moisture impurities, so that residual water vapor is prevented from hindering the sintering process. And then ball-milling and mixing the dried lithium source compound powder with pure aluminum powder, alloy element powder or alloy powder, and carrying out the working procedures of forming, sintering, extruding and the like on the prepared mixed powder to obtain the powdery aluminum-lithium alloy. During sintering, the compound of aluminum and lithium reacts to generate lithium and uniformly distributed dispersed phase, and the excellent performance of the aluminum-lithium alloy is obtained through the functions of powder metallurgy fine grain strengthening and dispersion strengthening.
In order to realize the technical scheme of the invention, the specific process steps comprise the following contents:
a) preparing mixed powder: weighing one or more of pure aluminum powder, alloy element powder or alloy powder and a lithium source compound according to required components, and preparing mixed powder by ball milling, wherein the mass fraction of lithium element in the mixed powder is 0.5-5 wt.%.
b) Molding: and (3) performing compression molding on the mixed aluminum lithium alloy powder by adopting one or two of cold isostatic pressing or mould pressing, wherein the compression pressure is 100-500MPa, and the pressure maintaining time is 30-300 s.
c) And (3) sintering: sintering densification is carried out in the protective atmosphere of vacuum, nitrogen or argon, the sintering temperature is 500-630 ℃, and the heat preservation time is 1-10h, so as to obtain the compact powder metallurgy aluminum lithium alloy sintering blank.
d) Deformation processing: and carrying out hot extrusion on the sintered billet at the temperature of 300-500 ℃ to obtain the low-cost powder metallurgy aluminum-lithium alloy with excellent performance.
Preferably, the lithium source compound in step 1) is one or more of lithium hydroxide, lithium carbonate, lithium chloride and lithium oxide.
Preferably, the lithium source compound of step 1) is dried in vacuum before mixing, the drying temperature is 80-170 ℃, and the drying time is 1-5 h.
Preferably, the mixed powder is prepared by ball milling in the step 1), the ball milling tank and the grinding balls are made of one or more of corundum, agate, zirconia, silicon carbide and boron carbide, and the ball milling environment is vacuum (the vacuum degree is 10)-1-10-2Pa), high-purity nitrogen and high-purity argon, wherein the ball-material ratio is 1:1-10:1, and the ball milling time is 1-10 h.
The technical key points of the invention are as follows:
1. lithium hydroxide, lithium carbonate, lithium chloride and lithium oxide which are low in price, wide in source and stable in property are used as lithium sources, and the problems that in the traditional process, a lithium simple substance is easy to oxidize, is difficult to store and is high in manufacturing cost are solved.
2. The lithium source compound is dried in vacuum before mixing, so that the moisture in the lithium source compound can be more fully volatilized, on one hand, the pressure in a ball-milling tank is increased due to the volatilization of water vapor caused by the heating of ball-milling mixing, and the explosion risk exists when the tank is opened; on the other hand, the water can increase the molding difficulty of the mixed powder, so that the strength of a molded green body is reduced, and the green body is easy to delaminate and lack edges.
3. By controlling the sintering temperature and the heat preservation time, the powder metallurgy aluminum lithium alloy sintering blank generates dispersed phase alumina in the preparation process, and the dispersed phase alumina is uniformly distributed in an aluminum matrix to play a role in dispersion strengthening. If the temperature during sintering is too low, dispersed phase alumina cannot be generated and cannot be uniformly distributed in the aluminum matrix. If the sintering temperature is too high, low-melting-point components (such as lithium) in the alloy can generate substance migration from defects such as crystal boundary, holes and the like, the crystal boundary phase is separated out and excessively grows, so that the mechanical property and the processing property of the material are seriously deteriorated, the phenomenon of sweating can be generated at the same time, the burning loss of lithium elements is serious, the utilization rate of a lithium source is reduced, and the cost is increased.
4. The sintered billet is subjected to hot extrusion at the temperature of 300-500 ℃, and the hot extrusion plays a role in regulating and controlling the formability, so that on one hand, residual pores in the sintered billet are further eliminated, the relative density of the material reaches 100 percent, and the toughness of the material is improved; on the other hand, the powder metallurgy aluminum lithium alloy with the required specification is obtained.
Compared with the prior art, the invention has the following advantages:
(1) the invention adopts lithium hydroxide, lithium carbonate, lithium chloride and lithium oxide as lithium sources, is easy to prepare, store and transport, solves the problems of easy oxidation, difficult storage and higher manufacturing cost of lithium simple substances in the traditional process, and is easy to realize industrialization.
(2) The dispersed phase alumina is generated in the preparation process, is uniformly distributed in an aluminum matrix, plays a role in dispersion strengthening, and has more excellent performance due to the powder metallurgy fine grain strengthening effect.
Detailed Description
Example 1
The lithium hydroxide powder was dried by heating under vacuum at 150 ℃ for 2 h. Ball milling and mixing 2020 aluminum alloy powder and dried lithium hydroxide powder to obtain lithiumThe mass fraction of the elements in the mixed powder was 1 wt.%. The corundum ball milling tank and the agate grinding balls are adopted at the vacuum degree of 10-1Ball milling is carried out in a Pa environment, the ball-material ratio is 1:1, and the ball milling time is 1 h. And (3) performing compression molding on the mixed aluminum lithium alloy powder by adopting isostatic cool pressing, wherein the compression pressure is 100MPa, and the pressure maintaining time is 300 s. Subjecting the molded green body to vacuum atmosphere (vacuum degree of 10)-1Pa), the sintering temperature is 580 ℃, the temperature is kept for 2h, and the sintering is cooled along with the furnace. And (3) carrying out hot extrusion on the sintered blank at 500 ℃, wherein the extrusion ratio is 10:1, and the low-cost powder metallurgy aluminum-lithium alloy with excellent performance is obtained.
Example 2
The lithium oxide powder was dried by heating under vacuum at 80 ℃ for 5 h. Mixing pure aluminum powder with dried lithium oxide powder, wherein the mass fraction of lithium element in the mixed powder is 3 wt.%. A silicon carbide ball milling tank and zirconia grinding balls are adopted for ball milling in a high-purity nitrogen environment, the ball-material ratio is 5:1, and the ball milling time is 4 hours. And (3) performing compression molding on the mixed aluminum lithium alloy powder by adopting isostatic cool pressing, wherein the compression pressure is 200MPa, and the pressure maintaining time is 180 s. And sintering the molded green body in high-purity nitrogen at the sintering temperature of 630 ℃, preserving heat for 7 hours, and cooling along with the furnace. And (3) carrying out hot extrusion on the sintered blank at 300 ℃, wherein the extrusion ratio is 15:1, and obtaining the low-cost powder metallurgy aluminum-lithium alloy with excellent performance.
Example 3
The lithium carbonate powder was dried by heating in a vacuum oven at 170 ℃ for 1 h. Mixing pure aluminum powder, aluminum-silicon alloy powder, aluminum-magnesium alloy powder, electrolytic copper powder and dry lithium carbonate powder, wherein the mass fraction of lithium element in the mixed powder is 0.5 wt.%. Ball milling is carried out in a high-purity argon environment by adopting a zirconium oxide ball milling tank and boron carbide grinding balls, the ball-material ratio is 3:1, and the ball milling time is 6 hours. And (3) performing compression molding on the mixed aluminum lithium alloy powder by adopting isostatic cool pressing, wherein the compression pressure is 400MPa, and the pressure maintaining time is 30 s. And sintering the molded green body in high-purity argon at 500 ℃, preserving heat for 4 hours, and cooling along with the furnace. And (3) carrying out hot extrusion on the sintered blank at the temperature of 410 ℃, wherein the extrusion ratio is 20:1, and the low-cost powder metallurgy aluminum lithium alloy with excellent performance is obtained.
Example 4
The lithium chloride powder was dried by heating in a vacuum oven at 120 ℃ for 3 h. Mixing 7050 aluminum alloy powder with dry lithium chloride powder, wherein the mass fraction of lithium element in the mixed powder is 5 wt.%. Adopts a zirconia ball milling tank and a corundum grinding ball at the vacuum degree of 10-2Ball milling is carried out in a Pa environment, the ball-material ratio is 10:1, and the ball milling time is 10 h. And (3) performing compression molding on the mixed aluminum lithium alloy powder by adopting isostatic cool pressing, wherein the compression pressure is 500MPa, and the pressure maintaining time is 120 s. Subjecting the molded green body to vacuum atmosphere (vacuum degree of 10)-2Pa), the sintering temperature is 540 ℃, the temperature is kept for 10h, and the furnace cooling is carried out. And (3) carrying out hot extrusion on the sintered blank at 350 ℃, wherein the extrusion ratio is 10:1, and the low-cost powder metallurgy aluminum-lithium alloy with excellent performance is obtained.