JPH036979B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to dispersion strengthening of metals. The present invention relates specifically to dispersion strengthening of aluminum alloys and provides a family of such alloys that can withstand welding temperatures.

BACKGROUND OF THE INVENTION Dispersion-strengthened metals and methods of enhancing various properties of metals by dispersing refractory particles in metals or alloys are well known.

Such metals and processes are described, for example, in US Pat. No. 3,028,234 (Alexander et al.);
(Iler et al.) and No. 3,468,658 (Herald et al.), the disclosures of which are hereby incorporated by reference.

Alexander et al. discovered a general method of mixing powdered, solid-dispersed refractory metal oxide particles in an inert metal with the melt of the metal (particularly nickel) to be hardened. Alexander et al. suggest the possibility of adding copper-alumina powder to a molten aluminum alloy (Example 1). However, in reality, if you follow the procedure of Example 1,
Copper-aluminum powders do not dissolve in aluminum alloys and cannot produce satisfactory dispersion hardened aluminum alloys. Furthermore, Alexander et al. teach protecting the copper-aluminum powder in an inert atmosphere to prevent the copper from oxidizing before adding the powder to molten aluminum. Alexander et al. also suggest sintering the copper-aluminum powder before introducing it into the melt.

Iler et al. disclose a mechanical method of producing dispersion hardened copper. The method includes producing a dense billet of copper powder dispersed with alumina particles. The copper powder is obtained by reducing a copper compound, and the copper powder is protected by an inert atmosphere to prevent reoxidation before compaction into a dense billet.

The Herald et al. suggest adding a dispersoid, such as aluminum oxide, to the metal in the molten state. The dispersoid is wetted by the metal being hardened to prevent agglomeration. "Wetting" is performed by saturating the metal with the anions of the dispersoid when the dispersoid is mixed with the molten metal.

SAP (Sintered Aluminum Powder) metal is an example of an oxide metal dispersion hardened aluminum alloy that is known to have service temperatures as much as 200°C higher than regular aluminum alloys. SAP is manufactured using mechanical processing methods. Although SAP has excellent properties, these properties are permanently lost at temperatures close to the fusion welding temperature.

Other U.S. patents demonstrating prior art include:
There is US Pat. No. 3,600,163 to Badia et al. This patent teaches dispersing graphite in molten aluminum by using a wetting process. The graphite particles preferably have an average cross-sectional area of 40 microns, but it has been reported that graphite particles as small as 20 microns have also shown excellent results.

Imich U.S. Patent No. 2793949
teaches wetting and adding emery, corundum, calcined alumina, flint, quartz, and various other ceramic materials to molten metal. Aimitsuchi is generally from 5% by volume.
A composite material containing 50 volume percent ceramic material is produced. The particle size of the ceramic material ranges from 0.5 micron (Example 11) to 30 mm as shown in Example 6.

(Means for Solving the Problems and Actions/Effects) One of the objects of the present invention is to provide an aluminum-based material that has high strength at 500°F (260°C) and has sufficient ductility like metal. Our goal is to provide alloys with the following properties. Sufficient ductility, like a metal, means that the product can be processed and shaped without excessive cracking. In this specification, the terms "aluminum" and "aluminum alloy" are used interchangeably, unless otherwise indicated or obvious.

To obtain products of this type, a combination of the following characteristics is required. (a) Separate particles of high melting point oxide (strengthening oxide) are dispersed throughout the matrix consisting essentially of aluminum or an aluminum alloy.

(b) less than 0.2 microns between particles, preferably
There should be a spacing of 0.05 micron to 0.15 micron.

(c) Particle size shall be in the range of 0.005 micron to 0.025 micron.

(d) The volume percentage of reinforcing oxide shall not exceed 1 volume percent so as to preserve ductility. Furthermore, (e) the reinforcing oxide is stable in the melt bath of aluminum or aluminum alloys and is free from Ostwald ripening. That is, the absence of Ostwald growth means that the oxide must have a relatively high free energy of formation and a relatively high melting point.

The present invention provides oxide dispersion hardened aluminum compositions with high temperature properties superior to those of currently available aluminum alloys. The alloys of the present invention can have practical service temperatures exceeding 500°C (260°C). The compositions of the present invention can also be used to replace titanium-based alloys in some applications where service temperatures exceed the performance of current aluminum alloys. Parts manufactured using the dispersion hardened compositions of the present invention can be welded in the field without significant deterioration of properties.

The oxide-dispersed hardened aluminum composition of the present invention comprises a wetted metal and internally dispersed refractory metal oxide dispersoid particles (also referred to herein as "reinforcing oxide" or "metal oxide filler"). ) is made of aluminum alloy. The wet metal and dispersoid are each included in effective amounts, the contents of which can vary over a wide range depending on the properties of the desired metal product (i.e., the hardened aluminum composition) and the particulate materials selected for use in the process. Different. For strengthening purposes, sufficient dispersoid is present to occupy at least 0.05 volume percent and up to about 1 volume percent of the metal product. The term ``refractory metal oxide'' or ``reinforcing oxide'' refers to
It includes all high-melting point metal compounds (most typically hydroxides or hydrated oxides) that are converted into oxides by sintering.

Desirable dispersoids are selected from the group consisting of alumina, zirconia, magnesia, thoria, and rare earth oxides, including rare earth metal oxides with atomic numbers 59-71. These dispersoids, at 1000℃,
per gram atom of oxygen in the oxide
It has a free energy of formation of 100 kilocalories. In practice, alumina is usually chosen as the dispersoid.

Dispersoid particle size, shape, volume fraction and
IPS (interparticle spacing) is all important to the properties of the compositions of the invention. In this disclosure, all such physical parameters, where applicable, are considered to be statistical, and it is assumed that individual particles may vary considerably from the average properties shown.

This dispersoid is contained in an amount effective to obtain the desired interparticle spacing (IPS), and is
is generally within the range of about 0.05 microns to 0.2 microns. IPS correlates with, and can therefore be measured from, the hardness and strength properties of the processed composition.

A preferred method for estimating the IPS of a composition is, first, to measure the particle size (average diameter) of the dispersoid particles by electron microscopy. Alternatively, dispersoid particles may be extracted and their surface area measured. And, for example, by chemical analysis,
Determine the volume fraction of dispersoids in the composition. By performing these two quantifications, IPS can be calculated from the following relational expression.

IPS=d [(1/1.9f)1/3-1)] where d is the average diameter of the dispersoid particles and f is the volume fraction of the dispersoids in this system.

The composition must be formulated to have an IPS of less than 0.2 microns. The strongest and hardest alloys generally have an IPS of about 0.05 microns to about
In the range of 0.15 microns.

In preferred embodiments of the invention, the dispersoid particles are approximately equiaxed. That is, the shapes of these particles are close to spherical, cubic, or regular octahedral.
Equiaxed particles are preferred over fibrous or plate-like particles, which tend to thicken the melt and can impart non-equiaxed properties to the resulting cast alloy. It is desirable that the alloy composition of the present invention exhibit equal strength and hardness properties in all directions after casting.
The use of equiaxed dispersed particles further enhances this objective.

As mentioned above, the volume percentage of dispersoid particles in the compositions of the present invention typically ranges from about 0.05% to about 1% by volume. In a preferred embodiment of the invention, the volume percentage of the high melting point oxide, or reinforcing oxide (dispersoid), ranges from about 0.05% to about 0.5% by volume.

The particle size of the dispersoid particles typically ranges from about 0.005 micron to about 0.025 micron, more desirably from about 0.005 micron to about 0.015 micron. What is referred to herein as "particle size" is the average diameter of the particles as measured by conventional scanning electron microscopy techniques.

Wetting the refractory metal oxide dispersoid with the wetting metal is an important consideration when adding the dispersoid to the molten aluminum alloy. This wet metal must react to form a dispersoid, a metal oxide that has a free energy of formation greater than the free energy of formation of the reinforcing oxide.

Magnesium metal is a common component of aluminum alloys and forms very stable oxides. Magnesium has a free energy of formation of 112 kcal/mol at a temperature of 1000°C (1832°). Two oxides that can be used as dispersoids according to the present invention have reported free energies of formation as follows.

Dispersoid Free Energy at 1000°C Alumina 104 Zirconia 100 Therefore, magnesium is the preferred wetting metal for these two oxides. Similarly, aluminum is a wetted metal for zirconia. The surface of the dispersoid particles is converted to a metallophilic state by reacting the surface of the particles with a wetting metal of the type mentioned above, especially magnesium. In the case of the above two metal oxide dispersoids of the present invention, magnesium reacts with alumina to form magnesia and aluminum, and further reacts with zirconia to form magnesium and zirconium.

Magnesium or other wet metals are
It usually reacts with the dispersoids to form an outer suboxide layer surrounding the dispersoid particles. (The term "suboxide," as used herein, means oxygen-deficient compared to pure metal oxides.) This outer suboxide layer combines the metal oxide inside the particle with the metal oxide outside the particle. It is wet (or attached) to both the surrounding metal. In this way, the reinforcing oxide is made metallophilic and can be wetted and added to the molten aluminum alloy. Aluminum itself acts as a wetting metal for the zirconia. When magnesium is used as the wet metal, its effective amount is generally about 0.1% by weight of the total weight of the composition.
to about 4% by weight.

Addition of oxygen to the system, other than the oxide particles being dispersed, is hardly tolerated. Excess oxygen consumes available magnesium or other wetter metal, leaving insufficient wetter metal to convert the intended dispersoid to a metallophilic state. When the dispersoids are added to the melt, excess oxygen that may accompany the dispersoids, such as copper oxide or iron oxide, will reduce the amount of copper or iron present in the metal product.
It should be kept to less than 0.1 weight percent, preferably less than about 0.05 weight percent, and most preferably less than 0.01 weight percent.

It is desirable to introduce the dispersoid to the molten aluminum bath under conditions that prevent agglomeration and particle growth of the dispersoid. The currently preferred way to accomplish such introduction is to first surround the dispersoid particles with a metal capable of reducing the oxide with hydrogen. Metals that can be used in this manner are copper and iron, and the coated particles are referred to in this disclosure as ``iron or copper master mixes.''

One procedure that can be used to form a refractory oxide master mix of iron or copper is to form the iron or copper as the metal oxide or hydroxide with a dispersed metal oxide (refractory filler). Co-precipitation around the particles. The master mix contains a sufficient amount of carrier metal (iron or copper) to effectively surround and mechanically entrain the individual particles of the dispersoid to keep them separate from each other. Excessive amounts of support metal, while acceptable, are not desirable. In any case, the minimum effective amounts and any incidental excess amounts of these metals introduced into the melt with the master mix are referred to in this disclosure as "carrier amounts."

Master mixes useful in preparing the dispersion-curing compositions of the present invention typically contain up to about 20 volume percent reinforcing oxide or dispersoid, but about 5
Volume percent to about 20 volume percent is believed to be a practical range, with about 5 volume percent to about 10 volume percent currently most desirable.

For proper dispersion of master mixes in the aluminum melt, several conditions must be met. (The term "aluminum melt" is used herein in a broad sense and includes substantially pure aluminum and useful aluminum alloys, particularly commercially available casting and processing alloys. ) First, the molten aluminum alloy must be in direct contact with the copper or iron of the master mix. Second, diffusion of aluminum into the copper or iron must occur to the extent necessary to dissolve or melt the copper or iron into the molten aluminum alloy. Thus, the melt must be hot enough so that the mixed metals become liquid and diffusion and mixing occur. Appropriate melt temperatures can be determined from the relevant phase diagram, such as that of copper and aluminum alloys in the melt (if copper is the mastermix metal). Third, the magnesium or other wetting metal in the molten aluminum alloy (and in some cases the aluminum itself) reacts with the colloidal particles of reinforcing oxide, rendering them metallophilic (melting There must be an opportunity for wetting (wetting by aluminum alloys).

The master mix may be added to the molten aluminum alloy by first compacting it into a slug or billet (generally at a pressure of about 30 tons per square inch). The billet is placed in a furnace and treated with hydrogen at a temperature effective to remove surface copper or iron oxides, resulting in light sintering.
The lightly sintered billet is stored in an oxygen-free inert (non-oxidizing) atmosphere, such as nitrogen or argon, until the billet is added to the molten aluminum alloy in an oxygen-free inert atmosphere, such as nitrogen or argon.

When a billet is surface oxidized, aluminum and other metals in the melt react with surface copper or iron oxides to form alumina around the billet, thereby isolating the billet from the molten metal and removing the support metal ( This has an undesirable tendency to impede the dissolution of the reinforcing metal (copper or iron) and the dispersion of the reinforcing metal in the melt.

Colloidal particles of reinforcing oxide of the particle size required for this invention, ie 0.005 micron to 0.025 micron, are very difficult to handle before and during addition to the melt due to agglomeration and coalescence problems. Coalescence occurs and results in a loss of strength when the particle size of the colloidal particles exceeds about 0.025 microns.

Colloidal particles of reinforcing oxide (dispersoid),
A measure of physically separating the particles from each other before they are actually introduced into the melt to ensure that they are dispersed in the molten aluminum alloy as separate individual particles without agglomeration or coalescence. I do. These measures involve surrounding individual particles of reinforcing oxide with carrier metal (e.g. copper) particles, and then surrounding the carrier metal particles or particles of carrier metal oxide from which the carrier metal is obtained by chemical reduction.
This consists of ensuring that particles of the reinforcing oxide do not coalesce or agglomerate when dispersed in the former. If the reinforcing oxide particles cannot be kept physically separated from each other, they will agglomerate when they come into contact with each other at melting temperatures.

To impart high temperature strength and maintain ductility to the metal products of this invention, it is essential to maintain the volume percentage of colloidal particles below 1 volume percent. At the same time, to obtain high strength,
It is essential that the interparticle spacing be less than 0.2 microns. To achieve these two conditions simultaneously, the particle size of the colloidal particles must be below 0.025 microns. Large particle sizes do not provide the necessary hardening and strengthening effects at high temperatures. Such an effect is necessary when using this metal product in aircraft and aerospace equipment or pistons and automobile engines operating at higher temperatures than currently available as a desirable goal.

EXAMPLES The following examples include the best current method of carrying out the invention.

Example 1 In a mixer at room temperature, 358 grams of water was mixed with 2.4 grams of 70% nitric acid.
A water-soluble alumina sol was prepared by mixing grams. Add alumina powder (Remet, New York) to this mixture with vigorous stirring for approximately 15 minutes.
40 grams (obtained from Alumina Corporation) to obtain a sol containing 10 weight percent alumina.

Solutions were prepared as follows.

(1) 206 grams of Cu(NO ₃ ) _{2.2H 2} O was dissolved and diluted in distilled water to obtain 500 ml of solution. (2) 20 ml of the above alumina sol was diluted with distilled water to obtain 500 ml of solution.
(3) Annimium hydroxide solution was prepared as follows. The concentration of ammonium hydroxide was determined by titrating a sample of the above copper nitrate solution to pH 5.7 using a 4.5N ammonium hydroxide (NH ₄ OH) solution. Next, the concentration of ammonium hydroxide was adjusted so that the pH would be 5.7 when equal volumes of ammonium hydroxide solution and copper nitrate solution were mixed.
Additionally, 500 ml of this ammonium nitrate solution was used along with the other two solutions mentioned above. The three solutions were added volumetrically in equal proportions to 100 ml of water placed in a mixer to form a copper hydroxide precipitate containing alumina dispersed particles. The precipitate was filtered and washed to remove all water-soluble salts. This filter cake was then dried in an oven at 175°C (347°C). This converted the filter cake from blue copper hydroxide to black copper oxide form. In this copper oxide form, alumina particles are surrounded by copper oxide particles.

After preparing the copper oxide, the copper oxide was placed in a quartz boat and placed in a tube furnace. In this tube furnace, a mixture of nitrogen and hydrogen was passed around the oxide to reduce it to metallic copper. This reduction temperature was adjusted to prevent premature sintering from occurring. In particular, the temperature of the furnace was increased to 200℃ (392〓) for 2 hours.
The temperature was then raised to 400°C (752°C) for the next 2 hours. The resulting material was a copper-alumina powder in which individual alumina particles were surrounded by copper particles.

At 400℃ (752〓), slight sintering of the copper particles occurs. As used herein, the term "mild sintering" means that the surface area of the material (copper particles) undergoing sintering is reduced by about a factor of 10 to 150.

After the reduction process, the copper-alumina powder was never exposed to an oxygen-containing atmosphere.

20tsi (tons/square inch) of copper-alumina powder
By compressing with
A billet approximately 3/16 inch (0.47 cm) thick was prepared. These billets were treated with hydrogen to reduce any surface copper oxide. The processing temperature should be adjusted slowly.
The temperature was raised to 600℃ (1112〓). The billet was then kept in an inert atmosphere free of oxygen until it was added to the molten aluminum-magnesium alloy. An oxygen-free argon atmosphere was maintained around the melt.

At 600°C (1112°), slight sintering of the copper particles in the billet occurs. It is desirable to cause a slight sintering of at least the outer surface of the billet to reduce the rate of dissolution of the billet in the melt bath of the aluminum alloy to which it is added. As the surface area of the copper particles decreases by as much as 1/100, total sintering becomes undesirable and must be avoided. In a typical dispersoid containing up to 20% by volume of alumina particles surrounded by copper particles,
For example, slight sintering occurs until temperatures reach a maximum of about 700°C (1292°C). The overall sintering is
For example, it occurs at 900℃ (1652〓). The maximum temperature at which total sintering can be avoided is 800℃ (1472
〓).

The above copper-alumina billet was added to a melt bath prepared as follows. 135 grams of 99.7% aluminum chips and 9 grams of magnesium were placed in a graphite crucible and melted at 900° C. (1652°) in an inert atmosphere (argon). In this molten metal,
Six grams of the copper-alumina billet described above was added. Dispersed within the billet were 10% by volume of alumina particles with an average particle size of 0.030 microns. Stir the melt using a graphite rod and a blow of argon and heat to 900 °C (1652 °C) for 1
It was kept for an hour and then cast. As a result, Al−4Cu− with alumina particles dispersed inside.
A 3Mg (4% by weight copper, 3% by weight magnesium) alloy was obtained.

Thin foils of this alloy were prepared by warm rolling thin sections of this alloy followed by jet electropolishing. The electrolytes used were 750 ml methanol, 225 ml glycerin and 25 ml perchloric acid. Polishing at 25℃ using a voltage of 26V to 30V
I went with (77〓). 3 mm disks with holes were prepared and immediately washed in ethanol. The specimen was examined using a 200kV electron microscope JEM-200CX. Energy Dispersive Spectroscope with KEVEX detector and analyzer
Qualitative chemical analyzes of various minute components were performed using a spectroscope (EDS).

The microstructure of this alloy was composed of three distinctly different grains in an aluminum matrix. The first type of particles were found mostly at grain boundaries and had a very smooth spherical shape.
EDS analysis revealed that these particles were mainly composed of silica. These particles appeared to exist as oxide impurities. The particle size of these silica particles was about 1 micron.

The second type of particles was also about 1 micron and was also found primarily at grain boundaries. Chemical analysis of these particles showed that they were primarily aluminum with large amounts of copper and small amounts of magnesium. These particles are believed to be theta precipitates resulting from incomplete dissolution of the billet. Upon examination, these particles were found to contain alumina particles dispersed within the particles.

The third type of particle is alumina, which has a diameter of
It was about 0.03 microns. Furthermore, these alumina particles were found to be evenly dispersed within the alloy matrix. The volume of alumina particles is
When calculated from the ingredients used, it was 0.1% by volume. Therefore, the particle spacing calculated from the above relationship was approximately 0.2 microns.

The microstructure of the casting composition shows that its appearance is SAP
, suggesting that the cast or welded part is expected to have physical properties similar to those of SAP.

Example 2 A copper-zirconia coprecipitate was prepared as follows. 100 grams of copper, 300 ml of concentrated nitric acid and 100 ml of water
dissolved in The final volume of the resulting copper nitrate solution is
The volume was adjusted to 500ml by adding water. Colloidal aquasols containing isolated particles of silconium oxide (zirconia) have been developed by Johnson
Purchased from Matthey. The average particle size of the zirconia particles was 0.005 micron. zirconia
The volume of this zirconia sol corresponding to 12.34 grams was made up to 500 milliliters by adding distilled water.
Equal amounts of copper nitrate solution and zirconia sol were measured and poured simultaneously into a container containing more than 100 ml of water with very vigorous stirring. At the same time, enough ammonia gas was added to maintain the pH at 5.5±0.1. Addition of these solutions was carried out over a period of 1 hour. After the precipitation was completed, the precipitate was filtered, washed with distilled water, and further dried at 290°C (554°C).

The resulting black copper oxide containing dispersed zirconia was ground into a powder of 100 meshes and heated at 300°C (572°C) until no water was released by the reduction reaction.
The reduction is carried out in hydrogen of
(1292〓) and held for 1 hour. The product from this process was powdered, lightly sintered copper particles surrounding individual zirconia particles dispersed throughout.

The copper-zirconia powder was bottled in an oxygen-free atmosphere and transferred to a glove box containing an inert atmosphere. The oxygen content of the gas within the glovebox was less than 0.05% by weight. The powder was sent to a compactor and compacted into a slag at a pressure of 32 tons/in² in the inert atmosphere described above. The content of oxygen in the form of copper oxide in the slag was less than 0.01% of the weight of copper.

Ninety-one grams of pure aluminum shavings and four grams of magnesium were added to the melting vessel in the inert atmosphere of a glove box. These metals were melted and the temperature raised to 900°C (1652°). A copper-alumina slag containing a total of 4.9 grams of copper was added to the previously described melt in an inert atmosphere, and the melt was maintained at a temperature of 900 DEG C. (1652 DEG) for one and a half hours. Thereafter, this melt was poured into a steel mold, and the casting was formed by extrusion. The casting was a cylinder 1 inch in diameter and 5 inches long (2.5 cm x 12.5 cm), and the extrusion was a rod 0.25 inch (0.625 cm) in diameter.

The cast and extruded product had a Vickers microhardness of 150 dph, while the control product, which had the same composition except for the zirconia, had a value of 65.
The grain size as cast was 76 microns, while the grain size of the control product was 25 microns, and after conversion to the T6 state the grain size was 21 microns.
The control product was 45 microns. T6 is approx.
Means a heat treatment consisting of solution heat treatment at 500°C (932°), quenching in water, and aging at about 177°C (350°) for about 9 to 11 hours.
After T6 treatment, the finer grain size of the products of the invention compared to the control reflects the retardation of grain growth by the dispersed reinforcing oxides. Finer grain size is desirable as it imparts higher strength to the product.

Example 3 This example is similar to Example 2 (the same copper-zirconia powder was used), except that 10 weight percent copper was added to the aluminum-1% magnesium melt. The product was cast and extruded and its tensile strength at 600° (316°C) was determined to be twice that of a control product without zirconia.

Example 4 This example is similar to Example 2 except that alumina with an average particle size of 0.005 microns is used as the dispersoid. The grain size of the cast 2024 aluminum alloy is that of the same alloy without dispersoids (control).
The relative difference in grain size increased after aging this casting for 100 hours at 600°C (316°C). Compared to the control, the tensile strength is
It doubled at 600° (316°C), and this improvement in performance persisted even after aging at 600° (316°C) for 100 hours.

As previously mentioned, an important feature of the present invention is the average particle size of the reinforcing oxide. For a constant volume of reinforcing oxide, any increase in particle size (by coagulation or agglomeration) results in an increase in particle spacing and a decrease in strength. Desired particle size (max.
Although it is possible to provide a reinforcing oxide from the beginning (0.025 microns), the reinforcing oxide is Care should be taken to avoid agglomeration or agglomeration.

Agglomeration of the reinforcing oxide can be avoided by keeping the particles separate from each other, which allows individual particles of reinforcing oxide to be mixed with other particles during various process steps. This can be achieved by surrounding it with These other particles are particles of a second oxide (e.g. copper oxide or iron oxide) or particles of a metal that has been chemically reduced from the second oxide, but which may be reduced during the process. different. Furthermore, care must be taken to avoid agglomeration or agglomeration of the surrounding particles. This is because when this happens, the reinforcing oxide particles are pushed toward the corners where they are not surrounded or mechanically entrained by other particles (i.e., secondary oxide or metal particles). I'll get hit. In this case, agglomeration of the reinforcing oxide particles cannot be easily avoided.

Agglomeration of adjacent particles is promoted by thermal stress. Initially, there are pores or voids between adjacent particles (i.e. gel-like structure), but under the influence of thermal stress, the particles enter or fill the voids, first forming necks between adjacent particles. the tendency for groups of 10 to 50 adjacent particles to agglomerate to form increasingly oval structures There is. Eventually, many small particles coalesce into one spherical particle.

The mechanism described above applies to copper oxide particles surrounding reinforcing oxide particles; once the copper oxide particles have coalesced, the reinforcing oxide particles are no longer surrounded by the reinforcing copper oxide particles as before; There is more room for the oxide particles to move, and the reinforcing oxide particles will further aggregate in the manner described above. When agglomerates of 10 to 50 particles are formed, and virtually all the reinforcing oxide particles are agglomerated in this way, the number of particles available for reinforcement is reduced by a factor of 10. to 1/50, and the particle spacing increases by a factor of 10 or 50.

Therefore, it is desirable to avoid conditions that reduce the extent to which reinforcing oxide particles become surrounded or mechanically entrained by other particles (eg, copper oxide or copper). moreover,
It is desirable to reduce conditions where reinforcing oxide particles are pushed aside by other particles or allow reinforcing oxide particles to migrate. Thus, it is necessary to reduce the amount of pores or voids in the mixture of reinforcing oxide and other particles mentioned above as much as practicable.

Since agglomeration can occur at the various process steps mentioned above, steps must be taken to minimize the chance of agglomeration occurring at each of these steps. Thus, for example, in a coprecipitation process where copper oxide is coprecipitated with colloidal alumina, concentrated solutions (e.g. 3 molar copper nitrate solutions) are preferably used and these solutions are placed in a vigorously stirred mixing vessel. It should be introduced where it is. Highly concentrated solutions produce dense coprecipitates with less volume occupied by pores and voids, reducing the chance of agglomeration,
In particular, the chance of agglomeration during drying during the coprecipitation process is reduced.
A dense coprecipitate is one in which the volume occupied by the pores or voids is less than the volume occupied by the particles.

During the reduction process in which copper oxide is converted to copper, interfacial energy tends to reduce the surface area of the copper particles (i.e., sinter them), and as the surface area of the copper particles is reduced, the reinforcing oxide particles are eliminated. The reinforcing oxide particles can agglomerate or coalesce during this process step if they are removed or pushed aside. Global sintering of the copper particles after reduction must be avoided by keeping the final temperature below 800°C (1472°C).

After adding the billet, agglomeration can occur in the melt bath, especially if copper or iron oxides are present. Copper or iron oxides tend to react with wet metals, such as magnesium, to form magnesium on acid (magnesia). As magnesia is formed, it tends to collect reinforcing oxide particles, such as alumina, in the form of magnesium aluminate. This collection of many alumina particles together reduces the number of alumina particles in the product and increases the particle spacing, resulting in reduced strength at high temperatures. Therefore, the content of copper oxide or iron oxide in the billet is controlled and the oxygen present as copper oxide or iron oxide accounts for 0.05 of the weight of copper or iron in the billet.
It is desirable that this oxygen is less than 0.01%.
% is even more desirable.

Agglomeration can also occur in the melt bath if the copper-alumina billet melts too quickly. It is desirable to compress the copper-alumina powder and lightly sinter the compressed billet to reduce its surface area and reduce its dissolution rate. In addition to this, the melting rate increases the temperature of the melting bath by increasing the melting point of the melting bath (i.e. aluminum alloy) by 100
It can also be reduced by controlling the temperature to a level above 150°C.

After the billet is completely dissolved in the melt bath,
Dispersed particles of reinforcing oxide may grow by a phenomenon known as Ostwald growth. For this reason, it is important to select a reinforcing oxide that has a low solubility in the molten metal; if the solubility is low, the reinforcing oxide has little tendency to grow in the molten metal. If the grains are grown by Ostwald growth, the grain size of these grains can easily exceed 0.025 microns and an effective high temperature strengthening mechanism will be lost. To avoid Ostwald growth, the free energy of formation and melting point of the reinforcing oxide must be relatively high. Oxides with free energies of formation lower than that of zirconia are undesirable, and it is desirable that the dispersoid have a melting point above 1500°C (2732°).

The foregoing detailed description has been presented for the purpose of clarifying the understanding of the invention and no unnecessary limitations should be found thereon as modifications will become apparent to those skilled in the art.

Claims (1)

Claims: 1. A metal product in cast form, comprising a matrix consisting essentially of aluminum and reinforcing oxide particles dispersed throughout said matrix, the reinforcing oxide has a free energy of formation of greater than 100 kilocalories per gram atom of oxygen in the oxide, said cast product further comprising wet metal for said reinforcing oxide, and said casting product further comprising wet metal for said reinforcing oxide; the wet metal is reactive to form an oxide having a free energy of formation greater than the free energy of formation of the aforementioned reinforcing oxide, and the average particle size of the aforementioned reinforcing oxide particles is 0.025
microns, the said reinforcing oxide particles do not exceed 1% of the volume of said metal product, said particle spacing is less than 0.2 microns, and further said casting products have a welding temperature which can be welded without losing its physical properties. 2. The product of claim 1, wherein said particles are substantially uniformly dispersed in said matrix. 3. A product according to claim 1, wherein said particles are discrete and substantially equiaxed. 4. A product according to claim 1, wherein said particles are substantially spherical. 5. The product of claim 1, wherein said reinforcing oxide is selected from the group consisting of magnesia, alumina, zirconia, thoria and rare earth metal oxides with atomic numbers 59-71. 6. The product of claim 1, wherein said reinforcing oxide has a melting point sufficiently higher than the melting point of said matrix such that said reinforcing oxide is stable when melting said matrix. 7. A product according to claim 1, wherein said reinforcing oxide has a melting point above 1500°C (2732°C). 8. A product according to claim 1, wherein the particles of said reinforcing oxide account for at least 0.05% of the volume of said product. 9. The product of claim 8, wherein said wetting metal is present in an amount sufficient to wet substantially all particles of said reinforcing oxide. 10 Claim 1, wherein said reinforcing oxide particles account for 0.05 to 0.5% of said product volume.
Products described in Section. 11. The product of claim 1, wherein said reinforcing oxide is alumina and said wetting metal is magnesium. 12 The above-mentioned magnesium is added to the above-mentioned product.
12. A product according to claim 11, which is between 0.1 and 4 percent by weight. 13. The product of claim 1, wherein said matrix consists of an aluminum-based alloy. 14. The product of claim 13, wherein said aluminum-based alloy comprises copper. 15. The product of claim 1, wherein said particle spacing is in the range of about 0.05 to 0.15 microns. 16. The product of claim 1, wherein said average particle size ranges from 0.005 to 0.015 microns. 17. A method for producing a metal product having a matrix consisting essentially of aluminum and discrete particles of a reinforcing oxide dispersed throughout the matrix, the method comprising the steps of: a process in which the aforementioned separating particles of reinforcing oxide are injected with a sufficient amount of a second oxide selected from the group consisting of copper oxide and iron oxide. a second oxide comprising substantially up to 20% by volume of said reinforcing oxide particles dispersed in said second oxide, said reinforcing oxide particles being surrounded by said reinforcing oxide particles and keeping said reinforcing oxide particles separated from each other and in a loose state; a process of forming a first dispersoid; a process of reacting the second oxide in the first dispersoid with hydrogen at high temperature to reduce the second oxide to a metal; continuing said reaction process until the oxygen content of the unreduced second oxide from the dispersoid is less than 0.1% by weight of the amount of said metal reduced from the second oxide; As a result of the aforementioned reaction process, a second particle consisting essentially of isolated particles of the aforementioned reinforcing oxide dispersed in the aforementioned metal particles substantially free of oxygen surrounding the isolated particles of the aforementioned reinforcing oxide is formed. forming a dispersoid; compressing said second dispersoid into a compressed shape; adding said compacted formation to said melt bath in the substantial absence of oxygen, and dispersing separated particles of said reinforcing oxide substantially uniformly into said melt bath; slowly melting the metal surrounding said reinforcing oxide particles into said melting bath; and pouring said melting bath containing said dispersed reinforcing oxide into a cast form. process and something that consists of. 18. The method of claim 17, wherein said reinforcing oxide comprises 5 to 20% by volume of said first dispersoid. 19. A method according to claim 17, comprising avoiding total sintering of said metal particles in said reaction process. 20 The temperature in the above reaction process was set to about 800°C.
(1472〓). 21. Claim 17, which comprises, prior to the addition step, heating the compacted product in an oxygen-free atmosphere to effect a slight sintering of the metal particles at least on the surface of the compacted product. The method described in section. 22. The method of claim 21, comprising limiting the temperature during said mild sintering of said compacted formation to no more than about 700°C (1292°C). 23. Claim 17 consisting of preventing said metal particles from agglomerating during said reaction process and preventing surface oxides from forming on said compacted product.
The method described in section. 24. The method of claim 23, wherein said metal particles consist of copper. 25. The method of claim 17, wherein said reinforcing oxide has a free energy of formation of greater than 100 kilocalories per gram atom of oxygen in said reinforcing oxide. 26. The method of claim 25, wherein said reinforcing oxide has a melting point sufficiently higher than the melting point of said melt bath such that said reinforcing oxide is stable within said melt bath. 27. Claim 26, wherein said reinforcing oxide has a melting point above 1500°C (2732〓), and further, the temperature of said melting bath is lower than the melting point of said reinforcing oxide.
The method described in section. 28 The above-mentioned reinforcing oxides include magnesia, alumina, zirconia, thoria, and atomic numbers 59 to 71.
27. The method of claim 26, wherein the rare earth metal oxides are selected from the group consisting of rare earth metal oxides. 29. said melt bath comprises a wetting metal for said reinforcing oxide, and the said method further comprises, in said addition step, wetting separated particles of said reinforcing oxide with said wetting metal; 18. The method of claim 17, comprising promoting the dispersion of said reinforcing oxide as loose particles. 30. The method of claim 29, wherein said reinforcing oxide is alumina and said wetting metal is magnesium. 31 The above-mentioned enclosing process causes (a)
Claim 17 comprising a co-precipitation of said reinforcing oxide and (b) said second oxide or a compound capable of being chemically reduced to form said second oxide. Method described. 32. A patent in which said chemically reducible compound is a hydroxide and said enclosing step consists of heating said hydroxide to convert it into said second oxide. 32. The method of claim 31. 33 The aforementioned metal surrounding the aforementioned reinforcing oxide particles is added to the aforementioned melt bath by limiting the temperature of the melt bath to no more than about 150° C. above the melting point of the aforementioned melt bath. 18. The method according to claim 17, which dissolves slowly. 34. In order to prevent said compression process from re-oxidizing said substantially oxygen-free metal,
18. The method of claim 17, which is carried out in an oxygen-free atmosphere. 35. The method of claim 34, wherein said addition step is carried out in an oxygen-free atmosphere. 36. Prior to said addition step, said compaction is exposed to a reducing atmosphere at an elevated temperature to reduce any oxides that may have been formed after said reaction step. Method. 37 Claims wherein the first and second dispersoids and the compacted product are maintained in an oxygen-free atmosphere between the first-mentioned surrounding step and the addition step. The method according to paragraph 17.