CN1767915A - Method and apparatus for producing metal alloys - Google Patents

Abstract

A method and apparatus for producing a metal component from a non-dendritic, semi-solid metal alloy slurry involves the use of a graphite agitator that is functionally equivalent to conventional metal rod agitators, and has the additional advantage of having a very low surface wettability, whereby labor and expenses associated with removing a metal alloy skin formed after withdrawal of the agitator from a metal slurry is eliminated or at least substantially reduced. The invention also provides an improved process and apparatus for producing a metal component from a non-dendritic semi-solid metal slurry by transferring the slurry to a cooling vessel for subsequent cooling and raising of the solids content without agitation after the slurry has been formed with agitation in a first vessel, whereby more rapid cooling of the slurry and increased production rates are achievable.

Description

Method and apparatus for producing metal alloys

Pursuant to Title 35, United States Code, Section 119(e), this application claims the title "PROCESS AND APPARATUSFOR PREPARING A METAL ALLOY" filed March 4, 2003 by James A Yurko et al. Priority Application No. 60/451,748, the entire disclosure of which priority text is hereby incorporated by reference, also claims James A Yurko et al. On the 6th, the title of "PROCESSAND APPARATUS FOR PREPARING A METAL ALLOY" (method and device for preparing metal alloys) and the priority of application number 60/476,438, the entire disclosure content of this priority text is cited by this application as a reference.

technical field

The present invention relates to the field of metal forming for industrial use, and in particular to an apparatus and method for forming metal parts from non-dendritic, semi-solid metal paste.

Background technique

It is well known that most metal alloy constituents are dendriticly consolidated. When the alloy composition is cooled below the liquidus temperature, it gradually forms dendritic or dendritic particles from the crystal nucleus. It is also well known that there are certain advantages to segmenting dendritic particles or arresting dendritic growth during consolidation to form non-dendritic or degenerated dendritic particles that are generally spherical or ellipsoidal. In particular, it has been discovered that various process and physical property advantages can be obtained by casting or otherwise forming metal parts from non-dendritic, semi-solid metal slurries. The non-dendritic metal particles in the semi-solid metal paste greatly reduce the viscosity of the specific solid fraction compared to semi-solid metal alloy compositions containing dendritic particles. The difference in viscosity is typically several orders of magnitude.

Advantages of non-dendritic semi-solid metal forming include: higher speed part forming, high speed continuous casting, lower mold corrosion, less energy loss, improved mold filling, reduced oxide (which improves the final metal machinability of the part), less entrapped gas (thus reducing its porosity). Other advantages of casting or otherwise forming metal parts from semi-solid slurries include less shrinkage during forming the metal part, fewer pores and less porosity in the formed metal part, lower and macrosegregation and More uniform mechanical properties (such as strength). It is also possible to form more complex parts using non-dendritic semi-solid alloy compositions in casting or other forming processes. For example, parts can be formed with thinner outer walls and improved strength properties.

Nondendritic semi-solid slurries for industrial casting and other metal forming processes have been prepared by using mechanical mixing during cooling of the liquid metal alloy composition below the liquidus temperature of the alloy composition. Other techniques that have been used include electromagnetic stirring during cooling (often used in continuous casting processes), cooling of liquid metal components as they travel through tortuous channels, prolonged heat treatment in the semi-solid temperature region, etc. These processes are well known and have been well employed in a variety of industrially important applications.

More recently, non-dendritic semi-solid slurries have been produced by pouring superheated molten alloys into relatively cool vessels such as furnaces or cooling chambers of die casting machines. These processes rely on cooling the alloy constituents from above the liquidus temperature to below the liquidus temperature as the alloy contacts the vessel walls during pouring. This process is effective in forming non-dendritic semi-solid metal pastes; however, it has process limitations. First, the process relies on heat removal from the vessel walls. Controlled heat removal using this technique is difficult due to the varying vessel wall temperature and discontinuous cylindrical surface area. Second, convection occurs through pouring; therefore, if the alloy is injected at too high a temperature, the convective forces dissipate before the alloy cools through the liquid phase, preventing the formation of a non-dendritic slurry.

Industrial products include various aluminum-magnesium alloy components for automotive applications, such as master brake cylinders, and various components for steering and suspension systems. Other actual or potential applications include rocker arms, engine pistons, wheels, transmission components, fuel system components, and air conditioning components.

A problem with known processes using mechanical agitation to form non-dendritic semi-solid metal slurries is that the surfaces of the agitator become wetted by the liquid metal in the slurry. Therefore, when the stirrer is removed from the metal slurry, some of the liquid metal in the slurry will stick to the surface of the stirrer. Some of the liquid metal that wets or sticks to the surface of the stirrer and/or vessel solidifies rapidly and forms a metallic coating that must be used before the stirrer and/or vessel can be used again to prepare more non-dendritic semi-solid metal slurry be removed. Removing metal deposits from agitator surfaces is often difficult, time-consuming and costly, and results in lower yields. Materials with lower wettability are generally not suitable for processing liquid metal alloy compositions (e.g. because they lack sufficient mechanical properties relevant to the production of non-dendritic semi-solid metal slurries at high temperatures) and/or do not have sufficiently high Thermal conductivity suitable for rapid heat removal from non-dendritic semi-solid metal slurries. Lower wetting properties can be achieved by applying a low-wetting coating to the surface of the metal stirrer. Boron nitride coatings have been used on stirrer and/or vessel surfaces to successfully reduce wetting without reducing their thermal conductivity. However, boron nitride coatings lack structural strength and require periodic replacement.

Another problem with using conventional processes to prepare non-dendritic semi-solid metal alloy compositions with relatively high solids content (eg, greater than about 10%) is that it often requires a significant amount of time to cool the metal slurry to achieve the desired solids content. The alloy components are usually stirred in a ceramic vessel or a preheated vessel to prevent the formation of nuclei and solids in the walls of the vessel in which the stirring is done. Consequently, cooling takes place relatively slowly, resulting in longer processing times and lower throughput. Rapid cooling can be obtained by using a cool container with sufficient mass, thermal conductivity and thermal capacity. However, this can create unacceptably high temperature gradients that are detrimental to the formation of a non-dendritic semi-solid metal paste, and/or cool the alloy composition to temperatures that are not suitable for configuring the alloy composition into the desired part.

US Pat. No. 6,645,323 discloses a skinless metal alloy composition containing no enclosed gas and comprising primary phase solid discontinuous degenerate dendrites uniformly distributed in the secondary phase. The disclosed alloys are formed by a process in which the metal alloy is heated in a vessel until it becomes liquid. Thereafter, the liquid is rapidly cooled while vigorously agitating under conditions that avoid trapping gas in solid nuclei that are formed uniformly distributed in the liquid. The cooling and agitation is accomplished using a cooling rotary probe that extends into the liquid. When the liquid contains a small amount of solid or the liquid-solid alloy is removed from the stirring source, the agitation is stopped while cooling is continued to form the primary phase solid discontinuous degenerate dendrites in the liquid secondary phase. A solid-liquid mixture is subsequently formed, for example by casting.

One problem with the process disclosed in US 6,645,323 is that the cooling rotating probe used for cooling and stirring tends to be coated with liquid metal which sticks to the surface of the stirrer. Accordingly, the agitators described in this patent require frequent cleaning and/or replacement. Additionally, there is a need for improved control of heat removal by aluminum alloy components. In certain aspects of the invention, methods and apparatus are provided that overcome these deficiencies.

Contents of the invention

The present invention provides an improved method for producing non-dendritic semi-solid alloy slurries for forming metal parts. In particular, the present invention provides an apparatus and method that facilitates rapid cooling of non-dendritic semi-solid metal slurries and/or eliminates or reduces problems associated with accumulation and removal of metal on apparatus surfaces that contact the metal slurries.

According to one aspect of the present invention, it provides a method and device for preparing a non-dendritic semi-solid metal alloy slurry using a graphite stirrer. The graphite stirrer has suitable high temperature strength properties and thermal conductivity which facilitate rapid cooling of the liquid alloy composition, and which also exhibits low wettability, thus eliminating or greatly reducing the need for moving the stirrer from The need to remove the metal from the stirrer surface after the metal slurry has been withdrawn, and any metal that has accumulated on the stirrer can be easily removed. Thus, graphite stirrers can be used to simultaneously remove heat from the alloy constituents, and can also promote convection that favors the formation of non-dendritic semi-solid alloy constituents, and can also prevent the metal slurry from freezing or depositing on the stirrer.

According to another aspect of the invention, depending on the initial temperature of the aluminum alloy composition prior to contact with the agitator and the rate at which the agitator removes heat, the amount of heat removed from the aluminum alloy composition can be determined by contacting the aluminum alloy composition with the agitator for a predetermined period of time. controlled by a set time period.

In yet another aspect, it provides a method and apparatus for rapidly cooling a non-dendritic semi-solid metal alloy slurry to a temperature at which the metal alloy slurry contains a relatively low solids content (e.g., from about 1% to about 10% by weight) The temperature at which the metal alloy paste contains a relatively high solids content (eg, from about 10% to about 65% by weight). The methods and apparatus described involve the use of a vessel having walls made of a material of high thermal conductivity that facilitate rapid cooling of a metal alloy slurry. A fan or blower can be used to direct cool air around the container walls.

These and other features, advantages and objects of the present invention can be further understood and appreciated by those skilled in the art in conjunction with the following description, claims and accompanying drawings.

Description of drawings

Fig. 1 is a schematic diagram of a device according to an embodiment of the present invention.

Fig. 2 is a schematic diagram according to another embodiment of the present invention.

Detailed ways

As shown in FIG. 1 , there is shown an apparatus 10 for preparing a non-dendritic semi-solid metal alloy composition according to an embodiment of the present invention. A non-dendritic semi-solid metal composition is a composition comprising liquid metal and discrete solid non-dendritic alloy particles distributed in the liquid metal. Non-dendritic particles are particles that are generally spherical or spheroidal in shape and that result from convection in the liquid phase during nucleation and cooling of the liquid below the liquidus temperature of the alloy constituents. One accepted theory is that the non-dendritic particles are produced by convection that breaks up the growing dendrite arms, with subsequent maturation helping to smooth the particles into their characteristic spherical and/or ellipsoidal shapes. For this reason, non-dendritic grains are sometimes referred to as degenerated dendritic grains.

The device includes a first holding container 12 for containing and maintaining a liquid alloy composition, and an agitator 14 is inserted into the liquid alloy composition and rotated to generate convection in the liquid alloy composition. The stirrer also conducts heat from the alloy constituents and forms crystal nuclei. As the cooling lowers the liquid metal alloy from a temperature just above the liquidus temperature to a temperature below the liquidus temperature, as the ingredients are agitated, non-dendritic solid particles 16 gradually separate from the liquid to form a semi-solid metal paste18. Ideally, the stirrer is made of a material and of a mass that is able to Quickly removes heat from alloy components. That is, it is desirable to design the stirrer 14 to rapidly remove the heat required to form a non-dendritic semi-solid metal alloy composition, which typically contains about 1% to 20% solids by weight. The duration of stirring with the stirrer controls the heat removal from the aluminum alloy composition. Therefore, if there is a variation in the initial metal temperature, the duration of stirring is controlled to produce a product of the same temperature. The temperature of the metal can be controlled using any of a variety of devices, such as optical pyrometers, thermocouples, and the like.

For example, the stirrer 14 may be cylindrical. Thus, stirrer 14 may differ significantly from conventional stirrers that physically disrupt the dendrites as they form. However, cylindrical stirrers capable of achieving rapid cooling produced crystal nuclei or degenerated dendrites distributed by convection generated by the stirring motion. Thus, it is unnecessary to use conventional mechanical agitation, which physically breaks up the dendrite arms, to form a non-dendritic metal slurry.

According to a preferred embodiment of the present invention, said stirrer has relatively high thermal conductivity (preferably comparable to that of copper) and relatively low wettability in the presence of aluminum (preferably comparable to that of copper) Compared with boron nitride) material. One recognized stirrer may be a copper stirrer coated with boron nitride. It is however more desirable to provide an uncoated stirrer that has the required thermal diffusivity to remove heat quickly, which is important for preventing the stirrer surface from approaching the liquidus temperature of the alloy constituents, and also has the required low wettability to prevent metal accumulation or accumulation on the surface of the agitator when it is removed from the metal slurry. A very useful material for making stirrer 14 has been found to be graphite. Graphite has a relatively high thermal diffusivity (as compared to copper) and relatively low wettability (as compared to boron nitride coatings). Graphite stirrers have been found to have strength and thermal properties functionally equivalent to stirrers commonly used to form non-dendritic semi-solid metal alloy slurries, with the added advantage of being substantially non-wetting to liquid metal alloys. Thus, it is possible to reuse the graphite stirrer for multiple individual cycles without removing the metal alloy from the stirrer surface. However, the rod surface must be at a temperature below the liquidus temperature of the alloy to quickly remove heat from the molten alloy. Furthermore, any accumulated metal can be easily removed, for example by passing the surface of a graphite stirrer against the sleeve.

The method of the present invention includes a first step of forming a metal alloy liquid composition. Said liquid alloy composition is located in container 12 and is allowed to cool while stirring the alloy to be cooled as hard as possible, for example by stirring under certain conditions, to form solid nuclei particles, while avoiding the encapsulation of gas in the stirred alloy composition. Efforts are made to agitate the alloy while the alloy is cooling in such a manner that the solid nuclei are distributed substantially uniformly throughout the metallic liquid alloy composition. The agitation can be carried out for a short period of time using a rapid cooling speed range within a temperature range, such as between about 1 second and about 1 minute, preferably between about 1 second and 30 seconds. The percent solidification of the alloy corresponds to between about 1% and about 20% by weight solids, preferably between about 3% and about 7% by weight solids. Said agitation can be achieved using a cool stirrer in any way that avoids creating too many cavities at the surface of the liquid and thus avoids trapping gas within the liquid. The agitator is cooled by a heat exchange fluid such as water. Representative suitable stirring means include one or more cylindrical rods provided with internal cooling means, helical stirrers or the like, which preferably extend through the depth of the liquid. The depth of the stirrer extending into the liquid basically reaches 100% of the liquid depth, so as to facilitate the uniform distribution of crystal nuclei. Then, the agitation is stopped in a batch production, or the liquid-solid alloy is removed from the agitation source in a continuous production. Thereafter, the formed liquid-solid metal alloy composition is cooled in a container so that spherical solid particles form around the solid nucleus particles and reach a certain concentration, wherein non-dendritic spherical and/or ellipsoidal solid particles increase the overall liquid-solid The viscosity of an ingredient where the liquid-solid ingredient can be moved to a forming step, such as a casting step. Typically, the upper weight percent of the non-dendritic primary phase solids is between about 40% and about 65%, and preferably contains 10% to 50% of the total weight of the liquid-solid components. In the absence of agitation, the formation of spherical and/or ellipsoidal solid particles can be achieved by coarsening without forming an interlinked dendritic network. Since the stirring is effected only for a short time, gas entrapment within the alloy components is avoided. Furthermore, it has been found that by operating in this manner, macrosegregation of elements is eliminated or minimized throughout the entire batch of metal alloy product produced. Thereafter, the liquid-solid composition is shaped, for example by casting.

The metal alloy composition comprising non-dendritic solid metal alloy particles and a liquid phase can be composed of a variety of metals or alloys which can form a dendritic network when frozen from the liquid state without agitation. The non-dendritic particles may consist of a primary phase having an average composition different from the average composition of the surrounding secondary phase (liquid or solid phase depending on temperature), said secondary phase The phases themselves may include primary and secondary phases depending on further solidification.

The non-dendritic solids (degenerate dendrites) are characterized by smooth surfaces and few branched structures, which are closer to spherical structures than usual dendrites and do not have dendrites, where dendrites In , the interconnection of primary phase particles is affected to form a dendritic network. Furthermore, primary phase solids are not substantially eutectic. The term "secondary phase solid" as used herein means the phase formed by the solidification of the liquid present in the metal slurry at a temperature lower than that at which non-dendritic solid particles are formed. Typically, solidified alloys have dendrites that separate from each other in the early stages of solidification, ie 15 to 20 weight percent solids, and form interconnected dendrites as the temperature decreases and the weight percent solids increase. mesh. On the other hand, the compositions of the present invention containing primary phase, non-dendritic solids prevent the formation of interconnected networks by maintaining discrete non-dendritic particles separated from each other, even up to 65% solid fraction (weight percent) obtained through the liquid phase.

After the formation of the non-dendritic solid, during the formation of the liquid phase by solidification, the secondary phase solid formed contains one or more types of phases that can be obtained during solidification by conventional shaping methods. That is, the secondary phase includes a solid solution, or a mixture of dendrites, compounds, and/or solid solution.

The size of the non-dendritic particles depends on the alloy or metal composition used, the temperature of the solid-liquid mixture, and the time the alloy spends in the solid-liquid temperature range. In general, the size of the primary phase particles depends on the composition and thermomechanical history of the metal paste, the number of nuclei formed, the cooling rate, and it ranges from about 1 micron to about 10,000 microns and across all metal alloy compositions. uniform. Preferably, the ingredients comprise from 10% to 50% by weight primary phase solids because they have a viscosity that promotes ease of casting or shaping.

The compositions of the present invention may be formed from any metal alloy system which, when formed from liquid freezing, forms a dendritic structure. Even if pure metals and eutectics melt at a certain temperature, they can be used to form the compositions of the present invention because, by controlling the net heat input or output to the melt, they exist in liquid-solid equilibrium at the melting point so that the metal or eutectic The substance contains enough heat at the melting point to melt only a portion of the metal or eutectic liquid. This situation arises because the complete removal of the heat of fusion in the metal paste used in the casting process of the present invention cannot be obtained by equalizing the heat supplied and the heat removed by the cooling means of the surrounding environment. Typical suitable alloys include, but are not limited to, lead alloys, magnesium alloys, zinc alloys, aluminum alloys, copper alloys, iron alloys, cobalt alloys. Examples of these alloys are lead-tin alloy, zinc-aluminum alloy, zinc-copper alloy, magnesium-aluminum alloy, magnesium-aluminum-zinc alloy, magnesium-zinc alloy, magnesium-silicon alloy, aluminum-copper-zinc-magnesium alloy, copper-tin bronze, brass, aluminum bronze, Steel, cast iron, tool steel, stainless steel, super heat-resistant stainless steel, and cobalt-chrome alloys, or pure metals such as iron, copper, or aluminium.

Fig. 2 shows an alternative embodiment of the present invention, and it comprises device 10, and this device is similar to the embodiment shown in Fig. 1 substantially, but it comprises a cooling container 20, and stirring is completed in holding container 12 and After the solids content has reached about 1% to about 20%, the metal slurry 18 is poured into a cooling vessel 20 . The cooling container 20 has a wall 22 made of a material with high thermal conductivity. The vessel wall 22 has a total heat capacity (the specific heat capacity of the wall multiplied by the mass of the wall) that allows the wall 22 to quickly reach temperature equilibrium with a given amount of metal paste 18 to maintain a relatively low predetermined temperature before the vessel wall 22 comes into contact with the metal paste. When the temperature is set, the metal slurry can be cooled rapidly to obtain the desired solid content. A fan or blower 24 may be used to generate a high velocity to move heat from the metal paste through the wall 22 and from there to the surrounding air, thereby cooling the metal paste 18 rapidly. This allows for higher production speeds.

Suitable materials with high thermal conductivity can be used for the walls of vessel 20, including steel, stainless steel and graphite. Graphite is well suited for high throughput at low cost because of its high thermal conductivity compared to metals and its surface exhibits low wettability for various metal alloys of interest, such as alloys of aluminum and magnesium. wetness. Accordingly, relatively rapid cooling of alloy slurries from lower solids contents (e.g., from about 1% to about 20%) to higher solids contents (e.g., from about 10% to about 65%) is possible, while the surface of vessel 20 High-speed production at low cost is possible because it can be reused without subsequent cleaning to remove metal deposits and/or can be removed relatively easily. When the vessel 20 is made of a metal or other material that has a wettable surface relative to the metal paste, the interior walls of the vessel that are in contact with the alloy paste are preferably coated with a low wettability coating, such as a boron nitride coating.

The cooling vessel 20 may be cooled by passing a heat transfer fluid through cooling channels formed or provided in the walls of the cooling vessel. Likewise, the cooling vessel may have suitable surface area, mass, and heat capacity to rapidly cool the slurry at rest from a lower solids content to a desired higher solids content without cooling the slurry to a suitable level. The temperature below which the desired metal part is formed.

After the metal paste 18 has cooled to the desired higher solids content without agitation (ie, at rest), the metal paste can be formed into the desired metal part, such as by casting.

First example of graphite stirrer

A batch of molten aluminum alloy is maintained in a container. The aluminum alloy has the following properties:

Temperature (T _I ) = 640°C

Latent heat of fusion (H _f ) = 400,000J/kg (where J is Joule, energy unit)

Heat capacity of aluminum (C _p )≈1,000J/(kg℃)

Amount of aluminum alloy (m) ≈ 4kg

In order to cool a partially solidified aluminum alloy to 610°C and a percent solid of 0.10, the following amount of heat must be removed:

Solid content (Δf _s ) = 0.10

Temperature ( _Tf ) = 610°C

$\mathrm{<span\; class="notranslate">\; \&Delta;H</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; m</span>}\underset{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\overset{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}\mathrm{<span\; class="notranslate">\; dT</span>}$

In order to remove 280,000 joules of energy, the rod must have sufficient mass and heat capacity to absorb this amount of energy. The rod must also have a high enough thermal diffusivity a to allow heat to be removed from the surface of the rod, keeping the surface temperature below the liquid temperature of the alloy.

Graphite cylindrical stirrer:

Outer diameter (R _O )＝0.025m

Column height (H) = 0.25m

Graphite density ≈1,800kg/m ³

Graphite mass = 0.88kg

If the rod has an initial temperature of 100°C and is raised to 500°C, the rod can remove the following amount of heat:

Rod temperature = 100°C

Mass of graphite container = 0.88kg

The heat capacity of graphite ≈800J/(kg℃)

The rod has sufficient mass and heat capacity to absorb the heat of the aluminum, thereby cooling the alloy from above its liquidus temperature to below it.

thermal diffusivity

The rod removes heat from the molten aluminum alloy through its surface according to the following heat transfer formula:

q(W)=hAΔT

Heat transfer coefficient (h) ≈ 1,500 W (m ² °C), where W is watts (J/s).

Rod surface area = 0.0393m ²

Average temperature difference = 250°C

The rod has to remove 280,000J of heat, and the heat transfer rate is 15,000W, so the time required to remove the heat transfer is about 19 seconds. This duration will vary depending on the thermophysical properties of the alloy, the initial temperature of the alloy, and the rod and mass and thermophysical properties.

The thermal diffusivity (α) is defined as the thermal conductivity (k) divided by the product of the density (ρ) and heat capacity (C _p ) of the material:

$\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}$

For materials with low thermal conductivity and high density, such as ceramic materials, the thermal diffusivity is low. The material cannot transfer heat from its surface to its interior, therefore, the surface temperature is in equilibrium with the alloy, and it cannot further reduce the temperature of the alloy.

In addition to being of sufficient mass to absorb energy from the alloy, the material of the rod must have a suitable thermal diffusivity to transfer heat from the surface of the rod to its interior.

If a heat transfer fluid is used to remove heat from the rod with agitation and heat removal, a rod with a high thermal diffusivity can have a lower mass than normally required to absorb enough energy within the alloy to initiate solidification.

Second Example of Graphite Stirrer

A continuous batch of molten aluminum alloy is kept in a container. Described aluminum alloy has following process:

The temperature of the first batch (T _I ) = 640°C

The temperature of the second batch (T _I ) = 657°C

Latent heat of fusion (H _f ) = 400,000J/kg (where J is Joule, energy unit)

Heat capacity of aluminum (C _p )≈1,000J/(kg℃)

Amount of aluminum alloy (m) ≈ 4kg

In order to cool a partially solidified aluminum alloy to 610°C and a solids content of 0.10, the following amount of heat must be removed:

Solid content (Δf _s ) = 0.10

Temperature ( _Tf ) = 610°C

$\mathrm{<span\; class="notranslate">\; \&Delta;H</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; m</span>}\underset{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\overset{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}\mathrm{<span\; class="notranslate">\; dT</span>}$

First batch:

Second batch:

The stick in this example can displace 15000W. In the first batch the rods had to remove 280,000J and in the second batch the rods had to remove 348,000J. The time required to remove the heat from the first batch and the second batch was 19 seconds and 23 seconds, respectively.

By measuring the temperature of the melt before cooling and stirring with the stirrer, temperature variations within the semi-solid slurry can be eliminated. The duration of agitation can be determined by an algorithm based on the temperature of the metal being added, the temperature of the rod and the time delay (energy lost to the surroundings), among others.

Examples of cylindrical containers (cooling cups)

A batch of partially solidified aluminum alloy is kept in a container. The aluminum alloy has the following properties:

Temperature (T _I ) = 610°C

Solid content (f _s ) = 0.10

Latent heat of fusion (H _f ) = 400,000J/kg (where J is Joule, energy unit)

Heat capacity of aluminum (C _p )≈1,000J/(kg℃)

Amount of aluminum alloy (m) ≈ 4kg

In order to cool a partially solidified aluminum alloy to 590°C and a solids content of 0.30, the following amount of heat must be removed:

Solid content difference (Δf _s ) = 0.20

Temperature ( _Tf ) = 590°C

$\mathrm{<span\; class="notranslate">\; \&Delta;H</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; m</span>}\underset{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\overset{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}\mathrm{<span\; class="notranslate">\; dT</span>}$

In order to remove 400,000 joules of energy, the container is designed to absorb this amount of heat. A thin-walled graphite container with the following properties can remove this heat.

Graphite cylindrical container:

Inner diameter (R _i ) = 0.0508m

Outer diameter (R _o )＝0.0568m

Column height (H) = 0.2346m

Wall thickness (t) = 0.006m

Graphite density ≈1,800kg/m ³

Graphite mass = 0.97kg

If it has an initial temperature of 90°C and is in equilibrium with aluminum at 590°C, the graphite can remove the following amount of heat:

The temperature of graphite = 90°C

Mass of graphite container = 0.97kg

The heat capacity of graphite ≈800J/(kg℃)

The graphite vessel required the same amount of heat to reach a temperature of 590°C. Thus, graphite containers are designed to quickly remove a predetermined amount of heat so as to range from a first value in the range of about 1% to about 10% by weight to a second value in the range of about 10% to 65% by weight. Two values, rapidly increasing solids content.

What has been described above is considered to be a preferred embodiment only. Various changes to the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it can be understood that the above-mentioned embodiments are only for illustrative purposes, and are not intended to limit the scope of the present invention. When interpreting according to the principles of patent law including the doctrine of equivalents, the scope of the present invention is defined by the following claims To limit.

Claims (27)

CLAIMS 1. A method of producing a metal part from a liquid metal alloy composition comprising: forming a liquid metal alloy composition free of solid matter; placing a certain amount of liquid metal alloy composition in a holding container; Insert graphite stirrer into holding liquid metal alloy composition in vessel; agitating said liquid metal alloy composition with said graphite stirrer while cooling the metal alloy composition to begin to solidify and form a non-dendritic semi-solid slurry; ceasing agitation and removing the graphite stirrer from the non-dendritic semi-solid slurry after the solids content of the slurry reaches a value of about 1% to 20% by weight; cooling the non-dendritic semi-solid slurry without stirring until the solids content rises from about 10% to about 65%; and The non-dendritic semi-solid slurry having a solids content ranging from about 10% to about 65% is transferred to a part forming device and the transferred material is formed into the desired metal part. 2. The method of claim 1, wherein the cooling of the non-dendritic semi-solid slurry is by transferring the non-dendritic semi-solid slurry with a solids content of from about 1% to about 20% by weight to This is achieved by cooling the container and cooling the slurry in the cooling container. 3. The method of claim 2, wherein said cooling vessel has walls made of a material selected from steel and stainless steel. 4. The method of claim 2, wherein the cooling vessel has walls made of graphite. 5. A method as claimed in claim 2, characterized in that air is blown along the walls of the cooling vessel. 6. A method according to claim 3, characterized in that the inner wall of the cooling vessel has a non-wetting or low-wetting coating. 7. The method according to claim 6, characterized in that: said coating is a boron nitride coating. 8. The method of claim 1, wherein the liquid metal alloy composition is stirred for a predetermined period of time based on the initial temperature of the metal alloy composition and the heat removal rate of the stirrer. 9. A device for directly producing non-dendritic semi-solid metal alloy slurry from a liquid state and then forming a metal part, comprising: Containers for metal alloy components; and A graphite stirrer for creating convection as the metal composition is rapidly cooled to begin to solidify and form non-dendritic solid particles in the metal alloy composition. 10. The apparatus of claim 9, further comprising a separate cooling vessel. 11. The apparatus of claim 10, wherein the cooling vessel has walls made of a material selected from steel and stainless steel. 12. Device according to claim 10, characterized in that the cooling vessel has walls made of graphite. 13. Device according to claim 11, characterized in that the inner wall of the cooling container has a non-wetting or low-wetting coating. 14. The device of claim 13, wherein the coating is a boron nitride coating. 15. A method of producing a metal part from a liquid metal alloy composition comprising: forming a liquid metal alloy composition free of solid matter; transferring a quantity of the liquid metal alloy composition into a holding vessel; inserting a stirrer into the liquid metal alloy composition held in the vessel; agitating the liquid metal alloy composition in the holding vessel with an agitator as it begins to solidify and form a non-dendritic semi-solid slurry as the liquid metal alloy composition cools in the holding vessel; ceasing agitation and removing the agitator from the non-dendritic semi-solid slurry after the solids content has risen to a value of about 1% to about 20% by weight; Transfer the slurry at a solids content of from about 1% to 20% by weight to a cooling vessel and cool the slurry without stirring until the solids content rises from about 10% to about 65% by weight up to the percentage; and The non-dendritic semi-solid slurry having a solids content of from about 10% to about 65% is transferred to a part forming device and the transferred material is formed into a desired metal part. 16. The method of claim 15, wherein the cooling vessel has walls made of a material selected from steel and stainless steel. 17. The method of claim 15, wherein the cooling vessel has walls made of graphite. 18. A method as claimed in claim 15, characterized in that air is blown along the walls of the cooling vessel. 19. The method of claim 16, wherein the inner wall of the cooling vessel has a non-wetting or low-wetting coating. 20. The method of claim 19, wherein the coating is a boron nitride coating. 21. The method of claim 15, wherein said liquid metal alloy composition is stirred for a predetermined period of time based on the initial temperature of the metal alloy composition and the heat removal rate of the stirrer. 22. An apparatus for producing a non-dendritic semi-solid metal alloy slurry from a liquid state to form a metal part, comprising: Containers for storing metal alloy components; an agitator for creating convection as the metal composition is rapidly cooled to begin to solidify and form non-dendritic solid particles in the metal alloy composition; and A cooling vessel to further cool the slurry and increase its solids content. 23. The apparatus of claim 22, wherein the cooling vessel has walls made of a material selected from steel and stainless steel. 24. The device of claim 22, wherein the cooling vessel has walls made of graphite. 25. Device according to claim 23, characterized in that the inner wall of the cooling container has a non-wetting or low-wetting coating. 26. The device of claim 25, wherein said coating is a boron nitride coating. 27. A method of producing a metal part from a liquid metal alloy composition comprising: forming a liquid metal alloy composition free of solid matter; placing a certain amount of liquid metal alloy composition in a holding container; inserting a stirrer into the liquid metal alloy composition held in the container; agitating the liquid metal alloy composition with the agitator while cooling the metal alloy composition to begin to solidify and form a non-dendritic semi-solid slurry; ceasing agitation and removing the agitator from the non-dendritic semi-solid slurry after the solids content of the slurry has risen to a value of about 1% to about 20% by weight; cooling the non-dendritic semi-solid slurry without stirring until the solids content rises from about 10% to about 65%; and The non-dendritic semi-solid slurry having a solids content of about 10% to 65% is transferred to a part forming device and the transferred material is formed into the desired metal part.

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