EP1230409B1 - Method for producing a metal-alloy material - Google Patents

Abstract

A process for the production of a material made of a metal alloy for subsequent forming of the material in the semi-solid state, provides that the metal alloy (X) is brought to a starting temperature that is above the liquidus. An additive is added which is capable of reducing an interfacial surface energy between the solid phase and the liquid phase after the metal alloy has been mixed with the additive and transformed into the semi-solid state. The volume fraction of the additive (Z) is selected in such a way that, in the semi-solid material at a liquid phase fraction (fL) of 15% to 75%, the grain size (D) and the degree of skeletization (fSCS) during a holding time (t) of more than 15 minutes remain essentially constant in order to retain the formability of a suspension.

Description

Technical field

The invention relates to a method for producing a metal alloy formed material according to the preamble of claim 1.

State of the art

The shaping of metal alloys in the semi-solid state using thixogasting, Thixo smiths or thixopresses wins as an alternative to the classic ones Manufacturing methods of molded parts by means of casting, forging and pressing increasingly in importance. So it is possible today, starting from a material in the semi-solid / semi-solid state - hereinafter referred to as semi-solid state - Manufacture cast or forged components with high quality requirements. In particular for the production of heavy-duty light metal molded parts with complex Geometry offers the shape in the semi-solid state great economic Potentials. The shape of aluminum or magnesium alloys in the semi-solid condition represents a hybrid process, which gives the high design freedom and production speed of die casting processes with the quality advantages united by forging processes.

A prerequisite for successful manufacturing by means of shaping the material in the semi-solid state is a thixotropic behavior of the material, whereby thixotropy is understood to mean a special rheological behavior in which a mechanical load caused by shear stresses leads to a considerable decrease in viscosity. It should be noted that the viscosity changes by several orders of magnitude under load. For example, in the unloaded state of a thixotropic metal alloy, its viscosity is approximately 10 ⁶ to 10 ⁹ Pas, which corresponds to the properties of a solid, whereas under shear stress the viscosity drops to values of 1 Pas, which is a viscosity between that of honey (10 Pas) and olive oil (10 ^-1 Pas).

It is known that in the unloaded state of a thixotropic material, the geometric Formation of the solid phase by coherent grain groups is characterized, which form a spatial skeleton. When applying one These superstructures are broken up by shear stress, and one is created flowable suspension of solid particles in a liquid matrix phase, hereinafter referred to as "solid-liquid suspension". The semi-solid state of a Material is therefore a necessary but not a sufficient condition for a thixotropic behavior. Rather, what counts is special training of the microstructure in which said spatial skeleton can be broken open under shear loading is. This condition cannot be met by all materials because on the one hand the melting interval must be sufficiently wide and on the other hand one special pretreatment is necessary so that the solid phase is not dendritic but is globular.

The setting of a thixotropic structure is described, inter alia, in EP 0090253 A, EP 0554808 A, EP 0745694 A, EP 0 765945 A and EP 0792380 B1. A distinction is essentially made between the two process variants of the conventional one Conventional Thixocasting (CTC) and the new Rheo forging (New Rheocasting, NRC). In the CTC procedure, one becomes common Portioned sections of inductively produced material in stirred continuous casting heated to the semi-solid state and then in a die casting machine transferred into a solid-liquid suspension, which in a mold is pressed. The globulitic material is produced in the NRC process through a controlled cooling of melt dosed in steel crucibles in the semi-solid state.

Regardless of whether the semi-solid condition of a material as in the CTC process by heating the solid phase or, as in the NRC process, by cooling is achieved by melt is a crucial criterion for transferability in a low-viscosity solid-liquid suspension the globulitic already mentioned Microstructure. The latter is essentially due to four structural parameters writable, the expediently the solid phase portion, the form factor the solid phase, the grain size of the solid phase and the degree of skeletonization. Limit values for the said structural parameters are only from the prior art partially known.

EP-A-0 554 808 A describes a generic method for the production of a metal alloy Material for a subsequent shaping of the Material in a semi-solid state. According to this teaching you bring the metal alloy to one located above the liquidus Starting temperature and then sets the so formed a grain refining agent. Subsequently the metal alloy is heated to any temperature cooled under solidus and the resulting material in the solid state during an essentially arbitrary one Time stored. Finally, the material by heating to a solidus and liquidus Holding temperature brought into the semi-solid state while holding for less than 15 Minutes. The shape of the material in semi-solid Condition must be within the less than 15 Minutes holding time can be made.

A disadvantage of the known method is that the materials that can be produced on the basis of less than 15 minutes limited hold time for use in conventional molding plants are not suitable. Accordingly requires processing by means of thixo casting, Thixo forges or thixopresses with the known Process manufactured materials special manufacturing equipment, which ensure that the shaping limited to less than 15 minutes Processing window is performed. Another disadvantage of the known method results from the fact that the Material from the molten state to the solid Condition must be cooled and only then in the semi-solid Condition for subsequent shaping can. This intermittent freezing is especially for an automated manufacturing and Molding process highly undesirable.

US Pat. No. 5,879,478, which in the following is the closest State of the art refers to a Process for thixoforming a thixotropic aluminum-silicon-copper alloy. This alloy belongs to the aluminum casting alloys, which is usually for thixoforming be used. Here is the chemical analysis of this group of alloys restricted to those with one Silicon content of 5 to 7.5%, which causes "embrittlement" occurs. This "embrittlement" is due to the presence of Silicon crystals in polyhedral or polygonal form traced in larger quantities because these angular silicon crystals how inner notches work. The process has the goal for aluminum alloys with a silicon content of ≥ 5% this embrittlement, which after the. Thixoforming to avoid occurring in the silicon crystal morphology refined, thereby reducing the internal notch effect becomes.

Presentation of the invention

The object of the invention is a generic method to improve, in particular the disadvantages mentioned to avoid.

This problem is solved by the one defined in claim 1 Method.

In the method according to the invention for producing a metal alloy formed material for a subsequent shaping of the material in the semi-solid state, the metal alloy is brought to a liquidus the initial temperature and then adds an additional material to it is capable, after transfer of the metal alloy mixed with the additional material in the semi-solid. State an interface energy between solid and to reduce the liquid phase. Here is the amount of the additional material to be selected so that in the semi-solid material with a solid phase content of 25% up to 85% the grain size and the degree of skeletonization during a holding time of Remain essentially constant for more than 15 minutes to form a suspension maintain.

The fact that the grain size and the degree of skeletonization during a holding time Remaining essentially constant for more than 15 minutes becomes phlegmatization of the semi-solid material, which is one of the most economical and ecological aspects allow more advantageous production. So the extension leads of the temporal process window to reduce scrap, which arises in the previously known processes whenever the thixotropic properties of the material is lost due to a too long holding time. Furthermore it is when using the inventive method thanks to the achievable It can be phlegmatized, the material is brought into the semi-solid state for the subsequent shaping directly from the melt, i.e. it is not necessary to allow the material to solidify in the meantime. To this The purchase of cost-intensive special manufacturing facilities can be done in this way avoid or at least limit, and there is the possibility of one extensive process integration of material production and subsequent Shaping. In addition, the process can also be carried out in existing ones Homogenize production facilities largely thanks to the reduced structure sensitivity. If storage of the material is desired, it can be opened a storage temperature below Solidus has cooled and only immediately before the shape can be brought into the semi-solid state without the advantageous phlegmatization is lost.

Starting from the material produced with the method according to the invention components can be produced by the following shaping, which is a good combination of strength and toughness and also heat-treatable, are weldable, pressure-tight and relatively inexpensive.

Advantageous embodiments are described in the dependent claims.

Basically, the process is for a wide variety of types of metal alloys applicable. In the preferred embodiment according to claim 2, the Metal alloy as the main component aluminum, and is used as an additional material Barium, wherein according to claim 3 the weight fraction of barium 0.1% to Is 0.8% of the material. In view of the enormous importance of aluminum components the advantages of these embodiments are obvious.

Particularly good results are achieved if, according to claim 4, the metal alloy a dispersoid-forming element adds to the formation of grains to promote small grain size. In the case of aluminum alloys one uses iron as a dispersoid-forming element or chromium or titanium or zirconium, wherein according to claim 6 the proportion by weight of the dispersoid-forming element is between 0.1% and 1% of the material.

Brief description of the drawings

Figur 1

Mittlere Korngrösse D und Formfaktor F für eine nach dem Stand der Technik hergestellte Aluminiumlegierung (EN AW-6082, nachfolgend: "Aluminiumlegierung X") bei einem konstanten Flüssigphasenanteil von 35% als Funktion der isothermen Haltezeit;

Figur 2

Kontiguität und Kontiguitätsvolumen der nach dem Stand der Technik hergestellten Aluminiumlegierung X bei einem konstanten Flüssiganteil von 35% als Funktion der isothermen Haltezeit;

Figur 3

Kontiguität und Kontiguitätsvolumen der nach dem Stand der Technik hergestellten Aluminiumlegierung X als Funktion des Flüssigphasenanteils nach einer konstanten isothermen Haltezeit von 5 Minuten;

Figur 4

Kraft-Weg Kurven der nach dem Stand der Technik hergestellten Aluminiumlegierung X als Funktion des Flüssigphasenanteils nach einer isothermen Haltezeit von 5 Minuten;

Figur 5

Kraft-Weg Kurven der nach dem Stand der Technik hergestellten Aluminiumlegierung X als Funktion der isothermen Haltezeit bei einem konstanten Flüssigphsenanteil von 35%;

Figur 6

das Kontiguitätsvolumen einer erfindungsgemäss hergestellten bariumhaltigen Aluminiumlegierung (X + Ba) im Vergleich zu der nach dem Stand der Technik hergestellten Aluminiumlegierung X als Funktion der isothermen Haltezeit bei einem konstanten Flüssigphasenanteil von 35%;

Figur 7

Kraft-Weg Kurven der erfindungsgemäss hergestellten bariumhaltigen Aluminiumlegierung (X + Ba) als Funktion der isothermen Haltezeit bei einem konstanten Flüssigphasenanteil von 35%.

The basic knowledge required for understanding the invention and an exemplary embodiment of the invention are described in more detail below with reference to the drawings, in which:

Figure 1

Average grain size D and form factor F for an aluminum alloy manufactured according to the state of the art (EN AW-6082, hereinafter: "aluminum alloy X") with a constant liquid phase fraction of 35% as a function of the isothermal holding time;

Figure 2

Contiguity and contiguity volume of the aluminum alloy X produced according to the state of the art at a constant liquid content of 35% as a function of the isothermal hold time;

Figure 3

Contiguity and contiguity volume of the aluminum alloy X produced according to the state of the art as a function of the liquid phase fraction after a constant isothermal hold time of 5 minutes;

Figure 4

Force-displacement curves of the aluminum alloy X produced according to the prior art as a function of the liquid phase fraction after an isothermal hold time of 5 minutes;

Figure 5

Force-displacement curves of the aluminum alloy X produced according to the prior art as a function of the isothermal hold time with a constant liquid phase fraction of 35%;

Figure 6

the contiguity volume of a barium-containing aluminum alloy (X + Ba) produced according to the invention in comparison to the aluminum alloy X produced according to the prior art as a function of the isothermal holding time with a constant liquid phase fraction of 35%;

Figure 7

Force-displacement curves of the barium-containing aluminum alloy (X + Ba) produced according to the invention as a function of the isothermal holding time with a constant liquid phase fraction of 35%.

Ways of Carrying Out the Invention 1. Basics

As already mentioned at the beginning, thixotropy becomes a special rheological Behavior understood in which a mechanical load due to shear stress leads to a significant decrease in viscosity. A thixotropic behavior can Materials in the semi-solid state, i.e. with one between the Solidus line and the liquidus line temperature should be expected when the semi-solid Material under shear load in a low-viscosity solid-liquid suspension is transferable. This formability of a suspension requires a special structure ahead in the semi-solid state where the solid components are not dendritic, but are globulitically trained.

The structure formation can be described by four structural parameters, namely by the solid phase fraction f ^S , the form factor of the solid phase F, the grain size of the solid phase D and the degree of skeletonization, the latter being expressed by the measured variable C ^S or preferably by the contiguity volume f ^S C ^S becomes. Instead of the solid phase component, the liquid phase component fL can also be specified, with the quantities f ^L and f ^S adding up to 1 under the permissible neglect of gaseous phase components.

Although no precise limit values for thixotropic behavior are given in the prior art for the solid phase component, it is assumed that the solid phase component should be approximately 40% to 60%. In addition to the solid or liquid phase fraction, the morphology and connectivity of the solid phase are the process-determining structural parameters. A quantitative description of the structure morphology can be made with the help of the form factor F and the grain size D. The form factor F is defined as F = U 2 4πA where U is the mean grain size and A is the mean projected grain area. F> 1 applies if the grains have a complex shaped surface and F = 1 if all grains have a spherical shape. (It must be pointed out that in some places the form factor is used as the reciprocal size of the form factor defined here, but this is readily apparent from the respective context). The form factor determines the viscosity of the solid-liquid suspension to a high degree, whereby an upper limit for the form factor must not be exceeded for the material to be sufficiently formable. This boundary condition is generally well met today by both CTC and NRC materials.

Although not a generally valid upper one for grain size D in the prior art Limit is given, experience shows that when shaping thin Components a grain size of about one twentieth of the wall thickness of the Component should not be exceeded. This results in a wall thickness of 3 mm as a further criterion to be observed, a maximum grain size of approximately 150 µm.

2. Characterization of materials in the semi-solid state

A commercially available thixi alloy from Tap AlMgSi (hereinafter referred to as "aluminum alloy X ")) with a composition similar to the alloy with the designation EN AW-6082 according to the European standard EN 573-3, namely with a chemical composition of 1.1% by weight silicon, 0.85% by weight Magnesium, 0.61% by weight manganese, 0.09% by weight iron, 0.08% by weight titanium, <0.01 % Chromium, <0.01% copper, <0.01% nickel, <0.01% lead and <0.01 wt% zinc was heated to a desired temperature in an infrared oven heated in the solidus-liquidus interval at 100 ° C / min, homogenized isothermally and then quenched. To deter the trial samples as quickly as possible To be able to, the infrared tube furnace was above a filled with ice water Boiler attached. The system is designed so that after reaching the desired one Temperature and homogenization of the sample by loosening the Bracket falls into the water bath. One in the center of gravity of the sample (15 mm x 15 mm x 15 mm) attached Pt / PtRh thermocouple ensures an exact temperature determination (+/- 0.1 ° C) and heating control. Before each attempt, the thermocouple checked for accuracy in a calibration oven. The measurements were limited on the microstructural structural developments in 5 selected Temperatures in the semi-solid range (613 ° C, 625 ° C, E33 ° C, 635 ° C and 638 ° C, corresponding to a liquid phase content of 10%, 20%, 30%, 35% or 40%) and with isothermal holding times of 1, 5, 10, 20 and 30 minutes.

Subsequent metallographic examinations of the quenched samples showed the change in the structure during reheating depending on the test parameters. The parameters form factor F, grain size D and contiguity C ^S or contiguity volume f ^S C ^S enable the structural changes to be determined on the basis of the size, shape and spatial relationship of the solid alpha phase in the liquid matrix.

Using the example of aluminum alloy X, FIG. 1 shows the change in form factor F and grain size D (in micrometers) as a function of the isothermal holding time t (in minutes) in the semi-solid state at a constant temperature of 636 ° C., corresponding to a liquid phase fraction f ^L of 35%. As the holding time increases, the solid phase is molded in and becomes more globulitic, ie the form factor F decreases and strives towards 1, and at the same time the grain size D increases.

In parallel with the growth of the solid phase, its connectivity, ie the strength of the spatial skeleton, also increases. The contiguity C ^{S of} the solid phase, which is defined as., Is used as a measure for the degree of skeletonization, ie for the contact of adjacent particles of a phase C S = 2S SS 2S SS + S SL

S ^{SS is} the grain boundary surface between the solid phase, ie the surface between the continuous grains that are not separated by melt, while S ^{SL is} the phase interface between the solid phase and the melt. The contiguity thus corresponds to the proportion that the interface to the same phase takes up in the entire interface of the solid phase. For the case C ^S = 0, the grains are isolated and completely surrounded by melt, while with increasing C ^S the grains have grown together and, accordingly, the skeleton formation is more pronounced. Very low values of C ^S are undesirable because the semi-solid material will then have no dimensional stability. Conversely, in the case of C ^S → 1, the solid phase is fully agglomerated and cannot be converted into a suspension by applying shear stresses. Accordingly, there is an upper limit for the contiguity for the transfer of a material with a coherent solid phase into a solid-liquid suspension. Since the skeletal strength depends on both the contiguity C ^S and the solid phase component f ^S , it makes sense to choose the product f ^S C ^S , i.e. the volume of contiguity, which corresponds to the volume of connected phase areas, as the determining variable for the degree of skeletonization.

2 again shows the change in the contiguity C ^S and the contiguity volume f ^S C ^S as a function of the holding time t (in minutes) in the semi-solid state at a constant temperature of 636 ° C., corresponding to a liquid phase fraction f ^L of 35%.

FIG. 3 shows for the same material X the change in the contiguity C ^S and the contiguity volume f ^S C ^S after an isothermal hold time of 5 minutes as a function of the liquid phase fraction f ^L , with the fact that for F ^L → 1 corresponding to C ^S → 0 applies. The respective values of C ^S and f ^S C ^{S are shown} for a liquid phase fraction f ^L of 10%, 20%, 30% and 40%, corresponding to a temperature of 613 ° C, 625 ° C, 633 ° C and 638 ° C ,

As can be seen from FIGS. 2 and 3, the contiguity volume f ^S C ^{S increases} with increasing holding time t and decreases with increasing liquid phase fraction f ^L , whereby, as expected, the skeleton formation increases with increasing holding time t. The properties required for successful shaping can, however, only be expected in a certain value range of the contiguity volume f ^S C ^S. The evaluation of the rheological properties set out below allows the appropriate interval for the volume of contiguity f ^S C ^{S to be determined} .

The flow behavior of known alloys was examined using a back extrusion forming test. For example, a cylindrical sample (⊘ = 26 mm, h = 35 mm) of the aluminum alloy X was heated to the desired temperature (616 ° C, 626 ° C, 633) in a steel mold at a heating rate of 100 ° C / min using an IR oven ° C, 636 ° C, 641 ° C or 641.5 ° C corresponding to a liquid phase fraction f ^L of 10%. 20%, 30%, 35%, 40% or 50%). After an isothermal holding time t of 1, 5, 10 or 30 minutes, a forming process was started, the sample being shaped by means of a bolt at a constant bolt speed of 200 mm / s. Travel path ℓ and force K were recorded using a computer.

FIG. 4 shows typical force-displacement curves of the aluminum alloy X after an isothermal holding time t of 5 minutes at different values of the liquid phase fraction f ^L , the force K being specified in kilonewtons and the displacement ℓ in millimeters. With a low liquid phase fraction f ^{L of} up to 20%, the force-displacement diagram has the characteristic shape for elastic-plastic behavior. In contrast, with a liquid phase fraction f ^L of 40% and 50%, the forming forces are very low, and you are in the thixotropic range to be aimed for in the process. With a liquid phase fraction f ^L of 30% between the above cases, a transition range from elastic-plastic to thixotropic behavior is observed, whereby the solid phase skeleton is still so strong that a low-viscosity suspension cannot arise. The plastic deformation dominates, but the liquid phase is squeezed out of the solid phase sponge so that a distinctive phase separation occurs.

In FIG. 5, for the same thix alloy with a liquid phase fraction of 35% (corresponding to a temperature of 636 ° C) the force-displacement curves according to different Isothermal holding times t (in minutes) are shown, the force K in kilonewtons and the path ℓ is given in millimeters. While after a holding time t a thixotropic behavior after 5 minutes leads to a longer holding time to a loss of thixotropic properties.

A comparison of FIG. 4 with FIG. 3 shows that the thixotropic behavior observed according to FIG. 4 with a liquid phase fraction f ^L of 40% and 50% is transferred to FIG. 3 with a decrease in the contiguity volume f ^S C ^S to values below 0.3 accompanied. The same result is obtained by comparing FIG. 5 with FIG. 2, according to which the loss of thixotropic properties that occurs in accordance with FIG. 5 after a holding time t of more than 5 minutes occurs in accordance with FIG. 2 with an increase in the volume of contiguity f ^S C ^S Expresses values of over 0.3.

3. Description of the method according to the invention

It follows from the foregoing that thixotropic behavior, ie convertibility of the material present in the semi-solid state into a homogeneous solid-liquid suspension, is only possible if the degree of skeletonization can be kept sufficiently low, which means in terms of numbers, that the contiguity volume f ^S C ^{S is} to be kept at a value below a critical value Y = 0.3.

This is ensured with the method according to the invention. Surprisingly, it was found that by alloying elements that are able to reduce an interfacial energy between solid and liquid phase, it becomes possible in the semi-solid material in a wide range of the liquid phase fraction f ^L from 15% to 75% the grain size D and To keep the degree of skeletonization substantially constant during a holding time of more than 15 minutes and in particular to keep the volume of contiguity f ^S C ^S at a value of less than Y = 0.3. It is therefore possible to desensitize the material with regard to its thixotropic properties.

Examples of additional materials Z effective in the above sense are in the case of aluminum alloys the elements barium, which is particularly preferred, and Antimony, strontium or bismuth. It should be noted that for some These elements, in particular for silicon, are known to be added to a Aluminum alloy brings about a positive finish, for example through training of the aluminum-silicon eutectic. The quantitative proportions used for refinement however, these elements are in the range of a few ppm and are in any case much too low to phlegmatize the thixotropic properties to effect. In contrast, there are those to be used in the method according to the invention Quantities of the additional material Z clearly above that for the modification a quantity of finishing agent commonly used in a eutectic.

Looking back, it can be assumed that those with the inventive The effect of the process is based on the fact that it is reduced the interfacial energy between the solid phase and the liquid phase of the semi-solid A driving force for the undesirable structural changes, which particularly the grain coarsening and the increasing skeletonization include, is reduced. By alloying elements that have this interfacial energy the speed and thus the extent of the structural changes occurring during a certain holding time are dramatically reduced. The proportion of the additional material is to be chosen so that the grain size D and the degree of skeletonization during a holding time t of at least 15 Minutes remain essentially constant. This is in the following embodiment illustrated.

4. Embodiment: characterization of a method according to the invention manufactured material

A melt of an aluminum alloy with a composition similar to that Alloy with the designation EN AW-6082 according to the European standard EN 573-3 0.2 percent by weight of barium was added as additional material Z by the required The amount of barium is first packed in an aluminum foil and then was melted. The material thus formed (hereinafter referred to as "Aluminum alloy X + Ba") with a chemical composition of 0.2% by weight barium, 0.8% by weight silicon, 0.41% by weight magnesium, 0.28% by weight Manganese, 0.2% by weight iron, 0.01% by weight titanium, 0.19% by weight chromium, 0.35% by weight Copper, <0.01 wt% nickel, <0.01 wt% lead and <0.01 wt% zinc according to the characterization method described in section 2 in an infrared oven to a specified temperature in the solidus-liquidus interval at 100 ° C / min heated and then homogenized isothermally. The microstructural structural developments were at 5 selected temperatures in the semi-solid range (618 ° C, 630 ° C, 637 ° C, 639 ° C and 642 ° C, corresponding to a liquid phase fraction of 10%, 20%, 30%, 35% or 40%) and with isothermal holding times t of 1, 5, 10, Measured 20 and 30 minutes.

FIG. 6 shows the course of the contiguity volume f ^S C ^S as a function of the isothermal holding time t (in minutes) with a constant liquid phase fraction f ^L of 35% on the one hand for the material produced with the method according to the invention, ie the aluminum alloy X + Ba, and on the other hand for the corresponding barium-free alloy X according to the prior art. By using the method according to the invention, the structural change was significantly reduced. In particular, the critical value Y = 0.3 for the contiguity volume f ^S C ^{S was} not reached in the material produced according to the invention even after a long holding time t of 30 minutes.

As in particular from those in FIG. 7 for the one produced according to the invention Material X + Ba reproduced force-displacement diagrams (where the force K in kilonewtons and the path ℓ is given in millimeters) at different holding times t (in minutes), the flow properties of the material are also after 30 Minutes hardly changed and continue to show the characteristic of thixotropic behavior Course. Accordingly, even after a 30-minute hold time, t the semi-solid material can be converted into a homogeneous solid-liquid suspension.

5. Other embodiments

The inventive concept presented above using the example of an aluminum alloy can be applied in an analogous manner to other metal alloys X, for example magnesium alloys but also steels and heavy metal alloys. It is in the area of professional skill to first determine in preliminary tests which values of grain size D and the degree of skeletonization or the contiguity volume f ^S C ^{S have to be} observed in order to maintain the formability of a suspension in the semi-solid state and also a suitable additional material Z with surface energy-reducing properties.

The aluminum alloys described in the previous embodiment with a composition similar to the alloy with the designation EN AW-6082 according to the European standard EN 573-3 contain an admixture Iron, which acts as a dispersoid-forming element, i.e. in a semi-solid state promotes the formation of grains of small grain size D. When using other metal alloys X is in addition to said additional material Z if necessary add suitable dispersoid-forming element E.

LIST OF REFERENCE NUMBERS

f ^p

Solid rate

f ^L

Liquid phase portion

F

Solid phase form factor

D

grain size

U

Korn scope

A

projected grain area

C ^S

contiguity

f ^S C ^S

contiguity

S ^SS

Grain boundary surface between the solid phase

S ^SL

Phase interface between solid phase and melt

K

force

ℓ

path

t

hold time

Y

critical value of the contiguity volume

Z

additional material

e

dispersoid-forming element

Claims (4)

1. Process for producing a material which is formed from a metal alloy for subsequent shaping of the material in the semi-solid state, in which the metal alloy (X), which as its main constituent contains aluminium, is brought to a starting temperature which is above the liquidus point and then an additive material (Z) is added, characterized in that the additive material (Z) is barium, which forms between 0.1 and 0.8% by weight of the metal alloy and is able, after the metal alloy to which the additive material has been added (X + Z) has been converted into the semi-solid state, to reduce an interfacial energy between solid and liquid phases, the quantitative fraction of the additive material (Z) being selected in such a way that in the semi-solid material with a liquid phase fraction (F^L) of 15% to 75% the grain size (D) and the degree of skeleton formation (f^SC^S) , during a holding time (t) of up to 30 minutes, does not exceed a value of 0.3, in order to retain the ability to form a suspension.
2. Process according to Claim 1, characterized in that a dispersoid-forming element (E) is added to the metal alloy (X) in order to promote the formation of grains with a small grain size (D).
3. Process according to Claim 1 or 2, characterized in that the dispersoid-forming element (E) used is iron or chromium or chromium or titanium or zirconium.
4. Process according to Claim 3, characterized in that the dispersoid-forming element (E) forms between 0.1% and 1% by weight of the material.

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