Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
  • C22C21/04—Modified aluminium-silicon alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/12—Making non-ferrous alloys by processing in a semi-solid state, e.g. holding the alloy in the solid-liquid phase
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon

Definitions

• the present invention relates to a method for bringing aluminium alloy blocks, such as ingots, billets and others to a semi-solid and semi-liquid state which allows them to be moulded when this state has been reached.
• a new type of moulding for metal alloys has been recently introduced, for example, moulding, pressure injection, forging and similar operations, in which the metal alloy forming the blocks (ingots or billets, for example) to be moulded are in a semi-solid or semi-liquid state and have a special homogeneous structure consisting of solid globules or granules immersed in a liquid phase.
• This special type of moulding requires the either partial or total fusion of the alloy phases at the lowest fusion point and the maintenance of the globular phases, which ensure that the moulding phase is reached.
• this structure of these metal alloys homogeneously consists of solid globules immersed in a liquid phase. Therefore, the structure has no dendrites, that is, it has no crystals growing around the crystallisation nuclei in a particular direction. Therefore, these structures, known to experts in the field as globular structures, have the so-called thixotropic property.
• Figure 1 which is a schematic diagram of the state of a metal alloy suitable for moulding as described above, shows that to the left of point A there is only material in a liquid state while to the right of point C, there is only material in a solid state. In the area between points A and C, there is material in a semi-solid or semi-liquid state.
• the area between points B and C there is a material in which there are solid granules or globules immersed in a liquid phase consisting of the eutectic alloy.
• the percentage of eutectic alloy found in the liquid state compared to the solid crystals increases from 0 to 100.
• point B to point A increases the percentage of solid solution crystals which pass to the liquid state from 0 to 100.
• the area of interest in relation to the thixotropic alloys is normally the area between points B and C in which there are solid crystals immersed in eutectic alloy in the liquid state and part of the area between points B and A depending on the liquid fraction required.
• a block of this alloy behaves like a solid element when it is handled for transfer and similar operations but behaves like a liquid element when it is subjected to any moulding operations.
• Su will refer to the physical state of the alloy block, meaning the globular structure of the block ideal for use in subsequent moulding to obtain the required semi-finished item.
• the first treatment of the aluminium alloys envisages, therefore, a casting phase starting at a temperature of around 700°C and progressive cooling of the aluminium alloy, using suitable time intervals, until ambient temperature is reached. This allows the alloy to be formed into ingots and billets of the dimensions required.
• the stirring treatment of the alloy is carried out when the alloy passes between the liquid temperature (around 610/620°C, point A of the curve in Figure 1) and the solid temperature (around 577°C, point C of the curve in Figure 1) .
• the alloy is agitated in such a way that it forms these globular structures ideal for bringing the alloy to its Su state and, therefore, for use in the subsequent heating phases which prepare it for its moulding phase.
• the second, so-called heat conversion treatment has substantially the same procedure of cooling the alloy until it reaches the ambient temperature so that it can be worked as described above.
• the billet (or ingot) following a short period of time at the ambient temperature, is heated again, preferably using a temperature gradient between 20 and 30°C per minute, until it reaches a temperature between the liquid temperature and the solid temperature (See Figure 1) .
• this temperature there is an operating phase for maintaining the billet at this temperature for a number of hours (2 hours, for example) and then bringing the billet back to ambient temperature in which its Su physical state is obtained.
• This type of treatment therefore, includes the permanence of the alloy at a temperature between the liquid and solid temperatures for the time necessary for the globulisation of the alpha-aluminium solid solution phase.
• the time for which the billet remains at the semi-solid and semi-liquid state is less than around five minutes if the starting alloy structure has been previously super-refined with the master alloy Al-Ti-B.
• the quantities of the components must be such that the Ti content is at least 0.26% of the weight.
• the treatment systems currently used for bringing the alloys, and therefore the billets made in this alloy, to the special physical state described above and referred to as Su envisage the following: the casting of the billet with a magnetic and mechanical stirring phase during the solidification phase in order to keep the alloy agitated and obtain the ideal globulisation of the alpha-aluminium phase (in this particular case) and, as an alternative to this, the heat conversion treatment system, in which the billets become globular only if they are maintained for a given period of time at a temperature between the solid temperature and the liquid temperature, which allows the dendrites to gradually become spherical.
• the object of the present invention is to provide a method for bringing the billets, ingots and similar objects to the semi-solid and semi-liquid state which allows them to be moulded, avoiding the need for these treatments described above for bringing the said aluminium alloy billets to the Su state essential for carrying out the subsequent moulding phase to obtain the semi-finished items and which has none of the disadvantages described with reference to the known prior art.
• the present invention discloses a method for bringing aluminium alloy blocks such as ingots, billets and others to the semi-solid and semi-liquid state which allows them to be moulded when this state has been reached, characterised in that it envisages the following operating phases: - a first phase for refining the grain of the said aluminium alloy, consisting of blocks, by adding to the said aluminium alloy, when it is melted, a silicon-boron alloy which produces a refined alloy consisting mainly of ⁇ -aluminium and eutectic silicon phases;
• FIG. 1 is the temperature-time-state graph for a possible thixotropic type metal alloy, equivalent to the aluminium alloy which is the subject of the present invention
• FIG. 2 is the temperature-time-state graph for the phase for heating from ambient temperature to the temperature between solid and liquid which is obtained so that the billet can be moulded.
• the present invention therefore, relates to a method for bringing aluminium alloy blocks, such as ingots, billets and others to a semi-solid and semi-liquid state which allows them to be moulded and therefore allows the manufacturing of a semi-finished product, car wheels, for example.
• the method envisages a first phase for refining the grain of the aluminium alloy which forms the blocks. In this respect, this degree of refinement is reached by adding a silicon-boron alloy to the aluminium alloy, when it is melted.
• the second operating phase envisages the heating of the billets or ingots made using the refined alloy, starting from the Su physical condition in which its temperature is substantially the ambient temperature ta, to bring the said refined alloy to a temperature in which there is a balance between its solid state and its liquid state and in which the phases of eutectic silicon are liquid and the phases of ⁇ - aluminium are solid.
• the temperature tf is reached in a suitable time which is shown in Figure 2 from TO to TF.
• the method then envisages a third operating phase for using the alloy billets, obtained by the previous operating phases, directly inside the moulding system in their semi- solid and semi-liquid state to obtain the resulting semi ⁇ finished products.
• the method according to the present invention envisages the substitution of the first phase for the refinement of the grain of the aluminium alloy described above with the use of already refined aluminium alloy blocks.
• the alloy used in place of the said first operating phase is a refined aluminium alloy obtained by adding a silicon-boron alloy to the aluminium alloy, when it is melted.
• This silicon-boron alloy has a boron weight of between 0.01 and 4.0% and is of a quantity which ensures that the resulting fusion of the aluminium alloy contains at least 50 p.p.m. of boron.
• This type of alloy is obtained with a special method which was the subject of an application for a European patent with the number EP 553 533 owned by ELKEM ALLUMINIUM ANS.
• the innovation of the Applicant is to use already refined ELKEM ALLUMINIUM blocks, subjecting these blocks directly to a first heating phase, starting from a condition in which their temperature is substantially the ambient temperature, to bring them to a temperature in which there is a balance between their solid state and their liquid state and in which the silicon phases are liquid and the ⁇ - aluminium phases are solid.
• the blocks are ready for the second operating phase, that is, for direct use inside the moulding system in their semi-solid and semi-liquid state to obtain resulting semi-finished products.
• the said second phase of heating the already refined blocks envisages the application of heat gradients to these blocks which keeps the temperature constant in all the areas of the blocks, both internally and externally.
• the said heating phase subjects the blocks to a temperature gradient with a high temperature increase co-efficient until the fusion or eutectic point of the refined aluminium-silicon-boron alloy is reached so that the blocks can then be subjected to a heat gradient with controlled co-efficients proportional to the requirements for keeping the temperature constant in all parts of the blocks.
• the first part of the curve has a steep heat co-efficient while the second part which approaches the temperature between solid and liquid (585°C), used for the moulding of the billets, has a low heat co-efficient.
• the billets are subjected to a low temperature increase gradient until the fusion or eutectic point of the refined aluminium- silicon-boron alloy is reached so that the billets can then be subjected to a heat gradient with controlled co-efficients proportional to the requirements for keeping the temperature constant in all parts of the billets.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Powder Metallurgy (AREA)

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• 1995
  • 1995-05-31 IT IT95BO000273A patent/IT1278230B1/it active IP Right Grant
• 1996
  • 1996-05-28 WO PCT/IT1996/000110 patent/WO1996038593A1/en not_active Application Discontinuation
  • 1996-05-28 EP EP96916293A patent/EP0775219A1/en not_active Withdrawn

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