Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/34—Methods of heating
• • 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

Definitions

• the invention relates to a method for heating a workpiece made of a solid metal alloy to a final temperature between the solidus and liquidus temperature of the alloy, in particular for producing a partially solid, partially liquid, thixotropic state of the workpiece.
• these partially solid, partially liquid metal alloy phases are first cooled to below the solidus temperature of the alloy - generally to room temperature - and only heated to the required processing temperature at which the thixotropic properties appear just before they are further processed.
• Coarsening of the cast grains is undesirable both in the production of the metal alloy phase with thixotropic properties and in the subsequent heating of the workpieces to the further processing temperature.
• the inventors have set themselves the goal of creating a method of the type mentioned at the outset with which the thixotropic state of a workpiece made of a metal alloy for whose further processing can be stopped inexpensively and without having to accept a significant coarsening of the grain.
• the workpiece is heated convectively in a first step, by heat conduction, heat radiation or another non-inductive heat transfer to a temperature just below the solidus temperature of the metal alloy and in a subsequent second step inductively to the final temperature.
• the desired final temperature is reached quickly by the inductive heating in the second step and consequently the dwell time of the workpiece in the partially solid, liquid state, in which the greatest tendency to coarsen the grain is observed, is kept as short as possible. Since in this second step there is only a temperature increase on the workpiece of approximately 30 ° to 100 ° C., the power and thus the size of the induction heating system can also be designed to be relatively small and therefore inexpensive. On the other hand, the energy loss during heating through non-inductive heat transfer in the first step, taking into account the large temperature interval, is significantly less than with a corresponding induction heating.
• the temperature reached after the first heating step is about 10 ° to 50 ° C below the solidus temperature of the metal alloy.
• the solidus temperature should never be exceeded.
• the inductive heating of the workpiece in the second step is preferably carried out with an alternating current frequency between 50 and 1000 Hz and a heating power between approximately 10 and 200 kW.
• the alternating current frequency and heating power are matched to one another in such a way that the surface temperature of the workpiece never exceeds the desired end temperature while maintaining the shortest possible time until the end temperature is reached.
• the process according to the invention is expediently carried out continuously under production conditions.
• the heating in the first step is preferably carried out in a continuous or tunnel oven and in the second step cyclically by transferring it into successive induction coils, the throughput speed of the workpieces through the continuous or tunnel oven, the cycle time of the induction heating system and the cycle time of the subsequent further processing system being coordinated will.
• Several lines of induction coils can also be used per continuous or tunnel furnace.
• the method according to the invention is preferably used in the production of workpieces intended for further processing with thixotropic properties, in particular for further processing bolts or ingots in die casting, forging, rolling and pressing systems.
• the method is particularly suitable for heating workpieces made of aluminum alloys.
• An alloy of the type AlSi7Mg with 6.9% by weight Si and 0.4% by weight Mg was cast in a continuous casting installation to produce a thixotropic structure to form a strand of 75 mm in diameter and cut into bolts of 180 mm in height.
• the average diameter of the globular cast grains was less than 100 ⁇ m.
• the solidus temperature of the alloy is 555 ° C.
• the bolts were heated to the set furnace temperature of 540 ° C for two hours in a holding oven with air circulation.
• the bolts were then heated in an induction coil with an output of 25 kW and an AC frequency of 250 Hz within 6 minutes to the final temperature of about 580 ° C - corresponding to a liquid metal content of 30 to 40%.
• Metallographic examination of bolt cross sections showed that no significant grain coarsening had occurred, i.e. the average grain size was still below 100 ⁇ m.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Forging (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=4217257

Family Applications (1)

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Cited By (8)

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Citations (5)

Family Cites Families (4)

• 1991
  • 1991-06-10 CH CH1730/91A patent/CH683267A5/de not_active IP Right Cessation
• 1992
  • 1992-05-21 EP EP92810382A patent/EP0518815B1/fr not_active Expired - Lifetime
  • 1992-05-21 DE DE59201065T patent/DE59201065D1/de not_active Expired - Fee Related
  • 1992-05-26 US US06/889,126 patent/US5282910A/en not_active Expired - Fee Related

Patent Citations (5)

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