Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES, PROFILES OR LIKE SEMI-MANUFACTURED PRODUCTS OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C23/00—Extruding metal; Impact extrusion
  • B21C23/002—Extruding materials of special alloys so far as the composition of the alloy requires or permits special extruding methods of sequences
• • 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
  • C22F1/053—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 of alloys with zinc as the next major constituent
• • 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
  • C22F1/057—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 of alloys with copper as the next major constituent
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S72/00—Metal deforming
  • Y10S72/70—Deforming specified alloys or uncommon metal or bimetallic work

Definitions

• ABSTRACT A method for extruding high strength, heat treatable aluminum alloys is disclosed which comprises providing a homogenized cast alloy billet, conducting a first hot extrusion of said billet to a reduction in area of from 20 75%, conducting a second hot extrusion at the solutionizing temperature of the alloy, and quenching said billet after said second extrusion.
• the method of this invention is particularly useful for the processing of Alloys 2014, 2024 and 7075, and eliminates the need of conducting a separate solution heat treatment after the extrusion operation is completed.
• solution heat treatment It has long been the practice to heat extrusions of heat-treatable aluminum alloys by a process known as solution heat treatment, to achieve the desired temper.
• solution heat treatment involves heating the extrusion to a temperature at which solution and diffusion of the heattreatable alloying constituents take place and produces, as nearly as practicable, a homogeneous solid solution.
• the extrusion is subsequently quenched (i.e., rapidly cooled) in order to prevent the hardening constituents from precipitating substantially from solid solution during the cooling period.
• Slow cooling would permit these constituents to precipitate to a greater extent, so that the alloy would be in a partially annealed condition unsuitable for subsequent precipitation heat treatment.
• Solution heat treatment, including the quench is considered a necessary preliminary to subsequent precipitation heat treatment to increase the mechanical properties of the alloy.
• the first inheres in the specific composition of the alloy and cannot be changed, and the second is a function of the physical means available for effecting a quench, and may be overcome by the choice of a suitable system from among those that exist in the art.
• the third characteristic has proved most difficult to overcome, and, it is the solution to the problem posed by this third characteristic with which the method of this invention is primarily concerned.
• the method of this invention relates to a process for extruding and heat treating high strength aluminum alloys, without the need of a separate solution heat treatment and quenching after extrusion, by the use of a prior hot extrusion preceding the final extrusion operation.
• the method of this invention facilitates the successful extrusion of high strength heat treatable aluminum alloys at commercial tempers without the employment of an additional solutionizing treatment after final extrusion.
• the product obtained by the method of this invention can be hot worked at their solutionizing temperature ranges without breaking up, and can develop characteristic mechanical strength properties when quenched and aged.
• the method of this invention comprises an extrusion operation for high strength heat-treatable aluminum alloys which eliminates the necessity of a postextrusion solution heat treatment by providing a hot extrusion of the cast billet to a reduction in area from 2075% preceding the final extrusion operation.
• the method of this invention may be employed with a broad range of aluminum alloys, and is particularly useful with high strength heat treatable alloys, such as those designated by the Aluminum Association as Alloys 2014, 2024 and 7075.
• high strength heat treatable alloys such as those designated by the Aluminum Association as Alloys 2014, 2024 and 7075.
• the compositions of these alloys are presented in Table I, below.
• these high strength heat treatable alloys may be extruded at solutionizing temperatures without causing break-up of the extrusion surface, and without the need of either reduced extrusion speeds or a previous solution heat treatment.
• a cast and homogenized billet of suitable diameter is prepared.
• the procedures of casting and homogenization are not critical and may be followed in accordance with conventional practice in the art.
• the billet is then reheated to a temperature of from about 700850 F. This heating must be uniform so that all parts of the billet are within the stated temperature range upon completion.
• the billet Upon completion of the reheating step, the billet is then extruded to a smaller diameter to obtain a reduction in area of about -75%.
• a reduction range would correspond to extrusion ratios of from about 1.25:1 to 4:1.
• This prior'hot working at a lower temperature than the conventional solutionizing extrusion step serves to break up and elongate the cast grain so that the alloy can better withstand the deformation at the subsequently applied high temperatures.
• Extrusion within the range of reductions set forth for the above would, at most, serve to reduce the diameter of the billet by about 50% and the resulting billet would remain large enough to undergo further extrustion.
• the billet Upon being partially extruded in the above manner, the billet is then cut to a usable length and reheated to a temperature in a range generally residing near the lower end of the solutionizing temperature range.
• the solutionizing temperature range varies with the particular alloy in question and thus, for example, the lower end of the temperature range would be 910 F for Alloy 2024, 925 F for Alloy 2014 and 860 F for Alloy 7075.
• the reheating range should be controlled to extend from an upper limit approximated by the solutionizing temperature ranges, above, to a temperature level roughly 30 F lower. This lower range is feasible because adiabatic heating during extrusion can cause some temperature rise to solutionizing temperatures and, in the event that solutionizing is not complete, the extrusion effect serves to provide extra strength to the alloy which compensates for the resulting loss of solutionizing.
• the control of the reheating step is considered critical, since, as noted earlier, the alloys in question possess a relatively small temperature range between solvus and solidus. Further, reheating must be conducted for a time sufficient to dissolve substantial amounts of soluble elements present within the alloy. The ability to control both reheating temperature and residence time are dependent upon the method of heating employed. Two methods of billet heating are presently in general use. Induction heating affords a rapid rise in temperature, and the desired temperature control, but is usually not maintained at that temperature for a time sufficient to constitute an effective solutionizing treatment.
• a conveyor-type furnace which is heated electrically or by gas flame, provides a longer heating time; however, the billet surface is usually directly exposed to the heat source elements, increasing the danger of overheating the surface with the result that partial melting may occur. This latter danger is especially great with high strength aluminum alloys having little spread between solvus and solidus temperatures.
• a modified induction heating method may be employed which makes use of a controlled time-hold cycle and, in the alternative, combines induction heatup with a hold in a circulating air furnace with a separate plenum chamber to isolate the heat source from the 'billet metal.
• the billet is then extruded in the conventional manner at a solutionizing temperature with the limitation, however, that the extrusion rate is controlled to prevent a rise in temperature during extrusion of more than about 20 F above the minimum solutionizing temperatures, described earlier.
• the temperature of the extrusion container or canister should only be permitted to rise higher than about 25 below billet temperature.
• the criticality of temperature control during extrusion is likewise necessitated by the temperature sensitivity of the high strength aluminum alloys involved. Temperature control in this instance is a function of the interrelationship between heat generated by the working process itself and heat conducted away by the extrusion tools and surroundings.
• extrusion speed must be regulated to prevent unacceptable temperature fluctuations and, as noted above, the container temperature should be well controlled.
• the actual temperature limits and the speed of extrusion will depend on the individual extruded shape and the alloy involved and, therefore, cannot be rigidly defined herein.
• extrusion ratio was determined with reference to a single hole die, and should not exceed about 30:1. In conjunction with this, the length-diameter ratio of the billets should not exceed 2521.
• the factor of extrusion speed is interrelated with the former two, in that extrusion speed is in part determined by magnitude of the extrusion ratio. Control of extrusion speed is important since excessive speed tends to cause break up of the extrusion as it exits from the die. In experiments dealing with the alloys relating to this invention, extrusion speeds of up to about 4 ft./min. were found to be acceptable, however, the process is not restricted thereto, provided the desired temperature limits are obtained and cracking does not occur.
• the finally extruded shape must then be quenched, in accordance with conventional practice in the art.
• the specific nature of the quenching operations is critical, for, as noted before, the alloys which are to be extruded by the method of this invention process quench sensitivity and are known to exhibit loss of strength and corrosion resistance.
• the quench must be started before the alloy has cooled enough to lose some of its solid solution, and must be rapid enough to assure than adequate mechanical strength and corrosion resistance are retained.
• quenching is conducted continuously with the extrusion moving through a water wall.
• the entire extruded length may be maintained at the solutionizing temperature range while it is being extruded and cut off or removed from the die. This can be accomplished by the use of an insulating tunnel or some similar apparatus. After cutting, the entire extrusion may be quenched by immersion in a horizontal through or by passing it through water sprays and the like. As an alternative, a moving saw may be placed as close as possible to the die face in order to quickly sever the extrusion and allow it to pass through a quench system without stopping. The determination of specific quenching time will vary with the alloy involved and the attendant extrusion conditions and need not be further developed at this time.
• the extruded alloy Upon emerging from the quench, the extruded alloy may be subjected to conventional processing such as stretch or roll straightening, natural or artificial aging depending upon the final temper which is desired.
• conventional processing such as stretch or roll straightening, natural or artificial aging depending upon the final temper which is desired.
• the quench shape may be subjected to aging treatment which may be conducted at a temperature of about 250 F for about 24 hours.
• aging treatment is applicable to specific alloys for which particular temper is sought and may vary considerably in relation to the particular alloy treatment desired.
• the heated billets may then be extruded on an extrusion press which employs a circular die of 8 inch diameter and an extrusion ratio of approximately 2.25:].
• the extruded cylindrical shape emerging from such extrusion may then be cut to length to serve as billet for final extrusion. It is first reheated to a temperature level which approximates the solutionizing temperatures of the respective alloys, and subsequently extruded in a 3,000 ton extrusion press which employs a die having an extrusion ratio of 25:], at a surface speed of from about 23 ft./minute for alloys such as Alloy 2024, and 1-2 ft./minute for alloys such as Alloy 7075. Upon existing from the end of the extrusion press, the extrusion enters a water wall quenching through to effect the rapid cooling which must follow solutionizing.
• the alloy products prepared by the above extrusion method are not prone to cracking and break-up during processing, and may be further processed to commercial tempers.
• extrusions of Alloy 7075 may be treated at 250 F for 24 hours to achieve T-6 temper for that alloy.
• Extrusions of Alloy 2024, if left in the naturally aged condition, are equivalent to T-4 temper.
• a method for extruding high strength, heat treatable aluminum alloys which comprises providing a homogenized cast alloy billet, conducting a first hot extrusion of said billet to a reduction in area of from 20-75%, conducting a second hot extrusion at the solutionizing temperature of the alloy, and quenching the resultant extruded shape after said second extrusion.

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

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Citations (5)

• 1974
  • 1974-05-23 US US472656A patent/US3874213A/en not_active Expired - Lifetime
• 1975
  • 1975-04-30 DE DE19752519362 patent/DE2519362A1/de not_active Withdrawn
  • 1975-05-13 IT IT23281/75A patent/IT1038082B/it active
  • 1975-05-20 CH CH645375A patent/CH585591A5/xx not_active IP Right Cessation
  • 1975-05-21 GB GB21791/75A patent/GB1504421A/en not_active Expired
  • 1975-05-23 FR FR7516232A patent/FR2272189B1/fr not_active Expired

Patent Citations (5)

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