US3801382A - Method of precipitation hardening of copper-aluminum alloys - Google Patents

Method of precipitation hardening of copper-aluminum alloys Download PDF

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Publication number
US3801382A
US3801382A US00205055A US3801382DA US3801382A US 3801382 A US3801382 A US 3801382A US 00205055 A US00205055 A US 00205055A US 3801382D A US3801382D A US 3801382DA US 3801382 A US3801382 A US 3801382A
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alloys
frequency
precipitation hardening
subjecting
hardening process
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US00205055A
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L Ettenreich
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Andritz Hydro GmbH Austria
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Andritz Hydro GmbH Austria
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    • 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
    • C21D1/04—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering with simultaneous application of supersonic waves, magnetic or electric fields
    • 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

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  • ABSTRACT A method of precipitation hardening of Cu-Al alloys, which comprises the steps of subjecting the alloys to the action of one or more electromagnetic alternating fields whose frequency is of a defined value and simultaneously applying heat to the alloys in a single temperature zone which is lower than the eutectoid temperature of the alloys, and finally quenching the alloys to ambient temperature by an aqueous coolant.
  • the entire process takes place at a much faster rate, and the structure of the resulting alloy has a finer grain and greater resistance to corrosion than that obtained by conventional precipitation hardening.
  • the present invention relates to precipitation hardening of copper-aluminum alloys in a single heating zone while subjecting the alloys to the action of one or more electromagnetic alternating fields.
  • precipitation hardening is effected in two or three successive stages, as follows:
  • Solution heat treatment homogenization heat treatment
  • precipitated crystals are brought to the form of a solid solution in the crystals of the main alloy constituent.
  • the state of the'solution which exists at the temperature of the solution is at first maintained by quenching, even at room temperature. At this temperature, however, a supersaturated solid solution will exist which is no longer in thermodynamic equilibrium andtherefore tends to change into a saturated solid solution, with the formation of precipitates.
  • the solution heat treatment followed by quenching will produce an increase of hardness and strength.
  • Hot age hardening (annealing or tempering) of the alloys immediately after the quenching or age hardening at room temperature Tempering up to determined temperatures results in precipitations from thesolid solution in a highly disperse form. As long as the precipitates are in this form, further increase in hardness and strength takes place. If, however, a determined temperature, the so-called critical dispersion degree, is exceeded, the precipitates are no longer in highly disperse form but in the form of coarse grains so that a reduction in strength occurs.
  • the process according to the invention has the advantage that it can be carried out regardless of the geometric forms of the alloys to be hardened, and that there is no retention period required since the heating-up step alone results in the metallurgical changes occurring in the alloys, bringing about the desired improvements in properties.
  • the hardness and strength of the alloys are increased in a manner which hitherto could be achieved only by solution heat treatment, including quenching, together with subsequent cold and hot age hardening.
  • the electromagnetic alternating fields applied according to the invention have the effect that the additional hardness and strength increase is obtained already during the solution heat treatment (including quenching).
  • the metallurgical processes which hitherto took place only during cold or hot age hardening occur already at the high temperature of the novel solution heat treatment.
  • alloys treated according to the invention show no further increase of hardness or strength after subsequent cold or hot age hardening. These steps are therefore'made superfluous by the use of the present invention.
  • the structure of an alloy precipitation hardened according to the invention has a finer grain and greater resistance to corrosion than if it had been treated by conventional precipitation hardening.
  • FIG. 1 is a phase diagram showing the composition of an exemplary copper-aluminum alloy on which the inventive process can be carried out;
  • FIG. 2 illustrates one type of an inductive heating and observation apparatus built for laboratory use
  • FIG. 3 is a diagram showing the solubility of Cu in Al.
  • composition of the alloy is, in addition to aluminum: 5.4 to 5.9 percent Cu, 0.3 percent Fe, 0.15 percent Si, 0.05 percent Mg, 0.2 percent Zn, 0.3 to 0.6 percent Pb, 0.3 to 0.6 percent Ni, all percentages being given by weight.
  • region A an a solid solution consisting mostly of aluminum and copper
  • region B the a solid solution and a mixture of a with a second type of crystal B, an intermetallic compound Al Cu, copper aluminide.
  • the eutectoid temperature is at 548 C and at that temperature the aluminum is capable of dissolving about 5.7 percent Cu by weight.
  • microhardness (load of a test diamond 100 p) of this alloy amounts to 77 to 81 kp per sq.mm, after solution heat treatment in a salt bath, cold and hot age hardening.
  • the retention time in the salt bath for the exemplary alloy will be one minute per each millimeter thickness of the material.
  • the alloy in question was subjected to the inventive process by exposing it to one (alternatively more) electromagnetic alternating fields(s) the frequency of which can be readily derived from the formula f(in c/s) 503 /11 H p wherein d depth of penetration in millimeters, in proportion to the dimensions of the alloy,
  • Heat beyond the depth of penetration, in the direction toward the core of the material, is applied by way of conduction.
  • an inductive heating apparatus for laboratory examinations was constructed so that it constitutes, at the same time, an inductively heated apparatus for microscopic observations. It is consequently possible for heating processes occurring at high speed to be continuously observed in the microscope and for all important parameters to be determined.
  • numeral 1 designates the test piece to be examined, which is in the form of a tube open at the top and closed at the other end, and the latter facing the objective of the microscope, schematically shown at 2.
  • the thickness of the cylinder wall of the test piece is 1 mm
  • the thickness of the bottom surface to be observed is 2 mm
  • the diameter of the tube is 9 mm
  • the height of the entire test piece is 35 mm.
  • Numeral 3 designates a protective glass between test piece 1 and objective 2.
  • Test piece 1 is surrounded by a ceramic tube 4.
  • An induction coil 5 is disposed around the latter.
  • Arrow 7 indicates that a protective gas may pass between test piece 1 and ceramic tube 4.
  • a thermocouple 8 serves to measure the temperature of the bottom surface of test piece 1.
  • the frequency of the induction current applied to coil 5 during the test was about 7 kcls (kHz).
  • the induction current was supplied by an RC generator and an amplifier.
  • test pieces such as 1 were introduced into induction coil 5. Temperature measurement was effected by means of thermocouple 8 and a mirror galvanometer. The test pieces were heat treated in an atmosphere of a protective gas in order to prevent oxidation of the surface to be observed. After reaching the dissolution temperature the test pieces were quenched with water.
  • test pieces were ground and polished on the observed surfaces. l-lalf of the test pieces were etched with NaOH before heating and the other half were left unetched for the purpose of thermal etching.
  • test pieces More than 100 test pieces were subjected in the laboratory to precipitation hardening, with continuous observation through the microscope in all cases. The examinations were carried out in such a manner that one parameter at a time was varied while all other parameters were kept constant. These parameters are: 1. heating-up time; 2. dissolution temperature; and 3. quenchingtime.
  • the optimum dissolution temperature at the recited composition of the exemplary alloy was found to be about 545C.
  • microhardness values after this precpitation hardening gave the same, and even slightly higher values, compared with conventional precipitation hardening.
  • the micro-hardness (loading of test diamond p) was 81 to 83 kp per sq.mm.
  • the structure of the alloy, precipitation hardened in this manner, is finer than the structure after conventional precipitation hardening. This effect is explained by the rapidity with which the entire precipitation process takes place. Microsections showing the structure after conventional precipitation hardening still reveal grain limits.
  • Bar material was precipitation hardened in a continuous pass-through process in which the bars ran through an induction coil.
  • the frequencies of the induction currents were from 500 to 2,000 c/s, depending on the diameters of the bars, and the necessary power for the precipitation hardening was about 300 kW per hour.
  • the electromagnetic alternating fields used according to the inventive process have the effect that the additional increase of hardness and strength, which otherwise occurs only during cold and hot age hardening, are obtained during the solution heat treatment proper.
  • the metallurgical processes which, according to the present state of the art, take place only during cold or hot age hardening, accordingly occur already at the high temperature of the novel solution heat treatment according to the present invention.
  • an alloy which is precipitation hardened by the method of the present invention actually shows no further increase of hardness or strength, either after subsequent cold age hardening or after hot age hardening.
  • the structure of an alloy precipitation hardened according to the present invention has a finer grain and greater resistance to corrosion than after conventional precipitation hardening.
  • Quenching is efi'ected generally by water of room temperature, i.e., about 20C.
  • the quenching time as mentioned, is in the order of seconds.
  • the electromagnetic alternating fields are produced, according to the invention, in the alloys to be subjected to precipitation hardening in one of the following manners:
  • Eddy currents are produced in the alloys by electromagnetic induction. Like all alternating currents, these eddy currents are always accompanied by electromagnetic alternating fields.
  • the alloys are conductively connected by appropriate terminals to a source of alternating current. Exactly as in the case of electromagnetic induction, alternating currents passing through the alloys produce electromag netic alternating fields therein.
  • alternating-current generators which produce currents of sufficiently high frequencies.
  • Such generators are, for practical purposes, not limited in respect of their outputs, and are excellently suited for carrying out the described process.
  • static converters which, with the aid of thyristors, convert an alternating current of the supply mains frequency (generally 50 or 60 c/s) into an alternating current of much higher frequency.
  • Two basic types of such converters are manufactured, namely load-controlled converters with a sliding frequency and self-controlled converters having a fixed frequency.
  • Load-controlled converters are controlled in such a manner that they are automatically adjusted to the resonant frequency of the load, in this case to that of the alloy to be precipitation hardened. These converters work with a sliding frequency and, therefore, are excellently suited to the production of electromagnetic alternating fields which in turn give rise to specific oscillations of the atomic lattice with maximum efficiency.
  • the second type of converters works with a fixed but adjustable frequency. These converters serve to produce the required optimum heating frequency. The technical prerequisites for this type of solution heat treatment are thus fulfilled.
  • An induction current of suitable frequency serves for heating, as exemplified earlier, and other induction currents, the frequencies of which are determined from the oscillograms, serve to produce particularly effective electromagnetic alternating fields.
  • the induction currents may either be simultaneously passed through a single induction coil or through a plurality of coils.
  • the heating process and consequently the dissolution process take place substantially more quickly than when the heating is effected from outside, such as by heat conduction and heat radiation.
  • the formula reproduced herein, forming the basis of the invention allows all critical parameters to be calculated for specific alloys to be treated according to the invention.
  • This includes the frequency of the electromagnetic alternating field (or fields) used in the process, the changing polarity of the magnet field (or fields) applied, the speed of the relative movement brought about between the field of the constantpolarity magnet (or magnets) and the alloys introduced into its (their) field, and/or the frequency of one of several simultaneously applied electric currents, which contributes to the heat applying step forming part of the inventive process.
  • the frequency of the remaining current (or currents) substantially corresponds to one (or more) discrete resonant frequency (frequencies) of the alloys under treatment.
  • the method according to the present invention provides a new technique for the precipitation hardening of Cu-Al alloys, while providing substantial technological and economic advantages, and can be applied to large-scale industrial production.
  • step of subjecting the alloys to the alternating field includes converting a mains-supply alternating current into a specific alternating current having a frequency in accordance with said formula, with static converter means having a sliding frequency output, including controlling the load of the converter means so as to regulate the frequency of the specific alternating current and adapt the same to the resonant frequency of the alloy load.
  • step of subjecting the alloys to the alternating field includes converting a mains-supply alternating current into a specific alternating current having a frequency in accordance with said formula, with self-controlled static converter means having an adjustable frequency output, including controlling the converter means so as to produce the required frequency for said heat applying step.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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US00205055A 1968-02-27 1971-12-06 Method of precipitation hardening of copper-aluminum alloys Expired - Lifetime US3801382A (en)

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Application Number Priority Date Filing Date Title
AT185468A AT309837B (de) 1968-02-27 1968-02-27 Verfahren zur Aushärtung von Legierungen

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US (1) US3801382A (enrdf_load_stackoverflow)
AT (1) AT309837B (enrdf_load_stackoverflow)
BE (1) BE729036A (enrdf_load_stackoverflow)
CH (1) CH493635A (enrdf_load_stackoverflow)
DE (1) DE1908473C3 (enrdf_load_stackoverflow)
FR (1) FR2002681A1 (enrdf_load_stackoverflow)
GB (1) GB1257261A (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4090889A (en) * 1976-11-12 1978-05-23 Chrysler Corporation Forming of high strength aluminum alloy
US5785776A (en) * 1996-06-06 1998-07-28 Reynolds Metals Company Method of improving the corrosion resistance of aluminum alloys and products therefrom
US20030201584A1 (en) * 2002-04-30 2003-10-30 Cerberus Pilot Acquisition Iii, Inc. Annealing apparatus
CN100449009C (zh) * 2007-04-17 2009-01-07 武汉晶泰科技有限公司 电磁场在提高金属材料寿命上的应用
CN100489124C (zh) * 2007-04-17 2009-05-20 武汉晶泰科技有限公司 一种利用电磁场提高金属材料耐磨性能的方法
US20090317459A1 (en) * 2006-01-31 2009-12-24 Ineos Healthcare Limited Material

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4437908A (en) 1979-10-13 1984-03-20 Inoue-Japax Research Incorporated Method of treating a magnetic material
DE102006006849A1 (de) * 2006-02-15 2007-08-16 Bayerische Motoren Werke Ag Verfahren und Vorrichtung zum Ausscheidungshärten von hochlegierten Nichteisenmetallen

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4090889A (en) * 1976-11-12 1978-05-23 Chrysler Corporation Forming of high strength aluminum alloy
US5785776A (en) * 1996-06-06 1998-07-28 Reynolds Metals Company Method of improving the corrosion resistance of aluminum alloys and products therefrom
US20030201584A1 (en) * 2002-04-30 2003-10-30 Cerberus Pilot Acquisition Iii, Inc. Annealing apparatus
US6702980B2 (en) * 2002-04-30 2004-03-09 Martinrea Industries, Inc. Annealing apparatus
US20090317459A1 (en) * 2006-01-31 2009-12-24 Ineos Healthcare Limited Material
CN100449009C (zh) * 2007-04-17 2009-01-07 武汉晶泰科技有限公司 电磁场在提高金属材料寿命上的应用
CN100489124C (zh) * 2007-04-17 2009-05-20 武汉晶泰科技有限公司 一种利用电磁场提高金属材料耐磨性能的方法

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AT309837B (de) 1973-09-10
DE1908473B2 (de) 1978-02-16
DE1908473A1 (de) 1969-09-18
DE1908473C3 (de) 1978-09-21
BE729036A (enrdf_load_stackoverflow) 1969-08-01
FR2002681A1 (enrdf_load_stackoverflow) 1969-10-31
GB1257261A (enrdf_load_stackoverflow) 1971-12-15
CH493635A (de) 1970-07-15

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