Classifications

• • 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
  • C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon

Definitions

• ABSTRACT A processing method for certain copper base alloys is described which reduces or eliminates the tendency for blister formation during annealing of alloy strip.
• the problem involves the formation of internal voids and subsequent migration and expansion of hydrogen within these voids, and the solution to the problem includes annealing under carefully controlled conditions of temperature and metal thickness so as to reduce the hydrogen level followed by a controlled deformation which heals the internal defects.
• Copper base alloys are widely used in industry and are characterized by high formability, good conductivity and pleasing appearance. A high percentage of all copper base alloys are utilized in the form of strip or sheet.
• the method of producing strip or sheet to final gauge usually involves alternate steps of deformation and annealing. It is often found in certain alloys that annealing after deformation, particularly at thinner gauges, produces undesirable blistering. These blisters are gas filled defects which become apparent when the alloy is heated. As the temperature is raised, gas pressure inside the defect increases, thus expanding and deforming the surrounding metal which has a low yield strength because of the elevated temperature. This problem is particularly common in CDA Alloy 638 which contains 2.5 to 3.1% aluminum, 1.5 to 2.1% silicon, 0.25 to 0.55% cobalt, balance essentiallly copper. Unless otherwise noted, all percentages in this application are weight percentages.
• the present invention comprises a process for the production of copper strip which results in a blister free product.
• the process is a comparatively simple one which can be applied using standard equipment commonly available in a commercial copper alloy production facility.
• the process of the present invention includes a hot rolling step followed by a diffusion annealing step performed under carefully controlled conditions.
• the diffusion anneal step reduces the hydrogen content of the alloy without permitting blister formation.
• the alloy is cold worked according to a particular schedule. This cold working operation welds shut the internal defects so that blistering will not occur during subsequent annealing operations.
• the present invention is broadly applicable to a wide range of copper alloys but is particularly useful in connection with the production of CDA Alloy 638.
• the present invention provides a process for producing blister free copper alloy sheet or strip through the use of a process which includes the steps of casting, hot working, diffusion annealing, cold rolling and optionally a further annealing step.
• a process which includes the steps of casting, hot working, diffusion annealing, cold rolling and optionally a further annealing step. The following description will provide detailed parameters for each of the steps in the process of the present invention.
• the casting of the alloy may be performed using any process which will produce a sound ingot. It is preferred, however, to use a process in which a minimum surface area of molten metal is exposed to the atmosphere during casting. For this reason it is preferred to use D.C. casting.
• an appropriate hot working temperature is from 800to 920C, preferably 850to 900C. In general, the hot working temperature will be from 0.7 to 0.95 T where T, is the absolute melting point of the alloy.
• Hydrogen in internal defects will combine to form molecular hydrogen, H Molecular hydrogen is essentially insoluble in copper alloys and will not diffuse through copper alloys. It is desirable to hot work more than 50 percent since partial healing or bonding of these internal cracks occurs. As increased deformation occurs, some of the defects heal as their surfaces bond together. It is preferred that the hot working reduction be from to percent since material made with reductions of this order of magnitude has fewer internal defects than material made with lower reduction. Complete healing of internal cracks is not possible because of the presence of hydrogen within the defect which interferes with the complete bonding of the internal crack surfaces. The final gauge after hot working must be from 0.200 to 0.750 inch and is preferably from 0.300 to 0.550 inch. The importance of this requirement will be made clear in a subsequent paragraph.
• the hot worked strip is then annealed under conditions which will permit the diffusion of hydrogen from within the strip to the surface of the strip and then to the surrounding environment.
• the temperature and metal thickness required are interrelated such that the metal will not yield under the action of the internal gas pressure, but rather will permit the hydrogen which is trapped in the defects to dissociate the diffuse out of the metal. It is most surprising that at the temperatures employed the molecular hydrogen within the defects can dissociate to permit its diffusion out of the void through the metal and to the surrounding environment. This is particularly unusual since at the temperatures involved, hydrogen in the surrounding atmosphere will not dissociate and thus cannot enter the metal.
• the annealing temperature should fall within the range of 0.4 to 0.7 T,, where T,, is the absolute melting point of the alloy.
• the temperature range is approximately 450 to 650C.
• the time of the treatment must be selected so as to permit the diffusion of the hydrogen out of the metal.
• the time limitation is affected by the thickness of the strip which controls the average diffusion distance for the hydrogen. It is further limited by the temperature of the treatment. In general, periods from 1 to 24 hours are appropriate. Increasing the strip thickness requires longer diffusion times for the same temperature, and for strips of the same thickness longer times are required at lower temperatures. It is important for the temperature range contemplated that the strip be no thinner than 0.200 inch since thin strips have less ability to resist the expansion of defects from increased internal hydrogen pressure than do thick strips.
• the length of the diffusion anneal treatment not be any longer than necessary since undesirable changes to the metallurgical microstructure and properties of the alloy may occur. These undesirable changes include changes in the amount anddistribution of second phases, depletion of solute elements and/or undesirable increases in grain size.
• the strip is cold rolled at least 60 percent and preferably at least 75 percent.
• This cold rolling operation serves to weld together the internal defects. Reductions of less than 60 percent do not provide adequate bonding of internal defect surfaces. However, if the strip is to be annealed subsequent to this cold rolling step reductions as low as 40% may be satisfactory.
• Such optional annealing may be carried out at temperatures of from 0.4 to 0.9 T,, for times of from seconds to 24 hours.
• bonding may also be obtained if the rolling operation is performed at temperatures above room temperature.
• the strip may optionally be annealed so as to obtain the desired mechanical properties such as strength and ductility.
• This annealing operation is desirable in that it will help to remove any vestige ofv the prior internal defects.
• further operations may be performed. If for example it is desired to have a final product having mechanical properties which correspond to those which result from percent cold work, it would be necessary to anneal the material following-the first cold rolling step and then cold roll to 10 percent since the first cold rolling step must incorporate a higher amount of deformation.
• a method for producing blister free copper alloy material using as a starting material a copper alloy which has been hot worked at least 50 percent to a v 4 thickness of from 0.200 to 0.750 inch including the steps of:
• the starting material contains from 2.5 to 3.1 percent aluminum, from 1.5 to 2.1 percent silicon, from 0.25 to 0.55 percent cobalt, balance essentially copper.
• Step A is performed in a protective reducing atmosphere.
• a method for producing annealed blister free copper alloy material using as a starting material a copper alloy which has been hot worked at least 50 percent to a thickness from 0.200 to 0.750 inch including the steps of:
• Step B cold working the material at least 40 percent at a temperature of less than the temperature used in Step A;
• the starting material contains from 2.5 to 3.1 percent aluminum, from 1.5 to 2.1 percent silicon,-from 0.25 to 0.55 percent cobalt, balance essentially copper.
• a method as in claim 7 wherein the thickness of the starting material is from 0.300 to 0.500 inch.
• Step A is performed in a protective reducing atmosphere.
• a method for producing blister free copper alloy material including the steps of:
• a method for producing blister free copper alloy material including the steps of:

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• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Conductive Materials (AREA)
• Lead Frames For Integrated Circuits (AREA)
• Heat Treatment Of Nonferrous Metals Or Alloys (AREA)

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Citations (3)

• 1974
  • 1974-08-30 US US501990A patent/US3929516A/en not_active Expired - Lifetime
• 1975
  • 1975-07-24 GB GB31013/75A patent/GB1507227A/en not_active Expired
  • 1975-07-24 CA CA232,192A patent/CA1045009A/en not_active Expired
  • 1975-07-28 AU AU83432/75A patent/AU502316B2/en not_active Expired
  • 1975-08-05 FR FR7524414A patent/FR2283239A1/fr active Granted
  • 1975-08-07 JP JP50096275A patent/JPS5143314A/ja active Pending
  • 1975-08-13 DE DE2536167A patent/DE2536167B2/de not_active Withdrawn

Patent Citations (3)

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