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
  • C22F1/04—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 is directed to a process for preparing continuous strip cast aluminum alloy suitable for use in the manufacture of deep drawn and wall-ironed articles such as cans and the like.
• the aluminum alloy sheet useful in the production of deep drawn and ironed beverage cans is cast by direct chill casting an ingot having a thickness of about 20-25 inches.
• the ingot is homogenized at 950-1125°F for 4-24 hours and then subjected to hot rolling wherein the ingot is passed through a series of breakdown rolls maintained at a temperature of 400-900°F to reduce the ingot in thickness to a reroll gauge of about 0.0130 inch.
• the reroll stock is subjected to an annealing step wherein the stock is heated at 600-900°F for 0.5-3 hours to effect recrystallization of the metal structure.
• the annealed reroll stock is subjected to a final work hardening step wherein the reroll stock is cold rolled (room temperature rolling) to a final gauge - of about 0.013 inch or about 90% of its original thickness to produce the substantially full hard (H19) temper required for two-piece can body stock.
• the thin, e.g. 0.2-1.0 inch solidified cast web is typically reduced in thickness to a gauge of about 0.130 inch by cold rolling with an intermediate recrystallization anneal at about 600-900°F. Thereafter, as in the manufacture of direct chill ingot cast stock, the thinned, annealed stock is subjected to a final work hardening step by cold rolling to a final gauge of about 0.013 inch to produce the H19 temper required for can body manufacture.
• continuous strip cast aluminum alloy is advantageously utilized for many fabricated products, such stock has not been used extensively for the manufacture of drawn and wall-ironed can bodies.
• U. S. 4,111,721 discloses a process for imparting an anti-galling character to continuous strip cast aluminum alloy wherein the alumunim strip is heat treated at a temperature of at least 900°F and advantageously at about l150°F for a period of time between about 16 to 24 hours prior to its final cold reduction pass.
• scallops, or ears represent an almost universally undesirable feature of the cup as the ears must be removed in order to present a smooth or flat upper lip on the cup. This of course necessitates cup trimming prior or subsequent to wall-ironing, with an attendant increase in production costs and material waste.
• the level of earing in a drawn cup is determined by the following equation: where he is the distance between the bottom of the cup and the peak of the ear and ht is the distance between the bottom of the cup and the valley of the ear.
• the aluminum alloy sheet when processed into a cup must exhibit a level of earing of no more than about 3.5% and preferably less than about 3% earing.
• the level of earing experienced with commercially available continuously cast strip of 3004 aluminum alloy is generally in the range of 5% or more.
• Buckle strength is determined by applying pressure within a drawn and wall-ironed can and then gradually increasing the pressure until the bottom end of the can deforms and bulges out, i.e., it buckles. The pressure at which the bottom buckles is then designated as the buckle strength.
• a can formed from the alloy sheet must exhibit a buckle strength of at least 90 pounds per square inch (psi), and preferably between 95 and 100 psi.
• Cans drawn and wall ironed from a hard temper sheet of the continuous strip cast aluminum alloy 3004 homogenized at 1050-1100° to eliminate galling exhibit a buckle strength of about 85 psi.
• the present invention is directed to a process for the preparation of non-galling, low earing can stock from continuously cast aluminum strip suitable for deep drawing and wall-ironing into hollow articles wherein the molten aluminum material is cast by continuous strip casting into a web generally of an inch or less in thickness.
• the strip material is heated to a temperature of from 950 to 1150°F for a time sufficient to homogenize the alloy.
• the homogenized strip material is cold rolled to effect a first reduction in sheet thickness of at least 25%.
• the cold rolled sheet is heated to a recovery temperature of up to about 550°F, and subjected to a second cold rolling to effect a reduction in thickness of at least 10%.
• the cold rolled sheet product is heated to effect recrystallization of the grain structure and then subjected to effect a final reduction in thickness of at least 75% of the original thickness of the sheet to impart an Hl9 temper to the sheet.
• the sheet is subjected to a second recovery heating of up to 550°F intermediate between the second cold reduction and the recrystallization heating step.
• the continuous cast web is heated at about 950 to about 1150°F and preferably about 1000 to about 1100°F for a period of time up to about 50 hours and preferably about 10 to about 25 hours.
• the homogenization treatment is conducted at a temperature of about 1100°F for at least about 10 hours. It is recognized that several hours are required to heat the metal to reach the temperature at which homogenization is effected.
• the homogenization step of the process of the present invention imparts a very critical change in the microstructure of the alloy primarily in the size, shape and distribution of the intermetallic particles present in the alloy matrix. It has been determined that the change in intermetallic particle disposition is dependent upon the temperature as well as the time of the homogenization treatment and that the degree of galling is inversely dependent upon the intermetallic particle size.
• continuous cast 3004 aluminum alloy strip cold rolled and size-reduced to 0.0135 inch gauge to H-19 temper by conventional practice typically has an intermetallic particle size in the order of 0.3-0.7 microns.
• this strip when subjected to ironing operations encounters severe galling.
• the intermetallic particle size increases with increasing homogenization temperature which results in a proportionate decrease in galling when the homogenized strip is subjected to wall-ironing conditions.
• the cooled web which has a thickness of up to one inch and typically about 0.25 to about 0.50 inch in thickness is subjected to a first cold rolling step to effect a total gauge reduction in excess of about 25% and preferably about 50 to about 75%. Thereafter, the cold rolled sheet is heated to a recovery temperature level.
• recovery temperature means the temperature at which the rolled metal is heated whereby it is softened without forming a new grain structure.
• the recovery temperature is in the range of about 300 to about 550°F.
• the recovery temperature to which the cold rolled web may be heated after the first cold roll reduction is about 350 to about 500°F for about 2 to about 6 hours and preferably from about 425 to about 475°F for 2 to 4 hours.
• the heated web After being heated at the recovery temperature the heated web is cooled to ambient temperature and subjected to a second cold rolling step to effect a total reduction in thickness of the web of at least 10% and preferably between about 10 to about 25%.
• heating the web to a recovery temperature intermediate between the two cold rolling steps is critical to imparting a low earing characteristic to the aluminum sheet.
• the temperature of the cold rolled web is raised to the "recrystallization temperature" level.
• recrystallization temperature means the temperature at which the rolled metal web softens simultaneously with the formation of a completely new grain structure.
• the grain structure changes from a substantially elongated structure to an equiaxed structure when the alloy is heated at the recrystallization temperature.
• the recrystallization temperature is in the range of about 600 to about 900°F, the heating being effected for about 1 to about 4 hours and preferably at a temperature between about 700 to about 800°F for about 2 to about 3 hours.
• the recrystallized web After heating at the recrystallization temperature for the prescribed time period, the recrystallized web is cooled to ambient temperature and then cold rolled, e.g., to at least about 50% and preferably about 60 to about 90%, to the final gauge dictated by can performance requirements, e.g., 0.012 to 0.0145 inch and Hl9 temper.
• the aluminum web is heated a second time to a recovery temperature, the second recovery heating occurring between the second cold rolling step and the recrystallization heating step.
• the second recovery heating is effected at a temperature between about 450 and 550°F for about 0.5 to about 3 hours and preferably between about 475 to about 525°F for about 0.75 to about 1.25 hours.
• the web may be cooled to room temperature between the second recovery heating step and the recrystallization step.
• the recrystallization heating is carried out without prior cooling to room temperature by direct heating from the second recovery temperature to the recrystallization temperature.
• An aluminum alloy preferred in the practice of the present invention is a 3004 aluminum alloy having incorporated therein 0.1-0.4% by weight chromium. Sheet formed from the chromium modified alloy 3004 when fabricated into a two piece drawn and wall-ironed can exhibits an improved level of buckle strength, that is, the ability of the can to withstand high internal pressure without bottom inversion.
• the chromium modified aluminum alloy 3004 preferred in the practice of the present invention has the following range of constituents expressed in percent by weight: about 0.5 to about 1.5% magnesium, about 0.5 to about 1.5% manganese, about 0.1 to about 1.0% iron, about 0.1 to about 0.5% silicon, 0.0 to about 0.25% zinc, 0.0 to about 0.25% copper, about 0.1 to about 0.4% chromium, the balance being aluminum and incidental elements and impurities.
• sheet formed from the chromium modified alloy 3004 it is essential that it be in the state resulting from a cold roll reduction of at least 50% of the material in the recrystallized state.
• the sheet in this state exhibits tensile yield strengths in the range of 40,000 to 45,000 psi and total elongation, measured in 2 inches gauge length samples, of 1.5% or more.
• a tensile yield strength of 40,000 to 45,000 psi in the sheet material has been found, when such sheet is drawn and wall ironed into a two piece beverage container, to correlate with a can buckle strength of at least 98 psi.
• U. S. 4,111,721 teaches that additaments to alloy 3004 such as chromium should be limited to trace amounts in the order of several hundred thousands of a weight percent or less as such additaments-tend to have profound effects on the intermetallic particle sizes in the alloy.
• U. S. 3,834,900 teaches that the presence of chromium in the strip cast aluminum alloy should be minimized, i.e., limited to a concentration of less than 0.001% by weight, to avoid casting defects.
• composition and processing limitations of the present invention must be closely followed in order to achieve the required high tensile yield strength properties which characterize the sheet prepared from continuous strip cast modified alloy of the present invention. It is critical to the practice of the present invention that the chromium concentration in the alloy be strictly adhered to. For example, if the maximum chromium concentration levels are exceeded, problems such as fracturing during can forming may result. If chromium levels of less than about 0.1% by weight are incorporated in the alloy, the tensile yield strength of sheet fabricated from the continuous strip cast alloy falls below the minimum requirements for beverage can performance.
• the aluminum and alloying elements are charged into a melting furnace from which a stream of alloy is fed to a conventional strip caster which solidifies a web of an inch or less in thickness preferably about 0.25 to 0.50 inch in thickness.
• the strip cast web is fabricated into sheet having non-galling, low earing and high strength characteristics by employing the homogenization and cold roll/anneal process conditions of the process of the present invention.
• the cooled strips were rolled in successive passes using a commercial rolling mill until the strip was reduced to varying degrees of thickness ranging from 66 to 75% (0.160 to 0.120 inch).
• the reduced thickness strips were subjected to a first recovery temperature wherein the strips were placed in a furnace previously heated to 450°F and held for 3 hours after which time the strips were removed from the furnace and allowed to cool to room temperature.
• the strips were subjected to a second cold roll reduction by being passed successively through a pair of reduction rolls until the strip was reduced 10-25% in thickness (to 0.120 inch).
• the strips were subjected to a second recovery heating at 500°F for one hour and then annealed at a recrystallization temperature of 800°F for 2 hours.
• Example II For purposes of contrast, the cold roll/anneal conditions of Example I were repeated with the exception that no recovery temperature heating was effected between the cold roll reduction step and the recrystallization step. These contrasting conditions are summarized in Table III below designated by the symbols "C 1 " and "C 2 ".
• the recrystallized strips were cooled to ambient temperature and then work hardened by passing the strips successively in a commercial rolling mill until the strip was reduced about 88% in thickness (Hl9 temper) to 0.0134 to 0.0148 inch.
• the H19 temper strips were examined under a scanning electron microscope in the back scattering mode and found to have an intermetallic particle size in the 1 to 3 microns range indicating that no galling would occur when the strips were subjected to the wall-ironing conditions of can making.
• Example I The procedure of Example I was repeated with the exception that there was simulated the heating and cooling conditions that would be expected to occur in a commercially produced 10-15 ton coil of continuous strip cast aluminum alloy 3004 of about 0.50 inch thickness which had been subjected to the heating sequence of the present invention.
• Example II For purposes of contrast, the cold roll/anneal conditions of Example II were repeated with the exception that no recovery temperature heating was effected between the cold roll reduction step and the recrystallization step. This contrasting condition is summarized in Table VIII below designated by the symbol C 3 .
• the cooled recrystallized strips of Table IX were work hardened to H19 temper and reduced in thickness to 0.0134 to 0.0148 inch.
• the H19 temper strips were examined under a scanning electron microscope in the back scattering mode and found to have an intermetallic particle size in the 1 to 3 microns range, indicating that no galling would occur when the strips were subjected to the wall-ironing conditions of can making.
• Cold roll/anneal cycle 6 which is identical to cycle 5, except that a second cold roll reduction of 25% is used instead of 10%, produces a reduction in earing, but the reduction achieved is less than that achieved using cycle 5, indicating that a second cold roll reduction of 10% is more advantageous in effecting a reduction in earing.
• Cold roll/anneal cycle 7 which utilizes a single recovery heating/single recrystallization heating sequence does not achieve the earing reduction level of cycle 5 but does produce a superior reduction in earing when compared to the single recrystallization heating of cold roll/anneal cycle C 3 .
• cycle 8 produces a reduction in earing when compared to control cycle C 3 , but does not provide an advantage over cycle 5 which utilizes only one recrystallization heating.
• a strip-cast aluminum alloy having the alloy composition of the present invention designated by the symbol “I” was prepared as well as alloy compositions having varying alloy constituents within the 3004 specification range designated by the symbol "A”. These alloys were then evaluated for use in the fabrication of drawn and wall-ironed can bodies.
• the composition of the alloys is summarized in Table XV below:
• the cooled strips were rolled in successive passes using a commercial rolling mill until the strip was reduced to varying degrees of thickness ranging from 66 to 75% (0.160 to 0.120 inch).
• the reduced (66-72%) thickness strips were subjected to a first recovery temperature wherein the strips were heated in a furnace to 450°F and held for 3 hours. After being subjected to the first cold roll/recovery temperature treatment, the strips were then subjected to a second cold roll reduction by being passed successively through a pair of reduction rolls until the strip was reduced 10-25% in thickness (to 0.120 inch).
• the strips were subjected to a second recovery heating at 500°F for one hour and then heated to recrystallization temperature of 800°F for 2 hours.
• the first series of cold roll/recovery-recrystallization heatings was varied whereby in a first variation the second cold reduction was eliminated and recrystallization carried out immediately after the first recovery heating. In a second variation, the recovery heating was eliminated and recrystallization was carried out immediately after the cold reduction.
• the recrystallized strips were cooled to room temperature and then were hardened by passing the strips successively in a commercial rolling mill until the strip was reduced about 88% in thickness (Hl9 temper) to 0.0133 to 0.0148 inch.
• the H19 tempered strips were examined under a scanning electron microscope in the back scattering mode and found to have an intermetallic particle size in the 1 to 3 microns range, indicating that no galling would occur when the strips were subjected to the wall-ironing conditions of can making.
• buckle strength of cans formed from continuous strip cast aluminum alloy 3004 correlates closely with the tensile yield strength of the H19 temper sheet.
• the correlation between buckle strength and tensile yield strengh is summarized in Table XXII below.
• the tensile ultimate strength, along with the tensile total elongation, is a measure of sheet formability. To be suitable for can body manufacture, the sheet must have a tensile ultimate strength of at least 42,000 psi.
• Tensile total elongation measured in percent is a measure of ductility. To be suitable for can body manufacture the sheet must have a tensile total elongation of at least 1.5%.
• Copper was incorporated in the alloys to simulate aluminum can scrap which had been found to contain 0.1 to 0.2 percent by weight copper.
• the aluminum alloys were continuously cast, using a Hunter type twin roll caster into sheet 0.26 inches thick which were wound into 5000 pound coils.
• the coils were allowed to reach room temperature over a 48 hour period.
• the cooled coils were then placed in a furnace and homogenized in a nitrogen atmosphere.
• the coil was brought up to 1076°F i7°F over a 12 hour period and held at that temperature for 16 hours. Thereafter, the coils were allowed to cool in the furnace to 200°F over a 32 hour period.
• the cooled coils were removed from the furnace and further allowed to cool to room temperature over the next 48 hours.
• the room temperature cooled coils were subjected to a first cold roll/recovery temperature treatment wherein the cooled coils were rolled in successive passes using commercial rolling equipment until each of the coils was reduced to varying degrees of thickness varying from 83 to 85% (0.052 to 0.059 inches).
• the reduced thickness coils were subjected to a first recovery temperature wherein the coils were placed in a furnace and heated to 450°F i3°F over a 4 hour period and held at this temperature for 4 hours whereupon the coils were allowed to cool in the furnace to 300°F over a period of nine hours. The coils were removed from the furnace and allowed to cool to room temperature over the next 48 hours.
• the coils were subjected to a second cold roll reduction by being passed successively through a pair of reduction rolls until each of the coils was reduced 25% in thickness (0.039 to 0.044 inches).
• the coils were placed back in the furnace and subjected to a second recovery heating by raising the temperature of the furnace to 500°F over a 3.5 hour period, and holding at that temperature for 1.5 hours.
• the coils were annealed at a recrystallization temperature by raising the temperature of the furnace to 800°F over a 6 hour period and held at this temperature for 3 hours.
• the coils were allowed to cool in the furnace to 300°F over a 14 hour period and then removed from the furnace and allowed to cool to room temperature over the next 48 hours.
• the recrystallized coils were then work hardened by passing the coils successively in a commercial rolling mill until the coil was reduced about 65 to 67% in thickness to 0.0135 inches.
• the work hardened coils were then fabricated into two-piece aluminum beverage cans on a commercial drawn and wall ironing manufacturing line, about 5000 cans being fabricated from each coil. No galling was encountered. Earing ranged from 2.0 to 2.6%.
• the cans were also evaluated for buckle strength, i.e., ability of the can to withstand high internal pressure without buckling.
• Buckle strength is determined by applying pressure within a drawn and wall-ironed can and then gradually increasing the pressure until the bottom end of the can deforms and bulges out, i.e., it buckles. The pressure at which the bottom buckles is then designated as the buckle strength.
• a can formed from the alloy sheet must exhibit a buckle strength of at least 90 pounds per square inch (psi).

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• 1983
  • 1983-07-14 ES ES524111A patent/ES524111A0/es active Granted
  • 1983-07-14 DK DK324383A patent/DK324383A/da not_active Application Discontinuation
  • 1983-07-14 NO NO832560A patent/NO165349C/no unknown
  • 1983-07-14 AR AR29360983A patent/AR231408A1/es active
  • 1983-07-14 PT PT7703083A patent/PT77030B/pt unknown
  • 1983-07-14 BR BR8303778A patent/BR8303778A/pt not_active IP Right Cessation
  • 1983-07-15 DE DE8383304131T patent/DE3378640D1/de not_active Expired
  • 1983-07-15 GB GB08319199A patent/GB2123319B/en not_active Expired
  • 1983-07-15 AU AU16875/83A patent/AU557719B2/en not_active Ceased
  • 1983-07-15 EP EP19830304131 patent/EP0099739B1/fr not_active Expired
• 1985
  • 1985-07-31 GB GB08519274A patent/GB2172303B/en not_active Expired

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