Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/10—Alloys based on aluminium with zinc as the next major constituent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
  • B22D11/003—Aluminium alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/002—Castings of light metals
  • B22D21/007—Castings of light metals with low melting point, e.g. Al 659 degrees C, Mg 650 degrees C

Definitions

• the present invention is defined in claim 1.
• the aluminum alloy strip has 0.07 wt. % to 0.14 wt. % zirconium.
• a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 9% or less. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 8% or less. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 7% or less. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 6% or less. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 5% or less.
• a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 6% to 15%. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 7% to 15%. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 8% to 15%. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 9% to 15%. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 10% to 15%.
• a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 11% to 15%. In one or more embodiments detailed herein, a variation of the zinc weight percent between a surface and a thickness center of the aluminum alloy strip is 12% to 15%.
• the casting of the aluminum alloy strip detailed herein may be accomplished via a continuous casting apparatus capable of producing continuously cast products that are solidified at high solidification rates.
• a continuous casting apparatus capable of achieving the above-described solidification rates is the apparatus described in U.S. Patent Nos. 6,672,368 and 7,125,612 .
• the aluminum alloy strip is continuously cast using the Micromill TM process described in U.S. Patent Nos. 6,672,368 and 7,125,612 .
• a molten aluminum alloy metal M may be stored in a hopper H (or tundish) and delivered through a feed tip T, in a direction B, to a pair of rolls R 1 and R 2 , having respective roll surfaces D 1 and D 2 , which are each rotated in respective directions A 1 and A 2 , to produce a solid cast product S.
• gaps G 1 and G 2 may be maintained between the feed tip T and respective rolls R 1 and R 2 as small as possible to prevent molten metal from leaking out, and to minimize the exposure of the molten metal to the atmosphere, while maintaining a separation between the feed tip T and rolls R 1 and R 2 .
• a plane L through the centerline of the rolls R 1 and R 2 passes through a region of minimum clearance between the rolls R 1 and R 2 referred to as the roll nip N.
• the molten metal M directly contacts the cooled rolls R 1 and R 2 at regions 2 and 4, respectively.
• the metal M Upon contact with the rolls R 1 and R 2 , the metal M begins to cool and solidify.
• the cooling metal produces an upper shell 6 of solidified metal adjacent the roll R 1 and a lower shell 8 of solidified metal adjacent to the roll R 2 .
• the thickness of the shells 6 and 8 increases as the metal M advances towards the nip N. Large dendrites 10 of solidified metal (not shown to scale) may be produced at the interfaces between each of the upper and lower shells 6 and 8 and the molten metal M.
• the large dendrites 10 may be broken and dragged into a center portion 12 of the slower moving flow of the molten metal M and may be carried in the direction of arrows C 1 and C 2 .
• the dragging action of the flow can cause the large dendrites 10 to be broken further into smaller dendrites 14 (not shown to scale).
• the metal M is semi-solid and may include a solid component (the solidified small dendrites 14) and a molten metal component.
• the metal M in the region 16 may have a mushy consistency due in part to the dispersion of the small dendrites 14 therein.
• a freeze front of metal may be formed at the nip N.
• the central portion 12 may be a solid central portion, 18 containing the small dendrites 14 sandwiched between the upper shell 6 and the lower shell 8.
• the small dendrites 14 may be 20 microns to 50 microns in size and have a generally globular shape.
• the three portions, of the upper and lower shells 6 and 8 and the solidified central portion 18, constitute a single, solid cast product (S in Figure 1 and element 20 in Figure 2 ).
• the aluminum alloy cast product 20 may include a first portion of an aluminum alloy and a second portion of the aluminum alloy (corresponding to the shells 6 and 8) with an intermediate portion (the solidified central portion18) therebetween.
• the solid central portion 18 may constitute 20 percent to 30 percent of the total thickness of the cast product 20.
• the rolls R 1 and R 2 may serve as heat sinks for the heat of the molten metal M.
• heat may be transferred from the molten metal M to the rolls R 1 and R 2 in a uniform manner to ensure uniformity in the surface of the cast product 20.
• Surfaces D 1 and D 2 of the respective rolls R 1 and R 2 may be made from steel, copper, nickel, or other suitable material and may be textured and may include surface irregularities (not shown) which may contact the molten metal M.
• the control, maintenance and selection of the appropriate speed of the rolls R 1 and R 2 may impact the ability to continuously cast products.
• the roll speed determines the speed that the molten metal M advances towards the nip N. If the speed is too slow, the large dendrites 10 will not experience sufficient forces to become entrained in the central portion 12 and break into the small dendrites 14.
• the roll speed may be selected such that a freeze front, or point of complete solidification, of the molten metal M may form at the nip N.
• the present casting apparatus and methods may be suited for operation at high speeds such as those ranging from 7.6 to 152 m (25 to 500 feet) per minute; alternatively from 12.2 to 152 m (40 to 500 feet) per minute; alternatively from 12.2 to 122 m (40 to 400 feet) per minute; alternatively from 30.5 to 122 m (100 to 400 feet) per minute; and alternatively from 45.7 to 91.4 m (150 to 300 feet) per minute.
• the linear rate per unit area that molten aluminum is delivered to the rolls R 1 and R 2 may be less than the speed of the rolls R 1 and R 2 or about one quarter of the roll speed.
• Continuous casting of aluminum alloys may be achieved by initially selecting the desired dimension of the nip N corresponding to the desired gauge of the cast product S.
• the speed of the rolls R 1 and R 2 may be increased to a desired production rate or to a speed which is less than the speed which causes the roll separating force increases to a level which indicates that rolling is occurring between the rolls R 1 and R 2 .
• Casting at the rates contemplated by an embodiment of the present invention i.e. 7.6 to 122 m (25 to 400 feet) per minute) solidifies the aluminum alloy cast product about 1000 times faster than aluminum alloy cast as an ingot cast and improves the properties of the cast product over aluminum alloys cast as an ingot.
• the rate at which the molten metal is cooled may be selected to achieve rapid solidification of the outer regions of the metal. Indeed, the cooling of the outer regions of metal may occur at a rate of at least 1000 degrees Celsius per second.
• the continuous cast strip may be of any suitable thickness, and is generally of sheet gauge (0.152 mm to 6.32 mm (0.006 inch to 0.249 inch)) or thin-plate gauge (6.35 mm to 10.2 mm (0.250 inch to 0.400 inch)), i.e., has a thickness in the range of from 0.152 to 10.2 mm (0.006 inch to 0.400 inch).
• the strip has a thickness of at least 1.02 mm (0.040 inch). In one embodiment, the strip has a thickness of less than 8.13 mm (0.320 inch).
• EMA Electron Probe Micro Analyzer
• EPMA line scans are set with an initial spot of 100 micrometers diameter about 50 micrometers from the sample surface moving in the thickness direction until the other surface is reached.
• the defocused beam spots are calculated to maintain a 50 micrometer separation to provide 50% overlap between points.
• a JEOL JXA 8530F Field Emission Electron Probe Microanalyzer Hyperprobe with 4 Wave dispersive spectrometers and JEOL SDD-EDS are used to gather the data.
• the operating conditions are:
• the wave dispersive spectrometer (WDS) crystal and spectrometers are used as detailed in the Table 1.
• the counting time is 10 seconds for all elements
• a background measurement is collected every 50 spots for 5 seconds on positive and negative background locations. Elements measured are quantitatively analyzed using the JEOL quant ZAF analysis package for metals with atomic number correction by Philibert-Tixier method and flourescence excitation correction by Reed method.
• the concentration of alloying elements through depth of a sample was determined using a quantometer consistent with the method used to analyze the samples from U.S. Patent No. 6,672,368 .
• Samples are first mounted and polished in Lucite using standard metallographic preparation techniques for aluminum.
• An EPMA is used to profile the distribution of the alloying elements across a thickness to show the micro-segregation of the alloying elements.
• EPMA line scans are set with a focused spot moving with a 1 micrometer step across several grains to provide overlapping points through multiple grains.
• a JEOL JXA 8530F Field Emission Electron Probe Microanalyzer Hyperprobe with 4 Wave dispersive spectrometers and JEOL SDD-EDS are used to gather the data.
• the operating conditions are:
• a background measurement is collected every 50 spots for 5 seconds on positive and negative background locations. Elements measured are quantitatively analyzed using the JEOL quant ZAF analysis package for metals with atomic number correction by Philibert-Tixier method and flourescence excitation correction by Reed method.
• Aluminum alloy samples were cast using the apparatus detailed in U.S. Patent No. 6,672,368 at a speed of 16.8 m (55 feet) per minute to 25.9 m (85 feet) per minute and had a final thickness detailed in the tables below.
• the average weight percentages of the zinc, magnesium and copper from the surface to 3,000 micrometers thickness depth in each sample was determined using either the "macro-segregation" procedure detailed herein or via quantometer.
• Table 2 below shows the average weight percentages of zinc, copper and magnesium from surface to a thickness depth of 3,000 micrometers in each of the cast samples and the method used to determine the weight percentages in each sample: Table 2 Sample Thickness (mm) Avg. Zn wt.% Avg.
• Table 3 shows the variation of zinc weight percentages in each of the samples from surface to a thickness depth of 3,000 micrometers: Table 3 Sample Min. Zn wt.% Max. Zn wt.% Avg. Zn wt.% Variation (%) 1 3.91 4.52 4.26 14.40 2 5.40 5.75 5.60 6.25 3 6.17 6.66 6.38 7.68 4 7.11 7.54 7.34 5.86 5 6.95 7.71 7.56 10.05 6 8.34 8.96 8.71 7.12 7 15.10 17.09 15.98 12.45 8 25.53 29.70 27.46 15.19
• Table 4 shows the average weight percentages of zinc, copper and magnesium from surface to a thickness center in each of the cast samples and the method used to determine the weight percentages in each sample: Table 4 Sample Thickness (mm) Avg. Zn wt.% Avg. Mg wt.% Avg.
• Table 5 shows the variation of zinc weight percentages in each of the samples from surface to a thickness center in each sample: Table 5 Sample Min. Zn wt.% Max. Zn wt.% Avg. Zn wt.% Variation (%) 1 3.91 4.52 4.27 14.29 2 5.48 5.75 5.64 4.79 3 6.17 6.57 6.36 6.29 4 7.11 7.54 7.33 5.87 5 6.95 7.71 7.54 10.08 6 8.44 8.96 8.71 5.97 7 15.10 17.09 15.97 12.46 8 25.96 29.70 27.54 13.58
• the inventors surprisingly found that the variation of the zinc weight percent between a surface and a thickness depth of 3,000 micrometers in samples 1-7 is less than 15%. Moreover, the variation of the zinc weight percent between a surface and a thickness depth of 3,000 micrometers of sample 8 is greater than 15%. Similarly, based on visual inspection of Figures 11-12 , the variation of the zinc weight percent between a surface and a thickness depth of 3,000 micrometers in the direct chill cast prior art product and the continuously cast prior art product is greater than 15%.
• the inventors surprisingly found that the variation of the zinc weight percent between a surface and a thickness center in samples 1-8 according to the present invention is less than 15%. Moreover, based on visual inspection of Figures 11-12 , the variation of the zinc weight percent between a surface and a thickness center of the direct chill cast prior art product and the continuously cast prior art product is greater than 15%.
• the weight percentages of the zinc, magnesium and copper across grains from the surface to 200 micrometers thickness depth in sample 6 was determined using the "micro-segregation" procedure detailed herein. The data is presented in Figure 13 .
• the weight percentages of the zinc, magnesium and copper across grains through thickness for a direct chill cast prior art product are shown in Figure 14 .
• Figure 15 shows the structure of sample 6.
• the structure of samples of aluminum alloys having average zinc contents of 16% and 25% cast using the apparatus detailed in U.S. Patent No. 6,672,368 at a speed of 16.8 m (55 feet) per minute are shown in Figures 16 and 17 , respectively.
• Figures 15-17 show products of the present invention have a globular grain structure and are substantially free of micro-segregation.
• the products of the present invention may be substantially free of dendrites and consist primarily of globular non-dendritic grains - i.e., a globular grain structure.
• the products are substantially free of micro-segregation effects.

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• 2017
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