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
  • 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
  • B22D7/00—Casting ingots, e.g. from ferrous metals
  • B22D7/005—Casting ingots, e.g. from ferrous metals from non-ferrous metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
  • C22C1/026—Alloys based on aluminium
• • 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
• • 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
• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
  • F28F21/081—Heat exchange elements made from metals or metal alloys
  • F28F21/084—Heat exchange elements made from metals or metal alloys from aluminium or aluminium alloys
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2215/00—Fins

Definitions

• the present invention relates to the fields of material science, material chemistry, metallurgy, aluminum alloys, aluminum fabrication, and related fields.
• the present invention provides novel aluminum alloys for use in the production of heat exchanger fins, which are, in turn, employed in various heat exchanger devices, for example, motor vehicle radiators, condensers, evaporators and related devices.
• the present invention provides an aluminum alloy fin stock material for use in heat exchanger applications, such as automotive heat exchangers.
• This aluminum alloy fin stock alloy material was made by direct chill (DC) casting.
• the aluminum alloy fin stock material according to the embodiments of the present invention has one or more of the following properties: high strength, desirable post-braze mechanical properties, desirable sag resistance, desirable corrosion resistance and desirable conductivity.
• the aluminum alloy fin stock material according to some embodiments of the present invention displays larger grain dispersoids and improved strength before brazing. Some embodiments of the aluminum alloy fin stock material are produced in a desirable pre-braze temper, for example, HI 4.
• the improved aluminum alloy fin stock material can be used in various applications, for example, heat exchangers.
• the aluminum alloy fin stock material can be used in automotive heat exchangers, such as radiators, condensers and evaporators.
• the aluminum alloy fin stock material is useful for high performance, light weight automotive heat exchangers.
• aluminum alloy fin stock material can be used for other brazed applications, including, but not limited to, HVAC applications.
• the present invention provides an aluminum alloy fin stock material.
• This aluminum alloy fin stock alloy material was made by direct chill (DC) casting.
• Some embodiments of the aluminum alloy fin stock material have one or more of improved strength, improved corrosion resistance or improved sag resistance.
• the aluminum alloy fin stock material exhibits desirable pre-braze (HI 4) temper mechanical properties and desirable post-braze mechanical properties, sag resistance, corrosion resistance and conductivity.
• the aluminum alloy fin stock material displays larger grain size after brazing and improved strength pre-brazing.
• the aluminum alloy fin stock material can be used in various applications, for example, heat exchangers.
• the aluminum alloy fin stock material can be used in automotive heat exchangers, such as radiators, condensers and evaporators.
• compositions of an aluminum alloy fin stock material fall within the scope of the present invention. Some exemplary embodiments of the aluminum alloy fin stock material compositions are described below. All % values used below and throughout this document in reference to the amounts of constituents of the aluminum alloy fin stock material compositions are in weight % (wt%).
• the aluminum alloy fin stock material comprises about 0.8- 1.4% Si, 0.4-0.8% Fe, 0.05-0.4% Cu, 1.2-1.7% Mn and 1.2-2.3% Zn, remainder aluminum.
• aluminum alloy fin stock material comprises about 0.9- 1.3% Si, 0.45-0.75% Fe, 0.10-0.30% Cu, 1.3-1.7% Mn and 1.30-2.2% Zn, remainder aluminum.
• the aluminum alloy fin stock material comprises about 0.9-1.2% Si, 0.50-0.75% Fe, 0.15-0.30% Cu, 1.4-1.6% Mn and 1.4-2.1% Zn, remainder aluminum.
• the DC fin stock material comprises 0.9-1.1% Si, 0.10-0.25%
• the aluminum alloy fin stock material comprises 0.90-
• the aluminum alloy fin stock material comprises 0.9-
• the aluminum alloy fin stock material comprises 0.9-
• the aluminum alloy fin stock material comprises 0.90-
• the aluminum alloy fin stock material comprises
• the aluminum alloy fin stock material comprises 0.90-
• the aluminum alloy fin stock material comprises 1.0-
• the aluminum alloy fin stock material comprises
• the aluminum alloy fin stock material comprises 1.15% ⁇ 0.05 Si, 0.25% ⁇ 0.05 Cu, 0.6% ⁇ 0.1 Fe, 1.5% ⁇ 0.05 Mn, and 2.0% ⁇ 0.1 Zn, remainder Al.
• Cr and/or Zr or other grain size controlling elements may be present in the aluminum alloy fin stock material compositions in an amount of up to 0.2% each, up to 0.15% each, up to 0.1%, each, up to 0.05 % each, or up to 0.03% each. It is to be understood that the aluminum alloy fin stock material compositions described herein may contain other minor elements, sometimes referred to as unintentional elements, in an amount typically below 0.05%.
• Some embodiments of the aluminum alloy fin stock materials of the present invention display a higher solidus temperature, referred to as onset of melting, leading to improved core shrinkage, a phenomenon in which brazed aluminum alloy units do not have the desired shape. While not wanting to be bound by the following statement, it is believed, based on differential scanning calorimetry (DSC) measurements and Thermo-Calc ® software (Stockholm, Sweden) simulations, that lowering the Si content and the Zn content and increasing the Mn content in aluminum alloy fin stock material compositions can lead to higher onset of melting temperature (solidus), which contributes to core shrinkage reduction.
• DSC differential scanning calorimetry
• Thermo-Calc ® software Stockholm, Sweden
• an aluminum alloy fin stock material composition according to the embodiments of the present invention displays a solidus temperature above 617°C and a coarse post braze grain size of about 400 ⁇ .
• limiting the Si content of the alloy to 0.9-1% (preferably to 0.9-0.95%) and the Zn content to 1.5-1.6%, while maintaining the Mn content relatively high (for example, around 1.5%) raises the solidus temperature of the alloy, which, in turn, strengthens the material at the brazing temperature, so that it can resist sag or high temperature creep that can result in core shrinkage.
• Some embodiments of the present invention relate to aluminum alloy fin stock materials having a defined composition and obtained by processes that include defined process steps and conditions.
• a combination of defined composition and production process can lead to improved properties of the aluminum alloy fin stock materials.
• improved pre-braze mechanical properties are improved pre-braze mechanical properties.
• Improved pre-braze mechanical properties also referred to as properties "in pre-braze condition" result in improved fin crush resistance during assembly, while maintaining suitable sag resistance and thermal conductivity after brazing (post-brazing).
• the processes of producing aluminum alloy fin stock materials involve the step of producing an ingot by a direct chill (DC) casting process, which is commonly used throughout the aluminum industry, whereby a large ingot -1.5 m x 0.6 m x 4 m is cast from a large holding furnace which supplies metal to a shallow mold or molds supplied with cooling water.
• the solidifying ingot is continuously cooled by the direct impingement of the cooling water and is withdrawn slowly from the base of the mold until the full ingot or ingots are completed.
• the ingot rolling surfaces are machined to remove surface segregation and irregularities.
• the machined ingot is preheated for hot rolling.
• the preheating temperature and duration are controlled to low levels to preserve a large grain size and high strength after the finished fin stock is brazed.
• Several ingots (about 8 to 30) are charged to a furnace and preheated with gas or electricity to the rolling temperature.
• the period of maintaining a temperature achieved by pre-heating can also be referred to as "soak" or "soaking.
• the minimum soak time at about 480°C is about 2 hours (in other words, at least 2 hours).
• the soak time is 4-16 hours at 480°C.
• Aluminum alloys are typically rolled in the range of about 450°C to about 560°C. If the temperature is too cold, the roll loads are too high, and if the temperature is too hot, the metal may be too soft and break up in the mill.
• the processes for making some embodiments of the aluminum alloy fin stock materials may involve one or more cold rolling steps. Each of the cold rolling steps may, in turn, involve multiple cold rolling passes.
• % CW can be defined as the degree of cold rolling applied to the aluminum alloy fin stock. As used in the present document, %CW is calculated as:
• % CW may be desirable in order to attain the required strength range of the aluminum alloy fin stock material.
• Some embodiments of the of the aluminum alloy fin stock materials are produced by processes that involve a cold rolling step achieving 25-35 %CW. In some examples, a cold rolling step achieving %CW of 25% or 29% may be employed.
• increasing %CW for example, to 35% leads to an increase in pre-braze tensile strength of the aluminum alloy fin stock material, which, in turn, beneficially reduces the fin crush during radiator assembly.
• increasing the %CW may be undesirable, as it may lead to finer post braze grain size due to an increase in the driving force for recrystallization, resulting in reduced sag resistance.
• the processes for making some embodiments of the aluminum alloy fin stock materials may also involve an inter-annealing step to attain desired properties of the aluminum alloy fin stock material according to the embodiments of the present invention.
• inter-annealing or "inter-anneal” (IA) refers to a heat treatment applied between cold rolling steps.
• IA temperature may affect the properties of the aluminum alloy fin stock materials according to the embodiments of the present invention. For example, an investigation of the IA temperature used in the processes for making certain embodiments of the aluminum alloy fin stock materials showed that reducing the IA temperature from 400°C to 350°C resulted in coarser post-braze grain size.
• a combination of %CW and IA temperature employed in the production process results in desirable properties.
• a combination of IA temperature of 350°C and %CW of 35% led to beneficial combination of post-braze grain size and sag resistance the aluminum alloy fin stock material.
• a combination of IA temperature of 300°C and %CW of 25% led to beneficial combination of post-braze grain size and sag resistance the aluminum alloy fin stock material.
• a combination of IA temperature and %CW during processing of the aluminum alloy fin stock material in H14 temper resulted in improved fin crush resistance. Accordingly, the processes of producing aluminum alloy fin stock materials employing specified IA temperature and %CW, which lead, in some examples, to higher pre-braze tensile strength and improved fin crush resistance during assembly, are included within the embodiments of the present invention.
• the ingot is hot rolled to form a coil which is then cold rolled.
• the cold rolling process takes place in several steps, and a step of inter-annealing is employed between cold-rolling steps to recrystallize the material prior to the final cold rolling step.
• IA temperature in the range of about 275-400°C, 300-400°C, 300-450°C, 340-460°C, or 325-375°C may be employed.
• IA temperature of about 300°C, 350°C or 400°C may be employed in the processes of producing aluminum alloy fin stock materials according to embodiments of the present invention.
• the aluminum alloy fin stock material is cold rolled in the final cold rolling step to obtain the desired final gauge or thickness.
• the aluminum alloy fin stock material can be slit into narrow strips suitable for the manufacture of radiators and other automotive heat exchangers.
• %CW employed in the final cold rolling step is 20-35% or 25-35%, for example, about 25% or 29%.
• Various combinations of production parameters may be beneficially employed in the processes for processes of producing aluminum alloy fin stock materials according to embodiments of the present invention.
• %CW in the range 25-35% is employed in the final rolling step, resulting in improved pre-braze yield strength and tensile strength of the aluminum alloy fin stock materials, which, in turn, leads to reduction in the fin crush occurrence during assembly.
• selecting IA temperature of about 350°C results in larger post-braze grain size.
• using %CW of about 29% during the final cold rolling step further increases post-braze grain size.
• inter-annealing at 350°C for 4 hours is employed in combination with 29% CW in the final cold rolling step, which results in a material with desirable characteristics of good pre-braze strength and large post-braze grain size, high thermal conductivity and good sag behavior.
• inter-annealing at 400°C for an average of about 3 hours is employed, followed by applying % cold work (CW) of about 29% to achieve final gauge.
• soaking at about 480°C for an average of 4 hours is employed during the hot-rolling step, in combination with interannealing at about 300-400°C and % CW in the final cold-rolling step of about 25-35% to final gauge.
• soaking at 480°C for 4-16 hours in hot rolling step is employed in combination with interannealing at 350°C and %CW of 29% in the final rolling step.
• soaking at 480°C for 4-16 hours in hot rolling step is employed in combination with interannealing at 400°C and %CW of 29% in the final rolling step.
• soaking at 480°C for an average of 4 hours in hot rolling step is employed in combination with interannealing at of 350°C and %CW of 35% in the final rolling step.
• inter-annealing at 325-375°C and 20-35% CW such as interannealing at 300°C and CW 25% in the final cold rolling step is employed.
• the aluminum alloy fin stock materials produced according to some embodiments of the present invention are produced as sheets varying in gauge (thickness) between 45 ⁇ and 80 ⁇ .
• the aluminum alloy fin stock material according to the embodiments of the present invention has one or more of the following properties: minimum ultimate tensile strength (UTS) of 130 MPa (in other words, 130 MPa or more, or at least 130 MPa) measured post-brazing (for example, 134 or 137 MPa); average conductivity value of about 43%, about 41.5%, about 42.7% or about 43.3% (International Annealed Copper Standard (IACS)); an open circuit potential corrosion value vs.
• UTS minimum ultimate tensile strength
• IACS International Annealed Copper Standard
• Standard Calomel Electrode of -680mV or less, -700 mV or less or -740 or less (for example, -710mv, -720 mv, -724 mv, -725 mv, -743 mv, -740mV or -758 mV); a sag value between 7 mm, where the final gauge was 47.5 ⁇ , and 5 mm, where the final gauge was 50 ⁇ , with a cantilevered length of 35 mm.
• SCE Standard Calomel Electrode
• the above properties of aluminum alloy fin stock material sheets are measured after applying a faster braze cycle, whereby the material is heated to a temperature of 605°C and cooled to room temperature in a period of about 20 minutes, to simulate the temperature time profile of a commercial brazing process.
• the aluminum alloy fin stock material according to the embodiments of the present invention can have UTS pre-brazing in the range of 180-220 MPa (for example, 185 or 190 MPa).
• the aluminum alloy fin stock material according to the embodiments of the present invention can also have grain size >200 ⁇ for example, 200 or 400 ⁇
• An aluminum alloy fin stock material was made by a process that involved DC casting, preheating the ingot to 480°C for about 8 hours, followed by hot rolling to about 2.5 mm, cold rolling, and inter-annealing at 350°C for about 2 hours prior to final cold rolling step.
• the composition range of the aluminum alloy fin stock material was within the following specification: 1.1 ⁇ 0.1% Si, 0.6 ⁇ 0.1% Fe, 0.2 ⁇ 0.05% Cu, 1.4 ⁇ 0.1% Mn and 1.50 ⁇ 0.1% Zn, with the remainder Al.
• the aluminum alloy fin stock material produced varied in gauge between 49 and 83 ⁇ .
• the aluminum alloy fin stock material had a minimum ultimate tensile strength of ⁇ 130MPa.
• the aluminum alloy fin stock material had an average conductivity after brazing of -43 IACS and an open circuit potential corrosion value vs. SCE of -741 mV. These values were measured after applying a simulated brazing cycle, whereby the sample was heated to a temperature of 605°C and cooled to room temperature in a period of about 20 minutes to simulate the temperature time profile of a commercial brazing process.
• Example 2
• Two samples of aluminum alloy fin stock material were made by a process that involved DC casting, followed by hot rolling with pre-heating at 480°C for 4-16 hours, cold rolling, and inter-annealing at 350°C for the first sample and at 400°C for the second sample, prior to final cold rolling to 29% %CW .
• the composition of the first sample was: 0.95% Si, 0.6% Fe, 0.2% Cu, 1.45% Mn and 1.55% Zn, with the remainder Al.
• the composition of the second sample was: 1.15% Si, 0.6% Fe, 0.25% Cu, 1.5% Mn and 2% Zn, with the remainder Al.
• the aluminum alloy fin stock material had a post-braze ultimate tensile strength of -134 MPa for the first sample and -137 MPa for the second sample.
• the aluminum alloy fin stock material had an average conductivity after brazing of -42.7 IACS for the first sample and -43.3 IACS for the second sample.
• the aluminum alloy fin stock material had an open circuit potential corrosion value vs. SCE of -710 mV for the first sample and -743mV for the second sample.
• the aluminum alloy fin stock material had a grain size of 400 ⁇ for the first sample and 200 ⁇ for the second sample.
• the aluminum alloy fin stock material exhibited pre-braze UTS of 185 MPa for the first sample and 190 MPa for the second sample. The comparison between the two samples revealed that both samples produced attractive mechanical properties, but the open circuit potential corrosion value of the first sample was lower, indicating that increase in Zn content may be desirable.
• the second sample had advantageously lower open circuit potential corrosion value.

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