Patent Application
20200080172
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 automotive heat exchanger industry presents a number of demands on the aluminum materials used for production of heat exchanger fins (“fin stock materials”). These demands may be difficult to balance. There is a need for aluminum alloy fin stock with high strength both in pre-braze and post-braze conditions, improved sag resistance which means good behavior during brazing, and reduced fin erosion. In order to make automobiles lighter, it is desirable to reduce the size and weight of automotive heat exchangers for resource saving and energy saving. Various methods have been studied for achieving this objective and one of the desirable solutions is to reduce the thickness of the aluminum fin stock material. In order to reduce the thickness of the fin material, it is important to achieve both higher strength after brazing and ensure adequate brazeability. At the same time, heat exchanger fins must have high conductivity and better corrosion performance compared to the rest of the heat exchanger components. For example, heat exchanger fins may be more anodic than the heat exchanger tube stock so that the fins act sacrificially. Desirable aluminum fin stock material would possess the properties and parameters that balance the above requirements.
Covered embodiments of the invention are defined by the claims, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification, any or all drawings and each claim.
It is desirable to produce aluminum fin stock material that would have a required combination of thickness (gauge), would be able to withstand brazing and would exhibit appropriate mechanical characteristics before, during and after brazing, strength and conductivity characteristics suitable for high performance heat exchanger applications, and suitable corrosion potential. In addition, it is desirable to produce aluminum fin stock material from an input metal that incorporates scrap aluminum in order to produce fin stock material in an environmentally friendly and cost-effective manner. Disclosed is an improved aluminum alloy fin stock material that possesses a combination of characteristics and properties that make it suitable for production of heat exchanger fins to be used, for example, in heat exchangers, such as those employed in the automotive industry. In one example, the improved aluminum alloy fin stock material can be produced in a sheet form at a desired thickness (gauge) that is suitable for production of light-weight heat exchanger units. The aluminum alloy fin stock material can be brazed and exhibits strength characteristics before, during, and after brazing that make it attractive for automotive heat exchanger applications. More specifically, the disclosed improved aluminum alloy fin stock material possesses pre-braze strength characteristics that reduce fin crush problems during brazing. The disclosed aluminum alloy fin stock material also possesses sufficiently high thermal conductivity suitable for heat exchanger applications, and has a corrosion potential that is sufficiently negative for the fins to act in a sacrificial manner during corrosion of the heat exchanger. In summary, the improved aluminum alloy fin stock material has one or more of the following properties: high strength, desirable post-braze mechanical properties, desirable sag resistance, desirable corrosion resistance, and desirable conductivity. At the same time, the aluminum alloy fin stock material can be produced from input aluminum that is at least in part recycle-friendly. More specifically, the improved aluminum alloy fin stock material contains levels of non-aluminum constituents, for example, Cu, Fe, Mn, and Zn, that are compatible with the levels of these elements found in certain scrap aluminum as input metal.
The disclosed aluminum alloy fin stock material is produced in sheet form, plate form, or shate form. Also disclosed are processes for producing the improved aluminum alloy fin stock material, which incorporate one or more of casting, rolling, or annealing steps. In some cases, the process steps employed during production of the improved aluminum alloy fin stock material confer beneficial properties and characteristics on the material. In one exemplary process, the improved aluminum alloy fin stock material is produced by using one or more cold rolling steps. Each of the cold rolling steps may, in turn, involve multiple cold rolling passes. A cold rolling step may be characterized by “% cold work” or “% CW” achieved. Achieving a specified range or value of % CW may be desirable in order to attain the required strength range of the aluminum alloy fin stock material. In one example, the aluminum alloy fin stock material may be produced by a process that involves direct chill casting and cold work (cold rolling) to produce a desirable pre-braze temper, for example, an H14 temper. In other examples, the improved fin stock aluminum alloy material can be produced in various other strain-hardened pre-braze tempers, such as H16, H18, or other H1X tempers. The process for producing the aluminum alloy fin stock material may also involve hot rolling after direct chill casting, and inter-annealing prior to final cold rolling steps (for example, between intermediate and final cold rolling steps). The term “inter-annealing (IA)” refers to a heat treatment applied between cold rolling steps. The IA temperature may affect the properties of the aluminum fin stock materials. For example, reducing the IA temperature from 400° C. to 350° C. results in a coarser post-braze grain size. A combination of % CW and IA temperature employed in the production, along with other factors such as the composition of the aluminum alloy, results in desirable properties.
The disclosed aluminum alloy fin stock material can be used in various applications, for example, for manufacturing fins for heat exchangers. In some cases, the improved aluminum alloy fin stock material is useful for high performance, light-weight automotive heat exchangers. As a few non-limiting examples, the aluminum alloy fin stock material can be used in motor vehicle heat exchangers such as radiators, condensers, and evaporators. However, the uses and applications of the improved aluminum alloy fin stock material are not limited to automotive heat exchangers and other uses are envisioned, as the characteristics and properties of the aluminum alloy fin stock material can also be beneficial for uses and applications other than the production of automotive heat exchanger fins. For example, the improved aluminum alloy fin stock material can be used for the manufacture of various devices employing heat exchangers and produced by brazing, such as devices employed in heating, ventilating, air conditioning, and refrigeration (HVAC&R) systems.
As discussed above, the compositions and the processes for producing the improved aluminum alloy fin stock material lead to a material possessing a combination of beneficial characteristics and properties that make it suitable for manufacturing heat exchanger fins. For example, the aluminum alloy fin stock material displays beneficial combinations of one or more of the following characteristics: pre- and post-braze mechanical properties, such as tensile strength and post-braze sag resistance, heat conductivity, and corrosion potential. One example is an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25 wt. % Mg, about 0.1-3.0 wt. % Zn, and up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %. Another example is an aluminum alloy comprising about 0.9-1.35 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25 wt. % Mg, about 0.1-3.0% Zn, and up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %. Another example is an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.35-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25 wt. % Mg, about 0.1-3.0 wt. % Zn, and up to about 0.10 wt. % Ti with remainder Al and impurities at ≤0.15 wt. %. Some other examples are as follows: an aluminum alloy comprising about 0.9-1.2 wt. % Si, 0.3-0.6 wt. % Fe, 0.40-0.55 wt. % Cu, 1.0-1.7 wt. % Mn, 0.01-0.1% Mg and 0.1-3.0 wt. % Zn, with remainder Al and impurities at ≤0.15 wt. %; an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.1-1.60 wt. % Mn, about 0.01-0.25 wt. % Mg, about 0.1-3.0 wt. % Zn, and up to 0.10 wt. % Ti with remainder Al and impurities at ≤0.15 wt. %; an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.05-0.2 wt. % Mg, about 0.1-3.0 wt. % Zn, and up to about 0.10 wt. % Ti with remainder Al and impurities at ≤0.15 wt. %; an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25 wt. % Mg, about 1-3.0 wt. % Zn, and up to about 0.10 wt. % Ti with remainder Al and impurities at ≤0.15 wt. %; and an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25 wt. % Mg, about 1.5 to 2.75 wt. % Zn, and up to about 0.10 wt. % Ti with remainder Al and impurities at ≤0.15 wt. %. In the disclosed aluminum alloys, one or more of Zr, V, Cr or Ni can be present at below 0.05 wt. %, below 0.04 wt. %, below 0.03 wt. %, below 0.02 wt. %, or below 0.01 wt. %. In some cases, one or more of Zr, V, Cr or Ni are absent (i.e., 0 wt. %).
In some examples, the disclosed aluminum alloys can have an ultimate tensile strength of one or both of: at least 200 MPa, measured in a pre-brazed condition, or at least 150 MPa, measured post-brazing. In one example, the aluminum alloy has an ultimate tensile strength of one or both of: 200-230 MPa, measured in a pre-brazed condition, or greater than 170 MPa, measured post-brazing. The aluminum alloy can have a corrosion potential of −760 mV or less, measured post-brazing. The aluminum alloy can have a thermal conductivity of greater than 40% IACS (International Annealed Copper Standard, which assumes pure copper conductivity for 100%), measured post-brazing.
The disclosed aluminum alloys can be produced by a process comprising: direct chill casting the aluminum alloy into an ingot; hot rolling the ingot after the direct chill casting; after the hot rolling, cold rolling the aluminum alloy to an intermediate thickness; after cold rolling, inter-annealing the aluminum alloy rolled to the intermediate thickness at a temperature between 200 and 400° C. (200-400° C.); and, after inter-annealing, cold rolling the aluminum alloy to achieve a % cold work reduction in thickness (% CW) of 20 to 40%, resulting in a sheet having a thickness of 45-100 μm, 45-90 μm, 47-85 μm, or 50-83 μm. In further processes, continuous casting may be used. % CW achieved in the above-described processes can be 30 to 40%. The inter-annealing can be performed at a temperature between 320° C. and 370° C. (320-370° C.), between 290° C. and 360° C. (290-360° C.) or between 340° C. and 360° C. (340-360° C.). The inter-annealing time can be 30 minutes to 60 minutes. Also disclosed is a heat exchanger comprising the improved aluminum alloys. The heat exchanger can be a motor vehicle heat exchanger. The heat exchanger can be a radiator, a condenser, or an evaporator. Also disclosed are processes for making objects and apparatuses comprising the improved alloys. One example of such a process is a process of making a heat exchanger, comprising joining by brazing at least one first aluminum alloy form fabricated from the improved aluminum alloy with a second aluminum alloy form, comprising: assembling and securing the two or more aluminum forms together; and heating the two or more aluminum forms to a brazing temperature until joints are created among the two or more aluminum forms by capillary action. Uses of the improved aluminum alloys for fabrication of heat exchanger fins and other objects and apparatuses are also included within the scope of the present description. Other objects and advantages of the invention will be apparent from the following detailed description.
Described herein are high-strength, corrosion resistant aluminum alloys and methods of making and processing the same. The aluminum alloys described herein exhibit improved mechanical strength, corrosion resistance, and/or formability. The alloys provided herein include increased silicon (Si), copper (Cu), manganese (Mn), and magnesium (Mg) as compared to existing alloys. The alloys provided herein may have improved post-braze strength as compared to existing alloys. The alloy material can be formed as fin stock and used in automotive heat exchangers, such as radiators, condensers, and evaporators. The aluminum fin stock may be used for other brazed applications, including, but not limited to, HVAC&R applications. Additionally, the aluminum alloy fin stock material is useful for high performance, light-weight automotive heat exchangers. Fin stock is designed to be less noble than the tube so that the former corrodes faster than the latter. Heat exchangers are designed based on this sacrificial corrosion prevention by fin stock over tube. Accordingly, the fin stock material described herein offers this sacrificial protection to the tube.
The terms “invention,” “the invention,” “this invention,” and “the present invention” used herein are intended to refer broadly to all of the subject matter of this patent application and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below.
In this description, reference is made to alloys identified by aluminum industry designations, such as “series” or “1xxx.” For an understanding of the number designation system most commonly used in naming and identifying aluminum and its alloys, see “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” or “Registration Record of Aluminum Association Alloy Designations and Chemical Compositions Limits for Aluminum Alloys in the Form of Castings and Ingot,” both published by The Aluminum Association.
As used herein, the meaning of “a,” “an,” or “the” includes singular and plural references unless the context clearly dictates otherwise.
As used herein, a plate generally has a thickness of greater than about 15 mm. For example, a plate may refer to an aluminum product having a thickness of greater than about 15 mm, greater than about 20 mm, greater than about 25 mm, greater than about 30 mm, greater than about 35 mm, greater than about 40 mm, greater than about 45 mm, greater than about 50 mm, or greater than about 100 mm.
As used herein, a shate (also referred to as a sheet plate) generally has a thickness of from about 4 mm to about 15 mm. For example, a shate may have a thickness of about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, or about 15 mm.
As used herein, a sheet generally refers to an aluminum product having a thickness of less than about 4 mm. For example, a sheet may have a thickness of less than about 4 mm, less than about 3 mm, less than about 2 mm, less than about 1 mm, less than about 0.5 mm, less than about 0.3 mm, less than about 0.1 mm, or less than about 0.05 mm.
Reference is made in this application to alloy temper or condition. For an understanding of the alloy temper descriptions most commonly used, see “American National Standards (ANSI) H35 on Alloy and Temper Designation Systems.” An F condition or temper refers to an aluminum alloy as fabricated. An 0 condition or temper refers to an aluminum alloy after annealing. An Hxx condition or temper, also referred to herein as an H temper, refers to an aluminum alloy after cold rolling with or without thermal treatment (e.g., annealing). Suitable H tempers include HX1, HX2, HX3 HX4, HX5, HX6, HX7, HX8, or HX9 tempers. For example, the aluminum alloy can be cold rolled only to result in a possible H19 temper. In a further example, the aluminum alloy can be cold rolled and annealed to result in a possible H23 temper.
The following aluminum alloys are described in terms of their elemental composition in weight percentage (wt. %) based on the total weight of the alloy. In certain examples of each alloy, the remainder is aluminum, with a maximum wt. % of 0.15% for the sum of the impurities.
As used herein, “electrochemical potential” refers to a material's amenability to a redox reaction. Electrochemical potential can be employed to evaluate resistance to corrosion of aluminum alloys described herein. A negative value can describe a material that is easier to oxidize (e.g., lose electrons or increase in oxidation state) when compared to a material with a positive electrochemical potential. A positive value can describe a material that is easier to reduce (e.g., gain electrons or decrease in oxidation state) when compared to a material with a negative electrochemical potential. Electrochemical potential, as used herein, is a vector quantity expressing magnitude and direction.
As used herein, the meaning of “room temperature” can include a temperature of from about 15° C. to about 30° C., for example about 15° C., about 16° C., about 17° C., about 18° C., about 19° C., about 20° C., about 21° C., about 22° C., about 23° C., about 24° C., about 25° C., about 26° C., about 27° C., about 28° C., about 29° C., or about 30° C.
All ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g., 1 to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10.
Described below are novel aluminum alloys. The properties of aluminum alloy fin stock materials vary based on their composition. The aluminum alloy fin stock material disclosed herein possesses a number of advantageous properties. The aluminum alloy fin stock material can be produced in the form of sheets, shates, or plates and possesses and possesses desirable strength before, during, and after brazing, even at gauges lower than 200 μm or 100 μm, that makes it suitable for manufacturing of fins for heat exchanger applications. The aluminum alloy material also possesses thermal conductivity and corrosion potential suitable for fin stock production.
The aluminum alloy fin stock material as disclosed herein can contain a higher content of one or more of Cu, Si and Mg, in comparison to known fin stock alloys. The composition of the aluminum alloy fin stock material and/or its production process lead to improved properties of the material, such as reduction of fin crush during brazing, higher post-braze strength, improved thermal conductivity, improved sag resistance and increased anodic corrosion potential. The aluminum alloy fin stock material possesses one or more of strength, heat conductivity and corrosion potential that is improved in comparison with known alloys used for fin stock production. The relatively high levels of non-aluminum constituents in the aluminum alloy fin stock material allow it to be produced from input metal that incorporates recycle-friendly aluminum, allowing for different metal inputs.
In some examples, the aluminum alloy fin stock material is produced by a process including a heat treatment (inter-annealing) step before a final cold rolling step. Inter-annealing is conducted at a temperature from 200° C. to 400° C. for a period from about 30 minutes to 2 hours (e.g., for a time period of about 1 hour to 2 hours). Inter-annealing is followed by cold rolling steps leading to a specified reduction of thickness (“% cold work,” defined later in this document). In some examples, the above combination of process steps (inter-annealing followed by cold rolling) results in an increase of pre-braze strength and improved coarse post-braze grain structure, which leads to improved sag resistance of the improved aluminum fin stock materials, and also affects heat conductivity and corrosion potential, thus leading to a material having a favorable combination of characteristics and properties.
In some examples, the alloys can have the following elemental composition as provided in Table 1.
In some examples, the alloys can have the following elemental composition as provided in Table 2.
In some examples, the alloys can have the following elemental composition as provided in Table 3.
In some examples, the alloys can have the following elemental composition as provided in Table 4.
In some examples, the alloys can have the following elemental composition as provided in Table 5.
In some examples, the alloys can have the following elemental composition as provided in Table 6.
In some examples, the alloys can have the following elemental composition as provided in Table 7.
In some examples, the alloys can have the following elemental composition as provided in Table 8.
In some examples, the alloys can have the following elemental composition as provided in Table 9.
In some examples, the alloys can have the following elemental composition as provided in Table 10.
In some examples, the disclosed alloy includes silicon (Si) in an amount from about 0.9% to about 1.4% (e.g., from about 0.95% to about 0.35%, from about 1.0% to about 1.30%, or from about 1.10% to about 1.30%) based on the total weight of the alloy. For example, the alloy can include about 0.90%, about 0.91%, about 0.92%, about 0.93%, about 0.94%, about 0.95%, about 0.96%, about 0.97%, about 0.98%, about 0.99%, about 1.00%, about 1.01%, about 1.02%, about 1.03%, about 1.04%, about 1.05%, about 1.06%, about 1.07%, about 1.08%, about 1.09%, about 1.10%, about 1.11%, about 1.12%, about 1.13%, about 1.14%, about 1.15%, about 1.16%, about 1.17%, about 1.18%, about 1.19%, about 1.20%, about 1.21%, about 1.22%, about 1.23%, about 1.24%, about 1.25%, about 1.26%, about 1.27%, about 1.28%, about 1.29%, about 1.30%, about 1.31%, about 1.32%, about 1.33%, about 1.34%, about 1.35%, about 1.36%, about 1.37%, about 1.38%, about 1.39% or about 1.40% Si. All percentages are expressed in wt. %. Among other things, Si content affects the melting temperature of an aluminum alloy. Increasing the content of Si reduces the melting point of the aluminum alloy. Accordingly, in order for the aluminum alloy fin stock to be brazeable, the Si content of the alloy should be sufficiently low so that the alloy does not melt during the brazing cycle. On the other hand, relatively high Si content in the alloy leads to the formation of AlMnSi dispersoids, resulting in beneficial dispersoid strengthening of the matrix and improved strength characteristics of the alloy. The Si content used in the disclosed fin stock alloy balances the above factors.
In some examples, the alloy also includes iron (Fe) in an amount from about 0.30% to about 0.60% (e.g., from about 0.35% to about 0.60%, from about 0.40% to about 0.60%, or from about 0.41% to about 0.47%) based on the total weight of the alloy. For example, the alloy can include about 0.30%, about 0.31%, about 0.32%, about 0.33%, about 0.34%, about 0.35%, about 0.36%, about 0.37%, about 0.38%, about 0.39%, about 0.40%, about 0.41%, about 0.42%, about 0.43%, about 0.44%, about 0.45%, about 0.46%, about 0.47%, about 0.48%, about 0.49%, about 0.50%, about 0.51%, about 0.52%, about 0.53%, about 0.54%, about 0.55%, about 0.56%, about 0.57%, about 0.58%, about 0.59% or about 0.60% Fe. All percentages are expressed in wt. %. In an aluminum alloy, Fe can be a part of intermetallic constituents which may contain Mn, Si, and other elements. It is often beneficial to control Fe content in an aluminum alloy to influence the content of coarse intermetallic constituents.
In some examples, the disclosed alloy includes copper (Cu) in an amount from about 0.2% to about 0.60% (e.g., from about 0.20% to about 0.40% or from about 0.40% to about 0.55%) based on the total weight of the alloy. For example, the alloy can include about 0.20%, about 0.21%, about 0.22%, about 0.23%, about 0.24%, about 0.25%, about 0.26%, about 0.27%, about 0.28%, about 0.29%, about 0.30%, about 0.31%, about 0.32%, about 0.33%, about 0.34%, about 0.35%, about 0.36%, about 0.37%, about 0.38%, about 0.39%, about 0.40%, about 0.41%, about 0.42%, about 0.43%, about 0.44%, about 0.45%, about 0.46%, about 0.47%, about 0.48%, about 0.49%, about 0.50%, about 0.51%, about 0.52%, about 0.53%, about 0.54%, about 0.55%, about 0.56%, about 0.57%, about 0.58%, about 0.59%, or about 0.60% Cu. All percentages are expressed in wt. %. Cu in solid solution increases strength of an aluminum alloy. Increasing Cu content may also lead to formation of Cu-containing AlMnCu dispersoids, which store Mn and dissolve during brazing, thus leading to a release of Mn into solid solution. This process results in improved post-braze strength. Relatively high Cu content of the fin stock alloys allows for cost reduction and an increase in recycling capacity.
In some examples, the alloy can include manganese (Mn) in an amount from about 1.0% to about 1.7% (e.g., from about 1.10% to about 1.65%, from about 1.15% to about 1.35%, or from about 1.2% to about 1.35%) based on the total weight of the alloy. For example, the alloy can include about 1.0%, about 1.01%, about 1.02%, about 1.03%, about 1.04%, about 1.05%, about 1.06%, about 1.07%, about 1.08%, about 1.09%, about 1.1%, about 1.11%, about 1.12%, about 1.13%, about 1.14%, about 1.15%, about 1.16%, about 1.17%, about 1.18%, about 1.19%, about 1.2%, about 1.21%, about 1.22%, about 1.23%, about 1.24%, about 1.25%, about 1.26%, about 1.27%, about 1.28%, about 1.29%, about 1.3%, about 1.31%, about 1.32%, about 1.33%, about 1.34%, about 1.35%, about 1.36%, about 1.37%, about 1.38%, about 1.39%, about 1.4%, about 1.41%, about 1.42%, about 1.43%, about 1.44%, about 1.45%, about 1.46%, about 1.47%, about 1.48%, about 1.49%, about 1.50%, about 1.51%, about 1.52%, about 1.53%, about 1.54%, about 1.55%, about 1.56%, about 1.57%, about 1.58%, about 1.59%, about 1.60%, about 1.61%, about 1.62%, about 1.63%, about 1.64%, about 1.65%, about 1.66%, about 1.67%, about 1.68%, about 1.69%, or about 1.7% Mn. All percentages are expressed in wt. %. Mn in solid solution increases the strength of an aluminum alloy and also moves corrosion potential towards a more cathodic state. (FeMn)—Al6 or Al15Mn3Si2 dispersoids increase the strength of an aluminum alloy by particle strengthening, when present in a fine and dense dispersion. Depending on the composition and solidification rate, Fe, Mn, Al, and Si combine during solidification to form various intermetallic constituents, i.e., particles within the microstructure, like Al15(FeMn)3Si2, Al5FeSi, or Al8FeMg3Si6, to name a few. A higher Mn content, particularly in combination with a higher Fe content, may lead to the formation of coarse Mn—Fe intermetallic constituents.
In some examples, the alloy includes zinc (Zn) in an amount from about 0.1% to about 3.0% (e.g., from about 0.5% to about 2.8%, from about 1.0% to about 2.5%, from about 1.5% to about 3.0%, from about 1.5% to about 2.75%, or from about 1.9% to about 2.6%) based on the total weight of the alloy. For example, the alloy can include about 0.1%, about 0.11%, about 0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about 0.17%, about 0.18%, about 0.19%, about 0.2%, about 0.21%, about 0.22%, about 0.23%, about 0.24%, about 0.25%, about 0.26%, about 0.27%, about 0.28%, about 0.29%, about 0.3%, about 0.31%, about 0.32%, about 0.33%, about 0.34%, about 0.35%, about 0.36%, about 0.37%, about 0.38%, about 0.39%, about 0.4%, about 0.41%, about 0.42%, about 0.43%, about 0.44%, about 0.45%, about 0.46%, about 0.47%, about 0.48%, about 0.49%, about 0.5%, about 0.51%, about 0.52%, about 0.53%, about 0.54%, about 0.55%, about 0.56%, about 0.57%, about 0.58%, about 0.59%, about 0.6%, about 0.61%, about 0.62%, about 0.63%, about 0.64%, about 0.65%, about 0.66%, about 0.67%, about 0.68%, about 0.69%, about 0.7%, about 0.71%, about 0.72%, about 0.73%, about 0.74%, about 0.75%, about 0.76%, about 0.77%, about 0.78%, about 0.79%, about 0.8%, about 0.81%, about 0.82%, about 0.83%, about 0.84%, about 0.85%, about 0.86%, about 0.87%, about 0.88%, about 0.89%, about 0.9%, about 0.91%, about 0.92%, about 0.93%, about 0.94%, about 0.95%, about 0.96%, about 0.97%, about 0.98%, about 0.99%, about 1.0%, about 1.01%, about 1.02%, about 1.03%, about 1.04%, about 1.05%, about 1.06%, about 1.07%, about 1.08%, about 1.09%, about 1.1%, about 1.11%, about 1.12%, about 1.13%, about 1.14%, about 1.15%, about 1.16%, about 1.17%, about 1.18%, about 1.19%, about 1.2%, about 1.21%, about 1.22%, about 1.23%, about 1.24%, about 1.25%, about 1.26%, about 1.27%, about 1.28%, about 1.29%, about 1.3%, about 1.31%, about 1.32%, about 1.33%, about 1.34%, about 1.35%, about 1.36%, about 1.37%, about 1.38%, about 1.39%, about 1.4%, about 1.41%, about 1.42%, about 1.43%, about 1.44%, about 1.45%, about 1.46%, about 1.47%, about 1.48%, about 1.49%, about 1.5%, about 1.51%, about 1.52%, about 1.53%, about 1.54%, about 1.55%, about 1.56%, about 1.57%, about 1.58%, about 1.59%, about 1.6%, about 1.61%, about 1.62%, about 1.63%, about 1.64%, about 1.65%, about 1.66%, about 1.67%, about 1.68%, about 1.69%, about 1.7%, about 1.71%, about 1.72%, about 1.73%, about 1.74%, about 1.75%, about 1.76%, about 1.77%, about 1.78%, about 1.79%, about 1.8%, about 1.81%, about 1.82%, about 1.83%, about 1.84%, about 1.85%, about 1.86%, about 1.87%, about 1.88%, about 1.89%, about 1.9%, about 1.91%, about 1.92%, about 1.93%, about 1.94%, about 1.95%, about 1.96%, about 1.97%, about 1.98%, about 1.99%, about 2.0%, about 2.01%, about 2.02%, about 2.03%, about 2.04%, about 2.05%, about 2.06%, about 2.07%, about 2.08%, about 2.09%, about 2.1%, about 2.11%, about 2.12%, about 2.13%, about 2.14%, about 2.15%, about 2.16%, about 2.17%, about 2.18%, about 2.19%, about 2.2%, about 2.21%, about 2.22%, about 2.23%, about 2.24%, about 2.25%, about 2.26%, about 2.27%, about 2.28%, about 2.29%, about 2.3%, about 2.31%, about 2.32%, about 2.33%, about 2.34%, about 2.35%, about 2.36%, about 2.37%, about 2.38%, about 2.39%, about 2.4%, about 2.41%, about 2.42%, about 2.43%, about 2.44%, about 2.45%, about 2.46%, about 2.47%, about 2.48%, about 2.49%, about 2.5%, about 2.51%, about 2.52%, about 2.53%, about 2.54%, about 2.55%, about 2.56%, about 2.57%, about 2.58%, about 2.59%, about 2.6%, about 2.61%, about 2.62%, about 2.63%, about 2.64%, about 2.65%, about 2.66%, about 2.67%, about 2.68%, about 2.69%, about 2.7%, about 2.71%, about 2.72%, about 2.73%, about 2.74%, about 2.75%, about 2.76%, about 2.77%, about 2.78%, about 2.79%, about 2.8%, about 2.81%, about 2.82%, about 2.83%, about 2.84%, about 2.85%, about 2.86%, about 2.87%, about 2.88%, about 2.89%, about 2.9%, about 2.91%, about 2.92%, about 2.93%, about 2.94%, about 2.95%, about 2.96%, about 2.97%, about 2.98%, about 2.99%, or about 3.0% Zn. All percentages are expressed in wt. %. Zn is typically added to aluminum alloys to move the corrosion potential towards the anodic end of the scale. In the disclosed fin stock aluminum alloy, relatively high Zn content of up to 3 wt. % compensates for the shift in corrosion potential due to increased Si and Cu content, thus resulting in more anodic corrosion potential. The more anodic corrosion potential allows the fins manufactured from the alloy to act sacrificially and protect heat exchanger tubes, thus improving the overall corrosion resistance of the heat exchanger.
In some examples, the alloy can include Mg in an amount from about 0.01% to about 0.25% (e.g., from about 0.05% to about 0.20% or from about 0.10% to about 0.20%) based on the total weight of the alloy. For example, the alloy can include about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about 0.06%, about 0.07%, about 0.08%, about 0.09%, about 0.1%, about 0.11%, about 0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about 0.17%, about 0.18%, about 0.19%, about 0.2%, about 0.21%, about 0.22%, about 0.23%, about 0.24%, or about 0.25% Mg. All percentages are expressed in wt. %. Mg contributes to the strength of the aluminum alloys described herein through solid solution strengthening.
In some examples, the ratio of Cu to Zn is from 2:1 to 1:15, e.g., from 1:1 to 1:10, or from 1:5 to 1:10. The ratio of Cu to Zn may be 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, or 1:15.
Aluminum alloys as described herein may include Titanium (Ti) in an amount up to about 0.10% (e.g., from 0 to about 0.05%, from about 0.001% to about 0.04%, or from about 0.01% to about 0.03%) based on the total weight of the alloy. For example, the alloy can include about 0.001%, about 0.002%, about 0.003%, about 0.004%, about 0.005%, about 0.006%, about 0.007%, about 0.008%, about 0.009%, about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about 0.06%, about 0.07%, about 0.08%, about 0.09%, or about 0.1% Ti. In some cases, Ti is not present in the alloy (i.e., 0 wt. %). All percentages are expressed in wt. %.
Optionally, the alloy compositions can further include other minor elements, sometimes referred to as impurities, in amounts of about 0.05% or below, 0.04% or below, 0.03% or below, 0.02% or below, or 0.01% or below each. These impurities may include, but are not limited to, Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, Sr, or combinations thereof. Accordingly, Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, or Sr may be present in an alloy in amounts of 0.05% or below, 0.04% or below, 0.03% or below, 0.02% or below, or 0.01% or below. In certain aspects, the sum of all impurities does not exceed 0.15% (e.g., 0.1%). All percentages are expressed in wt. %. In certain aspects, the remaining percentage of the alloy is aluminum.
In certain aspects, the disclosed alloy composition is a product of a disclosed method. Without intending to limit the disclosure, aluminum alloy properties are partially determined by the formation of microstructures during the alloy's preparation. In certain aspects, the method of preparation for an alloy composition may influence or even determine whether the alloy will have properties adequate for a desired application.
A process for producing aluminum alloy fin stock materials can employ direct chill (DC) casting an aluminum alloy into an ingot. Following DC casting, the process includes preheating the ingot for hot rolling. The preheating temperature and duration of hot rolling are finely controlled to low levels to preserve a large grain size and high strength after the finished fin stock is brazed. In some examples, prior to hot rolling, the ingots can be preheated to up to about 500° C., for example, to 450-480° C., in a furnace for up to about 12 hours at a suitable heating rate, for example 50° C./hr, followed by maintaining the temperature (“soak” or “soaking”) at about 450-500° C., for example, at about 470-480° C., for 5-7 hours. Following preheating and soaking, the ingots are hot rolled to 2-10 mm, e.g., 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm, which may be referred to as “exit gauge” after hot rolling.
A process for producing aluminum alloy fin stock materials next includes cold rolling steps to produce desired thickness (gauge) and other properties of the material. For example, following a hot rolling step, the hot rolled aluminum alloy is cold rolled to reduce the thickness of the material to 1-2 mm, for example, to 1 mm, thickness or gauge (initial cold rolling gauge) during an initial cold rolling step, which can include multiple cold rolling passes, followed by further cold rolling to 100-200 μm thickness or gauge (intermediate cold rolling gauge) during an intermediate cold rolling step, which can also involve multiple passes. Depending on the hot rolling gauge, desirable final thickness, and other properties discussed below, an aluminum alloy may require more or fewer cold rolling passes to achieve the desired gauge. The number of cold rolling passes is not limited and can be suitably adjusted, for example, depending on the desirable thickness of the final sheet and other properties of the material.
Following intermediate cold rolling, the process for producing aluminum alloy fin stock materials may include an inter-annealing step to produce desired properties of the aluminum alloy fin stock material. The term “inter-annealing” refers to a heat treatment applied between cold rolling steps. As described herein, inter-annealing is applied between the intermediate and final cold rolling steps. Inter-annealing involves heating the aluminum alloy to a temperature of from about 200° C. to about 400° C., for example, from about 225° C. to 400° C., from about 225° C. to about 375° C., from about 225° C. to about 350° C., from about 225° C. to about 325° C., from about 300° C. to about 375° C., from about 325° C. to about 350° C., from about 340° C. to about 360° C., from about 290° C. to about 360° C. or from about 345° C. to about 350° C. (“inter-annealing temperature”), and maintaining the inter-annealing temperature for 3-5 hours, for example, for about 4 hours, followed by cooling. The period of maintaining a temperature of about 200° C. to about 400° C. can also be referred to as “soak” or “soaking.” For heating and cooling the material before and after the soak, a constant rate of 40° C./hr to 50° C./hr, for example, 50° C./hr, can be applied. Inter-annealing conditions affect the structure and the properties of the aluminum alloy fin stock material in various ways. For example, higher inter-annealing temperatures can lead to lower post-braze strength. Accordingly, the inter-annealing conditions are selected within the ranges specified in this document to result in the desirable properties of the aluminum alloy fin stock material.
Following inter-annealing, final cold rolling is performed to achieve % cold work (% CW) during the final cold rolling step (which can comprise multiple cold rolling passes) of 20% to 45%, 25% to 40%, 20% to 40%, 20% to 35%, 25% to 35%, or 5% to 45%, wherein:
In some embodiments, the % CW is less than or equal to 35% while in some other embodiments, the % CW is greater than 35%. After the final cold rolling steps, the aluminum alloy fin stock material of the present invention possesses a thickness (gauge) of about 45-100 μm, 45-90 μm, 47-85 μm, or 50-83 μm.
The final cold rolling step affects the structure and properties of the aluminum alloy fin stock material. For example, as % CW increases, pre-braze strength (ultimate tensile strength (UTS), yield strength (YS), or both, measured in pre-brazed condition) of the aluminum material increases. Accordingly, the % CW employed is adjusted within the ranges specified in this document to achieve desirable properties of the aluminum alloy fin stock material.
The processes of producing aluminum alloy fin stock materials as disclosed herein can be performed in a manner to lead to an aluminum material having a desired temper. For example, the processes can be performed to provide an aluminum material that can be described as “strain-hardened,”“cold-worked,” and/or having or being in “H1X” temper (for example, H14 temper). In some examples, improved fin stock aluminum alloy material as described herein can be produced in H14, H16 or H18 tempers. It is to be understood that a particular range of properties is associated with the temper designation. It is also to be understood that the temper designation refers to the pre-braze properties of the material.
The aluminum alloy fin stock material disclosed herein possesses a number of advantageous properties, characteristics or parameters. These properties, separately or in various combinations, allow the aluminum alloy materials described in this document to be used in production of fins for heat exchangers. However, it is to be understood that the scope of the present invention is not limited to specific uses or applications, and the properties of the aluminum alloy fin stock materials can be advantageous for various other applications. Some of these properties are discussed below. Some other properties may not be specifically described, but may follow from the composition of and/or production processes employed for fabrication of the aluminum alloy fin stock material described herein.
Some embodiments of the aluminum alloy materials described herein are manufactured as sheets, for example, as sheets less than 4 mm thick, e.g., 45 to 100 μm thick. The aluminum alloy sheets can be produced in H1X temper (for example, H14 H16 or H18 temper). Aluminum alloy materials described herein can possess one or more of the following properties, in any combination: UTS of 210 MPa or more (in other words, at least 210 MPa) or 210-230 MPa, measured in pre-brazed condition; UTS of 150 MPa or more (in other words, at least 150 MPa) or 150-170 MPa, measured post-brazing; sag resistance of 25-33 mm measured post-brazing; thermal conductivity of 40-48, 43-47, or 44-45 IACS measured post-brazing; open circuit potential corrosion value (vs. Standard Calomel Electrode (SCE), also referred to as “corrosion potential”) of −740 mV or less (for example, −750 mV); and/or coarse post-braze grain microstructure of 80-400 μm. The parameters measured “after brazing” or “post-brazing,” also referred to as “post-braze,” are measured after a simulated brazing cycle, during which aluminum alloy samples are heated to a temperature of 595° C. to 610° C. and cooled to room temperature in a period of about 20 minutes. The parameters measured before brazing (“pre-brazing” or in “pre-brazed” condition), also referred to as “pre-braze” parameters, are measured before or without subjecting the material to any brazing cycle.
The disclosed aluminum alloy fin stock material have improved strength and conductivity and exhibit lower corrosion potential values. The disclosed aluminum alloy fin stock material is also capable of withstanding at least 20 days of Copper-Accelerated Salt Spray (CASS) Testing according to ASTM B368 (2014) without separating from a brazed joint. The CASS testing is generally conducted by forming a coupon of fin and tube, brazing to form a joint, and subjecting the brazed coupon to the testing. The above properties and advantages allow aluminum alloy fin stock material of the present invention to be advantageously employed in various uses and applications, discussed in more detail below.
The aluminum alloy fin stock materials described in this document can be used in various applications, for example, but not limited to, heat exchangers. In one example, the aluminum alloy fin stock material can be used in automotive heat exchangers such as radiators, condensers and evaporators, although they are not so limited. For example, the improved aluminum alloy fin stock material of can be used for manufacture of various devices employing heat exchangers and produced by brazing, such as devices employed in heating, ventilating, air conditioning, and refrigeration (HVAC&R). Uses and applications of the aluminum alloy fin stock materials described herein are included within the scope of the present invention, as are objects, forms, apparatuses and similar things fabricated with or comprising the aluminum alloys described herein. The processes for fabricating, producing or manufacturing such objects, forms, apparatuses and similar things are also included within the scope of the present invention.
Aluminum alloys described herein are suitable for fabrication or manufacturing processes that require the joining of metal surfaces by brazing. Brazing is a metal joining process in which filler metal is heated above a melting point and distributed between two or more close-fitting parts by capillary action. The uses of the aluminum alloys in brazing and the related processes and results, such as the objects fabricated according to the manufacturing process that involve brazing, are generally referred to as “brazing applications.” The parts of the heat exchangers described herein are joined by brazing during the manufacturing process. During brazing, the filler metal melts and becomes the filler metal that is available to flow by capillary action to points of contact between the components being brazed.
One exemplary object that can be fabricated using aluminum alloy fin stock materials described herein is a heat exchanger. Heat exchangers are produced by the assembly of parts comprising tubes, plates, fins, headers, and side supports to name a few. For example, a radiator is built from tubes, fins, headers and side supports. Except for the fins, which are typically bare, meaning not clad with an Al—Si alloy, all other parts of a heat exchanger are typically clad with a brazing cladding on one or two sides. Once assembled, a heat exchanger unit is secured by banding or such device to hold the unit together through fluxing and brazing. Brazing is commonly effected by passing the unit through a tunnel furnace. Brazing can also be performed by dipping in molten salt or in a batch or semi-batch process. The unit is heated to a brazing temperature between 590° C. and 610° C., soaked at an appropriate temperature until joints are created by capillary action and then cooled below the solidus of the filler metal. Heating rate is dependent on the furnace type and the size of the heat exchanger produced. Some other examples of the objects that can be fabricated using aluminum alloy fin stock materials described herein are an evaporator, a radiator, a heater or a condenser.
Embodiment 1 is an aluminum alloy, comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 0.1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 2 is an aluminum alloy of any preceding or subsequent embodiment, wherein the aluminum alloy comprises about 0.95-1.35 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 0.1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 3 is an aluminum alloy of any preceding or subsequent embodiment, wherein the aluminum alloy comprises about 0.9-1.4 wt. % Si, about 0.35-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 0.1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 4 is an aluminum alloy of any preceding or subsequent embodiment, wherein the aluminum alloy comprises about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.40 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 0.1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 5 is an aluminum alloy of any preceding or subsequent embodiment, wherein the aluminum alloy comprises about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.40-0.55 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 0.1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 6 is an aluminum alloy of any preceding or subsequent embodiment, wherein the aluminum alloy comprises about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.1-1.65 wt. % Mn, about 0.01-0.25% Mg, about 0.1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 7 is an aluminum alloy of any preceding or subsequent embodiment, wherein the aluminum alloy comprises about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.05-0.2% Mg, about 0.1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 8 is an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 1-3.0% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 9 is an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 1.5-2.75% Zn, up to about 0.10 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 10 is an aluminum alloy comprising about 0.9-1.4 wt. % Si, about 0.3-0.6 wt. % Fe, about 0.20-0.60 wt. % Cu, about 1.0-1.7 wt. % Mn, about 0.01-0.25% Mg, about 0.1-3.0% Zn, up to about 0.05 wt. % Ti, with remainder Al and impurities at ≤0.15 wt. %.
Embodiment 11 is an aluminum alloy according to any preceding or subsequent embodiment, wherein the alloy is produced by a process comprising: direct chill casting the aluminum alloy into an ingot; hot rolling the ingot after the direct chill casting; after the hot rolling, cold rolling the aluminum alloy to an intermediate thickness; after cold rolling, inter-annealing the aluminum alloy rolled to the intermediate thickness at 200-400° C.; and, after inter-annealing, cold rolling the aluminum alloy to achieve % cold work (% CW) of 20 to 40%, resulting in the sheet having a thickness of 45-100 μm, 45-90 μm, 47-85 μm, or 50-83 μm.
Embodiment 12 is an aluminum alloy of any preceding or subsequent embodiment, wherein the inter-annealing is at 250-360° C. or 290-360° C.
Embodiment 13 is an aluminum alloy according to any preceding or subsequent embodiment, wherein the inter-annealing time is 30 to 60 minutes.
Embodiment 14 is an aluminum alloy according to any preceding or subsequent embodiment, wherein % CW is 30 to 40%.
Embodiment 15 is an aluminum alloy according to any preceding or subsequent embodiment, wherein the aluminum alloy has ultimate tensile strength of one or both of: at least 200 MPa, measured in pre-brazed condition, or at least 150 MPa, measured post-brazing.
Embodiment 16 is an aluminum alloy according to any preceding or subsequent embodiment, wherein the aluminum alloy has corrosion potential of −740 mV or less, measured post-brazing.
Embodiment 17 is an aluminum alloy according to any preceding or subsequent embodiment, wherein the aluminum alloy has thermal conductivity of greater than 40% IACS, measured post-brazing.
Embodiment 18 is a heat exchanger comprising the aluminum alloy according to any preceding or subsequent embodiment.
Embodiment 19 is a process of making a heat exchanger comprising joining by brazing at least one first aluminum alloy form fabricated from the aluminum alloy of any preceding or subsequent embodiment with a second aluminum alloy form, comprising: assembling and securing the two or more aluminum forms together; and, heating the two or more aluminum forms to a brazing temperature until joints are created among the two or more aluminum forms by capillary action.
Embodiment 20 is the process of embodiment 19, wherein the first aluminum alloy is capable of withstanding at least 20 days of CASS testing in accordance with ASTM B368 (2014) without detaching from the joint.
Embodiment 21 is the use of an aluminum alloy according to any preceding or subsequent embodiment fabrication of heat exchanger fins.
The following examples will serve to further illustrate the present invention without, at the same time, however, constituting any limitation thereof. On the contrary, it is to be clearly understood that resort may be had to various embodiments, modifications and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the invention.
Nine aluminum alloy samples were prepared with the compositions shown in Table 11 below. Each sample comprised up to 0.15 wt. % impurities, with the remainder being Al. Each sample was prepared by direct chill casting the aluminum alloy into an ingot and then hot rolling. The ingots produced by DC casting were preheated for hot rolling. The ingots were then hot rolled to an exit gauge and then cold rolled to an initial cold rolling gauge. The ingots were then further cold rolled to an intermediate cold rolling gauge. Next, the ingots were inter-annealed. Following inter-annealing, final cold rolling was performed to achieve a % CW of 20 to 40%, resulting in each sample having a thickness from 45 μm to 100 μm.
The mechanical properties, conductivity, corrosion potential, and solidus temperature were then tested for each of the samples in Table 11 in pre-brazing condition, after standard brazing, and after a fast-braze. During standard brazing, the samples were heated to a temperature of 605° C. and cooled to room temperature for a period of about 45 minutes, to simulate the temperature time profile of a commercial brazing process. Fast-brazing was conducted at much faster heating and cooling rate compared to a standard braze cycle. The material was heated to a temperature between 600 and 605° C. and cooled to room temperature in a period of about 20 minutes. Yield strength, ultimate tensile strength, and uniform elongation were measured for all samples. The testing was performed according to ASTM B557 standards. Three samples were tested from each alloy variant and the average values were reported in both pre-braze and post-braze conditions. The electrical conductivity was reported as % IACS (International Annealed Copper Standard, which assumes pure copper conductivity for 100%). The results for yield strength, ultimate tensile strength, and elongation are shown below in Table 12. The solidus temperature is also reported in Table 12. The thermal conductivity and corrosion potential measured post-brazing are reported in Table 13. Experimental alloys had a minimum post-braze yield strength of 55 MPa and greater ultimate tensile strength than alloy of Comp. 1.
The open circuit potential corrosion value vs. Standard Calomel Electrode (SCE) of −764 mV for Comp. 1 as compared to −735 mV for alloy H indicated that fin variants will act sacrificially to any tube alloy if the difference in corrosion potential is maintained at approximately from 30 to 150 mV between tube and fin alloy.
Each of samples Comp. 1 and A-H were photographed using an optical microscope. Microstructure characterization was carried out to investigate dispersoids, and intermetallic sizes and distribution, as well as the pre and post-braze grain structure. The microstructure was examined by etching the samples in 2.5% HBF4 for 60 seconds followed by de-smutting in HNO3.
Alloy samples C, E, G and H were prepared as in Example 1, except that the % CW was varied when inter-annealing at 350° C. (pre braze). The results are shown below in Table 14 and in
Alloy samples C, E, G and H were prepared as in Example 1, except that the % CW was varied when inter-annealing at 350° C. (post braze). The results are shown below in Table 15 and in
Alloy samples C, E, G and H were prepared as in Example 1, except that the inter-annealing temperature at >35% CW (pre braze) was varied. The results are shown below in Table 16 and in
Alloy samples C, E, G and H were prepared as in Example 1, except that the effect of inter-annealing temperature at >35% CW (post braze) was varied. The results are shown below in Table 17 and in
Alloy samples C, E, G, and H were then subjected to either standard cycle or fast cycle brazing and photographed as described above. For samples inter-annealed at 250° C. and subjected to a standard cycle braze, the plain view grain size post braze is shown in
For samples inter-annealed at 250° C. and subjected to a fast cycle braze, the plain view grain size post braze is shown in
The comparative sample and samples C, E, G and H were prepared as in Example 1 and subjected to brazing. A coupon of fin and tube was joined for each sample and each coupon was then subjected to CASS Testing according to ASTM B368 (2014). The CASS test was conducted for a period of 40 days. Corrosion activity was characterized by examining the braze joint and the fin was at 10 days, 20 days and 40 days. At the end of the 40 days period, each fin acted sacrificially, thus protecting the tube.
The results shown for Examples 2-5 confirmed that some elements, such as Mg and Cu, play a role in contributing to the yield strength and ultimate tensile strength of the alloys. Increased Mg and Cu, however, are typically expected to also lead to increased corrosion, as compared to samples with lower Mg and Cu amounts. The images shown in
All patents, patent applications, publications, and abstracts cited above are incorporated herein by reference in their entirety. Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention as defined in the following claims.
This application claims priority to U.S. Provisional Application No. 62/727,806, filed on Sep. 6, 2018, the entirety of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62727806 | Sep 2018 | US |
