EP3847289B1

EP3847289B1 - Aluminum alloy for heat exchanger fins

Info

Publication number: EP3847289B1
Application number: EP19769682.6A
Authority: EP
Inventors: Jyothi Kadali; Kyle DASCH; Julia L. WOODS
Original assignee: Novelis Inc Canada
Current assignee: Novelis Inc Canada
Priority date: 2018-09-06
Filing date: 2019-09-03
Publication date: 2024-05-01
Anticipated expiration: 2039-09-03
Also published as: JP2021535285A; CN112654726A; WO2020051129A1; US20200080172A1; EP3847289A1; JP2023061968A

Description

PRIORITY CLAIM

This application claims priority to U.S. Provisional Application No. 62/727,806, filed on September 6, 2018 .

FIELD

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.

BACKGROUND

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.
WO 2016/022457 A1 relates to an aluminum alloy fin stock material comprising about 0.9-1.2 wt.% Si, 0.3-0.5 wt.% Fe, 0.20-0.40 wt.% Cu, 1.0-1.5 wt.% Mn, 0-0.1 wt.% Mg and 0.0-3.0 wt.% Zn, with remainder Al and impurities at ≤ 0.15 wt.%.
EP 1 323 839 A1 relates to an aluminum brazing alloy, ideally suitable as fin stock material, having the composition in weight %: Si 0.7-1.2, Mn 0.7-1.2, Mg < 0.2, Fe up to 0.8, Zn up to 3.0, Ni up to 1.5, Cu up to 0.5, optionally one or more selected from the group comprising Ti up to 0.20, In up to 0.20, Zr up to 0.25, V up to 0.25, Sn up to 0.25, Cr up to 0.25, impurities up to 0.05 each, up to 0.15 in total, Al balance.

SUMMARY

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. Claim 1 of the present invention relates to an aluminum alloy comprising 0.9-1.4 wt.% Si, 0.3-0.6 wt.% Fe, 0.40-0.55 wt.% Cu, 1.0-1.7 wt.% Mn, 0.10-0.25% Mg and 1.9-2.6 wt.% Zn, up to 0.10 wt.% Ti, with remainder Al and impurities each in 0-0.05 wt.% and in total at ≤0.15 wt.%, wherein optionally the impurities include Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, Sr, or combinations thereof. 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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-I show photographs of the particle structure for aluminum alloy samples prepared according to the present disclosure prior to brazing.
FIGS. 2A-I show photographs of the particle structure for aluminum alloy samples prepared according to the present disclosure after standard brazing.
FIGS. 3A-I show photographs of the particle structure for aluminum alloy samples prepared according to the present disclosure after fast brazing.
FIGS. 4A-I show photographs of the grain size for aluminum alloy samples prepared according to the present disclosure after standard brazing.
FIGS. 5A-I show photographs of the grain size for aluminum alloy samples prepared according to the present disclosure after fast brazing.
FIGS. 6A-I show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure prior to brazing.
FIGS. 7A-I show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure after standard brazing.
FIGS. 8A-I show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure after fast brazing.
FIGS. 9A-D show the effect of % cold work and inter-annealing on different properties of aluminum alloy samples prepared according to the present disclosure.
FIGS. 10A-D show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure and subjected to standard brazing.
FIGS. 11A-D show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure and subjected to standard brazing.
FIGS. 12A-D show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure and subjected to fast brazing.
FIGS. 13A-D show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure and subjected to fast brazing.
FIGS. 14A-E show photographs of corrosion test results for coupons comprising aluminum alloy samples prepared according to the present disclosure.

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.

Definitions and Descriptions:

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.
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 O 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. 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.

Alloy Compositions

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.
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.

The alloys described herein can have the following elemental composition as provided in Table 1 (not according to the invention).

Table 1

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.2 - 0.6
Mn	1.0 - 1.7
Zn	0.1 - 3.0
Mg	0.01 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys described herein can have the following elemental composition as provided in Table 2 (not according to the invention).

Table 2

Element	Weight Percentage (wt. %)
Si	0.95 - 1.35
Fe	0.3 - 0.6
Cu	0.2 - 0.6
Mn	1.0 - 1.7
Zn	0.1 - 3.0
Mg	0.01 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys described herein can have the following elemental composition as provided in Table 3 (not according to the invention).

Table 3

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.35 - 0.6
Cu	0.2 - 0.6
Mn	1.0 - 1.7
Zn	0.1 - 3.0
Mg	0.01 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys described herein can have the following elemental composition as provided in Table 4 (not according to the invention).

Table 4

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.2 - 0.4
Mn	1.0 - 1.7
Zn	0.1 - 3.0
Mg	0.01 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys according to the invention have the following elemental composition as provided in Table 5.

Table 5

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.40 - 0.55
Mn	1.0 - 1.7
Zn	1.9 - 2.6
Mg	0.10 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys can have the following elemental composition as provided in Table 6 (not according to the invention).

Table 6

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.2 - 0.6
Mn	1.1 - 1.65
Zn	0.1 - 3.0
Mg	0.01 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys described herein can have the following elemental composition as provided in Table 7 (not according to the invention).

Table 7

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.2 - 0.6
Mn	1.0 - 1.7
Zn	0.1 - 3.0
Mg	0.05 - 0.2
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys described herein can have the following elemental composition as provided in Table 8 (not according to the invention).

Table 8

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.2 - 0.6
Mn	1.0 - 1.7
Zn	1 - 3.0
Mg	0.01 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys described herein can have the following elemental composition as provided in Table 9 (not according to the invention).

Table 9

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.2 - 0.6
Mn	1.0 - 1.7
Zn	1.5 - 2.75
Mg	0.01 - 0.25
Ti	0.00 - 0.10
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The alloys described herein can have the following elemental composition as provided in Table 10 (not according to the invention).

Table 10

Element	Weight Percentage (wt. %)
Si	0.9 - 1.4
Fe	0.3 - 0.6
Cu	0.2 - 0.6
Mn	1.0 - 1.7
Zn	0.1 - 3.0
Mg	0.05 - 0.2
Ti	0.00 - 0.05
Others	0 - 0.05 (each)
Others	0 - 0.15 (total)
Al	Remainder

The disclosed alloy includes silicon (Si) in an amount from 0.9 % to 1.4 % (e.g., from 0.95 % to 0.35 %, from 1.0 % to 1.30 %, or from 1.10 % to 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 0.30 % to 0.60 % (e.g., from 0.35 % to 0.60 %, from 0.40 % to 0.60 %, or from 0.41 % to 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.
The disclosed alloy includes copper (Cu) in an amount from 0.40 % to 0.55 % based on the total weight of the alloy. For example, the alloy can include 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 %, or about 0.55 % 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.
The alloy includes manganese (Mn) in an amount from 1.0 % to 1.7 % (e.g., from 1.10 % to 1.65 %, from 1.15 % to 1.35 %, or from 1.2 % to 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 Al₈FeMg₃Si_6,, 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.
The alloy includes zinc (Zn) in an amount from 1.9 % to 2.6 % based on the total weight of the alloy. For example, the alloy can include 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 %, or about 2.6 % 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 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.
The alloy includes Mg in an amount from 0.10 % to 0.25 % (e.g., from 0.10 % to 0.20 %) 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 %, 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 0.10 % (e.g., from 0 to 0.05 %, from 0.001 % to 0.04 %, or from 0.01 % to 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. %.
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. The sum of all impurities does not exceed 0.15 % (e.g., 0.1 %). All percentages are expressed in wt. %. The remaining percentage of the alloy is aluminum.

Processes for Making Aluminum Alloy Fin Stock Material

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 employs 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 includes 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 200 °C to 400 °C, for example, from 225 °C to 400 °C, from 225 °C to 375 °C, from 225 °C to 350 °C, from 225 °C to 325 °C, from 300 °C to 375 °C, from 325 °C to 350 °C, from 340 °C to 360 °C, from 290 °C to 360 °C or from 345 °C to 350 °C ("inter-annealing temperature"), and maintaining the inter-annealing temperature for 3-5 hours, for example, for 4 hours, followed by cooling. The period of maintaining a temperature of 200 °C to 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: $% CW = \frac{thickness before cold rolling - thickness after cold rolling}{thickness before cold rolling} * 100 % .$
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 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.

Properties

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 150-170MPa, 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 80-400µm. 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 j oint. 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.

Uses and Applications

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.
The following examples will serve to further illustrate the present invention without, at the same time, however, constituting any limitation thereof.

Example 1

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.

Table 11

	Si (wt. %)	Fe (wt. %)	Cu (wt. %)	Mn (wt. %)	Mg (wt. %)	Zn (wt. %)
Comparative 1	1.0-1.2	0.4-0.45	0.27-0.3	1.31-1.5	0.05-0.1	2.0-2.1
Sample A*	1.0-1.2	0.4-0.47	0.2-0.4	1.2-1.4	0.1-0.2	1.9-2.1
Sample B*	1.0-1.2	0.4-0.47	0.3-0.5	1.2-1.4	0.05-0.2	1.9-2.1
Sample C*	1.0-1.2	0.4-0.47	0.3-0.5	1.2-1.4	0.1-0.2	1.9-2.1
Sample D*	1.0-1.2	0.4-0.47	0.3-0.5	1.2-1.4	0.05-0.2	2.3-2.6
Sample E*	1.15-1.3	0.4-0.47	0.2-0.4	1.2-1.4	0.05-0.25	2.1-2.3
Sample F*	1.15-1.3	0.4-0.47	0.3-0.5	1.4-1.6	0.1-0.25	1.9-2.1
Sample G*	1.15-1.3	0.4-0.47	0.3-0.5	1.5-1.7	0.1-0.25	1.9-2.1
Sample H	1.15-1.3	0.4-0.47	0.4-0.5	1.5-1.7	0.1-0.25	1.9-2.1

* not according to the invention

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.

Table 12

Sample	Yield Strength (MPa)			Ultimate Tensile Strength (MPa)			Elongation (%)			Solidus Temp. (°C)
	Pre-Braze	Std. Braze	Fast Braze	Pre-Braze	Std. Braze	Fast Braze	Pre-Braze	Std. Braze	Fast Braze
Comp. 1	204	54	57	213	149	157	2.7	8.4	9.5	622
A	203	53	57	209	148	158	1.7	9.7	9.6	622
B	201	52	56	207	151	150	1.7	10.8	8.5	624
C	206	57	60	214	158	162	1.9	9.4	9.7	619
D	169	57	55	210	151	157	1.4	7.9	10.4	618
E	201	55	56	209	152	161	1.8	7.8	9.6	623
F	206	59	59	212	157	151	1.5	7.6	6.5	621
G	212	59	65	214	164	173	0.8	8.7	10.2	616
H	226	59	60	229	169	168	0.8	11.1	10.4	618

Table 13

Sample	Thermal Conductivity (% IACS)			Corrosion Potential (mv)
	Pre-Braze	Std. Braze	Fast Braze	Std. Braze	Fast Braze
Comp. 1	48	38	41	-764	-764
A	48	41	40	-764	-765
B	47	38	41	-744	-748
C	48	38	40	-754	-746
D	45	38	40	-751	-745
E	45	37	40	-767	-758
F	47	34	39	-742	-742
G	45	37	39	-736	-736
H	42	39	39	-735	-735

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. FIGS. 1A-I show pre-braze microstructure, FIGS. 2A-I show the microstructure after standard brazing and FIGS. 3A-I show the microstructure after fast cycle brazing. Barker's etch was used to reveal the grain structure. FIGS. 4A-I show the plain view grain structure after standard brazing and FIGS. 5A-I show the plain view grain structure after fast cycle brazing. Each of samples Comp. 1 and A-H were also photographed to show the cross section grain structure pre-brazing (FIGS. 6A-I), after standard brazing (FIGS. 7A-I), and after fast brazing (FIGS. 8A-I). For each set of photomicrographs, the A figure corresponds to Comp. 1, the B figure corresponds to Sample A, the C figure corresponds to Sample B, and so forth.

Example 2

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 FIG. 9A. As shown below and in FIG. 9A, the yield strength was improved when greater than 35% CW was performed as compared to when 35% or less CW was performed. Except for Sample E, the ultimate tensile strength also increased when greater than 35% CW as compared to when less than 35% CW was performed. Except for Sample H, % elongation was decreased when greater than 35% CW was performed as compared to when less than 35% CW was performed.

Table 14

Sample	≤ 35% CW			>35% CW
	Yield Strength (MPa)	Ultimate Tensile Strength (MPa)	Elongation (%)	Yield Strength (MPa)	Ultimate Tensile Strength (MPa)	Elongation (%)
C	206	214	1.9	213	221	1.8
E	201	209	1.8	204	209	1.3
G	212	214	0.8	220	220	0.6
H	226	229	0.8	228	234	1.4

Example 3

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 FIG. 9B. As shown below and in FIG. 9B, except for Sample G, the yield strength was improved when greater than 35% CW was performed as compared to when 35% or less CW was performed. Except for Sample H, the ultimate tensile strength decreased when greater than 35% CW as compared to when less than 35% CW was performed. Generally, % elongation stayed approximately the same or decreased when greater than 35% CW was performed as compared to when when 35% or less CW was performed.

Table 15

Sample	≤ 35% CW			>35% CW
	Yield Strength (MPa)	Ultimate Tensile Strength (MPa)	Elongation (%)	Yield Strength (MPa)	Ultimate Tensile Strength (MPa)	Elongation (%)
C	60	161	9.7	62	154	6.1
E	56	161	9.6	58	159	9.5
G	65	173	10.2	63	166	10.3
H	60	168	10.4	65	171	9.8

Example 4

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 FIG. 9C. As shown below and in FIG. 9C, at a greater inter-annealing temperature, the yield strength, ultimate tensile strength, and % elongation all decreased.

Table 16

Sample	Inter-anneal at 250 °C			Inter-anneal at 350 °C
	Yield Strength (MPa)	Ultimate Tensile Strength (Mpa)	Elongation (%)	Yield Strength (Mpa)	Ultimate Tensile Strength (Mpa)	Elongation (%)
C	240	266	4.3	213	221	1.8
E	218	237	1.8	204	209	1.3
G	236	241	0.7	220	220	0.6
H	244	271	3.3	228	234	1.4

Example 5

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 FIG. 9D. As shown below and in FIG. 9D, at a greater inter-annealing temperature, the yield strength decreased, the elongation increased, and the ultimate tensile strength either stayed the same (for sample C) or decreased (samples E, G and H).

Table 17

Sample	Inter-anneal at 250 °C			Inter-anneal at 350 °C
	Yield Strength (MPa)	Ultimate Tensile Strength (Mpa)	Elongation (%)	Yield Strength (Mpa)	Ultimate Tensile Strength (Mpa)	Elongation (%)
C	68	154	4.9	62	154	6.1
E	62	164	9.2	58	159	9.5
G	66	169	9.2	63	166	10.3
H	72	176	7.7	65	171	9.8

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 FIGS. 10A-D, with FIG. 10A corresponding to sample C, FIG. 10B corresponding to sample E, FIG. 10C corresponding to sample G, and FIG. 10D corresponding to sample H. Similarly, for samples inter-annealed at 350 °C and subjected to a standard cycle braze, the plain view grain size post braze is shown in FIGS. 11A-D, with FIG. 11A corresponding to sample C, FIG. 11B corresponding to sample E, FIG. 11C corresponding to sample G, and FIG. 11D corresponding to sample H.
For samples inter-annealed at 250°C and subjected to a fast cycle braze, the plain view grain size post braze is shown in FIGS. 12A-D, with FIG. 12A corresponding to sample C, FIG. 12B corresponding to sample E, FIG. 12C corresponding to sample G, and FIG. 12D corresponding to sample H. Similarly, for samples inter-annealed at 350 °C and subjected to a fast cycle braze, the plain view grain size post braze is shown in FIGS. 13A-D, with FIG. 13A corresponding to sample C, FIG. 13B corresponding to sample E, FIG. 13C corresponding to sample G, and FIG. 13D corresponding to sample H. Based on the grain structure images, it is observed that increasing the %CW to >35 led to finer post braze grain size due to an increase in the driving force for recrystallization but this effect does not seem to have negative impact on sag resistance. Likewise, reducing the inter-anneal temperature from 350°C to 250°C in combination with lower %CW resulted in coarser post braze grain size. A combination of inter-anneal temperature and % CW was carefully selected based on desirable properties needed. For example a different combination of IA and %CW may needed to achieve fin crush resistance and or coarser grain size.

Example 6

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 FIGS. 14A-E are metallographic cross sections taken at 100x magnification. Surprisingly and unexpectedly, as shown in FIGS. 14A-E, the samples with an increased amount of Mg and Cu did not have increased corrosion, as compared to samples with lower Mg and Cu amounts. Accordingly, each of samples C, E, G and H performed similarly to the comparative sample in terms of corrosion but had other superior properties.
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 scope of the invention as defined in the following claims.

Claims

An aluminum alloy, comprising 0.9-1.4 wt.% Si, 0.3-0.6 wt.% Fe, 0.40-0.55 wt.% Cu, 1.0-1.7 wt.% Mn, 0.10-0.25 wt.% Mg, 1.9-2.6 wt.% Zn, up to 0.10 wt. % Ti, with remainder Al and impurities each in 0-0.05 wt.% and in total at ≤0.15 wt.%, wherein optionally the impurities include Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, Sr, or combinations thereof.
A method for producing the aluminum alloy of claim 1, wherein the method comprises:
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.
The method of claim 2, wherein the inter-annealing is at 250-360 °C or 290-360 °C;
and/or
wherein the inter-annealing time is 30 to 60 minutes; and/or

wherein %CW is from 30 to 40%.
A heat exchanger comprising the aluminum alloy of claim 1.
A process of making a heat exchanger comprising joining by brazing at least one first aluminum alloy form fabricated from the aluminum alloy of claim 1 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.
The process of claim 5, 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.
Use of the aluminum alloy of claim 1 for fabrication of heat exchanger fins.