WO2006039303A1

WO2006039303A1 - Aluminum composite

Info

Publication number: WO2006039303A1
Application number: PCT/US2005/034706
Authority: WO
Inventors: Zayna Connor; Scott H. Goodrich; Terri J. Burdoff; Timothy S. Jackson
Original assignee: Pechiney Rolled Products
Priority date: 2004-10-01
Filing date: 2005-09-28
Publication date: 2006-04-13
Also published as: WO2006039303B1

Abstract

The present invention provides composites of aluminum alloys having a braze clad and an inner liner. The composites have improved strength and corrosion resistance. The composites can be used for heat exchangers, evaporator tubes and other uses.

Description

ALUMINUM COMPOSITE

CROSS REFERENCE TO RELATED APPLICATIONS

The instant application claims priority to US Provisional Application No. 60/614/496 filed October 1, 2004, US Provisional Application No. 60/617,666 filed October 13, 2004 and US Provisional Application No. 60/627,085 filed November 12, 2004, the contents of each of which are incorporated herein by reference in their entirety.

Field of the Invention

The invention is directed to a composite of at least two aluminum alloys. The aluminum composite can be used for material applications such as use in heat exchangers or evaporator tubes.

BACKGROUND OF THE LTSfVENTION

Aluminum brazing sheet typically includes a core alloy of 3xxx and a lower melting braze clad of 4xxx series. 3xxx and 4xxx are designations set forth by The Aluminum Association. For 3xxx series aluniinunα alloys solid solution strengthening is one method of enhancing as-brazed strength.

Age hardening in 3005 based brazing sheets was demonstrated in earlier work. (See for example, N. D. A. Kooij, J. A. H. Sontgerath, A. Burger, K. Vieregge, A. Haszler, "New High Strength Alloys for Brazing v^ith Long Life Corrosion Properties", VTMS Conf. Proc, Indianapolis, Ind. 971882 (1997); N. D. A. Kooij, J. A. H. Sontgerath, A. Burger, K. Vieregge, A. Haszler, "The Development of Two High Strength Aluminum Brazing Sheet Alloys with Long Life Corrosion Properties", Alumitech Conf. Proc, Atlanta, Ga. (1997) p. 185-190; WO 99/55925 from Hoogovens Aluminium Walzprodukte "Aluminium Alloy for Use in a Brazed Assembly"; and H. Scott Goodrich and G. S. Murty, "Age hardening effects in 3xxx series brazing sheet core alloys", VTMS 4 Conf. PTOC, I Mech E 1999, London, p. 483. One mechanism of age hardening involves (i) diffusion of silicon from the braze clad into the core alloy, (ii) retention of silicon and magnesium in solution during cooling from the braze cycle, and (iii) then the precipitation OfMg₂Si during subsequent vehicle operation or post-braze aging treatment. However, 3xxx alloys are generally not heat treatable, and the primary strengthening mechanism is by solid solution strengthening.

In Goodrich et al., "Age hardening effects in 3xxx series brazing sheet core alloys", VTMS 4 Conf. Proc, I Mech E 1999, London, p.483, the aging response of different brazing sheets was monitored through room temperature tensile tests performed immediately after brazing and after aging for various times at 104° C, 150° C, 175° C and 200° C. Because the actual heat exchanger operating temperature is very often higher than room temperature, the material properties at elevated temperatures are of considerable interest. This especially applies to charge air coolers which are used in turbocharged engines and in diesel engines to cool tlie intake air compressed by the turbocharger prior to its injection into the cylinder chamber.

Charge air coolers are exposed to extreme temperature fluctuations and elevations in use, and thus, provides challenges in materials design. The materials must be able to exhibit sufficient strength after long-term exposure to temperatures greater than about 170° C. Standard 3xxx series alloy, e.g., 3003 allots have been used in the past in some heat exchanger applications since they are easily formed into sheet, fins and tubes. However, they have relatively low strength and generally cannot be used in high temperature applications. Some manufacturers have turned to copper and brass charge air coolers, however, these materials are much heavier and costlier than aluminum. There remains an increasing demand on aluminum alloy manufacturers to obtain a material that has good formability and acceptable strength over the complete temperature profile that is required for operating a charge air cooler.

U.S. Patent No. 6,756,133, describes a core alloy for an aluminum brazing sheet that includes from 0.4 wt% to 0.7 wt%. The core alloy is then brazed with a cladding that includes typically silicon. During brazing a Mg₂Si precipitate is formed by virtue of the Si from the clad migrating to the Mg of the core. The formation of these precipitates often have a negative impact on the strength of the as-brazed sheet as well as relatively poor stability if exposed to high temperatures, e.g., over 177° C, over an extended period, e.g., from 10 to 2500 hours. U.S. Patent No. 6,403,232 describes aluminum brazing sheet that restricts Mg content in the core alloy to less than 0.3 wt% and Fe to not more than 0.2 wt%. The core alloy has additional compositional limitations for Cu, Si and Mn. The brazing sheet includes an inner liner alloy on a surface of the core alloy. The inner liner alloy comprises less than 0.2 wt% Si and from 2.0 wt% to 3.5 wt% Mg.

Post-braze strength enhancement of braze sheet for folded tube applications also has important commercial applications for heat exchangers, e.g., car and truck radiators. In general, the folded tube material includes a modified 3xxx core, and a modified 7xxx inner liner, with a post-braze tensile strength of ~140 MPa. However, materials with a tensile strength of about 170 MPa or more would provide considerable design advantages.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Aluminum brazing sheet is a composite structure and typically includes a core alloy with an inner liner alloy on one side of the core alloy. Aluminum brazing sheet can also include brazing clad on an opposite side of the core alloy.

The invention is related to an aluminum composite comprising a 3xxx aluminum core alloy or an element alloy modification thereof. The 3xxx aluminum core alloy or the element alloy modification thereof comprises from 0.05 wt% to 0.4 wt% Mg. In contact with the aluminum core alloy is a 7xxx inner liner alloy or an element alloy modification thereof. The 7xxx liner alloy or the element alloy modification thereof comprises from 0.002 wt% to 1.5 wt% Mg.

The term "3xxx" alloy and the term "7xxx" alloy are known to those of ordinary skill in the aluminum art, and have a defined alloying element compositional range recognized by "The Aluminum Association". A 3xxx aluminum alloy will have a compositional range of at least the following alloying elements: less than 1.8 wt% Si; less than 1.0 wt% Fe; less than 0.9 wt% Cu; 0.05 wt% to 1.8 wt% Mn; and less than 0.35 wt% Ti. A 7xxx aluminum alloy will have a compositional range of at least the following alloying elements: less than 0.5 wt% Si; less than 1.4 wt% Fe; less than 2.6 wt% Cu; less than 0.8 wt% Mn; and less than 0.2 wt% Ti. Limiting the proportion of magnesium in the aluminum core alloy to within the compositional range of from 0.05 wt% to 0.4 wt% is believed to limit the degree OfMg₂Si that forms during brazing. In particular embodiments, the amount of Mg in the aluminum core alloy is from 0.05 wt% to 0.13 wt%, from 0.13 wt% to 0.16 wt%, from 0.16 wt% to 0.19 wt%, from 0.19 wt% to 0.2.3 wt%, from 0.23 wt% to 0.26 wt%, from 0.26 wt% to 0.29 wt%, from 0.29 wt% to 0.32 wt%, from 0.32 wt% to 0.36 wt%, from 0.36 wt% to 0.4 wt%.

In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.2 wt% to 0.35 wt% Mg. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.05 wt% Mg to less than 0.02 wt% Mg. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.1 wt% to 0.2 wt% Cr.

The aluminum core alloys can also contain one or more elements selected from Cr and Zr. These elements along with aluminum and silicon precipitate during homogenization to form small particles (e.g., from 0.05-0.5 μm in diameter). The formation of such precipitates is well known in the art.

IfZr is included in the alloy, the Zr is present from 0.1 wt% to 0.3 wt%, or from 0.13 wt% to 0.27 wt%.

If Cr is included in the alloy, the Cr is present is from 0.1 wt% to 0.3 wt%, or from 0.1 wt% to 0.2 wt%.

In one embodiment, both Zr and Cr are present in the core alloy. In this regard, the inclusion of both Zr and Cr elements is believed to provide a synergistic effect in terms of the increase in tensile strength and/or yield strength.

The composite aluminum alloy can be used in heat exchanger applications as well as evaporator tubes, and is formed by laminating an inner liner alloy on one surface of a core alloy, and optionally, a brazing clad alloy on the opposite surface of the core alloy. The alloy compositions for each of the alloy materials is described in greater detail below.

1. Core Alloy Beginning from 3xxx series alloy or an elemental modification thereof, one or more alloying elements can be present in the core alloy as follows.

Mg: Less Than 0.4 wt %. Mg is an effective element for improving the strength of the core alloy. IfMg is present at 0.4 wt % or greater, the brazing property of the aluminum composite is diminished. This is particularly true if the Nocolok Flux Brazing method is used to form the aluminum composite. In many of the core alloys, the Mg content is 0.3 wt % or less.

In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.2 wt % to 0.3 wt % Mg. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.05 wt % to 0.2 wt %

Mg.

Cu: Greater Than 0.2 wt % and Less Than 1.0 wt %. Cu is typically used to improve the strength of the core alloy. If the Cu content is greater than 1.0 wt %, the workability of the alloy is diminished. If the Cu content is less than 0.2 wt %, there is little, if any, improvement in the strength of the core alloy. In one embodiment, the Cu content is from 0.3 wt % to 0.7 wt%.

Si: Less Than 1.3 wt %. Si is typically used to improve the strength of the core alloy. If the Si content is greater than 1.3 wt %, the workability of the alloy is diminished. In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.05 wt% to 0.5 wt % Si. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.05 wt % to 0.2 wt % Si.

Mn: From 0.5 to 1.7 wt %. Mn is typically used to enhance the corrosion resistance and the strength of the core material. If the Mn content is less than 0.5 wt %, there is little, if any, improvement in the strength of the core alloy. If the Mn content is greater than 1.7 wt %, castability of the alloy is diminished. In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.8 wt% to 1.4 wt % Mn. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 1.2 wt % to 1.7 wt % Mn. Fe: Not More Than 0.4 wt %. If the Fe content is greater than 0.4 wt %, workability is diminished. In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.0 wt% to 0.2 wt % Fe. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.1 wt % to 0.3 wt % Fe.

Cr: Not More Than 0.25 wt %. Cr is typically used to enhance the corrosion resistance as well as the strength of the core alloy, however, the addition of Cr beyond 0.25 wt % provides little, if any, further improvement in the corrosion resistance or alloy strength. Also, the workability is degraded beyond 0.25 wt % Cr. In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.0 wt% to 0.2 wt % Cr. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.1 wt% to 0.2 wt% Cr. In still another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.01 wt % to 0.1 wt % Cr.

Zr: Not More Than 0.3 wt %. Zr is typically used to enhance the corrosion resistance as well as the strength of the core alloy, however, the addition of Zr beyond 0.25 wt % provides little, if any, further improvement in the corrosion resistance or alloy strength. Also, the workability is degraded beyond 0.25 wt % Zr. In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.0 wt % to 0.2 wt % Zr. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.13 wt % to 0.27 wt % Zr. In still another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.01 wt % to 0.1 wt % Zr.

In one embodiment, both Zr and Cr are present in the core alloy. In this regard, the inclusion of both Zr and Cr elements is believed to provide a synergistic effect in terms of the increase in tensile strength (yield strength). The total content of (Zr + Cr) is 0.4 wt % or less.

Ti: Not More Than 0.3 wt %. Ti is useful as a dispersoid. Ti is typically used to improve the corrosion resistance of the core alloy, however, the addition of Ti beyond 0.3 wt % provides little, if any, further improvement in the corrosion resistance. Also, the workability is degraded beyond 0.3 wt % Ti. In one embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.0 wt% to 0.2 wt % Ti. In another embodiment, the aluminum composite includes an aluminum core alloy comprising from 0.01 wt % to 0.1 wt % Ti.

2. Inner Liner alloy

Through additional experimentation applicant learned that the tensile strength of the aluminum composite can be enhanced by modifying the composition of the inner liner. For example, adding Mg or Zr to a 7xxx liner alloy or modification thereof increases the tensile strength of the aluminum composite. Again, the amount of Mg or Zr added to the 7xxx liner alloy or modification thereof must be within a well defined compositional range.

It is to be understood that any type of inner liner alloy known to those of ordinary skill in the aluminum art can be used to form an aluminum composite. The most common aluminum alloy used for an inner liner, particularly for heat exchanger applications, is a 7xxx series type alloy, e.g., 7072 alloy. Zn is typically added to improve the corrosion resistance of the inner liner alloy.

In one embodiment, the inner liner alloy will have the following alloying elements with the specified compositional range as follows.

Mg: Less Than 2.0 wt %. Mg is typically used to improve the strength of the inner liner. If the Mg content is greater than 2.0 wt %, the formability of the inner liner is diminished so that it becomes difficult to bond the inner liner alloy to the core alloy. In one embodiment, the aluminum composite includes an aluminum inner liner comprising from 0.0 wt% to 0.5 wt % Mg. In another embodiment, the aluminum composite includes an aluminum inner liner comprising from 0.005 wt % to 0.25 wt % Mg. In still another embodiment, the aluminum composite includes an aluminum inner liner comprising from 0.005 wt % to 0.1 wt % Mg. In still another embodiment, the aluminum composite includes an aluminum inner liner comprising from 0.005 wt % to 0.05 wt % Mg.

Zn: Not Less Than 0.5 wt % and Less Than 3.0 wt %. Zn is an element for lowering the electric potential of the cladding material serving as a sacrificial anode and improving the corrosion resistance of the inner face. If the Zn content is less than 0.5 wt %, improvement effect for the strength is little, and the corrosion resistance is degraded. Meanwhile, if Zn is added to more than 3.0 wt %, the formability of the cladding material is degraded, which is not preferable. Thus, the additive amount of Zn is defined as not less than 0.5 wt % and less than 3.0 wt %.

In one embodiment, the aluminum composite includes an aluminum inner liner comprising from 0.8 wt % to 1.5 wt % Mg, and from 1.1 wt % to 1.7 wt % Zn. In another embodiment, the aluminum composite includes an aluminum inner liner comprising from 1.0 wt % to 1.2 wt % Mg, and from 1.3 wt % to 1.5 wt % Zn. In still another embodiment, the aluminum composite includes an aluminum inner liner comprising from 0.005 wt % to 0.1 wt % Mg, and from 1.3 wt % to 1.5 wt % Zn. In still another embodiment, the aluminum composite includes an aluminum inner liner comprising from 1.0 wt % to 1.2 wt % Mg, and from 1.3 wt % to 1.5 wt % Zn.

In one particular embodiment, the aluminum composite includes a liner alloy comprising from 0.2 wt% to 0.4 wt% Mg. In another embodiment, the composite aluminum alloy will include a liner alloy comprising from 0.1 wt% to 0.3 wt% Zr. An alternative embodiment includes a liner alloy comprising both Mg and Zr. In one particular instance the total Mg + Zr concentration does not exceed 0.5 wt%.

3. Brazing Clad Alloy.

It is to be understood that any type of brazing clad alloy known to those of ordinary skill in the aluminum art can be combined with the aluminum composite to form an aluminum brazing sheet. The most common aluminum alloy used for brazing clad, particularly for heat exchanger applications, is a 4xxx series type alloy, e.g., 4045 alloy.

In one embodiment, the aluminum composite will have a hardness ratio defined as (inner liner alloy hardness):(core alloy hardness) of not more than 1.5. The hardness ratio has some relationship to the amount of warping and spring back following or during the material processing of the composite alloy. The hardness ratio can be adjusted by properly setting the final annealing condition. For example, the final annealing temperature can be set from between about 330° C to about 550° C followed by cooling to room temperature at a cooling rate of from about 2° C/hr to 20° C/hr. Examples 1-4, 6, 7, 9 and 10

Preparation of brazing sheets. Modified 3xxx aluminum alloys were prepared to yield cast ingots of the core alloy compositions shown in Table 1. The cast ingots were machined suitably for clad application. Brazing sheets of braze clad (4045), core alloy and inner liner were assembled according to the desired clad layer thicknesses according to methods well known in the art. The brazing sheets of Examples 1-4, and 7-9 were prepared with a 7xxx aluminum alloy inner liner and the brazing sheet of Example 6 was prepared with another modified 7xxx alloy in which 0.342 wt% actual Mg was added. The brazing sheet of Example 10 was prepared from a modified 7xxx alloy in which 0.166 actual Zr was added.

The brazing sheets were roll-bonded by hot rolling to 0.110" gauge. The hot band of 0.110" gauge was processed by the following steps.

Step # 1. Anneal hot band at 710° F for 2 hrs with a heat up rate of 50° F/hr and then air cool (O-temper). Step # 2. Cold rolled to 0.014" gauge. Step # 3. Anneal at 710° F for 2 hrs with a heat up rate of 50 °F/hr and then air cooled (O-temper). Step # 4. Cold rolled to final gauge of 0.010" (final cold reduction = 30%).

The clad thickness of different materials was measured by Image Analysis making use of optical metallography. Coupons of (i) 2-3/16" width and 4-7/8" length and (ii) 2-1/2" width and 8" length were CAB brazed using the following braze cycle:

Ramp to 572⁰F - 15 minutes

Hold at 572°F - 3 minutes

Ramp 572°F to 95O⁰F - 8 minutes

Hold at 950⁰F - 1 minute

Ramp 950⁰F to 1067⁰F - 6 minutes

Hold at 1067⁰F - I minute

Ramp 1067⁰F to 1112⁰F - 2 minutes

Hold at 1112⁰F - 3 minutes

Pull and air cool.

Comparative Example 1

The composites with inner liner can be compared to CAl 3 which has AA 4343 (10%) as blaze clad, K328 as core and AA7072 (10%) as liner. K328 is a 3xxx aluminum alloy comprising by weight %: 0.07 Si, 0.17 Fe, 0.50 Cu, 1.45 Mn, 0.09 Mg, 0.03 Ti and the balance aluminum and inevitable impurities. The composites with, inner liner may also be compared to CA55 which has AA 4343 as blaze clad, K328 as core and AA 4343 (10%) as liner. The brazing sheets of CA13 and CA55 were prepared substantially according to the process described for Examples 1-4, 6-7 and 9-10.

TABLE 1. Composites of Aluminum Core Alloys with Inner Liners

Tensile tests

Post-braze tensile tests were performed according to the procedures of ASTM:B557-94. Tensile specimens were machined from brazed coupons of 2-1/2" width and 8" length. Pre- and post-braze tensile properties of various materials are listed in Table 2. The addition of Mg to the core alloy exhibits improved tensile strength. The addition of Cr alone is shown not to be very effective in improving alloy strength.

TABLE 2. Tensile properties of Aluminum Core Alloys and Braze Sheets

Metallography

Metallographic examination of pre-braze and post-braze samples was conducted using standard methods of specimen preparation. The samples were anodized using Barker's etch for observing the grain structure. Mean linear intercept lengths were measured along the longer dimension of the grains in order to determine the grain size. See Table 3.

TABLE 3. Post-braze grain size data

* Mean linear intercept length (longer dimension of grains)

Sag and bend tests

In the sag test, coupons of 1.5" width and 3" length were clamped in a rack such that their span length is 2" (50 mm). The coupons were subjected to a CAB braze cycle as above and the resulting sag amount measured.

In the bend test, 0.5 inch wide strips were bent through 90° and 180° such that the braze clad is on the outside for the 90° bend and on trie inside for thel 80° bend. The bend radius is about 0.2 mm to 0.3 mm. The bent samples were subjected to a CAB braze cycle and core erosion was evaluated by Image Analysis. The core erosion is calculated as follows.

Core erosion (%) = [1 - (T_c/T_co)] x 100, wherein T_c is core thickness in the post-braze sheet, and T_co is the original core thickness in the pre-braze material.

TABLE 4. SAG TEST RESULTS

The pre- and post-braze microstructures of Example 1-4, 6-7 and 9-10 are illustrated in Figures 1-8. The post-braze grain structures of Examples 9 and 10 are shown in Figures 9(a) and 9(b), respectively. The post-braze grain size ^■values shown in Table 3 suggest a relative by coarse grain.

Post-braze grain structure of materials #9 and #10 are shown in Figure 9. Post braze microstructure of bent samples of materials #9 and #10 are shown, in Figures 10 and 11, respectively. The temper is H14. Post-braze grain structure of bent samples of materials #9 and #10 are shown in Figures 12 and 13, respectively. Corrosion damage according to the SWAAT standard for materials #9 and #10 are shown in Figures 14 and 15, respectively. Post-braze microstructures of bent composite aluminum alloys of Examples 1- 4 and 6-7 are shown in Figures 16-21.

Post-braze grain structures of Examples 1-4, 6 and 7 are shown in Figures 22(a)-22(f). Post-braze grain structures of bent composite aluminum alloys of Examples 1-4 and 6-7 are shown in Figures 23-28.

SWAAT corrosion damage of the composite aluminum alloys of Examples 1-

4 and 6-7 are shown in Figures 29-36.

Brazed drip strips were corrosion tested according to SWAAT, ASTM G85- A3. The corrosion damage in the SWAAT tests was evaluated by preparing failed SWAAT coupons and examining them metallographically. The SWAAT life of various coupons was in the range of 140 hrs to 344 hrs. All of the SWAAT coupons appear to exhibit lateral mode of corrosive attack, but their SWAAT life is lower than 345 hrs.

The sag amount for alloys 1-4, 6-7, and 9-10 is in the range of 2.39 to 7.55 mm (See Table 4). Good braze flow (> 50 %) is noted in the Example alloys.

Through-thickness corrosion potential profiles of Examples 1-4 and 6-7 from braze clad side and inner liner side (water-side) are shown in Charts 1 and 2, respectively. In general, the potential profiles from the braze clad side are nearly flat (Chart 1), whereas the potentials on the water-side are lower up to ~ 120 mV relative to mid-section levels (Chart T).

The effects of Mg addition to the core alloy on the corrosion potential profiles are shown in Charts 3 and 4.

The addition of Cr alone to the core did not affect the potential profiles (Charts

5 and 6). The effects of adding Mg, Cr and Zr to the core alloy on braze clad side and water side are shown in Charts 7 and 8, respectively. The effects of adding Mg to both the core alloy and inner liner alloy on braze clad side and water side are shown in Charts 9 and 10, respectively. Charts 11 and 12 show the corrosion potential of Examples 9 and 10 from the braze clad side and the inner liner side, respectively.

Claims

We Claim:

1. An aluminum composite comprising: a 3xxx aluminum core alloy or an element alloy modification thereof, wherein the 3xxx aluminum core alloy or the element alloy modification thereof comprises from 0.05 wt% to 0.4 wt% Mg; and a 7xxx inner liner alloy or an element alloy modification thereof, wherein the 7xxx liner alloy or the element alloy modification thereof comprises from 0.002 wt% to 1.5 wt% Mg.

2. An aluminum composite of claim 1 wherein the 7xxx inner liner alloy or the element alloy modification thereof comprises from 0.002 wt% Mg to 0.6 w% Mg.

3. An aluminum composite of claim 1 wherein the 7xxx inner liner alloy or an element alloy modification thereof comprises from 0.03 wt% Mg to 0.4 w% Mg.

4. An aluminum composite of claim 1 wherein the aluminum core alloy further comprises from 0.1 wt% to 0.3 wt% Cr, from 0.1 wt% to 0.3 wt% Zr, or a combination thereof.

5. An aluminum composite of claim 3 wherein the aluminum core alloy comprises about 0.3 wt% Mg.

6. An aluminum composite of claim 5 wherein the aluminum core alloy further comprises from 0.1 wt% to 0.2 wt% Cr

7. An aluminum composite of claim 2 wherein the aluminum inner liner alloy further comprises 0.1 wt% to 0.3 wt% Zr.

8. An aluminum composite of claim 4 wherein the aluminum inner liner alloy comprises 0.2 wt% to 0.4 wt% Mg, 0.1 wt% to 0.3 wt% Zr, or a combination thereof.

9. An aluminum composite of claim 1 further comprising braze clad, wherein the composite has an average, room temperature, post-braze ASTM:B557-94 yield strength value of at least 70 MPa.

10. An aluminum composite of claim 1 further comprising braze clad, wherein the composite has an average, room temperature, post-braze ASTM:B557-94 tensile strength value of at least 165 MPa.

11. An aluminum composite of claim 5 further comprising braze clad, wherein the composite has an average post-braze ASTM:B557-94 yield strength value ofatleast δO MPa.

12. An aluminum composite of claim 2 with an average post-braze grain size of at least about 200 μm.

13. A heat exchanger prepared with the aluminum composite of claim 1.

14. An evaporator tube prepared with the aluminum composite of claim 1.