WO2006041518A1

WO2006041518A1 - Brazing sheet suitable for use in heat exchangers and the like

Info

Publication number: WO2006041518A1
Application number: PCT/US2005/009841
Authority: WO
Inventors: Zayna M. Connor
Original assignee: Pechiney Rolled Products
Priority date: 2004-10-01
Filing date: 2005-03-23
Publication date: 2006-04-20
Also published as: WO2006039304B1; WO2006039304A1

Abstract

The present invention provides an aluminium alloy brazing sheet material, particularly suitable for heat exchanger tube applications, as well as to methods for their manufacture and use.

Description

BRAZING SHEET SUITABLE FOR USE IN HEAT EXCHANGERS AND THE

LIKE

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to provisional application No. 60/614,489 filed on Oct. 1, 2004, provisional application No. 60/614,483 filed on Oct. 1, 2004, provisional application No. 60/614,488 filed on October 1, 2004, provisional application No. 60/614,490 filed October 1, 2004, provisional application No.

60/617,161 filed October 12, 2004, provisional application No. 60/617,666 filed on

Oct. 13, 2004, provisional application No. 60/614,496 filed on Oct. 1, 2004, provisional application No. 60/627,085 filed November 12, 2004, and provisional application No. 60/646,985, filed January 27, 2005, all of which are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

Technical Field of the Invention

The present invention relates generally to aluminum alloy brazing sheet materials including brazing sheet tube stock, and more particularly to increased strength and erosion/corrosion resistant aluminum alloy brazing sheet materials, as well as, to methods for their manufacture and use.

Description of Related Art

Aluminum brazing sheet is widely used to manufacture various heat exchangers such as radiators, charge air coolers, evaporators and condensers in the automotive industry. One of the much-needed improvements in the automotive industry is the overall weight reduction in order to enhance fuel economy. The goal of weight reduction extends to all components of a vehicle including heat exchangers. Accordingly, research and development efforts are continuing to down gauge the tube stock in automotive radiators, while increasing strength and erosion/corrosion resistance. Long life of heat exchangers from the viewpoint of corrosion is of importance not only to improve their performance, but also towards down gauging of radiator tube stock. The material properties of interest in this regard are 'post-braze' strength, braze flow, and internal (water-side) and external (air-side) corrosion resistance of the brazing sheet.

Typically, radiator tube material is a composite, with a non-heat treatable core alloy of 3xxx series, which is sandwiched between an inner liner and a 'braze' clad of an Al-Si alloy. The strength is provided by the core alloy, whereas the inner liner improves the coolant-side corrosion resistance. The air-side corrosion resistance is affected by the core alloy and interactions between core and 'braze' clad alloys during the brazing process.

Formation of an anodic near-surface layer, known as 'brown band' through diffusion of Si into the core alloy during the brazing process is one of the methods of improving the external corrosion resistance. See, e.g., Marshall, et al., "Development of a Long Life Aluminum Brazing Sheet Alloy with Enhanced Mechanical Performance," SAE paper 940505, (1994). Another way of increasing the air-side corrosion resistance is by adding Ti to the core alloy. See, e.g., Yasuaki, et al., "Development of Corrosion Resistant Brazing Sheet for Drawn Cup Type Evaporators, Part 2: Application to Evaporator," SAE Technical paper No. 930149, (1993).

In US Patent No. 6,756,133, Palmer et al. provide aluminum alloy brazing sheet materials that have an increased yield strength when the materials have been "peak aged." The term "peak aged" refers to the treatment where a brazing alloy is subjected to a brazing cycle and then aged at various temperatures and times to determine its "peak age," i.e., the time and temperature combination where the maximum strength is observed. The peak-aged alloy of the Palmer et al. invention demonstrated yield strength at 175° C. The core alloy of the Palmer et al. invention comprises in weight percent based on the weight of the core alloy: less than 0.2% Si, less than 0.2% Fe, 1.3-1.7% Mn, 0.4-0.8% Mg, 0.3-0.7% Cu and less than 0.2% Ti and at least one element selected from the group consisting of Cr, Sc, V, Zr, Hf, and Ni, and balance aluminum and unavoidable impurities.

Previously, it was virtually unheard of to be able to use brazing sheet tubes without waterside clad liners for applications such as radiator tubes and the like such as for applications that involve high temperature fluids flowing therein. While AA 3005 has been attempted to be used, AA 3005 has many defects and is not capable of passing the OY water test. Moreover, AA 3005 generally does not have sufficient strength characteristics and corrosion/erosion resistance that is often desired in many applications.

SUMMARY OF THE INVENTION

It was therefore an object of the present invention to obtain an alloy that is capable of being used for heat exchanger applications without requiring the use of a waterside liner. This saves on manufacturing costs and also on the weight of the parts made thereof. Unexpectedly, the present invention found that the instantly disclosed alloys can be used with or without a waterside clad liner and can still pass the OY water test.

In accordance with these and other objects, there is provided a brazing sheet composite comprising an aluminum core alloy wherein the core alloy comprises an aluminum alloy modified with Mg to invoke solute strengthening, and/or to increase erosion/corrosion resistance. In one embodiment, a core alloy comprises 3xxx series aluminum alloy wherein Mg is from 0.0 to about 0.35%, along with a dispersoid- forming element such as Mn, Cr, and Zr.

A further embodiment of the invention includes liner alloys comprising lxxx series aluminum modified by Zn, Mn₅ Mg, and/or dispersoid forming elements.

Still a further embodiment includes a radiator tube core alloy that possesses improved 'post-braze' strength at room temperature and normal radiator operating temperatures. Other embodiments of the invention are core alloys with improved 'post- braze 'strength at elevated temperatures suitable for charge air cooler applications.

Further embodiments of the present invention are inner liner materials developed to improve water-side corrosion resistance of radiator tubes.

There are further provided methods for preparing brazing sheets as described herein as well as methods for use of brazing sheet materials including tube stock and heat exchangers as well as further applications.

Additional objects, features and advantages of the invention will be set forth in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention. The objects, features and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description of certain preferred embodiments given below, serve to explain the principles of the invention.

Figure 1 is a graph showing the effect of Mg, added to a 3xxx series aluminum core alloy, has on strength, measured in MPa.

Figure 2 is a graph showing the effect of various dispersoid forming elements, added to a 3xxx series aluminum core alloy, have on strength, measured in MPa.

Figure 3 is a graph showing the effect of various dispersoid forming elements, added to either a 3xxx series aluminum core alloy, or liner, have on strength, measured in MPa. Figure 4 is a graph showing the effect of various dispersoid forming elements, added to a 3xxx series aluminum core alloy, without an inner liner present, have on strength, measured in MPa.

Figure 5 is a graph showing the effect of various dispersoid forming elements, added to a 3xxx series aluminum core alloy, have on strength measured from 0-350° C.

Figure 6 is a graph showing corrosion pit depth data of liners with Zn.

Figure 7 is a graph showing the depth from the water-side surface in microns, of liners with Zn.

Figure 8 is a graph showing the effect of Mg in a liner composition, measured in terms of surface pit depth.

Figure 9 is a graph showing the corrosion potential, in mV, versus depth from water-side surface of Mg containing liners.

Figure 10 is a graph showing pit depth data of liners with and without Zn, and, as a core with no liner.

Figure 11 is a graph showing corrosion potential, in mV, versus depth from the water-side surface of liners with and without Zn, and, as a core with no liner.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Various improvements in materials for brazing sheet applications are disclosed herein, especially with reference to heat exchanger tube materials are presented herein. As disclosed herein, "heat exchanger tube materials," can include, but are not limited to radiators, charge air cooler, condenser, evaporator tubes and the like.

Particularly, heat exchanger tube core alloy development to improve 'post-braze' strength at room temperature and normal heat exchanger tube operating temperatures; development of core alloys to improve 'post-braze' strength at elevated temperatures for heat exchanger applications; and, inner liner materials developed to improve water-side erosion/corrosion resistance of heat exchanger tubes.

The 'post-braze' strength of 3xxx aluminum alloys can be improved to some extent through alloying modifications. The applicable strengthening mechanism is primarily solid solution strengthening. Grain size strengthening is another mechanism, wherein smaller grain size can contribute to an increase in strength at lower temperatures. Mg is an element of interest for solute strengthening. "Solute strengthening" is a metallurgical term, whereby solute atoms are of a size and lattice parameters that they allow for strengthening of the alloy to occur. Precipitation hardening to a small extent is also possible if Mg is present in the core alloy. The mechanism of age hardening involves precipitation of Mg₂Si during the 'post-braze' aging treatment. The gain in strength through age hardening, however, is not stable at elevated temperatures because of coarsening of precipitate particles.

Alloying additions, such as Mn, that result in fine dispersion of intermetallic particles (e.g. MnAl₆) may result in some dispersion strengthening. Intermetallic dispersoids, being thermally stable, may provide some elevated temperature strengthening, which is of interest to enhance the operating temperature of charge air coolers. Starting with a typical 3xxx aluminum alloy, the compositions were modified by magnesium addition to invoke a solute strengthening effect. Advantageously, Mg is present in an amount from 0.01 to about 0.4 % based on the weight of the alloy, particularly from about 0.10-0.35 weight %. Modifications involving dispersoid-forming elements such as Mn, Cr Ti and Zr are also disclosed. The dispersoid forming elements are preferably present in total in an amount from 0.75 to 2.15%. Mn if present is preferably present in an amount from 0.1-2.0, particularly preferably from 0.7 to 1.7%, Cr if present is from 0.01 to 0.5%, particularly from 0.05 to 0.2%, Zr if included is preferably included in an amount from 0.01 to 0.35%, particularly from 0.05 to 0.25%, and Ti, if included is preferably included in an amount advantageously from about 0.01 to 0.25%, particularly from 0.1-0.2%. An inner liner can be present on materials of the present invention. Alternatively, alloys of the present invention can be used unclad, or "bare." Alternatively, alloys of the present invention can function as liners themselves. Different alloy compositions of 3xxx aluminum alloys are disclosed which improve strength at ambient and elevated temperatures. Modifications of water-side liner compositions with the addition of Mg are also disclosed which enhance the 'post- braze' strength of the brazing sheet.

The mechanisms of water-side corrosion such as localized pitting and erosion- corrosion are of interest towards designing alloys for better corrosion resistance. Zn is commonly added to the liners in order to enhance the water-side corrosion resistance. The corrosion potential of Zn being lower (less noble) than Al, alloying with Zn makes the liner alloy more anodic. The Zn containing liner may serve as a sacrificial anode that promotes lateral attack rather than localized pitting. The corrosion response of Zn containing liners in terms of the effects such as the concentration of Zn in the liner is desired towards selecting the optimal composition.

Erosion-corrosion, as used herein means simultaneous mechanical and chemical action. For example, in charge air coolers and other heat exchanger applications, the tubes used in such applications are subject to both mechanical erosion through the high velocity of water or other liquid running therethrough, as well as, outside forces of rocks hitting the tubes when in use. At the same time, the tubes are subjected to chemical erosion due to environmental forces (salt/sand) as well as other contact with chemicals on their inner sides. The dual interaction, (mechanical/chemical), often leads to more rapid damage of the heat exchange material (such as radiator tubes). The extent of erosion-corrosion in applications such as radiator tubes is affected by variables such as fluid velocity, test temperature and mechanical properties of the material.

In accordance with one advantageous embodiment of the present invention, there are provided alloys of the following preferable composition: Mg up to 0.35% maximum, Si from 0.4 to 0.9%, Fe from 0.2 to 0.7%, Cu from 0.4 to 0.9%, Mn from 0.7 to 1.7%, Cr from 0.05 to 0.2%, Ti from 0.1 to 0.2%,

Zr from 0.05 to 0.25%, and Zn up to 0.1% maximum, the remainder, aluminum. All weights expressed herein are weight percentages based on the total weight of the alloy.

A wide range of different alloys can be used in connection with the present invention. Exemplary alloys are listed below:

Alloy 1

Si 0.4 max Fe 0.7 max

Cu 0.4-0.9

Mn 0.7-1.7

Mg 0.40 max

Cr 0.05-0.2 Ti 0.2 max

Zr 0.05-0.25

Zn 0.1 max

Remainder Al and trace elements

Alloy 2

Si 0.5- 0.9

Fe 0.2 max

Cu 0.4-0.7

Mn 1.0-1.7 Mg 0.40 max

Cr 0.05-0.2

Ti 0.1-0.2

Zr 0.05-0.25

Zn 0.1 max Remainder Al and trace elements EXAMPLES

Example 1

Keeping the above factors in view, different liner alloys were tested to explore their water-side corrosion response. In particular, the effects of alloying with Zn, Mn,

Mg and dispersoid forming elements were analyzed. A core alloy was exposed to a coolant directly without a liner in order to compare its performance to the performance of the same alloy used as a liner.

Various experimental core, 'braze' clad and liner alloy ingots were melted with appropriate alloying additions to yield desired compositions in each case and then cast into ingots of ~ 25 mm x 100 mm x 250 mm size making use of copper molds. The cast ingots were machined suitably for clad application. Various brazing sheet composites consisting of 'braze' clad (10-15% of total thickness), core alloy and liner alloy (0-20% of total thickness) were assembled and roll-bonded by hot rolling to 2.8 mm gauge. The hot band gauge was further processed to a final gauge of 0.25-

0.30 mm (Hl 4 / H24 temper) making use of appropriate combinations of cold rolling and annealing steps. The composites of some of the brazing sheets consisted of

'braze' clad and core alloy without a liner.

Coupons of the brazing sheets without fluxing were exposed to a standard brazing cycle in a CAB furnace. It involved a ramp up rate of 20°C/minute from room temperature to 600⁰C, holding at 600⁰C for 3 minutes and then air cooling.

'Post-braze' tensile tests were performed according to the procedures of ASTM:B557-94, (incorporated herein by reference), using tensile specimens of 12.5 mm gauge width and 50 mm gauge length. Elevated temperature tensile tests were carried out at temperatures up to 350^°C making use of a resistance heating furnace.

The water-side corrosion response of different liners was tested by using an internal corrosion test unit as known in the art. With this unit, coupons as well as full size radiators can be tested over a wide range of flow rates of the coolant. Various details of the test loop design and manufacture are available in Johnson et ah, in "A New Evaluation Method for the Measurement of Internal Corrosion Resistance in Braze Clad Alloys " SAE paper No. 02M-31, (2002), the content of which is incorporated herein by reference in its entirety.

Tests were performed using two different coolants, viz., (i) ASTM water and

(ii) OY water. Their compositions and test parameters are given below.

TABLE 1. Radiator Coolant Compositions

The two different waters were used as defined herein to determine performance of the tested materials. For purposes of this invention, the term "OY water test" means the instantly defined test using the OY water above. The term "ASTM water test" means the instantly defined test using the ASTM water above. On completion of the test, the coupons were cleaned with chromic acid to remove corrosion products and then examined metallographically making use of standard procedures. Pit depth measurements were performed using the Focal Difference (FD) method. In each material, the depths of what appeared to be the deepest 20 pits were measured. From these measurements, the maximum and average pit depth data are presented in the results. Through-thickness corrosion potential measurements were carried out at different depths from the surface on samples in the 'post-braze' condition according to the procedures of ASTM — G69. The corrosion potential profiles from the water¬ side surface were of interest to assess various inner liners in terms of their corrosion response. In order to measure corrosion potentials at different depths from the surface of a specimen, material was removed by electro-machining making use of an electrolyte of sodium chloride solution in water.

'Post-braze' strengthening of the tube stock at room temperature was also assessed. One set of composite 'braze sheets' was processed to H14 temper with a 4045 'braze clad' and an inner liner of 7xxx series alloy. Another set of composites was processed to H24 temper without an inner liner. Various experimental core alloys based on AA3003 are designated as IGA - K3G (Table 3).

TABLE 3. Core Alloy* Details

based on AA3003 Making use of these experimental core alloys, the effects of Mg and dispersoid forming elements Cr and Zr on tensile properties were evaluated. The results are summarized in Figures 1-4. In addition to core alloy modifications, the effect of Mg addition to the liner was also explored and the results are shown in Figure 3.

Progressive strengthening can be noted in Figure 1 with the increase in the amount of Mg. The operative mechanisms could be solute and precipitation (Mg₂Si) strengthening. The strengthening effects of dispersoid forming elements relative to Mg addition are illustrated in Figures 2 and 4. While some strengthening due to alloying with Cr and Zr is evident at a lower level of Mg, it is less significant at higher content of Mg (Figure 2). Some additional strengthening, beyond that of core modification arises from the liner by alloying it with 0.3% Mg (Figure 3). Among different 'braze' sheets with the experimental core alloys of this study, a maximum 'post-braze' tensile strength of ~ 180 MPa is observed at room temperature.

Experimental core alloys K3E, K3F and K3G were utilized to evaluate the 'post-braze' tensile properties at elevated temperatures. The yield and tensile strength results as a function of test temperature are presented in Figure 5. The observations are summarized as follows.

While the yield strength is stable up to a test temperature of ~ 225^°C, the tensile strength drops gradually from 150^°C onwards in these alloys. A maximum tensile strength of -140 MPa was observed at 225^°C. A rapid loss in tensile strength occurs at temperatures above 200^°C. The materials with core alloys containing Mg (K3E and K3F) exhibit a higher tensile strength of - 20 MPa up to 225^°C relative to that (K3G) without Mg. The elevated temperature response of brazing sheets K3E and K3F is similar over the entire temperature range. These results indicate that Mg as an alloying element is an effective strengthener even at elevated temperatures up to 225^°C.

Example 2

Evaluations of the experimental liners were divided into three categories: (i) Liners with varying amounts of Zn, (ii) Mg addition to liner, and (iii) Higher strength liner alloys. The designations of different liners based on AAl 100 are listed in Table 4.

TABLE 4. Liner Alloy* Designations

based on AAl 100 (i) Zn liners

Standard Zn containing liners from the production lots were tested in order to compare their corrosion response. The pit depth results and the corrosion potential profiles are shown in Figures 6 and 7. The following observations can be noted from these results:

OY water is more aggressive than ASTM water in all materials within the range of explored parameters. While minor pitting occurred with K3I and K4A liners, through-thickness perforations were observed in 7072 and K4B liners in OY water. Thus the highest pitting resistance is seen in K3I and K4A liners. The corrosion potential measurements indicate an anodic surface layer in all Zn containing liners except K4B where it appears that the Zn in the 'braze' clad did not appreciably diffuse into the core during the braze cycle. Profuse pitting occurred in the case of K4B liner, just as in the case without a liner. The overall internal corrosion test results suggest that the corrosion resistance of various liners decreases in the order of K3I, K4A, 7072 and K4B.

(ii) Liners with Mg and Zn

In order to evaluate the effect of Mg in the liner, K3I and K4A liners were modified with the addition of 0.3% Mg. The results of these liners with Mg are compared with the corresponding ones without Mg (Figures 8 and 9). In both the liners K3I and K4A, the corrosion performance deteriorated by alloying with Mg. While minor pitting was noticed in K3I and K4A, through-thickness perforations resulted on adding Mg under similar test conditions. The corrosion potential profiles were not, however, modified on adding Mg (Figure 9). Fine precipitates involving Al, Zn and Mg may be the sites of localized and severe pitting because of the differences in the corrosion potentials between the precipitates and matrix alloy.

(iii) Higher strength liners

Some of the higher strength liners with and without Zn were also explored. The corrosion response of a higher strength alloy (without Zn) directly as core without a liner was also evaluated in this study. The results shown in Figure 10 indicate perforations in liners K3J (with Zn) and K3K (without Zn) in OY water. On the other hand, the use of K3K as core without a liner exhibited minor pitting only. Thus, K3K as core is very effective in enhancing the pitting corrosion resistance. If erosion-corrosion mechanism were operative, the use of a higher strength alloy as a core may resist pitting and result in a longer life. An anodic surface layer that is typical of Zn containing liner is absent in the 'post-braze' state of K3J (Figure 11).

A maximum 'post-braze' tensile strength of 180 MPa at room temperature was obtained with the alloying modifications of the core alloy. A gain of ~10 MPa in yield strength and ~ 20 MPa in tensile strength was observed over a base alloy of

3xxx series in the temperature range of ambient to 225^°C. A maximum tensile strength of -140 MPa is noted in these alloys at 225^°C.

Among different Zn containing liners, the best corrosion resistance in this example was exhibited by a liner with 1.1 Mn and 1.4 Zn. Addition of Mg to the liners containing Zn reduced the corrosion resistance. While higher strength liners with and without Zn did not improve water-side corrosion resistance, a higher strength alloy without Zn exhibited good corrosion resistance when it was used as a core alloy without any liner.

The instantly disclosed alloys can also be used as clad layers on any desired core material if desired for any reason.

Additional advantages, features and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative devices, shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

All documents referred to herein are specifically incorporated herein by reference in their entireties. As used herein and in the following claims, articles such as "the", "a" and "an" can connote the singular or plural.

Claims

What is claimed is:

1. A heat exchanger material comprising an aluminum 3xxx series alloy including Mg in an amount from 0.05 to about 0.40% sufficient to invoke solute strengthening, and increase erosion/corrosion resistance.

2. The material of claim 1 further comprising at least one dispersoid-forming element.

3. A material of claim 2 wherein said dispersoid forming element is selected from the group consisting Mn, Cr, Ti and Zr.

4. A material of claim 1 comprising 0.1% Mg.

5. A material of claim 1 comprising 0.3% Mg.

6. A material of claim 2 comprising 0.1% Mg, 0.15% Cr, and 0.15% Zr.

7. A material of claim 2 comprising 0.3% Mg, 0.15% Cr, and 0.15% Zr.

8. A material of claim 1 comprising 0.25% Mg.

9. A material of claim 2 comprising 0.25% Mg, 0.15% Cr, and 0.15% Zr

10. A heat exchanger material comprising an aluminum 3xxx series core alloy including 0.15% Cr and 0.15% Zr.

11. A brazing sheet material comprising an aluminum 3xxx series core alloy including Mg in an amount from 0.0 to about 0.35% and Cr and Zr in an amount sufficient to invoke solute strengthening, and/or increase erosion/corrosion resistance.

12. A brazing sheet material of claim 4 having a tensile strength of about 120 MPa up to 225° C.

13. A material of claim 2 or 3, having a maximum 'post-braze'tensile strength of about 180 MPa at room temperature.

14. A brazing sheet material comprising an aluminum lxxx series as a core alloy, without a liner, said alloy including from about 0.01 to about 0.15% Mn, from about 0.01 to about 0.15% Cr, from about 0.01 to about 0.15% Zr and from about 0.0 to about 0.1% Ti.

15. A heat exchanger tube prepared from a brazing sheet material according to claim 2.

16. A tube stock prepared from a material of claim 2.

17. A radiator tube prepared from a material of claim 2.

18. A condenser tube prepared from a material of claim 2.

19. An evaporator tube prepared from a material of claim 2.

20. A method of reducing erosion/corrosion associated with fluid velocity in the interior of a heat exchange tube comprising forming said tube from a brazing sheet material of claim 2.

21. The heat exchanger material of claim 1 wherein the aluminum 3xxx series alloy comprises in weight percent based on the weight of the alloy:

Si 0.4 max

Fe 0.7 max

Cu 0.4 - 0.9

Mn 0.7 - 1.7

Mg 0.40 max

Cr 0.05 - 0.2

Ti 0.2 max

Zr 0.05 - 0.25

Zn 0.1 max

Remainder Al and inevitable trace elements.

22. The heat exchanger material of claim 1 wherein the aluminum 3xxx series alloy comprises in weight percent based on the weight of the alloy:

Si 0.5 - 0.9

Fe 0.2 max

Cu 0.4 - 0.7

Mn 1.0 - 1.7

Mg 0.40 max

Cr 0.05 - 0.2

Ti 0.1 - 0.2

Zr 0.05 - 0.25

Zn 0.1 max.

Remainder Al and inevitable trace elements

23. A material of claim 2, wherein said alloy is a core alloy.

24. A material of claim 2, wherein said alloy is a liner alloy.

25. A brazing sheet capable of being used without a waterside clad layer as a heat exchanger tube, said brazing sheet being capable of outperforming AA 3005 by up to 50% passing the OY water test.

26. A brazing sheet of claim 25, wherein said brazing sheet has improved properties of strength and erosion/corrosion resistance as compared with AA3005.

27. A brazing sheet of claim 25, comprising Mg in an amount from 0.05 to about 0.35% sufficient to invoke solute strengthening, and increase erosion/corrosion resistance and at least one dispersoid forming element.

28. A brazing sheet of claim 27, wherein said dispersoid forming element is Zr, Ti and/or Cr.

29. A brazing sheet wherein a clad layer thereof comprises Mg in an amount from 0.05 to about 0.35% and at least one selected from Zr, Ti and Cr.