Aluminium alloy for use as core material in brazing sheet

Abstract

An aluminium alloy for use as a core material in brazing sheet, consisting of, in weight %: Mn 0.7-1.5, Cu 0.6-1.0, Fe not more than 0.4, Si less than 0.1, Mg 0.05-0.8, Ti 0.02-0.3, Cr 0.1-0.25, Zr 0.1-0.2, balance Al and unavoidable impurities, wherein 0.2<=(Cr+Zr)<=0.4, the alloy being capable of obtaining in the post-brazing state 0.2% yield strength of at least 65 MPa and having a corrosion life of more than 11 days in a SWAAT test without perforations in accordance with ASTM G-85.

Description

[0001] This invention relates to an aluminium alloy for use as a core material in brazing sheet, to a brazing sheet comprising the aluminium alloy as core material, to the use of the aluminium alloy as core material of a brazing sheet in a brazed assembly and to a brazed assembly containing at least one member having the aluminium alloy as core material. The aluminium alloy is of the AA3xxx type. The invention has the particular advantage that the alloy is non-heat-treatable, i.e. it does not require post-brazing ageing treatment. A principle use of brazing sheet containing such alloy is in heat exchangers, such as vehicle radiators, in which water is one heat-exchanging medium. Herein the term sheet material includes tube material.DESCRIPTION OF THE PRIOR ART[0002] Many proposals for an aluminium alloy to be used as a core material in brazing sheet have been made. Generally, in the prior art, the alloy is used as a core layer in a brazing sheet with a clad layer on at least one fac...

AI Technical Summary

Benefits of technology

0076] Cu increases the strength of the aluminium alloy. With a Cu content of over 1.0% undesired coarse Cu-containing compounds can be formed. It has been found that with a Cu content in a range of 0.6-1.0% the strength is optimum, while the desired long-life corrosion resistance does not decrease. Preferably the Cu content is more than 0.6%, particularly at least 0.7%.

0077] The added Cr improves among other things the strength of the aluminium alloy in the post-brazed condition, particularly in combination with the high Cu content. With a Cr content of more than 0.25% there is decreasing advantage in respect of the increase in strength. Therefore the Cr maximum is taken at 0.25%. Preferably, the amount of Cr is 0.14-0.25%. The Cr content may optionally be substituted partially or wholly by V in the same amount, since V has an equivalent effect. Casting trials have indicated that with increasing Cr concentration there is an increased risk of the formation of coarse Cr containing intermetallic compounds. These compounds have been analysed to be predominantly Cr--Mn rich in composition and the risk of the formation of these particles increases with higher Mn levels as well as Cr level. These coarse intermetallics are detrimental to mechanical properties as they decrease the effective Mn and Cr for strength purposes, and are also detrimental for formability and corrosion.

0078] Zr has a sign

Problems solved by technology

Cu is said to decrease the corrosion resistance of the core alloy itself.

Cu at above 0.2 is said to be disadvantageous.

Si is used for strength improvement, but at less than 0.1% has insufficient effect.

At least 0.7% is required for obtaining the desired corrosion resistance, while an Mn content of over 1.5% does not produce any significant improvements in respect of the strength because coarse Al--Mn-containing compounds are formed.

A further disadvantage of coarse Al--Mn-containing compounds is that they reduce the rollability of the aluminium alloy.

As the Si content is increased the width of the precipitate band decreases, decreasing corrosion perfor

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