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

[0072] Fe is present in all known aluminium alloys but in the aluminium alloys in accordance with the invention it is not a required alloying element and is not deliberately added. With a high Fe content among other things the corrosion resistance decreases. The admissible Fe content is 0.4% maximum and preferably 0.2% maximum.

[0100] It is preferred in this method the cast ingot is homogenized prior to stage by at least a heat treatment of 1 / 2-24 hours at a temperature higher than 550.degree. C., and preferably lower than 625.degree. C. This achieves the effect of improving the formability of the aluminium alloy during rolling. With good process management of the homogenisation cycle this does not necessarily mean that the corrosion resistance of the finished product decreases.

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 performance.

Casting trials have indicated that with increasing Cr concentration there is an increased risk of the formation of coarse Cr containing intermetallic compounds.

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.

Zr is restricted to a maximum addition level of 0.2%, since above this level problems can be encountered in casting due to incomplete dissolution.

Cold-rolled sheet does not have optimum formability so that it is often necessary to anneal the sheet or combination in order to obtain the desired formability.

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