Composite metal panel

Abstract

The invention relates to a rigid composite metal panel comprising at least two metal parallel plates and / or sheets secured to the peaks and troughs of a corrugated aluminium stiffener sheet arranged between the parallel plates and / or sheets, wherein the corrugated aluminium stiffener sheet is an aluminium brazing sheet product made from an aluminium brazing sheet product including a core sheet (1) made of an aluminium alloy having on at least one surface of the core sheet clad, and preferably on both sides, an aluminium clad layer (2), the aluminium clad layer being made of an aluminium alloy comprising silicon in an amount in the range of 2 to 18% by weight, preferably 5 to 14%, and a layer (3) comprising nickel on the outer surface of the aluminium clad layer. The invention further relates to a method of manufacturing thereof.

Description

[0001] This is a continuation-in-part, claiming priority under 35 U.S.C. Section 120, of U.S. patent application Ser. No. 09 / 573,980, filed May 19, 2000, pending, incorporated herein by reference in its entirety.[0002] The invention is concerned with a composite rigid metal panel comprising at least two parallel metal plates and / or sheets secured to a corrugated aluminium stiffener sheet arranged between the parallel metal plates and / or sheets, and further to a composite panel comprising two parallel plates and / or sheets secured to aluminium stiffener sheet having a honeycomb structure. The invention further relates to a method of manufacturing thereof.DESCRIPTION OF THE RELATED ART[0003] Composite metal panels having an interior honeycomb structure are usually manufactured by means of adhesion bonding, such as for example disclosed in U.S. Pat. No. 6,054,200. Composite metal panels having an interior of corrugated sheet such that the peaks and troughs thereof are bonded to the para...

AI Technical Summary

Benefits of technology

[0006] It is a further object of the present invention to provide a composite metal panel which can be manufactured by means of brazing.

[0018] In an embodiment, the aluminium brazing sheet product according to the invention is further characterized by a layer comprising zinc or tin as a bonding layer between the outer surface of the aluminium clad layer and the layer comprising nickel. By the zinc or tin-comprising bonding layer a very effective bond between the aluminium alloy clad layer and the layer comprising nickel is formed, the bond remaining effective during subsequent deformation of the aluminium brazing sheet, for example by roll forming to obtain a corrugate stiffener sheet. The coverage of the nickel layer is no longer dependent on the surface characteristics of the bare clad layer. The aluminium brazing sheet product is suitable for fluxless brazing under controlled atmosphere conditions. This part of the invention is based in part on the insight that to obtain a well-bonded nickel layer on the Si-containing aluminium clad layer of the brazing sheet product, so that the bond remains effective under large deformation, pre-treatment of the aluminium clad layer is extremely important when manufacturing complex shapes of corrugated sheet. The prior art processes apparently aimed at applying the nickel in a distributed form, principally to the silicon particles at the surface of the aluminium clad layer, rather than trying to achieve a uniform nickel-lead layer. In the present invention the surface of the Si-containing aluminium clad alloy is altered in such way that the nickel coverage is independent of the silicon particles at its surface. The nickel plating does not take place on the silicon particles but on the applied thin bonding layer comprising zinc or tin. Since the nickel thus is deposited on the total surface of the aluminium alloy clad layer the necessary reaction before brazing can take place much more easily as compared to the process of the prior art. The zinc or tin applied does not interfere at all during the brazing process, and may contain a component to assist the brazing. Since the nickel is deposited smoothly and uniformly on the surface, the use of lead to promote wetting during brazing can be reduced or avoided, or other elements such as bismuth may be used for this purpose. A further important advantage of the nickel deposited smoothly and uniformly on the surface is that the total amount of nickel to be applied in order to achieve good fluxless brazing can be reduced.

[0020] In an embodiment the aluminium brazing sheet is characterized in that the bonding layer comprising zinc or tin is applied by a direct zinc plating treatment, or by a zincate treatment or a stannate treatment. Very good results may be obtained with an immersion zincate treatment or immersion stannate treatment, often also referred to as displacement plating. A further advantage is that this treatment lends itself to application in a continuous process operation.

[0029] In particular copper has been found to significantly reduce the liquidus temperature of the resultant metal filler. However, further metal layers may be applied in addition thereto.

[0032] In an embodiment the layer comprising copper or copper-based alloy being deposited by plating copper or copper-alloy using an aqueous copper-phosphate based plating bath. This aqueous plating bath demonstrated to be operational in a wide pH range, and can be used on industrial scale plating lines using a high current density, which in turn allows for fairly high line speeds. It can be composed using standard and readily available chemicals, and copper can easily be replenished to the plating bath.

[0042] A typical impurity element may be iron, in particular originating from the aluminium clad layer, and which may be tolerated in an amount of at most 0.8%. Other alloying elements may be present, and will typically, but not exclusively, originate from the aluminium clad layer. In this embodiment a metal filler is obtained which has a liquidus temperature in the range of 510 to 550.degree. C., and allows for the manufacturing of composite metal panels at significant lower temperatures compared to traditional industrial scale brazing temperatures for devices such as heat exchangers, and thereby allowing for a more unconventional choice of aluminium alloys, namely including those having low melting point constituants, for the parallel plates or sheets for the composite metal panel.

Problems solved by technology

This is of particular relevance since the use of lead for manufacturing brazed components and used in various market areas is undesirable and it is envisaged that in the near future there might possibly even be a ban on lead comprising products or products manufactured via one or more intermediate processing steps comprising lead or lead-based components.

A coating thickness of greater than 2.0 .mu.m requires a prolonged treatment time for plating, and may result in wrinkling of the molten filler material during subsequent brazing.

At a too high level of nickel salt in the aqueous bath there is the risk of the crystallization of the salt in the solution, which might damage a continuous process.

At too low levels the resultant bath becomes uneconomical due to too long plating times and low current density.

However, many bismuth compounds have been tried out but only very few appear to provide reliable and reproducible results.

For example also the combination of a bath of nickel-ions and bismuth-ions and a tartrate at a pH in the range of more than 8 resulted in the formation of an undesirable Ni containing sludge.

At too high levels of Bi-ion concentration in the aqueous bath the resultant deposit has an undesired high Bi-concentration.

At too low levels the resultant bath becomes uneconomical due to too long plating times and low current density.

Images