LU85522A1 - Zinc-aluminium hot dip coating baths - contg. boron, titanium and/or zirconium for grain refining - Google Patents

Abstract

Hot dip coating baths, contg. zinc and 9-70 (pref. max. 40)% Al, additionally contain one or more of B, Ti and Zr, pref. in amt. less than 1%. Pref. the baths comprise Zn, 3-7% Al and one or more of 0.005-0.050% B, 0.005-0.050% Ti and less than 0.5% Zr. When B and Ti are added together, the B:Ti ratio is pref. 1:5. The baths are useful for hot dip galvanising of steel sheet e.g. for the automobile industry. The additive gives reduced spangling and a structure of good homogeneity, by grain refining the galvanised coating.

Description

* C 2266/8308.

j METALLURGICAL RESEARCH CENTER - CENTRUM V00R RESEARCH IN DE METALLURGIE,

Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Bath for hot coating.

The present invention relates to a bath for hot coating and more particularly a bath as used in galvanizing, when one proceeds to the deposition of zinc or zinc alloys on a metallic substrate such as steel.

| It has long been known to use galvanization! to protect steel sheets from corrosion. Over time, we have extended the applications of galvanized sheets, for example in the automotive industry, and we have also diversified / i fi * 4 *! -2 - coatings by creating more or less complex zinc-based alloys.

In general, the criteria considered are as follows: i; "- the visual appearance of the surface? i; - the polish of the deposit; - the ability to paint, i - the homogeneity of the structure of the coating and its properties.

One of the major problems with the surface appearance relates to flowering, that is, the appearance of patterns on the surface of the coating.

One solution proposed in order to reduce this flowering consists of accelerated cooling after passage through the gavage bath. For this purpose, so-called flowering minimization systems are used which spray water vapor loaded with inoculants, zinc dust, etc. onto the coating.

1 However, these systems are expensive, difficult in their implementation and they complicate the work of a galvanizing installation.

The bath, object of the present invention, makes it possible to obtain a coating whose flowering is very weak and which moreover gives rise to a structure whose homogeneity is very good.

This bath comes from a conventional hot coating bath to which one or more judiciously chosen elements have been added. ment for their action of refining the grain of the coating obtained.

AT

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The bath for hot coating, object of the present invention, comprising zinc, from 0 to 70% aluminum and possibly other elements, is essentially characterized in that it also contains boron and / or titanium and / or zirconium; these v three elements can be alone or in the form of any possible combination between them or with other elements.

According to a first embodiment of the bath of the invention, it mainly comprises zinc and at most 40% aluminum.

According to a second embodiment of the bath of the invention, it comprises between 3% and 7% of aluminum.

According to another embodiment of the bath of the invention, it comprises mischmetall; the term mischmetall being a generic term to designate alloys based on lanthanum and cerium and other rare earths.

According to yet another embodiment of the bath of the invention, it comprises Pb, Sn, Ca, Cu, Mg, Co, Sb, Be in proportion less than 1%; preferably less than 0.5%.

According to a preferred embodiment of the invention, the boron content is less than 1%, preferably between 0.005 and 0.050%.

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According to a sixth embodiment of the invention, the titanium content is less than 1%, preferably between / between 0.005 and 0.050%.

According to a seventh embodiment of the invention, the zirconium content is less than 1%, preferably less than 0.5% & f

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According to another embodiment of the invention, the ratio between the boron and titanium contents is close to 1: 5.

not !

Claims (9)

1. Bath for hot coating, comprising zinc, O to 70% aluminum and possibly other elements, characterized in that it also contains boron and / or titanium and / or zirconium; these three elements can be alone or in the form of any possible combination between them or with other elements. 2. Bath according to claim 1, characterized in that it mainly comprises zinc and at most 40% aluminum. 3. Bath according to claims 1 or 2, characterized in that it comprises between 3% and 7% of aluminum. i i 4. Bath according to any one of claims 1 to 3, ca acterized in that it comprises mischmetall. 5. Bath according to either of claims 1 to 4, characterized in that it comprises Pb, Sn, Ca, Cu, Mg, Co, Sb, Be in proportion less than 1%, preferably less at 0.5%. 6. Bath according to either of claims 1 to 5, characterized in that the boron content is less than 1%, preferably between 0.005 and 0.050%. " 7. Bath according to one or more of claims 1 to 6, charac- terized in that the titanium content is less than 1%, preferably between 0.005 and 0.050%. y \ \ - 6 - 8. Bath according to one or more of claims 1 to 7, characterized in that the zirconium content is less than 1%, preferably less than 0.5%. 9. Bath according to either of claims 1 to 8, characterized in that the ratio between the boron and titanium contents is close to 1: 5.%