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(11) |
EP 1 186 679 A1 |
| (12) |
EUROPEAN PATENT APPLICATION |
| (43) |
Date of publication: |
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13.03.2002 Bulletin 2002/11 |
| (22) |
Date of filing: 12.09.2000 |
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International Patent Classification (IPC)7: C23C 2/06 |
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Designated Contracting States: |
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AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE |
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Designated Extension States: |
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AL LT LV MK RO SI |
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Applicant: n.v. Umicore s.a. |
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1000 Bruxelles (BE) |
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Inventor: |
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- Gilles, Mik,
c/o N.V. Union Miniere S.A.
2250 Olen (BE)
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Representative: Saelemaekers, Juul et al |
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Umicore Research
Patent Department
Kasteelstraat 7
2250 Olen
2250 Olen (BE) |
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| (54) |
Hot-dip galvanising alloy and process |
(57) Alloy and process for galvanising steel by immersion in a zinc alloy containing bath
comprising by weight 0.1 to less than 1% Bi, 0.01 to 0.05% Al, 0.04 to 0.12% Ni up
to 0.05% Mn, the rest being zinc and unavoidable impurities.
[0001] The present invention relates to a bath for hot-dip galvanising consisting of alloyed
zinc, that is particularly useful for batchwise galvanising steel articles.
[0002] Conventional galvanisation practice results in a coating thickness of 70 to 120 µm.
A drawback of such thick coatings is the reduced resistance to stress induced crack
formation.
[0003] The aim of the present invention is therefore to provide a bath composition for hot-dip
galvanising, which results in a coating thickness of 30 to 50 µm. Also, the thickness
of the intermetallic layer is reduced to approximately 30 to 35 µm. This induces an
increased resistance to stress induced crack formation as required e.g. for critical
parts in the automotive industry.
[0004] According to the invention the bath contains, by weight, 0.1 to less than 1 % Bi,
0.01 to 0.05 % Al, 0.04 to 0.12 % Ni, up to 0.05 % Mn, the rest being zinc and unavoidable
impurities. Preferably, the bath contains 0.3 to 0.8 % Bi, 0.02 to 0.04 % Al, 0.06
to 0.10 % Ni and up to 0.05 % Mn. A bath composition with 0.5 % Bi, 0.03 % Al and
0.08 % Ni is especially preferred.
[0005] The galvanising process using the alloy of the invention is particularly suitable
for coating low reactivity steel. By low reactivity steel is meant steel comprising,
by weight, Si and P in such amounts that Si < 0.03 % and % Si + 2.5 x % P < 0.09.
1. An alloy for hot-dip galvanising steel comprising, by weight, 0.1 to less than 1 %
Bi, 0.01 to 0.05 % Al, 0.04 to 0.12 % Ni, up to 0.05 % Mn, the rest being zinc and
unavoidable impurities.
2. An alloy according to claim 1, comprising, by weight, 0.3 to 0.8 % Bi, 0.02 to 0.04
% Al, 0.06 to 0.10 % Ni, up to 0.05 % Mn, the rest being zinc and unavoidable impurities.
3. A process for galvanising steel by immersion in a zinc alloy galvanising bath comprising
the step of immersing the steel articles in a molten bath of a zinc alloy comprising,
by weight, 0.1 to less than 1 % Bi, 0.01 to 0.05 % Al, 0.04 to 0.12 % Ni, up to 0.05
% Mn, the rest being zinc and unavoidable impurities.
4. A process according to claim 3, characterised in that the steel articles comprise, by weight, Si and P in such amounts that Si < 0.03 %
and % Si + 2.5 x % P < 0.09.