CA1158461A

CA1158461A - Zinc alloy powder for use in mechanical plating

Info

Publication number: CA1158461A
Application number: CA000346593A
Authority: CA
Inventors: Fumio Mizuno; Seil Sugimoto; Kenji Someno; Kazuaki Takahashi
Original assignee: Mitsui Mining and Smelting Co Ltd
Current assignee: Mitsui Kinzoku Co Ltd
Priority date: 1979-03-02
Filing date: 1980-02-28
Publication date: 1983-12-13
Also published as: DE3007850C2; DE3007850A1; FR2450281A1; GB2046302A; FR2450281B1

Abstract

ABSTRACT OF THE DISCLOSURE
There is disclosed various kinds of zinc-based alloy powders for use in mechanical plating of a substrate. For this purpose, useful zinc alloys include Zn-Al, Zn-Al-Cu, Zn-Al-Mg, An-Al-Cu-Mg and the other zinc alloys containing at least one of the metals selected from Ni, Si, Ti, Sb, Ag, Cr, Be, Ca, Co, Na, K, In, Li and Sr in the base metal or said alloys. Powders of these zinc alloys give tight adhesion of film coated onto a substrate, and excellent corrosion resistance when they are used in mechanical plating as compared with conventional mechanical plating using zinc powder.

Description

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m is invention relates to a zinc alloy pow~er ~or use in mechanical plating and an article thus plated.
In general, as metallic coating pro oe sses of various iron products, copper products and the like for improving the appearance and corrosion resist-an oe of those products, there are known the pro oe sses in which said products are coated with a molten metal by means of metal spraying, vaporization or direct dipping into the molten metal, as well as the so-called electroplating by which a metal to be coated is deposited electrically and the process in which the pro-ducts are coated mechanically. Am~ng these pro oe sses, the ~echanical coating pro-oe ss, i.e. the mechanical plating process, is advantageous in that a coating ofgiven thickness can be produoe d easily with a relatively simple apparatus so that the cost is low, and that faults observable in the other coating processes such as hydrogen embrittlement, blister, etc. do not appear at all, and this process is extensively employed currently. As plating materials for this process, powders of Zn, Cd, Sn, Pb, Sn-Zn alloy, Sn-Cd alloy and the like are used, among which Zn pcwder occupies the major part of the use.
Mechanical plating with such conventional compositions results in insufficient oorrosion resistant properties at circa 10 ~m film thickness to with-stand - 1- '~
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the 120 - 150 hour Neutral-Salt Spraying test, so that rust on the bare metal substrate can be seen. Thus, stronger corrosion resistance has been desired. Even where corrosion resistance is satisfactory, the thickness of the film would be unnecessarily thick, which is clearly uneconomical; there were some cases where adhesion was lowered thereby.
With the aim of improving the corrosion resistance of mechanical plating, the present inventors paid attention to the powder itself as a mechanical plating material and conducted extensive studies thereon. As the result, it was found that the corrosion resistance can be improved drastically and, at the same time, a good adhesion of coating film can be obtained by using, as a mechanical plating material, Zn-Al alloy powder, of which utilization in the powdery form has by no means been conceived hitherto though it has been used hitherto in zinc die casting, hot dip galvanizing, electroplating, etc. Furthermore, it was also confirmed that even some zinc alloy powders other than Zn-Al alloy powder can also improve the corrosion resistance, and in addition, that further improvement of the corrosion resistance can be achieved by incorporating a certain kind of additive elements to Zn-Al.
Thus, according to this invention, there is provided a method of coating a substrate by mechanical plating a substrate with a zinc alloy powder comprising zinc as base metal and one or more members selected from the group consisting of ~`~

~5~4~1 Al = 0.1 - 60, Ni - 5.0, M~ - 3.0, Cu - 3.0, Si - 2.0, Ti - 1.5, Sb - 1.0, Ag - 1.0, Cr - 0.5, Be - 0.5, Ca - 0.1, Co - 0.1, Na - 0.1, K - 0.1, In - 0.1, Li - 0.05, and Sr - 0.05 (each per oent by weight).
Thus, actual examples of the materials f m m which the zinc alloy powder of the present invention for use in mechanical pl~ting is to be produ oe d include Zn-Al, Zn-Al-Cu, Zn-Al-Mg, Zn-Al-Cu-Mg and other zinc alloys obtainable by incor-porating at least one of the other metals mentioned above into zinc or said alloys.
If the content of an individual ~itive element exceeds its cwn upper limit as a~ove, it may lead to various harmful effects such as formation of an intermetallic co~pound exercising an adverse influen oe upon adhesion, impossi-bility in alloying with zinc and formation of an needless oxides. If the oontent of individual ~;tive element is less than 0.01% by weight, no improNement of corrosion resistan oe may be observed sometimes with one additive element alone but even in such a case the effect can be e~hibited by adding tWD or more of addi-tive elements or cwing to the coexisten oe with Al. Regarding the content of Al, no improvement in corrosion resistan oe is o~servable when Al content is less than 0.1% by weight, while the coating cannot be practised sufficiently when Al oon-tent ex oe eds 60% by weight. ~hen Al content is 55% by weight or more, the adhe-sion becomes scmewhat poor. A~cordingly, the content of Al should be in therange of 0.1 - 60~ by weight and preferably in the range of 2 - 55% by weiqht.
Thus, Al is preferred as an alloying metal but not a prerequisite to obtaininq an alloy which can function in accordance with the obiectives of the invention. In ~ tion tD ~r in pla oe of Al, at least one of the above alloying elements with their per oe ntages may be inoorporated.
Such alloy powders can be prcduced by adding a given amDunt of the respective additive elements to Zn to adjust the composition of alloy to be pro-~' duced, and followed by any processes other than the distillation process, forexample, by means of mechanical processes such as dropping, graining, atomizing, grinding or the like, or dry or wet reduction process, electrolytic process, sub-stitution process or the like, amDng which atomizing process is mDst preferable.
m us, fine Zn alloy pow~ers having a dia~eter of 1 - 20 ~m and preferably 5 - 10 ~m can be obtained.
In this invention, there is no substantial inoonvenience even if one or more of Pb < 1.30% by weight, Fe < 0.025~ by weight, Cd < 0.40% by weight or Sn < 0.10% by weight are present in the zinc as possible impurities. Accordingly, zinc having a purity of grade 1 or higher, according to JIS H 2107, may be used in the present invention.
The substrate to be coated with the zinc alloy p~wder is not limited to metallic substrates such as iron, copper, brass and the like but it may also be nonmetallic ones. Further, the corrosion resistan oe can be much mDre improved if a conventional mechanical plating procedure is applied onto such a substrate with the zinc alloy pow~ers of the present invention and then, for example, - .~

1~5~4~1 a chromate treatment is carried out thereon.
The zinc alloy powders of this invention mentioned above satisfy the requirements regarding the characteristic properties necessary to the use in mechanical plating, such as activity to chemicals, particle size, shape and the like. Accordingly, when they are used for mechanical plating, the adhesion between metallic substrate and coating film is improved and that, the corrosion resistance of coating film increases about 2 to 10 times the conventional cases. Consequently a very desirable coating film can be formed, in addition to the advantages hitherto known in the mechanical plating.
The present invention will now be further described, by way of examples only, with reference to the accompanying drawings, in which:
Figure 1 illustrates the numerical evaluation for five rank standard of coating coverage after a peeling test.
Figures 2 and 3 illustrates films or coatings which were evaluated as "very good" and "bad" respectively, under a x 600 magnification.
After having formulated the components so as to give the composition as shown in the following table, according to the atomizing process the mixture was molten at 450 - 800C, the molten metal was rapidly cooled by injecting it with gas from a nozzle, and the powders thus obtained were subjected to surface cleaning and conditioning, drying and classification to give fine powders having a m~an particle diameter of 6 - ~ ~m.

4i~1 By using these powders, mechanical platings were carried out according to the known method. Thus, after degreasing a substrate to be treated, it was subjected to surface cleaning and conditioning, and flash-coating to form plating while tumbling it with an - Sa -~,~

~15~46i 1 impact media and chemical agents in a rotating barrel.
Thereafter, it was water-flooded and polished, after-treated, again water-washed and dried to obtain a film having a thickness of about 10 ~m.
The films thus obtained were examined for adhesion and for corrosion resistance after chromate treatment. The adhesion was evaluated by a method which comprises attaching the commercially available scotch tape No. 600 onto the surface of plating, peeling off the tape and then observing the coverage and adhesion of powder to the tape surface, and by a method which comprises microscopically observing the cross section of the plated body. The results of the tape peeling test were numerically expressed according to the five ran~
standard of evaluation as shown in Figure 1. The corrosion resistance was evaluated according to the neutral salt spray test (JIS Z 2371) by measuring the time period required for forming red rust in term of hour. It is generally considered that a corrosion resistance of 240 hours or more is desirable. Results of the examinations are summarized in Tables A and B.
The states of the films which were evaluated as "very good" and as "bad" in the adhesion ~est are s~own in Figure 2 (sample No. A-18) and Figure 3 (sample No. A-16), respectively.
Samples No. A-l to A-3 are controal examples by the use of zinc powder. Samples No. A-4, A-16, A-20 and A-22 are out of the scope of this invention, and ~L15~4bl 1 Samples No. B-l - 2 are control examples by the use of Zn powder alone. Samples No. B-12, B-16, B-20, B-27, B-30, B-39 and B-lll to B-113 are out of the scope of this invention.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of coating a substrate which comprises the step of mechanical plating of said substrate with a zinc alloy powder comprising zinc as base metal and one or more members selected from the group consisting of Al 0.1 - 60, Ni ? 5.0, Mg ? 3.0, Cu ? 3.0, Si ? 2.0, Ti ? 1.5, Sb ? 1.0, Ag ? 1.0, Cr ? 0.5, Be ? 0.5, Ca ? 0.1, Co ? 0.1, Na ? 0.1, K ? 0.1, In ? 0.1, Li ? 0.05 and Sr ? 0.05, each being in percent by weight of the total alloy.

2. The method according to claim 1 wherein the zinc alloy powder used for mechanical plating comprises 0.1 - 60% by weight of Al.

3. The method according to claim 2 wherein the zinc alloy powder used comprises one or two member(s) selected from Cu ? 3.0%
by weight and Mg ? 3.0% by weight, in addition to said 0.1 - 60% by weight of Al.

4. The method according to claim 2 or 3 wherein the zinc alloy powder used additionally comprises one or more members select-ed from the group consisting of Ni ? 5.0, Si ? 2.0, Ti ? 1.5, Sb ? 1.0, Ag ? 1.0, Cr ? 0.5, Be ? 0.5, Ca ? 0.1, Co ? 0.1, Na ? 0.1, K ? 0.1, In ? 0.1, Li ? 0.05 and Sr ? 0.05 each being percent by weight of the total alloy except the weight of impurities.

5. A coated article comprising a substrate mechanically plated with a zinc alloy powder, said zinc alloy powder comprising zinc as the base metal and one or more members selected from the group consisting of Al 0.1-60, Ni ? 5.0, Mg ? 3.0, Cu ? 3.0, Si ? 2.0, Ti ? 1.5, Sb ? 1.0, Ag ? 1.0, Cr ? 0.5, Be ? 0.5, Ca ? 0.1, Co ? 0.1, Na ? 0.1 K ? 0.1, In ? 0.1, Li ? 0.05 and Sr ? 0.05, each being in percent by weight of the total alloy.

6. An article as defined in claim 5 wherein the zinc alloy powder comprises 0.1 - 60% by weight of Al.

7. An article as defined in claim 6 wherein the zinc alloy powder additionally comprises at least one of 0.01 - 3.0% by weight of Cu and 0.01 - 3.0% by weight of Mg.

8. An article as defined in claim 6 or 7 wherein the zinc alloy additionally comprises one or more members selected from the group consisting of Ni 0.01 - 5.0, Si 0.01 - 2.0, Ti 0.01 - 1.5, Sb 0.01 - 1.0, Ag 0.01 - 1.0, Cr 0.01 - 0.5, Be 0.01 - 0.5, Ca 0.01 - 0.1, Co 0.01 - 0.1, Na 0.01 - 0.1, K 0.01 - 0.1, In 0.01 - 0.1, Li 0.01 - 0.05 and Sr 0.01 - 0.05, each being in percent by weight of the total alloy.