EP1722007B1 - Dissimilar metal joint member with good corrosion resistance and method for manufacturing same - Google Patents
Dissimilar metal joint member with good corrosion resistance and method for manufacturing same Download PDFInfo
- Publication number
- EP1722007B1 EP1722007B1 EP20050010354 EP05010354A EP1722007B1 EP 1722007 B1 EP1722007 B1 EP 1722007B1 EP 20050010354 EP20050010354 EP 20050010354 EP 05010354 A EP05010354 A EP 05010354A EP 1722007 B1 EP1722007 B1 EP 1722007B1
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- EP
- European Patent Office
- Prior art keywords
- corrosion
- metal
- ions
- aluminium
- zinc
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 238000005260 corrosion Methods 0.000 title claims description 40
- 230000007797 corrosion Effects 0.000 title claims description 40
- 229910052751 metal Inorganic materials 0.000 title claims description 40
- 239000002184 metal Substances 0.000 title claims description 40
- 238000000034 method Methods 0.000 title claims description 18
- 238000004519 manufacturing process Methods 0.000 title claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 36
- 229910052782 aluminium Inorganic materials 0.000 claims description 18
- 229910052742 iron Inorganic materials 0.000 claims description 18
- 239000004411 aluminium Substances 0.000 claims description 17
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 17
- 150000002500 ions Chemical class 0.000 claims description 15
- 239000011701 zinc Substances 0.000 claims description 14
- 125000001153 fluoro group Chemical group F* 0.000 claims description 13
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 12
- 229910052725 zinc Inorganic materials 0.000 claims description 12
- 229910000838 Al alloy Inorganic materials 0.000 claims description 10
- 239000000463 material Substances 0.000 claims description 10
- PTFCDOFLOPIGGS-UHFFFAOYSA-N Zinc dication Chemical compound [Zn+2] PTFCDOFLOPIGGS-UHFFFAOYSA-N 0.000 claims description 8
- 239000000956 alloy Substances 0.000 claims description 8
- -1 hexafluorosilicate ions Chemical class 0.000 claims description 7
- 238000006243 chemical reaction Methods 0.000 description 10
- 239000000126 substance Substances 0.000 description 8
- 150000002739 metals Chemical class 0.000 description 7
- 239000003973 paint Substances 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- 229910000831 Steel Inorganic materials 0.000 description 6
- 239000007769 metal material Substances 0.000 description 6
- 239000010959 steel Substances 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 238000005266 casting Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 229910007607 Zn(BF4)2 Inorganic materials 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 4
- 238000005507 spraying Methods 0.000 description 4
- 229910001297 Zn alloy Inorganic materials 0.000 description 3
- KCZFLPPCFOHPNI-UHFFFAOYSA-N alumane;iron Chemical compound [AlH3].[Fe] KCZFLPPCFOHPNI-UHFFFAOYSA-N 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 238000010420 art technique Methods 0.000 description 3
- 125000002091 cationic group Chemical group 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 239000002131 composite material Substances 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- 238000004070 electrodeposition Methods 0.000 description 3
- 238000007654 immersion Methods 0.000 description 3
- 229910000510 noble metal Inorganic materials 0.000 description 3
- 238000010422 painting Methods 0.000 description 3
- 230000001737 promoting effect Effects 0.000 description 3
- 230000009257 reactivity Effects 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 2
- 150000001450 anions Chemical class 0.000 description 2
- 150000001768 cations Chemical class 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000005238 degreasing Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 150000004761 hexafluorosilicates Chemical class 0.000 description 2
- 230000002401 inhibitory effect Effects 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000007747 plating Methods 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 150000003751 zinc Chemical class 0.000 description 2
- 229910001018 Cast iron Inorganic materials 0.000 description 1
- 229910000531 Co alloy Inorganic materials 0.000 description 1
- 229910017518 Cu Zn Inorganic materials 0.000 description 1
- 229910017752 Cu-Zn Inorganic materials 0.000 description 1
- 229910017943 Cu—Zn Inorganic materials 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- WAEMQWOKJMHJLA-UHFFFAOYSA-N Manganese(2+) Chemical compound [Mn+2] WAEMQWOKJMHJLA-UHFFFAOYSA-N 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- IOVCWXUNBOPUCH-UHFFFAOYSA-M Nitrite anion Chemical compound [O-]N=O IOVCWXUNBOPUCH-UHFFFAOYSA-M 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 238000003287 bathing Methods 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- TVZPLCNGKSPOJA-UHFFFAOYSA-N copper zinc Chemical compound [Cu].[Zn] TVZPLCNGKSPOJA-UHFFFAOYSA-N 0.000 description 1
- 238000005536 corrosion prevention Methods 0.000 description 1
- 238000005237 degreasing agent Methods 0.000 description 1
- 239000013527 degreasing agent Substances 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 238000001962 electrophoresis Methods 0.000 description 1
- 238000009713 electroplating Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- UQSQSQZYBQSBJZ-UHFFFAOYSA-M fluorosulfonate Chemical compound [O-]S(F)(=O)=O UQSQSQZYBQSBJZ-UHFFFAOYSA-M 0.000 description 1
- 229910001437 manganese ion Inorganic materials 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 229910001453 nickel ion Inorganic materials 0.000 description 1
- 229940005654 nitrite ion Drugs 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 229940085991 phosphate ion Drugs 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 230000004580 weight loss Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
- LRXTYHSAJDENHV-UHFFFAOYSA-H zinc phosphate Chemical compound [Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O LRXTYHSAJDENHV-UHFFFAOYSA-H 0.000 description 1
- 229910000165 zinc phosphate Inorganic materials 0.000 description 1
- 229910000368 zinc sulfate Inorganic materials 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/54—Contact plating, i.e. electroless electrochemical plating
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/78—Pretreatment of the material to be coated
Definitions
- This invention relates to the manufacture of a member having an excellent bimetallic corrosion resistance used at an aluminium-iron dissimilar metal joint portion employed such as in automobiles and the like.
- Such bimetallic corrosion as mentioned above occurs in such a way that a potential difference is caused between the metals due to the difference in ionization tendency therebetween, thereby causing a corrosion current to pass.
- the following counter measures are conventionally known.
- a metal indicating a less noble potential and a metal indicating a more noble potential are brought into contact with each other, a metal exhibiting an intermediate potential is sprayed onto a metal side indicating the less noble potential.
- the metal spraying may be effected on either of the less noble and more noble metals or both thereof. In this way, the potential difference between both metals can be lessened, thus enabling one to reduce electrolytic corrosion of the metal of the less noble potential.
- a paint having selective anion transmission action is undercoated on a surface of a metal, selected from two types of metals in contact with each other in an aqueous solution, on which an anode is formed. Thereafter, a paint having selective cation transmission action may be overcoated, or a cationic exchange film may be bonded with the undercoating paint to cover the undercoating therewith.
- an ionic exchange composite film may be bonded by means of an undercoating paint as used above such that a pain having cation transmission action is undercoated on a metal surface where a cathode is formed and another type of paint having selective anion transmission action is overcoated, or ionic electrophoresis between metals may be interrupted by other technique to prevent bimetallic corrosion.
- Terminals are attached to different types of metal materials, between which a DC voltage is applied so as to prevent the metal materials from being ionized, thereby inhibiting the occurrence of electrolytic corrosion.
- a conductive paint containing a large amount of a metal which is less noble than aluminium is applied onto metal surfaces of a relay box and an anchor housing.
- a counterpart metal material of dissimilar metal materials contacting with each other such as a Zn alloy, Fe, Al or the like, i.e. a less-noble metal material, is reduced in corrosion weight loss.
- a different type of metal is plated on both sides of a sheet made of a metal having an ionization tendency larger than iron to provide an anticorrosive sheet which has a natural electrode potential difference from a steel sheet at 0 to -'300 mV.
- This anticorrosive sheet is sandwiched between two jointing sheets of steel thereby forming an anticorrosive layer.
- US 2004/0016363 A1 discloses a corrosion-inhibiting coating process, and system, that provides a tight, adherent zinc- or zinc-alloy coating that is directly deposited onto steel or cast iron surfaces for corrosion prevention, wherein the process includes the application of two sequential aqueous baths.
- a method of preventing stress corrosion with the aluminium alloy casting is provided. More particularly, this method is to prevent stress corrosion of the aluminium alloy casting by interposing, at least a part of an area of contact between the casting and the steel member, a metal member or metal layer which is less noble by 100 mV vs SCE or over or is more noble by -1500 mV vs SCE in terms of mixed potential than the natural potential of the casting.
- metallic zinc is caused to exist, as deposited, in the vicinity of a jointed portion of an iron material that is electrochemically more noble than aluminium, and aluminium or an aluminium alloy material, so that a resistance to bimetallic corrosion can be reliably improved.
- Fig. 1 is a schematic view showing a deposited state of metallic zinc and a mechanism of suppressing corrosion in the vicinity of a joint portion (i.e. a joint-affecting portion) of an aluminium-iron joint member obtained according to the invention;
- Fig. 2 is a schematic view showing a mechanism of promoting corrosion in the vicinity of a joint portion (i.e. joint-affecting portion) of an aluminium-iron joint member.
- aluminium material or merely as aluminium aluminium
- iron material or merely as iron iron
- aluminium (Al) that is a metal less noble than iron (Fe) is converted to Al 3+ ions and dissolved out, thereby promoting corrosion. This is because a corrosion current flows between both materials due to a great potential difference between aluminium and iron.
- the deposited layer of iron is dense and high in adhesion and is thus unlikely to disappear through peeling-off or breakage and can be held as attached over a long time. As a consequence, the influence of potential difference is mitigated, thereby ensuring effective suppression of corrosion.
- fluoro complex ions are able to dissolve an oxide film on an aluminium surface and thus, serve to cause the above reaction to proceed smoothly.
- the salts containing fluoro complex ions include, for example, a hexafluorosilicate, tetrafluoroborate, hexafluorophosphate, and fluorosulfate.
- a hexafluorosilicate or a tetrafluoroborate In view of the stability and reactivity, it is preferred to use a hexafluorosilicate or a tetrafluoroborate.
- the treating time should preferably be within a range of 30 seconds to 3 minutes from the standpoint of ensuring corrosion resistance of joint member and productivity.
- the treating time is preferably not lower than 40°C in view of the reactivity and the ease in temperature control and not higher than 80°C in view of suppressing evaporation of treating solution.
- joint member means a portion interposed between members in ordinary cases, for which that portion cannot be treated by other methods such as electroplating, metal spraying and the like.
- the invention is more particularly described by way of example.
- a mild steel plate (30 ⁇ 100 ⁇ 0.8 mm) and each of aluminium plates (6022 and 5023 with a dimension of 30 ⁇ 100 ⁇ 0.8 mm) were spot welded under conditions of 12 kV and 200 ms.
- Treating procedure treating in the order of (a) degreasing ⁇ (b) rinsing with water ⁇ (c) surface adjustment ⁇ (d) chemical conversion (dipping) ⁇ (e) drying after chemical conversion ⁇ (f) rinsing with water ⁇ (g) rinsing with pure water ⁇ (h) drying by drainage ⁇ (i) painting.
- a cationic electrodeposition paint (commercially available from Nippon Paint Co., Ltd., with a commercial name of "Power Top V50 Gray”) was pained by cationic electrodeposition painting and baked at a temperature of 170°C for 25 minutes to form a 30 ⁇ m thick pain film.
- Test pieces made in (1) to (4) above were subjected to a composite corrosion test to evaluate bimetallic corrosion resistance.
- the corrosion test was conducted by repeating 100 times a cycle test having each cycle of 2 hours salt spraying, 2 hours drying and 2 hours wetting. Thereafter, the joint portion was peeled off and observed to assess corrosion resistivity (a maximum depth of corrosion of A1).
- the results of the assessment of the corrosion resistivity and chemical conversion are shown in Tale 1.
- the corrosion resistivity was evaluated by measuring a maximum depth of corrosion of A1 (mm) and ranking according to the following three phases ⁇ : 0 to 0. 01 (mm), ⁇ : 0.01 to 0.1 (mm), and ⁇ : larger than 0.1 (mm) .
- the chemical conversion was evaluated by measuring an amount of deposited film and ranking according to the following three phases: ⁇ :1 to 2 (g/m 2 ), ⁇ : 0.5 to 1 (g/m 2 ) and ⁇ : 0 to 0.5 (g/m 2 )
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- Chemical & Material Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrochemistry (AREA)
- Prevention Of Electric Corrosion (AREA)
Description
- This invention relates to the manufacture of a member having an excellent bimetallic corrosion resistance used at an aluminium-iron dissimilar metal joint portion employed such as in automobiles and the like.
- It is known in the art that when using dissimilar metals in combination at a joint of members of automobiles and the like, the metals are in mutual contact with each other to allow electric conduction therebetween, thereby promoting corrosion.
- Such bimetallic corrosion as mentioned above occurs in such a way that a potential difference is caused between the metals due to the difference in ionization tendency therebetween, thereby causing a corrosion current to pass. To avoid the bimetallic corrosion, the following counter measures are conventionally known.
- (1) Prior art 1 (
Japanese Laid-open Patent Application No. Sho 55-6411 - Where a metal indicating a less noble potential and a metal indicating a more noble potential are brought into contact with each other, a metal exhibiting an intermediate potential is sprayed onto a metal side indicating the less noble potential. The metal spraying may be effected on either of the less noble and more noble metals or both thereof. In this way, the potential difference between both metals can be lessened, thus enabling one to reduce electrolytic corrosion of the metal of the less noble potential.
- (2) Prior art 2 (
Japanese Laid-open Patent Application No. Sho 60-58272 - A paint having selective anion transmission action is undercoated on a surface of a metal, selected from two types of metals in contact with each other in an aqueous solution, on which an anode is formed. Thereafter, a paint having selective cation transmission action may be overcoated, or a cationic exchange film may be bonded with the undercoating paint to cover the undercoating therewith. Alternatively, an ionic exchange composite film may be bonded by means of an undercoating paint as used above such that a pain having cation transmission action is undercoated on a metal surface where a cathode is formed and another type of paint having selective anion transmission action is overcoated, or ionic electrophoresis between metals may be interrupted by other technique to prevent bimetallic corrosion.
- (3) Prior art 3 (
Japanese Laid-open Patent Application No. Sho 61-23777 - Terminals are attached to different types of metal materials, between which a DC voltage is applied so as to prevent the metal materials from being ionized, thereby inhibiting the occurrence of electrolytic corrosion.
- (4) Prior art 4 (
Japanese Patent Publication No. 54-28941 - A conductive paint containing a large amount of a metal which is less noble than aluminium is applied onto metal surfaces of a relay box and an anchor housing.
- (5) Prior art 5 (
Japanese Patent Publication No. 59-37753 - When Cr is plated on surfaces of metals such as Cu, Cu-Zn alloys and Ni, a counterpart metal material of dissimilar metal materials contacting with each other, such as a Zn alloy, Fe, Al or the like, i.e. a less-noble metal material, is reduced in corrosion weight loss.
- (6) Prior art 6 (
Japanese Laid-open Patent Application No. Hei 5-222557 - A different type of metal is plated on both sides of a sheet made of a metal having an ionization tendency larger than iron to provide an anticorrosive sheet which has a natural electrode potential difference from a steel sheet at 0 to -'300 mV. This anticorrosive sheet is sandwiched between two jointing sheets of steel thereby forming an anticorrosive layer.
- (7) Prior art 7 (
Japanese Laid-open Patent Application No. Hei 7-252679 - A body made of a different type of metal in contact with an aluminium alloy is plated with a zinc/cobalt alloy having a cobalt content of 1 to 5 wt% based on the alloy plating. (8) Prior art 8 (
Japanese Laid-open Patent Application No. Hei 9-157870 -
US 2004/0016363 A1 discloses a corrosion-inhibiting coating process, and system, that provides a tight, adherent zinc- or zinc-alloy coating that is directly deposited onto steel or cast iron surfaces for corrosion prevention, wherein the process includes the application of two sequential aqueous baths. - In a structure where an aluminium alloy casting having stress corrosion susceptibility and a steel member of a different type of metal come into contact with each other under a stress load, a method of preventing stress corrosion with the aluminium alloy casting is provided. More particularly, this method is to prevent stress corrosion of the aluminium alloy casting by interposing, at least a part of an area of contact between the casting and the steel member, a metal member or metal layer which is less noble by 100 mV vs SCE or over or is more noble by -1500 mV vs SCE in terms of mixed potential than the natural potential of the casting.
- As will be apparent from the above, a variety of methods of preventing bimetallic corrosion have been proposed. Assuming practical application to joint or jointing members, these prior art techniques have the following problems. More particularly, with the prior art 1, use of metal spraying involves a difficulty in application to members of complicated profiles. The
prior arts 2, 4 and 8 involve a difficulty in coating a joint at a very near proximity or slit thereof. With theprior art 3, it would be difficult to stably apply, in transport airplanes or building materials, a DC voltage after provision of terminals at metal materials. With the prior art 5 where Cr plating is effected on noble metals, limitation is placed on a size of a member to be applied, in addition, there also might be an environmental problem of chromium-pollution. With the prior art 6, inserting a sheet plated with a different type of metal at a joint is very difficult from a standpoint of fabrication, with the possibility that the sheet may be lost upon application of heat used for jointing. Where the technique of the prior art 7 is applied to a joint member, the plated metal at the joint portion is removed by melting, with a reduced effect being expected. - It is accordingly an object of the invention to provide a method of manufacturing, a member made of an iron material and aluminium or an aluminium alloy material jointed together by practically suitable means thereby imparting excellent corrosion resistance thereto.
- In order to achieve the above object, it is contemplated to provide the following methods.
- (1) A method for manufacturing a dissimilar metal joint member having an excellent corrosion resistance, which comprises immersing a member made of an iron material and aluminium or an aluminium alloy material jointed together in a solution containing fluoro complex ions and zinc ions so that metallic zinc is deposited in the vicinity of the jointed portion.
- (2) The method as recited in (1) above, wherein the fluoro complex ions consist of hexafluorosilicate ions or tetrafluoroborate ions.
- (3) The method as recited in (1)or (2), wherein : concentrations of the fluoro complex ions and zinc ions are, respectively, at 2 mmols/L or over.
- (4) Thereby, it is obtained a dissimilar metal joint member having an excellent corrosion resistance comprising an iron material and aluminium or an aluminium alloy material jointed together, and metallic zinc existing in the vicinity of a joint at a joint face side of the iron material.
- (5) The obtained dissimilar metal joint member as recited in (4) above, wherein the metallic zinc is made of a deposited one.
- (6) The obtained dissimilar metal joint member as recited in (4),
- According to the invention, metallic zinc is caused to exist, as deposited, in the vicinity of a jointed portion of an iron material that is electrochemically more noble than aluminium, and aluminium or an aluminium alloy material, so that a resistance to bimetallic corrosion can be reliably improved.
-
Fig. 1 is a schematic view showing a deposited state of metallic zinc and a mechanism of suppressing corrosion in the vicinity of a joint portion (i.e. a joint-affecting portion) of an aluminium-iron joint member obtained according to the invention; and -
Fig. 2 is a schematic view showing a mechanism of promoting corrosion in the vicinity of a joint portion (i.e. joint-affecting portion) of an aluminium-iron joint member. - When members of aluminium or an aluminium alloy material (hereinafter referred to as an aluminium material or merely as aluminium) and iron, steel or an iron alloy (hereinafter referred to as an iron material or merely as iron) are jointed, it is usual that aluminium (Al) that is a metal less noble than iron (Fe) is converted to Al3+ ions and dissolved out, thereby promoting corrosion. This is because a corrosion current flows between both materials due to a great potential difference between aluminium and iron.
- In order to prevent the promotion of the corrosion, it would occur that such a great potential difference is lessened by the existence of a metal having an ionization tendency intermediate between aluminium and iron at the.dissimilar metal joint-affecting portion. The previously stated prior art techniques also make use of such a principle as mentioned above so as to suppress contact corrosion.
- However, the prior art techniques have such problems as set out hereinbefore in practice. Especially, a difficulty is involved in permitting a metal having an intermediate ionization tendency to sufficiently exist in the closest vicinity of the joint portion or at a small interstice. This is why such techniques have never been put into practice.
- Under these circumstances in the art, intensive and continuous experimental efforts and studies have been made and, as a result, it has been found that when an aluminium and iron joint member is immersed in a solution containing fluoro complex ions and zinc ions to permit dense, strong and adhesive metallic zinc to reliably exist in the vicinity of the joint portion. The metallic zinc has an ionization tendency intermediate between aluminium and iron, so that the joint member shows an excellent resistance to bimetallic corrosion.
- According to this method of immersing a joint body in a solution containing fluoro complex ions and zinc ions, the potential difference between both materials is used to cause the following reaction
2Al + 3Zn2+ → 2Al3+ + 3Zn
to proceed at a site or portion which suffers an influence of potential difference resulting from dissimilar metal joint in the vicinity of the joint portion. Eventually, as shown inFig. 1 , metallic zinc can be deposited on and attached to the surface of the iron at this site, thereby causing the zinc to exist thereat. This zinc is formed by deposition, and thus, can be reliably and satisfactorily attached to the iron surface in the vicinity of the joint portion even if the joint portion is very narrow. In addition; the deposited layer of iron is dense and high in adhesion and is thus unlikely to disappear through peeling-off or breakage and can be held as attached over a long time. As a consequence, the influence of potential difference is mitigated, thereby ensuring effective suppression of corrosion. - Further, fluoro complex ions are able to dissolve an oxide film on an aluminium surface and thus, serve to cause the above reaction to proceed smoothly.
- The salts containing fluoro complex ions include, for example, a hexafluorosilicate, tetrafluoroborate, hexafluorophosphate, and fluorosulfate. In view of the stability and reactivity, it is preferred to use a hexafluorosilicate or a tetrafluoroborate.
- The treating time should preferably be within a range of 30 seconds to 3 minutes from the standpoint of ensuring corrosion resistance of joint member and productivity. The treating time is preferably not lower than 40°C in view of the reactivity and the ease in temperature control and not higher than 80°C in view of suppressing evaporation of treating solution.
- It will be noted that the vicinity of joint member means a portion interposed between members in ordinary cases, for which that portion cannot be treated by other methods such as electroplating, metal spraying and the like.
- The invention is more particularly described by way of example.
- A mild steel plate (30 × 100 × 0.8 mm) and each of aluminium plates (6022 and 5023 with a dimension of 30 × 100 × 0.8 mm) were spot welded under conditions of 12 kV and 200 ms.
- Immersed in solutions indicated in Table 1 at 60°C for 30 to 129 seconds.
- Treating procedure: treating in the order of (a) degreasing→(b) rinsing with water→(c) surface adjustment→(d) chemical conversion (dipping)→(e) drying after chemical conversion→(f) rinsing with water→(g) rinsing with pure water→(h) drying by drainage→(i) painting.
- (a) Degreasing: using an aqueous solution of 1.5 wt% of "A" agent and 0.9 wt% of "B" agent of an alkaline degreasing agent (commercially available from Nippon Paint Co., Ltd., with a commercial name of "Surf Cleaner SD250") for immersion at 43°C for 2 minutes.
- (b) Rinsing with water: immersed in city water at room temperature for 15 seconds.
- (c) Surface adjustment: using an aqueous solution of 0.1 wt% of a surface adjuster (commercially available with a commercial name of "Surf Fine 5N-10" for bathing for immersion of a target metal at room temperature for 30 seconds.
- (d) Chemical conversion: carried out by immersing a member to be treated in a bath of the following zinc phosphate treating agent at 50°C for 2 minutes.
Zinc ion: 1 g/liter, nickel ion: 1.0 g/liter, manganese ion: 0.8 g/liter, phosphate ion: 15.0 g/liter, nitrate ion: 6.0 g/liter, nitrite ion: 0.12 g/liter
Toner value: 2.5 pts, total acidity: 22 pts, free acidity: 0.3 to 0.5 pts - A cationic electrodeposition paint (commercially available from Nippon Paint Co., Ltd., with a commercial name of "Power Top V50 Gray") was pained by cationic electrodeposition painting and baked at a temperature of 170°C for 25 minutes to form a 30 µm thick pain film.
- Test pieces made in (1) to (4) above were subjected to a composite corrosion test to evaluate bimetallic corrosion resistance. The corrosion test was conducted by repeating 100 times a cycle test having each cycle of 2 hours salt spraying, 2 hours drying and 2 hours wetting. Thereafter, the joint portion was peeled off and observed to assess corrosion resistivity (a maximum depth of corrosion of A1).
- The results of the assessment of the corrosion resistivity and chemical conversion are shown in Tale 1. The corrosion resistivity was evaluated by measuring a maximum depth of corrosion of A1 (mm) and ranking according to the following three phases ○ : 0 to 0. 01 (mm), Δ: 0.01 to 0.1 (mm), and × : larger than 0.1 (mm) . The chemical conversion was evaluated by measuring an amount of deposited film and ranking according to the following three phases: ○:1 to 2 (g/m2), Δ: 0.5 to 1 (g/m2) and × : 0 to 0.5 (g/m2)
- From the table, it will be seen that the inventive examples 1 to 9 are excellent in both chemical conversion property and corrosion resistivity. On the other hand, with Comparative Example 10, because of the low reactivity of fluoro complex ions, the effect is unsatisfactory.
Table 1 No. Type of Al Zn ion (mmols/Liter) Fluoro Complex Ion (mmols/Liter) Treating Time (seconds) Component In Treating Solution [Concentration (g/Liter)] Chemical Conversion Property of Al Corrosion Resistance of Al Remarks 1 6022 2.5 2.5 30 ZnSiF6 0.5 O O Inventive Example 2 6022 22 22 30 ZnSiF6 4.5 O O Inventive Example 3 . 6022 4 8 30 Zn(BF4)2 1 O O Inventive Example 4 6022 19 38 30 Zn(BF4)2 4.5 O O Inventive Example 5 6022 27 27 30 ZnSiF6 5.5 O O Inventive Example 6 6022 23 46 30 Zn(BF4)2 5.5 O O Inventive Example 7 5023 27 27 30 ZnSiF6 5.5 O O Inventive Example 8 6022 0.4 0.8 120 Zn(BF4)2 0.1 O O Inventive Example 9 6022 1 1 60 ZnSiF6 0.2 O O Inventive Example 10 6022 30 30 60 ZnS04F 5.5 Δ X Comparative Example
Claims (3)
- A method for manufacturing a dissimilar metal joint member having an excellent corrosion resistance, which comprises immersing a member made of an iron material and aluminium or an aluminium alloy material jointed together in a solution containing fluoro complex ions and zinc ions so that metallic zinc is deposited in the vicinity of the jointed portion.
- The method according to Claim 1, wherein the fluoro complex ions consist of hexafluorosilicate ions or tetrafluoroborate ions.
- The method according to Claim 1 or 2, wherein concentrations of the fluoro complex ions and zinc ions are, respectively, at 2 mmols/liter or over.
Priority Applications (2)
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DE200560009665 DE602005009665D1 (en) | 2005-05-12 | 2005-05-12 | Component with connection between different metals and good resistance to corrosion and method of manufacture |
EP20050010354 EP1722007B1 (en) | 2005-05-12 | 2005-05-12 | Dissimilar metal joint member with good corrosion resistance and method for manufacturing same |
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EP20050010354 EP1722007B1 (en) | 2005-05-12 | 2005-05-12 | Dissimilar metal joint member with good corrosion resistance and method for manufacturing same |
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EP1722007B1 true EP1722007B1 (en) | 2008-09-10 |
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JPS5739165A (en) * | 1980-08-18 | 1982-03-04 | Koji Fujimori | Nonpower source plating method utilizing potential difference due to earthing |
JP4220678B2 (en) * | 2001-01-17 | 2009-02-04 | 株式会社神戸製鋼所 | Aluminum alloy material with excellent phosphatability |
US6818313B2 (en) * | 2002-07-24 | 2004-11-16 | University Of Dayton | Corrosion-inhibiting coating |
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