WO2013153682A1 - 鋼製部材の化成処理方法、電着塗装を施した鋼製塗装部材の製造方法、および鋼製塗装部材 - Google Patents
鋼製部材の化成処理方法、電着塗装を施した鋼製塗装部材の製造方法、および鋼製塗装部材 Download PDFInfo
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- WO2013153682A1 WO2013153682A1 PCT/JP2012/060643 JP2012060643W WO2013153682A1 WO 2013153682 A1 WO2013153682 A1 WO 2013153682A1 JP 2012060643 W JP2012060643 W JP 2012060643W WO 2013153682 A1 WO2013153682 A1 WO 2013153682A1
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- steel
- zinc phosphate
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- welding
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- 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
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- 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
- C23C22/05—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 using aqueous solutions
- C23C22/06—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 using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/34—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 using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
- C23C22/36—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 using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates
Definitions
- the present invention relates to a steel coating member suitable for an automobile undercarriage member and the like, which is obtained by welding and joining steel plates to each other and further subjected to chemical conversion treatment and electrodeposition coating, and in particular, to improve the corrosion resistance of a welded portion. It relates to a processing method.
- consumable electrode type arc welding is generally used for joining carbon steel, in which welding is performed in a shielding gas in which about 20% of CO 2 is mixed with Ar. Further, members obtained by joining these carbon steels are often electrodeposited continuously after welding in order to ensure corrosion resistance. However, there is a problem that corrosion occurs starting from the welded part when the electrode is used for a long period of time or is exposed to a severe corrosive environment, even though the electrodeposition coating is applied.
- Corrosion after painting occurs from the welded part, that is, the bead part directly above the weld bead and the weld bead toe, and the heat affected zone (including the back side of the weld bead part), and includes the welded part and its surroundings as time passes.
- the welded part that is, the bead part directly above the weld bead and the weld bead toe, and the heat affected zone (including the back side of the weld bead part), and includes the welded part and its surroundings as time passes.
- the thickness of the welded portion and the vicinity of the welded portion is reduced and the strength is lowered. For this reason, particularly in a member in which a welded part receives a load during use, for example, an underbody member of an automobile, the member itself may be broken due to insufficient strength.
- automobile underbody members for example, lower arms
- automobile underbody members are relatively thick for the purpose of ensuring strength and corrosion resistance. This leads to a significant weight reduction of the car body and is extremely effective for improving the fuel efficiency of automobiles. Therefore, a thin high-strength steel sheet is being applied as a material for an automobile underbody member.
- the high-strength steel plate is processed and formed into a desired shape by welding, followed by electrodeposition coating for the purpose of imparting corrosion resistance.
- chemical conversion treatment represented by zinc phosphate treatment is performed as a pretreatment for electrodeposition coating.
- the chemical conversion treatment is a treatment performed for the purpose of improving the adhesion between the steel sheet as the base material and the coating film formed by electrodeposition coating.
- the adhesion between the base material and the coating film is improved by growing zinc phosphate crystals on the surface of the steel plate and the welded portion as the base material.
- corrosion is frequently observed at and near the welds over time.
- a galvanized steel sheet may be used as a base material for forming a member such as a member for an automobile.
- the galvanization in the vicinity of the welded portion is locally evaporated by heating during welding. Therefore, although the effect of improving the corrosion resistance is recognized as compared with the non-plated material, the effect of the zinc-based plated steel sheet is limited.
- Corrosion observed in and around the weld has been studied in the past, and the main causes of corrosion are (1) slag that adheres mainly to the weld bead and (2) adheres to the weld. Welding fume or (3) surface oxidation of the welded portion. As shown in (1) to (3) above, even if chemical conversion treatment is applied to a member to which slag or welding fume adheres or surface oxidation has occurred, as shown in FIG. In the vicinity of the toe portion (within approximately 4 mm from the weld bead toe portion), there remains a region where the chemical conversion treatment layer is not formed.
- the adhesion of the coating film becomes insufficient during electrodeposition coating, or the adhesion of the formed coating film cannot be ensured sufficiently, and the corrosion resistance is significantly reduced.
- the thickness of the member decreases with the occurrence and progression of corrosion.
- Patent Document 1 relates to a technique for improving the post-painting corrosion resistance of an arc welded portion of a structure to be electrodeposited after arc welding and the vicinity thereof, and arc welding before electrodeposition coating.
- a technique of performing spray treatment or immersion treatment using a non-oxidizing acid having a pH of 2 or less and a liquid temperature of 30 ° C. or higher and 90 ° C. or lower at and near the portion According to such a technique, it is possible to remove the slag on the surface of the base material and the surface of the weld bead by dissolving the base material and the weld bead forming the structure with the specific acidic solution described above. In addition, it is possible to dissolve and remove oxides generated due to surface oxidation on the surface of the base material such as welding fume and welding heat affected zone with the above-mentioned specific acidic solution.
- Patent Document 2 relates to gas shield metal arc welding of carbon steel on the premise that electrodeposition is applied after welding in order to improve corrosion resistance, and the oxidation gas (CO 2 , O 2 ) in the shield gas. Techniques for reducing the amount have been proposed. According to such technology, the generation of slag is suppressed and electrodeposition coating properties are improved, and at the same time, oxidation in the heat affected zone is suppressed and adhesion of welding fume is suppressed, so that the corrosion resistance after coating of the welded portion and its vicinity is improved. It is supposed to improve.
- Patent Document 3 describes the total amount of Si and the total amount of Mn contained in the base metal and the welding wire in relation to gas shield metal arc welding of carbon steel on the premise that electrodeposition is applied after welding to improve corrosion resistance.
- a technique for reducing the above has been proposed. According to such a technique, the content of Si and Mn constituting the slag is reduced. As a result, the generation of slag is suppressed and the corrosion resistance after painting is improved.
- the composition of the base material and the welding wire is limited as in the technique proposed in Patent Document 3 and the amount of Si and Mn that cause slag is reduced, the corrosion resistance of the welded part and its vicinity after coating is reduced. Improvement can be expected.
- Si and Mn are extremely effective elements for improving the strength of steel sheets, and in recent years, the application of high-strength steel sheets containing a large amount of Si and Mn has been expanding for the purpose of reducing the weight of automobiles. Contrary to this trend, the technique proposed in Patent Document 3 requires the application of a steel sheet with a reduced amount of Si or Mn, so that the desired strength can be ensured by reducing the thickness of the steel sheet. I can't. Therefore, the technique proposed in Patent Document 3 cannot be expected to reduce the weight of the automobile.
- the present invention has been made in view of such circumstances, and provides a technique for improving the corrosion resistance of welded portions of steel coating members including automobile members such as suspension members. Specifically, with respect to a steel coated member obtained by subjecting a steel member formed by welding and joining steel plates to a chemical conversion treatment and then subjected to electrodeposition coating, even in a portion less than 2 mm from the weld bead toe, To provide a steel coated member having excellent coating film adhesion, in which zinc oxide crystals (chemical conversion treatment layer) are present, and a portion separated by 2 mm or more is completely covered with zinc phosphate crystals (chemical conversion treatment layer). Objective.
- the present invention is not limited to a portion that is 4 mm or more away from the weld bead toe, but even a portion that is only 2 mm away from the weld bead toe is made of zinc phosphate crystals. It is an object of the present invention to provide a steel coated member that is completely covered and that is partially formed with zinc phosphate crystals even at a portion of less than 2 mm from the weld bead toe.
- Deterioration of corrosion resistance in welded parts of steel coated parts is caused by slag or welding fumes adhering to the weld (on the weld bead, weld bead toe, weld heat affected zone), or surface oxidation generated in the weld To do.
- a zinc phosphate treatment is applied to a steel member as a chemical conversion treatment
- the steel to be treated is dissolved by the etching action of the zinc phosphate treating agent.
- the consumption of hydrogen ions causes a pH increase in a local region of the solid-liquid interface, and zinc phosphate crystals (chemical conversion treatment layer) are deposited on the surface of the steel member.
- the present inventors when a zinc phosphate treatment is performed as a chemical conversion treatment on steel members formed by welding steel plates together, a welded portion to which slag or welding fume adheres, and a welded portion in which surface oxidation has occurred.
- a highly etching zinc phosphate treating agent having a predetermined fluorine concentration is an extremely effective means. That is, when a zinc phosphate treating agent having a predetermined fluorine concentration is used, welding fumes and oxides derived from surface oxidation are dissolved and removed by the strong etching action of the treating agent. It was found that phosphozinc crystals were sufficiently precipitated without being inhibited.
- the present inventors examined means for sufficiently depositing zinc phosphate crystals at the weld bead toe.
- a zinc phosphate treating agent having a predetermined fluorine concentration when a surface conditioner mainly composed of zinc phosphate colloid is used as a pretreatment, it is advantageous for crystal formation at the weld bead toe.
- the surface conditioner mainly composed of zinc phosphate colloid has high dispersibility of the colloid in the surface conditioner and is formed after the surface condition. Because it is the same component as the zinc phosphate crystal, it acts more effectively as a precipitation nucleus, and even if an oxide is present, a chemical conversion treatment layer composed of a dense zinc phosphate crystal is easily formed.
- the present inventors are separated from the weld bead toe by more than 2 mm by applying the desired surface conditioning treatment and zinc phosphate treatment to the steel member formed by welding the steel plates together as described above.
- the desired surface conditioning treatment and zinc phosphate treatment to the steel member formed by welding the steel plates together as described above.
- a steel member covered with zinc phosphate crystals (chemical conversion treatment layer) that is only 2 mm away from the weld bead toe is obtained. It has been found that by applying electrodeposition coating to such a steel member, a steel coated member having dramatically improved corrosion resistance of the welded portion can be obtained.
- the present invention has been completed based on the above findings, and the gist thereof is as follows.
- the chemical conversion treatment is subjected to a surface conditioning treatment using a surface conditioning agent containing a zinc phosphate colloid, and then the fluorine concentration is 100.
- a chemical conversion treatment method for a steel member characterized in that a zinc phosphate treatment is performed using a zinc phosphate treatment agent having a mass ppm or more.
- a method for producing a steel coated member obtained by subjecting a steel member formed by welding and joining steel plates to chemical conversion treatment and electrodeposition coating to form a steel coated member.
- the corrosion resistance of a welding part can be improved significantly in the steel coating member by which the electrodeposition coating is performed after performing the chemical conversion treatment to the steel member formed by welding the steel plates together. . Therefore, it is possible to form automobile underbody members, etc., which have been used in severe corrosive environments and have conventionally been difficult to reduce the thickness of the members, with thin high-strength steel plates, and have a remarkable industrial effect. .
- FIG. 1 is a diagram schematically showing the shape of a fillet weld specimen used in the examples.
- FIG. 2 is an enlarged view of the welded portion of the cross-sectional view taken along the line AA in FIG.
- FIG. 3 is a diagram showing test conditions for the corrosion acceleration test used in the examples.
- FIG. 4A is an SEM photograph of the comparative example (Condition 1, test piece 11A) at a position 100 ⁇ m away from the weld bead toe.
- FIG. 4B is a SEM photograph of the comparative example (condition 1, test piece 11A) at a position 2 mm away from the weld bead toe.
- FIG.4 (c) is the SEM photograph in the position of 4 mm away from the weld bead toe part of the comparative example (condition 1, test piece 11A).
- FIG. 5A is a SEM photograph of the present invention example (Condition 3, test piece 31A) at a position 100 ⁇ m away from the weld bead toe.
- FIG. 5B is an SEM photograph of the present invention example (condition 3, test piece 31A) at a position 2 mm away from the weld bead toe.
- FIG.5 (c) is the SEM photograph in the position 4mm away from the weld bead toe part of the example of the present invention (condition 3, test piece 31A).
- FIG.6 (a) is a figure which shows typically the cross section around a weld bead part at the time of performing the conventional chemical conversion treatment to the steel members formed by arc-welding steel plates.
- FIG.6 (b) is a figure which shows typically the cross section around a weld bead part at the time of performing the chemical conversion treatment of this invention to the steel members formed by arc-welding steel plates.
- the chemical conversion treatment method for steel members according to the present invention is a surface conditioning treatment using a surface conditioner containing a zinc phosphate colloid in chemical conversion treatment of steel members formed by welding and joining steel plates.
- the zinc phosphate treatment using a zinc phosphate treating agent having a fluorine concentration of 100 mass ppm or more is performed.
- the type of steel plate constituting the steel member is not particularly limited, and any of a normal hot-rolled steel plate, cold-rolled steel plate, or galvanized steel plate is applicable.
- a galvanized steel sheet when a galvanized steel sheet is used, there is a portion where the galvanization in the vicinity of the bead portion partially evaporates and the plating becomes thin due to heating during welding.
- the technique of the present invention is applied, the chemical conversion treatment film is soundly formed even in the vicinity of the bead portion, so that the corrosion resistance improving effect is sufficiently obtained even in the portion where the plating becomes thin as described above.
- an alloyed hot-dip galvanized steel sheet is applied as the steel sheet constituting the steel member, the corrosion resistance is further improved by the effect of plating.
- the effect of the present invention is to improve the chemical conversion treatment failure caused by the oxide film in the heat affected zone. Therefore, in the present invention, conventionally known welding such as arc welding, spot welding, seam welding, or the like can be applied regardless of the type of welding when the steel plates are welded together. Among these, especially in the case of arc welding, since the subject regarding corrosion tends to occur in the welded portion, the present invention is particularly effective when arc welding is applied.
- the arc welding referred to here includes MAG welding, MIG welding, TIG welding, carbon dioxide arc welding, and the like, and is not particularly limited.
- the steel plates may be processed and formed prior to welding the steel plates together, or may be formed into a desired member shape after the steel plates are welded together.
- the steel plates may be processed and formed, and then the steel plates may be welded together and further processed and formed into a desired member shape.
- the steel pipe obtained by welding and joining the edge parts of a steel plate shall also be contained in the steel member in this invention.
- the chemical conversion treatment method of the present invention comprises a step of subjecting a steel member formed by welding steel plates to each other as described above, and a step of subjecting the steel member to a subsequent zinc phosphate treatment.
- the present invention is characterized by using a surface conditioner containing a zinc phosphate colloid and using a zinc phosphate treating agent having a fluorine concentration of 100 ppm by mass or more.
- the surface conditioner containing zinc phosphate colloid Compared with other surface conditioners such as surface conditioner containing Ti-based colloid, the surface conditioner containing zinc phosphate colloid High dispersibility. Moreover, since the zinc phosphate colloid is the same component as the zinc phosphate crystal formed after the surface conditioning treatment, it acts more effectively as a precipitation nucleus of the zinc phosphate crystal. Therefore, even if welding fume or oxide derived from surface oxidation exists, a chemical conversion treatment film composed of dense zinc phosphate crystals can be easily formed by applying the desired zinc phosphate treatment described later. Can do.
- Examples of the surface conditioner containing zinc phosphate colloid include Surffine GL-1 manufactured by Nippon Paint Co., Ltd., Preparen X and Preparen XG manufactured by Nihon Parkerizing Co., Ltd. Further, when the surface conditioning treatment is performed using these surface conditioning agents, it is not necessary to provide a special process, and it may be performed according to a conventional method. For example, a desired surface conditioner is dissolved in predetermined deionized water, stirred sufficiently, and then treated as a treatment liquid at a specified temperature (normally normal temperature, 25 to 30 ° C.). Soak for 20-30 seconds. The subsequent zinc phosphate treatment is performed without drying.
- the fluorine concentration of the zinc phosphate treatment agent used in the zinc phosphate treatment is 100 mass ppm or more.
- the fluorine concentration is 100 mass ppm or more.
- it is 250 mass ppm or more.
- the fluorine concentration is preferably 1500 ppm by mass or less. Moreover, it is more preferable to set it as 1000 mass ppm or less.
- the zinc phosphate treating agent having a desired fluorine concentration as described above is a commercially available zinc phosphate treating agent, generally, a commercially available steel / aluminum combined treating agent that can treat aluminum and steel in common. , By adjusting the fluorine concentration.
- commercially available treatment agents such as Palbond AX-35 manufactured by Nippon Parkerizing Co., Ltd., fluorides such as hydrofluoric acid, sodium hydrogen fluoride, sodium fluoride, ammonium fluoride, or silicic hydrofluoric acid, It can be obtained by adjusting the fluorine concentration by adding one or more complex fluorides such as sodium silicofluoride and zircon hydrofluoric acid.
- a commercially available zinc phosphate treating agent has a desired fluorine concentration
- the fluorine concentration can be measured using a commercially available fluorine ion meter.
- the fluorine concentration can be adjusted by appropriately changing the addition amount of the additive regulator (for example, AD-4905).
- the zinc phosphate treatment is performed using the zinc phosphate treatment agent adjusted to a desired fluorine concentration as described above.
- This zinc phosphate treatment is not particularly limited as long as it is a so-called zinc phosphate treatment that forms a film mainly composed of zinc phosphate crystals, which is generally used for steel, galvanized steel sheets, and the like. . That is, when performing the zinc phosphate treatment, it is not necessary to provide a special step other than adjusting the fluorine concentration of the zinc phosphate treating agent as necessary, and it may be carried out according to a conventional method.
- the surface of the steel member subjected to the above-described surface preparation treatment is immersed in an aqueous solution in which a zinc phosphate treatment agent adjusted to a desired fluorine concentration is dissolved in deionized water or sprayed with the aqueous solution for a predetermined time.
- a zinc phosphate treatment agent adjusted to a desired fluorine concentration is dissolved in deionized water or sprayed with the aqueous solution for a predetermined time.
- zinc phosphate crystals may be precipitated to form a crystal film having a desired thickness.
- the weight of the zinc phosphate coating per side is preferably 1-4 g / m 2 , more preferably 1.5-3 g / m 2 .
- a region where the chemical conversion treatment layer is not formed remains in the vicinity of the weld bead toe portion (within about 4 mm from the weld bead toe portion).
- zinc phosphate crystals can be sufficiently precipitated over the entire weld including the vicinity of the weld bead toe.
- the method for producing a steel coated member according to the present invention is a method for producing a steel coated member obtained by subjecting a steel member obtained by welding and joining steel plates to chemical conversion treatment and electrodeposition coating to obtain a steel coated member.
- electrodeposition coating is performed on the steel member that has been subjected to the chemical conversion treatment obtained by the chemical conversion treatment method of the present invention.
- the electrodeposition coating in the present invention is not particularly limited as long as it is a commonly used cationic electrodeposition coating.
- the film thickness of the coating film formed by electrodeposition coating varies depending on the application of the steel coating member, but it is preferably about 10 ⁇ m or more and 30 ⁇ m or less for the dried coating film.
- the steel coated member of the present invention is a steel coated member manufactured by using the above-described manufacturing method of the present invention, and at least a portion 2 mm away from the weld bead toe is covered with zinc phosphate crystals. It is characterized by that. As described above, when a steel member formed by welding and joining steel plates is subjected to the chemical conversion treatment of the present invention, not only a part 4 mm or more away from the weld bead toe part, but also 2 to 2 from the weld bead toe part. Even a portion 4 mm away can be completely covered with zinc phosphate crystals.
- the adhesion of the coating formed by the subsequent electrodeposition coating is dramatically improved, and the corrosion resistance of the weld is greatly improved.
- a steel painted member can be obtained.
- the steel coating member of this invention shows the outstanding corrosion resistance including a welding part, according to the use of a steel coating member, you may give top coat etc. after electrodeposition coating.
- the present invention is suitable for an automobile underbody member such as a lower arm.
- An automobile undercarriage member is usually manufactured by forming a steel material into a predetermined shape and then applying zinc phosphate treatment (chemical conversion treatment) and electrodeposition coating.
- the corrosion resistance of the welded portion is greatly improved, and corrosion and thinning of the welded portion are suppressed. Therefore, according to the present invention, it is possible to significantly reduce the thickness of the underbody member, which has been conventionally difficult.
- Alloy hot dip galvanizing treatment plating adhesion amount per one side: 45 g / h) on both surfaces of the hot rolled steel sheet (thickness 2.6 mm) having the components shown in Table 1 or the hot rolled steel sheet having the components shown in Table 1 (thickness 2.6 mm).
- a fillet weld test material as shown in FIG. 1 was prepared using the alloyed hot-dip galvanized steel sheet to which m 2 ) was applied and the welding rod shown in Table 2.
- FIG. 2 is an enlarged view of the welded portion of the cross-sectional view taken along the line AA in FIG. Welding is the MAG pulse welding using Ar-20vol% CO 2, showing the welding conditions shown in Table 3.
- test pieces were degreased by immersing them in an alkali degreasing solution of 40 ° C .: FC-E2001 (manufactured by Nippon Parkerizing Co., Ltd., alkalinity: 18.3 pt or 18.5 pt) for 120 seconds.
- FC-E2001 manufactured by Nippon Parkerizing Co., Ltd., alkalinity: 18.3 pt or 18.5 pt
- the chemical conversion treatment which sequentially performs the surface conditioning treatment and the zinc phosphate treatment was performed under the three conditions shown in FIG. Conditions 1 and 2 are comparative examples, and condition 3 is an example of the present invention.
- the surface conditioning treatment was performed by immersing the test piece after the degreasing treatment in various surface conditioning agents (room temperature) shown in Table 4 for 20 seconds.
- the zinc phosphate treatment was performed by immersing in various commercially available zinc phosphate treating agents (35 ° C.) shown in Table 4 for 120 seconds.
- test piece No. 11A condition 1, hot-rolled steel sheet, comparative example
- test piece No. SEM photographs of 31A Supplement 3, hot-rolled steel sheet, inventive example
- FIGS. 4 and 5 (a) is a SEM photograph (magnification: 1500 times) at a position 100 ⁇ m away from the weld bead toe (point a in FIG. 2)
- (b) is the weld bead toe
- 2C is a SEM photograph (magnification: 500 times) at a position 2 mm away from the part (point b in FIG. 2) and (c) at a position 4 mm away from the weld bead toe (point c in FIG. 2).
- an electrodeposition coating for automobiles was applied to the test pieces after the zinc phosphate treatment.
- the film thickness of the electrodeposition coating was adjusted to 20 ⁇ 1 ⁇ m at the flat part.
- the electrodeposition coating conditions for automobiles are as follows. Type of paint: Trade name GT-10 (manufactured by Kansai Paint Co., Ltd.)
- Baking temperature: 170 ° C. (as PMT ( reaching plate temperature)) ⁇ 20 minutes
- the electrodeposition coating specimen was subjected to a corrosion acceleration test (combined cycle test) based on SAEJ2334. That is, as shown in FIG. 3, after each test piece was kept in a humid environment of (i) 100% relative humidity and 50 ° C. for 6 hours, (ii) 25 ° C. brine (0.5 mass% NaCl + 0.1 And (iii) a series of cycles (i) to (iii) that are immersed in a dry environment of 50% relative humidity and 60 ° C. for 17 hours and 45 minutes, and then immersed in 15% by weight CaCl 2 + 0.075% by weight NaHCO 3 ).
- a corrosion acceleration test combined cycle test
- the scale is observed at a position 2 mm away from the weld bead toe.
- condition 3 not only the position 4 mm away from the weld bead toe, but also the position 2 mm away from the weld bead toe is completely covered with the zinc phosphate crystal. .
- the precipitation of zinc phosphate crystals is confirmed even at a position 100 ⁇ m away from the weld bead toe, and the zinc phosphate crystals around the weld and the weld are generated soundly.
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Abstract
Description
上記(1)~(3)のように、スラグや溶接ヒュームが付着したり表面酸化が生じた部材に化成処理を施しても、図6(a)に示すように、溶接ビード上や溶接ビード止端部近傍(溶接ビード止端部から約4mm以内)において、化成処理層が形成されない領域が残る。このようにして化成処理層が形成されない領域では、電着塗装時に塗膜の付着が不十分となったり、形成される塗膜の密着性を十分に確保することができないため、耐食性が著しく低下し、腐食の発生・進行に伴い部材の肉厚が減少する。
特許文献1で提案された技術では、アーク溶接部及びその近傍に、特定の酸性溶液を用いたスプレー処理もしくは浸漬処理を施しているが、塗装工程前に上記酸性溶液を洗浄することが必要となり、構造体や部材の製造工程が煩雑となる。また、鋼板を加工、溶接して所望の形状に成形された部材は、複雑多様な形状である。そのため、上記洗浄時、酸性溶液が十分に洗浄しきれずに部材の隙間に酸性溶液が滞留する場合があり、激しい腐食を誘発してしまうことがある。さらに、酸性溶液を使用するため、製造設備そのものが腐食環境に晒されることになり、設備が腐食してしまうことや、廃液や酸性溶液のヒュームなどが発生するため環境負荷が大きいことも、大きな問題となる。
[1] 鋼板同士を溶接接合してなる鋼製部材を化成処理するにあたり、該化成処理を、リン酸亜鉛コロイドを含有する表面調整剤を用いた表面調整処理を施したのち、フッ素濃度が100質量ppm以上であるリン酸亜鉛処理剤を用いたリン酸亜鉛処理を施す処理とすることを特徴とする鋼製部材の化成処理方法。
本発明の鋼製部材の化成処理方法は、鋼板同士を溶接接合してなる鋼製部材を化成処理するにあたり、該化成処理を、リン酸亜鉛コロイドを含有する表面調整剤を用いた表面調整処理を施したのち、フッ素濃度が100質量ppm以上であるリン酸亜鉛処理剤を用いたリン酸亜鉛処理を施す処理とすることを特徴とする。
リン酸亜鉛コロイドを含有する表面調整剤は、Ti系コロイドを含む表面調整剤などの他の表面調整剤と比較して、表面調整液中でのコロイドの分散性が高い。そのうえ、リン酸亜鉛コロイドは、表面調整処理後に形成されるリン酸亜鉛結晶と同じ成分であるため、リン酸亜鉛結晶の析出核としてより有効に作用する。したがって、溶接ヒュームや表面酸化由来の酸化物が存在する場合であっても、後述する所望のリン酸亜鉛処理を施すことにより、緻密なリン酸亜鉛結晶からなる化成処理皮膜を容易に形成することができる。
本発明においては、リン酸亜鉛処理で用いるリン酸亜鉛処理剤のフッ素濃度を100質量ppm以上とすることを要する。フッ素濃度が100質量ppm未満の場合、リン酸亜鉛処理剤のエッチング能が不十分となり、溶接部に付着した溶接ヒュームや表面酸化由来の酸化物を溶解除去することができず、リン酸亜鉛結晶の析出に必要となる鋼の溶解反応を十分に促進することができない。よって、フッ素濃度は100質量ppm以上とする。好ましくは250質量ppm以上である。一方、フッ素濃度が過剰に高くなると、不溶性のフッ化物が生成し易くなり、不溶性のフッ化物が化成処理後に残留すると、濡れ環境下での塗膜密着性が低下することが懸念される。そのため、被処理材の種類にもよるが、フッ素濃度は1500質量ppm以下とすることが好ましい。また、1000質量ppm以下とすることがより好ましい。
なお、本発明の鋼製塗装部材は、溶接部を含めて優れた耐食性を示すが、鋼製塗装部材の用途に応じて電着塗装後に上塗り塗装などを施してもよい。
本発明の化成処理方法を用いて得られた足回り部材では、溶接部の耐食性が大幅に改善され、溶接部における腐食および薄肉化が抑制されている。そのため、本発明によると、従来困難とされていた足回り部材の大幅な薄肉化が可能となる。
各処理条件について、7個の試験片のうち2個はリン酸亜鉛処理のままとし、以下に示す方法で溶接部周辺のリン酸亜鉛結晶の健全性を評価した。
溶接ビード止端部(溶接ビードと鋼板の界面)から100μm離れた位置(図2のa点)、溶接ビード止端部から2mm離れた位置(図2のb点)、溶接ビード止端部から4mm離れた位置(図2のc点)、溶接ビード止端部から7mm離れた位置(図2のd点)、並びに、溶接ビード上(図2のe点)を、走査型電子顕微鏡(SEM)で観察し(倍率:500及び1500倍、各5視野)、以下の基準に従い評価した。
◎:観察5視野の領域の全てが、リン酸亜鉛結晶で完全に覆われている。
○:観察5視野の平均スケ面積が20%以下の状態でリン酸亜鉛結晶が析出している。
△:観察5視野の平均スケ面積が20%超の状態でリン酸亜鉛結晶が析出している。
×:観察5視野領域の全てにおいて、リン酸亜鉛結晶が析出していない。
塗料の種類 :商品名GT−10(関西ペイント(株)製)
電着浴の浴温:28℃
負荷電圧:200~220V(試験片により適宜変更)
焼付け温度:170℃(PMT(=到達板温)として)×20分
Claims (7)
- 鋼板同士を溶接接合してなる鋼製部材を化成処理するにあたり、該化成処理を、リン酸亜鉛コロイドを含有する表面調整剤を用いた表面調整処理を施したのち、フッ素濃度が100質量ppm以上であるリン酸亜鉛処理剤を用いたリン酸亜鉛処理を施す処理とすることを特徴とする鋼製部材の化成処理方法。
- 前記鋼板が、合金化溶融亜鉛めっき鋼板であることを特徴とする請求項1に記載の鋼製部材の化成処理方法。
- 鋼板同士を溶接接合してなる鋼製部材に化成処理と電着塗装を施して鋼製塗装部材とする鋼製塗装部材の製造方法であって、前記鋼製部材に請求項1に記載の化成処理を施したのち、電着塗装を施すことを特徴とする鋼製塗装部材の製造方法。
- 前記鋼板が、合金化溶融亜鉛めっき鋼板であることを特徴とする請求項3に記載の鋼製塗装部材の製造方法。
- 前記鋼製塗装部材が自動車の足回り部材であることを特徴とする請求項3または4に記載の鋼製塗装部材の製造方法。
- 請求項3ないし5のいずれか1項に記載の製造方法を用いて製造された鋼製塗装部材であって、少なくとも溶接ビード止端部から2mm離れた部分がリン酸亜鉛結晶で覆われていることを特徴とする鋼製塗装部材。
- 前記鋼製塗装部材が自動車の足回り部材であることを特徴とする請求項6に記載の鋼製塗装部材。
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JP2019214779A (ja) * | 2018-06-14 | 2019-12-19 | スズキ株式会社 | 防食構造及びその形成方法 |
JP2020517827A (ja) * | 2017-04-21 | 2020-06-18 | ヘンケル・アクチェンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト・アウフ・アクチェンHenkel AG & Co. KGaA | 層を形成するためのスラッジフリー方式で連続して金属部品をリン酸亜鉛処理する方法 |
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JP2020517827A (ja) * | 2017-04-21 | 2020-06-18 | ヘンケル・アクチェンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト・アウフ・アクチェンHenkel AG & Co. KGaA | 層を形成するためのスラッジフリー方式で連続して金属部品をリン酸亜鉛処理する方法 |
JP7223707B2 (ja) | 2017-04-21 | 2023-02-16 | ヘンケル・アクチェンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト・アウフ・アクチェン | 層を形成するためのスラッジフリー方式で連続して金属部品をリン酸亜鉛処理する方法 |
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