JP4532310B2 - Manufacturing method of glass-coated bolt and electrolytic corrosion prevention structure of metal member - Google Patents

Description

  The present invention prevents the occurrence of electrical corrosion (electrolytic corrosion) in the fastening portion in a structure in which an alloy member such as magnesium or aluminum is fastened with a fastening member (bolt) made of a metal different from the alloy member. Related to technology.

  In recent years, in the automobile industry, further improvement in fuel consumption has been demanded as interest in environmental issues has increased. In order to meet such a demand, the automobile industry needs to consider reducing the weight of the automobile body, and light magnesium alloys and aluminum alloys are frequently used as parts among practical metals. In particular, recently, application to a part requiring extremely high corrosion resistance, such as an exterior or a structural part, is being promoted.

  However, since a magnesium alloy is the most basic practical alloy, there is a problem that when it is fastened with a dissimilar metal such as iron or aluminum, electrolytic corrosion is likely to occur in the presence of moisture containing an electrolyte. In particular, in an engine room of an automobile or in a suspension area, electrolytic corrosion is remarkably accelerated by the action of an electrolyte contained in rainwater, snowmelt salt, or the like, and there is a risk of causing a failure, that is, loosening in a fastening portion. Therefore, measures against such problems have been proposed (for example, patents) in which an aluminum washer is anodized to insulate it (see, for example, Patent Document 1) or a bolt is coated with a resin. Reference 2 and 3).

  However, anodization of an aluminum washer has the disadvantage that it is extremely costly, and there is a problem that a step for incorporating the washer is required and the efficiency is poor. Furthermore, the anodic oxide film has a drawback of being vulnerable to alkali. In addition, when the resin is coated on the bolt, the adhesion of the resin coating to the bolt and the durability associated therewith are required. However, in the above prior art, it cannot be said that the adhesion and durability are sufficient. It is feared that the galvanic oxide peels and galvanic corrosion occurs, and improving adhesion is a problem.

  As another method for forming a corrosion-resistant film, a method has been proposed in which glass is sprayed on an object heated to 100 ° C. or more to form a glass film (for example, see Patent Document 4).

Japanese Patent No. 2715758 Japanese Patent Publication No.58-40045 JP 2003-64492 A Japanese Patent No. 2937369

  However, as a result of the present inventors trying to coat the surface of the bolt by the method disclosed in Patent Document 4, when the glass is thermally sprayed on a bolt that has been subjected to normal quenching and tempering, the bolt becomes dull and the strength decreases. There was a problem of doing.

  Therefore, in the present invention, for example, in order to prevent electrolytic corrosion by insulating a fastening member such as a steel bolt or washer from a magnesium alloy member, the adhesion and durability of both are sufficiently secured without increasing the cost. It is an object of the present invention to provide an electrolytic corrosion prevention method and an electrolytic corrosion prevention structure that can be performed.

The method for preventing electrolytic corrosion of a metal member of the present invention is a method for producing a glass-coated bolt for fastening metal members made of different metals, and C: 0.37 to 0.53 wt%, Si: 0.10 -0.35 wt%, Mn: 0.30-0.60 wt%, a step of rolling a bolt made of Fe, and a step of rapidly cooling the bolt after heating it at 850-900 ° C for 10-60 minutes; A step of degreasing and cleaning the bolt, a base treatment step of forming a base coating having a thickness of 10 to 100 μm by performing a heat treatment at 350 ° C. or lower after coating the bolt surface with a layer made of a single metal or an alloy, and a bolt forming a glass layer having a thickness of 10~100μm by spraying the glass spraying material mainly containing SiO ₂ at least 850 to 1000 ° C. in surface treatment layer surface of the flange surface of ball It is characterized by comprising the steps of: once quench the door below 100 ° C. After spraying, and performing rapid cooling after heat treatment of 20 to 120 minutes at 400 to 550 ° C. The bolts.

  In the electrolytic corrosion preventing method of the present invention, the fastening member is quenched, the single metal or alloy component constituting the base treatment layer is provided on the surface of the fastening member, and heated to interface between the fastening member and the base treatment layer. Interfacial diffusion treatment is performed on the surface of the ground treatment layer, and the glass is sprayed and rapidly cooled, and finally tempered and heated, so that both components diffuse to each other at the interface between the fastening member and the ground treatment layer. Both components are also diffused at the interface between the treatment layer and the glass layer. Therefore, the base treatment layer is hardly peeled off from the surface of the fastening member, and electrolytic corrosion is effectively prevented. The glass layer is also difficult to peel off from the surface of the base treatment layer, and the durability is remarkably high. Conventionally, quenching and tempering were performed before the surface treatment of the fastening member, so that the strength of the fastening member was reduced by reheating in the surface treatment. The strength of the fastening member can be ensured by tempering the fastening member last as in the present invention.

Hereinafter, the electrolytic corrosion preventing structure and electrolytic corrosion preventing method for metal members of the present invention will be described in detail.
FIG. 1 shows a bolt which is an example of a metal member having the electrolytic corrosion preventing structure of the present invention. In FIG. 1 (A), the code | symbol 1 is a bolt body made from steel, for example, and the ground-treatment layer 2 which consists of a single metal or an alloy is in the location which contacts the to-be-fastened member which consists of a dissimilar metal among the surfaces. Is provided. Further, a glass layer 3 is provided on the surface of the base treatment layer 2. In addition, as shown in FIG. 1 (B), it is also possible to provide the base treatment layer 2 and the glass layer 3 on the entire surface of the bolt 1.

  The material of the bolt used in the present invention is a tempered material (steel material tempered for quenching and tempering) such as S40C to S50C (JIS G4051). This is because if the strength is not increased by heat treatment, an undesirable structural change is caused by the thermal treatment of glass spraying, leading to a decrease in the strength of the bolt. Moreover, such steel materials may contain phosphorus or sulfur as impurities.

  The bolt having such an electrolytic corrosion prevention structure can be manufactured by the following method. First, the steel material described above is forged into a bolt shape, the cylindrical portion is rolled to cut a thread groove, and then the bolt is quenched (step of quenching after heating). The temperature at this time is preferably 850 to 900 ° C. When the quenching temperature is 850 ° C. or less, the ferrite layer of the steel material cannot completely austenite, and there is a problem with the bolt strength. When the quenching temperature is 900 ° C. or more, no further increase in effect is observed. The energy cost will increase. The quenching time is preferably 10 to 60 minutes. If it is less than 10 minutes, heat is not transmitted uniformly to the bolt, and it cannot be transformed into the required structure. On the other hand, if it exceeds 60 minutes, the increase in the effect is not recognized, and the energy efficiency deteriorates. End up.

  In addition, quenching cannot be omitted by combining the quenching process and the glass spraying process described later. In the glass spraying process, the heating temperature is heated at a temperature sufficient for quenching, but since the spraying time is several seconds to 1 minute, the structure of the entire bolt becomes an austenitic structure as described above. It is necessary to perform quenching first.

  Following the quenching process, degreasing and cleaning are performed. In the prior art, tempering is performed immediately after quenching, but in the present invention, since the thermal spraying process is performed at 850 ° C. or higher, tempering is not performed immediately after quenching and the process proceeds to the next process.

  Next, a material for forming the base treatment layer is formed on the bolt surface. The metal used for the base treatment layer is not particularly limited and any metal can be used, but aluminum, iron, chromium, and the like are preferably used from the viewpoints of adhesion and durability. Moreover, when using an alloy, a stainless alloy and an aluminum alloy are used suitably. As a method of providing the base treatment layer on the bolt surface, it is possible to spray the base treatment layer component in a molten state.

  After the base treatment layer is formed on a part or the whole of the bolt surface, the interface diffusion treatment is performed by heating to about 350 ° C. By performing this treatment, the constituent components of the bolt and the constituent components of the base treatment layer diffuse to each other beyond the interface, and a so-called intermetallic compound is formed in the vicinity of the interface. Thereby, the adhesion between the bolt main body and the base treatment layer becomes stronger. The thickness of the base treatment layer is preferably 10 to 100 μm, and if it is less than 10 μm, the diffusion between the base treatment layer and the bolt is insufficient and the adhesion is deteriorated. When the thickness exceeds 100 μm, a uniform thickness cannot be obtained, and the effect of improving the adhesion does not increase any more, so that the energy efficiency is deteriorated. More preferably, it is 25-50 micrometers.

Subsequently, a glass layer is provided on the surface of the base treatment layer. The component constituting the glass layer preferably contains 85% or more of SiO ₂ as a main component. Examples of the method for forming the glass layer include spraying molten glass, and methods such as applying or immersing molten glass or spraying solid particles. When forming a glass layer by thermal spraying, it is preferable to carry out in the range of 850-1000 degreeC. When it is less than 850 ° C., the bolt surface temperature does not become 850 ° C. or more, and a ferrite layer is deposited on the bolt surface structure, causing a decrease in strength. On the other hand, when it exceeds 1000 ° C., the effect cannot be expected any further, and the energy efficiency deteriorates.

  10-100 micrometers is preferable and, as for the thickness of a glass layer, it is more preferable in it being 10-30 micrometers. When it is less than this range, a film is not formed uniformly and the insulating function is lowered. On the other hand, when this range is exceeded, the contact area becomes large, so that when the bolts come into contact with each other during transportation, chipping is likely to occur.

  After spraying the glass, quench and temper. This is because if tempering is performed without rapid cooling, a ferrite layer is deposited on the surface structure of the bolt, causing a decrease in strength. Tempering is performed at 400 to 550 ° C. for 60 to 120 minutes. When the tempering temperature is less than 400 ° C, many ferrite layers appear, causing low temperature tempering brittleness. On the other hand, when it exceeds 550 ° C, ferrite decreases and martensite increases, causing high temperature tempering brittleness. The toughness of the steel will decrease. If the tempering time is less than 20 minutes, heat is not transmitted uniformly to the bolt and the transformation to the required structure is not possible. On the other hand, if the tempering time exceeds 60 minutes, no increase in the effect is similarly recognized. Will get worse.

  Of the surface of the glass layer, the surface roughness of the surface in contact with the member to be fastened is preferably 6.3 to 25S. By setting it within this range, variation in torque coefficient is reduced, and accurate torque management is possible. When the surface roughness is less than 6.3S, the friction with the fastened member is too low, and an excessive axial force is generated when fastened with a predetermined torque, and the fastened member or bolt is broken or deformed. It can be a cause. On the other hand, when the surface roughness exceeds 25S, the necessary axial force is not generated when the surface is similarly fastened with a predetermined torque.

  According to the bolt of the present invention manufactured as described above, the member to be fastened comes into contact with the glass layer, so that the bolt and the member to be fastened are insulated and prevent electrolytic corrosion that has been a problem between different metals. can do. Further, since the adhesion between the bolt body and the base treatment layer and the adhesion between the base treatment layer and the glass layer are improved, the insulation and durability are improved during transportation and use. Furthermore, by defining the surface roughness within the range of the present invention, an appropriate range of axial force is generated for a predetermined torque, which is preferable.

Next, the effects of the present invention will be described in more detail by way of examples.
(1) Comparison of production methods <Example 1> (Glass sprayed bolt)
Bolts having a composition ratio of C: 0.45% by weight, Si: 0.20% by weight, Mn: 0.45% by weight, and the balance: Fe were forged, followed by rolling to cut screw grooves. This bolt was quenched at 850 ° C. for 30 minutes, degreased and washed, then sprayed with molten stainless steel (SUS-316L) to form a base treatment layer, and heated to 350 ° C. between the bolt base material and the base treatment layer. Interfacial diffusion treatment was performed. Subsequently, a glass material having a composition of SiO ₂ : 90 wt%, B ₂ O ₃ : 3 wt%, Al ₂ O ₃ : 2 wt%, LiO ₂ : 5 wt% is applied to the surface of the base treatment layer at 850 ° C. For 30 seconds and then cooled rapidly to room temperature. Subsequently, heat treatment (tempering) was performed at 425 ° C. for 60 minutes.
The thickness of the base treatment layer of this bolt was 45 μm, the thickness of the glass layer was 65 μm, the surface roughness was 12.5 S, and the bolt hardness was Hv 277 to 283.

<Comparative example 1> (Glass sprayed bolt)
Steel bolts were forged and rolled to cut thread grooves. This bolt was quenched at 850 ° C., subsequently tempered at 450 ° C., degreased and washed, then sprayed with molten stainless steel (SUS-316L) to form a base treatment layer, heated to 350 ° C. Interfacial diffusion treatment was performed between the base material and the base treatment layer. Subsequently, glass particles having the same composition as in Example 1 were thermally sprayed on the surface of the base treatment layer and baked at 700 ° C.

<Comparative Example 2> (Zinc plated bolt)
Steel bolts were forged and rolled to cut thread grooves. This bolt was quenched at 850 ° C., subsequently tempered at 450 ° C., degreased and washed, and then galvanized and chromated.

  Since the bolt of Example 1 was only quenched before the glass coating treatment and tempered after the glass coating treatment, the bolt strength (hardness) could be secured. Further, since the glass coating is applied, the insulating property is maintained even in contact with different metals, and no electrolytic corrosion occurs. On the other hand, since the bolt of Comparative Example 1 was quenched and tempered before the glass coating treatment based on the conventional bolt manufacturing method, the strength (hardness) of the bolt was reduced by firing after the glass coating treatment. . In addition, although the galvanized bolt has no problem in strength (hardness), it does not have a glass coating layer, and therefore it has galvanic corrosion due to contact with a different metal, resulting in a problem in durability.

(2) Glass film durability test during transportation 100 bolts of size (M6 × 30) were produced by the method of Example 1 of the present invention, and a buffer material was used for the transportation container (330 × 230 × 120 mm). Packed without. Further, 100 resin-coated bolts (the same size) of Comparative Example 3 were produced and packed in the same manner. These transport containers were set in a reciprocating sliding tester, and vibrations at the time of transportation were reproduced by applying vibrations having an amplitude of 15 cm and a vibration frequency of 1 Hz for 10 hours, and the durability test was performed.

  As a result of observing the appearance of each bolt after the endurance test, the glass film was observed to be damaged in 23 out of 100 bolts of Comparative Example 3, but the bolt of Example 1 was not damaged at all. Thus, it can be seen that the durability of the bolt of the present invention is significantly improved as compared with the conventional bolt.

(3) Durability test of resin by salt water spray and alkali immersion
In this durability test, the bolts of Example 1 and Comparative Examples 1 and 2 were used, a bolt subjected to anodizing described in Patent Document 1 and a bolt subjected to resin coating described in Patent Document 3 Were used as Comparative Examples 3 and 4, respectively. A magnesium alloy AZ91D material was used as a member to be fastened, and the bolts were fastened as shown in the schematic diagram of FIG. Each test piece was sprayed with salt water for 240 hours by a test method according to JIS K2731, and then the occurrence of rust in the magnesium alloy was examined. These results are shown in the column of insulation (initial) in Table 1. In addition, for each bolt of the example and the comparative example, a bolt is prepared after being struck by applying a vibration under the same conditions as the glass film durability test during transportation described in (2) above, and the salt spray test is the same. Went to. These results are shown in the column of insulation (after transportation) in Table 1. Furthermore, an alkaline immersion test was performed on each bolt of the example and the comparative example. Specifically, each bolt was immersed in a 0.1 mol / L sodium hydroxide aqueous solution for 100 hours. The results are also shown in Table 1. In Table 1, ◎: No rust, ○: Slight spot rust, △: A trace of rust was confirmed, but no problem in practical use, ×: Practical use with significant rust Rated as impossible. Moreover, the external appearance of the magnesium alloy plate after the salt spray test corresponding to ◎, Δ, and × is shown in FIG.

  As shown in Table 1, the conventional bolts could not satisfy the initial insulation, the post-transport insulation, and the insulation after alkali immersion, but all of the bolts of the present invention were satisfied. It can be seen that it has high durability.

(4) Evaluation of axial force stability Using the galvanized bolts of Example 1 and Comparative Example 2 (size: M6 × 30), a magnesium alloy AZ91D material to be fastened was fastened as shown in FIG. Torque was applied to the head of the bolt, the axial force generated between the fastened member and the flange of the bolt was measured, and their correlation was plotted. In addition, the surface roughness of the flange surface (seat surface) of the bolt of the Example which contacts a to-be-fastened member was 12.5S. As a result of performing these fastening and axial force measurements 10 times for each of the example and the comparative example, as shown in FIG. 3, the bolt of the example shows a correlation in the range sandwiched by the solid line, and the bolt of the comparative example is a broken line Correlation was shown in the range between.

  As is clear from FIG. 3, the torque coefficient of the bolt of the example is 0.20 to 0.25, which is the same level as the torque coefficient of the galvanized bolt 0.17 to 0.25, and the upper limit and the lower limit The variation is smaller than that of galvanized bolts and the axial force stability is improved. This shows that accurate torque management is possible.

(5) Bolt axial force retention characteristics at high temperature Using the galvanized bolts (size: M6 × 30) of Example 1 and Comparative Example 2, the magnesium alloy AZ91D material to be fastened was fastened as shown in FIG. . A predetermined torque was applied to the bolt head, and the axial force generated between the fastened member and the bolt flange was 600 kgf. Each of these test pieces was heated to 150 ° C. and held for 100 hours. As a result of measuring the remaining axial force after 100 hours, the axial force decrease rate of the example was 31%, the axial force decrease rate of the comparative example was 30%, and the bolts of the example were shafts at the same level as the comparative example. Has a power decline rate.

(6) Bolt hardness Since the strength classification of the bolt body used in the examples is 8.8 grade, Vickers hardness: Hv 250 to 320 is required as the standard for 8.8 grade bolts. And Vickers hardness was measured in each position of ad shown in Drawing 5 (A), respectively. As a result, it was Hv277-283 in covering part ac, and it was Hv280-283 in uncovered part d. The results are shown in the graph of FIG. As apparent from FIG. 5 (B), the glass-coated bolt of the present invention has a sufficient bolt hardness in the required range.

  According to the present invention, in order to insulate a magnesium alloy member and a fastening member made of a different material and prevent electrolytic corrosion, it is possible to ensure low cost and sufficient durability and insulation, and further, fastening torque. It is possible to provide a bolt capable of accurate torque management in which the relationship between the torque and the axial force is stable.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic cross section which shows the concept of the electrolytic corrosion prevention structure of this invention, (A) is sectional drawing of the volt | bolt which gave the electrolytic corrosion prevention process only to the contact part with a to-be-fastened member, (B) is the whole It is sectional drawing of the volt | bolt which performed the electrolytic corrosion prevention process. (A) is a schematic diagram of the salt spray test, (B) is a photographic diagram showing the state of the fastened member after the salt spray test. It is a graph which shows the relationship between the torque and axial force in this invention and the conventional volt | bolt. It is a schematic cross section which shows the fastening state of a volt | bolt. (A) is a photograph figure which shows the measurement location of bolt hardness, (B) is a graph which shows the measurement result of bolt hardness.

Explanation of symbols

1 Bolt body 2 Ground treatment layer 3 Glass layer 4 Magnesium alloy 5 Flange 6 Seat surface 7 Female thread

Claims (2)

A method of manufacturing a glass-coated bolt for fastening metal members made of different metals,
C: 0.37 to 0.53% by weight, Si: 0.10 to 0.35% by weight, Mn: 0.30 to 0.60% by weight, a step of rolling a bolt made of Fe,
A step of rapidly cooling the bolt after heating at 850 to 900 ° C. for 10 to 60 minutes;
Degreasing and washing the bolts;
A base treatment step of forming a base coating having a thickness of 10 to 100 μm by performing a heat treatment at 350 ° C. or less after coating the bolt surface with a layer made of a single metal or an alloy;
A glass layer having a thickness of 10 to 100 μm is formed by spraying a glass sprayed material mainly composed of SiO ₂ at 850 to 1000 ° C. on the surface of the base treatment layer on at least the flange surface (contact surface with a member to be fastened) of the bolt. Forming a step;
A step of rapidly cooling the bolt once to 100 ° C. or less after spraying;
And a step of rapid cooling after heat-treating the bolt at 400 to 550 ° C. for 20 to 120 minutes. A metal member made of magnesium, aluminum, or an alloy thereof is used as a member to be fastened, and a glass-coated bolt manufactured by the method according to claim 1 is used as a fastening member. .

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