JP2017218609A - Aluminum alloy-made high strength fastener and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy-made high strength fastener capable of stably maintaining high fastening force (axial force) even when used under high temperature environment.SOLUTION: There is provided a high strength fastener made of an Al ally containing Fe:1.5 to 6%, Zr:0.2 to 1.5%, Ti:0.15 to 1.2% and the balance: Al with inevitable impurities based on 100 mass% in total. The Al alloy preferably further contains Mg:0.2 to 2.5%. Such Al alloy does not permanently grow practically and is extremely excellent in dimensional stability. Therefor the fastener (bolt, nut or washer) contributes to stable maintenance of high fastening force (axial force) even when used under high temperature environment. By coating at least a slide contact face of the fastener with a burned Ni-P plating layer, increase of wear resistance or corrosion resistance of the fastener can be achieved.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a high-strength fastener made of an aluminum alloy (also simply referred to as “Al alloy”) and a method for manufacturing the same.

  Fasteners such as bolts, nuts, and washers are usually made of low-cost, high-strength steel, but the total weight of the fasteners increases with the number of uses. Therefore, for aircraft, automobiles, motorcycles, etc., where there are many parts to be assembled using fasteners and there is a strong demand for weight reduction, aluminum alloy fasteners are used instead of steel fasteners, and their use is considered. Have been.

  For such fasteners, an A5000-based (JIS) non-heat-treatable Al alloy or an A6000-based or A7000-based heat-treatable Al alloy is used. Non-heat-treatable Al alloys are used for low-strength bolts and the like, while heat-treatable Al alloys are used for high-strength bolts and the like. The description related to such high-strength bolts made of heat-treatable Al alloy is, for example, in Patent Documents 1 and 2 below.

JP 2013-234389 A JP2015-74009A Japanese Patent No. 5867332

  Since heat-treated Al alloy is strengthened by aging treatment, when the usage environment such as bolts becomes equal to or higher than the aging treatment temperature (120 to 220 ° C), the strengthening phase dispersed in the base material becomes coarse. Thus, the strength can be reduced. For this reason, conventional Al alloy high-strength bolts have a limited use environment (use temperature range).

  Moreover, even if it is a heat treatment type Al alloy, although A7000 type | system | group (Al-Zn-Mg-Cu type | system | group) alloy is higher intensity | strength than an A6000 type | system | group (Al-Mg-Si type | system | group) alloy, corrosion resistance (stress corrosion resistance) It is inferior to crackability. Therefore, in order to improve corrosion resistance and wear resistance, an anodized film is often applied to the screw surfaces and end surfaces (sliding contact surfaces) of bolts and nuts. However, the anodized film is cracked in the entire film at a high temperature range (for example, higher than 80 ° C.) due to a difference in thermal expansion from the base material (Al alloy). For this reason, the range which can improve corrosion resistance and abrasion resistance with an anodic oxide film was limited.

  Further, when the present inventor has studied, conventional Al alloy high-strength bolts and the like undergo dimensional changes (permanent growth) due to thermal history, natural aging, and the like. For this reason, the conventional high strength bolts made of Al alloy, etc., when used in a high temperature range, of course, it has been difficult to stably maintain the tightening force (axial force) over a long period of time.

  Patent Document 3 describes a wear-resistant member in which a coating layer made of a crystalline Ni-P layer is provided on a base made of an aluminum alloy. However, Patent Document 3 has no specific description regarding fasteners, permanent growth, and the like.

  The present invention has been made in view of such circumstances, and provides a high-strength fastener made of aluminum alloy that can stably maintain a high clamping force under various usage environments, and a method for manufacturing the same. For the purpose.

  As a result of diligent research to solve this problem, the present inventor has found an unknown attribute that a specific Al alloy does not substantially grow permanently in addition to being excellent in high-temperature characteristics (strength, hardness, etc.). Based on this discovery, we have newly conceived a fastener made of an Al alloy that can stably maintain a high tightening force (axial force) even when the use environment (especially the use temperature range) changes. By developing this result, the present invention described below has been completed.

《Aluminum alloy high strength fasteners》
(1) The aluminum alloy high-strength fastener (simply referred to as “high-strength fastener” or “fastener”) according to the present invention has a total Fe content of 100% by mass (simply referred to as “%”). 1.5 to 6%, Zr: 0.2 to 1.5%, Ti: 0.15 to 1.2%, balance: aluminum alloy composed of Al and inevitable impurities, first member and second member Used to fix.

(2) The Al alloy according to the present invention does not substantially grow permanently and is excellent in dimensional stability, and stably exhibits high strength not only in a room temperature range but also in a high temperature range. Therefore, according to the fastener of the present invention, a stable and high tightening force can be ensured even when used in an environment where the environment (particularly temperature) is likely to fluctuate.

(3) Furthermore, the fastener of the present invention has a coating layer excellent in wear resistance, corrosion resistance, etc. on the surface of an aluminum alloy (base material) constituting at least a sliding contact surface (screw surface, seat surface, etc.). preferable. Examples of such a covering layer include a plating layer and an anodized layer. The plating layer may be an electrolytic plating layer or an electroless plating layer, but is preferably an electroless plating layer from the viewpoint of uniformity and productivity. In particular, the electroless plating layer is preferably an electroless Ni—P plating layer having excellent corrosion resistance and the like. Furthermore, the plating layer according to the present invention is preferably a hard Ni-P plating layer that is hard and has excellent wear resistance obtained by baking the electroless Ni-P plating layer among the electroless nickel plating layers. . By providing such a coating layer, the fastener of the present invention can exhibit excellent corrosion resistance and wear resistance in addition to the dimensional stability described above.

《Method for manufacturing high strength fastener made of aluminum alloy》
The fastener described above can be obtained, for example, by forging a material made of an Al alloy according to the present invention or rolling a screw groove. Since the Al alloy (raw material) exhibits high workability in a wide temperature range, the plastic processing may be cold processing, warm processing, or hot processing at 450 ° C. or less.

  Moreover, when forming the baking Ni-P plating layer mentioned above on the surface of a fastener, the following manufacturing methods of this invention can be used, for example. That is, a plating step of forming an electroless Ni—P plating layer on a forged base material forged from a material made of an aluminum alloy or a rolled base material obtained by rolling thread grooves on the forged base material, and the electroless Ni— It is a manufacturing method of the aluminum alloy high intensity | strength fastener provided with the baking process which heats P plating layer at 300-450 degreeC, and makes it a baking Ni-P plating layer.

<Others>
(1) The dimensional stability of the Al alloy according to the present invention is indicated by, for example, the permanent growth rate. Since the Al alloy does not substantially grow permanently, the permanent growth rate can be said to be within ± 0.05% or even within ± 0.01%. The permanent growth rate here is the amount of change in length (ΔL = L) that occurs when the sample (length before the test: L ₀ ) is heated from room temperature to 350 ° C. and held for 10 minutes and then cooled to room temperature. -L ₀ / length after test of sample: L) is expressed as a ratio (100 × ΔL / L ₀ ) to the initial length (L ₀ ).

(2) The Al alloy according to the present invention stably exhibits high strength and hardness not only at room temperature but also at high temperatures. For example, the tensile strength in the room temperature region can be 400 MPa or more, 450 MPa or more, and further 500 MPa or more. And the tensile strength of a high temperature range (350 degreeC) can be 200 Mpa or more, 250 Mpa or more, and also 300 Mpa or more. Furthermore, the Al alloy according to the present invention hardly changes in hardness from room temperature to a high temperature range (350 ° C.), and can stably maintain a hardness of 150 Hv or higher, 155 Hv or higher, or 160 Hv or higher. In this case, the variation range of the hardness can be within 30 Hv, within 15 Hv, or even within 10 Hv.

(3) Although various forms can be considered for the fastener of the present invention, for example, a bolt, a nut, or a washer is representative. The sliding contact surface referred to in this specification includes, for example, a screw surface (a spiral surface of a thread groove), a bolt head rear surface (a neck lower surface), a nut end surface, and a washer seat surface (a contact surface with a bolt or a nut). Etc.

(4) Unless otherwise specified, “x to y” in this specification includes the lower limit value x and the upper limit value y. Any numerical value included in the various numerical values or numerical ranges described in the present specification can be newly established as a new lower limit value or upper limit value such as “ab”.

It is a graph which shows the relationship between 130 degreeC holding time and a permanent growth rate. It is a graph which shows the relationship between heating temperature and displacement. It is a graph which shows the change of a linear expansion coefficient when it heats from room temperature (RT) to each temperature. It is a graph which shows the relationship between a baking temperature and the hardness of a base material. It is a graph which shows the relationship between a calcination temperature and the hardness of a plating layer.

  The contents described in this specification can be applied not only to the fastener of the present invention but also to the manufacturing method thereof. One or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention. A component related to a method can also be a component related to an object in certain cases. Which embodiment is the best depends on the target, required performance, and the like.

<< Al alloy >>
(1) Component composition The Al alloy according to the present invention preferably contains Fe, Zr and Ti as essential elements in addition to Al as a main component, and further contains Mg. Specifically, each element is as follows. In addition, the composition range of each element was shown with the whole Al alloy as 100 mass%.

  Fe is preferably contained in an amount of 1.5 to 6%, more preferably 2.5 to 5.5%. Fe forms an intermetallic compound with Al (Al—Fe-based intermetallic compound: first compound phase) in the parent phase (α-Al phase). This first compound phase increases the strength and hardness of the Al alloy. If Fe is insufficient, sufficient strength and hardness cannot be obtained, and if Fe is excessive, ductility is lowered and workability such as forgeability and rollability can be lowered.

  Fe is not only effective for improving the strength and the like of the Al alloy, but can also function as a catalyst element (activation element) when performing electroless Ni—P plating. Specifically, Fe partially exposed from the surface of the Al alloy (base material, base material) is used as a starting point to promote the formation of a Ni—P plating layer. As a result, a Ni—P plating layer having excellent adhesion and uniformity can be easily formed on the surface of the fastener (particularly the sliding contact surface). This tendency is remarkable when Fe is 1% or more.

Zr and Ti, Al- (Zr, Ti) of L1 ₂ -type structure between the Al-based intermetallic compounds (second compound phase or precipitated phase) is formed, enhances the heat resistance of Al alloy. The reason is considered as follows. When the first compound phase described above is exposed to a high temperature atmosphere for a long time, it undergoes phase transformation or shape change (coarse), and is not necessarily thermally stable. On the other hand, the second compound phase is consistent with the parent phase, appears near the boundary (interface) between the first compound phase and the parent phase, and is stable up to a high temperature range. For this reason, the phase transformation and shape change of the first compound phase responsible for the strength and hardness of the Al alloy at a high temperature can be stably suppressed (so-called pinned) by the second compound phase. Thus, it is considered that the Al alloy according to the present invention has exhibited excellent high-temperature characteristics (softening resistance, heat resistance) by the synergistic action of the first compound phase and the second compound phase.

  Zr is preferably contained in an amount of 0.2 to 1.5%, more preferably 0.6 to 1.2%. Further, Ti is preferably contained in an amount of 0.15 to 1.2%, more preferably 0.3 to 0.8%. When Zr or Ti is too small, the above-described effects are poor, and when Zr or Ti is excessive, the workability of the Al alloy can be lowered. When the amount of Zr is larger than that of Ti, and the mass ratio of Zr to Ti (Zr / Ti) is 1.1 to 1.5, more preferably 1.15 to 1.4, the second compound phase is formed. The improvement of the high temperature characteristics of the Al alloy due to is more remarkable.

  Further, Mg is preferably contained in an amount of 0.2 to 2.5%, more preferably 0.6 to 1.8%. Mg is an element effective for improving the strength (particularly room temperature strength) of the Al alloy. If Mg is too small, the effect is poor, and if it is excessive, workability of the Al alloy material is lowered.

  In light of the above-described contents, the Al alloy according to the present invention has Fe: 1.5-6%, Zr: 0.2-1.5%, Ti: 0.15-1.2%, and the balance: Al. Preferably consisting of inevitable impurities. The mass ratio of Zr to Ti (Zr / Ti) is preferably 1.1 to 1.5. Further, the Al alloy may contain Mg: 0.2 to 2.5% and other modifying elements.

  Elements other than Al, Fe, Zr, Ti and Mg that are effective for improving the properties (strength, hardness, toughness, ductility, dimensional stability, etc.) of the Al alloy include Cr, Co, Mn, There are Ni, Sc, Y, La, V, Hf, Nb, and the like. The content of each element is usually a very small amount. Incidentally, “inevitable impurities” are impurities contained in the dissolved raw material, impurities mixed in at each step, etc., and are elements that are difficult to remove due to cost or technical reasons. For example, silicon (Si) and the like.

(2) Metallographic structure The Al alloy according to the present invention includes an Al matrix (α phase), an Al—Fe intermetallic compound phase (first compound phase), and an Al— (Zr, Ti) intermetallic compound. It is preferable that it consists of a composite structure having at least (second compound phase).

In particular, the second compound phase is in the form of nanoparticles, preferably having a high Zr concentration at the center and a high Ti concentration at the outer portion. That is, it is preferable that the concentration of Zr and Ti in Al ₃ (Zr, Ti) is inclined from the center to the outer shell. Such a second compound phase is easily formed when the mass ratio (Zr / Ti) is in the above-described range.

  The average size of the second compound phase is preferably 1 to 30, 2 to 20 nm, and more preferably 3 to 15 nm. Even if this size is too small or too large, the effect of improving the heat resistance of the Al alloy by the second compound phase can be lowered. The average size is obtained by observing a sample randomly extracted from the Al alloy with a transmission electron microscope (TEM) and analyzing the average diameter of 30 or more dispersed second compound phases by an image processing method.

  As described above, the Al alloy according to the present invention is composed of a fine metal structure, so that the permanent growth rate is substantially zero (near), excellent in high temperature characteristics, and also exhibits high plastic workability in a wide temperature range. Can do. For this reason, for example, it is also possible to set the processing temperature: room temperature (RT) to 400 ° C. and the processing rate: 10 to 90%. Therefore, the fastener made of an Al alloy according to the present invention is excellent in productivity, design freedom, and the like.

<Manufacture of Al alloy>
Various methods for producing the Al alloy described above are conceivable. For example, it can be obtained by hot plastic working at 300 to 500 ° C. a molded body (billet) made of a solidified body (powder, flakes, etc.) obtained by rapidly solidifying an alloy melt at a cooling rate of 100 ° C./second or more.

  The hot plastic working is, for example, extrusion or forging. The hot plastic working may be a step of forming a material (forged material) to be used for forging a fastener, or a forging itself for forming a fastener. In the case of forging a forging material, the forging temperature is preferably 150 to 450 ° C. in consideration of forgeability and maintaining the characteristics of the Al alloy (forging process).

<< Coating layer / Firing Ni-P plating layer >>
Various coating layers according to the present invention are conceivable as described above. Hereinafter, a fired Ni—P plating layer, which is a representative example, will be described in detail.

(1) The fired Ni—P plating layer (also simply referred to as “fired plating layer”) according to the present invention is, for example, an electroless Ni—P plating layer (also simply referred to as “electroless plating layer”) of 300 to 300. It is obtained by heating at 450 ° C., further 350 to 400 ° C. When the electroless plating layer is heated at 200 to 300 ° C. during the temperature raising process, the adhesion to the substrate is enhanced. This is considered to be because hydrogen taken in in the process of forming the plating layer is released and the adhesion between the substrate and the plating layer interface is improved (baking treatment). By further heating the plating layer at 300 ° C. or higher, a fired plating layer that has been made extremely hard can be obtained. This is considered to be due to dispersion strengthening due to precipitation of the Ni ₃ P compound in the plating layer. The surface hardness of the fired plating layer thus obtained can be 900 Hv or higher, 1000 Hv or higher, or even 1100 Hv or higher.

(2) The fired plating layer is not an amorphous Ni—P layer but a crystalline Ni—P layer mainly composed of Ni (crystalline phase) and Ni ₃ P (precipitated phase). For this reason, the fired plating layer according to the present invention can also be referred to as a crystalline Ni-P layer. However, the crystalline Ni-P layer does not need to be completely crystalline throughout the plating layer. It suffices if there is a crystal part that can be detected by X-ray. In addition, when hardness is not requested | required of a plating layer, you may just perform the baking process for improving adhesiveness.

  P contained in the fired plating layer is preferably, for example, P in the range of 1 to 13%, 5 to 10%, 6 to 9%, or 7 to 8% with the entire plating layer being 100% by mass. The fired plating layer according to the present invention may be obtained by firing an electrolytic Ni-P plating layer.

<Formation of baked plating layer>
The fired plating layer according to the present invention is obtained, for example, by a plating process for forming an electroless plating layer and a baking process for firing the electroless plating layer.

  The plating step is preferably a step of electroless plating treatment on the pretreated substrate surface. The composition of the electroless plating solution, the temperature of the plating solution, the plating time, and the like are adjusted as appropriate. The pretreatment includes a cleaning process for removing an oxide film and oil stains on the substrate surface, a zincate treatment process for activating plating on the substrate surface made of an Al alloy that is a difficult plating material, an activation process, and the like. Details thereof are described in detail in Japanese Patent No. 2648716, Japanese Patent No. 5867332, and the like.

  In the firing step, it is preferable to heat the electroless plating layer at 300 to 450 ° C, further 350 to 400 ° C. The electroless plating layer immediately after plating is amorphous and it is difficult to say that the adhesion and hardness are sufficient, and as described above, a highly adhesive and ultra-hard fired plating layer can be formed by the firing process. The heating time may be about 0.5 to 5 hours.

<Application>
(1) The fastener of the present invention can be used for fastening various members. However, in addition to being lightweight, the fastener of the present invention does not substantially grow permanently and is excellent in high temperature characteristics. For this reason, the fastener of the present invention preferably constitutes at least a part of a machine or apparatus that is required to be reduced in weight, and is preferably used for fastening a member used in a high temperature range. For example, it is preferably used for fastening components of an internal combustion engine (gasoline engine or diesel engine) and its auxiliary equipment.

  The first member and the second member (referred to as “fastened members”) fastened by the fastener of the present invention may be made of steel, cast iron, light alloy, resin, or the like, for example. However, it is preferable that the member to be fastened is also made of pure Al or an Al alloy (Al-based material) because electrolytic corrosion can be suppressed with the fastener of the present invention.

  Furthermore, fasteners coated with a fired Ni—P plating layer (referred to as “coated fasteners”) are excellent in corrosion resistance and wear resistance, and can be used repeatedly even in corrosive environments. Moreover, since the electrolytic corrosion is suppressed even when the member to be fastened is made of a material other than an Al-based material (particularly an iron-based material), the coated fastener can be used for fastening a wider variety of members.

  A test piece made of an Al alloy was manufactured, and the relationship between the dimensional change and the thermal history was clarified. Moreover, the characteristic change of Al alloy by the heat history and the baking Ni-P plating layer formed in the surface was evaluated. Based on these specific examples, the present invention will be described in more detail.

<Dimensional change and thermal history>
(1) Manufacture of sample A molten Al alloy having the composition shown in Table 1 was prepared (melt preparation step). This molten alloy was sprayed in a vacuum atmosphere to obtain an air atomized powder (solidified body) (solidification step). The obtained air atomized powder particles (atomized particles) were classified to prepare atomized powder having a particle size of 150 μm or less. Incidentally, the relationship between the size of the powder particles obtained by air atomization and the cooling rate is known, and it can be said that the atomized powder consists of particles rapidly cooled and solidified at a cooling rate of 10 ⁴ ° C / second or more.

  The atomized powder was cold isostatically pressed (CIP) to obtain a billet (raw material) having a diameter of 39 mm × 40 mm and a relative density of 85%. This billet was loaded into a container of an extruder and extruded at 370 ° C. to obtain a material for forging such as a bolt (hot plastic working). The extrusion ratio (cross-sectional area of the raw material / cross-sectional area of the raw material) at this time was 11. This material was further subjected to cold swaging and outer peripheral cutting to obtain a φ8 mm × 25 mm test piece (base material serving as a fastener) (forging process). This test piece is designated as sample 1.

  As a comparative sample, test pieces having the same shape made of a plurality of general types of Al alloys are also prepared. Sample C1 (A7050 alloy), Sample C2 (A6056 alloy), Sample C3 (A2618 alloy), Sample C4 (A6061 alloy) Sample C5 (Al-12% Si alloy).

(2) Heating test Each test piece was heated in the air atmosphere at 130 ° C. in units of 6 hours or 12 hours, and then the process of cooling to room temperature was repeated. For each heating step, the length (Ln) of the test piece was measured, and the ratio (permanent growth rate /%) of the change amount (Ln−L ₀ ) to the initial length (L ₀ ) of the test piece was calculated. The relationship between the permanent growth rate of each sample and the accumulated heating time (holding time) is shown in FIG.

  Moreover, the change of the length of each test piece when the heat history shown in FIG. 2 was added was measured with a thermal stress strain measuring apparatus (Seiko Instruments Co., Ltd. TMA / SS6000). The results are also shown in FIG.

  Furthermore, each test piece is heated from room temperature (RT) to 100 ° C., 200 ° C., 300 ° C. or 400 ° C., and the coefficient of linear expansion (CTE) in each heating process is determined by a thermal stress strain measuring device (TMA manufactured by Seiko Instruments Inc.). / SS6000). The results are shown in FIG.

(3) Evaluation As is clear from FIG. 1, the permanent growth rate of Sample 1 remained substantially 0% even when the holding time was increased. On the other hand, in the samples C1 and C2 made of the conventional heat-treatable Al alloy, the permanent growth rate greatly changed to the positive side in the initial stage of heating, and then the permanent growth rate changed to the negative side and was not stable.

  The same is apparent from FIG. That is, the sample 1 did not change in dimensions (permanent growth) even when subjected to a thermal history of room temperature (RT) → high temperature (350 ° C.) → room temperature. On the other hand, Sample C1 and Sample C5 were about 10-30 μm longer from the initial length due to the similar thermal history. In terms of the permanent growth rate, sample 1 was approximately 0% (0.001% or less), sample C1: 0.06%, and sample C5: 0.1%. From these results, it was found that by using the fastener according to Sample 1, it was possible to secure a stable tightening force or axial force even when receiving a thermal history. On the other hand, it has also been found that the fasteners according to the sample C1 and the sample C5 can lead to a situation where it is loose or difficult to remove.

  As can be seen from FIG. 3, it was also confirmed that the temperature dependence of CTE showed a tendency similar to that of samples 1 and C5.

<Formation of baked plating layer>
(1) Cleaning process A base material (φ8 mm × 25 mm) obtained by performing cold swaging on the above-mentioned material in the same manner and cutting the outer periphery is alkali-etched with a sodium hydroxide aqueous solution (concentration 50 g / L) and formed on the surface. The oxidized film was removed (etching process). After this was washed with water, the smut formed on the surface was removed with an aqueous nitric acid solution (concentration 30%) and further washed with water (desmutting step). Thus, the substrate surface was cleaned (cleaning process).

(2) Activation process The cleaned base material was further immersed in an aqueous sodium carbonate solution having a pH of 11.5 for activation treatment. This activation treatment was continued until the standard (natural) electrode potential of the substrate shifted to -1.4 to -1.35 V (vsAg / AgCl). The standard electrode potential was measured with a potentiometer after immersing the substrate after activation treatment and the Ag / AgCl electrode in the measurement solution. Thus, a pretreatment was carried out for direct plating without carrying out the zincate treatment.

(3) Plating step The pretreated substrate was immersed in a 90 ° C. plating solution for 60 minutes. A commercially available electroless nickel phosphorus plating solution (Okuno Pharmaceutical Co., Ltd. Top Nicolon BL) was used as the plating solution. Thus, an electroless plating layer was formed on the substrate surface.

(4) Firing step The substrate after the electroless plating treatment was placed in a heating furnace and heated in an atmospheric pressure atmosphere for 1 hour. The heating temperature (firing temperature) was 250 ° C., 300 ° C., 350 ° C. or 400 ° C. Thus, a test piece having a fired plating layer formed on the substrate surface was obtained. When the cross section of the test piece (firing temperature: 350 ° C.) was observed with a scanning electron microscope (SEM), the film thickness of the fired plating layer was about 10 μm.

<Characteristics of base material and plating layer>
(1) Hardness Each test piece heated at a different firing temperature was cut, and the hardness of the base material portion and the plating layer portion of the cut surface was measured at room temperature using a micro Vickers hardness meter (MVK- manufactured by Akashi Co., Ltd.). E). At this time, the test load was 0.245 N and the holding time was 20 seconds. This measurement was performed five times, and the average values of the hardness of each part are shown in FIGS. 4 and 5, respectively.

  For reference, FIG. 4 also shows the change in hardness when samples C3 and C4 are heated at similar temperatures. FIG. 5 showing the hardness of the plating layer also shows the general surface hardness of the sprayed alumina layer and the chromium plating layer formed on the substrate.

(2) Evaluation As is apparent from FIG. 4, the Al alloy according to the sample 1 has a hardness of 155 to 175 Hv (change width: 5 to 5) even when heated to 400 ° C., unlike the Al alloys of other samples. 15 Hv), stable and hardly changed.

  As is clear from FIG. 5, even when the electroless plating layer was heated to about 250 ° C., its hardness was about 450 to 550 Hv and hardly changed. However, when the plating layer was heated to 250 ° C. or higher (particularly 300 ° C. or higher), the hardness rapidly increased to about 950 to 1350 Hv.

When the surface of the plating layer heated at 250 ° C. was measured using X-rays, it was found that the X-ray diffraction peak was broad and the plating layer was in an amorphous state. On the other hand, when the plating layer heated at 400 ° C. was measured in the same manner, a clear X-ray diffraction peak appeared, and it was found that the plating layer was in a crystalline state. The X-ray diffraction peak mainly showed Ni and Ni ₃ P.

(3) Consideration Based on the above, it is clear that the Al alloy according to Sample 1 is excellent in dimensional stability and can stably exhibit high strength and hardness even when used in a high temperature environment. It became. Accordingly, such a fastener made of an Al alloy stably maintains a large clamping force (axial force) even if used in a high temperature environment (below the production temperature of the material / less than the hot extrusion temperature). It became clear to get.

  Moreover, since the plating layer formed on the base material surface made of such an Al alloy becomes a very hard fired plating layer by heating at 300 ° C. or higher, the fastener covered with the fired plating layer is excellent. In addition to the high temperature characteristics, it has also been revealed that it can exhibit high wear resistance and corrosion resistance.

(4) Al alloy It confirmed that the same result as the case of the sample 1 was obtained also about the Al alloy whose composition differs from the sample 1. Such an Al alloy composition is illustrated in Table 1.

Claims (12)

When the total is 100 mass% (simply referred to as “%”), Fe: 1.5-6%, Zr: 0.2-1.5%, Ti: 0.15-1.2%, balance : Made of aluminum alloy consisting of Al and inevitable impurities,
An aluminum alloy high strength fastener used to fix the first member and the second member.   The aluminum alloy high strength fastener according to claim 1, wherein the aluminum alloy further includes Mg: 0.2 to 2.5%.   The aluminum alloy high-strength fastener according to claim 1 or 2, wherein the aluminum alloy has a permanent growth rate within ± 0.05%.   The aluminum alloy high-strength fastener according to any one of claims 1 to 3, wherein the aluminum alloy has a tensile strength of 400 MPa or more.   The aluminum alloy high-strength fastener according to any one of claims 1 to 4, wherein the aluminum alloy has a hardness at room temperature of 150 Hv or more after being heated from room temperature to 400 ° C.   Furthermore, the aluminum alloy high intensity | strength fastener in any one of Claims 1-5 which has a coating layer which coat | covers the surface of the said aluminum alloy used as a sliding contact surface at least.   The aluminum alloy high-strength fastener according to claim 6, wherein the coating layer is a plating layer or an anodized layer.   The high strength fastener made of aluminum alloy according to claim 7, wherein the plating layer is an electroless Ni-P plating layer or a fired Ni-P plating layer.   The aluminum alloy high-strength fastener according to claim 8, wherein the fired Ni—P plating layer has a surface hardness of 900 Hv or more.   The aluminum alloy high-strength fastener according to any one of claims 1 to 9, which is a bolt, a nut, or a washer.   The high-strength fastener made of aluminum alloy according to any one of claims 1 to 10, wherein the first member or the second member is an aluminum alloy member. A plating step of forming an electroless Ni-P plating layer on a forged base material forged from a material made of an aluminum alloy or a rolled base material obtained by rolling a thread groove on the forged base material;
A firing step of heating the electroless Ni—P plating layer at 300 to 450 ° C. to form a firing Ni—P plating layer;
The manufacturing method of the high strength fastener made from an aluminum alloy of Claim 9 provided with these.

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