JPH08253852A - Formation of wear resistant film onto aluminum alloy substrate - Google Patents

Abstract

PURPOSE: To suppress thermal distortion in an aluminum alloy substrate at the time of forming sprayed film and furthermore to form wear resistant film having sufficient wear resistance on the surface of the aluminum alloy substrate. CONSTITUTION: On the surface of an aluminum alloy substrate 1, sprayed film harder than the aluminum alloy substrate 1 is formed by thermal spraying. After that, the sprayed film 2 is subjected to blasting treatment by using shot grains harder than the substrate 1 and softer than the sprayed film 2, by which the blast film 3 is formed from the components of the shot grains is on the sprayed film 2. Since the film thickness needed for its performance such as wear resistance can be obtd. by the wear resistant film 4 constituted of the sprayed film 2 and blast film 3, the sprayed film 2 can be thinned compared to the case in which the film thickness needed for its performance of wear resistance has been obtd. solely by sprayed film heretofore, so that thermal distortion in the aluminum alloy substrate 1 can be suppresed by reduced thermal spraying time at the time of forming the sprayed film 2.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming an abrasion resistant coating on an aluminum alloy substrate. INDUSTRIAL APPLICABILITY The method of the present invention can be suitably used for a surface treatment for improving wear resistance of a bore surface in a cast aluminum cylinder block for a vehicle engine, for example.

[0002]

2. Description of the Related Art Aluminum or aluminum alloys are used in a wide range of fields including automobile parts because they are lighter in weight and have better thermal conductivity and corrosion resistance than steel materials. However, aluminum alloys are generally inferior in strength, wear resistance, and heat resistance to steel materials, and the parts and parts that can be applied as substitute materials for steel materials are limited as they are. Further, even in the case where an aluminum alloy has already been used, in recent years, further improvement in durability has been demanded as the use environment becomes more severe.

Therefore, a technique for forming a coating having characteristics such as wear resistance on the surface of an aluminum alloy substrate has been developed. For example, Japanese Patent Laid-Open No. 6-240436 discloses an aluminum alloy cylinder for a vehicle engine. A technique of forming a thermal spray coating having high wear resistance on the bore surface of the block is disclosed. This uses a composite powder such as aluminum and iron-based metal as a thermal spray powder on the bore surface of a cylinder block to form a thermal spray coating by plasma spraying.

[0004]

However, in order to secure the characteristics such as abrasion resistance required for the bore surface only with the thermal spray coating as in the above-mentioned prior art, when the thickness of the thermal spray coating is increased, the following result is obtained. There are problems as shown. That is, since the film thickness of the thermal spray coating is proportional to the thermal spray time, if an attempt is made to increase the film thickness of the thermal spray coating, the thermal spray time will be correspondingly increased, and the amount of heat input to the aluminum alloy substrate will increase accordingly. Aluminum alloys, in particular, have high heat conductivity, so the temperature of the entire cylinder block easily rises, and the maximum temperature is 30 during thermal spraying.
It reaches about 0 ° C. Therefore, thermal strain occurs in the entire cylinder block. In order to allow this strain, the film thickness of the thermal spray coating needs to be a film thickness obtained by adding the above strain amount to the required film thickness for performance such as abrasion resistance. However, in order to increase the film thickness in this way, it is necessary to lengthen the thermal spraying time as described above, resulting in a vicious cycle in which the strain further increases.

The present invention has been made in view of the above circumstances, and it is possible to suppress the thermal strain of the aluminum alloy substrate at the time of forming the sprayed coating, and yet the surface of the aluminum alloy substrate has sufficient wear resistance. It is a technical problem to be solved to provide a method for forming an abrasion resistant coating on an aluminum alloy substrate capable of forming an abrasion resistant coating.

[0006]

A method for forming an abrasion resistant coating on an aluminum alloy substrate according to the present invention which solves the above problems is to form an abrasion resistant coating comprising a sprayed coating and a blast coating on the surface of an aluminum alloy substrate. How to do
A step of forming the sprayed coating, which is harder than the aluminum alloy base, on the aluminum alloy base by thermal spraying; and spraying using shot particles that are harder than the aluminum alloy base and softer than the sprayed coating. Blasting the coating to form the blast coating made of the shot grain components on the thermal spray coating.

[0007] In a preferred embodiment, the thermal spray coating is made of one or more alloys selected from the group consisting of iron alloys, nickel alloys and copper alloys. In a preferred embodiment, the shot particles include C: 0.4 to 2.0 wt%, or further P: 0.1 to 1.0 wt% and / or C.
r: 2.0 to 8.0 wt% is included, and the balance is Fe.

In a preferred embodiment, the aluminum alloy substrate is an aluminum alloy cylinder block made of cast metal, and the wear resistant coating is formed on the bore surface of the cylinder block.

[0009]

According to the method of forming the wear resistant coating on the aluminum alloy substrate of the present invention, the wear resistant coating composed of the thermal spray coating and the blast coating is formed on the surface of the aluminum alloy substrate.
In this way, a composite coating consisting of a thermal spray coating and a blast coating can provide the required film thickness for performance such as wear resistance. The film thickness of the sprayed coating can be reduced as compared with the case where it is obtained. Therefore, compared with the conventional method of forming a wear-resistant coating by using only the thermal spray coating, the thermal spray time at the time of forming the thermal spray coating can be shortened, whereby thermal distortion of the aluminum alloy substrate can be suppressed. In addition,
The temperature of the aluminum alloy substrate during thermal spraying is almost proportional to the thermal spraying time.

When the surface of the aluminum alloy substrate is directly blasted by using shot particles harder than the aluminum alloy substrate for the purpose of improving the wear resistance of the surface of the aluminum alloy substrate, the aluminum particles are projected by the shot particles. Since the surface of the alloy base is only ground, the blast coating composed of the shot grain component cannot be formed on the surface of the aluminum alloy base. In contrast,
In the method of the present invention, a spray coating harder than an aluminum alloy base is first formed on an aluminum alloy base by thermal spraying, and thereafter, shot particles that are harder than the aluminum alloy base and softer than the spray coating are used. Since the thermal spray coating is subjected to the blast treatment, it becomes possible to easily form the blast coating including the shot grain components on the thermal spray coating. Therefore, the surface of the aluminum alloy substrate can be provided with characteristics such as wear resistance according to the shot grain component.

Further, in the abrasion-resistant coating obtained by the method of the present invention, at the boundary portion between the thermal spray coating and the blast coating, the blast coating bites into the thermal spray coating to form a mixed layer, High adhesion between coating and blast coating. When the thermal spray coating is made of a high wear resistant alloy, the effect of improving the wear resistance by this thermal spray coating can be added, and the wear resistance is more effective than the case of the blast coating alone. It is possible to improve.

Further, the blasting treatment increases the adhesion at the interface between the aluminum alloy substrate and the thermal spray coating. This is because the impact force caused by shot particles colliding with the thermal spray coating acts on the interface between the aluminum alloy substrate and the thermal spray coating, and the thermal spray coating breaks into the aluminum alloy substrate and destroys the oxide layer at the interface. This is because the physical bond and the anchor effect are enhanced. Therefore, according to the method of the present invention, it is possible to increase the adhesion strength between the aluminum alloy substrate and the wear resistant coating, and to effectively prevent the peeling of the coating during surface finishing processing by mechanical processing after the coating formation. It will be possible.

Further, since the outermost surface of the wear resistant coating obtained by the method of the present invention is composed of the blast coating formed by the blast treatment, its surface roughness becomes smaller than that of the thermal spray coating. For this reason, the shear stress generated during the surface finishing process after the film formation is reduced, which also makes it possible to effectively prevent the film peeling during the process and the like.

Next, when the thermal spray coating is made of one or more alloys selected from the group consisting of iron alloys, nickel alloys and copper alloys, these alloys should be easily sprayed on the aluminum alloy substrate. In addition, since these hard alloys have high wear resistance, the additional effect of improving the wear resistance by the thermal spray coating can be enhanced. Also,
The shot particles include C: 0.4 to 2.0 wt%,
Alternatively, P: 0.1 to 1.0 wt% and / or Cr:
When the content of Fe is 2.0 to 8.0 wt% and the balance is Fe, the blast coating can be easily formed on the thermal spray coating by the blast treatment, and the wear resistance can be effectively improved. it can. That is, C, P, Cr
Contributes to the improvement of wear resistance, and the higher the content of these components, the higher the wear resistance. If the contents of C, P, and Cr are too large, the rate of film formation by the blasting process decreases, and the Schut grains are likely to crack during the blasting process. Therefore, the upper limits of the respective contents are specified.
On the other hand, the lower limit of the C, P, and Cr contents is defined as a value required to satisfy the wear resistance required for the cylinder bore. In addition, the more preferable range of the content of C, P, and Cr is C: 0.6 to 1.0 wt%, P: 0.6 to
0.8 wt% and Cr: 3 to 6 wt%.

Furthermore, when the aluminum alloy substrate is a cast aluminum alloy cylinder block and the wear resistant coating is formed on the bore surface of the cylinder block, thermal strain of the cylinder block can be effectively suppressed. In addition, it is possible to form a wear resistant coating having sufficient wear resistance on the bore surface of the cylinder block.
Further, conventionally, in a cast aluminum cylinder block, there was a problem that the amount of oil rises due to defects such as porosity appearing on the surface, but a wear resistant film is formed on the bore surface. As a result, surface defects can be eliminated, and the above problems can be solved.

[0016]

The present invention will be described below in detail with reference to examples. (Embodiment 1) FIG. 1 is a partially enlarged sectional view schematically showing an aluminum alloy cylinder block 1 having a bore surface 1a on which a wear resistant coating 4 composed of a thermal spray coating 2 and a blast coating 3 is formed. The manufacturing process will be described below.

First, a cylinder block 1 made of an aluminum alloy (JIS AC2B, hardness Hv95) is cast by ordinary low pressure casting, and the bore portion is bored under the following conditions to form a bore of φ87.5 × 140 mm. did. Tool: Carbide tip or high-speed tool steel Cut: 0.15 mm Peripheral speed: 540 m / min Feed: 0.2 mm / rev Stock: φ0.3 mm (diameter) Dry machining (without coolant) And this cylinder block 1 1 up to near 170 ℃
After preheating for about 0 seconds, a Fe-Cr alloy (composition: F) was used under the following conditions using a spray gun 5 as shown in FIG.
Plasma spraying using a sprayed powder consisting of e-7% C-62.5% Cr-2% or less Si) was performed to form the sprayed coating 2 on the bore surface 1a of the cylinder block 1. The thermal spray coating 2 has a hardness of HV850, a film thickness of 30 μm,
The surface roughness is Rz 20 μm. Further, the temperature of the cylinder block 1 at the time of this thermal spraying is about 190 ° C. at the maximum.

Spraying distance: 50 mm Spraying time: 7 seconds Spraying gun moving speed: 2400 mm / min Powder supply amount: 25 g / min Powder particle size: -325 mesh (-45 μm) Next, as shown in FIG. 62 or nucleus 61
Of shot particles (component: C: 0.45 wt%, Fe:
The rest) 6 was prepared. Then, the shot particles 6 were used to blast the surface of the thermal spray coating 2 under the following conditions to form a blast coating 3 of 6 shot particles on the surface of the thermal spray coating 2. The hardness of the blast film 3 is H.
V300, film thickness 60 μm, surface roughness Rz 30 μ
m.

Finally, the bore portion was finish-honed under the following conditions. Whetstone: GC180G16CGK, and GC
240D7YED Rotation speed: 39 rpm Reciprocating stroke speed: 16 m / min Grinding stone expansion pressure: 7 to 10 kg / cm ² Crosshatch angle: 45 degrees As described above, according to the method of this embodiment, the plasma spraying time is as short as 7 seconds, Since the temperature of the cylinder block 1 at the time of thermal spraying is about 190 ° C. at the maximum, there is almost no thermal strain of the cylinder block 1, and the surface roughness and shape accuracy of the wear resistant coating 4 (blast coating 3) formed are good. Therefore, it was possible to obtain a finished product simply by finishing honing.

(Examples 2 to 8) The above-mentioned Example 1 except that the shot grains 6 having the components shown in Table 1 were used.
Is the same as (Comparative Examples 1 to 3) The same as Example 1 except that the shot grains 6 having the components shown in Table 1 are used.

(Evaluation of Wear Resistance) The wear resistance of the bore portion of the cylinder block 1 according to Examples 1 to 8 and Comparative Examples 1 to 3 was evaluated. In addition, as shown in FIG. 4, this evaluation was performed on each of the methods of Examples 1 to 8 and Comparative Examples 1 to 3 on the outer peripheral surface of the aluminum alloy test ring (35 mm in outer diameter) similar to that of Example 1. According to the LFW-1 wear test, a wear resistant film 4 is formed in accordance with the test block and a test block (width 6.5 mm) 8 made of a material (flake graphite cast iron, Cr plated) corresponding to the piston ring is prepared. A wear test was conducted using a machine under the following conditions. The results are shown in Table 1.

Rotational speed: 160 rpm Load: 180 kg Time: 60 minutes Oil bath of engine oil (5W-30)

[0023]

[Table 1] As is clear from Table 1, the wear-resistant coatings 4 of Examples 1 to 8 had a maximum wear depth of 1.6 μm, which was much higher than those of Comparative Examples 1 to 3. .

(Evaluation of Adhesion Strength of Wear-Resistant Coating) The bore portion of the cylinder block 1 on which the wear-resistant coating 4 according to the above-mentioned Example 1 is formed is subjected to boring finishing (the above-mentioned Example 1).
Under the same conditions as those for the boring process shown in (1), the adhesion of the wear resistant coating 4 was evaluated. Further, this bore portion was subjected to honing finish processing (similar conditions to the honing finish processing shown in the above Example 1), and the adhesion of the wear resistant coating 4 was evaluated. The results are shown in Table 2. For comparison, a cylinder block 1 similar to that of the above-described Example 1 was used.
Fe alloy (component: 1 wt% C-Fe) on the bore surface 1a of
A thermal spray coating (film thickness 300 μm,
A surface roughness Rz of about 200 μm) was formed, and the bore portion was subjected to boring finishing and honing finishing in the same manner as above, and the adhesion of the thermal spray coating according to the conventional example was evaluated. The results are also shown in Table 2.

[0025]

[Table 2] In addition, the adhesion strength of the wear resistant coating 4 of the cylinder block 1 according to the above Example 1 was evaluated. In this evaluation, as shown in FIG. 5, the wear-resistant coating 4 was formed on the surface of the aluminum alloy test piece (thickness 5 mm) 9 similar to that of Example 1 according to the method of Example 1, After fixing the auxiliary member 11 to the surface of the wear resistant film 4 via the adhesive 10, only the wear resistant film 4, the adhesive 10 and the auxiliary member 11 are fixed with the test piece 9 fixed by the jig 12. It was carried out by applying a shear load. The results are shown in Table 3.

On the surface of a similar test piece 9 for comparison, F
A thermal spray coating (thickness: 300 μm) was formed by the same plasma spraying method as in Example 1 except that a thermal spraying powder made of an e alloy (component: 1 wt% C—Fe) was used. The results of examining the adhesion strength in the same manner as above are also shown in Table 3.

[0027]

[Table 3] (Evaluation of oil rising amount) The oil rising amount was evaluated for the bore portion of the cylinder block 1 on which the wear resistant coating 4 according to the above-mentioned Example 1 was formed. This is because the cylinder block according to the present embodiment is mounted on an in-line four-cylinder 1800 cc gasoline engine, and the oil level in the oil pan is kept constant under various operating conditions by bench evaluation to check the oil rise amount. It was As a result, cast iron (FC2
3C) shows the same value as that of the cylinder block. As a result, conventionally, in the cast aluminum cylinder block, there was a problem that the amount of oil rises due to defects such as porosity. However, as in the present embodiment, the bore surface 1a has wear resistance. It was confirmed that this problem can be solved by forming the film 4.

Further, the abrasion resistant coating 4 according to the present embodiment is subjected to compressive stress during the blasting treatment, and compared with a conventional thermal spray coating in which such compressive stress does not act,
Adhesion and wear resistance are improved. As the sprayed coating 2, it is possible to form a coating on an aluminum alloy substrate by spraying, and the adhesiveness of the sprayed coating alone by the above shearing method is 3 kg / mm ² or more and the hardness is Hv 400 or more. It is more preferable that the hardness is Hv 600 or higher in consideration of the hardness of the shot grains. For example, the thermal spray coating 2 can be composed of one or more of iron alloys, nickel alloys, and copper alloys having the compositions shown in Table 4. Considering the thermal spraying properties (adhesion strength, porosity in the coating and degree of oxidation), nickel-based alloys are most preferable, and iron-based alloys are the second most preferable, and iron-based or copper-based alloys in terms of cost. Alloys are preferred. The film thickness of the thermal spray coating 2 is preferably 10 to 50 μm. This is because when the film thickness of the sprayed coating 2 is thinner than 10 μm, a part where the sprayed coating is not formed remains, and when it is thicker than 50 μm, the spraying time is long and the thermal strain of the aluminum alloy substrate is large. As the shot particles, it is necessary to make the hardness lower than that of the sprayed layer.
It is necessary to perform a tempering treatment at 400 ° C. × 1H to adjust the hardness to an appropriate level and then perform a blast treatment.

[0029]

[Table 4] Further, the hardness of the blast coating 3 needs to satisfy the conditions that it is harder than the aluminum alloy substrate and softer than the thermal spray coating 2, but it is easy to form the coating by the blast treatment, and the mechanical processing after the coating is formed. In consideration of easiness and the like, it is preferable that the blast coating 3 is as soft as possible, and therefore the hardness of the blast coating 3 is preferably Hv400 or less, and more preferably Hv300 or less.
The thickness of the blast coating 3 is preferably 50-100 μm. This is because if the film thickness of the blast coating 3 is thinner than 50 μm, the film thickness after finishing honing is 20 μm or less, and it is difficult to secure a durable life, and if it is thicker than 100 μm, the blast treatment time is long and it is not economical.
Further, the preferable main component composition of the blast film 3 is as described above, but the impurities contained as a normal material are S
i: 0.35 wt% or less, Mn: 1.0 wt% or less, M
o: 0.2 wt% or less, S: 0.1 wt% or less, Ca:
It is acceptable if it is within the range of 0.1 wt% or less.

Further, in the above embodiment, an example of forming the sprayed coating 2 by the plasma spraying method has been described, but it is also possible to use an arc spraying method, HVOF spraying, plasma spraying, reduced pressure spraying method or the like.

[0031]

As described above, the method of forming an abrasion resistant coating on an aluminum alloy substrate according to the present invention forms an abrasion resistant coating consisting of a thermal spray coating and a blast coating on the surface of an aluminum alloy substrate. Therefore, compared with the conventional method of forming a wear-resistant coating by spray coating alone, it is possible to shorten the spray time during spray coating formation, thereby suppressing the thermal strain of the aluminum alloy substrate, Abrasion resistance can be imparted according to the component composition of the thermal spray coating and the blast coating.

Further, since the blast coating is formed on the spray coating by the blast treatment, the adhesion at the interface between the aluminum alloy substrate and the spray coating can be increased and the surface roughness of the blast coating can be reduced. Therefore, it becomes possible to effectively prevent the peeling of the coating film during the surface finishing process by the mechanical processing after the coating film formation.

[Brief description of drawings]

FIG. 1 is a partially enlarged cross-sectional view showing a state in which a wear-resistant coating composed of a thermal spray coating and a blast coating is formed on a bore surface of a cast aluminum cylinder block according to the present embodiment.

FIG. 2 is an explanatory view schematically showing how a thermal spray coating is formed on a bore surface according to the present embodiment.

FIG. 3 is a cross-sectional view of shot grains according to the present embodiment.

FIG. 4 is a perspective view schematically showing a wear test method.

FIG. 5 is a sectional view schematically showing a shear test method.

[Explanation of symbols]

1 is an aluminum cylinder block, 1a is a bore surface, 2 is a thermal spray coating, 3 is a blast coating, 4 is an abrasion resistant coating, and 6 is shot particles.

Claims (4)

[Claims] 1. A method for forming a wear resistant coating comprising a thermal spray coating and a blast coating on the surface of an aluminum alloy substrate, the thermal spray coating being harder than the aluminum alloy substrate on the aluminum alloy substrate. And a blast treatment of the spray coating with a shot grain that is harder than the aluminum alloy substrate and softer than the spray coating to form the blast consisting of the shot grain component on the spray coating. A method for forming an abrasion resistant film on an aluminum alloy substrate, which comprises the step of forming a film. 2. The aluminum alloy substrate according to claim 1, wherein the thermal spray coating is made of one or more alloys selected from the group consisting of iron alloys, nickel alloys and copper alloys. Method of forming abradable film. 3. The shot grains are C: 0.4 to 2.0.
wt%, or further P: 0.1 to 1.0 wt% and / or Cr: 2.0 to 8.0 wt% with the balance Fe.
The method for forming a wear-resistant coating on an aluminum alloy substrate according to claim 1, comprising: 4. The aluminum alloy substrate according to claim 1, wherein the aluminum alloy substrate is a cast aluminum alloy cylinder block, and the wear-resistant coating is formed on a bore surface of the cylinder block. Method for forming abrasion resistant coating of.