JPH08127851A - Production of forged aluminum alloy wheel excellent in corrosion fatigue resistance - Google Patents

Abstract

PURPOSE: To produce a forged Al alloy wheel excellent in corrosion fatigue resistance by subjecting an Al alloy contg. specified amounts of Mg, Si, Fe, Cu, Cr, Mn and Zn to forging and solution heat treatment and thereafter executing specified cold plastic working. CONSTITUTION: A forged Al alloy wheel is produced by an Al alloy contg., by weight, 0.3 to <=1.5% Mg, 0.2 to 1.2% Si, a trace amt. of <=0.7% Fe, <=0.4% Cu, <=0.4% Cr, <=0.2% Mn and <=0.8% Zn with inevitable impurities. At this time, a roller produced by a material harder than the same alloy is cold-pressed against the forged part softed by forging and solution heat treatment by 0.05 to 0.50mm penetrating quantity. Thus, at least the disk part or rim part of the Al alloy wheel is applied with plastic working and is subjected to aging treatment to harden the surface. If required, the roller is thereafter cold-pressed against the same again by 0.02 to 0.30mm penetrating quantity to impart higher residual compressive stress thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forged aluminum alloy wheel used in transportation equipment such as passenger cars, trucks, buses, linear motor cars, aircrafts, etc. Piece, 3
The present invention also relates to a method for manufacturing a forged aluminum alloy wheel having a higher fatigue strength than a T6 treated material using a normal Al-Mg-Si alloy.

[0002]

2. Description of the Related Art Al-Mg-Si system (JIS 6000
Type) aluminum alloys are widely used as materials for forged aluminum alloy wheels because of their excellent strength and corrosion resistance. Since the Al-Mg-Si alloy is a precipitation-strengthened alloy, it is usually subjected to a heat treatment method called T6 treatment, that is, solution treatment and aging treatment after processing to a predetermined shape, and strength by aging precipitation of Mg ₂ Si. Has been manufactured in a way to raise.

The aluminum alloy wheel is an important part for supporting the load of the vehicle, and therefore high fatigue strength is required. Therefore, the applicant first applied a method of cold pressing a roller to the surface of an aluminum alloy wheel to work harden the surface and impart a compressive residual stress to improve fatigue strength (Japanese Patent Laid-Open No. 6-79540). Proposed.

[0004]

[Patent Document 1] Japanese Patent Application Laid-Open No. 6-795
According to the method disclosed in Japanese Patent Laid-Open No. 40-40, in which a roller is pressed against the surface of an aluminum alloy wheel and the surface is work-hardened, the fatigue strength of the aluminum alloy wheel is improved. There is a limit to the amount of roller indentation because a microcrack is formed in the layer due to heavy working, and a fatigue crack is generated starting from the microcrack. Therefore, the effect of improving fatigue strength is limited.

In order to further improve the fatigue strength by eliminating the limit of the fatigue strength improving effect found in the above-mentioned conventional methods, the present invention uses a combination of surface layer processing by roller processing and heat treatment, Provided is a method for manufacturing a forged aluminum alloy wheel having excellent corrosion fatigue.

[0006]

In order to achieve the above object, the present inventors conducted a study for improving the fatigue strength of JIS 6000 series aluminum alloy wheels, and obtained the following findings in the process.

If the surface of the solution-treated aluminum alloy wheel after forging is subjected to aging treatment after roller processing, the hardness of the surface layer becomes higher than that of the inside.

After forging, the solution-treated aluminum alloy wheel is soft, and is disclosed in the above-mentioned JP-A-6-79540.
As compared with the prior art disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, the surface is not cracked even if the pressing amount is increased, as compared with the case where the roller processing is performed after the aging treatment.

After the forging, the surface of the solution-treated aluminum alloy wheel is subjected to the aging treatment after the roller processing, the compressive residual stress introduced during the roller processing is not completely lost, and the fatigue strength is improved. Effective compressive residual stress remains.

When the aluminum alloy wheel in the above state is subjected to the roller processing again, a compressive residual stress higher than before is applied to the surface layer having the increased strength.

When the solution-treated aluminum alloy wheel is subjected to roller processing and aging treatment after forging, not only the fatigue strength improvement due to the aging effect of the base metal but also the conventional T6 state is observed in this strengthened surface layer. Since a higher compressive residual stress can be applied, it is possible to significantly improve fatigue strength.

The present invention has been completed based on the above findings. That is, the method for manufacturing a forged aluminum alloy wheel excellent in corrosion fatigue of the present invention is
And Mg: 0.3-1.5%, Si: 0.2-1.2%
And a small amount of Fe: 0.7% or less, Cu: 0.4% or less, C
r: 0.4% or less, Mn: 0.2% or less, Zn: 0.8
% Or less and unavoidable impurities, when manufacturing a forged aluminum alloy wheel, after forging and solution heat treatment, a roller made of a harder material than the aluminum alloy is cold pressed into an amount of 0.05 to 0. Fifty
It is characterized in that the aluminum alloy wheel is pressed, and plastic working is applied to at least the outermost surface of the disk portion or the rim portion of the aluminum alloy wheel to perform aging treatment.

Another method of manufacturing a forged aluminum alloy wheel excellent in corrosion fatigue according to the present invention is as follows:
Mg: 0.3-1.5%, Si: 0.2-1.2% and a trace amount of Fe: 0.7% or less, Cu: 0.4% or less, Cr:
When manufacturing a forged aluminum alloy wheel with an aluminum alloy containing 0.4% or less, Mn: 0.2% or less, Zn: 0.8% or less, and unavoidable impurities, after forging and solution heat treatment, Roller made of hard material is pressed in cold condition 0.05 ~ 0.50mm
, Press at least, add plastic processing to at least the disk part of the aluminum alloy wheel, or the outermost surface of the rim part,
The aging treatment is performed, and the roller is cold pressed against the surface again with an amount of 0.02 to 0.30 mm to perform processing.

[0014]

[Action] Al-Mg-Si alloy (JIS 6000 series aluminum alloy) is an alloy which is strengthened by the precipitation of Mg ₂ Si, when Mg ₂ Si precipitation is introduced transferred by processing the deposited It is the core. Therefore, if Mg and Si are solid-soluted in the aluminum base material after forging and roller processing is performed to introduce a large amount of dislocations to the surface layer portion, the surface layer portion will not be removed during the subsequent aging treatment. Mg ₂ Si is finely and uniformly precipitated with the transition as a nucleus, and only the surface layer portion can have high strength.

The above is the cause of the increase in the strength of the surface layer according to the present invention, but the major difference from the T8 treatment in which pre-straining is performed before the T6 treatment is that the entire material is deformed in the normal T8 treatment. However, there is almost no residual stress.

In the roller processing according to the present invention, since only the surface layer portion is processed, there are a surface layer portion that is plastically deformed and a deep layer portion that is elastically deformed. Therefore, the compressive residual stress is generated in the surface layer portion after processing, and not only the surface layer portion is precipitation strengthened, but also the effect of improving the fatigue strength by the compressive residual stress is produced.

Generally, the residual stress is considered to be lost when heat treatment is applied, but since the aging heat treatment temperature of the 6000 series aluminum alloy is a relatively low temperature of 170 to 200 ° C., it is introduced by the roller processing after the solution treatment. The retained residual stress is not completely lost, and a compressive residual stress of 100 MPa or more remains even after the heat treatment, and a sufficient fatigue strength improving effect can be obtained.

Further, when the surface layer portion subjected to the roller processing after the solution treatment and the aging treatment is subjected to the roller processing again, the roller pushing amount to the surface layer portion having a high hardness was proportional to the increase in strength even though the same as the conventional method. Since high compressive residual stress can be applied, the fatigue strength can be further improved.

This is because the soft aluminum alloy after solution treatment was subjected to roller processing to give plastic deformation, and the depth of the surface layer was applied to the hardened aluminum alloy after aging to give plastic deformation. This is because the depth is deeper than the depth of the surface layer. That is, since the deep layer portion that is elastically deformed when the roller is processed after the aging treatment is a region that has undergone plastic deformation in the roller processing after the solution treatment that precedes it, the strength is increased during the aging treatment, This is because the compressive residual stress can be applied to the plastic deformation region of the surface layer portion with a higher elastic stress. Therefore, it is possible to significantly improve fatigue strength by combining roller processing and heat treatment.

Next, the reason for limiting the roller processing conditions for the surface layer will be described. With respect to the roller processing applied to the wheel surface after the solution treatment, if the indentation amount is less than 0.05 mm, the processing amount of the surface layer portion is small, so that sufficient compression residual stress cannot be obtained after the aging treatment, and if it exceeds 0.50 mm. Even with a soft aluminum alloy after solution treatment, the occurrence of surface microcracks due to heavy working cannot be avoided, and fatigue fracture occurs from the cracks.
It was limited to the range of 05 to 0.50 mm.

Since the roller processing after the solution treatment has an effect of improving the surface roughness, it is desirable to apply it to the surface having a relatively high roughness after removing the surface oxide layer by cutting after the forging.

The aging treatment performed after roller processing is preferably performed in a vacuum, in an inert gas, or in a heat treatment oil bath in order to prevent surface oxidation roughness during heating. When heat treatment is performed in the air, heat treatment is performed. After that, polishing or cutting to remove the surface oxide layer is necessary, and the strengthened surface layer part is partially lost, so that the effect of improving fatigue strength is reduced.

Rolling after the solution treatment and re-rolling on the wheel surface after the aging treatment,
If the indentation amount is less than 0.02 mm, sufficient residual stress is not given, and if it exceeds 0.30 mm, micro-surface cracks occur due to heavy working, so 0.02-0.30.
The range is limited to mm.

The material of the roller for roller processing may be harder than aluminum alloy, carbon steel such as S45C or tool steel such as SKD5 can be used, and it is necessary to match the size of the workpiece and the processing jig. The material may be selected according to the strength. Since the surface roughness after processing reflects the surface roughness of the roller, the surface roughness of the roller is R _max ≦ 6.3.
It is desirable to satisfy S.

The roller processing in the present invention is preferably applied to the entire surface of the wheel, but it requires a lot of labor and device modification to apply it to a portion having a large unevenness on the surface, so that it is used on a relatively smooth surface and used. Sufficient effect can be obtained only by applying it to a disk portion or a rim portion, which is sometimes heavily loaded.

Next, the reason why the chemical composition of the aluminum alloy used in the forged aluminum alloy wheel of the present invention is limited will be explained. The aluminum alloy needs to have a component composition that can obtain a sufficient precipitation strengthening action, and the aluminum alloy used in the present invention is intended for the 6000 series such as JIS 6061, 6063, 6151. In this case, if the Mg content is less than 0.3% and the Si content is less than 0.2%, the amount of precipitation of Mg ₂ Si is small and a sufficient precipitation strengthening action cannot be obtained. Also, Mg is 1.5%, S
When i exceeds 1.2%, the precipitated Mg ₂ Si easily coarsens, resulting in a decrease in ductility and deterioration of corrosion resistance.
Is limited to 0.3 to 1.5%, and Si is limited to 0.2 to 1.2%.

Further, although trace amounts of Fe, Cr, Cu, Zn, and Mn are inevitably mixed as impurities for the purpose of scrap recycling, mechanical properties due to miniaturization of casting structure and miniaturization of intermetallic compound are inevitable. Since it has both a positive effect of improvement and a negative effect of deterioration of corrosion resistance, their content is Fe: 0.7% or less, C in consideration of industrial practicality.
u: 0.4% or less, Cr: 0.4% or less, Mn: 0.2
% And Zn: 0.8% or less.

[0028]

Example A 6061 aluminum alloy ingot having the chemical composition shown in Table 1 was heated to 500 ° C., and then forged into a shape of an aluminum alloy wheel by hot pressing, and 530 ° C. ×
Solution heat treatment is performed for 0.5 hr, water cooling is performed, and then the surface oxide layer is removed by mechanical processing, and the rim width is 190.5 m.
m (5.5 in), rim diameter 571.5 mm (22.5i
The wheel of n) was produced and roller processing was performed under various conditions.

The roller is made of S45C steel and has the shape shown in FIG. 1. The outer peripheral surface has a radius of curvature A of 8 mm and a roller diameter B.
Is 45 mm, and it is attached to a lathe and is 0.52 mm / rev. It was pressed and processed with the feed amount of.

The aging treatment after roller processing is performed at 180 ° C. in a heating furnace in an inert gas atmosphere with Ar gas.
It was carried out under the condition of × 8 hr and then air-cooled.

The fatigue strength was measured by taking a test piece from the sampling position 3 shown by the chain double-dashed line on the disk portion 2 of the forged aluminum alloy wheel 1 shown in FIG. A bending fatigue tester was used to test the machined surface so that a predetermined stress was applied in a tensile-tensile state, and the fatigue life at 10 ⁶ times was evaluated. The results are shown in Table 2. In addition, the test is N when the roller processing is performed after the solution treatment by the implementation of the invention of claim 1.
o. Nos. 1 to 3 show the case where the roller processing was performed twice after the solution heat treatment and after the aging treatment by carrying out the invention of claim 2. It showed in 4-6. For comparison, as a conventional example, when the roller processing is not performed, No. 7 and No. 7 when roller processing was performed after aging treatment. No. 8 is shown, and as a comparative example, when the roller processing after the solution treatment is out of the range of the indentation amount of the present invention, it is No. When the number is as high as 9, No. 10 and the roller processing are performed twice after the solution treatment and the aging treatment, but when the indentation amount after the aging treatment is out of the range of the indentation amount of the present invention, No. 11 was shown.

[0032]

[Table 1]

[0033]

[Table 2]

To improve the fatigue strength of the wheel, 10
Although it is desirable to apply a compressive residual stress of 0 MPa or more, from the results of Table 2 above, according to the practice of the present invention, when the roller processing is performed after the solution treatment, the roller processing is performed after the solution treatment and the aging treatment. It can be seen that a sufficient compressive residual stress is applied in any of the cases. Further, in the example of the present invention, due to the effect of the precipitation strengthening of the surface layer and the residual stress, the conventional example No.
A fatigue strength higher than 8 is obtained.

Further, according to the present invention, the roller processing was performed twice after the solution treatment and the aging treatment. In the case of 4 to 6, the conventional example No. Fatigue strength significantly higher than that of No. 8 was obtained. Then, the indentation amount is out of the range of the present invention, and the comparative example No. It can be seen that all of Nos. 9 to 11 have lower fatigue strength than the examples of the present invention.

[0036]

According to the present invention, the same Al-M as the conventional one is used.
A forged aluminum alloy wheel having higher fatigue strength than conventional products can be provided by using a g-Si alloy.

[Brief description of drawings]

FIG. 1 is a side view (a) and a front view (b) showing a shape of a pushing roller used in an embodiment of the present invention.

FIG. 2 is a vertical sectional view (a) and a front view (b) of a forged aluminum alloy wheel made by carrying out the present invention, and FIG. 2 (b) shows a sampling position 3 of a test piece.

[Explanation of symbols]

 1 Forged aluminum alloy wheel 2 Disc part 3 Sampling position

Claims (2)

[Claims] 1. Weight% of Mg: 0.3-1.5%, S
i: 0.2 to 1.2% and a trace amount of Fe: 0.7% or less, C
u: 0.4% or less, Cr: 0.4% or less, Mn: 0.2
%, Zn: 0.8% or less, and when manufacturing a forged aluminum alloy wheel with an aluminum alloy containing unavoidable impurities, a roller made of a harder material than the aluminum alloy is cold-processed after forging and solution heat treatment. A forged aluminum alloy wheel excellent in corrosion fatigue, characterized by being pressed with an indentation amount of 0.05 to 0.50 mm, performing plastic working on at least the outermost surface of the disk portion or rim portion of the aluminum alloy wheel, and performing aging treatment. Manufacturing method. 2. Mg: 0.3 to 1.5% by weight, S
i: 0.2 to 1.2% and a trace amount of Fe: 0.7% or less, C
u: 0.4% or less, Cr: 0.4% or less, Mn: 0.2
%, Zn: 0.8% or less, and when manufacturing a forged aluminum alloy wheel with an aluminum alloy containing unavoidable impurities, a roller made of a harder material than the aluminum alloy is cold-processed after forging and solution heat treatment. The aluminum alloy wheel is pressed at a pressing amount of 0.05 to 0.50 mm, at least the outermost surface of the disk portion or the rim portion of the aluminum alloy wheel is subjected to plastic working, aging treatment is performed, and the roller is cold pressed again at the surface amount of 0.02. A method for manufacturing a forged aluminum alloy wheel excellent in corrosion fatigue, which comprises pressing and working with a width of 0.30 mm.