JPH0533094A - Expanded aluminum alloy for machining excellent in surface finishing property and corrosion resistance after machining - Google Patents

Abstract

PURPOSE:To improve the surface finishing properties and corrosion resistance of an aluminum alloy after machining while its mechanical strength is maintained by specifying Si, Mg, Cu, Cr and Pb and limiting the grain size of Pb grains dispersed in the metallic structure. CONSTITUTION:This aluminum alloy is formed of a compsn. constituted of, by weight, 0.4 to 0.8% Si, 0.8 to 1.5% Mg, 0.1 to 0.4% Cu, <=0.3% Cr, 0.3 to 2% Pb and the balance Al. Then, the grain size of Pb grains to be dispersed in the metallic structure is regulated to <=20mum, and they are uniformly dispersed. Thus, its surface finishing properties and corrosion resistance after machining can exceedingly be improved while its mechanical strength is maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy suitable for cutting, and more particularly, to a surface finish and corrosion resistance after cutting which are optimum for members particularly required to have corrosion resistance, such as automobile parts. It relates to an excellent wrought aluminum alloy.

[0002]

2. Description of the Related Art In recent years, in order to reduce the weight of automobiles due to fuel consumption regulations, in addition to body seats such as bonnets and doors, which have been made of aluminum for a long time, lower parts such as upper arms and lower arms and engine parts,
Aluminum alloys are also being used for automobile parts such as brake systems. Many of these parts are used as final products after cutting, polishing, etc. to semi-finished products obtained by performing extruding, drawing, forging, and other wrought processing after casting. Are required to have the following characteristics. Excellent machinability (cutting ability, surface finish after cutting). It has excellent corrosion resistance. Must have the specified strength. Conventionally, a large number of JIS 2011 alloys (corresponding to AA 2011 alloys), which are high-strength free-cutting alloys shown in Table 1, have been put to practical use for applications requiring machinability. But this JIS
2011 alloy is excellent in machinability and strength, but it is Al
Since it is a Cu-based alloy, its corrosion resistance is poor. Therefore, for applications requiring corrosion resistance, the AA6262 alloy, which is a corrosion-resistant free-cutting alloy shown in Table 1, has been widely put into practical use. However, this AA6262 alloy has a drawback that the surface finish after cutting is poor. Further, although the corrosion resistance is relatively excellent, it has not been able to sufficiently satisfy the requirements for the corrosion resistance, which is increasing more and more in recent years.

[0003]

[Table 1]

[0004]

As described above, the conventional alloy cannot satisfy all the required properties, and it is superior to the AA6262 alloy in that the surface finish after cutting is excellent and the corrosion resistance is further improved. There has been a demand for the development of excellent aluminum alloys.

[0005]

The present inventor has conducted extensive studies to solve the above-mentioned problems, and as a result, the conventional AA626 has been found.
The inventors have found that the above object can be achieved by improving the alloys No. 2 and Pb and Bi, and have completed the present invention.

That is, according to the present invention, Si 0.40 to 0.8% by weight, Mg 0.8 to 1.5% by weight, Cu 0.10 to 0.40% by weight,
Cr 0.30 wt% or less, Pb 0.30 to 2.0 wt%, the balance being aluminum and inevitable impurities, and
A wrought aluminum alloy for cutting having excellent surface finish and corrosion resistance after cutting, characterized in that the particle size of Pb particles dispersed in the metal structure is 20 μm or less.

[0007]

Next, the reason for adding each element and the reason for limiting the amount added in the present invention will be explained. The most important feature of the present invention is B
i is not added. In AA6262 alloy, Bi is conventionally added to improve the machinability.
According to the knowledge of the present inventor, Bi binds with Mg added for the purpose of improving strength and forms a coarse compound of Bi and Mg. The particle size of these compounds is 100 to 200 μm when lightly expanded, and 30 even when strongly processed.
It is about 50 μm. This coarse compound of Bi and Mg was stripped off by a tool during cutting and had an adverse effect on the surface finish after cutting. Further, this compound tends to be a source of corrosion generation under a corrosive environment such as an alkaline solution, salt water, and water in oil, which deteriorates the corrosion resistance. The present inventor has obtained such findings as a result of research,
Based on this, Bi was not added in the present invention.

Another feature of the present invention is AA6.
This is because the limited range of the added amount of Pb was made much wider than that of the 262 alloy (Pb; 0.40 to 0.7% by weight). If the amount of Pb added is within an appropriate range, the particle size in the alloy material is 20
Since it is uniformly dispersed as relatively fine particles of μm or less, the addition of Pb has the effect of improving the machinability without adversely affecting the surface finish and the corrosion resistance after cutting.
However, if the amount of Pb added is less than 0.30% by weight, it is difficult to obtain the above effects, while if added over 2.0% by weight, machinability is improved, but coarse compounds are formed, resulting in surface finish and corrosion resistance after cutting. Is deteriorated, which is not preferable. Therefore, in the present invention, the amount of Pb added is 0.30 to 2.0.
Limited to wt%. Even if the amount of Pb is relatively large even within the range of the present invention, or depending on the production conditions, a coarse compound having a particle size of more than 20 μm is produced, which deteriorates the surface finish and the corrosion resistance after cutting. There are cases.
Therefore, it is necessary to manufacture the Pb so that the particle diameter thereof does not exceed 20 μm.

Si and Mg have the effect of increasing strength by precipitating as Mg ₂ Si during heat treatment. However, if the amounts of Si and Mg added are less than 0.40% by weight and less than 0.8% by weight, respectively, the above effect cannot be obtained.
If it is added in an amount exceeding 1.5% by weight, the strength is improved, but the toughness and stress corrosion cracking resistance are deteriorated, which is not preferable. Therefore, in the present invention, the amounts of Si and Mg added are limited to 0.40 to 0.8% by weight and 0.8 to 1.5% by weight, respectively.

Cu has the effect of improving the strength, but if its addition amount is less than 0.10% by weight, its effect cannot be obtained, while if it is added in excess of 0.40% by weight, corrosion resistance is impaired. Therefore, in the present invention, the addition amount of Cu is limited to 0.10 to 0.40% by weight.

Cr has an effect of improving toughness and stress corrosion cracking resistance. However, if it is added in an amount of more than 0.30% by weight, a coarse intermetallic compound is produced, which impairs machinability and corrosion resistance. Therefore, in the present invention, the addition amount of Cr is 0.30% by weight.
Limited to:

Inevitable impurities such as Fe, Mn and Zn are
0.7 wt% or less, 0.20 wt% or less, 0.30 wt%
If the content is below, the effect of the present invention is not adversely affected.

[0013]

EXAMPLES A detailed description will be given below based on examples.

Example 1 Alloy ingot billets (diameter 200 mm) having compositions No. 1 and 2 (inventive alloy) and No. 3 (conventional alloy) shown in Table 2 were D
It was produced by C casting, and the ingot was subjected to a homogenizing treatment by holding it at 530 to 570 ° C. for 4 hours and then hot extruded at 400 to 500 ° C. to obtain a round bar having a diameter of 60 mm. 550 on these extruded rods
After performing a solution heat treatment at 1 ° C. for 1 hour and an artificial aging treatment at 180 ° C. for 8 hours, a tensile test, a cutting test and a corrosion resistance test were performed. Further, the metal structure of these extruded rods was observed, and the particle size of Pb, Bi or a compound thereof dispersed in the metal structure was examined. Cutting test is 50mm in diameter in advance
Using a cemented carbide bite with a rake angle of 10 degrees, cut the test piece processed into a round bar with a cutting depth of 0.5 mm and a feed of 0.05 to 0.1 mm.
/ Rev, cutting speed 100 mm / min., And the weight (g) per 100 chips is measured to check the chip disposability, and after cutting to check the surface finish after cutting. The surface roughness of the test piece of 1 was measured by a Kosaka surface roughness meter. The corrosion resistance test was carried out by measuring the weight change and pitting depth by the Cass test of 250 hours treatment.

[0015]

[Table 2]

The results of the tensile test are the same for Nos. 1, 2 and 3, and the tensile strength is 366 to 379 N / mm ² , and the proof stress is 344.
〜353 N / mm ² , elongation value 14〜15%. Table 3 shows the results of the cutting test and the corrosion resistance test. It is clear from Table 3 that the alloy of the present invention is significantly superior in surface roughness after cutting and corrosion resistance to the conventional AA6262 alloy. Both of these characteristics are greatly improved by the conventional AA626.
In the No. 2 alloy, coarse Bi and Mg compounds are scattered in the metallographic structure, whereas in the alloy of the present invention, fine Pb particles are uniformly dispersed in the metallographic structure. This is because it is not peeled off by a tool and it does not easily become a source of corrosion.

[0017]

[Table 3]

Example 2 Alloy cast rods (diameter 50 mm) having compositions No. 1 and 2 (inventive alloy) and No. 3 (conventional alloy) shown in Table 4 were prepared, and the cast rods were 530 to 550 ° C. After carrying out a homogenizing treatment for 4 hours, a round bar test piece having a diameter of 30 mm and a height of 50 mm was cut out. These test pieces were upset forged at a hot forging temperature of 400 ° C and a processing rate shown in Table 4, and the obtained forged product was 540 ° C.
After performing a solution heat treatment for 1 hour and then an artificial aging treatment at 180 ° C. for 8 hours, a tensile test, a cutting test, and a corrosion resistance test were performed. Further, the metal structure of these forged products was observed, and the particle size of Pb, Bi or a compound thereof dispersed in the metal structure was examined. For cutting test, after cutting the outer circumference of each forged product, using a cemented carbide bite with a rake angle of 10 degrees, cutting depth 1.0 mm, feed 0.1 mm / rev, cutting speed 1
Cutting at 00 mm / min. To check the chip disposability
The weight (g) per 100 pieces was measured, and in order to examine the surface finish after cutting, the surface roughness of the test piece after cutting was measured with a Kosaka surface roughness meter.
The corrosion resistance test was carried out by measuring the weight change and pitting depth by the Cass test of 250 hours treatment.

[0019]

[Table 4]

The results of the tensile test are the same for Nos. 1, 2 and 3, and the tensile strength is 335 to 348 N / mm ² , and the proof stress is 315.
~ 323N / mm ^2, was 16 to 18% elongation value. Table 5 shows the results of the cutting test and the corrosion resistance test. It is clear from Table 5 that the alloys of the present invention are significantly superior in surface roughness after cutting and corrosion resistance to the conventional AA6262 alloys.

[0021]

[Table 5]

[0022]

As described above, the alloy of the present invention significantly improves the surface finishing property and corrosion resistance after cutting while maintaining the chip disposability and mechanical strength of the conventional corrosion-resistant free-cutting alloy (AA6262 alloy). It is possible. Therefore, not only the automobile parts but also the various applications in which the AA6262 alloy has been conventionally used, the industrially remarkable effect is exhibited.

Claims (1)

Claims 1. Si 0.40-0.8 wt%, Mg 0.8-
1.5% by weight, Cu 0.10 to 0.40% by weight, Cr 0.30% by weight
Below, 0.30 to 2.0% by weight of Pb, the balance being aluminum and unavoidable impurities, and the particle size of Pb particles dispersed in the metallographic structure was 20 μm or less. And a wrought aluminum alloy for cutting with excellent corrosion resistance.