JP2002212660A - Aluminum alloy having excellent machinability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the machinability of a 6000 series alloy by jointly adding Sn and Bi in place of Pb thereto, and to obtain an aluminum alloy which combines excellent machinability, corrosion resistance and mechanical properties. SOLUTION: The aluminum alloy has a composition containing, by mass, 0.4 to 0.8% Si, 0.8 to 1.2% Mg, 0.4 to 0.55% Sn, 0.4 to 0.55% Bi and <=0.1% Cr, and, if required, containing one or more selected from 0.005 to 0.2% Ti, <=0.15% Mn and 0.05 to 0.2% Zr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy having excellent machinability.

[0002]

2. Description of the Related Art In order to improve the machinability of aluminum alloys, AA2011 alloy (Cu: 5.
0 to 6.0%, Pb: 0.2 to 0.6%, Bi: 0.2
~ 0.6%, balance Al) or AA6262 alloy (S
i: 0.4 to 0.8%, Mg: 0.8 to 1.2%, C
u: 0.15 to 0.4%, Pb: 0.4 to 0.7%, B
i: 0.4 to 0.7%, with the balance being Al), low-melting metals such as Pb and Bi are added as effective addition elements. These low-melting-point metals hardly form a solid solution in aluminum, but exist in a granular form in an aluminum alloy, and the low-melting-point metal particles are melted by the heat generated during cutting to separate chips (melt embrittlement), Improves the machinability of extruded aluminum alloy.

[0003] However, in response to the growing demand for global environmental protection in recent years, there has been an increasing movement to regulate the use of harmful components such as Pb. Pb accumulates when ingested by the human body,
Causes Pb poisoning such as neuropathy, anemia. In Japan, the Ministry of International Trade and Industry set the "Guidelines for Waste Management and Recycling by Item" in 1997, and set numerical targets for reducing Pb usage for automobiles and motorcycles. In response, automakers have formulated voluntary action plans. On the other hand, in the European Union, the EU has a Directive on Packaging and Packaging Waste and a draft EU Directive on End-of-Life Vehicles. Stipulates.

Regarding the 2000 series,
Bi and Sn are contained and Pb is not substantially contained.
Al having the same machinability and mechanical properties as A2011
-Cu alloy has been developed (Japanese Patent Application No. 11-363494).
No.). For the 6000 series, see Japanese Patent Application Laid-Open No. 9-1.
Japanese Patent Application Laid-Open No. 11-38511 describes an Al-Mg-Si alloy containing Sn and Bi and containing substantially no Pb.
In the publication of 1-140575, In, Sn, Bi
An Al-Mg-Si-based alloy substantially free of b is described.

[0005]

[0003] A member such as an ABS housing of an automobile is required to have excellent cutting properties because of the frequent use of cutting, especially drilling, in a manufacturing process, and is also required to have excellent corrosion resistance. Conventionally, the AA6262 alloy is used. Considering environmental issues, this AA626
Even when an aluminum alloy substantially containing no Pb is used instead of the two alloys, a 6000 series alloy having better corrosion resistance than the 2000 series alloy is desirable. However, looking at the examples of the above publication that discloses a 6000 series alloy containing no Pb,
In Japanese Patent Application Laid-Open No. 9-111385, the effect of co-adding Bi and Sn is unclear, and there is no disclosure about corrosion resistance. Japanese Patent Application Laid-Open No. H11-140575 does not disclose the mechanical properties of the alloy, and contains expensive In in the composition.

An object of the present invention is to obtain an aluminum alloy having excellent machinability, corrosion resistance and mechanical properties in the case where Sn and Bi are co-added in place of Pb to improve the machinability of a 6000 series alloy. Aim.

[0007]

The aluminum alloy having excellent machinability according to the present invention has an Si content of 0.4 to 0.8% and an M content of 0.4% to 0.8%.
g: 0.8-1.2%, Sn: 0.4-0.55%, B
i: 0.4 to 0.55%, Cr: 0.1% or less,
The balance consists of Al and impurities, and if necessary,
Ti: 0.005 to 0.2%, and / or Mn:
015% or less, one or more of Zr: 0.05 to 0.2%. The above-mentioned aluminum alloy has good chip breaking properties, and does not cause trouble such as wrapping of chips around a tool due to long chips. Corrosion resistance and mechanical properties are equivalent to those of the conventional AA6262 alloy. Further, since Pb is not added for improving the machinability, the environment is considered more in comparison with the AA6262 alloy.

Next, the reason for adding each element in the above aluminum alloy and the reason for limiting the amount of addition will be described. Si: 0.4 to 0.8% Mg: 0.8 to 1.2% Si and Mg are precipitated as Mg ₂ Si and have an effect of increasing the strength. If the amount of Si is less than 0.4% and the amount of Mg is less than 0.8%, the effect cannot be obtained.
If the g amount exceeds 1.2%, the deformation resistance due to the solid solution effect of Si and Mg alone increases too much, and the extrudability decreases. Si
Is more preferably in the range of 0.5 to 0.7%.

Bi: 0.4 to 0.55% Sn: 0.4 to 0.55% By adding Bi and Sn simultaneously, B having a low melting point can be obtained.
The fine particles of the i-Sn alloy are dispersed in the aluminum alloy, so that the chip is melted and embrittled by the cutting heat, so that excellent chip breaking properties are obtained. As the content of Bi and Sn is closer to the eutectic composition (Bi: Sn = 57: 43), the melting point of the dispersed particles can be reduced, and the efficiency of melt embrittlement of chips increases. On the other hand, as the content of Sn and Bi deviates from the eutectic composition, the melting point of the dispersed particles increases, the efficiency of melting embrittlement of chips by cutting heat is low, and the chip breaking performance is poor. If the content of either or both Bi and Sn is small, the effect of improving the machinability is small, and if the content of either or both is increased, elongation and corrosion resistance are reduced.
From the above points, in order to obtain an alloy excellent in all of the machinability, the mechanical properties, and the corrosion resistance, the contents of Bi and Sn are both set to 0.1.
It must be between 4 and 0.55%.

Cr: 0.1% or less Cr forms a compound of CrAl ₇ and serves as a starting point of chip breaking to improve chip breaking. However, when the ratio exceeds the upper limit, the deformation resistance is excessively increased and the extrudability is reduced. Ti: 0.005 to 0.2% Ti is added as necessary in order to refine the cast structure and stabilize the mechanical properties.
If it is less than 5%, the effect cannot be obtained, while if it exceeds 0.2%, the effect is saturated. Therefore, the addition amount of Ti is set to 0.005 to 0.2%.

Mn: 0.15% or less Mn has the effect of forming a solid solution to increase the strength of the material, and also enhances the strain hardening ability and promotes chip breaking, so that Mn is added as necessary. If it exceeds 15%, the effect is saturated. Zr: 0.05 to 0.2% Zr is added as necessary to form a ZrAl ₃ compound and to serve as a starting point of chip breaking to improve machinability. If the addition amount is less than 0.05%, there is no effect,
If it exceeds 0.2%, the effect is saturated.

Impurities Fe is an impurity most contained in the aluminum alloy, and if present in the aluminum alloy in an amount exceeding 0.35%, a coarse intermetallic compound is crystallized, thereby impairing the mechanical properties of the alloy. . Therefore,
The content of Fe is regulated to 0.35% or less. Further, when casting an aluminum alloy, impurities are mixed in from various routes such as a base metal and an intermediate alloy of an additional element. There are various elements to be mixed, but impurities other than Fe alone have 0.05% or less, and if the total amount is 0.15% or less, it hardly affects the characteristics of the aluminum alloy. Therefore, these impurities are set to 0.05% or less in a simple substance, and 0.15% or less in total.

The above-mentioned aluminum alloy is subjected to melting, casting, and homogenization according to a conventional method, and then, for example, is subjected to hot working such as extrusion or rolling to obtain an extruded material or a rolled material (rod or bar). The material can be immediately quenched from a high temperature state or reheated to perform solution treatment and quenching, followed by aging treatment to give a predetermined strength and then subjected to cutting.

[0014]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples. An alloy having a chemical composition shown in Table 1 was melted, and an extruded billet having a diameter of 200 mm was prepared by semi-continuous casting.
It was extruded into a block of 60 × 60 mm at an extrusion temperature of 500 ° C., and quenched by water cooling immediately after extrusion (press quenching). 170 ° C x 6 for extruded material after quenching
An artificial aging treatment of time was performed. Using this as a test material, a cutting test, a tensile test, and a corrosion resistance test were performed in the following manner. In order to check the extrudability, in the above extrusion, the extrusion load was kept constant (1200 tons), the extrusion speed (speed at which the extruded material came out) was measured, and the extrudability of each extruded material was evaluated in the following manner. did. Table 2 shows the test results.

[0015]

[Table 1]

Cutting test: Using a commercially available 4 mm diameter drill made of high-speed steel, rotation speed 1500 rpm, feed 300 mm /
The chip was cut under the same conditions as described above, and the occurrence of wrapping of the chip around the drill was observed, and the number of chips per 100 g was measured in order to examine the chip breaking property. Tensile test: Tensile strength, proof stress and elongation were measured using a JIS No. 4 test piece taken in the extrusion direction in accordance with the metal material test method specified in JISZ2241. Corrosion resistance test: 200 hours salt spray test according to JISZ127
The measurement was performed in accordance with the provisions of Example 1, and the weight loss per unit area was measured. Extrudability: When the value of the extrusion speed was 5 m / min or more, it was evaluated as ○ (excellent), when it was less than 2 to 5 m / min, Δ (poor), and when it was less than 2 m / min, it was evaluated as x (not usable). .

[0017]

[Table 2]

The alloys 1 to 3 corresponding to the embodiment of the present invention are:
All show excellent mechanical properties, machinability and corrosion resistance.
In addition, the extruded material has no surface peeling or burning marks, has good surface properties, and has excellent extrudability. On the other hand, the alloys 4 to 10 of the comparative examples are alloys whose compositions are out of the range of the present invention, and all have some characteristics inferior to those of the alloys of the examples 1 to 3. That is, alloy 4 has poor extrudability due to excessive contents of Si and Mg, alloy 5 has poor yield strength due to insufficient contents of Si and Mg, and alloy 6 has excessive contents of Sn and Bi because alloy 6 has excessive contents of Sn and Bi. Alloy 7 has low elongation and poor corrosion resistance, alloy 7 has insufficient Sn and Bi contents and therefore has poor machinability, and alloy 8 has C
The addition amount of r is large and the extrudability is inferior, alloy 9 is inferior in elongation and corrosion resistance due to the excessive addition amount of Sn, and alloy 10 is inferior in machinability due to insufficient Bi.

[0019]

As described above, according to the present invention, a predetermined amount of Mg
By adding Bi and Sn simultaneously to an aluminum alloy containing Si and Si, the machinability can be improved without using Pb as in the case of the conventional AA6262 alloy. I can respond. At the same time, since it has excellent mechanical properties and corrosion resistance, it is suitable for members such as ABS housings of automobiles.

Claims (3)

[Claims] 1. Si: 0.4 to 0.8% (mass%, the same applies hereinafter), Mg: 0.8 to 1.2%, Sn: 0.4 to 0.5%.
An aluminum alloy having excellent machinability, containing 55%, Bi: 0.4 to 0.55%, and Cr: 0.1% or less, with the balance being Al and impurities. 2. The aluminum alloy having excellent machinability according to claim 1, further comprising Ti: 0.005 to 0.2%. 3. Mn: 015% or less, Zr:
The aluminum alloy having excellent machinability according to claim 1 or 2, comprising at least one of 0.05 to 0.2%.