JP2002173726A - Aluminum alloy piping material having excellent intergranular corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy piping material for a heat exchanger which has high strength and corrosion resistance, and is further provided with producibility into pipe products (such as hot extrusion workability and cold reduction workability) and product workability (such as tensile characteristics, bending workability and terminal workability). SOLUTION: The aluminum alloy piping material for a heat exchanger has a composition containing, by weight, >0.8 to 1.5% Mn, >0.1 to l.5% Cu, >0.05 to 0.2% Cr and <=0.2% Si, and the balance aluminum with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy piping material used as a structural member such as a heat exchanger, which is excellent in strength, corrosion resistance, manufacturing workability, and product workability.

[0002]

2. Description of the Related Art In recent years, automobiles have been equipped with various pipes. Among them, heat exchanger pipes are JIS 6063 aluminum alloy (0.5 wt%) for the purpose of weight reduction.
Mg-0.35wt% Si-balance Al) or JIS 30
03 aluminum alloy (1.0wt% Mn-0.1wt
% Cu-0.1 wt% Si-0.4 wt% Fe-balance A
1) is adopted. And the JIS
The 6063 alloy is used as piping (flex hose) adjacent to the compressor and requiring fatigue resistance, and the JIS 3003 alloy is used as piping for automotive coolers and the like. The pipe material is subjected to terminal processing and bending processing to be processed into a pipe such as a car cooler. In the terminal processing, various beads (joint parts) are formed by combining diameter expansion processing, diameter reduction processing, rolling processing, etc. In recent years, in order to improve the reliability of the joint parts, FIG.
As shown in FIG. 1, shaft seal beads having a complicated shape, each of which has a shaft having different diameters, have come to be used.
Further, pipes such as the automotive cooler have been required to have strength to withstand refrigerant pressure and withstand vibration of an engine, a compressor, and the like. For example, Japanese Patent Application Laid-Open No. 11-140572 describes intergranular corrosion of a brazing sheet sacrificial material, but there is no description of a tube material using a bare material, and much less improvement of workability of a tube material product. There is no. In order to improve the strength of the pipe material, the strength can be improved by adding Cu or Mg, but in order to secure the seal bead property,
When the tube material is annealed, it is found that the susceptibility of the tube material to intergranular corrosion is increased.
This has been a problem in obtaining sufficient corrosion resistance in a severe (high-temperature, high-humidity) corrosive environment such as Southeast Asia.
Therefore, there has been a demand for the development of an aluminum alloy pipe material which has improved corrosion resistance and also has good shaft seal bead properties such as manufacturability.

[0003]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide not only high strength and corrosion resistance, but also processability (hot extrusion processability, cold drawing processability, etc.) into a tube product and product processability ( An object of the present invention is to provide an aluminum alloy piping material for a heat exchanger having tensile properties, bending workability, end workability, etc.).

[0004]

The above object has been achieved by the following means. (1) Mn exceeds 0.8 wt% and 1.5 wt% or less,
Cu exceeds 0.1 wt% and 1.5 wt% or less; Cr exceeds 0.05 wt% and 0.2 wt% or less;
Aluminum alloy piping material for heat exchangers containing less than wt%, the balance being aluminum and unavoidable impurities. (2) Mg is added to the aluminum alloy described in (1) in an amount of more than 0.01 wt% to 0.2 wt% or less, and
Aluminum alloy piping material for heat exchangers containing more than 5 wt% and containing 0.30 wt%, the balance being aluminum and unavoidable impurities.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The alloying elements of the aluminum alloy piping material of the present invention will be described below. Mn; Mn is an element that contributes to improvement in strength without impairing corrosion resistance. When the content of Mn exceeds 0.8 wt%,
The reason for specifying 1.5 wt% or less is that if it is less than 0.8 wt%, its effect and mechanical strength are insufficient, and if it exceeds 1.5 wt%, deformation resistance at the time of hot working increases, and extrudability deteriorates. It is because. The content of Mn is preferably
0.8 to 1.0 wt%. Cu; Cu contributes to improvement in strength. Cu dissolved in the base material has a noble natural potential and slightly improves corrosion resistance. Cu
The reason for specifying the content of more than 0.1 wt% to 1.5 wt% or less is that if the content is less than 0.1 wt%, the effect cannot be sufficiently obtained. Compounds and the like tend to selectively precipitate at crystal grain boundaries, and intergranular corrosion increases. Further, the extrudability is reduced due to an increase in hot deformation resistance. C
The content of u is preferably 0.1 to 1.0 wt%. Cr; Cr is an element necessary for reducing intergranular corrosion in the present invention. When an annealing treatment is performed on the pipe material to secure the seal bead property, Al-Mn-based precipitates are preferentially precipitated at the grain boundaries, and a Mn-deficient layer is formed in the vicinity of the precipitates. Precipitation causes intergranular corrosion. In addition, Cu or Mg added for improving the strength precipitates an Al-Cu-based compound at the grain boundary, and preferentially corrodes the vicinity thereof, causing intergranular corrosion. Similarly, Mg precipitates an Mg-Si-based compound at a grain boundary, and preferential dissolution of the compound causes intergranular corrosion. Cr has an effect of preventing preferential corrosion of the deficient layer by forming a solid solution in the deficient layer. Similarly, by partially binding Cr to the Mg-Si-based compound, there is an effect of preventing preferential corrosion of the compound and preventing intergranular corrosion. If this effect is less than 0.05 wt%, the effect cannot be obtained, and if it exceeds 0.2 wt%, intergranular corrosion is reduced, but other coarse compounds are crystallized to improve cold drawing and workability. Will drop. The content of Cr is preferably 0.1 to 0.2 wt%.

In the present invention, the inevitable impurity Si is 0.2
Defined to be wt% or less. The reason for this is that if the content exceeds the component range, pitting corrosion is likely to occur. Si is preferably 0.1% by weight or less. In the present invention, the following elements are further added as selective elements. Mg: Mg forms a solid solution in the matrix and precipitates a fine metal tube compound by the effect of increasing strength and the effect of aging precipitation, thereby contributing to improvement in strength. If the addition amount is less than 0.01 wt%, this effect is not obtained. If the addition amount exceeds 0.2 wt%, not only intergranular corrosion occurs to impair the corrosion resistance, but also when the drawing is performed a plurality of times by drawing. This is because work hardening becomes large, intermediate annealing is required during the drawing process, and productivity is reduced, and extrudability and formability (bendability) are also reduced. Ti: Ti has an effect of refining the cast structure and forming a concentration of components in the thickness direction of the tube when extruded.
The thickened part is noble, the surrounding area is base, and by making the corrosion a layer, in order to suppress the progress of corrosion in the thickness direction,
It has the effect of improving the corrosion resistance of the aluminum tube.
If the added amount is less than 0.05 wt%, the effect cannot be sufficiently obtained, and if it exceeds 0.30 wt%, a coarse compound of Ti is generated and the moldability is reduced.

[0007]

Next, the present invention will be described in more detail with reference to examples. An aluminum alloy having the specified composition of the present invention (the content of components is indicated by wt%) shown in Table 1 was melt-cast to form an ingot having a circular cross-sectional shape. After homogenizing the ingot at 610 ° C for 4 hours, Cut to a length of 1000 mm to obtain an extruded billet, which was reheated to 500 ° C.
Then, continuous drawing is performed a plurality of times in a cold manner to obtain a tube having an outer diameter of 8.0 mm and a wall thickness of 1.0 mm, and then the tube is annealed at 360 ° C. for 2 hours. To produce piping materials for automotive air conditioners. Comparative alloys deviating from the range specified in the present invention shown in Table 1,
In addition, a conventional alloy was manufactured in the same manner as the alloy of the present invention, and a piping material for an air conditioner for an automobile was manufactured. This test specimen was
After a CAS test based on SH8601 was performed for 400 hours, corrosion products were removed, the pit depth was measured using an optical microscope, and the maximum pit depth was determined. In addition, the pit cross section was polished, and the presence or absence of intergranular corrosion was confirmed. Also,
Manufacturing processability and product processability were evaluated by the following methods.

(Manufacturing workability) Evaluation was made based on hot extrusion workability and cold drawing workability. Hot extrusion processability was evaluated by measuring the extrusion speed (m / min) of the product when extruding while fixing the extrusion pressure. The higher the extrusion speed, the better the extrudability. The cold drawing property was evaluated based on the presence or absence of cracks or breaks generated during drawing. (Product workability) Evaluation was made based on tensile properties, bending workability, and end workability. Tensile characteristics are JIS Z22
Tested according to 01, tensile strength (TS), 0.2%
The proof stress (YS) and elongation were measured. The bending workability was evaluated by a tensile bending (stretch bend) method used in actual bending. The bending conditions were a bending radius of 30 mmΦ and a bending angle of 60 degrees. A tube having no abnormality after bending was judged as good, and a tube with broken or rough surface was judged as poor. The end workability was evaluated by forming a shaft seal bead processed portion 8 having the shape shown in FIG. 1 by combining pipe expansion, punching, and rolling, and checking for the presence or absence of cracks, wrinkles, and minute cracks in the processed portion.

The alloy components are shown in Table 1, and the results are shown in Table 1. As can be seen from Table 1, the alloys of the present invention exhibited better corrosion resistance and better manufacturing workability, mechanical strength, bending workability, and end workability than the comparative examples and the conventional examples. Comparative Example 1 is Si
However, it was out of the specified range of the present invention, and was inferior in corrosion resistance. In Comparative Example 2, the corrosion resistance was good, but the added amount of Cu was below the specified range of the present invention, and the mechanical strength was insufficient. Comparative Example 3
The Cu content exceeded the specified range of the present invention, grain boundary corrosion occurred, and the corrosion resistance was poor. In Comparative Example 4, Mn was below the range specified in the present invention, and the corrosion resistance was poor. In Comparative Example 5, although corrosion resistance was good, Mn exceeded the specified range of the present invention, and although corrosion resistance was good, manufacturing workability was poor. Comparative Example 6
The addition amount of r was less than the specified range of the present invention, intergranular corrosion occurred, and the corrosion resistance was poor. In Comparative Example 7, Cr exceeded the specified range of the present invention, and the workability was poor. In Comparative Example 8, Mg exceeded the specified range of the present invention, intergranular corrosion occurred, and the corrosion resistance was poor. In Comparative Example 9, Ti exceeded the specified range of the present invention, and although corrosion resistance was good, manufacturing workability was poor.
In Conventional Example 1, the corrosion resistance was poor and the strength was insufficient.

[0010]

[Table 1]

[0011]

As described above, according to the present invention, as an aluminum alloy piping material for a heat exchanger for automobiles, it has high strength and corrosion resistance and also has good workability (hot extrusion workability, cold drawing workability, etc.). Further, a pipe material for a heat exchanger having excellent product workability (tensile properties, bending workability, end workability, etc.) can be obtained.

[Brief description of the drawings]

FIG. 1 shows an example of a shaft seal bead using the piping material of the present invention.

[Explanation of symbols]

 8 Shaft seal bead processing part

Claims (2)

[Claims] 1. The method according to claim 1, wherein Mn exceeds 0.8 wt%,
%, Cu is more than 0.1 wt% and 1.5 wt% or less,
Aluminum alloy piping material for heat exchangers containing more than 0.05 wt% of Cr and not more than 0.2 wt% and not more than 0.2 wt% of Si and the balance of aluminum and unavoidable impurities. 2. The aluminum alloy according to claim 1, further comprising Mg in an amount exceeding 0.01 wt% and not more than 0.2 wt%.
Aluminum alloy piping material for heat exchangers containing more than 0.05% by weight and 0.30% by weight, with the balance being aluminum and unavoidable impurities.