Clad material, method of manufacturing brazed pipe, and brazed pipe

Abstract

A clad material includes a core material, a first skin material covering one side of the core material, and a second skin material covering the other side of the core material. The clad material is brazed in a state in which the first and second skin materials overlap each other. The core material is made of an Al alloy containing Mn (0.6 to 1.5 mass %), Ti (0.05 to 0.25 mass %), Cu (less than 0.05 mass %), Zn (less than 0.05 mass %), Fe (0.2 mass % or less), and Si (0.45 mass % or less) (balance: Al and unavoidable impurities). The first skin material is made of an Al alloy containing Si (6.8 to 11.0 mass %) and Zn (0.05 mass % or less) (balance: Al and unavoidable impurities). The second skin material is made of an Al alloy containing Si (4.0 to 6.0 mass %) and Cu (0.5 to 1.0 mass %) (balance: Al and unavoidable impurities).

Claims

1. A clad material comprising: a core material including a first surface and a second surface opposite to the first surface in a thickness direction of the core material, the core material being made of an Al alloy including Mn in an amount of 0.6 to 1.5 mass %, Ti in an amount of 0.05 to 0.25 mass %, Cu in an amount less than 0.05 mass %, Zn in an amount less than 0.05 mass %, Fe in an amount of 0.2 mass % or less, Si in an amount of 0.45 mass % or less, and Al; a first skin material directly provided on the first surface of the core material and made of an Al alloy including Si in an amount of 6.8 to 11.0 mass %, Zn in an amount of 0.05 mass % or less, and Al, the first skin material serving as a brazing material; and a second skin material directly provided on the second surface of the core material and made of an Al alloy including Si in an amount of 4.0 to 6.0 mass %, Cu in an amount of 0.5 to 1.0 mass %, and Al.

2. The clad material according to claim 1, wherein the second skin material does not include Zn.

3. The clad material according to claim 1, wherein the core material includes a first end and a second end opposite to the first end in a direction along which the first surface and the second surface extend, the first end is brazed to the second end such that the first skin material contacts the second skin material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view showing the overall structure of a heat exchanger used as a condenser of an air conditioning apparatus for a vehicle;

(2) FIGS. 2A and 2B is a pair of vertical sectional views showing a method of manufacturing a tubular body for brazed pipe used for the headers of the heat exchanger of FIG. 1; and

(3) FIGS. 3A to 3D is a set of partial enlarged views of FIGS. 2A and 2B.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(4) An embodiment of the clad material according to the present invention will next be described.

(5) The clad material according to the present invention is composed of a core material, a first skin material covering one side of the core material, and a second skin material covering the other side of the core material. As shown in FIGS. 2 and 3, the clad material is formed into a tubular shape such that a first surface (one side) of the core material covered with the first skin material is located on the outer side, and a second surface (the other side) of the core material covered with the second skin material is located on the inner side. Thus, opposite side edges portions of the clad material are caused to mate with each other such that the first and second skin materials overlap each other. In this state, the opposite side edges portions are brazed together. Therefore, in the blank state (a state before the clad material is formed and brazed), the above-described first slant surface 21 is covered with the first skin material of the clad material, and the above-described second slant surface 24 and second flat surface 25 are covered with the second skin material.

(6) The core material is made of an Al alloy containing Mn in an amount of 0.6 to 1.5 mass %, Ti in an amount of 0.05 to 0.25 mass %, Cu in an amount less than 0.05 mass %, Zn in an amount less than 0.05 mass %, Fe in an amount of 0.2 mass % or less, and Si in an amount of 0.45 mass % or less, the balance being Al and unavoidable impurities. The first skin material is made of an Al alloy containing Si in an amount of 6.8 to 11.0 mass % and Zn in an amount of 0.05 mass % or less, the balance being Al and unavoidable impurities. The first skin material serves as a brazing material. The second skin material is made of an Al alloy containing Si in an amount of 4.0 to 6.0 mass % and Cu in an amount of 0.5 to 1.0 mass %, the balance being Al and unavoidable impurities. Preferably, each of the first skin material and the second skin material has a clad ratio (the ratio of the thickness of the skin material to that of the core material) of 4 to 10%.

(7) Next, there will be described the alloy compositions of the core material, the first skin material, and the second skin material of the clad material.

(8) [Core Material]

(9) Mn increases the strength of the core material. When the Mn content is excessively small, a sufficient degree of strength cannot be attained. When the Mn content is excessively large, the strength of the core material becomes excessively high, which makes it difficult to machine the opposite side edge portions of the clad material into the shapes shown in FIG. 3. Therefore, the Mn content must be 0.6 to 1.5 mass %.

(10) Ti forms a Ti—Al compound in the Al alloy and disperses in layers. Since the spontaneous potential of the Ti—Al compound is noble, corrosion occurs in layers, and corrosion in the thickness direction (pitting corrosion) becomes unlikely to occur. Therefore, Ti improves the corrosion resistance. When the Ti content is excessively small, its effect of causing corrosion to occur in layers diminishes, and corrosion resistance decreases. When the Ti content is excessively large, its effect of improving the corrosion resistance saturates, and cost increases. Accordingly, the Ti content must be 0.05 to 0.25 mass %.

(11) Cu is contained in the core material as an unavoidable impurity. When the Cu content is excessively high, the spontaneous potential of the core material becomes noble with respect to the spontaneous potential of the eutectic brazing material present between the brazed first and second slant surfaces, whereby the eutectic brazing material is corroded preferentially. Accordingly, the Cu content must be less than 0.05 mass %.

(12) Zn is contained in the core material as an unavoidable impurity. When the Zn content is excessively high, the corrosion resistance of the core material itself decreases. Accordingly, the Zn content must be less than 0.05 mass %.

(13) Fe is contained in the core material as an unavoidable impurity. When the Fe content is excessively high, the corrosion resistance of the core material itself decreases. Therefore, the Fe content must be 0.2 mass % or less.

(14) Si is contained in the core material as an unavoidable impurity. When the Si content is excessively high, the resistance of the core material itself decreases. Therefore, the Si content must be 0.45 mass % or less.

(15) Notably, the amounts of Cu, Zn, Fe, and Si contained as unavoidable impurities may be decreased to zero.

(16) [First Skin Material]

(17) The first skin material is a typical Al alloy brazing filler, and serves as a brazing material. The Si content of the first skin material is 6.8 to 11.0 mass %.

(18) Zn is contained in the first skin material as an unavoidable impurity. When the Zn content is excessively high, the spontaneous potential of the eutectic brazing material present between the brazed first and second slant surfaces decreases and becomes less noble, whereby the eutectic brazing material is corroded preferentially. Accordingly, the Zn content must be 0.05 mass % or less. Notably, the amount of Zn contained as an unavoidable impurity may be decreased to zero.

(19) [Second Skin Material]

(20) Si brings the second skin material in a molten state when the opposite side edge portions of the clad material are brazed together in a state in which the first skin material and the second skin material overlap each other, to thereby facilitate dispersion of Cu from the first skin material to the molten material. When the Si content is excessively low, the melting of the second skin material becomes insufficient, and the dispersion of Cu from the first skin material to the molten material becomes insufficient. As a result, the spontaneous potential of the eutectic brazing material present between the brazed first and second slant surfaces fails to become higher than the spontaneous potential of the core material, whereby the eutectic brazing material is corroded preferentially. When the Si content is excessively high, the second skin material melts excessively. Therefore, when the clad material is used for manufacture of the brazed pipes 10 which constitute the two headers 2 and 3 of the above-described heat exchanger 1, the channels of the heat exchange tubes 4 may be clogged. Therefore, the Si content must be 4.0 to 6.0 mass %.

(21) Cu disperses from the first skin material to the molten material, when the opposite side edge portions of the clad material are brazed together in a state in which the first skin material and the second skin material overlap each other, whereby the spontaneous potential of the eutectic brazing material present between the brazed first and second slant surfaces is rendered higher than the spontaneous potential of the core material. When the Cu content is excessively low, its effect cannot be attained. When the Cu content is excessively high, the second skin material cracks when it solidifies during casting. Accordingly, the Cu content must be 0.5 to 1.0 mass %.

(22) Notably, the clad material is manufactured by press-bonding the core material, the first skin material, and the second skin material, which are cast separately.

(23) Specific examples of the present invention will now be described along with comparative examples.

(24) Five types of clad materials shown in Table 1 were prepared. In each clad material, the clad ratio of the first skin material and the second skin material is 8%.

(25) TABLE-US-00001 TABLE 1 First Second Spontaneous skin skin potential (mV) material material Eutectic Core material (mass %) (mass %) (mass %) Core brazing Al Mn Ti Cu Zn Fe Si Al Si Zn Al Si Cu material material Example 1 Bal 0.6 0.1 0.01 0.01 0.10 0.45 Bal 8.7 0.01 Bal 5.0 0.7 −730 −710 2 Bal 0.6 0.1 0.01 0.01 0.10 0.45 Bal 8.7 0.01 Bal 5.0 0.9 −710 −690 3 Bal 1.1 0.1 0.01 0.01 0.10 0.25 Bal 8.7 0.01 Bal 5.0 0.7 −730 −705 4 Bal 1.1 0.1 0.01 0.01 0.10 0.25 Bal 8.7 0.01 Bal 5.0 0.9 −730 −705 Comparative Bal 1.1 0.1 0.50 — 0.10 0.10 Bal 8.7 0.01 Bal 5.0 0.6 −680 −710 Example

(26) A blank plate 20 as shown in FIGS. 2 and 3 was prepared through use of each clad material. The blank plate 20 has a first slant surface 21, a first flat surface 22, a second slant surface 24, and a second flat surface 25. The first slant surface 21 is covered with the first skin material, and the second flat surface 25 and a portion of the second slant surface 24 on the side toward the second flat surface 25 are covered with the second skin material.

(27) Subsequently, the blank plate 20 was formed into a tubular shape, the slant surfaces 21 and 24 at the opposite side edge portions were brought into surface contact with each other, and the flat surfaces 22 and 25 at the opposite side edge portions were caused to butt against each other, whereby a tubular body 34 was obtained. Then, the tubular body was heated to a predetermined temperature, whereby the slant surfaces 21 and 24 of the tubular body 34 were brazed together, and the flat surfaces 22 and 25 of the tubular body 34 were brazed together, whereby the brazed pipe 10 was manufactured.

(28) The spontaneous potential of the core material of each of the manufactured pipes, and the spontaneous potential of the eutectic brazing material formed between the first and second slant surfaces were measured. The results of this measurement are also shown in Table 1.

(29) As is apparent from the results shown in Table 1, when the alloy compositions of the core material and the two skin materials fall within the ranges of the present invention, the spontaneous potential of the eutectic brazing material formed between the first and second slant surfaces becomes higher than and noble with respect to the spontaneous potential of the core material. Therefore, the preferential corrosion of the eutectic brazing material can be prevented.