JPH03193849A - Copper alloy having fine crystalline grain and low strength and its production - Google Patents

Abstract

PURPOSE:To obtain a Cu alloy having low strength and superior formability and excellent in stress corrosion cracking resistance, welding crack resistance, and solderability by regulating the crystalline grain size of a cold rolled sheet of a Cu-Zn alloy with a specific composition to a specific value or below by means of the final annealing and further carrying out cold rolling again, if necessary. CONSTITUTION:A hot rolled plate of a Cu alloy which has a composition consisting of, by weight, 3-25% Zn and the balance Cu or further containing 0.005-2.0%, in total, of one or >=2 elements among the group consisting of Pb, Fe, Sn, Al, Mn, Ni, P, As, Te, Cr, Co, Zr, V, Be, Cd, Si, B, In, Ti, Mg, Hf, and Ge is subjected to a repetition of cold rolling and annealing, by which an intermediate stock is prepared. This stock is annealed, cold-rolled at >=75% draft, and subjected to final annealing to undergo the regulation of crystalline grains to <=0.015mm, and then, cold rolling is applied, if necessary, to the above at 1-15% draft in order to improve solderability.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a material for heat exchangers such as condensers, feed water heaters, distillers, coolers, and water supply devices, particularly radiators used in automobiles, etc. The present invention relates to a method for producing a copper alloy that is optimal as a material for tanks, chives, fins, etc.

[Prior Art] As a copper alloy material conventionally used for radiators, brass consisting of 85% by weight of Cu and 35% by weight of Zn is known. Furthermore, in recent years, red copper comprising 80% by weight of Cu and 20% by weight of Zn has been used to improve stress corrosion cracking resistance. However, the radiator is in constant contact with the cooling medium, and while the car is running, it is exposed to exhaust gas, coastal air containing salt, and SO2 gas from factory exhaust, and these corrosive environments cause brass to crack due to stress corrosion. and dezincification corrosion, which has become a major problem. Furthermore, in recent years, copper alloy welded tubes made by high-frequency induction welding or high-frequency resistance welding have been adopted, especially for radiator tubes, in place of the conventional lock-seam tubes that are caulked to reduce costs and improve production efficiency. It's here. However, copper alloy welded pipes have the disadvantage that the welded part has significantly lower corrosion resistance than other parts due to the uniqueness of its welded structure.

[Problems to be Solved by the Invention] As a result of various studies on the above-mentioned problems, the present inventors have found that making the grain size finer reduces cracking in welds and improves corrosion resistance, especially stress corrosion cracking resistance. It has become clear that this is an effective method for improving However, when the crystal grains of a copper alloy are made finer, the strength is improved, but this causes problems such as increased load on tubes, fins, etc. during forming, increased wear of molds, and decreased formability.

Under these circumstances, the present invention aims to provide a material with fine crystal grains and excellent formability that does not suffer from an improvement in strength due to the refinement of the crystal grains.

[Means for Solving the Problems] The present invention provides Zn: 3 to less than 25% by weight or further Pb
5FeSSn, AI, Mn5Ni, P.

Ass Tes Cr S Co, 2 ``, V
S Be.

CdS Si, B, InS Ti,
Mg, Hf.

0.005 to 2 of one or two or more from the group consisting of Ge
．． After cold rolling an alloy material containing 0% by weight and the balance consisting of Cu and unavoidable impurities at a working degree of 75% or more, the crystal grain size is reduced to 0.015 mm or less by final annealing. After cold rolling a low-strength copper alloy and an alloy material with the above composition at a working degree of 75% or more,
This manufacturing method is characterized in that after final annealing the grain size is adjusted to 0.015 mm or less, cold rolling is further performed by 1 to 15%.

The reasons for limiting the alloy components and other constituent requirements constituting the present invention will be explained.

Cu and Zn are the basic materials of the alloy constituting the present invention, and have excellent workability and mechanical strength, as well as excellent thermal conductivity. The reason why the Zn content is 3 to less than 25% by weight is that if the Zn content is less than 3% by weight, workability or soldering properties will deteriorate, whereas if it is more than 25% by weight, dezincification corrosion or This is because stress corrosion cracking is more likely to occur.

Pb5Fes 5nSA1%Mn, N15P%As,
Tes Crs C0% Zr5V% Be5Cds
S i, B, In5Ti, Mg, Hf.

0.005 to 2 of one or two or more from the group consisting of Ge
．． The reason for containing 0% by weight is to improve the corrosion resistance of the material and welded parts; if it is less than 0.005% by weight, no improvement in corrosion resistance will be observed, and if it is contained more than 2.0% by weight, it will not improve the corrosion resistance. This is because the effect becomes saturated and the workability deteriorates.

Furthermore, the reason why the working degree of cold rolling before final annealing is set to 75% or more is to reduce the strength after final annealing and improve formability, and this effect is not recognized when the working degree is less than 75%. This is because there is no

The reason for reducing the grain size to 0.015 soi or less by final annealing is that reducing the grain size is effective in improving corrosion resistance, especially stress corrosion cracking resistance, and that welding caused by high-frequency induction welding or high-frequency resistance welding Cracking is caused by the embrittlement of grain boundaries when in contact with molten base metal, but this phenomenon can be significantly suppressed by reducing the grain size. .

This is because if the grain size exceeds 0.015 mm, weld cracking is likely to occur and deterioration of stress corrosion cracking resistance is observed.

In the present invention, the reason why cold rolling is performed at a working degree of 1 to 15% after final annealing is that cold rolling improves soldering properties, but the working degree is 1 to 15%. If it is less than %, no improvement in soldering properties is observed, and
This is because if it exceeds 15%, the mechanical strength will increase and the moldability, especially the moldability during processing of the radiator tube, will deteriorate.

[Example] Next, the present invention will be explained in detail.

Alloys having various compositions shown in Table 1 were melted and cast in a high-frequency melting furnace in air or an inert atmosphere, and after hot rolling, cold rolling and annealing were repeated to obtain intermediate thickness materials. This is 5
After annealing at 00° C. for 30 to 60 minutes, the samples were cold rolled at the working degree shown in Table 1 to form a plate with a thickness of 0.8 cm. This was further heat treated at 500°C for 60 to 900 seconds to adjust the crystal grain size shown in Table 1. Further, some of the samples were further cold rolled.

As an evaluation of such samples, Table 1 shows the strength of the material, Erichsen value, stress corrosion cracking test results, resistance to weld cracking, and solderability.

The stress corrosion cracking test was conducted using a JIS conical cup test tool type 17 cylindrical flat bottom punch with a drawing ratio of 2.
0 cup was made and exposed to an ammonia atmosphere of pH 1O made from sodium hydroxide and ammonium chloride, and the time until cracking started was measured.

A test for resistance to weld cracking was carried out by processing the alloys shown in Table 1 into the shape of a vibrator 1 as shown in Fig. 1, inner diameter a: 20 mm, outer diameter b: 21 mm.
611% length: loms), this was immersed for 3 seconds in molten metal of the same composition maintained at +50°C, melting point, and then taken out and placed in a holding furnace with the attached metal melted as shown in Figure 2. As shown in Figure 2, the vibrator I was held on the support stand 3 in the heating and holding furnace 4, and a free-falling object weighing 200 gv was dropped at a falling distance c: 5 hv to apply an impact. The cross section of the vibrator deformed at that time was observed under a microscope to confirm the presence or absence of intergranular fracture, and this was used to evaluate the resistance to melt cracking.

For soldering, heat the solder consisting of 5N20%-Pb80% to 230℃ in a cylindrical crucible with a diameter of 8011% and a height of 601111 to create a molten metal, and place the sample (surface When a cleaned sample (with a width of 1011% and a length of 50 mm) was immersed, the time required for the buoyant force exerted on the sample from the solder bath and the force drawn into the solder bath to reach equilibrium was measured and evaluated.

As is clear from Table 1, the alloy of the present invention obtained satisfactory results in all properties, but comparative alloy No. 1
5 to 20 and No, 22 are the invention alloy No.
The alloy composition and grain size are the same as 1.2.4.5.8 and 11.13, but because the degree of work before final annealing is lower, the tensile strength is higher and the Erichsen value is lower than the invention alloy. . Comparative alloy Nos. 23 to 27 are the invention alloys No. 1.4, respectively. Although the alloy composition and workability before final annealing are the same as B and Li2, the grain size is larger, so the stress corrosion cracking resistance is poorer than that of the invention alloy, and intergranular fracture occurred in the weld crackability test. , poor weld cracking resistance.

Comparative alloy No. 28 is tough pitch copper, but it has a low Zn content, so it has poor formability and soldering properties. or,
Comparative alloy No. 29 has too much Zn content, so it has poor stress corrosion cracking resistance. Furthermore, the present invention alloy No. 3.1
0 and Comparative Alloy No. 0, 21 is Invention Alloy No. 2.9 and Comparative Alloy No. 20 are subjected to skin pass cold rolling to improve solderability.

[Effects of the Invention] As detailed above, the present invention has low strength and excellent formability, and also has stress corrosion cracking resistance, welding cracking resistance, and soldering properties, and is suitable for heat exchangers, especially heat exchangers. We can provide the best materials for copper alloys for radiator tanks, plates, and tubes.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an alloy pipe with a thickness of 0.8 cm used in the weld cracking resistance test, and FIG. 2 is a schematic explanatory diagram of the weld cracking resistance testing apparatus. DESCRIPTION OF SYMBOLS 1... Alloy vibe, 2... Free falling body, 3... Support stand, 4... Heating and holding furnace.

Claims (4)

[Claims] (1) An alloy material consisting of Zn: 3 to less than 25% by weight, the remainder Cu and unavoidable impurities is cold rolled at a workability of 75% or more, and then final annealed to a grain size of 0.015mm or less. A copper alloy with fine grains and low strength. (2) Zn: 3 to less than 25% by weight and Pb, Fe, Sn
, Al, Mn, Ni, P, As, Te, Cr, Co, Z
r, V, Be, Cd, Si, B, In, Ti, Mg, H
f, one or two or more from the group consisting of Ge at 0.005
- 2.0% by weight of an alloy material, the balance of which is Cu and unavoidable impurities, is cold-rolled at a working degree of 75% or more, and then final annealed to have a crystal grain size of 0.015 mm or less. A copper alloy with fine grains and low strength. (3) After cold rolling an alloy material consisting of Zn: 3 to less than 25% by weight, balance Cu and unavoidable impurities at a workability of 75% or more, the grain size is adjusted to 0.015mm or less by final annealing. 1. A method for producing a copper alloy with fine grains and low strength, which comprises further cold rolling by 1 to 15%. (4) Zn: 3 to less than 25% by weight and Pb, Fe, Sn
, Al, Mn, Ni, P, As, Te, Cr, Co, Z
r, V, Be, Cd, Si, B, In, Ti, Mg, H
f, one or two or more from the group consisting of Ge at 0.005
After cold rolling an alloy material containing ~2.0% by weight and the balance consisting of Cu and unavoidable impurities at a working degree of 75% or more, and after adjusting the grain size to 0.015 mm or less by final annealing, further A method for producing a copper alloy with fine grains and low strength, which comprises cold rolling at a rate of 1 to 15%.