Copper ferrous alloy for shielding electromagnetic waves and method for preparing the same

Abstract

A rolled foil formed of the FeCu alloy according to an embodiment of the present invention is manufactured to consist of 3 to 30 wt % iron and 70 to 97 wt % copper having a thickness of 100 m to 10 m, by casting a molten metal of a FeCu parent alloy and a metal copper into a slab, heat-treating the slab, and roll-milling the heat-treated slab by using a multi-pass rolling mill with the total reduction ratio of 90% or higher. In this regard, the FeCu alloy rolled foil according to the present invention provides an effect of shielding electromagnetic waves of 80 dB or more within high frequencies ranging between 1 GHz to 1.5 GHz.

Claims

1. A method for preparing a copper ferrous (FeCu) alloy (CFA) rolled foil for shielding electromagnetic waves, the method comprising: a) a molten metal forming process forming a molten metal by melting a FeCu parent alloy and copper (Cu) comprising iron at an amount in a range of about 5 wt % to about 20 wt % and copper at an amount in a range of about 80 wt % to about 95 wt %; b) a molten metal coating process adding at least one selected from anhydrous borax and cryolite on a surface of the molten metal; c) a casting process casting the molten metal into a FeCu alloy slab; d) a rough roll-milling process preparing a first panel by rough roll-milling comprising hot-rolling the slab, face-milling the hot-rolled slab, and cool-rolling the resultant; e) a heat-treating process preparing a second panel by heat-treating the first panel to remove a remaining stress; and f) a roll-milling process roll-milling the second panel at a total reducing ratio of about 90% or higher by repeating the roll-milling to prepare a thin film having a thickness in a range of about 100 M to about 10 m.

2. The method according to claim 1, wherein a weight ratio of iron and copper in the FeCu parent alloy used in a) the molten metal forming process is about 50:50 or about 40:60.

3. The method according to claim 2, wherein e) the heat-treating process is performed in a nitrogen atmosphere or a nitrogen atmosphere containing hydrogen at a volume unit in a range of about 0.1% to about 10% within a temperature range of about 300 C. to about 800 C. for about 3 hours to about 21 hours; or performed within a temperature range of about 300 C. to about 800 C. for about 1 hour to about 7 hours three times so that a hardness of the second panel is in a range of about H to about H.

4. The method according to claim 3, wherein f) the roll-milling process is characterized in repeating the roll-milling five to six times by using a multi-pass rolling mill.

5. A electromagnetic wave shielding copper ferrous alloy (CFA) comprising iron at an amount in a range of about 5 wt % to about 20 wt % and copper at an amount in a range of about 80 wt % to about 95 wt %, wherein the CFA is prepared by using the method according to claim 4.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a graph of an electromagnetic wave shielding effect of 0.1 T rolled foil of a copper ferrous alloy (CFA90) according to an embodiment of the present invention.

(2) FIG. 2 is a graph illustrating the electromagnetic wave shielding effect of a 10 m-thick rolled foil of CFA90.

(3) FIG. 3 is a schematic view of a 20-step multi-pass rolling mill.

DETAILED DESCRIPTION

(4) Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the present invention is not limited to the following embodiments, and that the embodiments are provided for illustrative purposes only. The scope of the invention should be defined only by the accompanying claims and equivalents thereof.

Casting Slab of FeCu Alloy (10Fe-90Cu; CFA90)

(5) 150 kg of a FeCu parent alloy (50Fe-50Cu) ingot was inserted into a high frequency induction furnace, electricity was applied thereto to completely dissolve the ingot, 600 kg of metal copper was inserted thereto, and 300 g of a flux was continuously added thereto to increase a molten metal temperature to 1400 C. Then, supply of electricity was ceased, and the resultant was de-acidified. After about 5 minutes, the resultant was moved to a mold at a temperature of 1300 C. by using a vertical continuous casting method while maintaining the flux on a surface of the resultant to prepare a slab having a thickness of 150 mm, a width of 300 mm, and a length of 2000 mm.

Preparation of FeCu Alloy (10Fe-90Cu; CFA90) Rolled Foil Having a Thickness of 0.1 T

(6) The slab prepared in Example 1 was hot-rolled and face-milled by using a general method to have a thickness of 12 mm, and rough roll-milled at a thickness of 1 mm in a cool-rolling device to obtain a first flat plate, and the first flat panel was heat-treated in a nitrogen atmosphere within a temperature range of about 300 C. to about 800 C. for 20 hours to obtain a second flat panel.

(7) The second flat panel was used as a roll-milling material which was sequentially roll-milled to have a thickness which changed from 1T.fwdarw.0.7T.fwdarw.0.4T.fwdarw.0.28T.fwdarw.0.2T.fwdarw.0.14T.fwdarw.0.1T by using a 20-stage rolling mill as shown in [FIG. 3], and thus a FeCu alloy (10Fe-90Cu; CFA90) rolled foil having a thickness of 0.1 T with a total reduction ratio of 90% was prepared.

Preparation of FeCu Alloy (10Fe-90Cu; CFA90) Rolled Foil Having Thickness of 10 m

(8) The slab prepared in Example 1 was hot-rolled and face-milled by using a general method to have a thickness of 1 mm, and rough roll-milled at a thickness of 0.1 mm in a cool-rolling device to obtain a first flat plate, and the first flat panel was heat-treated in a nitrogen atmosphere within a temperature range of about 300 C. to about 800 C. for 20 hours to obtain a second flat panel.

(9) Then, the second flat panel was roll-milled, and thus a FeCu alloy (10Fe-90Cu; CFA90) rolled foil having a thickness of 0.01 T (10 m) with a total reduction ratio of 90% was prepared in the same manner as in Example 2.

(10) The multi-pass rolling mill used in Example 2 and Example 3 may be schematically described as follows. As shown in FIG. 3, a roll-milling device 2 has an unrolling unit 3 that unrolls a roll-milling material W; and a rolling unit 4 that rolls the roll-milling material W, and a multi-pass rolling mill 1 that roll-mills the roll-milling material W is disposed between the unrolling unit 3 and the rolling unit 4. The multi-pass rolling mill 1 allows reverse roll-milling as the roll-milling material W may move forward or backward by converting a panel passing direction (by reversing a panel passing direction between the black arrow and the white arrow shown in FIG. 3).

Evaluation Examples 1 and 2

(11) Electromagnetic wave shielding effect of each of the FeCu alloy (10Fe-90Cu; CFA90) rolled foils having a thickness of 0.1 T or 0.01 T (10 m) prepared in Example 2 and Example 3 was evaluated, and the results are shown in FIG. 1 and FIG. 2.

(12) FIG. 1 is the graph of electromagnetic wave shielding effect of the FeCu alloy (10Fe-90Cu; CFA90) rolled foil having a thickness of 0.1 T. The graph above shows the results measured by reference to the specification and test methods ASTM D4935-10 form the Korea Testing Laboratory. and FIG. 2 shows a graph illustrating the measurement results of electromagnetic wave shielding effect of the FeCu alloy (10Fe-90Cu; CFA90) rolled foil having a thickness of 10 m. Referring to the measurement results shown in FIG. 1 and FIG. 2, it may be confirmed that the FeCu alloy rolled foil of the present invention provides an electromagnetic wave shielding effect of 80 dB or higher at a high frequency range between 1 GHz to 1.5 GHz. Thus, in consideration of a copper material providing an electromagnetic wave shielding effect of 30 dB or lower, it may be known that the electromagnetic wave shielding effect of the FeCu alloy rolled foil of the present invention is very good.

(13) For additional information, when the electromagnetic wave shielding effects 80 dB and 30 dB are compared according to Equation in which an electromagnetic wave shielding effect is represented in %, the FeCu alloy rolled foil of the present invention is calculated as having 100000 greater electromagnetic wave shielding effect that of copper.
Electromagnetic wave shielding effect (%)=(110A/10)100[Equation]
(where, A is dB)

(14) That is, according to Equation, an electromagnetic wave shielding effect (%) of 80 dB is 99.999999%, and an electromagnetic wave shielding effect (%) of 30 dB is 99.9%. Thus, there are differences of 0.000001% transmission and 0.1% transmission based on 100% of the complete shielding effect, which denotes that in terms of electromagnetic wave shielding effect, 80 dB is 100000 better than 30 dB.

(15) As described above, according to one or more embodiments of the present invention, a copper ferrous (FeCu) alloy containing 3 to 30 wt % of iron and copper accounting for the remaining weight may form a thin film by roll-milling the FeCu alloy with a high reduction ratio to maximize electromagnetic wave shielding effect. An electromagnetic wave shielding cable prepared by using the FeCu alloy rolled foil has high strength, improved corrosion-resistance, and improved function of shielding electromagnetic waves compared to those of conventional cables using copper, aluminum, or iron as a shielding material. Also, a manufacturing process of the electromagnetic wave shielding cable is simple, and thus productivity of the process may increase and a manufacturing cost of the cable may decrease. Moreover, the FeCu alloy rolled foil provides an electromagnetic wave shielding effect of 80 dB or higher within a high frequency range between 1 GHz to 1.5 GHz, which denotes that the electromagnetic wave shielding effect of the FeCu alloy rolled foil of the present invention is significantly good in consideration of an electromagnetic wave shielding effect of copper, which is 30 dB or lower, thereby making it possible to control malfunction caused by noise in circuits of precision machines, robots, and automobiles, etc. and reduce noise in mobile phones. Accordingly, the FeCu alloy rolled foil may be widely utilized as a material for shielding electromagnetic waves.