WO2011155648A1 - Discoloration-resistant white copper alloy for manufacturing a coin - Google Patents

Abstract

The present invention relates to a discoloration-resistant white copper alloy for manufacturing a coin, which is composed of 10 wt% to 20 wt% of Mn, 10 wt% to 20 wt% of Zn, 0.1 wt% to 1.0 wt% of Sb or Sn, and the remaining weight percentage of Cu. Due to an Sb- or Sn-based compound formed on a surface of the alloy, dezincing corrosion and surface discoloration are suppressed. According to the present invention, even though the alloying element Ni, which is harmful to the human body and is expensive, is completely excluded, the copper alloy has the same level of whiteness as nickel, and also has improved discoloration resistance because dezincing corrosion is suppressed by virtue of the added Sb or Sn. Therefore, the discoloration-resistant white copper alloy can replace nickel which is conventionally used for manufacturing a high face-value coin.

Description

White series copper alloy for the manufacture of coins with excellent discoloration resistance

The present invention relates to a white-based copper alloy for producing coins, and more particularly, to a ternary alloy structure of Cu-Mn-Zn having Cu as a base metal, in which Sb or Sn is added to improve discoloration resistance. The present invention relates to a white-based copper alloy for producing coins having excellent discoloration resistance, which can completely exclude Ni, which is harmful to an expensive alloy element, or minimize Ni content.

Copper alloys are the mainstream for the production of distribution coins not only in Korea but also around the world. This is due to abundant reserves and excellent malleability and ductility compared to other metals of copper, which are known metals, and may be attributed to ease of processing. In addition, there is an advantage that can implement a variety of colors according to the alloying element addition and heat treatment conditions. Yellow-based copper alloys are preferred for low-liquid coin manufacturing and white-based copper alloys for high-liquid coin production. have. Cupronickel forms dense and electrochemically stable Ni oxide on the surface under corrosive environments. Such Ni oxide acts as a protective film of Cu, which is a base metal, and contributes to improving the corrosion resistance of copper. Therefore, while copper is excellent in corrosion resistance among other copper alloys, it has a disadvantage in that it contains Ni, an expensive alloying element that is harmful to the human body.

Korean Unexamined Patent Publication No. 2004-0037734 discloses a white series copper alloy composed of Cu 60-65 wt%, Zn 16-24 wt%, Ni 18-24 wt%, and Fe 1.5-2 wt%. U.S. Patent No. 4446674 describes a material for producing a coin composed of Cu, Zn, Ni, and Sn, and specifies a minimum content of Zn showing discoloration resistance in a copper alloy system for producing coins of 15 wt%. In addition, a white copper alloy composed of a combination of Cu 80wt%, Zn 20wt%, and Ni 20wt% is implemented.

In addition, US Pat. No. 6,40446, which realized the white color with copper alloy containing Zn 0.5 ~ 5wt%, Mn 7 ~ 17wt%, Al 0.5 ~ 4wt%, but there is not enough evidence to guarantee the corrosion resistance as a material for making coins It is not true.

The present invention has been made to solve all the problems of the prior art as described above, while completely eliminating Ni, which is harmful to the human body and an expensive alloying element, exhibits the same level of whiteness and discoloration improvement as compared to the cupronickel. It is a major problem to provide a copper alloy composition which can replace the cupronickel used as a cotton coin material.

As a means for solving the above problems, the white-based copper alloy for producing a coin having excellent discoloration resistance according to the present invention includes Mn 10 to 20 wt%, Zn 10 to 20 wt%, Sb or Sn 0.1 to 1.0 wt%, and the balance Cu. Degal zinc corrosion and surface discoloration are suppressed by the Sb-based or Sn-based compounds formed on the surface.

Here, the Sb-based compound is characterized in that consisting of SbCl ₃ or Sb ₂ O ₃ .

In addition, the Sn-based compound is characterized in that consisting of SnCl ₂ or SnO ₂ .

In addition, the white-based copper alloy for producing a coin having excellent discoloration resistance according to the present invention is characterized in that the heat treatment at 600 ~ 650 ℃ after cold rolling.

In addition, it is preferable that the white series copper alloy for producing coins having excellent discoloration resistance according to the present invention is configured to form a single phase of a face-centered cubic structure at room temperature.

Further, the white-based copper alloy for producing coins having excellent discoloration resistance according to the present invention, more preferably, the color difference value measured based on white copper composed of 75 wt% Cu and 25 wt% Ni is 3.00 or less.

1 is an image showing a microstructure according to the change in the amount of Sb added.

2 is a graph showing a change in current density over time.

3 is an image showing the surface state according to the immersion experiment.

Hereinafter, a preferred embodiment of a white series copper alloy for producing coins having excellent discoloration resistance according to the present invention will be described in detail.

Figure 1 shows the microstructure according to the amount of Sb addition, Figure 2 shows the change in current density with time, Figure 3 shows an image of the surface state according to the immersion experiment.

The white series copper alloy for producing coins of the present invention is composed of a Cu-Mn-Zn ternary alloy structure having Cu as a base metal, and has a structure in which Sb or Sn is added to improve discoloration resistance.

Here, Mn and Zn are each made of 10 to 20wt%, Sb or Sn added to improve discoloration resistance is made of 0.1 ~ 1.0wt%, the balance is made of Cu and other unavoidable impurities.

Cu, which forms a base metal in the copper alloy of the present invention, is a metal element that is easy to process a face centered cubic structure (FCC). For such Cu, Zn is dissolved at a maximum of about 40 wt% at room temperature to form a face-centered cubic structure. Brass, a Cu-Zn alloy, loses the inherent red color of Cu as the Zn content increases, and when about 20wt% is added, it shows a golden color. On the other hand, the addition of 20 ~ 30wt% of Zn is effective in reducing the hardness and improving the elongation, but may increase de-zinc corrosion under aqueous solution corrosion environment containing chlorine or oxygen as the Zn content increases.

In addition, Cu-Mn alloy increases the reflectance of the high-energy portion in the visible region according to the addition of Mn. However, the Cu-Mn alloy is an effective alloying element for realizing a white color, but may increase the hardness and reduce the burn rate, which may cause deterioration of machinability. .

On the other hand, in order to ensure the ease of machining (pressure toughness) of the coin material, it is preferable to form a single structure of face-centered cubic structure at room temperature after casting. To this end, in the present invention, in order to implement an alloy system having a white single crystal structure, a state diagram of a three-alloy of Cu—Mn—Zn having Cu as a base metal is derived by a CALPHAD (Calculation of Phase Diagram) technique.

Herein, when Mn is added below 10 wt%, it is not effective to realize white color, and when it is added above 20 wt%, a healthy ingot cannot be manufactured due to the deterioration of fluidity of the molten metal during melting of the alloy.

When the Mn content is fixed at about 20 wt%, the maximum amount of Zn for forming a Cu-Mn-Zn alloy-based cubic single phase (α-phase) is about 20 wt%, and when added to less than 10 wt%, The discoloration deteriorates and is not suitable as a coin material.

In addition, various oxides or chlorides formed by surface discoloration or corrosion may distort the electrical conductivity of coins and cause errors in the application of the vending machine. To this end, in the present invention, Sb or Sn is added to the ternary alloy system of Cu—Mn—Zn.

Such Sb and Sn form a thermodynamically stable colorless oxide film on the surface of the alloy to suppress de-zinc corrosion, thereby improving corrosion resistance and seawater resistance. The de-zinc corrosion refers to a corrosion phenomenon caused by elution of Zn, which is an electrochemically active metal, when a copper alloy containing 15 wt% or more of Zn is exposed to an aqueous solution corrosion environment containing chlorine and oxygen. In acidic solutions, a uniform dezinc layer is formed on the alloy surface, while in neutral and basic solutions, a local dezinc layer is formed. Porous Cu is exposed on the alloy surface after Zn eluting due to de-zinc corrosion, so it is not suitable in terms of discoloration resistance when applied as a coin material.

When the amount of Sb or Sn added to the Cu-Mn-Zn alloy system is less than 0.1 wt%, an open circuit potential (OCP) measurement results show no improvement in corrosion resistance. In addition, when added in excess of 1.0wt%, the corrosion resistance is improved, but the problem occurs that the cold workability can not be secured due to the occurrence of cracks in the side portion of the plate during cold rolling. This may be due to the presence of segregation along the grain boundaries, as shown in the microstructure observation results of the alloy heat-treated for 30 minutes at 600 ~ 650 ℃ temperature range after cold rolling of FIG.

As such, when Sb or Sn is added to the Cu-Mn-Zn alloy system, a Sb or Sn-based colorless compound is formed on the surface of the alloy, so that de-zinc corrosion and surface discoloration can be suppressed by the Sb or Sn-based compound. do.

Here, when Sb is added to the Cu-Mn-Zn alloy system, SbCl ₃ or Sb ₂ O ₃ may be formed on the surface of the alloy as the Sb-based compound. In addition, when Sn is added to the Cu-Mn-Zn alloy system, SnCl ₂ or SnO ₂ may be formed on the alloy surface as a Sn-based compound.

That is, in the case of general copper (Cu 75wt%-Ni 25wt%) in an aqueous solution corrosion environment containing chlorine and oxygen, the yellow compound NiCl ₂ or NiO by the corrosion reaction of Ni having a lower equilibrium electrode potential compared to Cu Is formed, causing surface discoloration. However, in the alloy system of the present invention to which Sb or Sn is added, the colorless Sb-based compound (SbCl ₃ or Sb ₂ O ₃ ) or Sn-based compound (SnCl ₂ or SnO ₂ ) formed on the surface acts as a protective coating. Zinc corrosion and surface discoloration can be suppressed.

On the other hand, the copper alloy of the present invention is preferably heat-treated at 600 ~ 650 ℃ after cold rolling to remove the stress inside the alloy. If the heat treatment is carried out at less than 600 ℃ can not remove the stress sufficiently, if the heat treatment is carried out at a temperature exceeding 650 ℃ can not form a single phase is inferior to the toughness. And the heat treatment time should be appropriately applied according to the thickness of the alloy plate.

In general, in order to indicate the boundaries alloy white CIE by the CIE LAB notation developed (International Commission on Illumination), L ^* (lightness) value is 80 ~ 90, a ^* (color) value of -5 ~ 5, b ^* ( The color value should be in the range of 5 to 15. To this end, in the present invention, the color difference value measured based on a general white copper made of 75 wt% Cu and 25 wt% of Ni is made to be 3.00 or less, so that the whiteness is equivalent to that of the white copper.

In the following, preferred experimental examples are presented to help understand the present invention. The following experimental examples are merely provided to more easily understand the present invention, and the contents of the present invention are not limited thereto.

Examples 1 to 7: Ingot preparation and heat treatment

Ingots were prepared by dissolving in an induction furnace at the induction furnace with the constituent and composition ratios shown in Table 1 below, and heat treatment was performed at 650 ° C. for 30 minutes for homogenization treatment.

Comparative Examples 1 to 4: Ingot production and heat treatment

Ingot production and heat treatment were performed in the same manner as in Examples 1 to 7, except for the components and the composition ratios described in Table 1 below. Comparative Example 4 shows a general cupronickel containing nickel.

Table 1 Composition (wt%) Cu Ni Mn Zn Sb EXAMPLE One Remaining amount 20 20 0.1 2 Remaining amount 20 20 0.2 3 Remaining amount 20 20 0.3 4 Remaining amount 20 20 0.4 5 Remaining amount 20 20 0.5 6 Remaining amount 20 20 0.6 7 Remaining amount 20 20 0.7 Comparative example One Remaining amount 20 10 2 Remaining amount 20 15 3 Remaining amount 20 20 4 Remaining amount 25 20

Experimental Example 1 Color Measurement

Ingots prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were cut to 2 mm in thickness, and then polished with SiC paper (# 600) to measure color difference with SPECTROMETER (X-RITE SP64). CIE LAB (L ^* , a ^* , b ^* ) notation developed by CIE (International Lighting Commission) was used as a method of displaying color numerically.

In this method, colors are represented by brightness (L ^* ) and colors (a ^* , b ^* ). At this time, if a is +, red is-, it is close to green, b is + is yellow, and-is close to blue. When the coordinates of the standard color are represented by L ₁ , a ₁ , and b _1, and the coordinates of the compared color are represented by L ₂ , a ₂ , and b ₂ , the color difference between these two colors is expressed as follows.

E ^* = (L ^{* 2} + a ^{* 2} + b ^{* 2} ) ^1/2

(L ^* = L ₂ ^* -L ₁ ^* , a ^* = a ₂ ^* -a ₁ ^* , b ^* = b ₂ ^* -b ₁ ^* )

The color difference values (E ^* ) measured based on copper (Comparative Example 4) are shown in Table 2, and the copper alloys for the production of coins composed of Cu-Mn-Zn and Cu-Mn-Zn-Sb have both white copper and color difference values of 3.00. It is shown below, which means that the copper alloy according to the present invention exhibits an equivalent level of whiteness to cupronickel.

TABLE 2 Color difference L ^* a ^* b ^* E ^* EXAMPLE One 87.93 -0.05 5.86 2.03 2 87.81 0.03 5.41 1.89 3 87.65 -0.01 5.46 1.77 4 87.43 0.16 5.41 1.50 5 87.82 1.40 7.47 2.52 6 87.79 1.01 7.59 2.55 7 87.88 0.32 6.84 2.19 Comparative example One 88.00 0.08 5.25 2.06 2 87.84 -0.01 5.88 1.93 3 87.74 0.00 6.20 1.92 4 86.17 0.93 5.62

Experimental Example 2 Evaluation of Corrosion Resistance

After the specimens were processed in the same manner as in the color difference measurement of Experimental Example 1, a potentiometric polarization test was performed in a 5wt% NaCl environment using EG & G Potentiostat 273A. SCE (Saturated Calomel Electrode) was used as a reference electrode and platinum was used as an auxiliary electrode. For the evaluation of corrosion resistance, the electric current density was measured by applying the potential of the active polarization region of the specimen, and the measured current density change for the alloy system is shown in FIG. 2.

In FIG. 2, the copper alloy composed of only Cu-Mn-Zn corresponds to Comparative Examples 1 to 3, and copper alloys to which Sb is added to Cu-Mn-Zn correspond to Examples 1 to 7, respectively, and Cu 75wt% —Ni 25wt Cupronickel composed of% corresponds to Comparative Example 4.

On the other hand, as the current density value increases, the dissolution of metal ions increases, indicating a decrease in corrosion resistance. Referring to FIG. 2, it can be seen that in Comparative Examples 1 to 3, corrosion resistance decreases due to an increase in current density as the Zn content increases. .

In addition, when comparing the Comparative Example 3 and Examples 1 to 7 containing the same Mn 20wt% and 20wt% Zn, compared to Comparative Example 3 without the addition of Sb in Examples 1 to 7 with the addition of Sb has the effect of improving the corrosion resistance You can see that it appears. This is believed to be due to suppression of the de-zinc corrosion reaction due to the addition of Sb.

In the surface image after the immersion experiment for 10 minutes in the 5wt% NaCl solution of Figure 3, the surface discoloration is observed in the copper copper (Comparative Example 4), while the surface discoloration is not observed in the alloy system of Examples 1 to 7 with Sb added Do not.

In the case of general copper (Cu 75wt%-Ni 25wt%) in a corrosion environment containing chlorine and oxygen, a yellow compound NiCl ₂ or NiO is formed by the corrosion reaction of Ni having a lower equilibrium electrode potential than that of Cu. Discoloration is caused. However, in the alloy system of the present invention to which Sb is added, SbCl ₃ or Sb ₂ O _{3, which} is a colorless Sb-based compound formed on the surface, acts as a protective coating, thereby suppressing de zinc corrosion and surface discoloration.

As a result, the copper alloy composition for white cast iron preparation in which Sb or Sn was added to Cu-Mn-Zn ternary alloy system without Ni, exhibited a whiteness level equivalent to that of conventional white copper, and also Sb or It shows the improvement of discoloration resistance through the suppression of de-zinc corrosion by the addition of Sn, making it suitable as a material for producing high-liquid coin for substitution of copper.

While the invention has been shown and described in connection with specific embodiments thereof, it will be understood that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

According to the present invention, while completely excluding Ni, which is harmful to the human body and an expensive alloying element, it exhibits the same level of whiteness as that of copper, and at the same time, exhibits improvement in discoloration resistance through suppression of de-zinc corrosion due to addition of Sb or Sn. It is possible to provide a white-based copper alloy for producing a coin having excellent discoloration resistance that can replace the copper used as a cotton coin material.

Claims (6)

Mn 10-20 wt%; Zn 10-20 wt%; Sb or Sn 0.1-1.0 wt%; Consisting of the balance Cu, De-zinc corrosion and surface discoloration are suppressed by the Sb-based or Sn-based compound formed on the surface of the white-based copper alloy for producing coins having excellent discoloration resistance. The method of claim 1, The Sb-based compound is SbCl ₃ or Sb ₂ O ₃ White-based copper alloy excellent for discoloration resistance, characterized in that consisting of. The method of claim 1, The Sn-based compound is a white series copper alloy for producing coins having excellent discoloration resistance, characterized in that consisting of SnCl ₂ or SnO ₂ . The method according to any one of claims 1 to 3, White-based copper alloy for the production of coins having excellent discoloration resistance, characterized in that the heat treatment at 600 ~ 650 ℃ after cold rolling. The method according to any one of claims 1 to 3, White series copper alloy for producing coins having excellent discoloration resistance, characterized by forming a single-phase cubic structure at room temperature. The method according to any one of claims 1 to 3, A white-based copper alloy for producing coins having excellent discoloration resistance, characterized in that the color difference value measured based on white copper composed of 75 wt% Cu and 25 wt% Ni is 3.00 or less.

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