Lead-free copper-zinc alloy that can withstand the marine environment

Abstract

The invention provides a copper-zinc alloy with low lead content useful in the manufacture of wire used in the manufacture of cages for aquaculture, where said wire suffers the least deterioration due to loss of zinc during exposure to stagnant water, water of little movement or sea waters.

Claims

1. A composition of matter comprises between about 64% to 66.15% by weight of Cu; between 32% to 34.5% by weight of Zinc; 0.00229% by weight of Si, 0.00112% by weight of S, and with an impurity content of 0.5% to 2% by weight consisting essentially of Pb, Sn, Ni, Sb, and Fe.

2. A composition of a ter comprising (% by weight): TABLE-US-00007 Zn Pb Sn P Mn Fe Ni 32.63 0.00786 0.534 0.00344 <0.001 0.0281 1.20 Si As Al S Sb Cu Zn.sub.eq 0.00229 <0.0005 0.196 0.00112 0.251 65.15 33.87

3. A composition of matter according to claim 1, having a fine and homogeneous grain with an average grain size of 33 μm.

4. A useful wire for the manufacture of cages for aquaculture, manufactured with an alloy comprising about 64% to 66.15% by weight of Cu; between 32% to 34.5% by weight of Zinc; 0.00229% by weight of Si, 0.00112% b weight of S and with an impurity content of 0.5% to 2% by weight consisting essentially of Pb, Sn, Ni, Sb, and Fe.

5. A useful wire for the manufacture of cages for aquaculture, made of the copper-zinc alloy of claim 2.

6. A wire according to claim 4, having properties of tensile strength of 583.5 MPa and 31% elongation.

7. A wire according to claim 4, having an average hardness value of 72 H.R.B. and a micro hardness of 141.3 HV in the cross section and 138 HV in the longitudinal section and on average 140 HV.

8. A process for the manufacture of alloy according to claim 1, comprising melting in a stationary casting furnace cooled by a water sleeve, a mixture of 64% to 66.15% by weight of Cu; of 32% to 34.5% by weight of Zinc, with an impurity content of 0.5% to 2% by weight consisting essentially of Pb, Sn, Ni, Sb and Fe.

9. The process according to claim 8, wherein the furnace is an electric induction furnace that brings the broth to a temperature of 1100° C., so that after a homogenization period, the broth reaches a discharge temperature of 1010° C.

10. The process according to claim 8, wherein the broth is poured into a vertical mold and cooled by means of a sleeve with water circulation.

11. A process for the manufacture of a wire with a composition according to claim 1, wherein the process is carried out by hot extrusion and the stretching process comprises pulling the material with the tool.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a micrograph of the 4 mm wire: a) longitudinal section and b) cross section, 100×.

(2) FIG. 2 micrograph of the 4 mm wire, a) longitudinal section and b) cross section, 500×

(3) FIG. 3 SEM micrograph, surface termination, 500×.

(4) FIG. 4 SEM micrograph, surface termination, 500×.

(5) FIG. 5 Longitudinal and cross section micrograph, dezincified layer measurement, 50×

DETAILED DESCRIPTION OF THE INVENTION

(6) Preferably the alloy of the present invention comprises between about 64% to 66.15% Cu; between 32% to 34.5% of Zinc, with an impurity content of 0.5% to 2% mainly Pb, Sn, Ni, Sb; Fe. With this composition, the minimum requirements necessary to be considered an alloy with low corrosion and lead-free are perfectly met for use in the manufacture of wires for marine aquaculture cages. It is also significant because it increases the machinability of the alloy, which will aid chip breakage and lubrication during wire machining to the normally required thickness of 4 mm.

(7) This alloy contains a relatively low amount of Beta phase to favor its machining, but enough to always maintain an acceptable level of hot forgeability.

(8) An alloy containing 65.5% Cu, 32.63% Zn, 0.534% Sn, 0.251% Sb and 1.20% Ni, for which its Zinceq results in 33.87. It was prepared according to the procedure described below and then it was used for the manufacture of a wire with a diameter of 4 mm, which is normally used for the construction of cages in aquaculture.

(9) In the optical emission spectrometer test to determine the composition of the manufactured 4 mm wire, a flat surface is prepared by cutting and machining, and three points were analyzed to average three analyzes. Table 1 shows the average of the chemical analysis.

(10) TABLE-US-00001 TABLE 1 Chemical analysis, average of three analyses, % weight Zn Pb Sn P Mn Fe Ni 32.63 0.00786 0.534 0.00344 <0.001 0.0281 1.20 Si As Al S Sb Cu Zneq 0.00229 <0.0005 0.196 0.00112 0.251 65.15 33.87

(11) Stationary casting furnace cooled through water sleeve.

(12) The melting of the materials used for the manufacture of the alloy occurs in electric induction furnaces that bring the broth to a temperature of 1100° C., and after a homogenization period it reaches a discharge temperature of 1010° C.; the broth is poured into a vertical mold and cooled by means of a sleeve with water circulation.

(13) To maintain an acceptable machining level but maintaining it is necessary to add in small percentages elements that will help the machining, and tin and silicon are the ones that had the best performance against the loss of zinc. Achieving a Machinability of 65%.

(14) Hot Extrusion Process (4 mm Wire Formation)

(15) Extrusion is a process used to create objects with defined and fixed cross section. The material is pushed or withdrawn through a die (extrusion die) with a cross section having the geometry of the desired product, the metal then flows in the direction of the piston movement in the case of direct extrusion and in the opposite direction for the case of indirect extrusion.

(16) In the case of brass, given the strong deformations of which the material is subjected and therefore the excessive stress to which it is subjected, the process is carried out by hot extrusion. In this process the ingot that is subjected to extrusion is previously heated.

(17) Because of the type of flow caused during this process, the beta phase bands will be directed (elongated) in the longitudinal direction to the flow of the material during extrusion.

(18) Bar Stretch

(19) The last step of the manufacturing process is obtaining the mechanical properties and adjustment of tolerances of the material, which is achieved by cold deformation, making a material pass through the geometry previously manufactured in a die. The stretching process is practically the same as the extrusion process, with the difference that in stretching the material is pulled through the tool, while the material is pushed in extrusion.

(20) Metallographic Study of the 4 mm Wire.

(21) The samples are cut longitudinally and transversely to then be polished and etched and finally observe in a light microscope and conduct a microstructure characterization. FIGS. 1 and 2 show the constituent microstructure of the wire alloy, which is formed by alpha phase. Recrystallized (twinned) alpha phase grains and cold work deformation bands are observed. Table 2 shows the average grain size of the alpha phase.

(22) TABLE-US-00002 TABLE 2 Grain size measurement, microns Measurement No. Grain size value μm 1 32.8 2 35.5 3 31.9 4 32.5 5 32.4 Average 33.0
Table 3 shows the results of the 4 mm wire tensile tests.

(23) TABLE-US-00003 TABLE 3 Summary of Mechanical Properties Initial Maximum Maximum Elongation Area area load stress of 50 mm reduction IDEM (mm.sup.2) (Kgf) (Mpa) (%) (%) 4 mm wire 12.56 747.8 583.5 31.0 73.7

(24) Table 4 shows the transverse and longitudinal VICKERS microhardness measurement of the 4 mm wire EQUIPMENT: Buehler micro durometer SCALE: Vickers, 300 g STANDARD: ASTM E-384

(25) TABLE-US-00004 TABLE 4 Vickers microhardness, longitudinal section. Indent HV Value 1 (center) 135.8 2 137.9 3 135.3 4 138.9 5 136.6 6 (edge) 143.3 Average 138

(26) TABLE-US-00005 TABLE 5 Vickers microhardness, cross section Indent HV Value 1 (center) 137.4 2 123.2 3 136.1 4 145.9 5 159.0 6 (edge) 146.1 Average 141.3
Table 6 shows the transverse and longitudinal ROCKWELL hardness measurement of the 4 mm wire.

(27) TABLE-US-00006 TABLE 6 Surface hardness test, Rockwell B Direction of measurement HRB Value: Longitudinal 74 Longitudinal 77 Cross 66 Cross 72 Average 72

(28) From the microstructure point of view, the wire made from the alloy object of the present invention has a fine and homogeneous grain with an average grain size of 33 μm, see FIGS. 1-2 and table 2. FIGS. 1 and 2 show twinned alpha phase.

(29) The tensile strength properties of the 4 mm wire are 583.5 MPa and 31% elongation, see table 3.

(30) The hardness results in an average value of 72 HRB, see table 6. Microhardness results in 141.3 HV in cross section and 138 HV in longitudinal section and on average 140 HV.

(31) The dezincification phenomenon is basically a loss of zinc (FIG. 7) on the brass in contact with stagnant waters, slightly acidic waters or waters that move at low speed, leaving a porous mass with a very low mechanical resistance. Such phenomenon is seen accelerated as the temperature increases. FIG. 7 shows the dezincified layer made according to the corrected ISO 6509 standard, where a 375 μm dezincification layer can be seen.

(32) There are correct manufacturing variables. Therefore, the wire manufactured from the alloy object of the present invention shows an adequate behavior in use for the manufacturing of cages for aquaculture.