WO2016132290A1

WO2016132290A1 - Metal alloy

Info

Publication number: WO2016132290A1
Application number: PCT/IB2016/050820
Authority: WO
Inventors: Leonardo PINZAUTI; Giuliano SIMONELLI; Gianni FAGGI; Teodoro Valente
Original assignee: Leofasi S.R.L.
Priority date: 2015-02-16
Filing date: 2016-02-16
Publication date: 2016-08-25
Also published as: EP3259379A1; EP3259379B1; PT3259379T; ES2748778T3

Abstract

The present invention concerns a metal alloy comprising the following components: - copper in a percentage varying between 62% and 57% by weight on the total weight of the alloy; - bismuth in a percentage varying between 3% and 1% by weight on the total weight of the alloy; and - zinc added to obtain 100% by weight on the total weight of the alloy.

Description

"METAL ALLOY"

TECHNICAL FIELD OF THE INVENTION

The present invention concerns a new metal alloy, in particular to be treated through hot forging, CNC milling and turning, laser and galvanic incision.

STATE OF THE ART

In order to make pieces through hot forging, CNC milling and turning, brasses with lead also called dry brasses are usually used, which have very high forgiability, shearability and machinability, which commercial lead-free alloys are currently unable to achieve.

Currently, the use of lead in general and thus also in metal alloys used for metal accessories of the fashion industry is forbidden because it is recognized as toxic above a certain value.

The toxicity of lead is recognized both at European level, as given in the update of the REACH regulation of 6/3/2012, and at international level, as expressed for example by Proposition 65 List of the State of California.

Lead-free brasses have also been proposed, which however have much poorer characteristics in terms of forgiability, shearability and machinability than leaded brasses and cannot be processed in certain conditions, apart from with very long treatment times.

US5637160A, CN104109774A and CN104004941A teach respective alloys according to the state of the art.

AIMS OF THE INVENTION

An object of the present invention is to provide a new metal alloy.

Another object of the present invention is to provide a new lead-free metal alloy or in any case one that respects the criteria of the most restrictive regulations, but that has forgiability, shearability and machinability that are comparable or better than those of leaded brasses.

Another object of the present invention is to provide a new metal alloy for making metal accessories for the fashion industry, like for example belt buckles, snap hooks, bag closures, charms and zipper pulls, etc., all accessories used in the field of leather and clothing, as well as for making technical items for industry, including in particular the lighting industry.

In accordance with an aspect of the invention, a metal alloy is provided according to claim 1.

- The dependent claims refer to preferred and advantageous embodiments of the invention.

EMBODIMENTS OF THE INVENTION

A metal alloy according to the present invention comprises the following components:

- copper in a percentage varying between 62% and 57% by weight on the total weight of the alloy;

- bismuth in a percentage varying between 3% and 1% by weight on the total weight of the alloy; and

- zinc added to obtain 100% by weight on the total weight of the alloy.

In an alloy according to the present invention:

- the copper content must not be less than 57%, since with values lower than this there would be an excessive amount of zinc, which would result in the formation of an alloy that is excessively fragile at room temperature and difficult to cut during the preparation of the semi-worked products;

- the copper content must not be more than 62%, since a greater amount of copper would result in the formation of a monophase alloy that is difficult to extrude and thus forge;

- the bismuth content must not be less than 1%, since a lower bismuth content would irredeemably harm the ability to process the alloy with machine tools;

- the bismuth content must not be more than 3%, since a greater bismuth content would reduce the mechanical characteristics without giving any benefits; on the other hand, as far as hot forging is concerned, with bismuth values greater than 3%, the preferential oxidation of the bismuth would produce a surface scale that would dirt the mold and could also affect the surface quality required for products, in particular in the fashion industry.

A bismuth percentage of 1-2% is most suitable for forging processes, whereas for machining processes with machine tools a bismuth percentage equal to 2-3 % by weight on the total weight of the alloy is most recommended.

Preferably, zinc is present with a percentage that varies between 42% and 35% by • weight on the total weight of the alloy.

Preferably, an alloy in accordance with the present invention comprises copper in a percentage varying between 58.8% and 62% by weight on the total weight of the alloy, bismuth in a percentage varying between 1.5% and 3% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy, for example 36%-40% by weight on the total weight of the alloy.

If so desired, an alloy in accordance with the present invention comprises copper in a percentage varying between 60% and 61% by weight on the total weight of the alloy, bismuth in a percentage varying between 2% and 3% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy, for example 36%-38% by weight on the total weight of the alloy.

Advantageously, a first preferred alloy in accordance with the present invention comprises copper in a percentage varying between 60.4% and 60.6% by weight on the total weight of the alloy, bismuth in a percentage varying between 2.4% and 2.6% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy, for example 36.9%-37.1% by weight on the total weight of the alloy.

Even more advantageously, such a first alloy comprises 60.5% copper by weight on the total weight of the alloy, 2.5% bismuth by weight on the total weight of the alloy and 37% zinc by weight on the total weight of the alloy.

A second preferred alloy in accordance with the present invention comprises copper in a percentage varying between 61% and 62% by weight on the total weight of the alloy, bismuth in a percentage varying between 1% and 2% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy. Advantageously, a second preferred alloy in accordance with the present invention comprises copper in a percentage varying between 61.2% and 61.4% by weight on the total weight of the alloy, bismuth in a percentage varying between 1.7% and 1.9% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy, for example 36.8%-37% by weight on the - total weight of the alloy.

Even more advantageously, such a second alloy comprises 61.3% copper by weight on the total weight of the alloy, 1.8% bismuth by weight on the total weight of the alloy and 36.9% zinc by weight on the total weight of the alloy.

A third preferred alloy in accordance with the present invention comprises copper in a percentage varying between 58.5% and 59.5% by weight on the total weight of the alloy, bismuth in a percentage varying between 1.5% and 2% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy.

Advantageously, a third preferred alloy in accordance with the present invention comprises copper in a percentage varying between 58.8% and 59% by weight on the total weight of the alloy, bismuth in a percentage varying between 1.6% and 1.8% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy, for example 39.3%-39.5% by weight on the total weight of the alloy.

Even more advantageously, such a third alloy comprises 58.9% copper by weight on the total weight of the alloy, 1.7% bismuth by weight on the total weight of the alloy and 39.4% zinc by weight on the total weight of the alloy.

A fourth alloy in accordance with the present invention comprises copper in a percentage varying between 60% and 60.2% by weight on the total weight of the alloy, for example 60.1%, bismuth in a percentage varying between 2.8% and 3% by weight on the total weight of the alloy, for example 2.9%, and 36.9%-37.1% zinc by weight on the total weight of the alloy, for example 37%.

A fifth alloy in accordance with the present invention comprises copper in a percentage varying between 57% and 58% by weight on the total weight of the alloy, for example 57.6%, bismuth in a percentage varying between 1% and 2% by weight on the total weight of the alloy, for example 1.5%, and zinc added to obtain 100% by weight on the total weight of the alloy, for example 40.9%.

Even more preferably, the alloy comprises only copper, bismuth and zinc.

Moreover, an alloy according to the present invention could comprise other metals ^• in small percentages not harmful to the alloy itself, such as: lead at a concentration less than or equal to 40 ppm, cadmium at a concentration less than or equal to 40 ppm, nickel at a concentration less than or equal to 0.3%, tin at a concentration less than or equal to 0.3% by weight on the total weight of the alloy, iron at a concentration less than or equal to 0.1% and/or aluminum at a concentration less than or equal to 0.70% by weight on the total weight of the alloy. Possible other elements could be present at a maximum concentration of 0.2% by weight on the total weight of the alloy.

Advantageously, as stated, the lead content in the alloy is less than 0.004% by weight on the total weight of the alloy. Greater concentrations of lead would be harmful for the reasons indicated above (toxicity).

Preferably, an alloy according to the present invention is used to make objects through hot forging, computerized numerical control (CNC) milling and turning, from semi-worked products with fine grain and equiaxial structure.

Preferably, in a method according to the present invention firstly the alloy is made in molten state and then the semi-worked product is made through a hot extrusion process. More specifically, the alloy is obtained by melting flakes of pure copper, subsequently adding billets of pure zinc and finally billets of pure bismuth.

On the other hand, as far as the hot extrusion of an alloy according to the present invention is concerned, it is carried out by means of a matrix of thickness 20÷25 mm, with a joining radius in the inlet part of the material comprised between 0.2 and 0.3 mm and with an outlet clearance angle comprised between 0.1° and 2°. Concerning this, it should be noted that the extrusion matrices are generally circular discs and have outer diameters between 150 and 300 mm. The dimensions of the hole from which the semi-worked product is extruded obviously depend on the nominal dimensions of the semi-worked product itself. Concerning this smaller inlet joining radii and smaller outlet clearance angles do not allow a material with the suitable surface finish and the due compactness to be obtained.

Advantageously, an object according to the present invention is a metal accessory for the fashion industry, like for example a belt buckle, a snap hook, a bag closure, ^• a charm and a zipper pull, etc. (all accessories used in the field of leather and clothing) or for industry, for example in the lighting industry.

A series of tests were carried out to identify the alloy according to the present invention, during which, with particular reference to the production cycle through hot forging, four types of tests were carried out for each type of material tested:

- forgiability test;

- shearability test;

- machinability test (measuring the cutting times of the billets); and

- stereomicrographic analysis on the morphology of the chips produced in the cutting test.

Since the first three tests are of the technological type, the tests on the materials examined were always accompanied by control tests on the standard commercial materials, in particular on leaded brass and on lead-free brass currently used, tested in the same conditions (same mold, same saw, same loads, etc.) so as to have comparative data, certainly more significant that single absolute data without reference.

In the present patent application, the term billets mean the semi-worked products in the form of bars with a circular, square or rectangular section, obtained from the alloy under examination.

The materials initially taken into consideration to identify a new alloy were brasses with bismuth and brasses with silicon.

Thereafter, the less satisfactory results of the first tests and considerations concerning the presumable low galvanizability of the silicon brasses led to focusing attention on alloys containing bismuth.

During the tests it also emerged that there was a need to have innovative brasses prepared not by fusion, but with technologies closer to those of brass bars on the market. Concerning this, some alloys produced by fusion had defects such as porosity, segregation and rough microstructure that could worsen the forgiability and machinability results.

Hereinafter, some of the main characteristics of the preliminary forgiability and ^• machinability tests are shown.

Forgiability test

The tests were carried out with:

- the same mold;

- the same dimensions of the billet;

- the alloys according to the present invention;

- the standard alloys with and without lead;

- absence of lubricant; and

- the same heating temperature.

During such tests the following was also evaluated:

- the filling of the mold;

- the ability to slip; and

- the "abutment", in other words the thickness of the sample following forging.

The leaded alloy tested had the following composition, in which the percentages indicated are by weight on the total weight of the respective alloy: copper 57-59%, cadmium less than 0.0075%, iron less than 0.3%, lead 1.6-2.5%, nickel 0.3%, tin 0.3%, aluminum less than 0.05% and the remainder zinc.

The lead-free alloy tested had the following composition, in which the percentages indicated are in weight on the total weight of the respective alloy: copper 57-59%, lead less than 0.009%, nickel less than 0.3%, tin less than 0.3%, iron less than 0.3%, aluminum less than 0.05%, cadmium less than 0.01% and the remainder zinc.

The so-called "lead- free" alloy had a small lead content that, in fact, constituted an impurity of the alloy.

Machinability test

Hereinafter, some of the main characteristics of the machinability tests are given. Comparative tests were carried out with:

- band saw;

- constant advancing load;

- alloys according to the present invention;

- standard alloys with and without lead; and

- billets of comparable diameter.

During the machinability tests the following was measured:

- the time necessary to complete the cutting; and

- the morphology of the chips.

Tests carried out

First batch of samples

The first batch of samples tested consisted of a few billets of Cu-Zn alloy of small diameter (8-9 mm) respectively containing silicon (see the table hereinafter on the left) and bismuth (see the table hereinafter on the right).

The machinability tests showed that brass with

same chip morphology that appears optimal being very short, whereas brass with silicon and lead-free brass give a long chip not suitable for cutting. Concerning this see figures 1 to 4, which show the morphology of the different types of chip obtained during the machinability test.

In such figures, figure 1 relates to a standard alloy with lead, figure 2 to a standard lead-free alloy, figure 3 to the alloy with bismuth, and figure 4 to the alloy with silicon.

• On the other hand, figures 5 to 8 show images relative to the results of forging tests. In such figures, figure 5 relates to a standard alloy with lead, figure 6 to a standard lead-free alloy, figure 7 to the alloy with bismuth, and figure 8 to the alloy with silicon.

In the table given below the abutment values detected after the forging tests for such alloys are given.

At the end of the tests on the first batch the following considerations emerg

- the alloys with bismuth showed, in the region where burrs are present, a behavior such as to indicate difficulty in forging both at high and low temperature.

It was thus considered that a lower zinc content should have substantially improved forgiability.

The machinability of the alloy with bismuth, on the other hand, was satisfactory, but it has to be clarified whether this was due to the effect of the bismuth or that of the presence of a high zinc content, which increased its hardness and fragility, for which reason it was considered necessary to perform further tests.

The forgiability of the alloy with silicon seemed satisfactory, whereas its machinability was analogous to that of lead-free brass.

However, there remained a need to carry out a more statistically significant number of tests, suitable galvanizability tests and to consider its ability to be produced in large batches.

Second batch of samples

In the second batch of samples many casts of silicon and bismuth brasses were carried out, producing billets having a diameter of about 19.5 mm. The larger ^• number of casts was useful for evaluating the ability to reproduce the process and the properties, whereas the larger size of the billets ensured greater usability thereof for forging.

The compositions of the new alloys tested were, respectively:

- silicon alloys: Cu=85%, Zn=l 1 %, Si=4%

- alloys with bismuth: Cu=60%, Zn=38%, Bi=2%

The percentages also in this case were by weight.

With reference to figures 9 to 11, the billets are illustrated with the respective porosities, said porosities being present even after turning of about 1 mm in thickness.

Concerning this, the samples had evident and deep surface porosities, due to difficulty in the casting and cooling step.

The machinability tests showed that silicon brass has behavior comparable with that of lead-free brass both at the chip morphology level (long) and at the cutting time level.

The machinability tests carried out on bismuth brass for all of the various casts showed behavior comparable with that of lead-free brass both at the chip morphology level (long) and at the cutting time level. However, a certain dishomogeneity was recorded in the results that led to reflection on the need to better standardize the production process. In particular, in one case there were much better cutting times even that leaded brass.

In the table given hereinafter, the abutment values detected after forging tests for the alloys tested are indicated. Alloy Abutment

Standard leaded alloy 6.14 ± 0.02 mm

Standard lead-free alloy 6.17 ± 0.02 mm

First alloy with silicon 6.15 ± 0.11 mm

Second alloy with silicon 6.19 ± 0.02 mm

In the table given hereinafter, the abutment values detected after forging tests for the alloys tested are indicated.

Alloy Abutment

Standard leaded alloy 6.11 ± 0.05 mm

Standard lead-free alloy 6.16 ± 0.03 mm

First alloy with bismuth 6.14 ± 0.03 mm

Second alloy with bismuth 6.10 ± 0.02 mm

Third alloy with bismuth 6.20 ± 0.02 mm

At the end of the tests on this batch of samples, the following conclusions were drawn.

In the alloys containing silicon, some difficulties were observed in identifying the correct forging temperature, which seemed higher than standard brass. Moreover, it seemed that the forgiability range was narrower.

The operator who carried out the tests observed that even by filling the mold, the rheology of these alloys is different from conventional ones and could cause difficulties for large productions. It is confirmed that the machinability is comparable with that of commercial lead-free brass, thus very low. Also considering the low galvanizability, it was decided to abandon these alloys with silicon to concentrate on alloys with bismuth.

The alloys containing bismuth, on the other hand, demonstrated good machinability and forgiability.

The products obtained from them had dishomogeneity, and it was necessary to evaluate the origin of such dishomogeneity to solve the fusion problems from which they presumably derived.

It was thus considered important to evaluate the production of hot or cold deformed alloys to control the size of the crystalline grain through recrystallization treatments. Another aspect to be evaluated concerned the microstructure, which had to be examined to verify the presence of bismuth on the grain edge and the initial - size of the grain.

Third batch of samples

In this study phase it was attempted to carry out tests adapted for regenerating the crystalline grain of the billets made of bismuth brass before the forging tests.

Alloys with slightly different composition from each other were used, in order to evaluate possible alternatives:

- samples of a first alloy with bismuth or alloys A: 60% Cu, 38% Zn, 2% Bi;

- samples of a fourth alloy with bismuth or alloys D: 62% Cu, 35.6% Zn, 2.4% Bi. The percentages also in this case were by weight.

Figures 12 and 13 illustrate the images of some billets fractured during the first thermomechanical treatments with heat and hammer, whereas figures 14 and 15 illustrate billets obtained by hammering or following deformation in a vice.

Figure 16, on the other hand, shows some billets after the thermomechanical treatment and turning.

It went ahead by trial and error, heating the billets to then deform them and promote the recrystallization processes. After a few unsatisfactory attempts, probably due to incorrect choices of temperature and the internal oxidation of the billets themselves (occurring due to the porosities), which tended to fracture, recrystallized billets were obtained, but the results were not satisfactory with reference to the methods and to their presumable reproducibility.

Before forging the deformed billets, they were brought by turning to a diameter of 17 mm and compared with other conventional commercially available ones of the same diameter made from brass with and without lead.

In order to make a more in-depth analysis, comparative tests were carried out not only with commercial brasses, but also on the samples of bismuth brass both as such and thermomechanically treated.

At the end of the analyses carried out on this batch, the following conclusions were drawn.

The alloys with bismuth of composition "A" and "D" continued to perform very ^■ well in terms of machinability and quite well in terms of forgiability.

The recrystallization treatment seemed to be effective to improve forgiability, whereas it did not have a negative impact on machinability.

It was necessary to make the recrystallization treatment more reproducible and quantitatively control the effect on the microstructure.

Fourth batch of samples

The samples produced and characterized in this batch were cut from bars produced by a third party firm.

Firstly, given the importance of the microstructure in forging, metallographic tests were carried out that showed a fine grain and equiaxial structure, as would be desirable to have before each heating for hot forging.

Figures 17 to 22 illustrate the microstructure of the cross and longitudinal sections of billets of diameter 17 mm at various magnifications.

More specifically:

- figures 17 and 18 are respective cross and longitudinal sections, obtained with a 50X magnification and with reference mark or line equal to 200 μιη;

- figures 19 and 20 are respective cross and longitudinal sections, obtained with a 200X magnification and with reference mark or line equal to 100 μηι; and

- figures 21 and 22 are respective cross and longitudinal sections, obtained with a 1000X magnification and with reference mark or line equal to 10 μηι.

Having much more material available than what is present in the previous batches, a more statistically significant number of samples were molded using many types of molds.

For each test samples were also produced made of brass with and without commercial lead.

The machinability tests gave extremely satisfactory results since the bismuth alloy shows cutting times even shorter than those of leaded brass.

Figures 23 to 25 show some molded and sheared samples and, more specifically, figure 25 concerns alloys according to the present invention.

^• Having carried out a greater number of tests, it was possible to better understand the origin of some "abutment" difficulties of the bismuth brass.

Figure 26 shows a graph relative to the correlation between forging temperature and thickness of the molded sample. Clearly, the more the material is hot molded, the greater the possibility of deforming it.

As is quite clear from such a graph, an alloy according to the present invention containing bismuth tended to be molded by the operator at a lower temperature with respect to the other alloys, and from this derived the lower deformability of an alloy according to the present invention with respect to standard alloys with or without lead.

It should be emphasized that in hot forging it is common practice for the forging temperature to be controlled visually by the operator, who based on his/her experience, easily manages to identify the correct heating level.

However, the color rendering of unknown materials, like the present alloy according to the present invention, could have led the operator to heat less.

The oblique line in the figure is to help understand how the rheology of the materials should be analogous and better training of the operator also with an alloy according to the present invention could result in a correct "abutment" being obtained.

The shearing tests showed that bismuth brass allows a quality of the finish of the sheared surface to be obtained that is comparable with that of commercial alloys. The synoptic tables of the machinability tests obtained on all of the batches tested are shown below.

Billet diameter 8

(mm)

Billet cutting 50.27

area (mm²)

Standard Standard lead- Alloy with Alloy with leaded alloy free alloy bismuth Silicon

Cutting time 9.0 12.5 14.5 12.8

(s)

Cutting 0.18 0.25 0.29 0.25 time/area

(s/mm²)

Chip type short long short long

(s/mm2)

Chip type short short short short

Standard Standard lead- First alloy Second alloy leaded alloy - free alloy with silicon with silicon 2 September

Cutting time 33 53 51 50.00

(s)

Cutting 0.130 0.208 0.200 0.20 time/area

(s/mm2)

Chip type short long long long

Fourth batch

Billet diameter 17

(mm)

Billet cutting 226.98

area (mm2)

Standard leaded Standard lead-free Alloy with bismuth alloy 1 st set alloy 1 st set 1 st set

Cutting time 13.8 22.8 10.9

(s)

Cutting 0.061 0.100 0.048

time/area

(s/mni2)

Chip type short long short

Standard leaded Standard lead-free Alloy with bismuth alloy 2nd set alloy 2nd set 2nd set

Cutting time 13.9 22.5 10.7

(s)

Cutting 0.060 0.099 0.047

time/area

(s/mm2)

Chip type short long short

The terms 1^st and 2^nd SET mean the groups of testing batches.

With reference to the results of the fourth batch, it should be noted how a bar obtained with an alloy according to the present invention has greater ease of cutting even that commercial leaded brass.

Production test with innovative industrial bar In the final phase of the project, industrial production of a component was simulated by carrying out all of the normal production cycle on groups of samples in a number sufficient to occupy the entire chain of the oven, using automatic positioning systems of the billet on the mold.

During the tests a further characterization of the forging behavior of the alloy ^• according to the present invention was carried out, varying the pre-heating temperatures and then observing the results in terms of filling and "abutment" of the mold, since during the previous tests some possible difficulties arose.

Each molded group of samples was tested after the oven reached normal operating conditions.

Samples were produced by pre-heating the chamber of the oven to temperatures comprised in the range from 725 to 830 °C, which resulted in a temperature of the billets, a moment before being molded, comprised between 640 and 760 °C. The temperatures were measured sample by sample through a suitably calibrated pyrometer. Thereafter shearing tests and the measurements of the abutment were carried out on the various batches.

The filling of the mold was satisfactory for all of the temperatures tested, showing and confirming the good moldability of an alloy according to the present invention. The data relative to the measurement of the abutment is given in figure 27. The shearability results were satisfactory and in line with those typical of other commercial alloys.

As already observed earlier, the abutment height is a function of the pre-heating temperature, since this determines a variation of the ease of deformation of the material. The abutment differences between one temperature and another are substantial and cannot be the result of only different thermal contraction, which has an impact on the dimensions considered only at a lower order of magnitude.

The samples produced were finally subjected to further galvanizability, machinability by machine tool and brazeability tests.

Concerning this, hot forging, machine tooling, milling, turning, CNC incision, laser incision, brazing and galvanization gave a positive result; in particular, milling, turning, CNC incision and galvanization did not show substantial differences with respect to what can be obtained using standard leaded alloys.

At the end of the research and characterization step it emerged that the alloy according to the present invention for hot forging, having average nominal composition 60% Cu, 38% Zn, 2% Bi, has greater machinability than that of ^• commercial lead-free brasses, and even greater than that of commercial leaded brass.

The forgiability and machinability (turning cutting and CNC milling) of an alloy according to the present invention appears satisfactory comparably with that of other commercial leaded alloys.

In order to evaluate the aptitude of an alloy according to the present invention to be machined with machine tools or through other machining, comparative tests were carried out, the results of which are commented upon below.

Turning tests

Such tests were carried out using the cutting parameters used for machining with commercial leaded brasses, both on 7 mm diameter bars and on 16 mm diameter bars made with an alloy according to the present invention, with nominal composition 60% Cu, 38% Zn, 2% Bi. Comparative tests were also carried out with commercial leaded and lead-free brass with bars of nominal size equal to those indicated above.

The tests on the 16 mm bars were carried out with the following cutting parameters:

- cutting speed: 40 m/min

- advancement: 0.09 mm/rev

- pass depth: 1 mm

From the analysis of the results of such tests no significant differences in behavior emerged between the leaded brass and an alloy according to the present invention, finding the same behavior when cutting with a single-cutting tool.

Contrarily, substantial differences emerged between an alloy according to the present invention and the commercial lead-free brass, the latter showing a continuous chip, which, in some machining operations, can create surface finishing problems and breaking of tools.

More specifically, morphological analyses of the chips were carried out documented through photography and optical stereomicroscopy, the results of which can be seen in figures 28 to 36, in which:

^• - figures 28 to 30 are relative to a 16 mm diameter bar of lead-free brass;

- figures 31 to 33 are relative to a 16 mm diameter bar of leaded brass; and

- figures 34 to 36 are relative to a 16 mm diameter bar of an alloy according to the present invention.

Milling tests

In order to confirm the results obtained with the tests on a band saw and on a lathe, the cutting behavior was evaluated in the case of a multi-cutting tool and milling tests were carried out on a flat bar with width in plan of 80x5 mm and carried out with an alloy according to the present invention (60% Cu, 38% Zn, 2% Bi). Machining operations were carried out with a miller having 4 blades with diameter of 2 mm, throats with a T-shaped tool, incisions, holes and threadings. The advancing and cutting speed parameters normally used for leaded brass were used. The milling test also gave a positive result, showing that the consumption of the tools to treat an object made from an alloy according to the present invention is comparable with that of leaded brass. Finally, it should be emphasized that after 900 pieces there was no breakage of the tool nor any degradation of the surface finish. Laser incision tests

The laser incision tests were carried out on components previously machined by machine tools from bars of an alloy according to the present invention (60% Cu, 38% Zn, 2% Bi). The same process parameters used in the case of commercial leaded brass were used and no appreciable differences in behavior were found. Cleaning and polishing and galvanic tests

The cleaning and polishing and galvanic tests were carried out on components that had been milled, turned, forged and some of them transformed with welds and/or laser incision and/or sandblasting to then be finished with cleaning and polishing, in order to have results of all of the machining processes that are normally carried ^• out on standard brass manufactured products.

Also in this case, no differences were found with respect to leaded brass.

Comparative tests of galvanic performance (damp heat, salt-spray, synthetic sweat and adherence) were carried out on equal pieces, made in the three alloys (alloy according to the present invention, leaded brass and lead-free brass) treated in the same way. Also in this case no behavior differences were detected.

The following table shows an extract of the corrosion tests carried out on galvanized samples on substrates made of an alloy according to the present invention.

72964 Thioacetamide 9 - Thioacetamide 48 Positive

(UNI EN ISO

4538)

Notes:

72960: No alteration

72961 : No significant alteration. Only a very slight exit of white salinity from the hole on the rear

72962: No significant alteration

72963: No alteration

72964: No alteration

Comparison with teachings of prior art documents

The Applicant of the present patent application carried out comparative machinability tests between alloys according to the present invention and alloys as taught by prior documents US5637160A, CN104109774A, CN104004941 A.

The results of such comparative tests are presented in the following table.

Alloy 7 14.4 0.4 65 60.1 39.7 1.1 0.13

Alloy 6 15.1 0.6 68 61.3 35.9 1.7 0.06 1

As comments on the tested alloys, it should be noted that:

- alloy 5 is a first preferred alloy according to the present invention;

- alloy 2 is a second preferred alloy according to the present invention;

* - alloy 1 is a third preferred alloy according to the present invention;

- alloy 9 is a fourth preferred alloy according to the present invention;

- alloy 3 is a fifth preferred alloy according to the present invention; and

- alloys 6, 7 and 8 represent alloys according to the teachings, respectively, of US5637160A, CN104109774A and CN104004941A.

The alloys were placed in order of decreasing machinability performance.

The tests carried out thus confirm that alloys according to the present invention have different concentrations with respect to those of documents US5637160A, CN104109774A and CN104004941A and better performance (such as machinability) relative to them.

It should also be noted that the alloys of such prior art documents are foreseen to be subjected to die-casting, to casting and not to forging like an alloy according to the present invention.

Moreover, the alloys of the aforementioned prior art documents are for making taps and not for components for the fashion industry.

It should also be noted that US5637160A, CN104109774A and CN104004941A are focused on obtaining alloys with high resistance to corrosion and to obtain a fine grain after solidification, aspects that are totally irrelevant for an alloy according to the present invention, since the objects obtained with such an alloy are foreseen to be extruded in solid state and then coated and protected from the external environment through galvanic layers.

As will be understood, an alloy according to the present invention achieves the preset purposes, since it has demonstrated, amongst other things, that it has forgiability, shearability and machinability comparable to or even better than those of brasses with or without lead.

Modifications and variants of the invention are possible within the scope of protection defined by the claims.

Claims

1. A metal alloy comprising the following components:

- copper in a percentage varying between 62% and 57% in weight on the total weight of the alloy;

- bismuth in a percentage varying between 3% and 1% in weight on the

' total weight of the alloy; and

- zinc added to obtain 100% in weight on the total weight of the alloy, said alloy further comprising lead at a concentration less than or equal to 40 ppm by weight on the total weight of the alloy, cadmium at a concentration less than or equal to 40 ppm by weight on the total weight of the alloy, nickel at a concentration less than or equal to 0.3% by weight on the total weight of the alloy, tin at a concentration less than or equal to 0.3% by weight on the total weight of the alloy, iron at a concentration less than or equal to 0.1% by weight on the total weight of the alloy and/or aluminum at a concentration less than or equal to 0.70% by weight on the total weight of the alloy.

2. An alloy according to claim 1, comprising copper in a percentage varying between 58.8% and 62% by weight on the total weight of the alloy, bismuth in a percentage varying between 1.5% and 3% by weight on the total weight of the alloy and zinc in a percentage varying between 36% and 40% by weight on the total weight of the alloy.

3. An alloy according to claim 1 or 2, comprising copper in a percentage varying between 60% and 61% by weight on the total weight of the alloy, bismuth in a percentage varying between 2% and 3% by weight on the total weight of the alloy and zinc in a percentage varying between 36% and 38% by weight on the total weight of the alloy.

4. An alloy according to claim 3, comprising copper in a percentage varying between 60.4% and 60.6% by weight on the total weight of the alloy, bismuth in a percentage varying between 2.4% and 2.6% by weight on the total weight of the alloy and zinc in a percentage varying between 36.9% and 37.1% by weight on the total weight of the alloy.

5. An alloy according to claim 4, comprising 60.5% copper by weight on the total weight of the alloy, 2.5% bismuth by weight on the total weight of the alloy and 37% zinc by weight on the total weight of the alloy.

6. An alloy according to claim 3, comprising copper in a percentage varying between 60% and 60,2% by weight on the total weight of the alloy, bismuth in a

^• percentage varying between 2,8% and 3% by weight on the total weight of the alloy and zinc in a percentage varying between 36.9% and 37.1% by weight on the total weight of the alloy.

7. An alloy according to claim 1 or 2, comprising copper in a percentage varying between 61% and 62% by weight on the total weight of the alloy, bismuth in a percentage varying between 1% and 2% by weight on the total weight of the alloy and zinc added to obtain 100% by weight on the total weight of the alloy.

8. An alloy according to claim 7, comprising copper in a percentage varying between 61.2% and 61.4% by weight on the total weight of the alloy, bismuth in a percentage varying between 1.7% and 1.9% by weight on the total weight of the alloy and zinc in a percentage varying between 36.8% and 37% by weight on the total weight of the alloy.

9. An alloy according to claim 8, comprising 61.3% copper by weight on the total weight of the alloy, 1.8% bismuth by weight on the total weight of the alloy and 36.9% zinc by weight on the total weight of the alloy.

10. An alloy according to claim 1 or 2, comprising copper in a percentage varying between 58.5% and 59.5% by weight on the total weight of the alloy and bismuth in a percentage varying between 1.5% and 2% by weight on the total weight of the alloy.

11. An alloy according to claim 10, comprising copper in a percentage varying between 58.8% and 59% by weight on the total weight of the alloy, bismuth in a percentage varying between 1.6% and 1.8% by weight on the total weight of the alloy and zinc in a percentage varying between 39.3%-39.5% by weight on the total weight of the alloy.

12. An alloy according to claim 11 , comprising 58.9% copper by weight on the total weight of the alloy, 1.7% bismuth by weight on the total weight of the alloy and 39.4% zinc by weight on the total weight of the alloy.

13. A metal alloy according to any one of claims 1 to 12, comprising only copper, bismuth and zinc.

14. An item molded starting from a metal alloy according to any one of the * preceding claims, comprising a metal fitting for the fashion industry, such as a belt buckle, a snap hook, a bag closure, a charm, a zipper pull or a metal fitting for the industry, for example for the lighting fixture.

15. A method for the production of an item according to claim 14, comprising a forging step of a metal alloy according to any one of claims 1 to 13.

16. A method according to claim 15, wherein said forging comprises a step of hot forging, turning, computerized numerical control milling, processing with machine tools, processing with laser machine and/or galvanizability.

17. A method according to claim 15 or 16, wherein firstly the alloy is made in molten state and then the semi-worked product is made through a hot extrusion process, and wherein said alloy is obtained by melting flakes of pure copper, subsequently adding billets of pure zinc and finally billets of pure bismuth.

18. A method according to claim 17, wherein said hot extrusion is carried out by means of a matrix of thickness 20÷25 mm, with a joining radius in the inlet part of the material comprised between 0.2 and 0.3 mm and with an outlet clearance angle comprised between 0.1° and 2°.

19. Use of a metal alloy according to any one of claims 1 to 13, for the implementation of a metal fitting for the fashion industry, such as a belt buckle, a snap hook, a bag closure, a charm, a zipper pull or a metal fitting for the industry, for example for the lighting fixture.