US 2013 O153097A1

(19) United States

(12) Patent Application Publication (10) Pub. No.: US 2013/0153097 A1
Dionne et al. (43) Pub. Date: Jun. 20, 2013

(54) GOLD ALLOY WITH IMPROVED HARDNESS (52) U.S. Cl.

CPC. C22F I/14 (2013.01); C22C5/02 (2013.01)
(75) Inventors: Jean-Francois Dionne, Kerzers (CH): USPC ........... 148/678; 420/507; 420/511; 420/512;
Stewes Bourban, Cudrefin (CH) 148/405
(73) Assignee: The Swatch Group Research and (57) ABSTRACT
Development Ltd., Marin (CH)
The invention concerns a gold alloy.
(21) Appl. No.: 13/805,230 It comprises at least 75% of gold, 0.5% to 2.1% of aluminium
(22) PCT Filed: Jun. 16, 2011 able to form precipitates with gold, an additional metal able to
favour a stable face centred cubic structure and able to
(86). PCT No.: increase the solubility of aluminium in gold, and a precipitate
selected to obtain a hardness of more than 250 HV. The
S371 (c)(1), selected precipitate of aluminium with gold is the aluminium
(2), (4) Date: Mar. 8, 2013 and gold precipitate All-Aus.
It includes 0.5% to 2.1% of aluminium and a complement of
(30) Foreign Application Priority Data additional metal including a majority of silver.
Jun. 30, 2010 (EP) .................................. 10167859.7 The method of obtaining this alloy regulates the controlled
growth of the precipitate during a structuring tempering treat
Publication Classification ment following dilution and hardening.
The invention concerns the use of the aluminium and gold
(51) Int. Cl. precipitate Al-Aus for hardening a gold alloy.
C22F L/4 (2006.01) The invention concerns a timepiece or piece of jewellery
C22C5/02 (2006.01) including at least one component made of this type of alloy.
US 2013/0153097 A1 Jun. 20, 2013

GOLD ALLOY WITH IMPROVED HARDNESS method of obtaining a gold-based alloy with improved hard
ness and several possible compositions:
FIELD OF THE INVENTION (0013 15% to 19% of copper and 4 to 10% of silver, and 0.3
0001. The invention concerns a gold-based alloy with to 1% of aluminium and/or magnesium.
improved hardness. (0014) or 15 to 19% of copper, 4 to 10% of silver, 0.3 to 1%
0002 The invention also concerns a method of obtaining a of aluminium and/or magnesium, and 0.3 to 2% of zinc.
gold-based alloy with improved hardness. 0.1% to 1% of ruthenium and/or cobalt is incorporated into
this mixture. However, this composition corresponds to a rose
0003. The invention further concerns the use of a precipi gold, which is not claimed here.
tate for hardening a gold alloy. (0015 The document referred to as D2: EP Patent Appli
0004. The invention further concerns a timepiece or piece cation No. 0978 5762 A1 in the name of HAFNER discloses
of jewellery including at least one component made of this an alloy with 70 to 80% of gold and 15 to 25% of copper, to
type of alloy. which 0.1 to 5% of gallium is added. According to some
0005. It is an object of the invention to make a gold-based variants it may also contain: 0.1% to 3% of zinc, and/or 0.5 to
alloy, which has improved hardness qualities compared, not 5% of silver, and/or 0.1 to 0.5% of silicon and/or 0.1 to 2% of
only to pure gold, but also to known gold-based alloys. iron and/or 0.1 to 0.3% of indium, and/or 0.1 to 0.5% of
0006. The main applications are horology, jewellery and aluminium and/or 0.1 to 3% of tin.
dentistry. (0016. The document referred to as D3: US Patent Appli
cation No. 538 378 A in the name of OHTA MICHIO dis
BACKGROUND OF THE INVENTION closes a dental gold alloy which ages slowly for 20 to 30 days
0007 Hardening gold is an old problem, which, since during which its hardness increases further. It includes 82 to
ancient times, has led to the use of alloys in order to obtain 67% of gold, 18 to 33% of copper, and 0 to 2% of a hardening
Sufficient mechanical features to ensure at least the resistance accelerator chosen from between gallium and zinc. The alloy
of the manufactured articles. Indeed, the method of cold is heated to between 650 and 700° C. and water quenched. In
working material by plastic deformation, which is well suited another composition, it includes 2 to 8% of this type of
to some metals, is ill Suited to gold because gold has very little accelerator which includes at least one metal chosen from
consolidation during deformation, and also recrystallises at among the group consisting of 1 to 4% of gallium, 0.4 to 2%
relatively low temperatures. The grain size refinement of aluminium and 1 to 5% of zinc. In another composition, it
method, which theoretically raises the elastic limit of the includes 1 to 4% of gallium. In another composition it
material, is not suitable for gold either, as gold has a face includes 1 to 5% of zinc.
centred cubic structure, called “FCC'hereinafter, since there 0017. The document referred to as D4: The article “18
are enough active sliding systems for the free passage of carat yellow gold alloys with increased hardness” by SUSS.
dislocations from one grain to another. RAINER, published in 2004, discloses gold alloys with
0008 Solution heat treating alloy elements is the method increased hardness and the influence of the additional metals,
most commonly used, often empirically, and at best, it pro both as regards obtaining physical characteristics and particu
vides only mediocre hardness, of around 150 to 155 HV on lar colours.
the Vickers scale. 0018. The document referred to as D5: The article “Met
0009 Various attempts have been made, for example to allurgy of gold” by FISCHER-BUHNER, published on 20
refine grain size as in EP Patent No. 0284.699 in the name of May 2010, details the metallurgy of gold and its alloys.
Steinemann with a binary alloy containing gold and another 0019. It has been shown that, from all the many studies
metal chosen from among aluminium, gallium or silicon, or made, it is known how to select gold alloys with suitable
even with a similar pseudo-binary alloy also including cop hardness, without always understanding the physico-chemi
per, with a maximum gold concentration of 15%. This type of cal mechanism which infallibly results in the desired hard
CSS.
compound gives a centred cubic structure and a grain size of
less than 50 microns, which provides some ductility, which is 0020. In short, the known methods are often empirical, are
not the quality desired here. not well grasped and create alloys which, on the one hand,
0010. The preparation of dental alloys with hardness only have average hardness, and on the other hand have a very
which increases over time and at body temperature is also particular colouring which is very different from that of pure
known, from U.S. Pat. No. 5,338,378 in the name of Kyushu gold.
University, which implements an alloy with 67% to 82% of SUMMARY OF THE INVENTION
gold, 18% to 33% of copper and 2% to 8% of at least one other
metal selected from among gallium, aluminium and zinc. 0021. The invention is concerned with developing an alloy
This alloy undergoes a hardening operation after being heated which has good hardness properties, greater than 250 HV on
to between 650° C. and 700° C. prior to use. Likewise, EP the Vickers scale, and equivalent core hardness properties
Patent No. 0978 572 in the name of Hafner GmbH discloses compared to hardness of around 155 HV currently obtained
an alloy comprising 70% to 80% of gold, 15% to 25% of by Solution heat treating metallic alloy elements.
copper, 0% to 15% of silver and 0.1% to 5% of gallium, 0022. It is also important for the appearance of gold and its
which, in an unexplained way, barely oxides during a second brilliance to be preserved.
treatment at 400°C. which follows a first treatment at 800° C. 0023 The invention therefore concerns a gold-based
and acquires a hardness which increases with time at ambient alloy, known as 3N 18 caratyellow gold, characterized in that
temperature. it is formed of a mixture comprising in weight percent:
0011. The following documents are also known: (0024 at least 75% of gold,
0012. The document referred to as D1: JP Patent Applica 0025 from 0.5% to 2.1% of a second metal chosen for its
tion No 8 O13060 A in the name of PILOT PEN discloses a ability to form precipitates with gold, said second metal being
US 2013/0153097 A1 Jun. 20, 2013

aluminium, 20% to 25%, or preferably 22.4% to 24.5% of at 0041 said at least one selected precipitate is grown in a
least one additional metal chosen for its ability to favour a controlled manner by maintaining said tempering struc
high temperature stable FCC structure, and for its ability to turing treatment for a sufficient period of time, at least 60
increase the Solubility of said second metal in gold, and to minutes, to obtain the desired hardness;
adjust the colour of the alloy, 0.042 cooling at ambient temperature is carried out.
0% to 0.5% of one or more components selected for the 0043. According to a feature of the invention, the selection
fluidity and grain size refinement of said alloy, said mixture of said at least one selected precipitate is limited to a single
further including at least one said precipitate from the reac precipitate.
tion between said second metal and gold, selected from 0044 According to another feature of the invention, said
among said precipitates of said second metal with gold to tempering structuring treatment is performed at least 24 hours
form an intermetallic compound providing said alloy with after said rapid cooling.
more than 250 HV hardness so as to improve the structural 0045. According to another feature of the invention, silver
hardening of said alloy, said selected precipitate being the is chosen as said additional metal.
aluminium and gold precipitate All-Aus. 0046 According to another feature of the invention, silver
0026. According to another feature of the invention, said is chosen as said additional metal and another additional
additional metal is silver. metal is added in a lower concentration than the silver.
0027. According to yet another feature of the invention, 0047. In particular, copper is chosen as said other addi
said additional metal is silver and it is completed by another tional metal.
additional metal in a lower concentration than that of silver. 0048. The invention further concerns the use of a precipi
0028. According to a particular feature of the invention, tate for hardening a gold alloy, characterized in that said
said other additional metal is copper. precipitate is an aluminium and gold precipitate Al-Aus for
hardening a gold alloy comprising at least 75% of gold, 0.5%
0029. The invention further concerns a method for obtain to 2.1% of aluminium and 20% to 25% of at least one addi
ing a gold-based alloy with improved hardness, characterized tional metal, chosen from among silver and copper for its
in that:
ability to favour a stable FCC structure on the one hand, and
0030 a second metal is chosen for its ability to form for its ability to increase the solubility of aluminium in gold
precipitates with gold, said second metal being alu on the other hand, and 0% to 0.5% of one or more components
minium; selected for the fluidity and grain size refinement of said gold
0031 at least one additional metal is chosen for its alloy, said use resulting from the insertion of said aluminium
ability to favoura stable FCC structure on the one hand, and gold precipitate Al-Aus into an FCC structure resulting
and for its ability to increase the high temperature solu from the solution heat treatment of said mixture comprising
bility of said second metal in gold on the other hand; gold, aluminium, said at least one additional metal, said
0032 the conditions are created for inserting precipi selected components if said alloy has any, and aluminium and
tates of said second metal with gold into an FCC struc gold precipitates, said insertion being achievable via this
method.
ture resulting from the solution heat treatment of a mix
ture of gold, said second metal and said at least one 0049. The invention further concerns a timepiece, piece of
additional metal; jewellery or dental piece including at least one component
0033 a mixture is prepared comprising in weight per made of an alloy of this type.
Cent: 0050. In the preferred embodiment of the description, con
cerning an 18 carat alloy, the alloy preserves the specific
0034) at least 75% of gold, appearance of pure gold. Because of its increased hardness,
0035 0.5% to 2.1% of said second metal, the alloy obtained is more scratch resistant and is entirely
0036 20% to 25% of preferably from 22.4% to Suitable for timepiece and pieces of jewellery and in particu
24.5% of at least one said additional metal, lar for the visible components thereof such as bezels and
0037 0% to 0.5% of one or more components middle parts of watches, and jewellery structures, bracelets,
selected for the fluidity and grain size refinement of clasps, buckles and other items.
said alloy, 0051. The invention provides a method that is simple to
implement and reproduce, and which reliably produces a gold
said second metal and said additional metal being selected to alloy with the required hardness of more than 250 HV in a
obtain from among said precipitates of said second metal with short treatment time. The alloy obtained can be used imme
gold, at least one said particular precipitate of said second diately, without requiring any additional ageing.
metal with gold to form an intermetallic compound giving
said alloy a hardness of more than 250 HV: BRIEF DESCRIPTION OF THE DRAWINGS
0038 said mixture is solution heat treated by being 0052. Other features and advantages of the invention will
heated to between 650° C. and 700° C.; appear upon reading the following description, with reference
0039 after said solution heat treatment, rapid cooling is to the annexed drawings, in which:
performed in the form of ambient temperature harden 0053 FIG. 1 is a diagram of phases of a pseudo-binary
ing: alloy Au-Ag-Al according to the invention, in the example
0040 after said rapid cooling, a tempering structuring of an 18 carat alloy, which represents the various phases
treatment is carried out at a temperature of between 200° according, on the X axis, to the concentration of aluminium,
C. and 250° C. to create said at least one selected pre i.e. the ratio between the aluminium mass and the total alloy
cipitate from said second metal with gold which is the mass, and on they axis, to temperature, shown here in degrees
aluminium and gold precipitate A12Au5; Celsius.
US 2013/0153097 A1 Jun. 20, 2013

0054 FIG. 2 is a diagram of Vickers hardness on they axis the longest possible FCC phase, i.e. for the broadest possible
according to time on the X axis, of an alloy according to the range of aluminium content. High temperature stability
invention made within a preferred domain A of the diagram of means that only the FCC phase is present in the temperature
FIG. 1 compared to an 18 carat gold obtained by a standard range concerned, which can be seen along the elongated
method. single domain of the equilibrium diagram of FIG. 1.
0065 Different trial pseudo-binary alloys have been
DETAILED DESCRIPTION OF PREFERRED tested.
EMBODIMENTS 0066. The second metal can be chosen from among alu
0055. It is an object of the invention to make a gold-based minium, silver, chromium, copper, iron, hafnium, manga
alloy, which has improved hardness qualities compared, not nese, niobium, palladium, platinum and Vanadium although
only to pure gold, but also to known gold-based alloys. this list is not exhaustive.
0056. The invention implements a structural hardening 0067. An additional metal may preferably be chosen from
method, by the selection of particular elements, which are among silver, aluminium, chromium, copper, iron, hafnium,
chosen here to form particular precipitates. Among the vari manganese, niobium, palladium, platinum and Vanadium.
ous precipitates which gold can form with other metals in 0068 Experiments demonstrate that the choice of silver as
very particular physico-chemical conditions, those precipi the additional metal is the most particularly favourable for the
tates whose germination and growth can be controlled, by solubility of the intermetallic compound at a high tempera
implementing an appropriate treatment, to optimise mechani ture, and for obtaining along FCC phase, since the silver-gold
cal characteristics, and in particular here to increase hardness, solubility is complete, and since the silver can also dissolve
should be chosen. the aluminium.
0057. In particular, the mechanical feature which the 0069. Innovatively, the invention has attempted to create
present invention improves, by creating a particular method, the pseudo-binary alloy phases Au-Ag-Al as seen in FIG.
is hardness which concerns both the core hardness of the 1. This diagram shows the various phases in a conventional
alloy, and Surface hardness which is very important in horol manner, according, on the X axis, to the concentration of
ogy and jewellery to ensure scratch resistance or at least to aluminium, i.e. the ratio of aluminium mass to the total alloy
minimise the effects of scratches. mass, and on the y axis, to the temperature, shown here in
0058. This is therefore a very different case to most gold degrees Celsius. The diagram in FIG. 1 shows the preferred
alloys used in jewellery, which are usually developed to case of a 75% gold mass concentration i.e. the preferred case
include the minimum gold content required to ensure an of an 18 carat alloy.
appearance close to that of gold, and with the requirement for 0070 This is a partial solubility diagram showing the lim
a high level of formability, so as to allow lamination, or its of solubility, which are substantially vertical in the dia
stretching, in hollow bodies or sheets, which are easy to shape gram, and which separate the phases. Each phase has a
and weld. defined composition which is different to the next phase. In
0059. The inventive step of the invention has consisted in each of these phases, the atoms are reorganised locally to
researching the possibility of inserting precipitates into a face form precipitates, which are defined compounds of fixed
centred cubic structure or FCC, and letting them grow in a composition.
controlled manner, so as to obtain a greater hardness than the 0071. In order to obtain the desired Al-Aus precipitate,
usual hardness and only that precipitate, it is advisable to remain within a first
0060. The invention more particularly concerns the field domain called A in FIG. 1, in which there exist only the alloy
of gold alloys with a high gold content, and more specifically, elements in FCC form on the one hand, and the Al-Aus
18 carat alloys comprising at least 75% of gold content by precipitates on the other hand. To remain within this domain,
weight. the concentration of aluminium must remain less than 2.1%.
0061 The selection of aluminium is peculiar to the inven The range of concentrations to be observed is 0.1% to 2.1% of
tion because of the ability of this metal to form different aluminium to ensure that only Al-Aus is obtained.
precipitates with gold: Al-Aus. AlAu, Al Au. These three 0072 A second domain called B in FIG. 1 corresponds to
precipitates can produce alloys with improved hardness. a phase where the Al-Aus and AlAu precipitates co-exist
0062. These alloys Au?Ag/Al/ Al-Aus or Au/Cu/Al/ with the alloy elements in FFC form.
Al-Aus or Au/Ag/Cu/Al/ Al-Aus do not exist in the natural (0073. The third domain called C in FIG. 1 corresponds to
state and they have to be made in order to be used. The a phase where only the AlAu precipitates co-exist with the
invention proposes a preferred manufacturing method below. alloy elements in FCC form.
0063. It is preferable to carry out the method so as to obtain 0074 The diagram in FIG. 1 shows that, to obtain an alloy
the Al-Aus precipitate, which when incorporated in an alloy in an optimum composition within domain A, one method
provides normal resistance during machining or transforma consists in heating all the alloy elements, to then be within
tion operations. Thus, this Al-Aus precipitate is created and domain D of FIG. 1 which corresponds to a solution heat
preferably only this Al-Aus precipitate is created since it treatment of the aluminium. A dilution heat treatment at a
yields better properties than the other two precipitates AlAu temperature between the Solidus and liquidus delimiting
and Al Au. domain Dallows a homogeneous solution heat treatment: the
0064. The Al-Aus precipitate must be obtained at the core gold is in an FCC structure, owing to the additional element or
of the FCC structure. A binary alloy formed solely of gold and elements chosen, particularly silver, and the FCC structure is
aluminium is difficult to work and is very fragile, which stable. A high solubility of aluminium is observed in the
makes it unsuitable for most jewellery uses. It is therefore phase FCC A1, at high temperature, in particular attempera
necessary to stabilise the FCC phase by incorporating at least tures comprised between 400° C. and 700° C. The additional
one other alloy element to ensure the solubility of the inter element or elements also facilitate the solubility of alu
metallic compound at a high temperature, and also to ensure minium in gold.
US 2013/0153097 A1 Jun. 20, 2013

0075. The alloy is then made metastable. The rise in tem phase, which is physically impossible: the teaching of this
perature, achieved for example between around 400° C. and document cannot be accepted.
700° C. for the extreme part of domain A and ideally around I0085 Document D4 discloses a pinkish yellow gold. It is
650°C., is followed by rapid cooling, such as water hardening impossible to evaluate the specific role of aluminium since all
or similar. Thus, the aluminium atoms do not have time to the other elements present in the alloy already contribute to
reorganise. After a variable period time, but preferably close the hardening process. This document comments that with
to 24 hours, the alloy undergoes a structuring tempering treat more than 0.4% aluminium, the alloy blackens considerably.
ment, within the temperature range defined by the solvus of This drawback is not visible in the case of the alloy developed
domain A for the aluminium concentration concerned. In any according to the invention, even with 2% aluminium content.
event, this structuring tempering treatment does not exceed a It should be noted that the experimenter who follows the
temperature of 400° C. During tempering, the Al-Aus pre instructions of document D4 will not obtain Al-Aus precipi
cipitates develop and grow. Preferably, the structuring tem tate not only because of the added elements such as Zinc,
pering temperature is higher than 200° C. to facilitate the which modify the solubility of aluminium, but also because of
precipitate growth, and also to limit the duration of the heat the low aluminium concentration >0.4%.
treatment. I0086 Document D5 explains the hardening of the gold
0076 FIG. 2 is a diagram of Vickers hardness on the x axis (75%)-silver-copper alloy by the well known order/disorder
according to time on the abscissa. It is seen, in the example of transformation with copper. The composition of 75% gold
FIG. 2 of a structuring tempering treatment at 200°C., that a 12.5% silver-12.5% copper of FIG. 7.12 of document D5
hardness of more than 250 HV is obtained very quickly, after gives an expected hardness of 220 HV, which is much lower
around 2 hours. This hardness will increase further if the than that obtained by the invention.
structuring tempering treatment is extended, but asymptom I0087. In short, the fabrication of the aluminium and gold
atically, even if maximum hardness is desired, and there is no precipitate Al-Aus increases the HV hardness by around 50
point in extending the treatment beyond 10 hours, where a HV.
hardness of around 280 HV is obtained. FIG.2 shows, by way In short, the invention differs from the prior art in that it
of comparison, the level of hardness 150 HV obtained with a creates the conditions for developing Al-Aus precipitate
conventional 18K or 18 carat gold alloy. within an alloy of Suitable composition comprising gold,
0077. If the structuring tempering treatment is performed aluminium and at least one additional metal selected for its
at a lower temperature, for example 100° C., a hardness of ability both to favour a stable FCC structure and to increase
more than 200 HV will only be obtained after 10 to 15 hours, the solubility of aluminium in gold, this additional metal
and the treatment must be extended further to reach a level of preferably being silver.
around 250 HV. I0088. The optimum weight percent composition is from
0078. The Al-Aus precipitate obtained is harder than gold. 0.1% to 2.1% of aluminium, and preferably from 0.5% to
0079. It is essential, according to the invention, to favour 2.1% and at least 75% of gold so as to respect the legal
the presence of the All-Aus precipitate and preferably to standard for jewellery, and the complement formed by at least
restrict the formation of precipitates comprising only gold one additional metal, which may be completed by a small
and aluminium to this one Al-Aus precipitate, which has the proportion of at least one other component selected for flu
best features, in order to resolve the technical problem of idity and grain size refinement.
hardening the alloy. I0089. The additional metal may also be copper. It is also
0080 Preferably, in order for the Al-Aus precipitates to possible to combine several metals each having the properties
develop optimally, the alloy does not include any other metal that this additional metal is required to have, namely the
apart from gold, aluminium and an additional metal, prefer ability to favour a stable FCC structure on the one hand and
ably silver, selected to increase intermetallic compound solu the ability to increase the solubility of aluminium in gold on
the other hand.
bility and to lengthen phase Das much as possible in terms of
the amplitude of the range of aluminium concentrations. 0090 Silver is the best element, and the other metal ele
0081 Returning to some of the aforecited prior art teach ments in the list set out above may be added to adjust the
ings, it is evident that the role of aluminium is not demon colour of the alloy. This list of elements was drawn up so that
strated. the elements comprised therein satisfy the condition of
increasing the solubility of aluminium in the FCC structure at
0082 Document D1 discloses a pink gold...alloy. It cannot a high temperature.
be affirmed that aluminium is significant as the alloy harden 0091. In particular, copper is less favourable than silver in
ing agent by analysing the variance of the results of document satisfying these particular conditions in the presence of gold
D1. Copper, like silver, is a hardening element, C.-0.05. The and aluminium. The use of copper remains possible for rea
effect of copper is to create an order/disorder reaction with Sons of cost, but is considerably less advantageous than silver,
gold, with the formation of an AuCu type compound, with and if used should always be combined with silver, while
increased hardness. The effect of the silver/copper mixture is ensuring that the concentration of silver is always higher than
similar to the effect of copper by itself. the concentration of copper in the alloy.
0083. The same is true of document D2, which also dis 0092. With the use of additional metals other than silver or
closes a pink gold. The addition of aluminium does not seem copper, for example chosen from among chromium, copper,
to play any particular part therein, which is understandable if iron, hafnium, manganese, niobium, palladium, platinum and
the processing method is not carried out for the purpose of vanadium (this list is not exhaustive), it should be borne in
forming a single gold and aluminium precipitate which is mind that aluminium could form precipitates with certain of
advantageous for increasing the hardness of the alloy. these additional metals, but that preferably it is desired to
0084 Document D3 is also dedicated to fabricating pink form Al-Aus precipitates. Thus, in addition to silver and alu
gold. This document claims that the alloy remains single minium, preferably only these elements should be used: chro
US 2013/0153097 A1 Jun. 20, 2013

mium, copper, iron, hafnium, manganese, niobium, palla resulting from the solution heat treatment of a mixture of
dium, platinum and Vanadium. gold, said second metal and said at least one additional
0093 Moreover, each new composition with different metal;
additional metals requires thorough testing to define the cor 0107 preparing a mixture comprising in weight per
responding phase diagrams, which do not exist in the litera Cent:
ture, to analyse the precipitates and other intermetallic com (0.108 at least 75% of gold,
pound components created within each of the phases, and to 0109 0.5% to 2.1% of said second metal,
check that these compounds do not adversely affect the 0110 20% to 25% of preferably from 22.4% to
mechanical properties of the gold alloy. These studies and 24.5% of at least one said additional metal,
experiments take a long time and are expensive and cannot be 011 1 0% to 0.5% of one or more components
conducted at random. The object thereof is also to determine, selected for the fluidity and grain size refinement of
on a case by case basis, the aluminium concentration range to said alloy,
be observed to obtain Al-Aus precipitates and preferably only said second metal and said additional metal being selected to
this precipitate. obtain from among said precipitates of said second metal with
0094. In short, the invention provides a 3N 18 caratyellow gold, at least one said particular precipitate of said second
gold-based alloy, characterized in that it is formed of a mix metal with gold to form an intermetallic compound giving
ture comprising in weight percent: said alloy a hardness of more than 250 HV, said selected
0095 at least 75% of gold, precipitate being the aluminium and gold precipitate Al-Aus;
0096 from 0.5% to 2.1% of a second metal chosen for its 0112 solution heat treating said mixture by heating to
ability to form precipitates with gold, said second metal being between 400° C. and 700° C. and preferably between
aluminium, 650° C. and 700° C.;
0097. 20% to 25%, or preferably 22.4% to 24.5% of at 0113 rapid cooling after said solution heat treatment,
least one additional metal chosen for its ability to favour a preferably in the form of ambient temperature harden
high temperature stable FCC structure, and for its ability to ing:
increase the Solubility of said second metal in gold, and to 0114 performing a structuring tempering treatment
adjust the colour of the alloy, after said rapid cooling at a temperature of between 200
0098 0% to 0.5% of one or more components selected for and 400° C. and preferably between 200° C. and 250° C.
the fluidity and grain size refinement of said alloy, to create said at least one selected precipitate of said
said mixture further including at least one said precipitate second metal with gold which is the aluminium and gold
from said second metal and gold, selected from among said precipitate Al-Aus;
precipitates of said second metal with gold to form an inter 0115 allowing the controlled growth of said at least one
metallic compound providing said alloy with more than 250 Selected precipitate by maintaining said structuring tem
HV hardness so as to improve the structural hardening of said pering treatment for a sufficient period or time, prefer
alloy, said selected precipitate being the aluminium and gold ably at least 60 minutes, to obtain the required hardness;
precipitate All-Aus. 0116 cooling at ambient temperature.
0099 Advantageously, the second metal is aluminium and 0117 Preferably, the choice of selected precipitates is lim
the precipitate chosen is the aluminium and gold precipitate ited to one precipitate, in this case the aluminium and gold
Al-Aus which provides an alloy with very good hardness precipitate All-Aus.
characteristics, i.e. a hardness of more than 250 HV and close 0118 Advantageously, the structuring tempering treat
to 280 HV. This All-Aus precipitate also gives the alloy very ment is performed at least 24 hours after the rapid cooling.
good resistance during transformation or when machined, 0119 Preferably, aluminium is chosen as the second
since it does not make the alloy brittle. metal, and the aluminium and gold precipitate Al-Aus is
0100 Preferably, the additional metal is silver, which chosen as the selected precipitate.
ensures that the whole of the mixture is properly soluble. I0120 Advantageously, silver is selected as the additional
metal.
0101. In a particular embodiment, the additional metal is 0.121. In a variant, silver is selected as the additional metal
silver, preferably in a weight percent content of 10% to 12.5% and another additional metal having similar characteristics to
of the total, and it is completed by another additional metal, silver is added, to adjust the colour of the alloy.
preferably in a weight percent content of 10% to 12.5% of the 0.122 Other methods such as mechanosynthethis or PVD
total, to adjust the colour of the alloy. may also involve the creation of the aluminium and gold
0102 Advantageously, at least one said component precipitate All-Aus. However, as in the operating modes listed
selected for the fluidity and grain size refinement of said alloy above, the conditions for inserting this very particular pre
is chosen from among Zinc, cobalt or iridium. cipitate into the face centred cubic structure of the alloy and
0103) The method for obtaining a gold-based alloy, with the conditions for developing this precipitate in order to give
improved hardness, preferably consists in: the alloy the desired hardness characteristics should be cre
0104 choosing a second metal for its ability to form ated.
precipitates with gold, said second metal being alu I0123. The invention further concerns the use of a precipi
minium; tate for hardening a gold alloy. According to the invention,
0105 choosing at least one additional metal for its abil this precipitate is an aluminium and gold precipitate Al-Aus
ity to favour a stable FCC on the one hand, and for its for hardening a gold alloy comprising at least 75% of gold,
ability to increase the high temperature solubility of said form 0.5% to 2.1% of aluminium and from 20% to 25% or
second metal in gold on the other hand; preferably from 22.4% to 24.5% of at least one additional
010.6 creating the conditions for inserting precipitates metal selected from among silver and copper and chosen for
of said second metal with gold into an FCC structure its ability to favour a stable FCC structure on the one hand,
US 2013/0153097 A1 Jun. 20, 2013

and for its ability to increase the solubility of aluminium in (iii) tempering the cooled mixture at a temperature of
gold on the other hand, and from 0% to 0.5% of one or more between 200° and 250° C. to form at least one alu
components selected for the fluidity and grain size refinement minium and gold precipitate comprising Al-Aus, said at
of said gold alloy, said use resulting from the insertion of said least one precipitate being capable of inserting into the
aluminium and gold precipitate Al-Aus into an FCC structure FCC structure of the at least one first additional metal
resulting from the solution heat treatment of said mixture and forming an intermetallic compound capable of
formed of gold, aluminium, said at least one additional metal, imparting a desired hardness of more than 250 HV to a
said selected components if said alloy includes any, and alu resulting gold-based alloy;
minium and gold precipitates, said insertion being preferably (iv) maintaining the tempering for at least 60 minutes to
achievable by the method described above. grow the intermetallic compound in a controlled manner
0.124. The invention further concerns a timepiece, piece of to obtain the resulting gold-based alloy with the desired
jewellery or dental piece including at least one component hardness; and
made of an alloy of this type. (V) cooling the resulting gold-based alloy at ambient tem
1-16. (canceled) perature.
17. A 3N 18 carat yellow gold-based alloy, comprising in 25. The method according to claim 24, wherein the rapid
weight percent: cooling (ii) is achieved by water hardening.
at least 75% of gold; 26. The method according to claim 24, wherein the at least
from 0.5% to 2.1% of an aluminium metal capable of one precipitate is a single precipitate.
forming at least one precipitate with gold; 27. The method according to claim 24, wherein the tem
from 20% to 25% of at least one first additional metal pering (iii) occurs for at least 24 hours after the rapid cooling
having an ability to favor a stable face centered cubic (ii).
(FCC) structure and to increase high temperature solu 28. The method according to claim 24, wherein the at least
one first additional metal is silver.
bility of the aluminum metal in the gold; 29. The method according to claim 24, wherein the mixture
0% to 0.5% of at least one component affecting fluidity and further comprises at least one second additional metal in a
grain size refinement of the alloy; and lower concentration than that of the silver.
at least one aluminium and gold precipitate comprising 30. The method according to claim 29, wherein the second
Al-Aus forming an intermetallic compound which pro additional metal is copper.
vides the alloy with more than 250 HV hardness so as to 31. The method according to claim 24, wherein the mixture
improve structural hardening of the alloy. comprises between 22.4% and 24.5% of the at least one first
18. The alloy according to claim 17, wherein the first additional metal.
additional metal is silver.
32. A timepiece or a piece of jewellery, comprising at least
19. The alloy according to claim 18, wherein the first one component made of the gold-based alloy of claim 23.
additional metal is 10% to 12.5% weight percent silver, and 33. A method for hardening an 18 carat gold-based alloy,
the alloy further comprises 10% to 12.5% weight percent of a the method comprising forming at least one precipitate from
second additional metal of lower concentration than that of
the silver. aluminium and gold comprising All-Aus which forms an
intermetallic compound within a gold-containing alloy and
20. The alloy according to claim 19, wherein the second thereby imparts a resulting gold-based alloy with a hardness
additional metal is copper. of more than 250 HV.
21. The alloy according to claim 17, wherein a content of 34. The method of claim 33, wherein:
the at least one first additional metal is between 22.4% and the gold-based alloy comprises:
24.5%.
22. The alloy according to claim 17, wherein the at least at least 75% of gold;
one component affecting fluidity and grain size refinement of 0.5% to 2.1% of aluminium;
20% to 25% of at least one additional metal selected
the alloy is selected from the group consisting of zinc, cobalt from the group consisting of silver and copper, said
and iridium.
23. The alloy according to claim 17, comprising, as the additional metal having an ability to favor a stable
only precipitate of aluminium and gold, the aluminium and face centered cubic (FCC) structure and to increase
gold precipitate comprising Al-Aus. solubility of aluminium in gold; and
24. A method for obtaining a gold-based alloy with 0% to 0.5% of at least one component affecting fluidity
improved hardness, the method comprising: and grain size refinement of the gold-based alloy;
(i) heat treating a mixture comprising: the method further comprises inserting the intermetallic
compound into the FCC structure during a solution heat
0.5% to 2.1% of aluminium; treatment of a mixture comprising the gold, the alu
at least 75% of gold; minium, the at least one additional metal, and the at least
20% to 25% of at least one first additional metal having one component if present; and
an ability to favor a stable face centered cubic (FCC) the at least one additional metal is selected from the group
structure and to increase high temperature solubility consisting of aluminium, silver, chromium, copper, iron,
of the aluminum in the gold; and hafnium, manganese, niobium, palladium, platinum,
0% to 0.5% of at least one component affecting fluidity and Vanadium.
and grain size refinement, 35. The method of claim 34, wherein the at least one
to a temperature between 650° C. and 700° C. to form a heat additional metal is silver.
treated mixture; then 36. The method of claim 35, wherein the alloy further
(ii) rapidly cooling the heat treated mixture by ambient comprises at least one second additional metal having a lower
temperature hardening to form a cooled mixture; concentration than that of the silver.
US 2013/0153097 A1 Jun. 20, 2013

37. The method of claim 36, wherein theat least one second
additional metal is copper.
38. The method of claim 34, wherein the gold-based alloy
comprises 22.4% to 24.5% of the at least one first additional
metal.
39. The method of claim 34, where the A12Au5 is the only
aluminium and gold precipitate in the gold-based alloy.
k k k k k