Technical Field
[0001] The present invention relates to an aluminum alloy, and a process for producing a
cast product made of an aluminum alloy. More particularly, it relates to an aluminum
alloy which shows castability suitable for even producing thin-thickness cast products
and the like, and high strength as well as good ductility even as cast, and a process
for producing cast products comprising the aluminum alloy.
Background Art
[0002] Recently, it has been required to lightweight various products, conventional cast-iron
products are about to give way to light aluminum alloy products rapidly. For example,
in the case of automobiles, it is possible to expect mileage improvement by lightweighting,
and the lightweighting is effective in environmental improvement as well.
[0003] By the way, high strength and high ductility have come to be required even for thin-thickness
cast products (die-cast products especially), to which the requirements for strength
and ductility have been moderate relatively. As a method for producing high-strength
and high-ductility thin-thickness cast products, it has been proposed such a method
that the resulting cast products are heat treated after casting while vacuuming the
inside of dies, or after casting while filling the inside of dies with oxygen contrarily,
for example. However, in such a method, heat treatments are needed to result in the
increment of production costs. Moreover, the thinner and larger cast products are,
the more the heat treatments cause strains of the cast products (swelling, deformations,
and the like), and accordingly it takes more costs for the correction.
[0004] Hence, in order to solve such problems, the development of aluminum alloys which
reveal high strength and high ductility even as cast has been carried out extensively.
For example, in ① Japanese Unexamined Patent Publication (KOKAI) No. 9-3582, ② Japanese
Unexamined Patent Publication (KOKAI) No. 11-293375, ③ Japanese Unexamined Patent
Publication (KOKAI) No. 11-193434, and ④ Japanese Unexamined Patent Publication (KOKAI)
No. 9-268340, Japanese Unexamined Patent Publication (KOKAI) No. 9-316581 and Japanese
Unexamined Patent Publication (KOKAI) No. 11-80872, and the like, there are disclosures
on such aluminum alloys. Hereinafter, the aluminum alloys set forth in the respective
publications will be described in detail.
[0005] In ① Japanese Unexamined Patent Publication (KOKAI) No. 9-3582, an aluminum alloy
cast product is disclosed which contains Mg: 3.0-5.5% (% by mass: being the same hereinafter),
Zn: 1.0-2.0% (Mg/Zn: 1.5-5.5), Mn: 0.05-1.0%, Cu: 0.05-0.8%, and Fe: 0.1-0.8%. This
Al-Mg-Mn-Zn-Cu system alloy contains Zn and Cu falling in a predetermined range as
essential elements.
[0006] When the present inventors tested and studied cast products made of this alloy, intermediate
phases, such as MgZn
2 and Mg
32(Al, Zn)
49, are precipitated in the cast products, strength characteristic change by natural
aging, and stress corrosion cracks appeared. Moreover, it was also understood that
this alloy was such that hot tearing is likely to occur so that it was not suitable
for casing thin-thickness members.
[0007] In ② Japanese Unexamined Patent Publication (KOKAI) No. 11-293375, a highly ductile
aluminum alloy die cast is disclosed which is characterized in that it comprises Mg:
2.5-7.0%, Mn: 0.2-1.0%, and Ti: 0.05-0.2%, and Fe in an amount of 0.3% and Si in an
amount of 0.5% or less, a porosity is 0.5% or less at a heavy-thickness part ranging
from 1 to 5 mm, the average circle-equivalent diameter of crystallized substances
is 1.1 µm or less, and the areal ratio of crystallized substances is 5% or less. This
Al-Mg-Mn-Ti system alloy is such that Fe is treated as an inevitable impurity and
the content is limited to less than 0.3%.
[0008] When the present inventors tested and studied thin-thickness die-cast products using
this alloy, they were such that hot tearing was likely to occur. Moreover, when the
Mg content increased, shrinkage cavities were likely to occur at the heavy-thickness
center. The occurrence of hot tearing and shrinkage cavities is not preferable, because
it enlarges the fluctuation of strength characteristic and elongation.
[0009] In ③ Japanese Unexamined Patent Publication (KOKAI) No. 11-193434, an aluminum alloy
for high-toughness die-cast products is disclosed, aluminum alloy which comprises
Mg: 3.0-5.5%, Mn: 1.5-2.0%, and Ni: 0.5-0.9%.
[0010] In this Al-Mg-Mn-Ni system alloy, Ni is an essential constituent element, and the
toughness of die-cast products are improved by adjusting the content appropriately.
Moreover, since the Mn content is much, the crystallized amount of its compounds is
so much that the elongation is 10% approximately as indicated by the examples.
[0011] In ④ Japanese Unexamined Patent Publication (KOKAI) No. 9-268340, a highly ductile
aluminum alloy is disclosed which comprises Mg: 0.01 to 1.2%, Mn: 0.5 to 2.5%; and
Fe: 0.1-1.5%.
[0012] In this Al-Mg-Mn-Fe system alloy, defects such as hot tearing and shrinkage cavities,
are inhibited from occurring by decreasing the Mg content so as to merely improve
the castability and elongation. Accordingly, it is seen from the examples as well
that the alloys are not satisfactory in view of the strength because the tensile strength
is even less than 190 MPa. Note that the aluminum alloys, disclosed in Japanese Unexamined
Patent Publication (KOKAI) No. 9-316581 and Japanese Unexamined Patent Publication
(KOKAI) No. 11-80872, are as poor as this alloy.
Disclosure of Invention
[0013] The present invention has been done in view of such circumstances. Namely, it is
an object to provide an aluminum alloy in which the occurrence and the like of hot
tearing and micro porosity is less and accordingly which is good in terms of the castability.
In particular, it is an object to provide an aluminum alloy from which cast products
of high strength and good ductility can be obtained even as cast. Moreover, it is
an object to provide an aluminum alloy whose cast products suffer the time change
of mechanical characteristics and so forth less.
[0014] In addition, it is an object to provide a process for producing cast products, process
in which this aluminum alloy is used.
[0015] Hence, the present inventors have been studying earnestly in order to solve this
assignment, and have been repeated various systematic experiments, as a result, have
discovered an aluminum alloy, which is good in terms of the castability, and moreover
from which cast products of high strength and high ductility can be obtained even
as cast, by appropriately controlling the composition proportion of Mg, Mn and Fe,
and have arrived at completing the present invention.
(Aluminum Alloy)
[0016] Namely, an aluminum alloy according to the present invention comprises: from 4.0
to 6.0% magnesium (Mg); from 0.3 to 0.6% manganese (Mn); from 0.5 to 0.9% iron (Fe);
and the balance of aluminum (A1) and inevitable impurities when the entirety is taken
as 100% by mass.
[0017] Since the present aluminum alloy (Al-Mg-Mn-Fe alloy) contains Mg, Mn and Fe with
an appropriate composition proportion, the castability is improved, and high strength
as well as high ductility are revealed. Hereinafter, the reasons conceivable at present
and how to arrive at the above-described composition will be described.
[0018] It has been known that the strength of aluminum alloys is improved by solving Mg
or Mn in Al matrices, however, when producing thin-thickness die-cast products with
Al-Mg-Mn alloys, hot tearing, porosity and the like, accompanied by solidification
shrinkage, occur so that the castability is poor. Moreover, correlating therewith,
the fluctuation of elongation enlarges.
[0019] Hence, in order to obtain an aluminum alloy which is good in terms of the castability
and which is of high strength and high ductility, the present inventors focused on
the relationship between the crystallization form of crystallized substances in the
solidification process and the castability or mechanical properties. And, they ascertained
that the hot tearing of cast products made of aluminum alloys occurs often in brittle
liquid phase portions which reside between primary-crystal Al dendrites growing in
the solidification process. This is believed to be as follows: upon the solidification
shrinkage, shrinkage stresses act on cast products when the cast products are constricted
by dies in a temperature range (semi-solidus temperature range) in which the cast
products are shaped and begin to have strength in the process in which the cast products
are being formed by the development and combination of primary-crystal dendrites;
and the stresses concentrate on the brittle liquid phase portions which reside between
the dendrites so as to cause the hot tearing frequently.
[0020] Hence, the present inventors thought of adding Fe to Al-Mg-Mn alloys, and changed
the crystallization behavior in the solid-liquid coexisting zone by adjusting the
Mn and Fe contents according to the Mg content so that they succeeded in obtaining
good hot tearing resistance. Specifically, the crystallization temperature zone of
primary-crystal Al was narrowed so that Al-Mn-Fe eutectics were crystallized between
the network isthmuses of primary-crystal Al, which had finished crystallizing, without
growing the dendrites of primary-crystal Al greatly. And, since the connection between
respective solid phases developed rapidly under the circumstance, it is believed that
the hot tearing was less likely to occur.
[0021] Moreover, in accordance with the present aluminum alloy, since Al(Mn, Fe) compounds
crystallize micro-finely after micro-fine Al crystallizes out of the liquid phases
as primary crystals, there are less coarse crystallized substances which result in
lowering the ductility, and accordingly it is believed that it comes to reveal good
ductility while even sustaining high strength.
[0022] Especially, when the present aluminum alloy can comprise primary-crystal aluminum
and compounds which are dispersed uniformly, the primary-crystal aluminumhaving a
dendritic cell size of 10 µm or less, the compounds having a grain diameter of 5 µm
or less, it is more suitable in view of the strength and ductility. Moreover, it is
more preferable when the dendritic cell size of said primary-crystal aluminum can
be 5 µm or less and the grain diameter of said compounds can be 3 µm or less.
[0023] Here, the size of the dendritic cells (dendrite) is a length when measured in the
longitudinal direction, and is an average value of the measured values for 100 pieces
of the cells. Moreover, the grain diameter of the compounds is assessed in the longitudinal
direction (the maximum length) , and is an average value of measured values on 10
view fields of a structural photograph (view field area, 70 × 100 µm) which is taken
with a magnification of 100 times by using an image processor.
[0024] Thus, in accordance with the present aluminum alloy, even when thin-thickness die-cast
products are produced, for example, it is possible to obtain cast products provided
with sufficient strength and good ductility without hardly causing porosity such as
hot tearing and shrinkage cavities. For instance, it is possible to obtain an aluminum
alloy which exhibits a 0.2% proof stress of 130 MPa or more and a fracture elongation
of 13% or more as cast being free from being subjected to a heat treatment after casting.
[0025] Moreover, the aluminum alloy solution-strengthened by Mg and Mn falling in the aforementioned
composition range is provided with an advantage that the change of mechanical properties
with time is less without scarcely causing the hardness change by natural aging.
(Production Process for Cast Product Made of Aluminum Alloy)
[0026] A cast product comprising the above-described present aluminum alloy can be obtained
by the following production process, for example.
[0027] Namely, a process according to the present invention for producing a cast product
made of an aluminum alloy comprises the steps of: pouring an aluminum alloy molten
metal into a die, the aluminum alloy molten metal comprising: from 4.0 to 6.0% Mg;
from 0.3 to 0.6% Mn; from 0.5 to 0.9% Fe; and the balance of Al and inevitable impurities
when the entirety is taken as 100% by mass; and solidifying the aluminum alloy molten
metal by cooling it after the pouring step.
[0028] And, it is suitable that said solidifying step can be a step being solidified by
cooling at a cooling rate of 20 °C/sec. or more.
[0029] It is because, with this arrangement, cast products made of an aluminum alloy can
be obtained securely, cast products in which the above-described micro-fine primary-crystal
aluminum and compounds are dispersed uniformly. It is further preferable that the
cooling rate can be 50 °C/sec. or more.
[0030] By the way, the "aluminum alloy" set forth in the present invention not only involves
aluminum alloys as a raw material for casting but also cast products (manufactured
goods) made of aluminum alloys after casting.
[0031] Namely, the present invention can be grasped as a cast product made of an aluminum
alloy, the cast product comprising: from 4.0 to 6.0% Mg; from 0.3 to 0.6% Mn; from
0.5 to 0.9% Fe; and the balance of Al and inevitable impurities when the entirety
is taken as 100% by mass.
[0032] Moreover, the "castability" set forth in the present specification is a concept which
involves not only the molten metal fluidity, the releasability and the like but also
the occurrence rate and so forth of hot tearing and shrinkage cavities (porosity).
Brief Description of the Drawings
[0033] Fig. 1 is a cross-sectional view for illustrating a vertical die-casting machine
equipped with a die for assessing hot tearing, die which is capable of varying the
constriction length.
[0034] Fig. 2 is a cross-sectional view taken along the line "A-A" in Fig. 1.
[0035] Fig. 3 is a bar graph for illustrating the relationship between the constriction
length and castability on each test sample.
[0036] Fig. 4 is a graph for illustrating the relationship between the hot tearing characteristics
and the Fe content.
Best Mode for Carrying out the Invention
A. Mode for Carrying Out
[0037] Next, the present invention will be described in more detail while naming embodiment
modes.
(1) Alloy Composition
① Mg
[0038] Mg is an element which solves in the matrix of aluminum to improve the mechanical
strength (for example, the tensile strength) of aluminum alloys. Moreover, Mg is an
element which exerts influences on the ductility and castability of aluminum alloys
as well.
[0039] When Mg is comprised less than 4.0% (percentage by mass, being the same hereinafter),
the improvement of mechanical strength is not sufficient, especially, it is difficult
to secure a proof stress (a 0.2% proof stress, being the same hereinafter) of 130
MPa or more. Moreover, when Mg is comprised in excess of 6.0%, the oxidation of molten
metals is significant. In addition, since the composition of Mn and Fe whose coarse
crystallized substances start crystallizing as primary crystals according to the Mg
content increment moves to a lower concentration side, the ductility is deteriorated
by the crystallization of the coarse crystallized substances when the Mg content exceeds
6% in the case where Mn and Fe fall in the aforementioned composition range.
[0040] Therefore, it is preferable that Mg can be comprised from 4.0 to 6.0%, and it is
further preferable that it can be comprised from 4.0 to 5.0%, when the entirety is
taken as 100% by mass.
② Mn
[0041] Mn is an element which improves the mechanical strength of aluminum alloys by solving
in the matrix of aluminum similarly to Mg, or by generating compounds with aluminum
to precipitate them micro-finely in the matrix. Moreover, it also produces an effect
of improving the anti-seisurability to dies.
[0042] When Mn is comprised less than 0.3%, the improvement of mechanical strength is not
sufficient, and when it is comprised in excess of 0.6%, it is not preferable because
coarse crystallized substances crystallize to result in lowering the ductility.
[0043] Therefore, it is preferable that Mn can be comprised from 0.3 to 0.6%, and it is
further preferable that it can be comprised from 0.3 to 0.5%, when the entirety is
taken as 100% by mass.
③ Fe
[0044] Fe is an element which changes the crystallization process in solidification to inhibit
hot tearing resulting from solidification shrinkage. Moreover, Fe also produces an
effect of improving the anti-seisurability to dies when die-casting is carried out.
[0045] When Fe is comprised less than 0.5%, it is insufficient to change the crystallization
process greatly, and the effect of inhibiting hot tearing is less. On the other hand,
when Fe is comprised in excess of 0.9%, it is not preferable because coarse crystallized
substances crystallize to lower the ductility. Therefore, it is preferable that Fe
can be comprised from 0.5 to 0.9% when the entirety is taken as 100% by mass.
[0046] According to a further study by the present inventors, it became apparent that it
is further preferable that Fe can be comprised from 0.5 to 0.8% or from 0.5 to 0.7%.
④ Cr
[0047] Cr is an element which improves the mechanical strength of aluminum alloys by solving
in the matrix of aluminum similarly to Mg and Mn.
[0048] When Cr is comprised less than 0.1%, the improvement of mechanical strength is not
sufficient, and when it is comprised in excess of 0.7%, it is not preferable because
coarse crystallized substances crystallize to result in lowering the ductility.
[0049] Therefore, it is preferable that Cr can be comprised from 0.1 to 0.7%, and it is
further preferable that it can be comprised from 0.2 to 0.5%, when the entirety is
taken as 100% by mass.
⑤ Ti and B
[0050] Ti and B become the nucleation site of primary-crystal Al. Accordingly, when those
elements are added to increase, the respective crystalline grain diameters of primary-crystal
Al diminish. As a result, a solid-liquid fluidic state is maintained to a higher solid-phase
ratio side, and consequently the timing of stress occurrence by solidification shrinkage
is put off on a lower temperature side so that it is believed that the resistance
against hot tearing is improved. Specifically, it is believed as follows.
[0051] Ti becomes the nucleation site of α-Al, constitutes micro-fine structures, and reveals
the effects of inhibiting hot tearing as well as improving the ductility, moreover,
can improve the proof stress of aluminum alloys as well.
[0052] Hence, it is suitable that 0.01-0.3% Ti can be included when the entirety is taken
as 100% by mass. It results from the fact that, when Ti is comprised less than 0.01%,
no micro-fine structure can be obtained; and when Ti is comprised in excess of 0.3%,
coarse crystallized substances (Al
3Ti and the like) crystallize to result in lowering the ductility. It is more preferable
that Ti can be comprised from 0.1 to 0.2%.
[0053] B reveals a great effect of micro-fining crystalline grains, especially when it coexists
with Ti.
[0054] When B is comprised less than 0.01%, no micro-fine structure can be obtained, and
when it is comprised in excess of 0.05%, it is not economical because the variation
of crystalline grain diameters is less. Therefore, in the coexistence with Ti, it
is suitable that 0.01-0.05% boron (B) can be included when the entirety is taken as
100% by mass. It is more suitable that it can be comprised from 0.03 to 0.05%. Note
that it is economical that B can be added as titanium boride such as TiB
2 in addition to the case where it is added as a simple substance.
⑥ Be
[0055] Be reveals an effect on the oxidation resistance even independently, and inhibits
decrease of Mg resulting from oxidation when it dissolves.
[0056] Therefore, even being independent (without coexisting with Ti and the like), it is
suitable that 0.001-0.01% beryllium (Be) can be included when the entirety is taken
as 100% by mass. It is more suitable that it can be comprised from 0.005 to 0.01%.
Of course, it is needless to say that Be can coexist with Ti and so forth.
⑦ Mo
[0057] Mo produces an effect of inhibiting the
slag generation accompanied by the oxidation of Al-Mg alloy molten metals.
[0058] When Mo is comprised less than 0.05%, the oxidation inhibition effect is not sufficient,
and when it is comprised in excess of 0.3%, it is not preferable because coarse crystallized
substances crystallize to result in lowering the ductility.
[0059] Therefore, it is preferable that Mo can be comprised from 0.05 to 0.3%, and it is
further preferable that it can be comprised from 0.1 to 0.2%, when the entirety is
taken as 100% by mass.
⑧ Inevitable Impurities
[0060] As far as inevitable impurities do not exert an adverse effect on the characteristics
of aluminum alloys, the types and contents are not limited, however, the present inventors
found out that the castability of aluminum alloys, and the strength or ductility can
be improved by controlling the content of Si and Cu, inevitable impurities.
[0061] Namely, it is suitable that Si, an inevitable impurity, can be comprised 0.5% or
less, and that Cu can be comprised 0.3% or less.
[0062] Si is an inevitable impurity which is included in aluminum bare metal, and, when
it is contained in excess of 0.5%, it is not preferable because Mg
2Si precipitates in the matrix by natural aging to change the mechanical characteristics
of aluminum alloys with time.
[0063] Cu not only promotes hot tearing but also lowers corrosion resistance. Therefore,
when an aluminum alloy according to the present invention is used as structural members,
especially, it is preferable that it can be comprised 0.3% or less.
(2) Applications
[0064] The present aluminum alloy or process for producing a cast product can be utilized
in a variety of cast products made of aluminum alloys.
[0065] For example, in the field of automobiles and two-wheeled vehicles, when the present
aluminum alloy or process for producing the same is used in members for body structures,
chassis members, wheels, space frames, steering wheels (armatures), seat frames, suspension
members, engine blocks, transmission cases, pulleys, oil pans, shit levers, instrument
panels, door impact panes, surge tanks for intake, pedal brackets, front shroud panels,
and the like, it is possible to produce each of these members at a lower cost without
subjecting them to heat treatments.
[0066] Note that, although the present aluminum alloy is of high strength and high ductility
even as cast, it is naturally advisable to carry out cold working or heat treatments
after casting.
B. Examples
[0067] Subsequently, while giving examples, the present invention will be described in more
detail.
(Production and Testing of Test Samples)
(1) Example No. 1
[0068] Aluminum alloys were used which had an alloy composition of Sample Nos. 1 through
5 and Sample Nos. C1 through C7 set forth in Table 1, test samples were produced for
each of the samples, test samples whose constriction length was changed variously,
and each of the hot tearing characteristics was assessed. Note that Table 1 indicates
them while Al, themajor component, is abbreviated (being the same hereinafter).
[0069] To be more precise, as illustrated in Fig. 1, various test samples were produced
by a vertical die-casting machine equipped with a die whose cavity had a cross-section
of 7 mm in thickness and 10 mm in width and constriction length was changeable variously,
and the hot tearing characteristics assessment was carried out.
[0070] The casting conditions were such that the melting temperature was 750 °C; the die
temperature was from 50 to 100 °C; the casting pressure was 63.7 MPa; and the plunger
speed was 0.6 m/s. After the respective molten metals were poured by pressurizing
with the plunger (a pouring step) , they were solidified at a cooling rate of 100
°C/sec. approximately (a solidifying step).
[0071] The assessment of the hot tearing resistance was examined by a constriction length
at which a crack occurred. It indicates that the longer the constriction length is,
the less likely an alloy is to cause hot tearing. The thus obtained test results of
the respective test samples are illustrated in Fig. 3.
[0072] Note that this test was carried out while a 0.5 mm in thickness × 10 mm in height
insulating sheet was bonded three-way around the aforementioned cavity in the middle
in the direction of the constriction length in order to localize positions at which
a hot tearing occurred. How this insulating sheet was bonded three-way is illustrated
in Fig. 2, a cross-sectional view taken along the line "A-A" in Fig. 1.
(2) Example No. 2
[0073] Aluminum alloys were used which had an alloy composition of Sample Nos. 6 through
14 and Sample Nos. C8 through C10 set forth in Table 1, and plate-shaped cast products
whose thickness was 2 mm, width was 50 mm and length was 70 mm were produced by the
vertical die-casting machine.
[0074] The casting conditions were such that the melting temperature was 750 °C; the die
temperature was from 50 to 100 °C; the casting pressure was 63.7 MPa; and the plunger
speed was 1.4 m/s. Moreover, after the molten metals were poured by pressurizing with
the plunger (a pouring step) , they were solidified at a cooling rate of 100 °C/sec.
approximately (a solidifying step).
[0075] From these as-cast plate-shaped cast products, plate-shaped tensile test samples
were produced whose flat-surface portions were as-cast surfaces. The respective test
samples were used to examine the tensile strength, 0.2% proof stress and fracture
elongation. The results are set forth in Table 2. Note that the tensile test on the
respective test samples was carried out with an autograph tensile testing machine
made by SHIMAZU, and the aforementioned characteristics were found from the stress-strain
diagram obtained for the respective test samples.
(3) Example No. 3
[0076] Aluminum alloys were used which had an alloy composition of Sample Nos. 15 through
19 and Sample Nos. C11 and C12 set forth in Table 1, and as-cast plate-shaped cast
products were produced in the same manner as Example No. 2.
[0077] Here, in order to examine the influence of the mechanical characteristic change of
the respective plate-shaped cast products with time (artificial aging) , the as-cast
plate-shaped cast products, and plate-shaped cast products, the same having been heated
at 175 °C for 10 hours, were prepared, and the hardness (the Vickers hardness) of
the respective plate-shaped cast products was examined. The results are set forth
in Table 3.
[0078] Note that the Vickers hardness was such that a hardness meter made by AKASHI was
used; a load of 5 kg was loaded for 30 seconds; and the hardness was determined by
converting the size of the indentation made in this instance.
(4) Example No. 4
[0079] Moreover, the relationship between the hot tearing resistance and Fe content of Al
alloy cast products was examined in detail. Namely, test samples were produced in
the same manner as Example No. 1, test samples which comprised the alloy composition
of Sample Nos. 20 through 26 set forth in Table 4 and had various constriction lengths.
The respective samples were such that the Fe content was varied mainly while the Mg,
Mn and Ti contents were made equal approximately. Assessing the hot tearing resistance
by the constriction length at which a crack occurred was the same as the case of Example
No. 1 as well. The thus obtained test results of the respective test samples are illustrated
in Fig. 4.
(5) Example No. 5
[0080] The influence of the alloy composition exerting on the oxidation resistance of Al
alloy molten metals was examined. First, Al alloy molten metals were prepared which
comprised the alloy composition of Sample No. 27 and Sample No. 28. The respective
molten metals were measured for the weight in advance. These molten metals were put
in a crucible made of alumina, and were held at 750 °C for 5 hours in an aerial atmosphere.
[0081] After cooling the molten metals, the weight of the solidified Al alloys was measured.
And, the weight gain of the Al alloys was found from the weight difference before
and after holding them in said heating. The results are set forth in Table 5 altogether.
Note that, in Table 5, there are recited the oxidation increment proportions (oxidation
increment rates) with respect to the weight of the molten metals before holding them
in said heating.
(Assessment)
(1) Castability
[0082] It is seen from Fig. 3 that all of the aluminum alloys of Sample Nos. 1 through 5
falling within the present composition range had a sufficiently longer constriction
length, at which a crack occurred, than those of Sample Nos. C1 through C7. Specifically,
no crack occurred up to a constriction length of 50 mm for Sample No. 1, a constriction
length of 70 mm for Sample Nos. 2 and 3, and a constriction length of 80 mm for Sample
Nos. 4 and 5.
[0083] From these, when a proper amount of the Fe content was added while the Mn content
was controlled, it was understood that the hot tearing resistance is improved remarkably.
Moreover, when Ti making the nucleation sites was added while Mg, Mn and Fe had fallen
in the present composition ranges, it was also appreciated that the hot tearing resistance
was further improved.
[0084] In particular, as can be apparent from Table 4 and Fig. 4, the Al alloy cast products
of Sample Nos. 22 through 24, in which the Fe content was contained from 0.5 to 0.8%
while having Mg, Mn and Fe fallen within the present suitable composition ranges,
were such that the hot tearing resistance was furthermore improved.
(2) Strength and Ductility
[0085] ① All of Sample Nos. 6 through 14 were aluminum alloys falling within the present
composition range. And, as can be understood from Table 2, all of those aluminum alloys
exhibited a tensile strength of 250 MPa or more, a 0.2% proof stress of 130 MPa or
more, and in addition an elongation of 15% or more. Therefore, even as cast, it was
appreciated that the aluminum alloy according to the present invention reveals good
ductility while maintaining sufficient strength. Especially, there also exist those
which exhibited a tensile strength of 300 MPa or more, a 0.2% proof stress of 150
MPa or more, and an elongation in excess of 20%.
[0086] Moreover, Sample No. 7, an aluminum alloy of Sample No. 6 with Ti contained, was
such that the crystal grains were more micro-fined so that the ductility was further
improved.
[0087] ② On the other hand, the aluminum alloys of Sample Nos. C8 through C10 falling outside
the composition range according to the present invention could not make the strength
and ductility compatible. For example, since Sample No. C8 was such that the Mn content
exceeded 0.6% by mass, the elongation was less than 10% so that it was of low ductility,
though the tensile strength and 0.2% proof stress were high. On the contrarily, Sample
No. C9 which comprised less than 0.3% by mass Mn, and Sample No. C10 which comprised
less than 4.0% by mass Mg were such that the strength was insufficient, though they
were of high ductility.
(3) Influence of Aging
[0088] All of Sample Nos. 15 through 19 were aluminum alloys falling within the present
composition range. As can be understood from Table 3, these aluminum alloys were such
that the hardness variation was insignificant between as cast and after being heated
at 175 °C for 10 hours.
[0089] On the other hand, since the aluminum alloys of Sample Nos. C11 and C12 included
Si abundantly beyond the level of inevitable impurities, the hardness variation was
significant between as cast and after being heated at 175 °C for 10 hours. That is,
age hardening occurred, and accordingly there arise a fear that the characteristics
are changed by natural aging in aluminum alloys with such a composition.
(4) Oxidation Resistance
[0090] As indicated by Sample Nos. 27 and 28 of Table 5, when Mo was further comprised from
0.1 to 0.2% while having Mg, Mn, Ti and Fe fallen within the present suitable composition
ranges, it become apparent that the Al alloy molten metals show much better oxidation
resistance.
TABLE 1
Sample No. |
Aluminum Alloy Composition (% by Mass) |
|
Mg |
Mn |
Fe |
Si |
Cu |
Ti |
Cr |
1 |
4.98 |
0.31 |
0.75 |
Less than 0.1 |
Less than 0.01 |
- |
- |
2 |
5.68 |
0.60 |
0.80 |
↑ |
↑ |
0.15 |
- |
3 |
4.98 |
0.32 |
0.50 |
↑ |
↑ |
↑ |
- |
4 |
4.98 |
0.32 |
0.76 |
↑ |
↑ |
↑ |
- |
5 |
4.31 |
0.30 |
0.76 |
↑ |
↑ |
↑ |
- |
6 |
4.30 |
0.30 |
0.75 |
↑ |
↑ |
- |
- |
7 |
4.31 |
0.30 |
0.76 |
↑ |
↑ |
0.15 |
- |
8 |
5.68 |
0.60 |
0.80 |
↑ |
↑ |
↑ |
- |
9 |
5.62 |
0.32 |
0.76 |
↑ |
↑ |
↑ |
- |
10 |
4.79 |
0.52 |
0.85 |
↑ |
↑ |
0.16 |
- |
11 |
4.98 |
0.32 |
0.76 |
↑ |
↑ |
0.15 |
- |
12 |
4.01 |
0.53 |
0.76 |
↑ |
↑ |
↑ |
- |
13 |
4.02 |
0.31 |
0.75 |
↑ |
↑ |
0.16 |
- |
14 |
4.30 |
0.30 |
0.75 |
↑ |
↑ |
- |
0.21 |
15 |
5.68 |
0.60 |
0.80 |
↑ |
↑ |
0.15 |
- |
16 |
4.79 |
0.52 |
0.85 |
↑ |
↑ |
0.16 |
- |
17 |
4.01 |
0.53 |
0.76 |
↑ |
↑ |
0.15 |
- |
18 |
4.31 |
0.30 |
0.76 |
↑ |
↑ |
↑ |
- |
19 |
4.00 |
0.50 |
0.75 |
0.25 |
↑ |
↑ |
- |
C1 |
5.01 |
0.80 |
0.75 |
Less than 0.1 |
↑ |
- |
- |
C2 |
4.99 |
1.20 |
0.15 |
↑ |
↑ |
- |
- |
C3 |
5.00 |
1.20 |
0.15 |
↑ |
↑ |
0.15 |
- |
C4 |
3.50 |
0.80 |
0.15 |
↑ |
↑ |
- |
- |
C5 |
3.50 |
0.80 |
0.15 |
↑ |
↑ |
0.15 |
- |
C6 |
2.88 |
0.97 |
0.96 |
0.09 |
↑ |
- |
- |
C7 |
3.38 |
0.81 |
0.74 |
0.06 |
0.25 |
- |
- |
C8 |
4.79 |
1.05 |
0.91 |
↑ |
↑ |
- |
- |
C9 |
4.00 |
0.10 |
0.75 |
↑ |
↑ |
- |
- |
C10 |
3.00 |
0.50 |
0.75 |
↑ |
↑ |
- |
- |
C11 |
4.26 |
- |
0.15 |
1.98 |
↑ |
- |
- |
C12 |
4.00 |
0.50 |
0.75 |
0.75 |
↑ |
0.16 |
- |
TABLE 2
Sample No. |
Tensile Strength (MPa) |
0.2% Proof Stress (MPa) |
Fracture Elongation (%) |
6 |
290 |
139 |
20.0 |
7 |
324 |
165 |
15.0 |
8 |
321 |
160.3 |
17.7 |
9 |
310 |
154 |
18.3 |
10 |
304 |
146 |
21.5 |
11 |
284 |
140 |
19.6 |
12 |
270 |
135 |
19.8 |
13 |
290 |
140 |
23.0 |
14 |
298 |
149 |
19.0 |
C8 |
309 |
167 |
9.0 |
C9 |
265 |
120 |
22.0 |
C10 |
260 |
112 |
22.6 |
TABLE 3
Sample No. |
Hardness (HV) |
|
As Cast |
After Heat Treatment (175 °C × 10 hr.) |
15 |
79.1 |
82 |
16 |
73.7 |
76 |
17 |
67.3 |
68 |
18 |
70.1 |
72 |
19 |
68 |
69.2 |
C11 |
83.5 |
107.5 |
C12 |
68 |
78.2 |
TABLE 4
Sample No. |
Aluminum Alloy Composition (% by Mass) |
|
Mg |
Mn |
Ti |
Fe |
Si |
Cu |
20 |
4.46 |
0.39 |
0.14 |
0.12 |
Less than 0.1 |
Less than 0.01 |
21 |
4.46 |
0.36 |
0.15 |
0.36 |
↑ |
↑ |
22 |
4.32 |
0.37 |
0.14 |
0.50 |
↑ |
↑ |
23 |
4.31 |
0.30 |
0.15 |
0.76 |
↑ |
↑ |
24 |
4.62 |
0.32 |
0.14 |
0.80 |
↑ |
↑ |
25 |
4.55 |
0.39 |
0.14 |
0.88 |
↑ |
↑ |
26 |
4.36 |
0.34 |
0.12 |
0.98 |
↑ |
↑ |
TABLE 5
Sample No. |
Aluminum Alloy Composition (% by Mass) |
Oxidation Increment Rate (%) |
|
Mg |
Mn |
Ti |
Fe |
Mo |
Si |
Cu |
|
27 |
4.46 |
0.39 |
0.14 |
0.12 |
0.18 |
Less than 0.1 |
Less than 0.01 |
0.0063 |
28 |
4.46 |
0.36 |
0.15 |
0.36 |
- |
↑ |
↑ |
0.0081 |