Technical Field
[0001] The present invention relates to aluminum alloy with superior abrasion resistance,
extrusion property and forge processing property, such aluminum alloy being used for
parts such as compressors in automobiles and home electric appliances.
Background Art
[0002] Properties such as abrasion resistance and the like are required with aluminum alloy
used for compressors and the like in automobiles and home electric appliances. For
example, regarding an aluminum alloy used for compressors, Si is added to the Al-Si
by 10 mass% (herein after referred to as %) or more, in order to improve abrasion
resistance and to decrease the rate of thermal expansion. Patent Literature 1 discloses
an aluminum alloy for sliding use with superior fatigue resistance and seizure resistance.
In order to obtain such fatigue resistance and seizure resistance, Si is added to
the aluminum alloy as an essential element by 1 to 15%. However, the literature also
discloses that the aluminum alloy becomes brittle when the amount of Si added exceeds
15%.
Citation List
Patent Literature
SUMMARY OF INVENTION
Technical Problem
[0004] As mentioned above, aluminum alloys used for compressors and the like are added with
a quite amount of Si to obtain the required properties of superior abrasion resistance,
rate of thermal expansion and the like. Although such aluminum alloys are improved
in abrasion resistance, rate of thermal expansion and the like, they have problems
in that processability such as extrusion processability may decrease and surface texture
may deteriorate. This is observed since processability decreases by increasing the
concentration of additives in the aluminum alloy. In particular, Si added to the aluminum
alloy for improving abrasion resistance decreases the productivity in the processes
of extrusion process and forge process. In practical use, abrasion resistance, rate
of thermal expansion and the like of the aluminum alloy often exceed the degree required
for its actual use. Therefore, when such an extremely superior abrasion resistance
and the like are not necessary, it is desirable to optimize the required properties
(such as abrasion resistance) of the aluminum alloy within the required degree, from
the view of productivity.
[0005] Accordingly, by balancing the required property and the productivity as necessary,
aluminum alloy with highly advantageous effect in cost can be obtained without losing
productivity.
[0006] Thus, development of a balanced aluminum alloy with required property while suppressing
the loss of productivity to its minimum is desired.
[0007] Taking the afore-mentioned circumstances into consideration, an object of the present
invention is to provide an aluminum alloy of Al-Si series which possesses superior
extrusion property and forge property, and also enables the production of forged products
maintaining their abrasion resistance.
Solution to Problem
[0008] The present inventors have made a diligent investigation and found that an aluminum
alloy with balanced required properties and productivity can be obtained, by adjusting
the amount of each compositions and controlling the size of eutectic Si. That is,
the present inventors have found that the object of the present invention can be achieved
by the following means.
[0009] That is, according to the present invention, an aluminum alloy possessing superior
abrasion resistance, extrusion property and forging property, comprising: 5.5 to 7.0
mass% (hereinafter referred to as %) of Si, 1.0 to 2.0% of Cu, 0.4 to 0.8% of Mg,
0.05 to 0.15% of Cr, 0.05 to 0.25% of Ni, with the rest consisting of Al and unavoidable
impurities, wherein Sc (defined as the size of an eutectic Si in the central portion
of the cross section which is vertical with respect to the longitudinal direction
of the aluminum alloy extruded) and Ss (defined as the size of the eutectic Si at
the surface side of the cross section which is vertical with respect to the longitudinal
direction of the aluminum alloy extruded) satisfies an equation of "Sc-Ss ≤ 15 µm
2", and the number of the eutectic Si particles having the size of 20µm
2 or smaller is 1000 to 3000 /mm
2, is provided.
[0010] Preferably, an aluminum alloy with superior abrasion resistance, extrusion property
and forge processing property further containing 0.01 to 0.05% of Sr is provided.
Advantageous Effects of Invention
[0011] According to the present invention, aluminum alloy material for manufacturing extrusion
material and forged material with superior extrusion property and forge processing
property, while also maintaining abrasion resistance, can be provided by controlling
the content of each composition and the size of the eutectic Si in the aluminum alloy.
Brief Description of the Drawing
[FIG 1]
[0012] This is a figure showing the forge processing of the extruded product manufactured
by extrusion.
Description of Embodiments
[0013] Hereinafter, the embodiments of the present invention will be described.
[0014] First, each of the elements added to the aluminum alloy will be explained.
[0015] Si contributes to the improvement in abrasion resistance by forming a Si compound.
In addition, Si, together with Mg, forms Mg
2Si, and thereby contributes to the improvement in strength. When the amount of Si
added is less than 5.5%, the effect observed for the improvement in strength and abrasion
resistance is low. When the amount of Si added exceeds 7.0%, the surface texture deteriorates,
and the extrusion property lowers.
[0016] Cu contributes to the improvement in strength. When the amount of Cu added is less
than 1.0%, the effect observed for the improvement in strength is low. When the amount
of Cu added exceeds 2.0%, the extrusion processability and corrosion resistance lowers.
[0017] Mg, together with Si, forms Mg
2Si and contributes to the improvement in strength. When the amount of Mg added is
less than 0.4%, its effect is low. When the amount of Mg added exceeds 0.8%, the extrusion
processability lowers. Preferably, Mg is added by 0.55 to 0.65%.
[0018] Cr is effective for refining the crystalline grain, and contributes to the improvement
in strength. When the amount of Cr added is less than 0.05%, such effect is low. When
the amount of Cr added exceeds 0.15%, further increase in such effect cannot be observed.
Preferably, Cr is added by 0.07 to 0.10%.
[0019] Ni is effective for improving heat resistance and abrasion resistance, and also contributes
to the improvement in strength. When the amount of Ni added is less than 0.05%, such
effect is low. When the amount of Ni added exceeds 0.25%, further increase in such
effect cannot be observed. In addition, extrusion property lowers. Preferably, Ni
is added by 0.07 to 0.13%.
[0020] Sr, by being added, is an element which contributes to the improvement in mechanical
properties. Sr is used for the modification treatment of the crystallized Si, and
addition of Sr gives fine crystals of Si. The amount of Sr added is preferably 0.01
to 0.05%. When the amount of Sr added is less than 0.01%, such effect is low. When
the amount of Sr added exceeds 0.05%, further increase in such effect cannot be observed.
[0021] Fe and Mn are contained by 0.5% or less, since these elements form compounds with
other additive elements and thus leads to lowering of the effects obtained by the
additive elements.
[0022] Here, the aluminum alloy according to the present invention consists of the afore-mentioned
elements, unavoidable impurities and Al. For example, the aluminum alloy may contain
a small amount of Ti, Zr or Zn in the range so long as it does not impair the effect
of the present invention. Such range is 0.05% or less.
[0023] The uniformity of surface texture and abrasion resistance in extrusion material and
forged material depend on the size and distribution of the eutectic Si in these materials,
since eutectic Si have influence on such properties. That is, the aluminum alloy of
the present invention attained the superior extrusion property and forge processing
property by controlling the content of Si and other compositions. In addition, by
controlling the size and distribution of the eutectic Si, variation in the surface
texture and the properties among the portions of the material can be avoided. Therefore,
the present invention can provide extrusion material and forged material having uniform
properties with high productivity.
[0024] When Ss and Sc are controlled so as to satisfy the equation of "Sc-Ss ≤ 15 µm
2", the surface texture of the extrusion material becomes superior, and the variation
in abrasion resistance among the surface side and the central portion of the extrusion
material can be suppressed. Here, regarding the size of eutectic Si, Ss is obtained
as the size of eutectic Si as follows: A cross section obtained by cutting the extrusion
material in the vertical direction with respect to the longitudinal direction thereof
is used for the observation. The size of the eutectic Si existing slightly inward
of 50µm from the surface side of the cross section of the extrusion material is observed
under an optical microscope with magnification of 100 times. Within this visual field
under the microscope, the size of the eutectic Si is observed for four sites, each
site being placed with an interval of 90 degrees of central angle, with respect to
the center of the visual field. Ss refers to the largest size of eutectic Si thus
observed. Sc is defined as the size of eutectic Si observed at the central portion
of the cross section of the extrusion material under an optical microscope with magnification
of 100 times. The size of eutectic Si in the present invention means the crystal area
of the eutectic Si.
[0025] Further, the roughness of the surface of the extrusion material can be suppressed
by keeping the size of the eutectic Si contained in the extrusion material 20µm
2 or smaller. In addition, the number of eutectic Si particles should be kept in the
range of 1000 to 3000 /mm
2 in order to obtain the abrasion resistance. When the number of eutectic Si particles
with the size of 20µm
2 or smaller is less than 1000 /mm
2, the effect on abrasion resistance after the material being forged is low. When the
number of eutectic Si particles exceeds 3000 /mm
2, the extrusion property and the forge processing property are inhibited.
[0026] Here, it should be noticed that there is no particular limitation with respect to
the production conditions and the thermal refining of the aluminum alloy of the present
invention. The thermal refining should be selected depending on the intended application,
within the usual production conditions.
[0027] When the extrusion material is used as the forged product, the processability during
the forging process is influenced by the hardness of the material. Therefore, the
type of thermal refining adopted for the extrusion material of the present invention
is preferably F, T1 or O, and more preferably O.
[0028] In addition, the type of thermal refining after the forging process should be selected
depending on the required properties. Here, in the present invention, T6 is preferable.
Examples
[0029] The present invention will be described in detail by referring to the Examples. However,
the present invention shall not be limited to these Examples.
[0030] First, each of the alloy having the composition described in Table 1 was heated within
the temperature range of 700°C to 740°C to give the molten aluminum alloy, and then
molding was conducted using a metallic mold. The amount of cooling water was adjusted
to 70 to 100 L/min.
[0031] After obtaining ingots with 220mm diameter, these ingots were subjected to surface
finishing for four hours at 490°C. The ingots were then extruded through a single
hole at 500°C to give a round bar with 30mm diameter.
[0032] The samples thus obtained as the extrusion materials were subjected to observation.
Here, the cross section which is vertical with respect to the longitudinal direction
of the extrusion material was used for such observation. The size of the eutectic
Si existing slightly inward of 50µm from the surface side of the cross section of
the extrusion material was observed under an optical microscope with magnification
of 100 times. The largest size of the eutectic Si (Ss) was obtained by observing four
sites within this visual field under the microscope, each site being placed with an
interval of 90 degrees of central angle, with respect to the center of the visual
field. Further, the size of eutectic Si at the central portion (Sc) was observed at
the cross section of the extrusion material under an optical microscope with magnification
of 100 times. Here, the size and the number of the eutectic Si particles were analyzed
using the software "image analysis software A-ZO-KUN" available from Asahi Kasei Engineering
Corporation. Surface texture was evaluated by stroking the surface with a pencil with
hardness of HB, and the results were judged as passed "Good" when no scratch was observed,
and the results were judged as failed "Not Good" when scratch was observed. The results
are shown in Table 2. Samples which satisfied the predetermined criteria were judged
as passed, and samples which did not meet the predetermined criteria were judged as
failed.
[0033] Next, the round bars were subjected to annealing treatment for five hours at 400°C
to give an O-material. Before evaluating the forged product, the samples were confirmed
that the size and number of eutectic Si particles were in the range of the present
invention.
[0034] The round bars were then cut by 100mm length in the longitudinal direction, and were
subsequently subjected to upset forging with the processing rate of 80%. The forged
products were then subjected to solution treatment for two hours at 520°C, followed
by immediate heat treatment with 50°C water. The forged products further went through
artificial aging treatments for ten hours at 180°C to give forged products with thermal
refining of T6.
[0035] Here, the processing rate for the upset forging is a value obtained by calculation
using the formula: (r1-r2) / r1 X 100 with respect to Fig. 1.
[0036] Tensile strength test, observation of appearance after upset forging and abrasion
test were conducted for the test samples of forged alloy products obtained as above.
Results are given in Table 3.
(1) Appearance after upset forging
[0037] Appearance after upset forging with the processing rate of 80 % was observed. Samples
with no cracks were judged as passed (shown as "Good"), and samples with cracks were
judged as failed (shown as "Not Good").
(2) Tensile strength test
[0038] Test pieces for the tensile strength test were prepared so that the longitudinal
direction of the extrusion bar is used for the longitudinal side of the test piece.
The test pieces were prepared in accordance with the Japanese Industrial Standards
(JIS) as test piece No. 4. The results of the test were evaluated as "passed" when
the tensile strength (TS) was 300 MPa or higher, and were evaluated as "failed" when
TS was lower than such value.
(3) Abrasion test
[0040] As shown in Table 1 and Table 2, the extrusion materials 1 to 10 according to the
present invention showed superior surface texture, while the extrusion materials of
comparative Examples 11 to 17 showed inferior surface texture.
[0041] Surface texture of Examples 1 to 10 of the present invention are superior since the
composition is within the preferred range. That is, their smooth surface provides
superior extrusion property and thus productivity is high.
[0042] The composition of the extrusion materials of Comparison Examples 11 to 14, 16 and
17 were out of the preferred range, and thus their surface texture caused the extrusion
material to get caught during extrusion, leading to poor extrusion processability.
[0043] The extrusion material of Comparison Example 11 contains a large amount of Si, and
the value of Sc-Ss is large. Therefore, the surface texture of the extrusion material
caused the extrusion material to get caught during the extrusion, leading to poor
extrusion processability.
[0044] The extrusion material of Comparison Example 12 contains a small amount of Si, and
the value of Sc-Ss is large. Therefore, the surface texture of the extrusion material
caused the extrusion material to get caught during the extrusion, leading to poor
extrusion processability.
[0045] The extrusion material of Comparison Example 13 contains a small amount of Si and
Cu. Therefore, the surface texture of the extrusion material caused the extrusion
material to get caught during the extrusion, leading to poor extrusion processability.
[0046] The extrusion material of Comparison Example 14 contains a large amount of Si, Cu,
Mg and Cr. Therefore, the surface texture of the extrusion material caused the extrusion
material to get caught during the extrusion, leading to poor extrusion processability.
[0047] Sr contained in the extrusion material of Comparison Example 16 is out of the preferred
range, and the number of eutectic Si particles having the size of 20µm
2 or smaller is large. Therefore, the surface texture of the extrusion material caused
the extrusion material to get caught during the extrusion, leading to poor extrusion
processability.
[0048] The extrusion material of Comparison Example 17 contains a large amount of Si, contains
a small amount of Mg, and the value of Sc-Ss is large. Therefore, the surface texture
of the extrusion material caused the extrusion material to get caught during the extrusion,
leading to poor extrusion processability.
[0049] The composition of the extrusion material of Comparison Example 15 is within the
preferred range, however, the value of Sc-Ss is large. Therefore, the surface texture
of the extrusion material caused the extrusion material to get caught during the extrusion,
leading to poor extrusion processability.
[0050] As shown in Table 3, Examples 1 to 10 according to the present invention showed superior
appearance after forging, tensile strength and comparative abrasion quantity, while
the Comparison Examples 11 to 17 showed inferior results.
[0051] The forged materials of Examples 1 to 10 according to the present invention showed
good results in tensile strength test and possessed good comparative abrasion quantity.
In addition, since the forged materials have good forge processing property, the appearance
after upset forging was superior.
[0052] The forged material of Comparison Example 11 contains a large amount of Si in its
composition. Therefore, crack is observed in the appearance of the material after
upset forging. That is, the forge processing property of Comparison Example 11 is
low, and thus such material is not suitable as a forge material.
[0053] The forged material of Comparison Example 12 contains a small amount of Si in its
composition. Therefore, the tensile strength is low, and the abrasion resistance is
inferior. Further, as shown in Table 2, abrasion resistance is inferior since the
number of eutectic Si particles having the size of 20µm
2 or smaller is large.
[0054] The forged material of Comparison Example 13 contains a small amount of Si and Cu
in its composition. Therefore, the tensile strength is low, and the abrasion resistance
is inferior.
[0055] The forged material of comparative Example 14 contains a large amount of Si, Cu,
Mg and Cr. Therefore, crack is observed in the appearance of the material after upset
forging. That is, the forge processing property of Comparison Example 14 is low, and
thus such material is not suitable as a forge material.
[0056] The forged material of Comparison Example 15 has its composition within the preferred
range, and thus all of the appearance after upset forging, results of the tensile
strength test and the comparative abrasion quantity were satisfactory. However, as
shown in Table 2, the productivity of the extrusion material of comparative Example
15 is poor due to its poor extrusion processability. Therefore, productivity of the
forged material of comparison 15 is poor.
[0057] The forged material of Comparison Example 16 contains a large amount of Si, Cu and
Sr in its composition. In addition, as shown in Table 2, crack is observed in the
appearance of the material after upset forging since the number of eutectic Si particles
having the size of 20µm
2 or smaller is large. That is, the forge processing property of this material is poor,
and is not suitable as a forged material.
[0058] The forged material of Comparison Example 17 contains a large amount of Si and a
small amount of Mg in its composition. Accordingly, crack is observed in the appearance
of the material after upset forging. That is, the forge processing property of this
material is poor, and is not suitable as a forged material.
Explanation of Symbols
[0059]
- 1
- extruded bar after cutout (before forging)
- 2
- forging machine
- r1
- height of material before upset forging
- r2
- height of material after upset forging
- 3
- rotating ring
- 4
- material for evaluation (aluminum alloy)