U.S. patent application number 09/161833 was filed with the patent office on 2001-08-16 for mold structure for injection molding of a light alloy and method of injection molding a light alloy using the same.
Invention is credited to ISHIDA, KYOSO, SAKAMOTO, KAZUO, YAMAMOTO, YUKIO.
Application Number | 20010013402 09/161833 |
Document ID | / |
Family ID | 17395727 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013402 |
Kind Code |
A1 |
SAKAMOTO, KAZUO ; et
al. |
August 16, 2001 |
MOLD STRUCTURE FOR INJECTION MOLDING OF A LIGHT ALLOY AND METHOD OF
INJECTION MOLDING A LIGHT ALLOY USING THE SAME
Abstract
In order to provide a die structure for injection molding of a
light alloy free from gas defects, and a method of molding a light
alloy parts using the die, the die structure is used for converting
a light alloy into a semi-molten state, wherein a solid phase and a
liquid phase coexist, or a molten state at a temperature just above
a melting point and injecting the molten metal into an interior
cavity portion, and S.sub.1/S.sub.2 of a gate sectional area
S.sub.1 with respect to a maximum sectional area S.sub.2 of the
cavity of the mold which area is almost perpendicular to the
flowing direction of the melt therein is set in a range of 0.06 to
0.5.
Inventors: |
SAKAMOTO, KAZUO;
(HIROSHIMA-SHI, JP) ; ISHIDA, KYOSO;
(HIROSHIMA-SHI, JP) ; YAMAMOTO, YUKIO;
(HIROSHIMA-SHI, JP) |
Correspondence
Address: |
NIXON PEABODY, LLP
8180 GREENSBORO DRIVE
SUITE 800
MCLEAN
VA
22102
US
|
Family ID: |
17395727 |
Appl. No.: |
09/161833 |
Filed: |
September 29, 1998 |
Current U.S.
Class: |
164/113 ;
164/133 |
Current CPC
Class: |
B22C 9/08 20130101; B22D
17/007 20130101 |
Class at
Publication: |
164/113 ;
164/133 |
International
Class: |
B22D 037/00; B22D
013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 1997 |
JP |
P09-263893 |
Claims
What is claimed is:
1. A mold structure for injection molding into an interior cavity
portion of the mold through a gate adjacent to the cavity a molten
light alloy which is in a semi-molten state where a solid and a
liquid phases of the alloy coexist or in a full molten state at a
temperature just above the liquidus point, wherein the gate and the
cavity are set to be not less than 0.06 of a areal ratio S1/S2 of a
sectional area S1 of the gate with respect to a maximum sectional
area S2 of the cavity perpendicular to the molten metal flow
direction.
2. the mold structure according to claim 1, wherein the area ratio
is set to be less than 0.5.
3. The mold structure according to claim 1, wherein the mold
structure further comprises a core pin capable of inserting the
molten metal to be pressurized in the internal cavity after
injection molding.
4. The mold structure according to claim 1, wherein the gate is a
two-stage gate structure comprising a first and a second gates in
series in which the area of the first gate near the internal cavity
side is more than that of the second gate on the runner side.
5. A method of molding a light alloy product, comprising steps of:
preparing the light alloy material into a semi-molten state where a
solid phase and a liquid phase coexist, wherein a solid fraction of
the molten metal is not less than 10%; and, injecting the molten
metal into an internal cavity of the mold, wherein the mold
comprises the gate and the cavity being set to be not less than
0.06 in areal ratio S1/S2 of a sectional area S1 of the gate with
respect to a maximum sectional area S2 of the cavity which is
perpendicular to the molten metal flow direction.
6. A method of molding a light alloy product, comprising steps of:
preparing the light alloy material into a semi-molten state where a
solid phase and a liquid phase coexist, wherein a solid fraction of
the molten metal is not less than 5%, and the average grain size of
the solid phase is not less than 50 .mu.m; and, injecting the
molten metal into an interior cavity of the mold, wherein the mold
comprises the gate and the cavity being set to be not less than
0.06 in areal ratio S1/S2 of a sectional area S1 with respect to a
maximum sectional area S2 of the internal cavity which is
perpendicular to the molten metal flow direction.
7. The method according to claim 5, wherein the areal ratio is set
to be less than 0.5.
8. The method according to claim 5, wherein the light alloy
comprises a magnesium based alloy containing 4.0-9.5% of Al by
weight.
9. The method according to claim 5, wherein prior to the step of
injecting, the internal cavity of the mold is evacuated for a sort
time immediately before injecting.
10. The method according to claim 5, wherein the method further
comprise a step of heat treating the product to Temper T6.
11. The method according to claim 5, wherein the injection-molded
product is forged at a forging draft of not less than 25%.
12. The method according to claim 6, wherein the areal ratio is set
to be less than 0.5.
13. The method according to claim 6, wherein the light alloy
comprises a magnesium based alloy containing 4.0-9.5% of Al by
weight.
14. The method according to claim 6, wherein prior to the step of
injecting, the internal cavity of the mold is evacuated for a sort
time immediately before injecting.
15. The method according to claim 6, wherein the method further
comprise a step of heat treating the product to Temper T6.
16. The method according to claim 6, wherein the injection-molded
product is forged at a forging draft of not less than 25%.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Filed of the Invention
[0002] The present invention relates to a die structure for
injection molding of a light alloy free from casting defects, and
method for injection molding using the same.
[0003] 2. Prior Art
[0004] Light alloys containing of a matrix of aluminum or
magnesium, particularly magnesium based alloys containing aluminum
as an alloy component, have attracted special interest recently as
materials, which are of light-weight and capable of securing a
predetermined mechanical strength by means of plastic working such
as forging. However, these light alloys show greatly thermal
shrinkage during casting or molding, and this allows the fluidity
to be lowered unless the casting temperature is raised in the
gravity casting. Consequently, any perfect, sound cast free of
cavity defect is not obtained. However, the high casting
temperature of the melt can show the coarse-grained microstructure
in the cast alloy because of low cooling rate in the cooling step
of the casting process, then resulting in the reduce in workabilty
of the material.
[0005] On the other hand, a desirably fine-grained structure can be
obtained by die casting the alloy. In this process, since the
molten metal is injected at a high pressure in a spraying state
into a cavity of the mold, a great number of small voids or pores
are left in the die cast due to a contained gas, and reduce
mechanical strength of the cast so that any cast material having
high properties can not be obtained. Particularly, for a
thick-walled part, the strength is drastically lowered in this die
casting process.
SUMMERY OF THE INVENTION
[0006] An object of the present invention is to provide a mold
structure for injection molding a molten light alloy, capable of
producing it with a fine-grained structure free from gas defects,
then improving mechanical property of the light alloy cast
material.
[0007] Another object of the present invention is to provide a
method for injection molding a molten light alloy capable of
producing it with a fine structure free from gas defects, then
improving mechanical property of the light alloy cast material,
then improve mechanical property of the light alloy cast.
[0008] The present invention provide a mold for injecting and a
method for obtaining fine-grained microstructure free from casting
defects such as blow holes or shrinkage voids in the alloy during
injection molding.
[0009] In the invention, the molten metal is injected into the
internal cavity of the die in a laminar flow state in the injection
molding method, a fine structure free from gas defects can be
obtained.
[0010] The present invention provides a mold structure for
injection molding into an interior cavity portion through a gate a
light molten alloy which is in a semi-molten state where a solid
phase and a liquid phase of the alloy coexist or in a full molten
state remaining at a temperature just above the liquidus point of
the alloy, wherein a ratio S1/S2 of a sectional area S1 of the gate
with respect to a maximum sectional area S2 of the internal cavity
perpendicular to the molten metal flowing direction is set to be
not less than 0.06.
[0011] According to the present invention, by setting the gate
sectional area larger than such special value to the maximum
sectional area of the internal cavity portion in the direction
perpendicular to the metal flowing, or poured, direction toward the
cavity, the molten alloy can become in the laminar flow state in
the cavity. As a result, no generation of such gas defects as blow
holes or shrinkage voids is substantially observed in the
injection-molded product produced.
[0012] For the injecting mold of the invention the lower limit of
the areal ratio S1/S2 should be 0.06. As the areal ratio S1/S2 is
less than 0.06, as shown in FIG. 3, the relative density of the
product is drastically lowered because the generation rate of such
gas defects increases.
[0013] On the other hand, the upper limit of the areal ratio S1/S2
of the mold preferably may be 0.50. As the ratio S1/S2 is more than
0.5, the relative density of the molded material would be on almost
the same level as that of the conventional die cast, causing an
advantage of using such semi-melt injection molding method to
disappear.
[0014] In the case where a thick-walled product is molded, in the
melt filled in the corresponding thick portion of the cavity is apt
to be finally solidified to produce shrinkage cavities or voids in
the portion. In this case, it is preferred to insert core pins into
the internal cavity portion of the mold, and then, in use, to
pressurize the molten metal by push the core pins inward the cavity
immediately after pouring, thereby to prevent shrinkage cavities
from occurring during solidification. Thus the core pins cause the
semi-molten alloy which is solidifying to flow plastically,
resulting in crushing of the shrinkage cavities in the product.
[0015] However in this case of the thick-walled product, as a solid
fraction (a volume fraction of the solid phase in the semi-molten
melt) is low in the melt, the gas defects tends to be formed in the
alloy product. The solid fraction lower than 10% causes both the
relative density and tensile strength to be rapidly lowered as
shown in FIGS. 7 and 8. Accordingly, for production of the
thick-walled product, the semi-melt injection molding is preferably
performed at the solid fraction which may be prepared to be not
less than 10%.
[0016] With the decrease of the solid fraction, the average solid
grain size is liable to become small and the creep characteristics
at high temperature are liable to be lowered as shown in FIG. 6. To
secure the predetermined creep characteristics, injection molding
must be performed under the condition that not only the solid
fraction is not less than 5%, but also the average crystal grain
size in the solid phase contained in the melt is not less than 50
.mu.m.
[0017] The relative density of the injection-molded material of the
present invention can be improved by optionally pressed or forged.
The draft (a ratio of difference of the an initial thickness and
the deformed thickness of the material with respect to the initial
thickness) due to pressing or forging should be set to not less
than 25%. The reason is that the relative density, as shown in FIG.
4, is rapidly increased from the draft of 20% and is saturated at
25%.
[0018] The method of the present invention is preferably applied to
magnesium based alloy containing 4 to 9.5% by weight of aluminum as
a main alloying component, as the light alloy. When the aluminum
content is smaller than 4% by weight, an enhancement in mechanical
strength is not expected. On the other hand, when the content
exceeding 9.5% by weight can significantly lower workability (by
limiting upsetting rate).
[0019] The light alloy obtained by the present method is preferably
subjected to heat treatment for Temper T6 (composed of a solution
treating followed by an artificial aging or an single age hardening
treatment) for further improving the mechanical strength.
[0020] Thus, the present invention can provide the molded material
of a light alloy free from gas defects by injection molding
process, so that such molded material, even if it may have a rough
shape, can be forged into a final product having excellent
mechanical strength and precise dimensions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1A to 1F are views showing the whole steps of a
semi-melt molding process including a forging process after thereof
in the invention.
[0022] FIG. 2 is a schematic diagram showing a mold structure for
the semi-melt molding method of the present invention.
[0023] FIG. 3 is a graph showing a relation between the ratio of
the gate sectional area S1 to maximum sectional area S2 in the
product portion poured in the cavity and the relative density of
the product made by the semi-melt molding method of a magnesium
alloy.
[0024] FIG. 4 is a graph showing a relation between the rolling
area reduction and the relative density of the product by injection
molding the semi-molten material obtained by the present
invention.
[0025] FIG. 5 is a graph showing a relation between the solid phase
fraction and the steady creep rate of the injection-molded material
obtained using the method of the present invention.
[0026] FIG. 6 is a graph showing a relation between the mean grain
size of the solid phase in the semi-molten alloy and the steady
creep rate of the injection-molded material obtained using the
method of the present invention.
[0027] FIG. 7 is a graph showing a relation between the solid
fraction and the relative density of the injection-molded material
obtained by the method of the present invention.
[0028] FIG. 8 is a graph showing a relation between the solid
fraction and the tensile strength of the injection-molded material
obtained using the method of the present invention.
[0029] FIG. 9 is a bar graph showing the relative density of the
injection-molded material obtained by the method of the present
invention, compared with a conventional molding method.
[0030] FIG. 10 shows a top plan view of the molding cavity arranged
in the mold of a embodiment of a die used in the method of the
present invention.
[0031] FIG. 11 shows a top plan view showing the molding cavity
having the positions where penetration and casting crack easily apt
to occur in the conventional injection molding.
[0032] FIG. 12 shows a top plan view of the molding cavity in
another embodiment of a die used in the method of the present
invention.
[0033] FIG. 13 shows a top plan view of the molding cavity in a
further different embodiment of a die used in the method of the
present invention.
[0034] FIG. 14 is a top plan view showing a furthermore different
embodiment of a die used in the method of the present
invention.
[0035] FIGS. 15A and 15B are schematic sectional views showing a
method of removing a gate and a runner from the injection-molded
product by the method of the present invention.
[0036] FIGS. 16A and 16B are schematic sectional views showing an
improved method of removing a gate and a runner from the
injection-molded product obtained by the method of the present
invention.
[0037] FIG. 17 is a sectional view showing a non-deformed area to
remain in a metal block during the forging step.
[0038] FIGS. 18A and 18B are schematic sectional views showing a
profile of the injection-molded material before and after forging
said material, which is obtained by the method of the present
invention.
EMBODIMENT FOR CARRYING OUT THE INVENTION
[0039] The embodiment for carrying out the invention will be
described in detail with reference to the accompanying
drawings.
[0040] a magnesium based alloy is injection-molded by using a
semi-melt injection molding machine, as shown in FIGS. 1A and 1B.
In these Figures, a cylinder 31 is provided with a screw 32
therein, a high-speed injection mechanism 33 at the rear end and a
mold 4 at the front end. The mold 4 comprises two separable
half-molds 4a and 4b having each plans in contact with each other,
in which each concave to form at least a cavity 40 for molding is
shaped.
[0041] A plurality of heaters 35 are arranged around the cylinder
31 in the fixed intervals along the cylinder axis, which thereby
heat and melt the alloy material in order while the material is
being charged through a hopper 36 provided at the inlet end of the
cylinder 31.
[0042] the molten material, which is heated at a predetermined
temperature in the cylinder 31, is pressurized by pushing the screw
rotor 32 inside the cylinder 31 toward the front end and then
injected into the cavity in the mold 4, to solidify the solid body
to be shaped to the inversive inner profile of the cavity 40.
[0043] The injection-molded rough-surfaced product 1 is removed
after the half-molds 4a and 4b are separated as shown in FIG. 1B,
and then placed and forged between an upper a lower forging dies 91
and 92 as shown in FIGS. 1C and 1D. The product 1 is separated
between the forging dies 91 and 92 as shown in FIG. 1E to obtain a
forged product 2 as shown in FIG. 1F. Thereafter, the forged
product 2 is machined for finishing and then subjected to heat
treatment to temper T6.
[0044] In the following examples, the Alloys A to C were used as
magnesium based alloy, and as such molding machine, Model JLM-450E
manufactured by Nippon Seikosho Co. may be used under the
conditions as an example shown in Table 2.
1TABLE 1 Composition of Magnesium Alloy (wt %) Al Zn Mn Fe Cu Ni Mg
Alloy A 7.2 0.7 0.17 0.002 0.001 0.008 Bal Alloy B 6.2 0.9 0.24
0.003 0.001 0.008 Bal Alloy C 9.2 0.7 0.22 0.004 0.002 0.008
Bal
[0045]
2TABLE 2 Condition of Injection Molding Injection 80 Mpa pressure
Injection speed 2 m/sec Mold temperature 180.degree. C.
EXAMPLE 1
[0046] The mechanically cut pellets of the magnesium alloy C,
having the composition as shown in the Table 1, are charged into
the hopper 36 of the above injector. In the heating cylinder 31,
the powder is heated at a temperature adjusted such that pellets
begin to be gradually molten when moved at the position of about
1/4 of the whole length in the interior of the cylinder from the
hopper and to reach the desired solid fraction in the state of
solid liquid phases mixture at the position of about 1/2 of the
whole length from the hopper. On adjusting the melt to the solid
fraction of about 10% prior to injecting, it was injected into the
mold so as to obtain the average solid grain size of about 50 .mu.m
in the molded alloy.
[0047] It is seen that a significant change in relative density
occurs at 0.06 of the areal ratio S1/S2 of the gate sectional area
S1 to the maximum sectional area S2 of the internal cavity portion
almost perpendicular to the molten metal flow direction as
indicated as an arrow as shown in the schematic diagram of the mold
structure of FIG. 2. FIG. 3 shows that as the areal ratio S1/S2 is
more than 0.06, the relative density is saturated at 99%, as shown
in.
[0048] Then, a sample of a shape of 16 cm in diameter and 22.5 mm
in length, having the relative density of 96% was made of the
injected-molded material of the above alloy C and forged at the
temperature of 300.degree. C. to different forging draft
percentages. A relation between the forging draft and the relative
density of the product is shown in FIG. 4. The relative density
increases with a increase in forging draft. The relative density is
99% at the forging draft of 25%, and is saturated with the higher
draft.
[0049] The injection-molded materials were prepared by
injection-molding the above alloy C under the conditions that the
average solid grain size is fixed to 50 .mu.m and the solid
fraction is changed, using a mold of the area ratio S1/S2 of 0.1.
Creep characteristics of the resulting injection molded materials
was examined at 125.degree. C. under 50 MPa. The solid fraction was
determined by measuring the area proportion in the microstructure
of the molded product, using image analysis.
[0050] As is apparent from FIG. 5, the steady creep rate
(X10.sup.-3%/hr) is lowered with a increase in solid fraction, and
the excellent high-temperature creep characteristics are obtained
at the solid fraction of not less than 5%.
[0051] For investigation of the creep characteristics, the
injection-molded materials were prepared by injection-molding the
same alloy C under the conditions that the average solid fraction
was fixed constant and the average crystal grain size (.mu.m) of
the solid phase in the melt was changed, using a mold having the
areal ratio S1/S2 of 0.1.
[0052] Steady creep rates of the resulting injection molded samples
were examined at 125.degree. C. at a constantly applied tensile
stress of 50 MPa. FIG. 6 shows the obtained relation between the
average solid fraction and steady creep rate, in which steady creep
the rate is decreased with a increase in solid grain size. Thus,
the excellent high-temperature creep characteristics are obtained
at the solid fraction of not less than 5%.
EXAMPLE 2
[0053] In the same manner as described in Example 1 except for
using alloys A and B as specified in Table 1, injection molding was
performed and the relation between the solid fraction and the
relative density of the alloys A and B was studied wherein the
grain size of the solid phase was adjusted to 10%.
[0054] The results are shown in FIG. 7. As the solid fraction is
below 10%, the relative density is rapidly lowered, and as it is
over 10%, the relative density gradually increases. Thus, it is
found that high relative density is obtained with the solid
fraction in excess of 10%, dependently on the alloy
composition.
[0055] The Alloy B is apt to show poorer run as a melt in a cavity
of the mold and apt to be lower in density as a solids than the
Alloy A, on the same conditions of molding with respect to moth the
Alloys
[0056] For Alloy A with the solid grain size of 50 .mu.m, the
relation between the solid fraction (%) and tensile strength (MPa)
is shown in FIG. 8. It is also found that a rate of a change of the
tensile strength to the solid fraction varies at the solid fraction
of 10%. Accordingly, it is necessary to perform injection molding
free from gas entrapment using a mold whose area ratio S1/S2 is not
less than 0.06 in order to obtain high tensile strength. It is also
found it necessary to perform injection molding at the solid
fraction of not less than 10%.
EXAMPLES 3 AND 4
[0057] The Alloy C was injection molded using the mold having the
areal ratio S1/S of 0.2, at the solid fraction of 10% in the same
manner as described in Example 1.
[0058] In Example 3, the cavity of the mold was evacuated for 5
seconds before injection and the injection pressure was maintained
to the melt filled in the cavity at 80 MPa until solidification of
the melt has finished.
[0059] In Example 4, evacuation was not performed and the injection
pressure was maintained at 80 MPa until solidification has
finished.
[0060] In Comparative Example 1, evacuation was not performed and
the injection pressure was maintained at a lower level of 25 MPa
until solidification have finished.
[0061] As is apparent from the results as shown in FIG. 9, the
combination of evacuation of the molding cavity and maintenance of
the injection pressure is effective for enhancement of the relative
density, because they prevent gas defects and shrinkage cavities
during molding.
[0062] Maintenance of the injection pressure is performed for the
purpose of avoiding a pressure-unloaded state caused by a working
time-rag in turning on or off a pressure switching valve. As shown
in FIG. 10, a filter 44f, having pores whose diameter is smaller
than that of the solid grain size of the solid phase in the molten
light alloy, may be provided in the mold, allowing the molten metal
not to be transferred to the evacuation path 44p of the mold.
EXAMPLE 5
[0063] For the mold as shown in FIG. 11, as the alloy, which easily
is apt to be subjected to casting crack of the molded body or
sticking to the molding cavity in molding, is injection molded in
the mold at the area ratio S1/S2 of not less than 0.06, sticking of
the body to the mold occurs at the thermal sticking position 47
where a distance between the wall portion of the cavity to be
initially contact with the molten metal and a gate 42 is minimum.
On the other hand, casting crack is apt to occur at the position 46
in the cavity at which the latest flow of the molten metal finally
arrives, with a great amount of the cooled then and solidified
metal in the melt included.
[0064] Therefor, it is preferred to set the position of the gate in
the mold such that the distance between the side wall of the cavity
initially contact with the molten metal and the gate is elongated
as far as possible, and to contrive the mold design of reducing the
speed of the molten metal when the mold side wall is contacted
therewith. For example, in the case of a ring-shaped product to be
molded, preferably at least two gates 42 and 42 are provided
separately around the rim of the ring, as shown in FIG. 12, thereby
to adjust the injecting speed of the molten metal from the gates to
not less than 30 m/second and to supply the molten metal flow along
the tangent line to the center of the ring.
[0065] In another example, as shown in FIG. 13, a porous material
46 is arranged on the side wall of the cavity to be in earliest
contact with the injected molten metal, thereby making it possible
to reduce the metal flow speed when the mold side wall is contacted
with the molten metal. Also, it is preferable to enhance the solid
fraction in the melt at the portion which the molten metal reaches
the latest.
[0066] Furthermore, the temperature of the melt may controlled in
the respective heating zones by heaters 35 around the injection
cylinder 31, thereby to change the solid fraction in the molten
alloy longitudinally along the cylinder 31, as shown in FIG. 1A. By
enhancing the solid fraction inside the cylinder 31 in a part of
the melt present, for example, on the rear side thereof, it is
possible to enhance the solid fraction at the portion in the cavity
which the molten metal reaches finally.
[0067] The cavity of mold may have a form of rectangular
hexahedron. In this case, the gate 42 connected with the runner 41
is preferably provided at the end portion of tha cavity 40
elongated in the longitudinal direction, as shown in FIG. 14, to
elongate the distance between the side wall of the cavity 40 to be
contact with the earliest molten metal as long as possible.
EXAMPLE 6
[0068] In the present invention, when the sectional area of the
gate 42 is enhanced to area the ratio S1/S2 is greater than 0.06, a
pealed or broken defect is apt to occur at the root portion of the
gate 12 of the product 1 at the time of separation of the runner 11
by cutting it at the gate, as shown in FIGS. 15A and 15B.
[0069] Therefore, it is preferred to constitute a two-stage gate
structure, as shown in FIG. 16A, wherein the area of the gate 12a
(for example, section of the gate; 4 mm in width, 2.0 mm in
thickness) on the cavity side (product side) is larger than that of
the gate 12b (for example, section of the gate; 4 mm in width, 1.7
mm in thickness) which is on the runner side and away by 0.1 mm
from the cavity. After molded, the product is separated at the
smaller (thinner) gate 12b from the runner by bending the runner,
and the remaining portion of the runner, or the gate 12a, on the
product surface is then ground to be removed; consequently, the
smooth surface at the portion of the product can be easily
obtained, without forming such a pealed defect due to the gate, as
shown in FIG. 16B.
EXAMPLE 7
[0070] In case of uniform forging, a pair of non-deformed regions
18 and 18 are formed in the material 1 under the center upper and
lower surfaces which are pressed opposite to each other, as shown
in FIG. 17, and shrinkage cavities in the region thereof is
possible to be left without being crushed. To densify the injection
molded product 1, it is preferred to forge the product at the
minimum forging draft not less than 25% in not only the
non-deformed portion but also the upper and lower center surfaces.
In order to forge the product into a rectangular cross section, an
injection-molded product 1 may be molded in advance into a
barrel-shaped cross section, in which the central upper and lower
surfaces to be pressed are expanded as shown in FIG. 18A, and then
such injection-molded product 1 may be forged so as to deform the
portions under the convexed barrel surfaces with higher draft.
Thus, a forged product 2 having a rectangular cross section is
formed by forging, as shown in FIG. 18B.
[0071] As described above, the various effects of the present
invention using the magnesium alloys was confirmed in those
examples. The relations of the solid fraction and grain size to the
mechanical strength or creep characteristics are phenomena peculiar
to the light alloy to be injection-molded from the semi-molten
state, and therefore, the method of the present invention is widely
applicable to light alloys containing magnesium and aluminum to
improve such mechanical properties.
* * * * *