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The present invention is a ternary alloy of magnesium, lithium and aluminum, containing 11% by
weight or more of lithium to make it light-weight and body-centered cubic, and having 2% by
weight or less of aluminum change in aging. The present invention relates to a diaphragm for
acoustic equipment. In general, in the case of a vibrator for an audio device, for example, a
speaker, a microphone, a headphone, etc., weight reduction of a vibration system has been
advanced in order to increase the electro-acoustic conversion efficiency. In particular, the
material of the diaphragm is required to have a small specific gravity and a large Young's
modulus. For this purpose, magnesium and lithium alloys have attracted attention as low specific
gravity and high Young's modulus materials. Magnesium and lithium alloys are suitable for
speaker diaphragms because their specific gravity is extremely small compared to other metals
and their internal loss is large. However, magnesium is easily oxidized by moisture in the air, and
lithium is a very active metal at ordinary temperature, so there is a problem with durability.
Recently, ternary alloys of magnesium, lithium and aluminum, each containing 9 to 15% by
weight of lithium and aluminum have been devised, but when the aluminum content is 2% by
weight or more, 6% of aluminum as shown by the dotted line in FIG. There is a clear age
hardening in%, which proceeds even at room temperature, so that the hardness of the diaphragm
will change with the passage of time and will not maintain the original speaker performance.
Also, the precipitation phase due to age hardening is the theta phase, which is easily decomposed
into a mixture of aluminum and lithium, and does not maintain the original hardness. Therefore,
for example, when it is used as a speaker diaphragm, the frequency characteristic near the high
frequency limit frequency changes, and there is a drawback that the performance at the initial
stage of design can not be maintained. In addition, since it becomes hard and fragile, in the case
of a fixed edge which is often put to practical use by a dome-shaped diaphragm or the like, the
edge portion is often broken and there is a defect that the input resistance is small. Generally,
magnesium alloys are close-packed hexagonal crystals and have a small number of sliding
surfaces, resulting in poor elongation, and rolling at the time of manufacturing a foil for use in a
speaker diaphragm, and about 260 ° when forming into a diaphragm shape. It is necessary to
heat to the temperature of C. Also, when the aluminum content increases, heating is required
during rolling and forming. When the lithium content is 11% by weight or less, the magnesium
alloy is a close-packed hexagonal crystal and is heated at the time of rolling and forming, so the
surface of the magnesium alloy containing chemically active lithium is oxidized and can be put to
practical use. In addition, it is necessary to roll and shape in an inert gas such as preon or argon
gas or in vacuum, which is not practical.
The present invention was invented to eliminate the above-mentioned drawbacks, and is
characterized in that in a ternary alloy of magnesium, lithium and aluminum, it comprises 11 to
16% by weight of lithium and 0.5 to 2.0% by weight of aluminum. Is a diaphragm for audio
equipment. Since the magnesium alloy of the present invention is configured as described above,
it has a low specific gravity and light weight, and as shown by the solid line in FIG. 1, there is no
age hardening with 1% by weight of aluminum. By making the lithium content 11% by weight or
more, it becomes a body-centered cubic crystal, can be rolled and formed at normal temperature,
and realizes a revolutionary low specific gravity 1.30 to 1.35 as a metal diaphragm for audio
equipment. The present invention provides a diaphragm for an audio device which is stable in
quality and good in processability. In the following, a 50 micron thick foil of a magnesium alloy
according to the invention, stored in an argon gas container, with a mold of normal temperature
and a pressure of 4 kf /-and a dome-like fixed edge of 25ψ% A speaker diaphragm is prepared
and treated with an alkaline II chromate to complete an anticorrosion on the surface. In the
embodiment of the present invention, although a magnesium alloy of 141% by weight of lithium
equivalent to an ASTM No-LA 141 alloy and 1.5% by weight of aluminum can be formed at room
temperature, 13% by weight of lithium equivalent to an ASTM No-LAl 36 alloy and 6% of
aluminum % Magnesium alloy has a specific gravity of 1.37 and a high aluminum content as
shown in Table 1, and therefore the elongation at normal temperature is bad. A mold heated to
190 to 2100 C while spraying argon gas so as not to oxidize by heating. The contact must be
placed on top for about 30 seconds for preheating, and press forming must be performed
gradually with a pressure of 4 kg / di and a die lowering speed of 5 seconds / 儒. As shown in
Table 1, the magnesium alloy having 13% by weight of lithium and 1% by weight of aluminum in
Table 1 has a specific gravity of 1.35. In the frequency characteristic diagram shown in FIG. 2,
the lithium content is the same as 13% by weight, but the speaker incorporating the magnesium
alloy diaphragm with an aluminum content of 1% by weight shown by the solid line A sound
pressure improvement of about 0.15 d BO can be seen from a speaker incorporating a
magnesium alloy diaphragm by weight. The diaphragm for an audio device of the present
invention exhibits a low specific gravity and an improvement in negative pressure activity,
exhibits a remarkable feature of light weight of magnesium alloy, is highly efficient, has one
response good, and has stable quality.
Brief description of the drawings
Fig. 1 shows the hardness over time by Rockwell Fig. 2 shows the frequency characteristic chart
Patented by Onkyo Co., Ltd.
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