Hypoeutectic aluminum silicon magnesium nickel and phosphorus alloy

A hypoeutectic aluminum silicon magnesium alloy includes 4-5.5% silicon, 0.15-3.5% magnesium, 0.005 to 0.08% phosphorus and aluminum. The presence of the phosphorus causes formation of a spherical percipitates of silicon magnesium and the aluminum. The phosphorus suppresses the magnesium silicon aluminum eutectic which allows the aluminum to remain liquid for a longer period of time and consequently providing a better fill of casting during the time the alloy is solidifying in a die or a mold. This alloy which preferably includes nickel is particularly useful for marine, hydraulic and refrigeration components.

BACKGROUND OF THE INVENTION 
Aluminum for some time has been alloyed with various amounts of silicon. 
Based on the percentage content of silicon, the alloy can be characterized 
as a hypereutectic or hypoeutectic alloy. A hypoeutectic mixture is one 
which contains more aluminum than aluminum silicon eutectics. A 
hypereutectic alloy is therefore one which has more silicon than aluminum 
silicon eutectic. 
The hypereutectic alloy is saturated with silicon thus having excess free 
silicon. Frequently magnesium is added to such hypoeutectic as well as 
hypereutectic alloys. For example, Goetzel U.S. Pat. No. 2,155,651 and 
Hall U.S. Pat. No. 1,871,607 both disclose hypoeutectic aluminum silicon 
magnesium alloys. Hypereutectic aluminum silicon alloys are disclosed, for 
example, in Hasegawa et al U.S. Pat. No. 3,841,919, Rasmussen U.S. Pat. 
No. 3,953,202 and Sterner-Rainer U.S. Pat. No. 1,940,922 which discloses 
an aluminum silicon magnesium alloy which has 5-40% silicon. A silicon 
content of 5-40% includes hypoeutectics and hypereutectics. 
Phosphorus has also been added to hypereutectic aluminum silicon alloys. 
Its use is disclosed in the Sterner-Rainer reference. Further, Noguchi 
U.S. Pat. No. 4,147,074 discloses the addition of phosphorus to 
hypereutectic aluminum silicon alloys, but indicates that phosphorus is 
not required where the alloy contains less than 14% silicon. On the other 
hand, Desre U.S. Pat. No. 3,762,660 teaches the need to dephosphorize 
aluminum. 
SUMMARY OF THE INVENTION 
The present invention is premised upon the realization that a hypoeutectic 
aluminum silicon magnesium alloy can be formulated having substantially 
improved physical characteristics by adding an effective amount of 
phosphorus to the aluminum silicon magnesium alloy whereby the aluminum 
silicon magnesium precipitate forms around the phosphorus atom in a 
spherical formation. This enables the alloy to remain in a liquid state 
for a longer period of time enabling it to efficiently and effectively 
fill a mold prior to solidification for improved density. 
Further, the strength of this alloy is comparable to aluminum alloys which 
are significantly more expensive. Such an alloy can be cast at lower 
temperature which in turn reduces the expense of using this alloy. 
These advantages are particularly realized an alloy having the following 
components: 
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Silicon 4.0-5.5% 
Iron .5% Max. 
Magnesium .15-.35% 
Copper .60% Max. 
Zinc .30% Max. 
Nickel .30-.50% 
Lead .1% Max. 
Tin .1% Max. 
Titanium .15% Max. 
Chromium .05% Max. 
Phosphorus .005-.008% 
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Such an alloy is particularly useful in forming marine, hydraulic and 
refrigeration components. 
DETAILED DESCRIPTION 
The present invention is a hypoeutectic aluminum silicon magnesium alloy 
incorporating an effective amount of phosphorus to cause the formation of 
aluminum silicon magnesium precipitate in a spherical formation. As with 
most aluminum alloys, the primary component of the present invention is 
aluminum. In the present application all percentages are given in terms of 
weight percentages unless otherwise specified. 
The hypoeutectic alloy of the present invention being a hypoeutectic 
includes less than 12% silicon and generally less than 10% silicon. 
Further, the advantages of the present invention are appreciated generally 
only when the silicon content exceeds 4%. At less than 4% the silicon 
magnesium aluminum precipitate simply does not form. 
The alloy or the present invention further includes magnesium and 
specifically less than 1% magnesium. When the magnesium exceeds 1% the 
alloy becomes over modified and very sluggish lacking various mechanical 
properties. Generally there should be at least 0.1% magnesium in order to 
form the magnesium aluminum silicon precipitate and generally 0.15 to 
0.35% magnesium is preferred. 
In order that the aluminum silicon magnesium eutectic forms as a spherical 
precipitate phosphorus must also be added. Generally at least about 0.05% 
phosphorus will be added to the melt. Since phosphorus is unstable most of 
this (about 90%) will burn off leaving about 10% residual phosphorus in 
the alloy. It is important that there not be so much phosphorus that there 
would be an excess of 0.01% residual phosphorus. Residual phosphorus 
refers to phosphorus present in the alloy either part of the aluminum 
magnesium silicon precipitate or the aluminum matrix. Once the residual 
phosphorus content exceeds 0.01 it will actually have an opposite effect 
on the composition interfering with the eutectic formation. Generally it 
is preferred that there be no more than about 0.008% residual phosphorus 
in the casting. Thus the residual content of phosphorus in the casting is 
maintained at about 0.005 to about 0.008%. To accomplish this, generally 
0.05 to about 0.08% phosphorus is added to the initial mixture. 
The alloy of the present invention preferably includes an effective amount 
of nickel which acts much like a plasticizing agent increasing the 
toughness of the formed alloy. Generally this can in present up to about 
0.5% generally from about 0.3% to about 0.5%. 
Accordingly, in a preferred embodiment, the present invention is formed by 
combining the following components 
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Silicon 4.0-5.5% 
Iron .5% Max. 
Magnesium .15-.35% 
Manganese .25% Max. 
Copper .60% Max. 
Zinc .30% Max. 
Nickel .30-.50% 
Lead .1% Max. 
Tin .1% Max. 
Titanium .15% Max. 
Chromium .05% Max. 
Phosphorus .05-.08% 
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with the balance being aluminum. 
The alloy of the present invention is formed by combining all the 
components with the exception of phosphorus. These are melted and mixed in 
an appropriate furnace such as reverberatory furnace or an induction type 
furnace. Once all the components are melted and mixed the pumps or other 
mixing devices are stopped and the phosphorus generally elemental 
phosphorus is added to the melt and mixed with an inert gas such as 
nitrogen. About 90% of the added phosphorus burns off. After an adequate 
mixing time, the melt is tapped and the alloy cast into ingots. Generally 
the alloy is formed at temperatures from about 1300.degree. to about 
1400.degree. F.

EXAMPLE 
In order to compare the alloy of the present invention with commercially 
available 714-214 type alloys, an alloy made according to the present 
invention was formed by combining the following elements 
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Silicon 4.96% 
Magnesium 
.30% 
Iron .43% 
Manganese 
.01% 
Zinc .18% 
Copper .14% 
Nickel .30% 
Phosphorus 
.06% 
Tin .02% 
Lead .01% 
Titanium 
.01% 
Chromium 
.01% 
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This leaves about 0.006% residual phosphorus. The average tensile strength 
of the alloy was 33,600 psi with an average yield strength of 20,300 psi 
and average elongation of 6.0%. This compared to a 714 aluminum alloy 
having an average tensile strength of 32,700 psi, average yield strength 
of 20,300 psi and an average elongation of 6.5%. 
Both the alloy of the present invention and the 714 alloy were subjected to 
a load test (Blade Break Test Propellor). As cast, the 714 alloy withstood 
1210 lbs. and the alloy of the present invention withstood 1230 lbs. After 
3 weeks, the 714 alloy withstood 1950 lbs. whereas the alloy of the 
present invention withstood 2050 lbs. 
An alloy formed according to the present invention has physical 
characteristics comparable to a 714-214 type aluminum alloy, but at the 
same time is less expensive and requires less energy to process. It has a 
casting temperature approximately 200.degree. F. less than the casting 
temperature of a 714 alloy. Further, due to the formation of basically 
spherical aluminum silicon magnesium eutectic, it remains liquid for a 
longer period of time thus allowing for a more uniform filling of a mold. 
Also due to this physical nature, it does not erode the dies as easily as 
a 714 type alloy. 
The above has been a description of how to make and practice the present 
invention along with the description of the preferred embodiment.