Improvements in Aluminium Alloys and in the Method of Casting them.
Year: 1899

page_text: Date of Application, 23rd Oct., 1899-Accepted, 9th Dec., 1899
COMPLETE SPECIFICATION.
Improvements in Aluminium Alloys and in the Method of Casting
them.
We, WILLIAM ALBERT MCADAMS, of No. 281, Clifton Place, in the Borough
of Brooklyn, in the City and State of New York, United States of America,
Manufacturer, and DWIGHT DANA 'BOOK, of No. 149, Cumberland Street, in 'the
Borough of Brooklyn aforesaid, Civil Engineer, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particu-
larly described and ascertained in and by the following statement:-
The invention relates to an improvement in aluminium alloys and the
method of casting them, and more particularly to aluminium alloys in which the
aluminium predominates, and which contain, in addition to the aluminium,
zine or copper, or both, and with or without a small percentage of nickel.
Aluminium, when melted, cools slowly, so slowly that other metals, which are
present, in molten state, in the molten aluminium, are permitted to segregate
and form large crystals before the slowly-cooling aluminium checks to any con-
siderable degree their segregation and crystallization, thereby materially reduc-
ing the strength of the casting.
Furthermore, the zine and copper, because of their greater specific gravity,
have a tendency to fall toward the bottom of the molten mass, and thus render
the casting non-homogeneous.
The object of the present invention is to prevent such segregation, crystalliza-
tion, and lack of homogeneity, in alloys of the above-named character, and
thereby add material strength to the castings.
In an alloy composed of 70% aluminium, 23% zinc, and 7% copper, or an
alloy composed of 66% aluminium, and 33% zinc, or an alloy composed of
90% aluminium and 10%, copper, or similar alloys, with or without a small
percentage of nickel, and in which the aluminium forms a greater part of the
alloy, the hereinabove described segregation and crystallization of the com-
mingled metals will be liable to take place, unless the molten mass is cooled
so rapidly, after pouring, as to check the segregation and crystallization before
it can have proceeded to any great extent.
By means of numerous experiments, we have found that the cooling should
take place rapidly within certain well-defined, practical limits, and that the
heat should be taken from the molten mass at as nearly a uniform rate as
possible.
This may be accomplished, where the casting is thin or small, by using a
metal mould of sufficient thickness to quickly remove the heat from the casting,
and when the casting is to be thick or large, the mould may be surrounded by a
cooling medium to assist it in removing the heat with the required speed and
uniformity.
To carry out the method successfully, assuming the castings to be a sphere one
inch in diameter, the heat should be removed from the casting as rapidly as at
the rate of one fifth of a calorie per second, and, on the other hand, it should

page_text: not be removed more rapidly than at the rate of two calories per second, as,
when removed more rapidly than this rate, the sudden chill is found to produce
the same weak structure that is produced when the heat is removed at a rate less
than one-fifth of a calorie per second. The best results are obtained by removing
the heat at the rate of from one to one and one-tenth calories per second,―a rate
much more rapid than is common in the ordinary use of metallic moulds. In
castings of different weights & forms, a corresponding rate of cooling should be
observed.
We have found that this treatment of aluminium alloys, in which the
aluminium forms the greater part of the alloy, will increase the strength of the
casting from 80 to 100%.
For instance, we have found, by careful experiment, that a bar composed of
aluminium, zinc, and copper, combined in substantially the proportions herein-
above mentioned, viz.: 70% aluminium, 23% zinc, and 7% copper, .968 of a square
inch area, in cross section, cast by the method hereinabove set forth, when
supported upon inverted V edges twelve inches apart, and with the weight
applied by a V edge, midway of its point of support, showed a transverse stress
of 3200 pounds, with a deflection of 21 of an inch under a load of 3200 pounds,
the same bar showing a tensile strength of 39,000 pounds.
A two-inch length of bar, standing, supported a load of 70,000 pounds without
visible deformation, and actually sustained over 98,000 pounds before breaking
with a shearing crack.
We have further found, by careful experiment, that a similar bar of metal
composed of the same material, and in the same proportions, cast as castings are
ordinarily made, and allowed to cool at a rate less than one-fifth of a calorie
per second, showed a transverse stress, under the same conditions as before,
of only 2050 pounds, a deflection of .13 of an inch under load of 1900 pounds,
and a tensile strength of 22,000 pounds.
The same proportionate increase of strength is found by the above method
of casting, in bars which are composed of aluminium and zinc, or aluminium
and copper, as hereinabove recited, as is found in bars composed of aluminium,
zinc, and copper, the tests of which have been particularly mentioned.
The addition of a small percentage of nickel to any of the several alloys
hereinabove mentioned, will have a tendency to make the metal flow more
readily, and enter more completely the small interstices or extremities of the
walls of the mould, and will also tend to increase the malleability of the alloy.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is-
1. The method of casting alloys containing aluminium and zinc, aluminium
and copper, or aluminium, zinc, and copper, either with or without, a small
percentage of nickel, and in which the aluminium predominates, consisting in
rapidly removing the heat from the molten mass at a rate corresponding to not
less than one-fifth of a calorie per second, from a spherical casting one inch in
diameter, riz. more rapidly than has hitherto been common in the ordinary
use of moulds, thereby preventing the segregation of the metals and the forma-
tion of large crystals, substantially as set forth.
2. An aluminium alloy composed of aluminium, zinc, and copper, with or
without a small percentage of nickel, substantially in the proportions of 70%
aluminium, 23% zine, and 7% copper.
Dated this 11th day of October 1899.
NEWTON & SON,
Agents for the Applicants.