U.S. patent application number 09/766023 was filed with the patent office on 2002-12-19 for fluxing agent for metal cast joining.
Invention is credited to Gunkel, Ronald W., Meyer, Thomas N., Podey, Larry L..
Application Number | 20020189780 09/766023 |
Document ID | / |
Family ID | 26872986 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020189780 |
Kind Code |
A1 |
Gunkel, Ronald W. ; et
al. |
December 19, 2002 |
FLUXING AGENT FOR METAL CAST JOINING
Abstract
A method of joining an aluminum cast member to an aluminum
component. The method includes the steps of coating a surface of an
aluminum component with flux comprising cesium fluoride, placing
the flux coated component in a mold, filling the mold with molten
aluminum alloy, and allowing the molten aluminum alloy to solidify
thereby joining a cast member to the aluminum component. The flux
preferably includes aluminum fluoride and alumina. A particularly
preferred flux includes about 60 wt. % CsF, about 30 wt. %
AlF.sub.3, and about 10 wt. % Al.sub.2O.sub.3.
Inventors: |
Gunkel, Ronald W.;
(Jacksonville, FL) ; Podey, Larry L.; (Greensburg,
PA) ; Meyer, Thomas N.; (Murrysville, PA) |
Correspondence
Address: |
ALCOA INC
ALCOA TECHNICAL CENTER
100 TECHNICAL DRIVE
ALCOA CENTER
PA
15069-0001
US
|
Family ID: |
26872986 |
Appl. No.: |
09/766023 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60177153 |
Jan 20, 2000 |
|
|
|
Current U.S.
Class: |
164/102 ;
164/75 |
Current CPC
Class: |
B22D 19/0081 20130101;
B22D 19/04 20130101 |
Class at
Publication: |
164/102 ;
164/75 |
International
Class: |
B22D 019/04 |
Goverment Interests
[0002] This invention was made with government support under
Contract No. 86X-SU545C awarded by the Department of Energy. The
government has certain rights in this invention.
Claims
We claim:
1. A method of joining an aluminum cast member to an aluminum
component comprising the steps of: coating a surface of an aluminum
component with flux comprising cesium fluoride; placing the flux
coated component in a mold; filling the mold with molten aluminum
alloy; and allowing the molten aluminum alloy to solidify thereby
joining a cast member to the aluminum component.
2. The method of claim 1 wherein the flux further comprises
aluminum fluoride and alumina.
3. The method of claim 2 wherein the flux comprises about 60 wt. %
CsF, about 30 wt. % AlF.sub.3, and about 10 wt. %
Al.sub.2O.sub.3.
4. The method of claim 1 wherein the surface of the component to be
coated with flux is roughened.
5. The method of claim 1 wherein the aluminum component comprises
an AA 6000 series aluminum alloy.
6. The method of claim 5 wherein the aluminum component comprises
AA 6061.
7. The method of claim 1 wherein the molten aluminum alloy
component comprises a casting alloy comprising Al, Mg and Si.
8. The method of claim 7 wherein the casting alloy comprises AA
A356.
9. The method of claim 1 wherein the aluminum component comprises
an extrusion, a casting or a sheet product.
10. The method of claim 1 wherein the flux is preferably coated on
the surface at a thickness of about 5 to 20 .mu.m.sup.2.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Serial No. 60/177,153 filed Jan. 20, 2000 entitled
"Fluxing Agent for Metal Cast Joining".
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a fluxing agent for a metal
cast/joint, more particularly, to a method for flux joining
aluminum components in a mold.
[0005] 2. Prior Art
[0006] The fabrication of large aluminum structures has
traditionally been in an assembly process wherein an assortment of
parts are joined together by welding, riveting, bolting, adhesive
bonding or the like. Each of these processes are labor intensive
and are often difficult to accomplish for the geometries of certain
components. For example, welding of components to form a large
structure is problematic because the components must be made to
stringent tolerances to ensure proper mating between the
components, machining operations to achieve these tolerances must
be carefully controlled to achieve consistent component fit and
size of the welds. The assembly fixtures, welding power sources and
welding process steps are costly.
[0007] One alternative to assembling numerous parts has been
casting. Casting processes have been developed to reduce costs and
improve repeatability as well as consistency of the assemblies.
Casting processes typically eliminate the number of parts and
reduce the assembly steps of fabricating a large structure.
[0008] Casting of molten metal onto an extruded aluminum member is
disclosed, for example, in U.S. Pat. No. 5,273,099. A flux
including potassium and fluorine is applied to the extruded
aluminum member. Molten aluminum alloy is poured into a mold
containing the flux coated aluminum member. Upon solidification, a
joint forms between the cast aluminum and the flux coated aluminum
member. While potassium and fluoride base fluxes may be used to
cast join aluminum components, the strengths of the bonds between
the components have been insufficient.
[0009] Accordingly, a need remains for a flux for cast joining
aluminum components with a metallurgical bond that has the strength
of a brazed or soldered joint.
SUMMARY OF THE INVENTION
[0010] This need is met by the method of the present invention of
joining an aluminum cast member to an aluminum component. The
method includes the steps of coating a surface of an aluminum
component with flux comprising cesium fluoride, placing the flux
coated component in a mold, filling the mold with molten aluminum
alloy, and allowing the molten aluminum alloy to solidify thereby
joining a cast member to the aluminum component. The flux
preferably includes aluminum fluoride and alumina. A particularly
preferred flux includes about 60 wt. % CsF, about 30 wt. %
AlF.sub.3, and about 10 wt. % Al.sub.2O.sub.3. The flux is
preferably coated on the surface to be joined in a thickness of
about 5 to 20 g/m.sup.2. Prior to placing in a mold, the surface of
the component to be coated with flux is roughened to enhance
adhesion of flux and metal thereto. Components suitable for use
with the present invention include castings, extrusions or sheets
of AA 6000 series wrought aluminum alloys. The molten aluminum
alloy may be an Al--Mg--Si casting aluminum alloy.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The present invention includes a process for joining
aluminum components. This process provides for joining of a
component, such as a cast component (casting), an extruded member
(extrusion) and sheet product, by directly casting a cast member in
place onto the component. A cast joint reduces the cost associated
with producing large aluminum structural assemblies. The components
joined by cast joining may be made to less stringent tolerances,
thereby eliminating the machining operations used to guarantee
consistent fit and welds gaps. Costly assembly fixtures and other
equipment such as welding power sources are not necessary. The
labor of conventional welding processes is greatly reduced. In
addition, the cast joining process of the present invention enables
joints to be formed at locations where welding and other prior
techniques are difficult to achieve.
[0012] The present invention includes the steps of 1) coating at
least one surface of an aluminum alloy component with flux, 2)
placing the flux coated component in a mold, 3) filling the mold
with molten aluminum alloy and 4) allowing the molten metal to
solidify whereby the molten metal solidifies as a casting on the
component. The flux distributes itself closely between the surface
of the component and metal to be joined, typically via capillary
action. The liquidus of the flux is preferably less than the
solidus of the metal of the component being joined. The flux
removes oxides on the surface of the component and oxygen in the
atmosphere adjacent the surfaces being joined. Hence, the flux must
begin to melt at a temperature low enough to minimize oxidation of
the parts, be essentially molten at the time that the molten metal
contacts the component to be joined, flow over both the surface to
be joined and the molten metal to shield the component and the
molten metal from oxidation, penetrate oxide films present on the
component to be joined, and lower the surface tension between the
solid metal of the component and the liquid (molten) metal to
promote wetting.
[0013] The flux used in the present invention is preferably
non-corrosive, non-hygroscopic, and generates minimal fumes during
cast joining. A preferred flux for practicing the method of the
present invention is a cesium fluoride composition. The flux
preferably includes CsF, AlF.sub.3, and Al.sub.2O.sub.3, more
preferably, about 60 wt. % CsF, about 30 wt. % AlF.sub.3, and about
10 wt. % Al.sub.2O.sub.3.
[0014] The flux of the present invention may be provided in a
carrier such as water or alcohol and may be applied by dipping,
brushing, spraying, or the like. The flux is preferably coated on
the surface to be joined in a thickness of about 5 to 20 g/m.sup.2.
Preferably, the surface of the component to be joined is roughened,
such as by shot blasting, glass bead blasting, and cleaning with a
wire brush. The surface may also be cleaned with a mild caustic
etch solution and washed with acetone.
[0015] Components which may be joined via the method of the present
invention may be formed from a metal which has a solidus above the
liquidus of the molten (casting) metal. Suitable metals for the
components to be joined include aluminum alloys such as Aluminum
Association (AA) alloys of the 6000 series, preferably AA 6061. The
solidus of AA 6061 is 1140.degree. F., and the liquidus of AA 6061
is 1205.degree. F. The molten metal may be a casting alloy
containing Al, Mg and Si, preferably AA A356. The solidus of AA
A356 is 1007.degree. F., and the liquidus of A356 is 1135.degree.
F.
[0016] Although the invention has been described generally above,
the particular examples give additional illustration of the product
and process steps typical of the present invention.
EXAMPLES
Example 1
[0017] Extrusions of AA 6061 tube with 1 inch outside diameter and
1/8 inch thick wall were coated with a flux containing about 60 wt.
% CsF, about 30 wt. % AlF.sub.3, and about 10 wt. % Al.sub.2O.sub.3
and placed in sand molds each having a cavity for forming a
circular flange on the extrusion. Molten casting alloy A356 was
injected into the molds and allowed to solidify to form a circular
flange on the exterior of the extrusion. Tensile test evaluations
were made of the joint between each extrusion and flange. The
strength of the cast joints was compared to two flange castings TIG
welded onto an extrusion. The assemblies were bolted to a fixture
on the lower side of a tensile test machine and held in grips on
the upper side of the machine. All assemblies were pulled until
failure. All failures occurred in the extrusion. None of the cast
joints pulled apart. The tensile strength of the extrusion at the
failure was in line with the properties for the welded assemblies
(samples 7 and 8) as set forth in Table 1.
1TABLE 1 Ultimate Tensile Test (Sand Cast Joints) SAMPLE LOAD
(lbs.) AREA (sq. in.) UTS (ksi) UTS (Mpa) 1 4900 0.345 14.26 98.33
2 4872 0.345 14.18 97.77 3 4854 0.345 14.13 97.43 4 4766 0.345
13.87 95.64 5 4736 0.345 13.78 95.02 6 4640 0.345 13.50 93.09 7
(welded) 5540 0.345 16.12 111.15 8 (welded) 7764 0.345 22.60
155.83
[0018] The extrusions of the two welded samples (examples 7 and 8)
exhibited higher ultimate tensile strengths than the extrusions of
the cast joined samples (1-6), and this is believed to be due to
the impact of heat on the extrusion during casting.
Example 2
[0019] An extrusion of 2.5 inches outside diameter AA alloy 6061
with 1/4 inch wall thickness was stainless steel shot-blasted. Flux
containing about 60 wt. % CsF, about 30 wt. % AlF.sub.3, and about
10 wt. % Al.sub.2O.sub.3 was brushed on the extrusion and allowed
to dry. The flux coated extrusion was placed in a permanent mold.
The permanent mold defined a rectangular flange casting cavity
surrounding a cylindrical extrusion. Molten casting alloy A356 was
injected into the mold and allowed to solidify to form a
rectangular flange (6 inches wide, 4.75 inches long, 0.625 inch
thick) on the exterior of the extrusion with a cylindrical section
(0.25 inch thick wall) extending from the rectangular flange and
surrounding the extrusion.
[0020] The dendrite arm spacing (DAS) of two samples each from four
different castings were evaluated. One sample was taken at random
in an area with good metallurgical bond and one sample was taken
from an area with no metallurgical bond. Large DAS (average 27.7
microns) was evident in areas with good metallurgical bonds and
smaller DAS (average 14.8) was found in the areas where there was
no bond as set forth in Table 2. The smallest DAS noted in the
bonded area was 22.67 microns and the largest DAS in a no bond area
was 16.03 microns.
2TABLE 2 Dendrite Arm Spacing vs. Bond or No Bond SAMPLE I.D.
BOND/NO BOND DAS (MICRONS) 920 1 No Bond 16.03 920 3 Bond 32.39 931
2 Bond 27.00 931 3 No Bond 14.01 939 1 No Bond 14.68 939 5 Bond
28.70 954 2 Bond 22.67 954 8 No Bond 14.50
[0021] The solidus and liquidus of both the extrusion alloy and the
casting alloy as well as the melting temperature of the flux are
critical to the cast joining process of the present invention. The
brazing temperature is preferably about 70.degree. F. less than the
solidus temperature of the metal component. For example, the
temperature of an extrusion of AA 6061 should be about 1070.degree.
F. and the temperature of the casting of A356 should be in excess
of 1135.degree. F. for ideal bonding conditions. If the cast metal
is greater than 1140.degree. F., the threat of melting the AA 6061
extrusions exists. The temperature of the molten cast metal lowers
as the molten metal enters and fills the mold. On the other hand,
the temperature of the extrusion increases as the mold is filling.
As the temperature of the cast metal drops, the percentage of solid
increases and if the temperature is too low, no bonding will take
place.
[0022] The amount of flux is also important for achieving good cast
joining. Excess flux results in a line of gas porosity at the
interface between the casting and the extrusion. A flux layer of
about 5-20 g/m.sup.2 thick is preferred. Excess oxygen will consume
the flux, therefore, flux usage may depend to a degree on casting
and mold design. Application of flux to a rough surface finish can
result in excess flux.
[0023] It will be readily appreciated by those skilled in the art
that modifications may be made to the invention without departing
from the concepts disclosed in the foregoing description. Such
modifications are to be considered as included within the following
claims unless the claims, by their language, expressly state
otherwise. Accordingly, the particular embodiments described in
detail herein are illustrative only and are not limiting to the
scope of the invention which is to be given the fall breadth of the
appended claims and any and all equivalents thereof.
* * * * *