BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a substantially Pb-free aluminum alloy composition,
and method for making said alloy composition, while achieving the machinability characteristics
of their Pb-containing counterparts.
2. Description of Related Art
[0002] Historically Pb-containing aluminum alloys such as 2011 and 6262 (registered with
the Aluminum Association in 1954 and 1960, respectively) have been used for demanding
machinability applications. These applications require an alloy that can be machined
at high material removal rates while maintaining good machined surface finishes and
producing machine chips that are small and easily removed from the work area to prevent
jamming the machine tools. Aluminum alloys containing Pb met this need by providing
intermetallic phases that acted as chip breakers in the material which enabled faster
material removal rates, small machine chips and good machined surfaces. While Pb does
provide an effective solution, it is a heavy metal and considered a hazardous material.
[0003] In an effort to reduce the adverse health effects and environmental risk these alloys
may pose, alternative Pb-free aluminum alloys capable of similar machinability performance
are desired. There have been several attempts at developing free machining / Pb free
alloys over the years including alloys 2012, 2111, 6020 and 6040. These alloys utilized
Bi and / or Sn as a substitute for Pb. While many of these alloys were successful
from a machining chip size and machined surface finish perspective, many producers
of thin wall, complex parts found they could not achieve the material removal rates
that were attained with Pb bearing incumbent alloys because the parts had a tendency
to crack. Many of these alloys were thus taken off the market or customers were cautioned
to limit material removal rates for some applications. This is problematic, considering
many of the applications for the Pb bearing aluminum alloys are sold through distribution
channels so the end machining application was unknown to the material producer.
[0004] In an effort to avoid potential failures as a result of this crack tendency, the
Pb-free alternative alloys that are still available are often restricted in their
availability and often have limits placed on the machining parameters that do not
achieve the same levels of performance as the Pb-containing alternatives. As a result
there is still a market need for a product that meets the machinability characteristics
of the Pb-containing alloys, while also meeting the strength requirements. Typically,
for example, Pb-containing alloy 2011-T3 has a minimum yield strength of 38 KSI /
262 MPa.
BRIEF SUMMARY OF THE INVENTION
[0005] The substantially Pb-free aluminum alloy composition of the present invention provides
a free machining product that achieves the same or superior machining performance
in terms of high material removal rates, machining chip size and machined surface
finish as their incumbent Pb-containing predecessors.
[0006] The substantially Pb-free aluminum alloy composition of the present invention is
not susceptible to cracking in thin wall, complex machining under severe material
removal conditions. This is a critical distinction that has not been achieved in other
inventions attempting to solve the afore-mentioned technical problem. Materials that
are susceptible to such cracking conditions render the machining performance irrelevant
either by requiring substantially lower material removal rates or disqualifying the
material altogether to ensure the integrity of the final part.
[0007] The substantially Pb-free aluminum alloy composition of the present invention substantially
meets or exceeds the material property requirements of the current free machining
materials. Specifically, in a preferred embodiment, the substantially Pb-free aluminum
alloy composition meets the minimum material properties for AA2011-T3 including Ultimate
Tensile Strength ≥ 45.0 KSI / 311 MPa, Yield Strength ≥ 38.0 KSI / 262 MPa, and %
Elongation minimum ≥ 10%.
[0008] The substantially Pb-free aluminum alloy composition comprises, or consists essentially
of, the following components (in weight percent): Si < 0.40; Fe < 0.70; Cu 5.0 - 6.0;
Zn < 0.30; Bi 0.20 - 0.80; Sn 0.10 - 0.50 with the remainder being aluminum and incidental
impurities. In a preferred embodiment, the substantially Pb-free aluminum alloy composition
maintains a Bi/Sn ratio of less than 1.32/1 (in terms of weight percent; 1.32/1 being
the eutectic ratio for Bi-Sn). In addition to this, producing the material in a T8
temper provides specific advantages for machining applications that are sensitive
to machining cracks because of their high material removal rates and thin wall geometries.
Conversely, specific machining applications that are not sensitive to machining cracks
because of more robust part geometries, but which would benefit from even higher material
removal rates can be produced in a T6 temper.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The features and advantages of the present invention will become apparent from the
following detailed description of a preferred embodiment thereof, taken in conjunction
with the accompanying drawings, in which:
FIG. 1 is a schematic showing the operational process sequence for the substantially
Pb-free aluminum alloy composition produced in the various examples in accordance
with the present invention;
FIG. 2 is a conceptual drawing of the representative part used for evaluating machinability
from a chip size perspective of a substantially Pb-free aluminum alloy composition
in accordance with the present invention;
FIG. 3 is a graph showing machinability for alloy / temper combinations evaluated
in Example 1, as measured in chips / gram;
FIG. 4 is a conceptual drawing of the machining crack susceptibility test part;
FIG. 5 shows pictures of observations made from the Machine Crack Susceptibility Test
showing the four classifications used;
FIG. 6 is a graph showing Machining Crack Susceptibility Test results for Example
1 as measured in % with no tears or blowouts;
FIG. 7 is a graph showing Machinability results for Example 2 as measured by chips
/ gram;
FIG. 8 is a graph showing Machining Crack Susceptibility Test results for Example
2 as measured in % with no wrinkles, tears or blowouts;
FIG. 9 is a graph showing machinability results for Example 3 as measured by chips
/ gram;
FIG. 10 is a graph showing machinability results for Example 3 as measured by chips
/ gram for 2.000" diameter rod; and
FIG. 11 is a Bi - Sn Phase Diagram.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The substantially Pb-free aluminum alloy composition comprising, or consists essentially
of, the following components (in weight percent): Si < 0.40; Fe < 0.70; Cu 5.0 - 6.0;
Zn < 0.30; Bi 0.20 - 0.80; Sn 0.10 - 0.50 with the remainder being aluminum and incidental
impurities. In a preferred embodiment, Si, Fe, Cu, Zn, Bi, and Sn are the only components
intentionally added to the alloy composition such that any other material exist only
as incidental impurities. Said incidental impurities are present in a total amount
of less than 1 wt.%, or less than 0.5 wt.%, or less than 0.1 wt.%, or less than 0.05
wt.%. In one embodiment, the substantially Pb-free aluminum alloy composition maintains
a Bi/Sn ratio of less than 1.32/1 (in terms of weight percent; 1.32 being the eutectic
ratio for Bi-Sn).
[0011] Preferably, the substantially Pb-free aluminum alloy composition of the present invention
substantially meets or exceeds the material property requirements of the current free
machining materials. Specifically, in a preferred embodiment, the substantially Pb-free
aluminum alloy composition meets the minimum material properties for AA2011-T3 including
Ultimate Tensile Strength ≥ 45.0 KSI / 311 MPa, Yield Strength ≥ 38.0 KSI / 262 MPa,
and % Elongation minimum ≥ 10%.
[0012] Generally, the phrase "substantially Pb-free" is defined as having no intentional
additions of Pb to the aluminum alloy composition as it is being produced. Preferably,
any Pb that may be contained in the aluminum alloy composition is the result of tramp
contamination. In a preferred embodiment, the aluminum alloy composition of the present
invention contains <0.05 wt.% Pb. In another embodiment, the aluminum alloy composition
of the present invention contains <0.01 wt.% Pb. In another preferred embodiment,
the aluminum alloy composition of the present invention contains <0.005 wt.% Pb. In
another preferred embodiment, the aluminum alloy composition of the present invention
contains ≤0.003 wt.% Pb.
[0013] It is understood that the ranges identified above for the substantially Pb-free aluminum
alloy composition include the upper or lower limits for the element selected and every
numerical range and fraction provided within the range may be considered an upper
or lower limit. For example, it is understood that within the range of Si < 0.40,
the upper or lower limit for Si may be selected from 0.30, 0.25, 0.20, 0.15, and 0.10
wt.%. In one embodiment, the amount of Si ranges from < 0.20 wt.%. In another embodiment,
the amount of Si ranges from <0.16 wt.%. In another embodiment, the amount of Si ranges
from 0.10-0.16 wt.%. For example, it is also understood that within the range of Fe
< 0.70, the upper or lower limit for Fe may be selected from 0.60, 0.50, 0.40, 0.30,
0.20, and 0.10 wt.%. In one embodiment, the amount of Fe ranges from 0.30-0.50 wt.%.
In another embodiment, the amount of Fe ranges from 0.33-0.44 wt.%. For example, it
is also understood that within the range of Cu 5.0 - 6.0, the upper or lower limit
for Cu may be selected from 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, and 5.9. In one
embodiment, the amount of Cu ranges from 5.1-5.8 wt.%. In another embodiment, the
amount of Cu ranges from 5.13-5.63 wt.%. For example, it is also understood that with
the range of Zn < 0.30, the upper or lower limit for Zn may be selected from 0.20,
0.10, 0.05, 0.01, and 0.005 wt.% In one embodiment, the amount of Zn ranges from 0.002-0.05.
In another embodiment, the amount of Zn ranges from 0.002-0.044. For example, it is
also understood that within the range of Bi 0.20 - 0.80, the upper or lower limit
for Bi may be selected from 0.30, 0.40, 0.50, 0.60, and 0.70. In one embodiment, the
amount of Bi ranges from 0.40-0.80. In another embodiment, the amount of Bi ranges
from 0.20-0.40. For example, it is also understood that within the range of Sn 0.10
- 0.50, the upper or lower limit for Sn may be selected from 0.20, 0.30, and 0.40.
In one embodiment, the amount of Sn ranges from 0.20-0.50. Additionally, for example,
it is also understood that within the range of Bi/Sn ratio of less than 1.32/1, the
upper or lower limit for Bi/Sn ratio may be selected from 1.30/1, 1.25/1, 1.20/1,
1.15/1,1.10/1, 1.05/1, 1.00/1, and 0.80/1. In one embodiment, the Bi/Sn ration may
be between 1.32/1-0.80/1. It is further understood that any and all permutations of
the ranges identified above are included within the scope of the present invention.
For example, the substantially Pb-free aluminum alloy composition may consist essentially
of the following components (in weight percent): Si < 0.15; Fe < 0.50; Cu 5.1-5.7;
Zn < 0.05; Bi 0.40 - 0.80; Sn 0.20 - 0.50 with the remainder being aluminum and incidental
impurities, while maintaining a Bi/Sn ratio of less than 1.32/1 (in terms of weight
percent; 1.32/1 being the eutectic ratio for Bi-Sn) or a Bi/Sn ratio from 1.32/1 to
0.80/1, having incidental impurities present in a total amount of less than 1 wt.%,
or less than 0.5 wt.%, or less than 0.1 wt.%, or less than 0.05 wt.%.
[0014] In addition to this, producing the material in a T8 temper provides specific advantages
for machining applications that are sensitive to machining cracks because of their
high material removal rates and thin wall geometries. As such, a free machining, machining
crack insensitive aluminum alloy may be produced. The aluminum alloy product has been
homogenized to improve the recrystallization for improved grain size control. In a
preferred embodiment, the alloy has a Bi/Sn ratio (in weight percent) of less than
1.32/1. In yet another preferred embodiment, the alloy has a Bi/Sn ratio (in weight
percent) ranging from 1.32/1 to 0.8/1. In yet another preferred embodiment, the alloy
has a Bi/Sn ratio (in weight percent) ranging from 1.20/1 to 1/1.
[0015] Conversely, specific machining applications that are not sensitive to machining cracks
because of more robust part geometries, but which would benefit from even higher material
removal rates can be produced in a T6 temper. As such, a superior free machining aluminum
alloy material for applications that do not require machine crack insensitive properties
may be produced. The aluminum alloy product has been homogenized to improve the recrystallization
for improved grain size control. In a preferred embodiment, the alloy has a Bi/Sn
ratio (in weight percent) is less than 1.32/1. In yet another preferred embodiment,
the alloy has a Bi/Sn ratio (in weight percent) ranging from 1.32/1 to 0.8/1. In yet
another preferred embodiment, the alloy has a Bi/Sn ratio (in weight percent) ranging
from 1.20/1 to 1/1.
[0016] It is important to note that the preferred process in accordance with the present
application does not include any naturally aging beyond that which is inherent in
the described processes disclosed herein. Specifically, the present invention does
not include any T3 or T4 naturally aging of the alloy composition.
[0017] Preferred processes for making the alloy composition of the present invention are
similar to the processes described in
US Patent 5,776,269 and
US Patent 5,916,385, the contents of which are expressly incorporated herein by reference. In one embodiment,
the alloy is initially cast into ingots and the ingots homogenized at a temperature
ranging from about 900° to 1170° F for at least 1 hour but generally not more than
24 hours, optionally followed either by fan or air cooling. In one embodiment, the
ingot is soaked at about 1020° F for about 4 hours and then cooled to room temperature.
Next, in one embodiment, the ingots are cut into shorter billets, heated to a temperature
ranging from about 500° to 720° F and then extruded into a desired shape. However,
it should be understood that one of ordinary skill in the art may select different
times and temperatures and still remain within the scope of the present invention.
[0018] In one embodiment, the extruded alloy shapes are then thermomechanically treated
to obtain the desired mechanical and physical properties. For example, to obtain the
mechanical and physical properties of a T8 temper, solution heat treatment is conducted
at a temperature ranging from about 930° to 1030° F, preferably at about 1000° F,
for a time period ranging from about 0.5 to 2 hours, water quenched to room temperature,
cold worked, and artificial aged at a temperature ranging from about 250° to 400°
F for about 2 to 12 hours. However, it should be understood that one of ordinary skill
in the art may select different times, quenching conditions, and temperatures and
still remain within the scope of the present invention.
[0019] In one embodiment, to obtain the properties of a T6 of T6511 temper, prior to extrusion,
the billets are homogenized at a temperature ranging from about 950° to 1050° F and
then extruded to a near desired size. The rod or bar is then straightened using any
known straightening operation such as stress relieved stretching of about 1 to 3 %.
To further improve its physical and mechanical properties, the alloy is heat treated
by precipitation artificial age hardening. Generally, this may be accomplished at
a temperature ranging from about 250° to 400° F for a time period from about 2 to
12 hours. However, it should be understood that one of ordinary skill in the art may
select different times, quenching conditions, and temperatures and still remain within
the scope of the present invention.
[0020] The following examples illustrate various aspects of the invention and are not intended
to limit the scope of the invention.
Example 1:
[0021] Billets were produced in 10 inch (254 mm) diameter with the target compositions found
in Table 1. These billets were extruded and processed into T3, T4, T6 and T8 tempers
using the process parameters shown in FIG.1 to produce 1.000 inch (25.4 mm) diameter
rod. Casting of the billets was done using conventional direct chill casting techniques.
The 6040 alloy variants were produced in both press quenched (T6511 temper) and separate
solution heat treatment (T651 temper) processes. Homogenization, extrusion, solution
heat treatment, quenching, drawing and artificial aging operations were all completed
using typical industry practices. Samples from this material were evaluated for tensile
properties and machinability. The tensile property results are shown in Table 2. The
mechanical property limits for 2011-T3 were used as a minimum acceptable criteria.
These results show that all but BISN-31- T451 materials pass the aluminum association
minimum properties for 2011-T3 (Yield Strength 38.0 KSI / 262 MPa; Ultimate Strength
45.0 KSI / 311 MPa; 10% Elongation).
Table 1: Compositions for Example 1 (weight percent)
Alloy |
Cast |
Si |
Fe |
Cu |
Mn |
Mg |
Zn |
Cr |
Pb |
Bi |
Sn |
Ti |
Zr |
B |
Ni |
BISN-01 |
0969 |
0.11 |
0.36 |
5.22 |
0.00 |
0.00 |
0.044 |
0.020 |
0.001 |
0.40 |
0.35 |
0.020 |
0.003 |
0.001 |
0.00 |
BISN-03 |
0971 |
0.11 |
0.38 |
5.32 |
0.00 |
0.00 |
0.003 |
0.000 |
0.002 |
0.49 |
0.27 |
0.025 |
0.002 |
0.001 |
0.00 |
BISN-31 |
0973 |
0.12 |
0.42 |
5.40 |
0.00 |
0.00 |
0.004 |
0.000 |
0.002 |
0.63 |
0.49 |
0.019 |
0.002 |
0.001 |
0.00 |
BISN-31 |
0975 |
0.12 |
0.39 |
5.47 |
0.00 |
0.00 |
0.003 |
0.000 |
0.002 |
0.60 |
0.42 |
0.022 |
0.002 |
0.001 |
0.00 |
BISN-31 |
0977 |
0.11 |
0.40 |
5.40 |
0.00 |
0.00 |
0.003 |
0.000 |
0.002 |
0.60 |
0.42 |
0.021 |
0.002 |
0.001 |
0.00 |
BISN-04 |
0978 |
0.12 |
0.44 |
5.63 |
0.00 |
0.00 |
0.003 |
0.000 |
0.001 |
0.85 |
0.50 |
0.029 |
0.002 |
0.001 |
0.00 |
BISN-06 |
0979 |
0.13 |
0.40 |
5.16 |
0.00 |
0.00 |
0.002 |
0.000 |
0.001 |
0.57 |
0.45 |
0.024 |
0.002 |
0.000 |
0.00 |
2111-06 |
0981 |
0.12 |
0.35 |
5.37 |
0.00 |
0.00 |
0.003 |
0.000 |
0.001 |
0.64 |
0.20 |
0.025 |
0.002 |
0.000 |
0.00 |
2111-31 |
0983 |
0.12 |
0.33 |
5.13 |
0.00 |
0.00 |
0.003 |
0.000 |
0.001 |
0.56 |
0.20 |
0.023 |
0.002 |
0.001 |
0.00 |
BISN-02 |
0985 |
0.13 |
0.39 |
5.34 |
0.00 |
0.00 |
0.009 |
0.002 |
0.001 |
0.67 |
0.60 |
0.015 |
0.002 |
0.001 |
0.00 |
SNBI-CU |
0986 |
0.11 |
0.36 |
4.36 |
0.00 |
0.00 |
0.003 |
0.000 |
0.001 |
0.59 |
0.41 |
0.023 |
0.002 |
0.002 |
0.00 |
SNBI-NI |
0989 |
0.13 |
0.40 |
5.24 |
0.00 |
0.00 |
0.003 |
0.000 |
0.005 |
0.58 |
0.42 |
0.013 |
0.002 |
0.001 |
1.51 |
TEN604 0 |
40-1 |
0.60 |
0.44 |
0.56 |
0.11 |
0.93 |
0.090 |
0.055 |
0.006 |
0.17 |
0.89 |
0.020 |
0.002 |
0.000 |
0.00 |
LAX604 0 |
0445 |
0.72 |
0.29 |
0.43 |
0.07 |
0.95 |
0.170 |
0.078 |
0.025 |
0.29 |
0.85 |
0.036 |
0.000 |
0.000 |
0.00 |
Table 2: Mechanical Properties of Material Evaluated in Example 1
Lot ID |
Cast # |
Alloy |
Temper |
Yield (KSI/MPa) |
Ultimate (KSI/MPa) |
% Elongation |
299 |
969 |
BISN-01 |
T3 |
45.9 / 317 |
52.3 / 361 |
17.2 |
300 |
985 |
BISN-02 |
T3 |
46.1 / 318 |
52.5 / 363 |
15.0 |
301 |
971 |
BISN-03 |
T3 |
45.3 / 313 |
51.5 / 355 |
16.5 |
302 |
978 |
BISN-04 |
T3 |
46.3 / 319 |
52.6 / 363 |
15.3 |
303 |
975 |
BISN-31 |
T3 |
46.0 / 317 |
52.4 / 362 |
16.5 |
304 |
973 |
BISN-31 |
T451 |
24.5 / 169 |
43.9 / 303 |
33.8 |
306 |
979 |
BISN-06 |
T3 |
44.5 / 307 |
50.2 / 346 |
16.8 |
307 |
983 |
2111-31 |
T3 |
43.8 / 302 |
49.6 / 342 |
17.3 |
308 |
981 |
2111-06 |
T3 |
45.5 / 314 |
51.4 / 355 |
15.8 |
310 |
989 |
BISN-NI |
T3 |
38.9 / 268 |
42.9 / 296 |
13.0 |
311 |
986 |
BISN-CU |
T3 |
40.3 / 278 |
45.1 / 311 |
16.5 |
305 |
977 |
BISN-31 |
T8 |
42.1 / 290 |
55.9 / 386 |
15.2 |
233 |
001 |
2011 |
T3 |
46.8 / 323 |
51.6 / 356 |
15.5 |
312 |
822 |
6040 |
T651 |
44.6 / 308 |
49.3 / 340 |
18.5 |
000 |
000 |
6040 |
T6511 |
52.3 / 361 |
55.6 / 384 |
13.0 |
[0022] Machinability testing was conducted by producing a representative part that utilizes
several machining operations. This part is depicted conceptually in FIG. 2. Material
removal rates were kept constant between materials by keeping the cutting speed and
feed rate constant for all machining operations. The chip size is evaluated by determining
the number of clean, dry chips per gram. The results from this evaluation are shown
in FIG.3 and are compared with current Pb-containing free machining material, 2011-T3,
as a benchmark comparison. This shows that the alloy / temper combinations tested
were better or comparable to the incumbent material. Also tested in this matrix were
Pb-free 6040 compositions that are currently available in the market. These have historically
not performed as well as 2011-T3, and this test validated their inferior performance.
[0023] In order to test that the materials were not susceptible to cracking in thin wall,
severe machining applications, a severe machining test was developed. This involves
drilling out the center of the 1.000" (25.4 mm) rod using 0.969" (24.6 mm) diameter
twist drill, resulting in a 0.015" (0.38 mm) wall thickness, as shown in FIG.4. The
RPM and feed rate was kept constant at 1500 RPMs and 0.035" (1.27 mm) / revolution
feed rate. Once this test was completed, the specimens were examined for conditions
as depicted in FIG. 5. This test was developed for testing the materials susceptibility
to cracking under extreme machining conditions with thin walls, high material removal
rates and high torque applied. This test was replicated a minimum of 12 times for
each material tested that had acceptable performance from a chip size and material
property perspective. The percentage of parts with tears (or cracks) and blowouts
was recorded and the results are shown in FIG. 6. The BISN-31 is designated with the
different tempers (T3, T4 and T8) in this figure for simplification. This shows that
the 2011 (incumbent Pb-containing alloy) consistently passed, as expected, as well
as the Pb-free 6040 alloy variants (note these alloy variants did not perform well
from a chip size perspective, however). The only experimental alloy that passed was
BISN-31-T4, but unfortunately this failed the tensile property requirements.
[0024] Analysis of these results indicates that alloy / temper combinations with lower yield
to ultimate strength ratios perform better from a machining crack susceptibility perspective.
Closer analysis of BISN-01 through BISN-04 compositions indicates that lower Bi+Sn
content and lower Bi/Sn ratios are beneficial from a machining crack susceptibility
perspective when taking into account the severity of the failures. The Bi/Sn ratio
appears to be the stronger influence relative to the composition related performance
input variables. This is illustrated in Table 3. Note that the Bi-Sn eutectic composition
from a weight percent basis is at a ratio of 1.32 Bi/Sn (as shown in FIG. 11).
Table 3: Severity of Machining Crack Susceptibility Results for Alloys BISN-01 through
BISN-04
Alloy |
Bi+Sn |
Bi/Sn |
% Wrinkled |
% Tom |
% Blowout |
BISN-01 |
0.75 |
1.14 |
17% |
77% |
6% |
BISN-02 |
1.27 |
1.12 |
21% |
50% |
29% |
BISN-03 |
0.76 |
1.81 |
7% |
13% |
80% |
BISN-04 |
1.35 |
1.70 |
20% |
20% |
60% |
Example 2:
[0025] Billets were cast in 10" (254 mm) diameter and processed into 1" (25.4 mm) rod using
the process depicted in FIG.1 and the compositions listed in Table 4. The % ROA (reduction
of area) during the drawing operation was evaluated in this study, particularly in
the T3 temper. The effect of homogenization was also evaluated with cast 1110 being
homogenized and compared to the unhomogenized cast 1108. The 1" (25.4 mm) rod was
evaluated for mechanical properties, machinability, and machining crack susceptibility
using the same techniques described in Example 1.
Table 4: Compositions and Tempers for Example 2 (weight percent)
Alloy |
Cast |
Bi |
Sn |
Cu |
Mg |
Fe |
Si |
Ni |
Mn |
Pb |
Cr |
Bi/Sn |
Bi+Sn |
Temper |
% ROA |
BI26 |
1102 |
0.27 |
0.24 |
5.31 |
0.00 |
0.42 |
0.15 |
0.00 |
0.00 |
0.00 |
0.00 |
1.13 |
0.51 |
T3 |
20.3 |
BI26 |
1103 |
0.28 |
0.23 |
5.40 |
0.00 |
0.35 |
0.13 |
0.00 |
0.00 |
0.00 |
0.08 |
1.22 |
0.51 |
T3 |
15.8 |
BI26 |
1104 |
0.27 |
0.24 |
5.35 |
0.00 |
0.36 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.13 |
0.51 |
T3 |
9.3 |
BI26 |
1105 |
0.26 |
0.24 |
5.36 |
0.00 |
0.38 |
0.15 |
0.00 |
0.00 |
0.00 |
0.00 |
1.08 |
0.50 |
T8 |
15.8 |
BI26 |
1106 |
0.26 |
0.24 |
5.34 |
0.00 |
0.35 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.08 |
0.50 |
T651 |
17.4 |
BI39 |
1111 |
0.39 |
0.36 |
5.37 |
0.00 |
0.41 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.08 |
0.75 |
T3 |
20.3 |
BI39 |
1108 |
0.37 |
0.35 |
5.31 |
0.00 |
0.39 |
0.15 |
0.00 |
0.00 |
0.00 |
0.00 |
1.06 |
0.72 |
T3 |
15.8 |
BI39 |
1109 |
0.39 |
0.36 |
5.41 |
0.00 |
0.41 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.08 |
0.75 |
T3 |
9.3 |
BI39 |
1112 |
0.40 |
0.36 |
5.28 |
0.00 |
0.33 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.11 |
0.76 |
T8 |
15.8 |
BI39 |
1113 |
0.40 |
0.36 |
5.24 |
0.00 |
0.40 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.11 |
0.76 |
T651 |
17.4 |
BI39 |
1110 |
0.39 |
0.36 |
5.32 |
0.00 |
0.40 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.08 |
0.75 |
T3 |
15.8 |
BI39MG |
1114 |
0.40 |
0.37 |
5.47 |
0.50 |
0.42 |
0.14 |
0.00 |
0.00 |
0.00 |
0.00 |
1.08 |
0.77 |
T451 |
17.4 |
[0026] The mechanical properties are shown in Table 5. This shows that all of the composition
and temper combinations were capable of achieving the minimum 2011-T3 target mechanical
properties (Yield Strength 38 KSI / 262 MPa; Ultimate Strength 45.0 KSI / 311 MPa;
10% Elongation). The addition of Mg was successful in achieving these properties as
well in the T4 temper.
Table 5: Mechanical Properties of Material Evaluated in Example 2
Lot ID |
Cast # |
Alloy |
% ROA |
Temper |
Yield (KSI/MPa) |
Ultimate (KSI/MPa) |
% Elongation |
338 |
1102 |
BI26 |
20.3 |
T3 |
45.3 / 313 |
50.5 / 348 |
15.0 |
341 |
1103 |
BI26 |
15.8 |
T3 |
43.8 / 302 |
49.8 / 344 |
18.0 |
344 |
1104 |
BI26 |
9.3 |
T3 |
39.8 / 275 |
46.6 / 322 |
18.0 |
345 |
1105 |
BI26 |
15.8 |
T8 |
39.2 / 270 |
53.8 / 371 |
15.0 |
347 |
1106 |
BI26 |
17.4 |
T651 |
40.2 / 277 |
58.8 / 406 |
23.0 |
339 |
1111 |
BI39 |
20.3 |
T3 |
46.9 / 324 |
51.4 / 355 |
14.0 |
342 |
1108 |
BI39 |
15.8 |
T3 |
43.8 / 302 |
49.7 / 343 |
18.5 |
343 |
1109 |
BI39 |
9.3 |
T3 |
38.4 / 265 |
47.1 / 325 |
12.0 |
346 |
1112 |
BI39 |
15.8 |
T8 |
39.2 / 270 |
53.9 / 372 |
14.0 |
348 |
1113 |
BI39 |
17.4 |
T651 |
39.9 / 275 |
57.5 / 397 |
22.0 |
350 |
1110 |
BI39 |
15.8 |
T3 |
43.9 / 303 |
50.3 / 347 |
17.0 |
351 |
1114 |
BI39 |
17.4 |
T451 |
38.7 / 267 |
58.2 / 402 |
20.0 |
[0027] The machinability test, relative to chip size was evaluated with the results depicted
in FIG. 7. These results show that higher Bi+Sn compositions (BI39) perform better
from a machinability perspective, as measured by chips / gram, and perform as good
or better than the incumbent 2011-T3. The lower Bi+Sn compositions (BI26) generally
did not perform as well as the incumbent 2011-T3, but were comparable. It also shows
that there is very little difference on the machinability as related to percent reduction
area for T3 tempers, regardless of Bi+Sn levels. The addition of homogenization did
not improve the machinability, but examination of the grain structure revealed significant
improvement relative to peripheral coarse grain (recrystallized grain size on outer
periphery of the rod). Therefore the use of homogenization, while not necessary for
machinability, may be beneficial for some applications requiring improved surface
appearance (such as parts requiring anodizing). The T651 temper material, regardless
of alloy composition, performed very well, with small chip size. The T8 tempers generally
performed better than the T3 counterparts for a given alloy, particularly the BI26
composition.
[0028] In terms of the machining crack susceptibility test, these results are shown in FIG.8,
in this case, wrinkles on the surface (per FIG.5) were also considered unacceptable.
These results show that while composition BI26 performed significantly better than
BI39 (confirming that higher Bi+Sn makes the material more susceptible to machining
cracks), the temper has a much stronger influence. Note that all of the compositions
in this example had less than 1.32 Bi/Sn ratios. The T8 tempers did not crack in this
test regardless of composition, while the T6 samples performed very poorly. The T3
tempers all had some failures, with the higher Bi+Sn containing materials having significantly
higher failure rates. The BI26-T3 compositions had no failures in terms of tears or
blow-outs per FIG.5, thus the Bi+Sn has a significant impact on performance.
[0029] These results therefore demonstrate that by producing the material in a T8 temper,
higher Bi+Sn levels can be utilized, thus achieving the superior machinability from
a chip size perspective as well.
Example 3:
[0030] Billets were cast in 10" (254 mm) diameter and processed into 1" (25.4 mm) and 2"
(50.8 mm) T3 and T8 rod using the process depicted in FIG. 1 and the compositions
listed in Table 6. The rods were evaluated for mechanical properties, machinability,
and machining crack susceptibility using the same techniques described in Example
1.
Table 6: Compositions and Tempers for Example 3 (weight percent)
Alloy |
Cast |
Si |
Fe |
Cu |
Mn |
Mg |
Zn |
Cr |
Pb |
Bi |
Sn |
Ti |
Bi+Sn |
Bi/Sn |
SN01 |
1172 |
0.16 |
0.45 |
5.76 |
0.03 |
0.00 |
0.00 |
0.00 |
0.002 |
0.25 |
0.21 |
0.009 |
0.46 |
1.21 |
SN01 |
1173 |
0.14 |
0.36 |
5.32 |
0.03 |
0.02 |
0.00 |
0.00 |
0.000 |
0.24 |
0.20 |
0.010 |
0.44 |
1.20 |
SN02 |
1175 |
0.15 |
0.39 |
5.55 |
0.03 |
0.00 |
0.01 |
0.00 |
0.002 |
0.35 |
0.21 |
0.013 |
0.56 |
1.65 |
SN02 |
1176 |
0.15 |
0.36 |
5.25 |
0.03 |
0.02 |
0.00 |
0.06 |
0.002 |
0.34 |
0.19 |
0.010 |
0.53 |
1.83 |
SN03 |
1178 |
0.10 |
0.38 |
5.77 |
0.03 |
0.02 |
0.00 |
0.01 |
0.000 |
0.26 |
0.33 |
0.005 |
0.59 |
0.80 |
SN03 |
1182 |
0.16 |
0.39 |
5.37 |
0.03 |
0.01 |
0.00 |
0.01 |
0.003 |
0.24 |
0.30 |
0.009 |
0.55 |
0.81 |
SN04 |
1180 |
0.15 |
0.36 |
5.35 |
0.03 |
0.02 |
0.00 |
0.00 |
0.002 |
0.35 |
0.35 |
0.006 |
0.70 |
1.00 |
SN04 |
1184 |
0.14 |
0.37 |
5.25 |
0.04 |
0.02 |
0.00 |
0.00 |
0.002 |
0.35 |
0.31 |
0.011 |
0.66 |
1.15 |
[0031] The mechanical properties are shown in Table 7. This shows that all of the composition
and temper combinations were capable of achieving the minimum 2011-T3 target mechanical
properties (Yield Strength 38 KSI / 262 MPa; Ultimate Strength 45.0 KSI / 311 MPa;
10% Elongation).
Table 7: Mechanical Properties of Material Evaluated in Example 3
Alloy / Temper |
Cast |
Lot ID |
Diameter (inch / mm) |
Yield (KSI/MPa) |
Ultimate (KSI/MPa) |
% Elongation |
SN01-T3 |
1172 |
402 |
1.000/25.4 |
45.0 / 311 |
50.4 / 348 |
14.0 |
SN02-T3 |
1175 |
403 |
1.000/25.4 |
44.4 / 306 |
50.3 / 347 |
16.0 |
SN03-T3 |
1182 |
404 |
1.000/25.4 |
44.5 / 307 |
50.7 / 350 |
15.0 |
SN04-T3 |
1184 |
405 |
1.000/25.4 |
43.9 / 303 |
49.6 / 342 |
16.0 |
SN01-T8 |
1173 |
398 |
2.000/50.8 |
44.2 / 305 |
56.6 / 391 |
13.0 |
SN02-T8 |
1175 |
399 |
2.000/50.8 |
42.1 / 290 |
56.2 / 388 |
14.0 |
SN03-T8 |
1182 |
400 |
2.000/50.8 |
43.3 / 299 |
56.8 / 392 |
14.0 |
SN04-T8 |
1184 |
401 |
2.000/50.8 |
44.8 / 309 |
57.2 / 395 |
14.0 |
SN01-T8 |
1172 |
760 |
1.000/25.4 |
42.7 / 295 |
55.8 / 385 |
14.0 |
SN02-T8 |
1176 |
761 |
1.000/25.4 |
45.4 / 313 |
57.3 / 395 |
15.0 |
SN03-T8 |
1178 |
762 |
1.000/25.4 |
41.5 / 286 |
55.3 / 382 |
15.0 |
SN04-T8 |
1180 |
763 |
1.000 / 25.4 |
42.8 / 295 |
55.0 / 380 |
15.0 |
[0032] The machinability test relative to chip size was evaluated with the results depicted
in FIG. 9 for the 1.000" (25.4 mm) diameter material. The results show that the T8
performed superior to the Pb-containing 2011 material, while the T3 material, which
still performed acceptably, was not as good as the Pb-containing 2011 material. The
test was replicated with the 2.000" (50.8 mm) diameter to ensure the material machined
well over a wider range of diameters. While the 2.000" (50.8 mm) diameter results
were slightly worse than the Pb-containing 2011 incumbent material in this test, it
must be noted that from a chips per gram basis, it was better than any of the 1.000"
(25.4 mm) diameter test results. Thus it can be concluded that the material performs
well throughout these diameter ranges.
[0033] Machining crack susceptibility testing was also performed on the 1.000" (25.4 mm)
diameter material considering wrinkles, tears and blow-outs (per FIG. 5) as failures.
The results of this testing are shown in Table 8.
Table 8: Summary of Results for the Machining Crack Susceptibility Testing for 1.000"
(25.4 mm) Diameter Example 3
Alloy |
Temper |
Cast |
Lot ID |
Bi/Sn |
Percent Passing |
SN01 |
T3 |
1172 |
402 |
1.21 |
5% |
SN02 |
T3 |
1176 |
403 |
1.83 |
0% |
SN03 |
T3 |
1178 |
404 |
0.80 |
0% |
SN04 |
T3 |
1180 |
405 |
1.00 |
0% |
SN01 |
T8 |
1172 |
760 |
1.21 |
100% |
SN02 |
T8 |
1176 |
761 |
1.83 |
45% |
SN03 |
T8 |
1178 |
762 |
0.80 |
100% |
SN04 |
T8 |
1180 |
763 |
1.00 |
95% |
[0034] These results confirm that for applications with severe material removal rates and
part geometries with thin walls that are susceptible to tearing, processing the material
in a T8 temper and maintaining Bi/Sn ratios less than 1.32 virtually eliminates this
failure mechanism.
[0035] Although the present invention has been disclosed in terms of a preferred embodiment,
it will be understood that numerous additional modifications and variations could
be made thereto without departing from the scope of the invention as defined by the
following claims:
1. A method for forming an aluminum alloy comprising the steps:
a. casting an alloy billet of an aluminum alloy composition, the composition comprising,
optionally consisting of, the following components (in weight percent of the aluminum
alloy composition):
0-0.10 Pb; Si 0- 0.40; Fe 0- 0.70; Cu 5.0 - 6.0; Zn 0- 0.30; Bi 0.20 - 0.80;
Sn 0.10 - 0.50; with the balance being aluminum save for incidental impurities, said
alloy composition having a ratio by weight of Bi/Sn of less than 1.32/1;
b. optionally homogenizing the cast billet;
c. extruding the cast billet to form an extrusion having a profile shape;
d. solution heat treating the extrusion by heating to a soak temperature between 900-1060
°F (482-571 C) and quenching from the soak temperature to room temperature;
e. cold working the extrusion after step d) via drawing, stretching or rolling to
a minimum of 5% reduction of cross sectional area; and
f. artificial aging the extrusion of step e) to peak hardness using only a T8 or T6
temper to produce said aluminum alloy having an Ultimate Tensile Strength ≥ 45.0 KSI
/ 311 MPa, Yield Strength ≥38.0 KSI / 262 MPa, and % Elongation minimum ≥ 10%.
2. The method of claim 1 wherein
said step of homogenizing the cast billet occurs at a temperature within the range
of 900-1050 °F for a time period of not less than 1 hour; and
said step of solution heat treating the extrusion by heating to a temperature between
900-1060 °F (482-571°C) occurs for 0.5 to 2 hours.
3. A substantially Pb-free aluminum alloy composition comprising, optionally consisting
of, the following components (in weight percent of the aluminum alloy composition):
Pb 0-0.10; Si 0 -0.40; Fe 0-0.70; Cu 5.0 - 6.0; Zn 0-0.30; Bi 0.20-0.80; Sn 0.10 -
0.50; with the balance being aluminum save for incidental impurities;
said alloy composition having a ratio by weight of Bi/1 Sn of less than 1.32/1
said alloy composition manufactured using only artificial aging at a T8 or T6 temper
to provide an alloy composition having an Ultimate Tensile Strength ≥ 45.0 KSI / 311
MPa, Yield Strength ≥ 38.0 KSI / 262 MPa, and % Elongation minimum ≥ 10%.
4. The method or composition of any one of claims 1 to 3 wherein said aluminum alloy
composition has <0.05 wt. % Pb.
5. The method or composition of any one of claims 1 to 4 wherein said aluminum alloy
composition comprises 0.10-0.16 wt. % Si.
6. The method or composition of any one of claims 1 to 5 wherein said aluminum alloy
composition comprises 0.30-0.50 wt. % Fe.
7. The method or composition of any one of claims 1 to 6 wherein said aluminum alloy
composition comprises 5.1-5.8 wt. % Cu.
8. The method or composition of any one of claims 1 to 7 wherein said aluminum alloy
composition comprises 0.002-0.05 wt. % Zn.
9. The method or composition of any one of claims 1 to 8 wherein said aluminum alloy
composition comprises 0.20-0.40 wt. % Bi.
10. The method or composition of any one of claims 1 to 9 wherein said aluminum alloy
composition comprises 0.20-0.50 wt. % Sn.
11. The method or composition of any one of claims 1 to 4 wherein said aluminum alloy
compositions comprising, optionally consisting of, the following components (in percent
(weight / weight) of the aluminum alloy composition):
Si 0-0.16; Fe 0-0.50; Cu 5.1-5.8; Zn 0- 0.05; Bi 0.20 - 0.40; and Sn 0.20 - 0.50.
12. The method or composition of any one of claims 1 to 11 wherein said aluminum alloy
composition has a ratio by weight of Bi/Sn in the range from 1.32/1 to 0.8/1.
13. The method or composition of any one of claims 1 to 12 wherein said incidental impurities
are present in a total amount of less than 0.5 wt. %.
14. The method or composition of any one of claims 1-13, wherein said artificial aging
includes a T8 temper.
15. The method or composition of any one of claims 1-14, wherein said aluminum alloy is
not subjected to a T3 or T4 temper.