Final report

Material 
Phase 1 Hardness 
Incoming Material 
(pre anneal) 
Phase 2 
Hardness RTS 
(post anneal) 
Copper-Plated Zinc (Incumbent Material) 
N/A 
62–72 
Aluminized Steel (Ryerson) 
N/A* 
83 
Aluminized Steel (Atlas) 
N/A* 
74 
Aluminum-Magnesium (Al-Mg) Alloy 5052-H32 
N/A* 
70 
Copper-Plated Steel – JZP 
N/A** 
61 
Copper-Plated Steel – Royal Mint 
N/A** 
78 
302HQ Stainless Steel 
82 
73 
430 Stainless Steel 
N/A* 
83 
* Material supplied as strip, but not annealed for these tests. 
** Material supplied as RTS planchet; therefore, no annealing required. 
Table 2-3. 
Rockwell 15T Hardness for 5-Cent Coin Alternative Material Candidates 
Material 
Phase 1 
Hardness 
Incoming 
Material 
(pre anneal) 
Phase 2 
Hardness 
RTS 
(post anneal) 
Cupronickel (Incumbent Material) 
88 
60–69 
Dura-White-Plated Zinc 
N/A** 
69.5 
Multi-Ply-Plated Steel (Lot # 11-137) 
N/A** 
65.5 
Multi-Ply-Plated Steel (Lot # 11-170) 
N/A** 
65 
Nickel-Plated Steel 
N/A** 
75 
G6 Mod 
88.5 
69 
302HQ Stainless Steel (Blanked at CTC) 
82 
77 
302HQ Stainless Steel (Blanked at Carpenter Technology) 
82 
74 
430 Stainless Steel 
N/A* 
87.5 
669z 
90 
73.5 
Nickel-Plated 31157 
N/A* 
71 
Unplated 31157 
N/A* 
68 
* Material supplied as strip, but not annealed for these tests. 
** Material supplied as RTS planchet; therefore, no annealing required. 
43 

Table 2-4. 
Rockwell 15T Hardness for Quarter Dollar Coin Alternative Material Candidates 
Material 
Phase 1 Hardness 
Incoming 
Materials 
(pre anneal) 
Phase 2 
Hardness 
RTS 
(post anneal) 
Cupronickel-Clad C110 (Incumbent Material) 
83 
50–60 
Multi-Ply-Plated Steel 
N/A** 
65 
Nickel-Plated Steel 
N/A** 
77.5 
669z-Clad C110 
87.5 
45 
302HQ Stainless Steel 
N/A* 
73.5 
Dura-White-Plated Zinc 
N/A** 
66.5 
* Material supplied as strip, but not annealed for these tests. 
** Material supplied as RTS planchet; therefore, no annealing required. 
2.4.1.2  Tensile Properties 
Tensile properties for incoming materials delivered in sheet or strip form are shown in Tables 2-5 
through 2-7; tensile tests were not performed on material received as planchets.  As mentioned 
above, the primary purpose of these measurements was to more fully characterize the incoming 
materials. 
From the results of these tensile tests, there does not seem to be a direct correlation between 
tensile properties and coining performance, particularly since these properties were measured in 
the as-delivered state, without heat treatments or further preparations for producing RTS 
planchets. 
x   Yield strength represents the point at which a material begins to deform plastically (0.2% 
plastic offset), measured in thousands of pounds of force applied per square inch of cross 
section of material (ksi).
46 
x   Ultimate tensile strength (UTS) is the maximum load per initial unit area (ksi) that the 
material can withstand before fracture. 
x   Elongation measures how much the material stretches plastically before breaking.  It is 
measured in percentage, which refers to the ratio of the extension (i.e., the linear amount 
that the specimen was stretched) divided by the original length of the unloaded specimen. 
x   Young’s Modulus is a measure of material stiffness and is measured in millions of pounds 
per square inch (Msi). 
46 
Pascals are used to measure load per unit in the metric system.  1 Pascal  = 0.000145037 psi. 
44  

Table 2-5. 
Tensile Properties of One-Cent Coin Alternative Material Candidates 
Material 
Tensile Properties 
Yield 
Strength 
(ksi) 
UTS 
(ksi) 
Elongation 
(%) 
Young’s 
Modulus 
(Msi) 
Copper-Plated Zinc (Incumbent Material) 
22 
26 
80 
10 
Aluminized Steel (Ryerson) 
52 
62 
27 
37 
Aluminized Steel (Atlas) 
29 
49 
37 
13 
Al-Mg Alloy 5052-H32 
25 
36 
11 
11 
Copper-Plated Steel 
N/A 
N/A 
N/A 
N/A 
302HQ Stainless Steel 
N/A* 
N/A 
N/A 
N/A 
430 Stainless Steel 
47 
73 
32 
45 
*See 5-cent coin alternative material candidates result below.  
Table 2-6. 
Tensile Properties of 5-Cent Coin Alternative Material Candidates  
Material 
Tensile Properties 
Yield 
Strength 
(ksi) 
UTS 
(ksi) 
Elongation 
(%) 
Young’s 
Modulus 
(Msi) 
Cupronickel (Incumbent Material) 
95 
96 
2.5 
32 
Dura-White-Plated Zinc 
N/A 
N/A 
N/A 
N/A 
Multi-Ply-Plated Steel (Lot # 11-137) 
N/A 
N/A 
N/A 
N/A 
Multi-Ply-Plated Steel (Lot # 11-170) 
N/A 
N/A 
N/A 
N/A 
Nickel-Plated Steel 
N/A 
N/A 
N/A 
N/A 
G6 Mod 
122 
126 
3.5 
23 
302HQ Stainless Steel 
35.5 
83.5 
43.5 
33 
430 Stainless Steel 
56.5 
86.5 
27 
32 
669z 
112 
112 
3 
25 
31157 (Plated and Unplated) 
N/A 
N/A 
N/A 
N/A 
45  

Table 2-7. 
Tensile Properties of Quarter Dollar Coin Alternative Material Candidates 
Material 
Tensile Properties 
Yield 
Strength 
(ksi) 
UTS 
(ksi) 
Elongation 
(%) 
Young’s 
Modulus 
(Msi) 
Cupronickel-Clad C110 (Incumbent 
Material) 
64.5 
65.5 
5.3 
26 
Multi-Ply-Plated Steel 
N/A 
N/A 
N/A 
N/A 
Nickel-Plated Steel 
N/A 
N/A 
N/A 
N/A 
669z-Clad C110 
74.3 
74.5 
3 
29 
302HQ Stainless Steel 
N/A 
N/A 
N/A 
N/A 
Dura-White-Plated Zinc 
N/A 
N/A 
N/A 
N/A 
2.4.1.3  Steam Corrosion Testing 
Steam corrosion tests results from Phases 1, 2 and 4 are shown in Tables 2-8 through 2-11.  The 
test values represent the total change of the color of the material surface in three-dimensional (3­
D) CIE Lab space after 2 hours of exposure to low-pressure steam.  The International 
Commission on Illumination (CIE) established the first scientific system for defining color in 
1931 [6].  The modified version of this system, CIE Lab, is still considered the best quantitative 
definition of perceived color.  Three values are measured:  “L” represents the lightness of the 
color; “a” the degree to which a color is more red or more green; and “b” the degree of 
yellowness versus blueness.  “L” can only take positive values; “a” is positive for red colors and 
negative for green colors; and “b” is positive for yellow colors and negative for blue colors.  The 
3-D Lab number can be treated as a vector which points to a specific color.  Determining the 
‘total color vector change’ provides a single number that represents the magnitude of color 
change.  The total color vector change was used to define the color change resulting from 
corrosion during the steam corrosion tests.  The details of how the color changes are less 
important than identifying the magnitude of any change in color. 
Higher ‘total color vector change’ numbers, as shown in Tables 2-8 through 2-11, represent larger 
changes in visual appearance.  Previous United States Mint studies have shown that Phase 1 total 
color vector change numbers are better predicators of color change during circulation and Phase 2 
and Phase 4 total color vector change numbers are indicative of blank/planchet finishing 
effectiveness in maintaining a consistent workpiece color.
47 
As indicated in Tables 2-9 and 2-10, the three copper alloys (G6 mod, 669z and unplated 31157) 
have a greater total color vector change than the incumbent cupronickel alloy.  This suggests that 
these alloys may undergo greater discoloration during circulation. 
47 
This information was received from a United States Mint engineer in approximately March 2012. 
46  

Table 2-11 includes results for dollar coin alternative materials.  These materials were not 
subjected to the full range of tests in this study; only their corrosion performance and color values 
were measured.  Of these potential materials, only 88Cu-12Sn-plated zinc is not significantly 
worse in color change resulting from the two-hour steam corrosion tests. 
RTS planchets are treated with chemicals designed to protect the surface and provide some 
lubrication during striking.  As a result, these product forms are expected to show less color 
change than untreated materials.  Prior to testing, incoming materials were lightly sanded 
according to United States Mint Steam Corrosion Test Protocol (using 1200-grit silicon carbide 
paper), to remove any surface treatments and provide a measurement of the inherent corrosion 
behavior of a given material. 
Appendix 2-D contains pictures of incoming candidate material and RTS planchets after steam 
corrosion testing.  Appendix 2-E contains pictures of nonsense pieces before and after steam 
corrosion testing.  It is very difficult to show the subtle color shifts typical of this test in 
photographs; however, the relative magnitude of the sensitivity of these materials to steam 
corrosion can be easily seen from the photographs by comparing the results of several different 
alloys. 
Table 2-8. 
Steam Corrosion Color Change of One-Cent Coin Alternative Material Candidates 
Material 
Phase 1 Steam 
Corrosion 
Incoming Material 
Phase 2 Steam 
Corrosion 
RTS 
Phase 4 Steam 
Corrosion 
as Struck 
Total Color Vector 
Change 
Total Color 
Vector Change 
Total Color 
Vector Change 
Copper-Plated Zinc (Incumbent 
Material) 
N/A 
5.5 
6.6 
Aluminized Steel (Ryerson) 
13.7 
N/A* 
10 
Aluminized Steel (Atlas) 
14 
N/A* 
7.7 
Al-Mg Alloy 5052-H32 
2.5 
2.6 
4.9 
Copper-Plated Steel – JZP 
N/A** 
16.3 
14.9 
Copper-Plated Steel – RM 
N/A** 
5.7 
6.5 
302HQ Stainless Steel 
8.4 
3.5 
2.8 
430 Stainless Steel 
1.3 
1.3 
N/A*** 
* Materials were not processed further for striking.  RTS results are equivalent to “Incoming Material” results.  
** Supplied as RTS planchets.  
*** Material did not feed through the press during striking trials at the United States Mint.  Therefore, no 430 
stainless steel one-cent nonsense pieces were available for subsequent evaluations.  
47  

Table 2-9. 
Steam Corrosion Color Change of 5-Cent Coin Alternative Material Candidates 
Material 
Phase 1 Steam 
Corrosion 
Incoming 
Material 
Phase 2 Steam 
Corrosion 
RTS 
Phase 4 Steam 
Corrosion 
as Struck 
Total Color Vector 
Change 
Total Color 
Vector Change 
Total Color 
Vector Change 
Cupronickel (Incumbent Material) 
19 
4.7 
4.4 
Dura-White-Plated Zinc 
N/A* 
1.0 
2.7 
Multi-Ply-Plated Steel (Lot # 11-137) 
N/A* 
2.3 
0.9 
Multi-Ply-Plated Steel (Lot # 11-170) 
N/A* 
3.4 
0.7 
Nickel-Plated Steel 
4.2 
3.9 
3.3 
G6 Mod 
33 
5.9 
7.1 
302HQ Stainless Steel 
8.4 
3.5 
0.8 
430 Stainless Steel 
8.0 
1.2 
0.4 
669z 
34.5 
8.7 
6 
Nickel-Plated 31157 
N/A* 
0.5 
0.7 
Unplated 31157 
25.5 
12 
5.5 
* 
Supplied as RTS planchets. 
Table 2-10.  
Steam Corrosion Color Change of Quarter Dollar Coin Alternative Material 
Candidates 
Material 
Phase 1 Steam 
Corrosion 
Incoming Material 
Phase 2 Steam 
Corrosion 
RTS 
Phase 4 Steam 
Corrosion 
as Struck 
Total Color Vector 
Change 
Total Color 
Vector Change 
Total Color 
Vector Change 
Cupronickel-Clad C110 (Incumbent 
Material) 
21.5 
8.5 
4.5 
Multi-Ply-Plated Steel 
N/A* 
4.2 
2.4 
Nickel-Plated Steel 
4.1 
2.1 
3.3 
669z-Clad C110 
34.5 
8.7 
4.8 
302HQ Stainless Steel 
** 
** 
4.4 
Dura-White-Plated Zinc 
** 
** 
1.8 
* Supplied as RTS planchets.  
** See results under 5-cent coin alternative material candidates table.  
48 

Table 2-11. 
Steam Corrosion Color Change of Dollar Coin Alternative Material Candidates 
Material 
Phase 1 Steam 
Corrosion 
Incoming Material 
Phase 2 Steam 
Corrosion 
RTS 
Total Color Vector 
Change 
Total Color 
Vector Change 
Manganese Brass-Clad C110 (Incumbent 
Material) 
14.5 
4 
88Cu-12Sn-Plated Zinc 
14 
4.2 
C69250 
39 
5.7 
K474 
37 
7.0 
2.4.1.4  Eddy Current Electrical Conductivity 
Eddy current electrical conductivity
48 
measurements from Phases 1 and 2 are reported in Tables 2­
12 through 2-14.  These measurements were conducted over a range of frequencies.  The highest 
and lowest frequency values are reported in the tables. 
x   At high frequencies (e.g., 960 kilohertz [kHz]), the input signal is quickly absorbed by the 
test material.  Therefore, under these frequencies, the test method is sensitive only to the 
materials near the surface of a specimen.  Conversely, at low frequencies (e.g., 60 kHz), 
the signal passes further into the specimen allowing for the determination of the materials 
below the surface (i.e., at the core) of a test specimen. 
49 
The standard eddy current 
measurements cannot be directly correlated with coin-processing equipment performance.  
Each model of coin-processing equipment must be tested using established and proprietary 
test methods developed by each coin-processing equipment manufacturer.  However, if 
eddy current electrical conductivity values across the frequency spectrum are similar for 
two materials, it is likely that they will be recognized as the same material by those 
sensors that rely upon electrical conductivity.  Note that no standard exists among coin-
processing equipment manufacturers relative to frequency; each manufacturer relies upon 
its own frequency (or frequencies).  The 60 to 960 kHz frequency range approximately 
covers the full range of values used among the many coin-processing equipment 
manufacturers that fabricate and/or market their products within the US.  There is further 
discussion of coin-processing technology in the Outreach Chapter. 
x   In order for any material to be recognized by current coin-processing equipment, an 
alternative material must have a stable and detectable electrical conductivity signature.  A 
value of ‘F’ in Tables 2-12 through 2-14 signifies that the instrument could not determine 
48 
Electrical conductivity is given as percentage of the International Annealed Copper Standard (%IACS) electrical 
conductivity of pure copper at 20 degree Celsius (°C).  In other words, %IACS is a ratio (expressed as a percentage) 
of the electrical conductivity of a given material to that of pure copper at 20 °C.
49 
This difference in response to different frequencies, and the corresponding ability to predict the surface material 
from that of the core of a coin, is important in modern coin-processing technology.  It points to the increased security 
inherent in clad coins (and plated coins to a lesser degree).  Note that the specific frequencies used and signal 
processing algorithms applied varies with each coin-processing equipment manufacturer.  Electrical conductivity 
performance across a range of frequencies is therefore important for each of the alternative material candidates. 
49  

an electrical conductivity value, indicating that the material was ferromagnetic.
50 
These 
materials create a signature that is so far removed from those of incumbent US circulating 
coins that some coin-processing equipment would not identify coins made from these 
materials.  When this occurs, coins cannot be validated, which significantly reduces the 
security of coins.  For example, 430 stainless steel would not be recognizable to some of 
the coin-processing equipment currently fielded in the US. 
x  As-received materials were tested.  In addition, the electrical conductivity for RTS 
planchets was also measured for each of the alternative material candidates.  Since little or 
no difference was seen between the two measurements for any given alternative material 
candidate, it is clear that the blanking, annealing, cleaning, drying and upsetting processes 
(necessary for materials received as sheet) did not impact the electrical conductivity of 
these candidate materials. 
Table 2-12. 
Electrical Conductivity for One-Cent Coin Alternative Material Candidates 
Material 
Phase 1 Electrical 
Conductivity 
Incoming Material 
Phase 2 Electrical 
Conductivity 
RTS 
%IACS 
%IACS 
Test Frequency 
60 kHz 
960 kHz 
60 kHz 
960 kHz 
Copper-Plated Zinc (Incumbent Material) 
N/A 
N/A 
28 
29.5 
Aluminized Steel (Ryerson) 
F 
1.1 
F 
1.1 
Aluminized Steel (Atlas) 
F 
1.4 
F 
1.4 
Al-Mg Alloy 5052-H32 
35 
35.5 
35 
35.5 
Copper-Plated Steel – JZP 
N/A 
N/A 
0.3 
11.5 
Copper-Plated Steel – RM 
N/A 
N/A 
0.5 
9.1 
302HQ Stainless Steel 
1.6 
2.3 
1.6 
2.3 
430 Stainless Steel 
F 
F 
F 
F 
50 
A ferromagnetic material is attracted to a magnetic. 
50 

Table 2-13. 
Electrical Conductivity for 5-Cent Coin Alternative Material Candidates 
Material 
Phase 1 Electrical 
Conductivity 
Incoming Material 
Phase 2 Electrical 
Conductivity 
RTS 
%IACS 
%IACS 
Test Frequency 
60 kHz 
960 kHz 
60 kHz 
960 kHz 
Cupronickel (Incumbent Material) 
N/A 
N/A 
5.1 
5.5 
Dura-White-Plated Zinc 
N/A 
N/A 
28.4 
29.0 
Multi-Ply-Plated Steel (Lot # 11-137) 
N/A 
N/A 
0.3 
13.8 
Multi-Ply-Plated Steel (Lot # 11-170) 
N/A 
N/A 
0.7 
9.5 
Nickel-Plated Steel 
N/A 
N/A 
F 
0.8 
G6 Mod 
5.3 
6.4 
5.3 
6.4 
302 Stainless Steel 
1.6 
2.3 
1.6 
2.3 
430 Stainless Steel 
F 
F 
F 
F 
669z 
5.45 
5.8 
5.4 
5.8 
Nickel-Plated 31157 
N/A 
N/A 
4.8 
5.2 
Unplated 31157 
N/A 
N/A 
5.4 
5.5 
Table 2-14. 
Electrical Conductivity for Quarter Dollar Coin Alternative Material Candidates 
Material 
Phase 1 Electrical 
Conductivity 
Incoming Material 
Phase 2 Electrical 
Conductivity 
RTS 
%IACS 
%IACS 
Test Frequency 
60 kHz 
960 kHz 
60 kHz 
960 kHz 
Cupronickel-Clad C110 (Incumbent Material) 
N/A 
N/A 
81 
10 
Multi-Ply Plated Steel 
N/A 
N/A 
0.3 
12.7 
Nickel-Plated Steel 
N/A 
N/A 
F 
0.7 
669z-Clad C110 
79.5 
10 
79.5 
10 
302HQ Stainless Steel 
1.6 
2.3 
1.6 
2.3 
Dura-White-Plated Zinc 
N/A 
N/A 
28.7 
31.6 
51  

2.4.1.5  Color Measurement 
Color measurements were performed in Phase 2 on cleaned materials in the RTS state, as shown 
in Tables 2-15 through 2-18.  The spectrophotometer provides three values in the CIE Lab color 
space. 
x  The “L” value represents relative ‘lightness’, with 0 representing pitch black and 100 
bright white. 
x  Positive “a” values correspond to red colors, while negative values represent green colors. 
x  Positive “b” values correspond to yellow colors, while negative values indicate blue 
colors. 
Coppery colors, such as those of a newly minted incumbent one-cent coin, have positive “a” and 
“b” values.  Yellow colors have low “a” and positive “b”, and white colors have low “a” and “b” 
values. 
Table 2-15. 
Color Measurement of One-Cent Coin Alternative Material Candidates 
Material 
Color Measurement – CIE 
L 
a 
b 
Copper-Plated Zinc (Incumbent Material) 
78.3 
13.6 
17.1 
Aluminized Steel (Ryerson) 
77.0 
0.02 
1.1 
Aluminized Steel (Atlas) 
83.2 
–0.02 
0.6 
Al-Mg Alloy 5052-H32 
87.5 
–1.2 
1.5 
Copper-Plated Steel – JZP 
81.5 
15.8 
19.1 
Copper-Plated Steel – RM 
83.7 
15.2 
19.0 
302HQ Stainless Steel 
72.1 
0.9 
4.9 
430 Stainless Steel 
76.2 
0.2 
1.5 
52  

Table 2-16. 
Color Measurement of 5-Cent Coin Alternative Material Candidates