COLD WORKING OF NON-FERROUS METALS
INTRODUCTION:
When crystalline solids are subjected to loads there is a tendency (on the atomic scale)
to pull the material apart. Very strong bonds (ionic and covalent) will tend to cleave and fall
apart, while metallic bonds will slip along a preferred slip plane in a preferred slip direction.
Dislocations allow the slip phenomena to occur, but during plastic deformation, the dislocation
density increases which frequently results in a stronger material. Deformation by dislocation is
one of the characteristics of metals that make them the most useful of engineering materials.
In the manufacturing of many metal items, the thickness of as-cast ingots is reduced to
workable sizes by a process known as rolling. Cold rolling is a mechanical deformation process
where the thickness of a metal is reduced by the compressive force exerted by two rotating
rolls. Cold rolling differs from hot rolling in that no external heat is applied to the metals or the
rolling equipment during the rolling process.
OBJECTIVE:
1. To investigate how the hardness and ductility of a pure as well as an alloyed non-ferrous
metal changes as it is cold worked.
2. To relate differences in physical properties with microstructure.
3. To learn how to measure hardness with a Rockwell hardness tester.
EQUIPMENT:
Rolling mill, Rockwell hardness Tester, micrometer, strips of annealed copper and brass.
PROCEDURE:
1. Carefully measure and record the initial thickness of the metal strips to the nearest
.001” using the micrometers.
2. Determine the hardness of the metals by taking the average of three Rockwell “A”
hardness readings. Record this value next to the measured thickness. Be sure to check
with the instructor or lab technician on the proper use of the hardness testers if you are
unsure of their operation.
3. Cut off one small sample of each metal, approximately 1/4” long and keep it to the side
for a future laboratory experiment.
4. Cold roll the strips approximately 5% reduction in thickness and again, determine the
average hardness values. Record the thickness of each strip as well as the hardness.
5. Continue reducing the thickness by approximately 5% per rolling pass until 30%
reduction has been achieved. Record the actual thickness and hardness after each
rolling sequence.
Note: Cut-off and save ¼” long samples of both materials after the rolling operation
corresponding to 20% reduction.
6. Increase the reduction per pass to 10% and record thickness as well as hardness values
until 70% reduction is achieved.
Again, cut-off and save ¼” long samples of both materials after the rolling pass
corresponding to 40% and 60% reduction.
RESULTS:
Prepare graphs of the data obtained from the experiment with the hardness values on
the y-axis, and the corresponding total percent reduction on the x-axis. Provide appropriate
labels for the axes, as well as a title for each graph. Do NOT use “Hardness vs. % Reduction” as
a title.
 original _ thickness  final _ thickness 
  100%
Total _ % _ reduction  
original _ thickness


Also, compare the ductility of copper versus brass based on calculations of the
maximum reduction observed for each of the metals.
CONCLUSIONS:
Think about the following questions while you are formulating your conclusions.
Answer the questions in the ‘Discussion’ section of the report.
 Why are the graphs shaped this way? How has the microstructure of the
samples been altered during the rolling sequence? Where have you seen a
similar graph with respect to metallic samples?
 If the temperature of the materials was raised or lowered significantly during the
experiment, would we get the same results?
 How can the difference in ductility between the metals be explained?
 Given that the atomic radius of a copper atom is 0.128 nm, while an atom of zinc
has a radius of 0.137 nm, do you think the brass alloy is an interstitial or
substitutional alloy?
 Do you think all metals behave in a similar manner as the non-ferrous samples
used in this lab?
 Is there an easy way to convert from hardness to strength? Show an example if
you can locate one.
 What other material properties have been affected by the rolling process?
COLD WORKING OF NON-FERROUS METALS
Addendum
If time permits, additional rolling may be done on the metal samples until a point where
the ductility reaches a maximum value. Prior to this, a thermal process known as annealing
may be carried out to alleviate some or all of the lattice strain caused by cold working.
In the second part of this lab, some of the metal strips will be annealed before further
reduction is applied. In the case of annealing, recrystallization takes place, and depending on
the length of time at temperature, grain growth will also occur. Once the metal is fully
recrystallized, we have a “fully annealed structure”.
PROCEDURE:
1. Roll both strips until the thickness is approximately .040” and record hardness values as
previously done.
2. Anneal one pair of samples (copper and brass) and record the hardness.
3. Combine the annealed and as-rolled samples from two lab groups and continue rolling.
4. Observe the structure of the metal for any changes, and note what changes occur at
different thickness readings.
RESULTS:


Continue the comparison of ductility of copper and brass with regard to
annealed vs. non-annealed samples.
Once a metal has been annealed, the percent reduction is effectively at zero.
Based on this, is there a trend that can be established for total % reduction for
the anneal-roll sequences of brass?
CONCLUSIONS:
 Is cold-work a reversible process? How can you tell?
 What properties were ‘restored’ during the annealing operation?
 If annealing allows the metal to be reduced further, at what percent reduction
would you recommend the brass and copper be annealed? Why? What
manufacturing concept needs to be balanced here?
 Why did annealing discolor the metals? How might this be prevented?