Name

mechatronics, group 27

Report on „Mechanical deformation and recrystallization of metals”.

1. The aim of the experiment.

On March 19^th we conducted an experiment which aim was to determine the dependence of deformation scale on the grain size after recrystallization of aluminum. Such experiment allows people to examine changes that happens in metal after recrystallization: change of grain size, material’s hardness, strength, plasticity etc.

Recrystallization in metallurgy can be defined as the temperature at which destroyed grains of a crystal structure are replaced by the new strain free grains.

1. Experiment course.

We had six aluminum samples of the same gauge length (l₀ = 50 mm). We deformed each of them with a special device and then had to check the final gauge length l.

We put deformed samples into the furnace (T ≈ 500˚) for 30 minutes in the air atmosphere.

Then, we cooled the samples and they were chemically etched to reveal the aluminum microstructure (grains boundaries). We used the reagent of such a composition: 9 parts of HCl, 3 parts of HNO₃, 2 parts of HF and 5 parts of H₂O

Then, we were divided into pairs and estimated number of grains on 1 cm² on each sample. At the end we prepared a table with the data collected.

1. Results comparison.

No	l0 [mm]	l [mm]	Strain ε [%]	x	d [mm^2]
1.	50	51	2	16	6.25
2.		52	4	35	2.86
3.		53.5	7	140	0.71
4.		56	12	300	0.34
5.		58.5	17	500	0.20
6.		59.4	18.8	800	0.125

x - number of grains within the test area of 1 cm²

d – average grain size

Annealing temperature/time [˚C/min] was in each case 500/30

We calculated the strain using the formula: $\varepsilon = 100*\frac{(l - l_{0})}{l_{0}}$

To calculate average grain size, we use a formula: $d = \frac{100}{x}$

We got the similar graph to the one that we were shown during the classes.

(grain size/deformation level graph)

As we were told before, there were also other factors involved in this process, such as temperature and annealing time. The grain size after recrystallization depends on many factors like: prior deformation level, annealing temperature, annealing time. The average grain surface size decreases with the level of deformation. From this it is possible to get some conclusions plasticity or strength of material. Deformation affects the final grain size. Increasing the deformation, or reducing the deformation temperature, increases the rate of nucleation faster than it increases the rate of growth. As a result the final grain size is reduced by increased deformation.