Prakt. Met. Sonderband 46 (2014) 249 
porous large preparations consisted of mechanical wet grinding down to 5 pm with SiC and polishing 
ing selective with aluminum oxide suspension (0,05 um). 
oO nitrogen or 
y dispersion 
nal oxidation 
cess can be 
3s containing 
indaries and 
g a very high 
ree of plastic 
ssure torsion 
an especially 
g processing 
e die [6,7,8]. 
al properties 
inalysis and 
al on 10 was Fig. 1: Schematic illustration of the ECAP process and the microstructure before (a) and 
not yet been after (b) deformation. 
> mechanism 
articles with 3. RESULTS AND DISCUSSION 
After internal oxidation of non-deformed sample we obtained IOZ with fine dispersed oxide 
particles (Figure 2a, Area 1). The core of the sample (Figure 2a, Area 2) remained a one 
phase Cu-0.4%Al solid solution with slightly increased grains as a consequence of grain 
coarsening at higher temperatures. Contrary to this, in the 10Z precipitated oxide particles 
section of 10 hindered the process of grain growth. The internal oxidation front (IOF) is straight because 
casting and of the diffusion of oxygen through the volume of the grains, which prevailed against 
diffusion along the grain boundaries. The mean width of the 10Z was 2650 um. 
meters were During the process, oxygen atoms penetrate into the Cu matrix where they react with 
ad. The tool aluminium. The critical concentration of oxygen for this chemical reaction is very low 
that meet at because of the very high negative free energy of Al oxide formation. Afterwards the 
deformed by 1 ; Al203 2 max : 
) metric tons solubility product for the oxide (Kp? = Ca C5) is exceeded by the fine oxide particles 
> using route precipitated from the solid solution [9]. Figures 2b and 2c show Al,O3 particles at the IOF 
vith motor oil and in the I0Z near the free surface of the billet. The particles at the IOF have different 
with starting shapes, from spherical to rod-like, while the particles in the I0Z near the free surface of 
the billet have a spherical shape. The mean size of the particles increases with the depth 
ing direction of the 10Z from 50 nm near the free surface (Figure 2c) to 300 nm at IOF (Figure 2b). The 
xidized. The increase in the mean size of the Al,O; particles with increasing depth of 10Z is a 
er metal and consequence of the hindered diffusion of oxygen to the IOF that stimulates contra diffusion 
, 60min and of the alloying element Al down the concentration gradient towards the IOF. At lower 
composition depths of the IOZ the influence of oxide particles on the diffusion of oxygen is negligible. 
xygen in the Moreover, with increasing depth of 10Z the velocity of oxygen diffusion decreases because 
of the numerous obstacles - oxide particles. Consequently, there is more time at the IOF 
ection of the for growing the precipitated oxide particles [4]. 
nethods and 
)as analysed 
etallographic