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Fig. 2. Hardness of Al-Cu with different TiB2 contents after aged for 48 hours
Fig. 2 above shows the age hardening response of the base Al-6Cu alloy and its composites. It is clearly evident from the figure that the peak hardness for Al-6Cu, Al-6Cu-3wt.%TiB2 and Al-6Cu-6wt.%TiB2 were reached at 30, 30 and 5 hours, respectively. The figure also shows that the peak hardness increases with increasing reinforcement TiB2 content (wt.%). The hardness of Al-6Cu alloy increases from 170 Hv in the base alloy to 188 Hv for the 6TiB2 composite at optimum peak. Thus, the TiB2 particles not only increase the hardness but also enhance the aging kinetics of Al-6Cu alloy.
3.3 Corrosion Characterization
Polarization is the displacement of an electrode potential from its equilibrium value and the magnitude of this displacement is the overvoltage which is expressed in terms of plus or minus volts (or mV) relative to the equilibrium potential. Potentiostatic polarization can be used to calculate the electrochemical parameters. Anodic and cathodic polarized potentials were measured to a reference sample and Al-Cu alloys in 0.1 M HCl solution in current density range of 2 to 6 mA/cm2 as shown in Figure 3. The electrochemical parameters; corrosion potential (Ecorr), corrosion current (Icorr) and corrosion current density (in nm/s) were calculated from Figure 3 and summarized in Table 2. Corrosion potential decreases with increasing the TiB2 content in the alloys. The corrosion current decreases with increasing the TiB2 content reaching a minimum at 3 wt. %TiB2 and then begin to increase with increasing the TiB2 content.
Table 2. Electrochemical parameters for Al-Cu with different TiB2 alloys in 0.1 M HCl solution
TiB2 [%] Ecorr [mV] Icorr [mA/cm²] CR [mm/y]
0 -568.0 1.942 22.50
3 -566.0 1.39 16.15
6 -574.9 5.06 58.7
Fig. 3. Anodic and cathodic polarized curves of Al-6wt.%Cu alloys and Al-6wt.%Cu-TiB2 in 0.5 M NaCl solution
The corrosion current and corrosion rate show an optimal value at 3 wt. %TiB2. Addition of TiB2 has a positive influence on the corrosion resistance in Al. This behavior can be attributed to the positive influence of TiB2 addition on the grain size refinement. The fine grained materials have a more advantageous behavior with respect to corrosion and oxidation have been approved .
From Figure 3 above, Al-6wt.%Cu alloy with 3wt.%TiB2 showed the best corrosion resistance compare to other composition of TiB2. The value of corrosion rate at 3 wt.% TiB2 was 16.15 x 10-3 mm/y, then decrease to 58.8 x 10-3 mm/y for Al-Cu with 6wt.%TiB2. The susceptibility of the Al-Cu alloys towards corrosion decreases in the order of:
Al-Cu-3wt.%TiB2> Al-Cu> Al-Cu-6 wt%TiB2 (2)
The lowest value of corrosion rate exhibit the alloy has a good property to withstand the corrosion.
From the research, we can conclude several conclusions which are;
In-situ Al-Cu alloy composites containing different weight fractions of particles of TiB2 phase were synthesized successfully by the salt-metal reaction method and the particles were distributed evenly in the matrix of the composites.
The susceptibility of the Al-Cu alloys towards corrosion decreases in the order of: Al-Cu-3wt.%TiB2> Al-Cu> Al-Cu-6 wt%TiB2.
The composition of 3wt.%TiB2 gave the best corrosion rate compare to cast Al-Cu alloy which were 16.15 and 22.50 x 10-3 mm/y.
This work was financially supported by FRGS from Ministry of Education (MOHE), Malaysia and Faculty of Applied Sciences UiTM, Shah Alam, Selangor.
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