**3. Corrosion behavior of Aluminum metal matrix composites**

The corrosion behaviour of alloys in sea water 3.5 Wt % NaCl represents an adequate measure of its corrosion resistance. Important results of corrosion studies undertaken in the last decade would be discussed under the following categories.


Alloy Designation Toughness Value

The strains to failure (%) for different Al2O3 reinforcement are shown in Table 4 Strain to

Al 6061 29.26

Table 4. Strain to failure of Alloy Al 6061 with increasing volume fractions (Dehlan and

Al MMC are finding increasing applications as rotor material in automotive brake systems (Shorowords et al., 2004). Effect of Studies on the effect of sliding velocity on wear friction and tribochemistry of MMC reinforced with 13% SiC or B4C have shown that sliding velocity leads to lower wear rates and lowers friction coefficient for both MMCs.. Studies on interaction between MMC and phenolic brake pads showed that the transfer layer consisting of phenolic pad material acted as a protective layer and reduced wear rates and coefficient of friction. Honda has used aluminum metal matrix cylinder liners in some of their engines

The effect of cutting speed on tool wear has been investigated. The cutting tool wear increased with increased reinforcement ratios. At constant speed and feed rate, the lowest wear rate has been found in 5 Wt % SiC (p) and the highest wear with 15 Wt % SiCp

From the above description, it may be concluded that the development of MMC has been a big breakthrough in search for stiff high strength materials for aerospace and automotive industry particularly. Whereas the mechanical properties of MMC have remained the focus of attention, the work on corrosion behavior of MMC did not proceed hand in hand with the mechanical and tribological properties. The work on corrosion was undertaken the last decade and a considerable progress has been made in the understanding of corrosion

The corrosion behaviour of alloys in sea water 3.5 Wt % NaCl represents an adequate measure of its corrosion resistance. Important results of corrosion studies undertaken in the

Al 6061 / 10 vol.% Al2O3 4.72 Al 6061 / 20 vol.% Al2O3 2.29 Al 6061 / 30 vol% Al2O3 1.42

Vf % Percent strain to failure (Ef)mm/mn\*100

Al2009/ SiC/15(%) W (T 8) 51 mpa √m Al6061 – 40% SiC(p) 122 mpa √m Al6013-29SIC(p) 19.5 KSi√2

Table 3. Fracture toughness of selected MMCS

including B2lAl and H23A, F20 C and F22C.

increased cutting speed increased the tool wear rate.

behaviour of metal matrix composites in recent years.

**3. Corrosion behavior of Aluminum metal matrix composites** 

last decade would be discussed under the following categories.

Syed, 2006)

failure decreases with increase of volume fraction of reinforcement.

e. Corrosion mechanism

## **3.1 Immersion & long term exposure studies**

The above studies were conducted in accordance with ASTM designation G 31 – 72 (ASTM, 2004). The results of studies on Al6092 – T6, Al/*B*4C/20P, Al 6092 – T6 /2oSiC(p), and 6092 – T6 20vol%Al2O3 and monolithic 6061-T6 Al, immersed for 90 days in air exposed 0.5 Na2SO4 solution, 3.5 wt% NaCl, ASTM sea water and real sea water were recently described (Hongho et al. 2009). In alloy 6092 – T6 Al/B 4C/20P MMC specimen in ASTM Sea water bubbles were observed. The current over most of the area was found to be anodic. The solution at the anode site was found to be acidic (PH 6.4). Corrosion products were formed as observe after monitoring for three days and the area became more alkaline (PH 8.4). A similar phenomena occurred with alloy 6092 reinforced with 20 Vol. % SiC (p) and gradually the alkalinity increased because of its change of area from and anodic to cathodic. The corrosion rates of MMCS in sea water and ASTM sea water were lower than those in 0.5 M Na2SO4 and 3.5 wt % NaCl. The rates of monolithic 6061 – T6 Al in both real and ASTM sea water were significantly lower than those in 3.5 wt % NaCl. The surface morphology after the test showed similar general features, one major feature of the surface morphology was the presence of intermetallic precipitates on the surface. The EDS studies suggested these precipitates to contain Al, Mg, O, and C. Mg and HCO3 irons as the main species corrosion products.

The formation of precipitates is a greater concern in MMC, as localised corrosion is controlled by the formation of such precipitates. The role of precipitates would be discussed in the relevant section of the paper. In general the corrosion rate of Al MMC decreased with time due to the formation of precipitates.
