Abstract:The microstructure and corrosion behavior of as-cast and friction stir processed in-situ Al-TiB₂ based composite in 3.5 wt.% sodium chloride solution were investigated. The microstructure was characterized using X-ray diffractometry, scanning electron microscopy and electron backscattered diffraction technique while corrosion behavior was evaluated using linear/cyclic potentiodynamic, electrochemical impedance spectroscopy and ASTM–G67 tests. The composite contains sub-micron TiB₂ particles in an aluminum matrix with both blocky and fine clusters of Al₃Ti agglomerated around TiB₂ and displays a low uniform corrosion rate. It is also resistant to pitting as substantiated by the absence of a positive loop in cyclic potentiodynamic tests. This is due to the non-conductive nature of TiB₂ particles and a controlled amount of blocky Al₃Ti phase. However, both friction stir processed and as-cast composites are susceptible to inter-granular corrosion where Al₃Ti and TiB₂ at grain boundaries provide initiation sites for corrosion. Electrochemical impedance study attributes this to the adverse effect of Al₃Ti and TiB₂ on the protective oxide surface film, which increases with immersion time.

Key words: friction stir processing; corrosion behavior; Al composite; electrochemical impedance spectroscopy (EIS)