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The corrosion behavior of TiC particles reinforced Mg-Al alloy in 3.5% NaCl solution has been evaluated using electrochemical techniques. Tested alloys included an Mg-9Al (Mg AZ91E) alloy with and without 56 wt. % TiC particles. Electrochemical techniques included potentiodynamic polarization curves, linear polarization resistance, electrochemical noise, and electrochemical impedance spectroscopy measurements. All techniques showed that the composite exhibited a lower corrosion rate than the base alloy. Evidence of galvanic effects that increased the composite corrosion rate was found between the matrix and the TiC particles. Additionally, the tendency to suffer from pitting corrosion was higher for the base alloy than that for the composite. Electrochemical impedance results showed the importance of adsorption/diffusion phenomena in both materials.

A transmission electron microscopy (TEM) study was carried out of the heat affected zone (HAZ) of an AISI 304 austenitic stainless steel gas metal arc welded with a magnetic field of 14.7 mT. Thin foils for TEM observation were prepared from the as-received 304 stainless steel and the HAZ of samples welded with and without magnetic field. M 7 C 3 carbides were observed in conventional bright field (BF) and high resolution (HR) confirmed their presence in the as-received stainless steel. Elemental line scans performed in the base metal showed that the austenite/M 7 C 3 interface was Cr-depleted in the austenite side. The results revealed that welding with magnetic field modified the distribution of Cr within the carbides and healed the Cr-depleted zones. This evidence accounts for the enhanced corrosion behaviour previously reported by the authors and strengthens the proposed mechanism where the interaction between the external magnetic field and the magnetic field generated by the direct current of the welding process promotes diffusion of Cr in short distances, healing thus Cr depletion.

CONACYT-Me ´xico for providing his scholarship.

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