부산대학교 도서관

The role of ultrasonic melt treatment in improving the corrosion resistance of A356 alloy was investigated. It was confirmedthat ultrasonic melt treatment improved the corrosion resistance of the A356 alloy, using polarization curves and immersiontests in 3.5 wt%NaCl solution. The ultrasonic melt treatment led to four microstructural benefits; (i) refining the primaryα-Al structure, (ii) uniform distribution of eutectic Al–Si, (iii) reducing the formation of intermetallics, and, (iv) uniformdistribution of the solutes within the Al matrix. Kelvin prove force microscope results showed that the uniform distributionof solutes within matrix induced by ultrasonic melt treatment hardly affected the Volta potential of the constituent phases. On the other hand, observation of the corroded surface indicated that ultrasonic melt treatment reduced the formation ofintermetallics, delaying the initial stage of corrosion. In addition, ultrasonic melt treatment suppressed the formation ofcoarse eutectic Si aggregates regions, hindering corrosion propagation that originated in the intermetallics. In summary,the results suggest that the improvement of corrosion resistance by ultrasonic melt treatment can mainly be attributed to areduction in the formation of intermetallics, and the uniform distribution of eutectic Al–Si.