Role of Ultrasonic Melt Treatment in the Improvement of Corrosion Resistance of Al-7Si-0.4Mg Cast Alloy

초록

The role of ultrasonic melt treatment in improving the corrosion resistance of A356 alloy was investigated. It was confirmed that ultrasonic melt treatment improved the corrosion resistance of the A356 alloy, using polarization curves and immersion tests in 3.5 wt%NaCl solution. The ultrasonic melt treatment led to four microstructural benefits; (i) refining the primary alpha-Al structure, (ii) uniform distribution of eutectic Al-Si, (iii) reducing the formation of intermetallics, and, (iv) uniform distribution of the solutes within the Al matrix. Kelvin prove force microscope results showed that the uniform distribution of 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 of intermetallics, delaying the initial stage of corrosion. In addition, ultrasonic melt treatment suppressed the formation of coarse 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 a reduction in the formation of intermetallics, and the uniform distribution of eutectic Al-Si. [GRAPHICS] .

키워드