Improved Corrosion Resistance of 5XXX Aluminum Alloy by Homogenization Heat Treatment

The corrosion resistance of homogenized Al-Mg (6.5%) alloy-adding Si, Zn, Mn, and Fe (0.2%) to improve various properties-was observed. Differential scanning calorimetry (DSC) and a JMatPro simulation revealed that the optimal homogenization temperature was 450 degrees C. The homogenization was carried out at 450 degrees C for 3, 6, 12, 18, 24, and 30 h in order to view the corrosion resistance change. Corrosion resistance was analyzed by a polarization test in 3.5 wt % NaCl solution. The corrosion resistance improved with increasing homogenization time up to 24 h, but there was no change with longer time periods. To observe the reason for the change in corrosion resistance, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDS) analyses were performed. Precipitates containing Mg, such as Al3Mg2 and Mg-32(Al, Zn)(49), decreased at the grain boundary. After homogenization, the amount of Mg measured by SEM-EDS at the grain boundary decreased from 36% to 8%, while Si increased. Generally, the potential difference between the grain boundary and the grains leads to intergranular corrosion. Reduction of Mg, whose standard electrode potential is lower than that of Al, and an increase of Si, which is present in higher concentration than Al at the grain boundaries, improved the corrosion resistance of 5XXX Al alloy by reducing the intergranular corrosion.