Effect of samarium in Al-Zn-Cu as a micro-alloying element for low voltage sacrificial anode

Abstract

Development of a low-voltage sacrificial anode for offshore structure has attracted increasing attention in recent years. The low-voltage operation can prevent the structure from overprotection and the resulting stress corrosion cracking. One of the efforts made to create this low-voltage sacrificial anode is by replacing indium as a conventional alloy with other elements such as copper, silicon, or gallium. Previous research showed that copper has the potential for low voltage properties, but the presence of interdendritic corrosion reduces the efficiency of the anode. The addition of samarium is aimed at a grain refinement that is expected to reduce the interdendritic phases’ size and disperses evenly. In this research, Al-Zn-Cu alloy with a variation of samarium composition by 0.1% Sm, 0.3% Sm, and 0.5% Sm was produced and it was followed by characterization which include metallographic test, differential scanning calorimetry, scanning electron microscopy, and energy dispersive spectroscopy. The results showed the dendrite size was reduced, in proportion with the addition of samarium, from 383 μm to 261 μm. Intermetallic Al-Cu-Sm phases were found in many interdendritic areas. Samarium also produced undercooling phenomena during the solidification process. Samarium contents below 0.3% acted as a grain refiner. Above that level, it will transform into a new phase. These findings indicate the Al-Zn-Cu-Sm alloy is a potential alloy to be developed into a low-voltage sacrificial anode.