Investigation of corrosion resistance AZ۶۳-۱.۵lanthanides in seawater solution

In spite of its impressive corrosion resistance, AZ۶۳ alloys cannot satisfy the increasing demandsfor higher corrosion resistance, especially for long-term submersion in seawater [۱-۳]. Rare elements can dramatically increase corrosion resistance in AZ۶۳ alloys. In this study, corrosion resistance of AZ۶۳-۱.۵% mischmetal RE elements (AZ۶۳-۱.۵RE) is compared with the AZ۶۳alloy. The self-corrosion process involves both alloys being more corrosion prone at the beginning,and then gradually decreasing as immersion continues (Fig. ۱). Corrosion rates of AZ۶۳ and AZ۶۳-۱.۵RE alloys are ۰.۰۵۴ and ۰.۰۴۲ mg cm‒۲ h‒۱, respectively. Thus, chemical corrosion resistance of AZ۶۳-۱.۵RE is higher than that of AZ۶۳ alloy. As a result of the addition of %۱.۵RE, the OCP value shifted to a more negative value (from ‒۱.۵۰۹ to ‒۱.۵۳۶ V vs SCE) (Fig. ۲a). The ۱.۵%REalloy has lower anodic Tafel slope (۰.۰۳۸ mV dec‒۱) and the lower current corrosion (۰.۲۶ mA cm-۲), therefore it has the lowest corrosion polarization (۵۱.۹۰ Ω cm۲). The EIS plots (Fig. ۲b) show that with an Rct of ۲۹۸ Ω cm۲ and an Rl of ۱۸۰ Ω cm۲, the as-cast alloy has an Rp of ۱۱۲.۲۲ Ω cm۲.The addition of RE helps in increasing the corrosion resistance of the alloy by formation of rod like Al–RE phases. The Al-RE phase acts as a corrosion resistant phase and forms before thesolidification of β and α phase, therefore reducing the amount of Al available for β formation and it acts as a nucleating agent, which leads to grain refinement.

کلیدواژه ها:

Magnesium Alloy ، Corrosion ، Self-corrosion ، Anode