الفهرس 
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Abstract
Aluminum Galvalum III anodes are widely used as sacrificial anodes to protect steel structures from corrosion like different types of tanks, vessels and pipelines onshore and offshore steel structure. It is required to replace these anodes after consumption so the plant should be out of service (Shut down) to replace these anodes which has great economic impact.
This research aims to improve the efficiency of Aluminum anodes galvalum III and get higher electrical energy (Current capacity) from the anodes to be utilized for longer time without replacement.
Four Galvalum III specimens were produced with different Tin concentrations (0%, 0.01%,
0.05% and 0.1%).
Heat treatment was carried out by heating to homogenization temperature 510 ᵒC for enough time (5 hours). After homogenize, samples were annealed by slow cooling in furnace and other samples were quenched by rapid cooling to room temperature in water bath.
All investigated alloys as cast, Annealed and Quenched were subjected to electrochemical Tests (Weight loss Method and Tafel slope polarization test). Current capacity and efficiency were calculated using NACE Standard TM0190-2012. Polarization test (Tafel slope) is carried out according to ASTM G 59 – 97 (Reapproved 2003) to calculate the corrosion rate for each anode individually.
Electrochemical tests show the following results:
Adding 0.1 % Tin (Sn) to Galvalum III anode enhance the current capacity of as received aluminum Galvalum III anode and raise it from 2232 A.hr/Kg to 2343 A.hr/Kg.
Current capacity of re-melted Galvalum III anode increases with increasing Tin (Sn)
concentration from 2016 A.hr/Kg for 0% Sn to 2343 A.hr/Kg for 0.1% Sn
Corrosion rate of Galvalum III anodes is decreased from 0.21 mm/year to 0.15 mm/year after adding 0.1% Tin (Sn) which means lower self-corrosion with adding Tin.
Quenched condition alloys show higher current capacity and efficiency in comparison with as cast and Annealed condition in most cases.
Corrosion rate of as cast Galvalum III anode is decreased from 0.15 mm/year to 0.003 mm/year after carrying out annealing heat treatment and from 0.15 mm/year to 0.005 mm/year after carrying out water Quenched heat treatment which means lower self- corrosion for anodes after heat treatment.
Quenched condition for 0.01% Tin (Sn) gives higher current capacity (2729 A.hr/Kg) and this value is higher than as received Galvalum III anode with 22 %.
All specimens examined with SEM and EDX analysis showed that Zn is dissolved in Al matrix and form solid solution and this comply with Al-Zn phase diagram and also comply with hume rothery theory.
The result of microstructure investigation shows the presence of Intermetallic compounds (second phase precipitates) which may be responsible for the behavior of investigated alloys. These intermetallic compounds form local corrosion cells between these intermetallic compound and Aluminum-Zinc matrix which allow for matrix to corrode and give current for protection.
When as-cast anode is homogenized by heating at 510 °C for 5 h, the existing precipitates in the as-cast anode are allowed to diffuse away from grain boundaries and achieve better distribution through aluminum matrix which maintain uniform corrosion through the matrix instead of localized corrosion at the segregated location at grain boundaries.
The indium and Tin achieve super saturation in aluminum as water quenched following the homogenizing treatment. This homogenization improves the current efficiency by reducing the possibility of forming local action cells as a result of precipitation and micro segregation of indium and Tin.