Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Heat treatment > The heat treatment of non-ferrous metals and their alloys > The heat treatment of aluminum and its alloys

Research on Al-Zn-Sn Series Anode Materials of Ga, Bi Alloying and Heat Treatment

Author WangGuoWei
Tutor WenJiuBa
School Henan University of Science and Technology
Course Materials Science
Keywords Al-based sacrificial anode material Gallium alloying heat-treatment activation mechenism
CLC TG166.3
Type Master's thesis
Year 2009
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Aluminum base anodes materials have been extensively researched for their advantages of high theoretical capacities, moderately operating potential abundance and accessibility. The research of improving electrochemical properties on Al-Zn-Sn-based anode alloy which current efficiency is just 70%~80% with the methods of micro alloying and heat treatment may developing new aluminum base anodes materials and would provide new options for engineering application. With studies on microstructure and electrochemical process, activation mechanism of aluminum those anode alloys which treated by micro alloying and heat treatment is examined further. And those researches still can enrich materials design and activation mechanism theories of aluminum alloy anode Further.Electrochemical properties of alloying (Gallium) and compound-alloying (Gallium and Bismuth) for Al-Zn-Sn-based anode alloy were researched in this paper. And effects of heat treatment for those Al-Zn-Sn series alloys were still studied. Microstructure was characterized by metallographic microscope, SEM and EDS. And electrochemical reaction process of aluminum base anode after compound alloying and heat treatment still studied by polarization curves and EIS. Activation mechanisms of Al-Zn-Sn micro alloying alloys and synergism relationship of those elements in activation process was analyzed . Differences of microstructure and activation mechanism caused by heat treatments were also examined.The results show that open circuit potential and operating potential shifts negatively, the current efficiency increases drastically, corrosion products does not adhesion as the supplement of gallium(0.01%~0.02%) in Al-Zn-Sn ternary alloy. The Al-Zn-Sn-Ga alloy contenting 0.015% gallium shows best electrochemical performance, which open circuit potential is -1.091V and current efficiency reach 96.4%. The new Al-Zn-Sn-Ga-Bi anode material which has steady operating potential, uniform dissolution, current efficiency of 97.4%, exhibit better properties as Ga and Bi compound alloying. Through analyzing EIS of Al-Zn-Sn series alloys, the corrosive mechanism of Al-Zn-Sn and Al-Zn-Sn-Bi which chief activating elements are Sn or Bi can be characterized by equivalent circuit of RS(CpRp(QR1)(L1Rad1)(L2R ad2)). And equivalent circuit of RS(QR1(C1Rw1)(C2Rw2) (LRad)) can demonstrate activation mechanism of Ga which is chief activation-element in Al-Zn-Sn-Ga and Al-Zn-Sn-Ga-Bi alloys.The heat treatments on new aluminum base anode materials have also been studied. The results show that annealed and solution treatment between 470℃and 530℃cannot markedly improve the electrochemical performances of Al-Zn-Sn-0.01Ga and Al-Zn-Sn-0.02Ga alloys. But Al-Zn-Sn-0.015Ga alloy exhibits better comprehensive properties with negative operating potential, uniform dissolution and high efficiency of more than 95.0%, which treated by annealed at 480℃or solution at 460℃. Al-Zn-Sn-Ga-Bi alloys with solution treatment have high and steady negative operating potential, uniform dissolution which current efficiency decline slightly. Alloy with solid solution at 480℃exhibit optimum comprehensive performance with open circuit potential of -1.071V, operating potential of -1.063V~-1.078V, current efficiency reach 96.6% and dissolution homogeneous.As analyzing,It is believed that corrosion process of Al-Zn-Sn-Ga-Bi alloy is composed of“second-phase priority dissolution”mechanism of segregation phase and“dissolution-deposition”mechanism of chief activation elements(Ga)which solution in matrix. The change of dominant factors in activation process under different treatments led to differences of corrosion appearance. As more second-phase or segregation phase dispersed in cast and annealed alloys, the“second-phase priority dissolution”mechanism of them become control step in electrode reaction, this function cause pit corrosion in-depth development and form localized corrosion morphology. But the“dissolution-deposition”mechanism of Ga becomes a key factor for less second-phase exist in the water cooling matrix, so quenched alloys is homogeneous dissolution, which pitting growth has a suitable ratio between rang enlarging and depth deepening.

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