Study On The Thermodynamics, Crystallization And Corrosion Behaviors Of Al-based Amorphous Alloys

In this thesis, the amorphous forming ability (AFA) of Al-Ni-La, Al-Ni-La-Cu, and Al-Ni-La-Zr systems was evaluated, and the amorphous ribbons of these three alloys were prepared by melt-spinning (MS) method. The thermodynamics of the amorphous ribbons was investigated by the differential thermal analysis methods, i.e., DSC and DTA, and the effects of the additions of Cu and Zr and their content on the thermodynamics behavior and AFA of the Al-Ni-La system were discussed. The crystallization process of the Al88-xNi6La6Cux(X=0,2) was studied. Furthermore, the corrosion behaviors of the three alloy systems were studied by the electrochemistry method, focusing on the effects of crystallization and the addition elements of Cu and Zr on the corrosion behavior of Al-Ni-La based amorphous alloy. The results indicated that the amorphous ribbon of Al₈₈Ni₆La₆ exhibits a glass transition and two-step crystallization. The glass transition occurs at the temperature of 224°C, and the first step crystallization occurs at 233°C, and the second step crystallization occurs at 333°C, and the crystallization products are determined to be Al, Al3Ni and Al11La3 phases. The additions of Cu and Zr have obvious influence on the AFA and thermodynamic behaviors of Al-Ni-La system. Adding 2at.% Cu to the Al₈₈Ni₆La₆ can slightly promote the crystallization temperature of the amorphous alloy. The alloy with 2at.% Cu addition exhibits no obvious glass transition and more complicated crystallization process. Zr addition can also promote the AFA and thermal stability of Al86Ni9La5 amorphous alloy. However, when the content of Zr is over 5at.%, the AFA of the alloys will decrease. The corrosion behavior of the amorphous alloys is strongly dependent on the crystallization extent. Partially crystallized Al₈₈Ni₆La₆ alloy exhibits improved corrosion resistance in 0.01mol·L-1 NaCl alkaline solution in comparison to the fully amorphous alloy. While partially crystallized Al86Ni6La6Cu2 alloy exhibits lower corrosion resistance than that of the fully amorphous alloy. Full crystallization deteriorates the corrosion behavior of these two alloys. The composition has an important influence on the corrosion behavior of the amorphous alloy. The addition Cu to Al₈₈Ni₆La₆ can promote the formation of the passivation film on the surface of the alloy, resulting in the improvement of the corrosion resistance of the alloy, and by changing the crystallization products, Cu addition can change the corrosion behavior of the partially crystallized Al86Ni6La6. Zr addition to Al-Ni-La can improve the corrosion behavior of the alloy, and with the increase of Zr content, the corrosion resistance of the alloy increases in 0.01 mol·L-1NaCl alkaline solution.