EFFECT OF MINORITY ALLOYING ELEMENTS Zn AND Zr ON THE CORROSION BEHAVIOR OF AMORPHOUS ALLOYS ALCUMG(Zn) AND ALCUMG(Zr) AND THEIR NANOCRYSTALLINE ANALOGUES

Rapidly solidified ribbons based on Al74Cu16Mg16 alloy were produced by Chill Block Melt Spinning (CBMS) method. In order to obtaine a crystalline structure the rapidly solidified ribbons were annealed in Ar atmosphere. The amorphous and nanocrystalline structure was confirmed by XRD and TEM analyzes. The effect of minority alloying elements Zn and Zr on the corrosion behavior of rapidly solidified Al74Cu16Mg16 alloy in amorphous and nanocrystalline analogues was studied. Gravimetric tests for general corrosion at 25 degrees C and at 50 degrees C in environment of 3.5% NaCl are carried out. At 25 degrees C the corrosion rate of amorphous alloys was found to be 1.5 to 4 times lower than the rate of their crystalline analogues. The effect of amorphous - nanocrystalline structure transformation on the corrosion rate at 50 degrees C is negative and most significant in the Zn-containing alloy. Electrochemical tests for general and local corrosion in 3.5% NaCl environment were performed and the galvanic mechanism of local corrosion in alloys was explained. The main reason for the registered enhanced local corrosion in the crystalline alloys is the chemical and structural inhomogeneity due to the presence of the active intermetallic phases Al2CuMg, Al-2(Cu,Zn), Al3Zr4 in the aluminum matrix. The influence of the surface irregularity, of the structure of the layer of corrosion products deposited on the metal surface and of the annealing for the transformation of the amorphous structure on the corrosion behavior of the alloys are discussed.