Lyacine RABAHI

’évolution de la concentration des défauts ponctuels en fonction de la température et de la composition d’alliage a été étudié en utilisant le model de Wagner-shottky. L’interaction entre les différents défauts doubles et triples dans les phases de Laves du system Fe-Zr, a été prise en compte dans l’approximation de Bragg-Williams.

The microstructure and texture evolution of an AZ31 alloy were investigated after hot rolling and subsequentannealing using electron backscatter diffraction (EBSD). First, the alloy was hot-rolled at 350 ? C up to low,medium and high strain (20, 50 and 85% of thickness reduction, respectively). The alloy samples where thenannealed at 350 ? C for 2, 10 and 60 min. The effect of strain level and annealing on corrosion behavior inseawater was also evaluated using electrochemical tests. At low strain, the microstructure was characterised bythe absence of twinning, mainly due to the prior thermo-mechanical history of the as-received alloy. However,various modes of twinning were observed at medium strain. At high strain, the dynamic recrystallization processresulted in a microstructure with a typical basal texture. The results demonstrate that twins are responsible forthe deviation of {0002} basal poles from normal towards the transversal direction. Annealing at 350 ? C for up to60 min led to normal grain growth in all the samples. In medium and highly strained samples, the deformationtexture was retained, while the low strain sample underwent noticeable changes due to the absence of dynamicrecrystallization. A synergetic effect of grain refinement and texture weakening was responsible for the alloy’senhanced corrosion resistance.AZ31 alloyCorrosionDynamic recrystallizationStatic recrystallizationRolling

The corrosion behaviour of Mg-0.3Ce, Mg-0.41Dy, Mg-0.63Gd, Mg-1.44Nd and Mg-1.43La (wt.%) alloys in3.5 wt% NaCl solution was investigated using electrochemical tests. The as-cast microstructures of theMg-RE alloys were characterized by the presence of second phases (MgxCe, Mg41Dy5 , Mg12Gd, Mg12Nd, Mg41Nd5, Mg24Nd and Mg12La) with different volume fraction and distribution. Results show that thecorrosion mechanism was altered from uniform to localized corrosion mechanism depending on thespecific RE alloying elements. The corrosion resistance of the Mg-RE alloys is increasing in the followingorder: Mg-1.43La, Mg-1.44Nd, Mg-0.3Ce, Mg-0.63Gd and Mg-0.41Dy. Accordingly, the corrosionmorphology in the best resistant Mg-0.41Dy alloy and the worst Mg-1.43La alloy were observed andcompared after 2h and 24 h of immersion using SEM-EDS, XPS and XRD analysis. The formation of theDy 2 O 3 oxide prevents the Mg-0.41Dy alloy from pitting corrosion and lead to an excellent corrosionsurface even after 24 h of immersion. Meanwhile, the presence of a high fraction of the Mg 12 La phasealong the grains boundaries in the Mg-1.43La alloy causes severe pitting corrosion by acting as anodicphase.