*3.4.1 Effect of ECAP die and processing temperature on corrosion rate*

The corrosion results of AZ80/91 Mg alloy processed through die A and die B at 598 K after 4-ECAP passes including as-received and homogenized samples were shown in **Figure 14**.

From **Figure 14**, it was observed that the channel angle of ECAP significantly influences the grain refinement and distribution of secondary phases which contribute towards corrosion resistance. ECAP processing through die A at 598 K leads to lower corrosion rate after 4 passes of ECAP compared to die B under the same conditions for both AZ80/91 Mg alloys. This is mainly due to the lower dislocation density at recrystallization temperature [29]. Therefore the reduction of the grain size and the increase of the distribution of secondary phases can cause an improved corrosion resistance. In other words, the column chart shows the variation of corrosion rates of Mg alloys before and after ECAP process for both AZ80/91 Mg alloys. The more ECAP passes are related to the nobler corrosion potentials and the lower current density. The Mg alloy processed through die A and die B after four ECAP passes results that the ECAPed Mg processed through die A has nobler Ecorr and Icorr values, leads to more corrosion resistance than the specimen extruded through die B, as-received and homogenized. Specifically, AZ91 Mg alloy processed through ECAP after 4 passes exhibited improved corrosion resistance than the ECAPed AZ80 Mg alloys this mainly due to elemental composition of AZ91 Mg alloy.
