Improvement of corrosion properties of az91 magnesium alloy with ti micro alloying

In this study, relationship between Corrosion Behaviour-Tolerance Limit of Fe content (0.02, 0.025, 0.05 and 0.1 Fe wt.%) in AZ91 and Ti microalloyed AZ91 alloys (0.5 wt.% Ti), cast under similar chemical compostion and cooling rate, were investigated. The alloys were produced by casting of the alloys at 750 °C'de under SF6 gas into gravity mould. The microstructures of Mg alloys were analysed by Scanning Electron Microscopy (SEM) and X Ray Difractometry (XRD). Their corrosion behaviours were evaluated by immersion tests and electrochemical polarization measurements in 3.5 wt.% NaCl solution. It was observed from the experimental results that dispersion, net like structure and coarsening of the intergranular β (Mg17Al12) intermetallic phase was increased by increasing Fe content of the both alloys (AZ91 and AZ91Ti alloys) used. The coarsening of β phase was more pronounced in AZ91 alloy than AZ91Ti alloy as the Fe content of the alloys were increased. Polarisation tests showed that corrosion current density (Icor) values of the both alloys were increased with increasing Fe content in which the increments in Icor values of 0.5 %wt. Ti containing alloys were in much less extent. Results indicated that the limit content value of Fe in AZ91 alloys was 0.05 wt.% above which the corrosion loss had increased abruptly. The corrosion resistance was increased considerably, even above 0.1 wt.% Fe content, by Ti addition to AZ91 alloy.