Microstructure And Corrosion Performance Of Mg-Y-Zn Alloy With Long Period Stacking Ordered Structures

In recent years, ternary Mg-Y-Zn alloys with long-period stacking order (LPSO) structures have attracted considerable attention due to their excellent mechanical properties and unique micro structures. However, the duplex-phase magnesium alloy has poor corrosion resistance since the presence of the second phase; it has very important significance to study the corrosion of Mg-Y-Zn Alloy with Long-period Stacking Ordered Structures.Mg-Y-Zn alloys with long-period stacking ordered structures were prepared by an ingot casting method. The microstructure evolution of Mg-Y-Zn alloys was analyzed by OM, SEM, EDS, and XRD. The corrosion performance of Mg-Y-Zn alloys was studied by combining collecting gas test, immersion test and electrochemical measurements in order to determine the corrosion rate and mechanism of the alloys. The results showed that the LPSO structure was presented in the studied Mg-Y-Zn alloys prepared by a conventional casting method. The morphology and volume fraction of X-phase were found to be greatly affected by the Zn and Y content. The X-phase changed from the discontinuous distribution in Mg98.5Zn0.5Yi alloy to continuous distribution in Mg97Zn1Y2alloy. Furthermore, the volume fraction of X-phase increased from 11.5%in Mg98.5Zn0.5Y1alloy to about63.2%in Mg88Zn4Y8alloy. In addition, most of the corrosion points were observed in the junctions of X-phase and Mg matrix, indicating the X-phase accelerated the galvanic corrosion of Mg matrix. Mg97Zn1Y2alloy shows the lowest corrosion rate among the alloys due to the continuous distribution and proper volume fraction of X-phase. Because the electrode potential of the X-phase is relatively higher than a-Mg phase, the corrosion points generated in the junction of X-phase and a-Mg, which means the micro-galvanic corrosion generated. The X-phase has a dual role in corrosion of alloys:It can not only promote micro-electric galvanic corrosion, but also stop the corrosion extended of alloys as long as it distribution as network. The corrosion rate measured by hydrogen evolution is smaller than that of weight loss method as the uncorroded part fall off from the alloys.The corrosion film is inhomogeneous after corrosion as the Mg-Y-Zn alloys has duplex structure. It cannot give well corrosion protection to the uncorroded a-Mg phase. In the study of corrosion of magnesium alloy, Al element is one of the most important elements because it can improve the corrosion resistance of magnesium alloys. Therefore, in this paper, the Mg97Zn1Y2alloy with the best corrosion resistance which basis on the study progress of the corrosion of four kinds of Mg-Y-Zn alloys were selected to add with traces and regular amount of Al and to study the microstructure and corrosion behavior. The results showed that the alloys has not changed significantly adding with0.1%and0.2%Al. Mg97Zn1Y2alloys produced a small amount of complex phase which ingredients for Mg3Y2ZnAl3phase when the Al added to0.3%. When the Al amount to0.5%, there are more Mg3Y2ZnAl3phase groups growing and both a-Mg and X-phase contain a certain amount of Al. The interlocking protrusions between X-phase anda-Mg phase disappeared when the Al amount to1%. As the increase of Al the diamond Al4MgY phase produced. Adding trace Al can increase the corrosion of alloys substantially as the Al solution ina-Mg phase can improve the integrity of the surface film and promote the filiform corrosion happened.