Title: Microstructure dependent corrosion of Mg-Li alloys

Abstract

Increasing pressures associated with environmental factors such as carbon oxides in the atmosphere and increasing fuel costs are driving many industrial branches to look for advanced lightweight materials with the lowest possible densities such as magnesium or aluminum alloys. One way to decrease the weight of the materials is the use of alloying elements such as Li, which has a density of 0.534 g cm-3. Li can reduce magnesium alloys densities from 1.75 g cm-3 for the AZ31 alloy and its addition improves their mechanical properties. This study describes the corrosion resistance of dual-phased Mg-7.5Li-3Al-1Zn (AZ31+7.5Li). The microstructure of the extruded conventionally, and the extruded by forward backward extrusion with a rotating die (KoBO) was characterized using scanning electron microscopy (SEM) in backscattered electron mode (BSE), and by electron back scattered diffraction (EBSD). The X-ray diffraction (XRD) was made to recognize phases formed in the materials. The alloys microstructures consisted of α (Mg), β (Li), MgLi2Al and Mg17Al12. The potential under open circuit conditions, potentiodynamic and mass loss measurements in chloride containing solutions were done to describe the corrosion behaviour of the alloys. The results showed that corrosion of dual phased Mg-Li alloys is microstructure dependent, and is related to the relative concentration and distribution of β(Li) phase in the α(Mg) matrix. In the traditionally extruded alloys, the higher amount of β (Li) reduces the area ratio of cathodic to anodic sites of corrosion. The corrosion behaviour of the materials extruded via KoBo was varied due to different distribution of β (Li) phase in the α (Mg) matrix.