A high-specific-strength and corrosion-resistant magnesium alloy

Abstract

Ultra-lightweight alloys with high strength, ductility and corrosion resistance are desirable for applications in the automotive, aerospace, defence, biomedical, sporting and electronic goods sectors. Ductility and corrosion resistance are generally inversely correlated with strength, making it difficult to optimize all three simultaneously. Here we design an ultralow density (1.4 g cm(-3)) Mg-Li-based alloy that is strong, ductile, and more corrosion resistant than Mg-based alloys reported so far. The alloy is Li-rich and a solute nanostructure within a body-centred cubic matrix is achieved by a series of extrusion, heat-treatment and rolling processes. Corrosion resistance from the environment is believed to occur by a uniform lithium carbonate film in which surface coverage is much greater than in traditional hexagonal close-packed Mg-based alloys, explaining the superior corrosion resistance of the alloy.

Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium

“…From Fig. 5 36 However, these conclusions also suggest that the Mg-Li alloy proposed by these authors is most corrosion resistant for alkaline service conditions (>pH 10) where the carbonate compounds are most stable, which is a noteworthy finding.…”

“…For example, a Mg-Li alloy has been developed for aerospace applications that offers spectacular strength-to-weight ratio while also having good atmospheric corrosion resistance, which is attributed to the formation of a passivating Li 2 CO 3 surface layer. 36 The specific Li alloying concentration was designed to stabilize a solid-solution body-centered cubic crystal structure for a Mg-based solid solution instead of the normal hexagonal close-packed crystal structure. 36 While the Li addition was intended to improve corrosion resistance by promoting a homogenous solid-solution phase, it was also reported to have the unanticipated benefit of forming a Li-based passivating film.…”

“…36 The specific Li alloying concentration was designed to stabilize a solid-solution body-centered cubic crystal structure for a Mg-based solid solution instead of the normal hexagonal close-packed crystal structure. 36 While the Li addition was intended to improve corrosion resistance by promoting a homogenous solid-solution phase, it was also reported to have the unanticipated benefit of forming a Li-based passivating film. 36 The conditions of stability for this vital passivating film can be explored using chemical stability diagrams.…”

“…36 While the Li addition was intended to improve corrosion resistance by promoting a homogenous solid-solution phase, it was also reported to have the unanticipated benefit of forming a Li-based passivating film. 36 The conditions of stability for this vital passivating film can be explored using chemical stability diagrams.…”

“…As is common for outdoor exposure, and as was found in this Mg-Li study, carbonate compounds are formed and can be considered along with the usual oxide/hydroxide compounds. 2,24,30,[32][33][34][36][37][38] The stability of a carbonate compound depends on the concentration of the carbonate ion as a function of pH, as the carbonate ion can participate in proton exchange reactions according to the stability of its variously protonated species as a function of pH. 39 The total concentration of each carbonate species present as a function of pH can be calculated as expressed by Eq.…”