Electrochemical codeposition of typical α + β phases Mg-Li alloys from the molten LiCl-KCl-MgCl2 system

Abstract

Electrochemical codeposition of Mg-Li alloys on molybdenum electrodes was investigated in LiCl-KCl (50 wt.%:50 wt.%) melts containing different concentrations of MgCl 2 at 973 K. Cyclic voltammograms show that the underpotential deposition of lithium on pre-deposited magnesium leads to the formation of liquid Mg-Li alloys. The deposition potentials of Mg(II) and Li(І) ions gradually near each other with MgCl 2 concentration decreasing. Mg-Li alloys with typical α + β phases could be obtained by potentiostatic electrolysis from LiCl-KCl melts containing 5 wt.% MgCl 2 at −2.25 V vs. Ag/AgCl (cathodic current density 1.70 A⋅cm -2 ) for 2.5 h. α phase, α + β phases, and β phase Mg-Li alloys with different lithium contents were obtained by potentiostatic electrolysis from LiCl-KCl melts with the different concentrations of MgCl 2 . The samples were characterized by X-ray diffraction and scanning electron microscopy.

Recent progress in magnesium–lithium alloys

“…Ito et al 107,108 have produced a series of Al-based alloys by codeposition from the molten salts of aluminium chloride-1-ethyl-3methylimidazolium chloride (AlCl 3 -EtMeImCl). Mg-Li alloys prepared via codeposition were also investigated by Zhang et al [109][110][111] Mg-Li alloys were directly prepared by the coelectrodeposition method on an inert electrode in a molten LiCl-KCl (50 : 50 wt-%) system at 753 K. However, a dendritic deposit of solid Mg-Li is formed. When the experiment temperature was increased to 943 K (above the melting point of magnesium 923 K), lithium was codeposited on liquid magnesium at more positive potentials causing a lithium-magnesium liquid solution being uniform in shape (better coalescence).…”

“…In the alloys with (azb) phases, during aging, the precipitation of a phase together with the metastable MgLi 2 Zn phase occurs at grain boundaries between a and b phases, and also b and b grains. The orientation relationships are (0001) a//(011) MgLi2Zn and [0110] a// [111] MgLi2Zn . The age hardening in the b alloy is caused by the precipitation of the MgLiZn phase and over aging is attributed to the precipitation of the a and MgLi 2 Zn phases.…”

“…Research on the interface between SiC w and Mg-Li matrix shows that a clear interface can be obtained. SiC w connects with the matrix in (111) and forms 70?5u or 109?5u stages on the whisker surface in (111). 83 B, B 2 O 3 and B 4 C reinforced Mg-Li composite…”

“…The codeposition of Mg and Li happens when the current density exceeds about 0·35 A cm −2 (value of limited current density of MgCl 2 in LiCl–KCl melts containing 5 wt-% MgCl 2 ). Mg–Li alloys with typical α+β phases could be obtained by potentiostatic electrolysis from LiCl–KCl melts containing 5 wt-% MgCl 2 at −2·25 V versus Ag/AgC1 for 2·5 h. The inductively coupled plasma (ICP) analyses of all samples obtained by galvanostatic 109,110 and potentiostatic 111 electrolysis are listed in Tables 3 and 4. Under the same MgCl 2 concentration (5 wt-%) in the LiCl–KCl melts, lower current intensities induced less lithium contents of Mg–Li alloys.…”