The Role Of Magnesium-rare Earth
Rare earths in magnesium alloy melt with hydrogen, oxygen, sulfur, iron removal, apart from the inclusion of function and achieve the melt degassing refining, purifying effect.
In the melting process of magnesium alloy oxidized and burns, the industrial production of magnesium alloy melting by covering or gas shielded flux method, but there are many disadvantages, if we can improve the ignition temperature magnesium alloy melt directly under it is possible to achieve the atmosphere of magnesium alloy melting, it means a lot to the further application of magnesium alloys. Is magnesium alloy melt surface activity of rare earth elements in dense composite oxide film formed on the surface of the melt, effectively prevent melting and atmospheric contact, greatly improving ignition temperature magnesium alloy melt.
Rare earth element enrichment components caused by extreme cold at the solid-liquid interface frontier, supercooled form new nucleation and a fine equiaxed grains, in addition rare earth enrichment make it to hinder the effect of α--Mg of grain growth, further promoting the grain refinement. According to the Hall2Petch formula alloy strength increases with the refinement of the grain size, and body-centered cubic and face-centered cubic Crystal, effect of grain size on the strength of dense hexagonal metal more, thus strengthening effect of grain refinement of magnesium alloy is extremely significant.
Solid solution strengthening
Most of the rare earth elements has a higher solid solubility in mg, when solid solution of rare earth elements in mg, due to rare earth elements and Atomic radii of magnesium and elastic modulus of difference, the mg lattice distortion. Resulting stress will impede dislocation motion, so that the mg was strengthened. Solid solution strengthening effect of rare earth elements are mainly slow diffusion rate impede dislocation movement, thereby strengthening the matrix, increases the strength of alloy and high-temperature creep properties.
Rare earth and magnesium or other alloying elements in alloy solidification process of forming stable intermetallic compounds, those containing rare earth intermetallic compounds with high melting point, high thermal stability and other characteristics, they are small compound particles dispersed in grain boundary and intragranular, pinning grain boundaries in high temperatures, inhibition of grain boundary sliding and impede dislocation movement, strengthen the alloy.
Aging precipitation strengthening
Magnesium rare earth elements in the higher solid Solubility decreases as temperature decreases when single-phase solid solution in a high-temperature rapid cooling, forming unstable supersaturated, after a long period of time, then precipitation precipitation of fine dispersion. Precipitation phases and interaction between dislocation and increase the strength of the alloy.