The role of rare earth elements in magnesium alloys

Rare earth elements play a prominent role in heat-resistant magnesium alloys. More than 90% of these alloys contain rare earth elements. Due to their special electronic structure, rare earth elements have unique physical and chemical properties and can improve magnesium alloys' performance in many ways. The main functions of rare earth elements in magnesium alloys include five aspects, such as purifying the melt.

1.Purify the melt

Rare earth elements have very active chemical properties. They can react with hydrogen, oxygen, sulfur, and other components in magnesium alloys to convert harmful metal inclusions such as iron, cobalt, nickel, and copper, in the solution into intermetallic compounds and remove them, thereby improving the alloy's corrosion resistance.

2.Improve the casting and processing properties of the alloy

Adding rare earth elements to magnesium alloys can reduce the alloy's oxidation tendency in liquid and solid states and improve its casting properties. For example, Mg-Y alloy has outstanding high-temperature oxidation resistance. Adding appropriate rare earth elements can also improve the fluidity of magnesium alloy liquid.

3.Strengthen fine grain

In rare earth magnesium alloys, the added rare earth elements are enriched at the front of the solid-liquid interface, causing supercooling of the components. New nucleation zones are formed in the supercooling zone to form fine equiaxed crystals. In addition, the enrichment of rare earths inhibits the growth of α-Mg grains, further promoting grain refinement; and hinders recrystallization and grain growth during hot working and annealing.

4.Strengthen solid solution

Most rare earth elements have a large solid solubility in magnesium. The rare earth atoms dissolve into the magnesium matrix, and the trivalent rare earth ions replace the bivalent magnesium ions, which slows down the atomic diffusion rate and hinders the dislocation movement, thus strengthening the matrix and improving the strength and high temperature creep performance of the alloy.

5.Diffusion strengthening effect

Rare earth and magnesium or other alloying elements form stable intermetallic compounds during the solidification process of the alloy. These rare earth-containing intermetallic compounds generally have the characteristics of high melting point and high thermal stability. They are dispersed at grain boundaries and inside grains in the form of fine compound particles. At high temperatures, they can pin grain boundaries, inhibit grain boundary slip, and hinder dislocation movement, thereby strengthening the alloy matrix.