Mg Li alloy is the lightest structural alloy at present, with high specific strength and specific stiffness. It is the best material for manufacturing lightweight parts. However, they have high chemical activity, low corrosion resistance and are very sensitive to some impurities, especially sodium. When the sodium content is greater than 0.06%, the plasticity of alloy will drop sharply.
The main advantage of Mg Li alloy is that it has good plastic deformation ability, especially excellent superplasticity. At the temperature of 250 ℃ ~ 375 ℃, the true strain rate of Mg-8.5% Li alloy is 10-5 / S ~ 10-3 / S; Mg-8.5% Li alloy has superplasticity behavior, which can be 610% at 350 ℃ and 10-4 / s strain rate.
The density of magnesium is 1738kg / m3, and the density of lithium is only 534kg / m3. It is a rare light metal. Adding it to magnesium melt can make the lightest metal structure alloy in the world. In addition, it also has the following characteristics: high specific stiffness, high specific strength, high damping, high radiation resistance, high anti electromagnetic interference and high shock absorption.
Among wrought magnesium alloys, Mg Li alloy is a special kind of alloy, which has the lowest density among the metal materials used in structure. It is called ultra light alloy. The density of magnesium is 1738kg / m3 and that of lithium is 534kg / m3. Therefore, according to the composition, the density of Mg Li alloy is 970kg / m3 ~ 1350kg / m3, and the lightest one can float on the water. It has a significant weight reduction effect for manufacturing structural parts of aerospace.
Alloys with lithium content > 10.3%:
This kind of alloy has good cold and thermoplastic processability and formability, and the processing rate can reach 50% ~ 60%. However, the lithium content of the alloy used in industry should not be less than 13%. The tensile strength of magnesium alloy containing about 15% Li further decreases to about 100N / mm2, and then increases the content of Li. The strength no longer increases, the elongation begins to decline, and the processing formability deteriorates, which indicates that the content of Li of Mg Li alloy with commercial value should be ≤ 16%.
Heat treatment of magnesium lithium alloy:
Mg Li alloy can be age hardened, but it will be over aged at higher temperature. Industrial mg Li alloys are usually treated with T7, solution treatment 288 ℃ and stabilization treatment 177 ℃. Stabilization treatment can eliminate the stress corrosion cracking sensitivity of Mg Li alloy. However, the weldment of Mg Li alloy must be stress relieved immediately after welding to eliminate stress corrosion cracking.
