The Refining Of Cu-Li Alloys And The Study Of The Effects Of Lithium To Pure Copper

In this thesis, the development of copper and copper alloys, especially copper alloys with high strength and high conductivity, are reviewed in details. On the basis of thorough analysis to the applied limits of copper alloys according to the alloys' defects, new Cu-Li alloys with high and high conductivity are manufactured and studied by means of rich lithium resource in Sichuan province. The relative effects of lithium to pure copper, such as purification , the effects to solidification characteristics , anti-corrosion and anti-oxidation properties , are discussed. Furthermore, the effects and the micro-mechanism of lithium to copper's strength and conductivity are studied emphatically. The main creative results and new progress in this thesis are presented as follows:1. The manufacturing technology of Cu-Li alloys is optimized. It simplifies the process of adding lithium to molten copper. The Cu-Li series alloys that lithium is dispersed in copper uniformly have been developed. The process overcame the difficulty that lithium is not easy to be well dispersed because of great disparity in density between lithium and copper in earlier research.2. The purification effect of lithium to pure copper is studied. The result showed that the oxygen and sulfur contents decreased sharply when lithium is added to pure copper, but the iron, phosphors and silicon contents have little change. This is different from the earlier report that lithium also has purification effect to the iron, phosphors and silicon.3. Although the earlier researchers think that lithium can decrease copper grain size, different results are presented in this thesis. The study of lithium effect on solidification characteristics of copper shows as follows: 1) The copper grain size increases when trace lithium is added to copper liquid, the maximum grain size is 1.7 times of pure copper, but when lithium content is high, the grain size decreases, the minimum is only half of pure copper. 2) The dendrite crystal area of Cu-Li alloys is diminished after lithium is added to molten copper. It becomes equiaxed structure. So far, this kind of effect is reported firstly.4. The research result on the effect of lithium to anti-oxidation and anti-corrosion properties shows as follows: 1) Lithium added in copper changes the oxidation regularity. Different content of Lithium added in the pure copper can improve its anti-oxidation property at low temperature below 300 "C. But when the temperature is higher(500*C), the anti-oxidization decreased with the increase of lithium content. 2) Trace lithium added to pure copper can improve its anti-corrosion ability in NaCl saturated solution, but the ability decreases with the lithium's content increasing.5. It has been showed that lithium added in pure copper improved its re-crystallization temperature from 400 *C to 440 "C. It is because trace lithium dissolved in copper make copper's crystal lattice distort, hinder the movement and re-arrangement of dislocations, restrain the nucleating and grain boundary moving during re-crystallization process.6. The tensile strength and elongation percentage of pure copper was improved when trace lithium was added. This is because copper's lattice deformity formed, leading to solid solution strengthening due to the addition of trace lithium. Secondary, the partial energy changes because of the difference of elastic coefficient between lithium and copper, so it increases the obstruction of dislocation. At the same time, the re-crystallization temperature of pure copper was improved due to the addition of lithium. The Cu-Li alloy samples still have much deformation organization at conventional heat-treatment system, so the strength decreased and elongation percentage increases slightly after annealing.7. Trace lithium added in copper liquid increased copper's resistance slightly. The resistance increased gradually with the residual lithium content increasing. This is because lithium atom solutes in copper lattice, leading to copper's crystal deformation.