Ti,Zr,Sc Refining Pure Al Grain Comparatively Studied By Valence Electrons Theory

In this thesis,the mechanism of Ti,Zr,Sc refining a-Al grain is studied by the EET (The Empirical Electron Theory in Solid and Molecule)theory.The valence electron structure and bond energy of pure Al, Ti, Zr, Sc and AlTi,AlZr,AlSc,Al3Ti,Al3Zr,Al3Sc are calculated on the basis of BLD.The result is that,when adding a little Ti, Zr or Sc(Less than the peritectic composition) Al3Ti,Al3Zr,Al3Sc phase is generated in alloys and pure aluminum can be refined.The valence electrons number is 2.53 in one pure Al crystal cell. The valence electrons number is 2.55196 in one Ti crystal cell. The valence electrons number is 11.0024 in one AlTi crystal cell.So,they meet this nonequality nAl3Ti>3nAl+nTi.The Al3Ti,Al3Zr,Al3Sc phase are the heterogeneity nucleation. Because the heterogeneity nucleation imbibe valence electrons from surrounding Al, they are elactronegativity;the Al is electropositivity because of losting valence electrons.The pure Al and heterogeneity nucleation are face-centered structrue.They have better relation of coherence.Because pure Al can better grow on heterogeneity nucleation, so the effection of refinement is better when the contents of microelement is low.The refinement effection of Ti is better than Zr.Because the covalent electron pairs of the strongest bond (Al-Ti bond) in Al3Ti plase is 0.399; the covalent electron pairs of the strongest bond(Al-Zr bond) in Al3Zr plase is 0.30611. The covalent electron pairs in Al3Ti plase of the strongest bond is more than the covalent electron pairs in Al3Zr plase of the strongest bond. So Ti can closelier integrate with around Al than Zr. The crystal face (111) interfacial electron density difference (111)Al3Sc//(111)Al is 127.13%; the crystal face (111) interfacial electron density difference (111)Al3Zr//(111)Al is 11.04%. The crystal face (111) interfacial electron density difference in Al3Ti molecule is larger than the crystal face (111) interfacial electron density difference in Al3Zr molecule.The larger interfacial electron density difference,the difficulter growing of grain, the grain refining effection is better. So refinement effection to pure Al of Ti is more better than Zr. The crystal face (100) interfacial electron density difference in Al3Sc molecule (100)Al3Sc//(100)Al is 114.58778%; the crystal face (100) interfacial electron density difference in Al3Ti molecule (100)Al3Ti//(100)Al is 49.5732%. The crystal face (100) interfacial electron density difference in Al3Sc molecule is larger than the crystal face (100) interfacial electron density difference in Al3Ti molecule. So refinement effection to pure Al of Sc is more better than Ti. On the other hand,the Sc can refine the pure Al because the atomic radius of Sc is 0.164nm,more bigger than radius of Ti 0.143nm.It can better hold back dislocation movement and hold back crystals growwing. The summary is that,the effection refinement to pure Al of Sc is better than Ti and Zr.