Properties Of In Situ Autogenous TiB₂/Al-Cu Composites And Effects Of Mn And V On TiB₂ Particles

With the aim of monitoring the morphology of TiB₂ particles generated locally in Al-Cu matrix,this paper successfully prepared TiB₂ particles reinforced Al-Cu matrix composites by in-situ reaction method of mixed salt assisted by mechanical stirring.The effects of in-situ TiB₂particle yield and different TiB₂ content on the properties of Al-4.5Cu alloy were examined by XRD diffractometer,universal stretcher,field emission scanning electron microscope and other common laboratory instruments,and the optimal TiB₂ particle content was confirmed.On the basis of this content,0.4wt.%Mn and 0.18wt.%V are added into the matrix.The effects of these two elements on the morphology and distribution of in-situ TiB₂ particles are analyzed.The evolution process of TiB₂ and the effects of TiB₂ particles on the properties of Al-Cu-Mn and Al-Cu-V alloys are discussed.The following research results have been obtained:（1）The yield of TiB₂ particles synthesized in situ by molten salt method and the optimal content of TiB₂ particles in Al-Cu matrix was studied.The results showed that the yield of TiB₂particles developed in situ by mixing K₂Ti F₆ and KBF₄ salt could reach more than 98%.When the content of TiB₂ particles in Al-Cu matrix exceeds 3 wt.%,the particles begin to agglomerate,and agglomerate becomes more serious with the increase in content.When the addition of TiB₂particles is 5wt.%,heat treatment properties of TiB₂/Al-Cu composites are the best.The yield strength and tensile strength of TiB₂/Al-Cu composites are 219.76 MPa and 354.65 MPa,respectively,under the premise of 5.76%elongation,which are increased by 68.94%（130.08MPa）and 32.65%（267.35 MPa）,respectively.The tensile strength of the as-cast 5wt.%TiB₂/Al-4.5Cu-0.4Mn composite is 249.3MPa,which increases by 20.7%（206.60 MPa）when the elongation reaches 7.3%.The tensile strength of the as-cast 5wt.%TiB₂/Al-4.5Cu-0.18V composite reaches 231.34MPa,which is 31.10%（176.46 MPa）higher than that of the as-cast5wt.%TiB₂/Al-4.5Cu-0.18V composite when the elongation reaches 6.7%.（2）The evolutionary process of TiB₂ particles and the influence of Mn and V elements on TiB₂ particles was studied.The results show that the evolution of in situ TiB₂ particles in Al-Cu matrix mainly goes through four stages:free growth of quasi-spherical,surface growth of polyhedral shape,anisotropic growth of chambered hexagonal prism and hexagonal prism morphology.When 0.4wt.%Mn is added into Al-Cu matrix,the morphology of TiB₂ shows a relatively flat plate-like hexagonal prism morphology.Because Mn has the capacity to inhibit the diffusion of Ti and B atoms,Ti and B atoms cannot be dispersed over long distance to supplement the continuous growth of TiB₂ particles.When 0.18wt.%V is added,the morphology of TiB₂ shows chambered hexagonal prism and convex hexagonal prism.Because V can be adsorbed on the surface of TiB₂ particles to form vanadium-rich shell,which becomes the diffusion barrier of Ti and B atoms,hinders the rapid growth of TiB₂ particles,and retains part of the chambered hexagonal prism morphology in the matrix.Moreover,it provides additional opportunities for the nucleation of TiB₂,so that the size of TiB₂ particles is relatively small and uniform.（3）The adsorption of Mn and V atoms on the surface of TiB₂ crystal was studied.The results showed that Mn atoms can be preferential adsorption of the{0001}plane in TiB₂,followed by{10（?）0},finally the{10（?）1}.The growth of{0001}and{10（?）0}planes are relatively inhibited,and the low energy state of TiB₂ particles with plate hexagonal prism morphology is preserved in Al-Cu-Mn matrix.Whereas V atomic adsorption on the{10（?）0},followed by{0001}face,finally the{10（?）1}surface.Makes the TiB₂ crystal surface than{0001}{10（?）0}growth speed is slow,also is the side of the six-prism morphology than underside growth speed slow,finally presents the comparison raised six prism morphology.