Study On Evolution And Control Of TiC In Al-Si Alloys

Due to the non-stoichiometric characteristics of the TiC crystal structure,there are a large number of vacancies in the crystal lattice,which may be unstable under certain conditions.In the aluminum melt,TiC will release free Ti when it reacts with Al to form Al₄C₃,but its reaction rate is extremely low.When Si exists in the aluminum melt,the instability of TiC in the aluminum melt will increase,and Si will accelerate the evolution of TiC,which will limit the application of TiC in cast aluminum-silicon alloy.Therefore,improving the stability of TiC in the aluminum-silicon melt has become an urgent problem to be solved.In this paper,the evolution of TiC in aluminum-silicon melt was studied.TiC particles are formed in the aluminum melt by melt reaction method,and the negative effect of Si element on the stability of TiC was studied.The stability of TiC in Al-Si alloy was improved by the doping of B element,and the mechanism of B element was analyzed.Subsequently,The effect of ultrasonic treatment on the dispersion of TiC particles in the alloy was studied.Finally,the B-doping process and ultrasonic treatment technology were applied to the preparation of the piston alloy,and the micro-nano TiC particle reinforced aluminum-silicon piston alloy was successfully prepared.Microstructure and phase analysis were carried out by scanning electron microscopy?SEM?,optical microscopy?OM?,energy dispersive spectrometer?EDS?,X-ray diffraction?XRD?and transmission electron microscopy?TEM?.The mechanical properties of the alloy were tested by an electronic universal tensile tester.The main results can be describes as follows:?1?The stability of TiC in aluminium alloy is reduced by Si.As the silicon content increases,the amount and size of TiC particles gradually decreases.When the silicon content reaches 12%,only a small amount of TiC particles remain in the alloy.The TiC particles gradually change from an angular polyhedral shape to a spherical shape due to the addition of Si.The TiC particles can react with Al in the aluminum melt to form Al₄C₃ and TiAl₃ phase,and the reaction is promoted by Si.When Si is contained in the molten aluminum,Si can spontaneously diffuse into the TiC lattice and form disordered layers at the TiC edge.Thus,the lattice structure of TiC is destroyed,the diffusion of Ti and C atoms in TiC is accelerated,and the reaction is promoted.?2?The stability of TiC in Al-Si melt is effectively improved by B element.When the B content reaches 0.25%,the TiC content of the Al-5Ti-0.25C-12Si alloy sample is comparable to that in the Si-free Al-5Ti-0.25C alloy.B elements diffuse into TiC particles to form B-doped TiC particles,after adding B elements before TiC formation reaction.When B spontaneously diffuses into the TiC lattice,it does not cause large lattice distortion,so not destroy the lattice structure of TiC.B atoms will preferentially occupy the occupied positions in the TiC?C vacancies,lattice gaps,etc.?,which will increase the resistance of Si atoms into the TiC lattice.Finally,the effect of Si on the reaction between TiC and Al is inhibited.?3?Ultrasonic melt treatment can effectively improve the distribution of TiC in the alloy,reduce its aggregation tendency,and make the TiC particles evenly distributed in the alloy.The Al-Si piston alloy reinforced by micro-nano TiC particles is successfully prepared by adding B-doped TiC/Al alloy in the melting process of piston alloy combined with ultrasonic melt treatment process.?4?With the increase of TiC content,the tensile strength of piston alloy at 350?increases first and then decreases.When TiC content is 0.5%,the tensile strength reaches the maximum value of 85.96 Mpa,which is 12.12MPa higher than that of the alloy without TiC particles.The elongation at 350?of piston alloy gradually decreases with the increase of TiC content.When TiC content is 0.8%,the elongation decreases from 14.46% to 11.07%compared with piston alloy without TiC particles.