Fabrication Of Ti@(Al-Si-Ti)_p/A356 Composite By Powder Thixoforming And Effect Of Process Parameters On Solid Solution Treatment

To overcome the problem of inverted strength and ductility of particulates reinforced metal based composites(PRMMCs),in this paper,powder thixoforming(PTF)technology was used to form core-shell structure(CS)particles reinforced A356 aluminum(Ti@(Al-Si-Ti)_p/A356)based composites.Firstly,the effect of process parameters(partially reheating temperature and duration)on microstructure and tensile properties of Ti@(Al-Si-Ti)_p/A356 composites was studied,and the optimal parameters were obtained.After that,the solid solution treatment of the composite was studied,and the strengthening model was proposed to predict the yield strength of the composites during solid solution treatment.Finally,by studying the effect of process parameters on the solid solution treatment of composites,the best solid solution treatment process together with the process parameters was obtained.The main conclusions are as follows:(1)The process parameters mainly affect the microstructure densification(by changing the liquid fraction),the size of primary phase particle,the eutectic Si phase content and the morphology and component of CS reinforcing particles,and therefore the tensile properties of the composites.The optimal process parameters are:partially reheating temperature is 595℃and duration is 50 min,the obtained ultimate strength(UTS),yield strength(YS)and elongation are 259 Mpa,158Mpa and 18.2%,respectively.(2)Solid solution treatment of the composite formed at 595℃for 40 min was carried out by considering the continuous reaction of the CS reinforcing particles during solid solution treatment.With the prolongation of solid solution time,the coarsening rate change of primaryα-Al phase particles is consistent with the dissolution rate change of eutectic Si phase,meanwhile,the morphology and phase of CS reinforcing particles also changed.The mechanical properties of the composite reached peak values solutionized at 545℃for 1h,the UTS,YS and elongation were263.9 Mpa,172.1Mpa and 20%,respectively,which increased 7.3%,11.7%and 12.4%compared to as-fabricated one.In addition,vickers hardness also increased from 59.3to 72.8,an increase of 22.8%.In addition,A kind of strengthening model was proposed to more accurately predict the YS of the composites during solid solution treatment,combined with the shear lag model and the indirect strengthening mechanism(fine grain strengthening,geometric essential dislocation strengthening,thermal mismatch strengthening and solid solution strengthening),the effective volume fraction of CS reinforcing particulates and the strengthening of eutectics also be considered.(3)The changes of eutectic Si phase,primaryα-Al particles and CS reinforcing particles are closely related to the partially reheating process.Considering the changes,the composites thixoformed with partially reheating at 595℃for 40 mi n were used for solid solution treatment.Under this condition,both strengthening and toughening effects of CS reinforcing particulates are ideal,and the best comprehensive tensile properties can thus be obtained.