Study On The Preparation And Squeeze Casting Of In-Situ Submicron ?-Al₂O_3p/AlSi9Cu3 Composites

In this paper,the shell parts commonly used in automobile,aviation and other industrial fields were taken as the application objects,and the in-situ?-Al₂O_3p/AlSi9Cu3 composites that met the strength,hardness and other performance requirements of such parts were designed from Al-SiO₂ reaction system.The tungsten argon arc cladding technology and the remelting and diluting process were adopted under the assistance of high energy ultrasound to solve the technical problems such as the reaction temperature and particle dispersion during the fabrication of this kind of composites.The squeeze casting of the?-Al₂O_3p/AlSi9Cu3 composites was studied,and with the aids of XRD,OM,SEM,TEM and EDS,the effects of tungsten argon arc cladding process parameters,ultrasound conditions,particle volume fraction,squeeze casting pressure,and T6 heat treatment on the microstructures of the composites were analyzed.The mechanical properties such as room temperature tensile properties and hardness of?-Al₂O_3p/AlSi9Cu3 composites were studied and the strengthening mechanism of?-Al₂O_3p/AlSi9Cu3 composites was briefly discussed.Al-SiO₂ preform with high density was prepared by high energy ball milling and rolling process,then?-Al₂O_3p/Al composites were successfully fabricated by tungsten argon arc cladding technology.With the increase of arc current,the in-situ reaction degree deepened and the distribution of silicon phase was more uniform.With the optimum current?120A?,the microstructure of?-Al₂O_3p/Al composites was the best,the size of?-Al₂O₃ particles was about 500nm¹?m,and the silicon phase was distributed along the grain boundary in a short rod shape.The?-Al₂O_3p/Al composites were diluted by high energy ultrasound when A356alloy was in semi-solid state,then Cu and Si elements were added to prepare AlSi9Cu3matrix alloy,and finally?-Al₂O_3p/AlSi9Cu3 composites were successfully obtained,the size of the particles was maintained about 500 nm¹?m.When the volume fraction of the?-Al₂O₃ particles was less than 5%,high-energy ultrasound could effectively disperse?-Al₂O₃ particles in AlSi9Cu3 matrix,and the optimum time of ultrasonic treatment was 5 min.However,pore defects could be observed in gravity castingcomposites.As the particle volume fraction increasing from 0%to 5%,the secondary dendrite arm spacing of?-Al decreased from 42.3?m to 26.4?m,which indicated that the?-Al₂O₃ particles could refine grains.Squeeze casting of 5vol.%?-Al₂O_3p/AlSi9Cu3 composites showed that with the increase of pressure,the microstructure of?-Al₂O_3p/AlSi9Cu3 composites became denser.When the pressure was 80MPa,the pore defects in the?-Al₂O_3p/AlSi9Cu3composites were basically eliminated,the secondary dendrite arm spacing of?-Al decreased from 26.4?m to 16.8?m,and the eutectic silicon was passivated,while the distribution of?-Al₂O₃ particles in the matrix was basically unaffected.The results of T6 heat treatment showed that the coarse eutectic Si and the bone-like primary CuAl₂ phase in the as-cast structure of?-Al₂O_3p/AlSi9Cu3 composites were dissolved and granulated,and finally the strengthening phase of?-CuAl₂ was precipitated to enhance the structure of the composites.The refinement of eutectic silicon by squeeze casting could superimpose with T6 effect,the microstructures of the composites were optimized.The results of room temperature tensile test and hardness test indicated that the5vol.%?-Al₂O_3p/AlSi9Cu3 composites showed the best properties when the squeeze casting pressure was 80 MPa.The tensile strength of T6-treated composites was 332MPa,the elongation was 3.81%,and the hardness was 133.7HV.Compared with those of the gravity casting T6-treated composite,the corresponding property increase was12.16%,57.44%,14.08%.Compared with the matrix under the same conditions,the tensile strength increased by 12.16%,the elongation decreased by 5.08%,and the hardness increased by 7.65%.Fracture morphology analysis showed that the fracture modes of as-cast AlSi9Cu3matrix and?-Al₂O_3p/AlSi9Cu3 composites were mainly brittle fracture,while those of the matrix and the composites after T6 treatment are ductile-brittle mixed fracture and ductile fracture.The strengthening mechanisms of?-Al₂O_3p/AlSi9Cu3 composites mainly included particle strengthening,fine grain strengthening and dislocation strengthening.