Hybrid nano-(SiCp + TiCp)/Al composites were fabricated by liquid ultrasonic assisted semisolid stirring processing. The eutectic silicon of Al matrix changes from acicular to fine granular with addition of nanoparticles and the dendrite size of primary α-Al decreases with increased nanoparticles. After adding the hybrid nanoparticles with 3 vol%, the minimum average dendrite size can be refined to 30 μm. EDS analysis shows that nano-SiCp and -TiCp particles are uniformly dispersed in Al matrix. The YS and UTS of the composites have reached 200 MPa and 228 MPa, respectively, which are increased by 34.1% and 33.3%, respectively. The elongation of the composites has reached 9.8%, which is increased by 40%. The strengthening mechanism of hybrid nano-(SiCp + TiCp)/Al composites is mainly Orowan strengthening and minorly Hall–Petch strengthening, and the effect of load transfer strengthening is the least.
This paper studies the precipitation regularity of TiAl3 compound in different temperature, holding time and cooling rate. Besides, this paper studies the influence of Al-5Ti-1B on the mechanical properties of the 7050 alloy such as the aluminum alloy grain size, microstructure and strength through changing holding time and amount of Al-5Ti-1B. Through water cooling, the solute Ti forms new fine TiAl3 compounds firstly. While through natural cooling, the solute Ti is easy to grow up around the agglomerate TiAl3 compounds. The variation of the undissolved TiAl3 compound as follows: the size of the block-like TiAl3 does not change at 700 °C for 10 min; while the size has stabilized at 750 °C for 5 min. The dissolution of the rod-like TiAl3 is not obvious when holding for 20 min, but the rod-like TiAl3 fuses easily. After adding the Al-5Ti-1B into the 7050 alloy, the grain shape of α-Al changes from dendritic crystal to equiaxed crystal, and the refining effect is obvious; While the adding amount increases, the size of α-Al become larger, but it has a tendency towards to dendritic crystal. The mechanical properties of 7050 alloy without Al-5Ti-1B is in the worst condition. Transcrystalline rupture may occur in grain of 7050 alloy in tensile test due to it is coarse grain. After adding the refiner, the mechanical properties are optimal when keeping the temperature 750 °C for 5 min. Dimple could be found in the tensile fracture, and the dimples mainly are equiaxial.
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