Translated Abstract
High specific strength composites can be prepared by adding Al3Ti with low density and high modulus into aluminum matrix by using the in-situ casting, which can be used in automobile industry to achieve lightweight. Generally, large Ti based intermetallics(Al3Ti) in the aluminium melt decrease castability and subsequently increase the casting defects. The research draws a probable solution to this issue such as re-distribution of particles by external field, that is ultrasonic treatment. By combining ultrasonic treatment with in situ casting, under the effect of ultrasonic cavitation and acoustic flow, the in-situ reinforced particles are dispersed uniformly and more finer. Moreover, the melt is refined and degassed effectively. Therefore, particulate reinforced aluminum matrix composites with excellent properties can be prepared by using the high-intensity ultrasound.
In this research, the small-sized blocky Al3Ti particles reinforced A356 matrix composites are prepared from A356-K2TiF6 system by an ultrasonic assisted in-situ casting technique at 800℃. The microstructure feature and mechanical properties of ultrasonic-treated and non-ultrasonic composites are examined in detail. The phase composition, morphology, size and distribution characteristics of the newly formed reinforced particles as well as the evolution of matrix microstructures are studied by using XRD, SEM, EPMA and TEM. In addition, the effects of ultrasound on the characteristics of Al3Ti particles in the matrix are analyzed. Futhermore, the mechanical properties tests, including Brinell hardness and tensile tests, are carried out at room temperature. And the strengthening mechanism of composites after T6 heat treatment resulting from the addition of Al3Ti are studied.
The in-situ 5 wt.% Al3Ti/A356 composites with high strength and good ductility are successfully fabricated via an ultrasound assisted in situ casting technique. And the results show that in-situ formed Al3Ti particles contain around 9-11 at. % Si element. In the ultrasonic fields, in-situ formed Al3Ti particles are changed from rod-like to blocky in morphology with a reduced average size of 4 μm, and the Al3Ti particles can be distributed uniformly in the matrix. Owing to the nucleating effect and uniform distribution of Al3Ti, both the equiaxed transition from long columnar dendrite structure and refining of α-Al crystals occur in the ultrasonic-treated sample, which contributes to the improvement of both strength and ductility. The ultrasonic-treated composite exhibits the best comprehensive mechanical properties, and the yield strength, ultimate tensile strength and elongation of T6-ultrasonic-treated composite are 108.3HBW, 234MPa, 290MPa and 8.06%, respectively, which are improved by 12.0%, 27.2% and 313.3% compared with T6-A356. Among the strengthening mechanisms related to the reinforced particles, the coefficient of thermal expansion mismatch strengthening is the major contributor to the increment of the yield strength of the composites.
Translated Keyword
[Al0.5CoCrFeNi, High entropy alloys, Selective laser melting(SLM), Wear]
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