High shearing technology for the fabrication of in situ Al3Ti/Al compositesWednesday (08.11.2017) 17:00 - 17:20 Part of:
Lightweight materials have drawn much attention in aerospace, automotive and numerous other applications with the consideration of energy saving and environmentally friendly. So far, Al alloy as a variety of widely used lightweight metal material has been widely developed, while its stiffness is still insufficient in meeting the high technical requirements. In the past few decades, particle reinforced Al composites have been investigated intensively, which can coordinate the lightweight objective and requirement of high stiffness. Typically, ceramic particles such as SiC, B4C and Al2O3 are used as reinforcements to improve stiffness of the Al matrix. However, owing to the poor wetting between Al matrix and ceramic particles, it is really a challenge to realize the introduction of the particles into the melt and also get a homogeneous distribution of reinforced particles. Another point is the poor interface bonding between reinforced particles and the Al matrix results in worse mechanical properties because the external load cannot be transferred totally from the matrix to the particles. Alternatively, the intermetallic Al3Ti was selected as a novel reinforced particle in Al composites instead of ceramic particles. It has the comparable density (3.4 g/cm3) with SiC (3.2 g/cm3), relatively high stiffness (216 Gpa) and more excellent wetting with the Al matrix.
In the work, Al composites with different volume fraction of Al3Ti particles are fabricated from Ti particles and Al melt reaction via melt stirring means with a high shearing mixer. Process parameters (i.e. stirring velocity, time, process temperature and initial Ti particle size) are investigated, and conclusions are drawn as follow: 1) Due to the inherent features of the mixer, intensive shearing effect and sufficient macroscopic flow of the melt can be achieved, which directly results in the homogeneous distribution of reinforced particles in macroscopic and microscopic scale. 2) Al3Ti particles are demonstrated as effective nuclei for heterogeneous nucleation of a-Al, thus the grain size of Al matrix is decreased significantly. 3) Benefitting from the fine grain size of the matrix and excellent properties of Al3Ti particles, the stiffness and strength of the Al composites are greatly enhanced.
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