Characterization and Formation of Rod-Shaped (Al,Si)3Ti Particles in an Al-7Si-0.35Mg-0.12Ti (Wt Pct) Alloy

Abstract

In this study, the rod-shaped particles in an Al-7Si-0.35Mg-0.12Ti (wt pct) casting alloy have been characterized using transmission electron microscopy. It is found that these particles invariably contain Ti, Al, and Si and that they have the structure of the equilibrium phase (Al,Si) 3 Ti. A near-rational orientation relationship is observed between the (Al,Si) 3 Ti particles and the a-Al matrix phase. For this orientation relationship, the long axes of the (Al,Si) 3 Ti rods are invariably parallel to the moire´planes defined by the intersection of closest-packed planes of the (Al,Si) 3 Ti and a-Al phases. In contrast to the (Al,Si) 3 Ti or Al 3 Ti particles form directly from the melt act as heterogeneous nucleation sites for aluminum grains and thus grain-refined Al-Si foundry alloys, the (Al,Si) 3 Ti particles are found to form during solution treatment at temperatures above 673 K (400°C). Their formation occurs in the center of aluminum grains and/ or dendrites which is Ti enriched due to partitioning during solidification. The low diffusivity of Ti in a-Al allows the particles to form in the Ti-enriched areas near the center of grains as the Ti concentration is not able to be homogenized during typical solution treatment times.

Effects of Al-5Ti-0.62C-1.07La intermediate alloy on the microstructure and mechanical properties of A356 aluminum alloy

“…However, when the addition amount of Al-5Ti-0.62C-1.07La master alloy reaches 7 wt%, the coarsening degree of SDAS and eutectic Si increases. The main reason may be that when the addition amount of Al-5Ti-0.62C-1.07La master alloy exceeds 6 wt%, there will be excessive Ti produced by the dissolution of Al 3 Ti in the melt [15], while the titanium silicide formed by Ti and Si not only damages the nucleation efficiency of Al 3 Ti and TiC [24,25], but also the modification of Si by La is affected. Nevertheless, as there is no direct experimental evidence, the theoretical analysis is a reasoning model, so there will be further research in the near future.…”