Elasticity, Anelasticity and Yield Strength of Al-Si Alloys Obtained by Directional Crystallization

Abstract

Acoustic measurements of Young’s modulus and internal friction at frequencies of longitudinal vibrations of about 100 kHz were made in the (5×10-7 to 2×10-4) vibration strain amplitude range for Al-Si alloys. Quasi-static bending stress-strain diagrams were studied as well. The samples of the alloy were prepared using a directional crystallization by Stepanov’s method. The compositions varied from 8 to 25 wt.%Si. The micro-plastic deformation of the materials (acoustic experiments) is explained by dislocation motion in grains of α solid solution. The micro-plastic yield stress has a minimum near the eutectic composition; the flow stress of plastic bending increases smoothly when the Si content increases.

Measurement of young’s modulus and hardness of Al-50 wt % Sn alloy phases using nanoindentation

“…In this case, a large fraction of atoms is found at a location other than their normal position in the crystal lattice; the volume fraction of grain bound aries, near boundary volumes, and triple junctions increases as the subgrain size decreases [16]. For example, according to Mughrabi's composite model [17], the Young modulus can be decreased by increas ing the volume fraction of intergranular space, includ ing grain boundaries and triple junctions, the mechan ical properties of which are different from those of a grain body. In addition, a decrease in grain sizes increases the proportion of the free volume within the grain boundaries, near boundary regions, and triple junctions, which is accompanied by a weakening of the atomic bonds in the material.…”