Hypereutectic Al– x %Si–0.8Sc alloys ( x =13, 16, 19 and 22 wt%) were produced by spray forming. The microstructures of all the alloys exhibited very fine silicon phase with average size of about 5–10 µm irrespective of the silicon content of the alloy. Transmission electron microscopy revealed the presence of a nano-scale scandium rich phase, identified as AlSi 2 Sc 2 (V-phase) uniformly distributed in the alloy. The presence of V-phase resulted in higher matrix hardness (1.34 GPa) in contrast to 1.04 GPa observed in the case of binary Al–Si alloys by nanoindentation. Isothermal heat treatment at 375 °C revealed insignificant coarsening of silicon phase in both binary and ternary alloys. The Al– x %Si–0.8Sc alloys exhibited higher flow stress and tensile strength in contrast to their binary alloy counterparts which was attributed to the bi-modal size distribution of the strengthening phases in the form of nano-scale V-phase and sub-micron to 10 µm size silicon particles. The pin-on-disk wear tests exhibited appreciable improvement in the wear performance of the relatively low-silicon content ternary alloys over their binary counterparts while the high-silicon content binary and ternary alloys exhibited no much difference in the wear performance.

Effect of scandium addition on the microstructure, mechanical and wear properties of the spray formed hypereutectic aluminum–silicon alloys

http://www.mathematik.uni-ulm.de/stochastik/personal/schmidt/publications/Alloys.pdf

3D connectivity of eutectic Si as a key property defining strength of Al–Si alloys

Hypereutectic Al–Si and Al–Si–Sc alloys were spark plasma sintered from corresponding gas-atomized powders. The microstructures of the Al–Si and Al–Si–Sc alloys possessed remarkably refined silicon particles in the size range of 0.38–3.5 µm and 0.35–1.16 µm respectively in contrast to the silicon particles of size greater than 100 µm typically found in conventionally cast alloys. All the sintered alloys exhibited significant ductility of as high as 85% compressive strain without failure even with the presence of relatively higher weight fraction of the brittle silicon phase. Moreover, the Al–Si–Sc alloys have shown appreciable improvement in the compressive strength over their binary counterparts due to the presence of intermetallic compound AlSi2Sc2 of size 10–20 nm distributed uniformly in the matrix of those alloys. The dry sliding pin-on-disc wear tests showed improvement in the wear performance of the sintered alloys with increase in silicon content in the alloys. Further, the Al–Si–Sc ternary alloys with relatively lesser silicon content exhibited appreciable improvement in the wear resistance over their binary counterparts. The Al–Si–Sc alloys with bimodal distribution of the strengthening phases consisting of ultra-fine (sub-micron size) silicon particles and the nano-scale AlSi2Sc2 improved the strength and wear properties of the alloys while retaining significant amount of ductility.

The role of the bimodal distribution of ultra-fine silicon phase and nano-scale V-phase (AlSi2Sc2) on spark plasma sintered hypereutectic Al–Si–Sc alloys

The microstructural characteristics and mechanical properties of Al–6.5Si and Al–18Si alloys have been investigated. The alloys were spray-deposited and hot extruded at 480C with an area reduction ratio of 6:1. The microstructure of the spray-deposit of Al–6.5Si alloy
showed spherical morphology of the primary a-phase with a globular shape of the eutectic Si phase in the inter-particle boundaries. On the other hand, a fine particulate morphology of primary Si phase uniformly dispersed in the matrix of the a-phase was observed in spray-deposit of Al–18Si alloy. Microstructural refinement was further increased in the hot extruded alloys. The room temperature tensile tests of spray formed and extruded alloys showed considerable increase in their strength and ductility over that of the as cast alloys. The improvement in mechanical properties of spray formed alloys is discussed in light of the microstructural modifications induced during spray deposition process.

Microstructure and mechanical properties of Al–Si alloysproduced by spray forming process

Near-eutectic Al–Si alloys were produced by conventional casting and spray forming resulting in microstructural differences due to process dependent cooling rates. The as-sprayed alloy exhibited fine equiaxed Si particles uniformly distributed throughout the matrix in contrast to the as-cast alloy, which exhibited acicular morphology with relatively large needle-like Si particles. The effect of Si morphology on the microstructural stress distribution of the as-cast and as-sprayed alloys was estimated by simulating uni-axial tensile loads on microstructures using Object Oriented Finite Element code (OOF2). Microstructures of the as-sprayed alloy experienced relatively low and uniform stress distribution, while the microstructural stress distribution in the as-cast alloy was significantly influenced by the orientation of the needle shaped silicon particles.

Study of the Influence of Silicon Phase Morphology on the Microstructural Stress Distribution in Al–Si Alloys Using Object Oriented Finite Element Modeling

Aslam Kunhi Mohamed

Papers

Study of the Influence of Silicon Phase Morphology on the Microstructural Stress Distribution in Al–Si Alloys Using Object Oriented Finite Element Modeling