Abstract
Bimodal ultrafine eutectic composites (BUECs) exhibit a good combination of strength and plasticity owing to a dual-hierarchy in eutectic length-scales in the microstructure. The present study investigates the variation of phase, morphology, feature length-scales and modality of microstructures obtained in a Al81Cu13Si6 (at. %) ternary alloy after laser surface remelting. A novel approach of varying component bimodal eutectic volume fractions by controlling the cooling rate of the laser solidification process has been presented. The volume fraction of the fine eutectic matrix has a profound effect on the flow strength. Laser remelted microstructures with volume fractions of the fine eutectic varying from 25 to 40% exhibiting compressive flow strengths ranging from 500 to 900 MPa have been obtained. The volume fraction of the fine eutectic decreased with cooling rate and completely ceased to exist at cooling rates greater than 4times {10}^{4},^circ {rm{C}}/{rm{s}}.
Highlights
Three distinct eutectic structures were obtained based on location within the laser trace: Al-Al2Cu-Si ternary eutectic, Al-Al2Cu binary eutectic and Al-Si binary eutectic
The formation of bimodal eutectics was favored at cooling rates under ~4 × 104 °C/s
Argon gas environment was employed to protect the sample from oxidation during arc melting
Summary
Argon gas environment was employed to protect the sample from oxidation during arc melting. The specimens were laser surface remelted using solid state disk laser (TRUMPF Laser HLD 4002) at a wavelength of 1030 nm. The absorption coefficient of Al at this wavelength is low (2–3%)[53]. Lower wavelength laser irradiation resulted in a more efficient remelting process (absorption coefficient of 10%), permitting the use of lower powers and higher scan speeds. The absorption was further improved by coating the sample with graphite (Bonderite L-GP G aerosolized graphite lubricant) prior to remelting. Argon shielding gas (flow rate of 9.4 L/min) was used during the laser melting process to prevent oxidation. The temperature history was obtained at approximately the middle of laser scan path, to avoid anomalous free-edge heat transfer effects
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