Ultrahigh strength and plasticity in laser rapid solidified Al–Si nanoscale eutectics

Abstract

As-cast Al-20wt.% Si alloys were processed via laser rapid solidification (LRS) techniques to create eutectic microstructures with nanoscale interconnected, nanotwinned Si fibers. LRS morphologies exhibit higher flow stress, exceeding 800 MPa and uniform plastic deformation above 20% compared to as-cast alloy that fractures at strains below 8% at flow strength of approximately 200 MPa. The strengthening mechanisms of LRS morphologies are interpreted in terms of the interfacial constraints: increase in yield strength as well as strain hardening rate due to nanoscale confined slip in fibrous Al-Si eutectic, and load transfer and eventual plasticity in the nanoscale Si fibers. IMPACT STATEMENT Interconnected, nanotwinned Si fibers in hypereutectic Al-Si alloy achieved by LRS increase the flow stress to over 800 MPa while maintaining homogeneous plastic deformation to over 20% strain, due to confined slip in nanoscale eutectic that increases yield strength and strain hardening with reducing size and promotes plastic co-deformability between disparate phases.

Mechanical Behavior of Al–Al2Cu–Si and Al–Al2Cu Eutectic Alloys

“…The high strength of laser-treated Al-Al 2 Cu lamellae eutectics should be ascribed to the nanoscale lamellar spacing. Decreasing the inter-lamellar spacing results in more Al-Al 2 Cu phase boundaries (PB) being introduced, facilitates the dislocation-PB interactions, and affords more room for dislocation storage, which sustains more pronounced strain hardening in the Al-Al 2 Cu eutectics [16,19]. Four Al-Al2Cu-Si micropillars cut from the laser-treated (LT) region and as-cast base are named laser-remelted and as-cast lamellae, respectively.…”

“…A limitation for all the as-cast metal-intermetallic eutectic systems has been the lack of plastic deformability [2,3], often even under compression loading. Recent work on a chill cast or laser surface-remelted eutectics has shown that high strength at room temperature can be achieved without loss of plastic deformability in a wide range of refined eutectic microstructures in Al-, Ti-, Ni-, Zn-, and Fe-based alloys [4][5][6][7][8][9][10][11][12][13][14][15][16].…”

Hierarchical and heterogeneous multiphase metallic nanomaterials and laminates

“…14 cracking resulting in meandering of the crack from its primary plane. 14 Similar hierarchical microstructures have also been processed via laser rapid solidification of Al-Si eutectic alloy by Lien et al 15 For a nominal melt pool composition of Al-16Si (hypereutectic), two kinds of microstructures are observed. One was a fully eutectic morphology with interconnected and nanotwinned Si fibers of ≈ 40-nm diameter, and the other, a fully eutectic + primary Al dendritic morphology (which sometimes contains nanoscale Si precipitates).…”

In situ characterization of tensile behavior of laser rapid solidified Al–Si heterogeneous microstructures

“…Correspondingly, cast Al-Si binary alloys have low strength ( < 200 MPa) and low tensile ductility ( < 5%) at room temperature. Refinement of eutectic Si could be an effective way to improve mechanical properties of Al-Si alloys [4,5]. Many strategies have been demonstrated to refine Si phase, such as adding alloy elements during casting [6], changing solidification rate [5,7], severe plastic deformation [3] and friction stir processing [8].…”

“…Herein, we fabricated ultrafine heterogeneous Al-Si microstructure composed of nanoscale Al-Si eutectic and fine Al dendrites by laser rapid solidification (LRS). Compression tests revealed that heterogeneous Al-Si microstructure with primary Si and fibrous eutectic Al-Si had peak flow strength up to ≈ 600 MPa with compressive plasticity of ≈ 20% [4]. However, most nanocrystalline and nanocomposite materials exhibit enhanced yield strength but lack tensile ductility even though plasticity could be observed in compression.…”