**2. Experimental Procedure**

The Al–Al2Cu–Si (Al81Cu13Si6, at%) and Al–Al2Cu (Al81Cu19, at%) eutectic as-cast ingots were fabricated by an arc-melter at the Materials Preparation Center, Ames Laboratory, Iowa State University, under a protective argon gas environment. Plates with dimensions of 20 × <sup>10</sup> × 2 mm<sup>3</sup> were cut from the as-cast ingot. The plates were mechanically ground and polished. Laser surface processing experiments were conducted on a solid-state disk laser (TRUMPF Laser HLD 4002 (Trumpf Laser, Plymouth, MI, USA) at a wavelength of 1.03 μm. Details of synthesis and laser re-melting have also been published elsewhere [17,18]. In an earlier study [18], the effects of the processing parameters on the microstructures of Al–Cu–Si ternary eutectic were reported. The laser power was varied between 500 and 1000 W and the laser spot diameter and scan speed ranged from 0.8 to 1.2 mm and 2.54 to 101.4 mm/s, respectively. In this study, samples processed with nominal parameters of 500 W laser power, 2.54 mm/s scan speed, and 1 mm spot size were used for micropillar compression testing. Argon shielding gas (flow rate of 9.4 L/min) was used during the laser melting process to prevent oxidation. The micropillar compression tests were performed on a TI-750 TriboIndenter (Bruker, Minneapolis, MN, USA) with a conical indenter in displacement-control mode, and the experimental compressive strain rate was 2.5 × <sup>10</sup>−2·s−1. An FEI Helios 650 NanoLab dual-beam scanning electron microscope (SEM) was used to capture the microstructures of the eutectic micropillars before and after compression tests. Thin foil samples fabricated by FIB were studied on a JEOL 3011 transmission electron microscope (TEM) with an operating voltage of 300 kV.
