This study was set to examine the fundamentals of solidification microstructure and room-temperature fracture toughness of different eutectic aluminum (Al) alloys strengthened by T-Al₆Mg₁₁Zn₁₁ and/or β-Al₃Mg₂ intermetallic phases. The thermodynamic calculations for an Al-Mg-Zn ternary system assessed three alloy compositions of Al-22.5Mg-23.5Zn, Al-35.5Mg-2Zn and Al-34.5Mg-5Zn (mol%) corresponding to α-Al/T, α-Al/β and α-Al/T/β eutectic compositions, respectively. The designed alloys were prepared by different cast process for changing the cooling rate in solidification. The Al-22.5Mg-23.5Zn and Al-35.5Mg-2Zn alloys exhibited a number of fibrous α phase surrounded by of T-phase and β-phase matrix, respectively. The morphologies of eutectic microstructures were refined by high cooling rate in solidification. The three-phase microstructure of α, T and β phases was often observed in slowly solidified Al-34.5Mg-5Zn alloy, whereas only the α/β two-phase eutectic microstructure was observed in the rapidly solidified alloy sample. The indentation fracture method using Vickers indentation test was applied to measure the room-temperature fracture toughness of the experimental alloys prepared by mold-casting. The α/β twophase eutectic alloys exhibited a low fracture toughness of 1.1 MPa·m ^0.5 in comparison with the α/T two-phase eutectic alloy. The lower fracture toughness would be responsible for the brittleness of β-phase matrix in the α/β twophase eutectic alloys.

This work examined the effect of artificial aging (AA), solution heat treatment (SHT) and T6 (SHT followed by AA) heat treatment on the microstructural evolution and mechanical properties of Al-10Si-0.4Mg (mass%)/SiC composites fabricated by Selective Laser Melting (SLM) method. The microstructure of the As-build specimen consisted of an α-Al (fcc) phase, a (α-Al-Si) eutectic phase, SiC particles and needle-like Al₄SiC₄ compound. SHT results in coarsening of Si particles from eutectic phase. While, fine Mg₂Si was supposed to be precipitated by AA. The spheroidizing of Al₄SiC₄ was partially enhanced by SHT. As-build specimen exhibited high compressive strength (＝564 MPa), and the strength was decreased by SHT process due to coarse Si particles. Interestingly, we found that AA improved Young's modulus of the Al-10Si-0.4Mg/SiC composites.