Effects of Spark Plasma Sintering Parameters on Microstructure and Properties of Al–50 wt.% Si Alloys

l–Si alloy powder was prepared by the gas atomization method, followed by the production of the Al–50 wt.% Si alloy used in electronic packaging by spark plasma sintering (SPS) under different parameters. Afterward, the alloy’s microstructure, phase composition, mechanical properties, coefficient of thermal expansion (CTE), and thermal conductivity (TC) were analyzed. The results show that the uniform Al–50 wt.% Si alloy with a primary silicon size of less than 10 μm can be obtained by gas atomization and SPS techniques. Compared with the powder, the XRD alloy patterns remain the same after SPS, with α-Al and β-Si diffraction peaks and no other phase formation. The change of SPS temperature and time may affect the accumulation of primary silicon in the alloy and thus influence the alloy’s mechanical and thermal properties. The tensile strength of the alloy gradually increased to 220 MPa (550°C, 15 min) with the rise of SPS temperature. In contrast, the coefficient of thermal expansion (and thermal conductivity of the alloy decreased with a further increase in the temperature. Optimal values of coefficient of thermal expansion (10.6 × × 10 –6 K –1 ), thermal conductivity (128 W · m –1 · K –1 ), and tensile strength (210 MPa) were obtained at 500°C and 15 min of the SPS process. A relationship between the primary silicon morphology and material properties was established to understand the alloy’s thermal behavior changes. This change is mainly caused by the CTE and TC values difference between the Al matrix and Si-phase. The initially uniformly distributed primary silicon accumulates and modifies the properties of the alloy. The coefficient of thermal expansion and thermal conductivity variation were discussed in terms of changes in alloy particle morphology, and the theoretical model of CTE was then analyzed.