Fabrication of Al-Si controlled expansion alloys by unique combination of pressureless sintering and hot forging

The present work reports the synthesis of Al-X wt.% Si (X = 20, 30, 40 and 50) alloys by a unique combination of pressureless sintering (PLS) and hot forging at 800 and 1000 MPa forging pressures with 37.5 and 50% deformation, respectively, in a specially designed die. The effect of hot forging parameters on densification, hardness, compressive strength and microstructures of the alloys was studied as well as suitably compared with the conventional PLS alloys. The 'PLS + forged' alloys, specifically 50% deformed at 1000 MPa, yielded excellent densification and subsequent very good mechanical properties. The combination of hot forging pressure and temperature enabled the high densification due to pore collapse, fracturing of Si particles leading to Al flow between the fractured Si particles and better interfacial diffusion between Si and Al. Moreover, the alloys showed excellent electrical conductivity (similar to 67% of that of pure Al), low coefficient of thermal expansion (CTE) and high thermal conductivity (TC) at par with the same alloys prepared with other methods, like spark plasma sintering, hot pressing and Osprey techniques. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.