AA2024/fly ash lightweight composites fabricated by powder metallurgy

Abstract

The paper presents the experimental results on the fabrication of lightweight aluminum alloy AA2024 matrix composites reinforced with fly ash microspheres using powder metallurgy (PM) via hot pressing. The primary aim was to achieve a composite with the highest possible matrix density while preserving undamaged microspheres. A mixture of powders consisting of AA2024 alloy powder and 10 wt% fly ash was pressed at 550°C and pressures of 5, 10, 20, and 30 MPa for two minutes. The obtained composites had densities in the range of 1.93 - 2.31 g/cm3. Microstructural analysis revealed uniform distribution of the fly ash microspheres in the aluminum alloy matrix. The hardness of the composites was comparable only between the samples pressed at 10, 20, and 30 MPa, falling within the range of 118 to 122 HV0.1. The sample pressed at 5 MPa exhibited significantly lower hardness of 98.8 HV0.1. The composites produced by pressing at 20 and 30 MPa were characterized by high yield strength and compression strength, ranging from 211 to 216 MPa and 300 to 354 MPa, respectively. The composites pressed applying lower pressures, especially those at 5 MPa, exhibited significantly lower values of plastic yield strength and compression strength, with values of 109 MPa and 115 MPa, respectively. Taking into account the density, the number of damaged microspheres, and the microstructure of the AA2024/fly ash composite, the optimal pressing range is between 10 - 20 MPa, but superior mechanical properties were achieved after pressing at 20 and 30 MPa.