Microstructure and mechanical properties of wrought aluminium alloy prepared by recycling of aluminium matrix composites reinforced with Inconel 601 fibres

The microstructure and mechanical properties of Al-2.2Cu-1.7Mg-1.1Ni-1.1Fe-0.9Si-0.3Zn-0.2Cr-0.2Mn-0.2Ti (wt.%) alloy prepared by recycling of composite scrap containing Inconel 601 fibres in aluminium matrix were investigated. The structure of recycled alloy consisted of α-Al dendrites and a multiphase interdendritic region. Transmission electron microscopy and energy dispersive X-ray spectroscopy showed that the interdendritic region contained coarse Al9Fe(Ni, Si), Al7Cu4Ni, Al4CuMg5Si4, (Cu, Al)2Mg and Mg2Si intermetallic phases distributed in the α-Al matrix. Heat treatments resulted in additional hardening of the alloy through the precipitation and growth of fine θ-Al2Cu, S-Al2CuMg and β-Mg2Si intermetallic particles in the α-Al matrix. Peak microhardness, hardness and yield strength values were reached after 20, 12 and 8 h ageing at 180, 190 and 200°C, respectively. During the early stages of plastic deformation both intermetallic particles in the interdendritic region and small precipitates in the α-Al matrix contributed to the high strain hardening of the alloy. The breakage of coarse intermetallic particles resulted in a considerable reduction of the strain hardening exponent and quasi-steady strain hardening rate. The alloy failed by the coalescence of cavities formed within broken intermetallic particles and small voids formed around the precipitates.