Role of Al2O3 fibers (Saffil) in thermal treatment of 2014-Al2O3(f) composite

The effect of Al2O3 (Saffil) short fibers on the response of 2014-Al2O3(f) composite to thermal treatment was investigated. Composite samples were produced by squeeze casting starting from ceramic preforms of Saffil (13% vol. of fibers). Their behaviour was compared to that of 2014 unreinforced alloy fabricated by squeeze casting as well. The best process parameters suitable for solution of alloying elements were assessed by means of differential scanning calorimetry (DSC) and electron microprobe analysis (SEM-EDS). Ageing path and kinetic of precipitation phenomena occurring at 463 K were studied by coupling DSC and SEM-EDS. The materials strengthened through two steps involving the formation of metastable phase containing Al, Cu, Mg, Si, Mn and Fe and the subsequent precipitation of θ′ (Al2Cu). Alumina fibers accelerated the overall ageing process, chiefly enhancing the θ′ rate formation through an heavy reduction of the related activation energy. Heterogeneous precipitation at the matrix/fibers interface and at the grain boundaries greatly affected the composite microstructure. Microstructure changes have been correlated to both micro- and macrohardness of the material. The maximum hardening was due to the contemporary presence of λ′ and θ′.