Microstructural characterization of spray formed A380 alloy

The microstructural features of spray formed deposits are a function of both the dynamic and the thermal behavior of the atomized droplets during its flight toward the substrate and of the thermal and solidification behavior of the deposited material. In this work, the microstructural evolution of Al-9Si-3Cu (A380-type) alloy during spray deposition process has been investigated, with special emphasis on the formation of intermetallic compounds, which may act as stress raisers with detrimental effects on the mechanical properties of the cast alloy. Argon has been used as gas atomizer and a cooper plate as substrate. The microstructure was evaluated by a combination of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray difraction (DRX). The formation of Al-Si irregular cutectic structure with Si flakes, normally observed in conventionally cast material, was suppressed in both overspray powder and deposit. The microstructure was formed by equiaxed grains of alfa-Al with Si as spheroidal-type particles in the intergranular region and inside the grains. The equilibrium Al-15(MnFe)(3)Si-2 and Al2Cu phases were hard to identify due to its metastable state. On the other hand, the amount of the detrimental Al5FeSi phase, usually found in conventionally cast material was reduced and it was observed as very fine platelets with lengths shorter than 15 microns.