1 Effect of grain and secondary phase morphologies in the mechanical and damping behavior of Al7075 alloys H. Puga a,b* , V. H. Carneiro b , J. Barbosa a,b , D.Soares a,b a Centre for Micro-Electro Mechanical Systems (CMEMS) b Department of Mechanical Engineering University of Minho, Campus of Azurém, 4800-058 Guimarães – Portugal *Corresponding author: H. Puga (PhD) – puga@dem.uminho.pt Abstract The present study evaluates the role of the microstructure in the static and dynamic mechanical behavior of as-cast Al7075 alloy promoted by ultrasonic treatment (US) during solidification. The characterization of samples revealed that US treatment promoted grain and intermetallics refinement, changed the shape of the intermetallic phases (equilibrium phases of soluble M and/or T (Al, Cu, Mg, Zn) and their insoluble Al-Cu-Fe compounds) and lead to their uniform distribution along the grain boundaries. Consequently, the mechanical properties and damping capacity above critical strain values were enhanced by comparison with values obtained for castings produced without US vibration. This results suggest that the grain and secondary phases refinement by US can be a promising solution to process materials to obtain high damping and high strength characteristics. Keywords Ultrasonic Treatment, Intermetallic phases, Grain refinement, Mechanical properties, Damping. 1. Introduction The application of light-alloys, particularly those which are aluminum based, are still a promising solution for the manufacturing of structures for the automotive and aerospace industries. Even though these alloys present an advantage due to their low density and common availability, they generally need to be processed to compete with other common alloys [1]. One