Probing effects of solute trapping on the mechanical properties of α-Al in rapidly solidified hypoeutectic Al-10at.%Cu after surface laser melting

After scanned laser surface remelting the resultant rapid solidification microstructures of multicomponent alloys exhibit morphological gradients, with scale refinement and non-equilibrium features, including non-equilibrium solute trapping, which are associated with property changes. Combinations of site-specific mechanical property measurements by nano-indentation and microstructural analyses by electron microscopy have been used to determine microstructure-property relationships for the characteristic features of the rapid solidification microstructure of a hypo-eutectic Al-Cu alloy containing 10 atom percent Cu. A microstructure gradient developed as the solidification rate increased monotonically during the re-solidification process. For a laser scan velocity of 3 mm/s most of the rapid solidification microstructure is comprised of micrometer scale refined dendritic cells of alpha-Al(Cu) and nanometer scale refined intercellular theta-Al2Cu phase or eutectic. The cellular alpha-Al (Cu) constituent consistently showed Cu-solute supersaturation and a 36 % hardness increase relative to the ascast state. The eutectic microconstituent exhibited increases in hardness that correlated quantitatively with the increasing lamellar spacing refinement obtaining for increasing solidification rate. The possible contributions from precipitation, solute and grain-size strengthening mechanisms to the hardness increase in the alpha-Al(Cu) cells have been assessed. The hardness increase of the alpha-Al(Cu) cells was attributed to a combination of solute and grain size strengthening.