William A. Cassada

Microstructure and mechanical properties of spray-deposited Al-17Si-4.5Cu-0.6Mg wrought alloy

High Si content in Al-Si alloys usually leads to the formation of coarse, brittle Si phase under slow solidification conditions. In the present study, an Al-17Si-4.5Cu-0.6Mg (referred to hereafter as AS17) was synthesized using spray deposition to modify the Si phase. In the spray deposition process, the master alloy of AS17 was atomized using N2 gas, and was deposited on a collecting substrate directly into a three-dimensional material. The microstructure and mechanical behavior of the spray-deposited AS17 were studied using optical microscopy (OM) scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, and tensile tests. The present results indicate that in the spray-deposited AS17, the eutectic Si phase was modified from a “flakelike” morphology, characteristic of ingot metallurgy (IM) materials, into a “particulate” morphology. The formation of the coarse primary Si blocks was suppressed. Moreover, the size and morphology of Si particulates were found to have significant influences on the deformation behavior. During plastic deformation, extensive fracture of Si occurred. The percentage of fractured Si increased with the increasing amount of plastic deformation and the size of Si particulates. Finally, the room-temperature mechanical properties of the spray-deposited AS17 were compared with its IM counterpart A390 (an IM alloy with identical composition as AS17). The strength and ductility of AS17 were improved over those of A390. In the T6 condition, the yield strength and tensile elongation of AS17 were 503 MPa and 3.0 pct, respectively, whereas those of A390 were 374 MPa and 1.3 pet, respectively.

Heterogeneous nucleation and growth of δ′ in Al at.% Li

Abstract The nucleation of δ′ at dislocations at small undercooling is investigated. The primary site for heterogeneous nucleation is matrix dislocations with strong edge components. The edge dislocation half-plane and the development of a δ′ anti-phase boundary is considered. The morphological development of the δ′ precipitate is that of a “kidney” shape with a consistent relationship with the edge dislocation half-plabe. A model is developed based on the energetics of loss of coherency of a spherical precipitate and is employed to predict coherency loss of the δ′ precipitate and to compare it to the experimentally determined diameter of 400 nm. The loss of coherency is shown to be assisted by the growth of the equilibrium precipitate, δ.