High deposition rate additive manufacturing (AM) processes with minimal feedstock costs are desirable to reduce part fabrication times and minimize the cost of implementation. Wire-based AM processes meet these demands but suffer from higher heat inputs that can lead to thermal distortion and large heat-affected zones neighboring the melt pools. Here, the tensile deformation response of an Al 4043 (Al-Si) alloy deposited on an Al 6061-T6 substrate using a laser hot-wire AM process was investigated. Digital image correlation during tensile testing was combined with optical microscopy and electron backscatter diffraction data to understand the deformation mechanisms that occurred in samples from a deposited wall in the as-built condition. During tensile testing, localized deformation was observed at the melt pool boundary regions that correlated with serrations on the stress-strain curve. The primary aluminum dendrites in regions adjacent to the melt pool boundary regions were coarser than in bulk deposited material, leading to localized deformation of the coarser microstructure. EBSD post-test analysis confirmed that the accumulated strains had occurred in the melt pool boundary regions. Analysis of the thermal and solidification conditions in the melt pool indicated that the coarsened region was associated with partial remelting of the eutectic phase. This understanding of deformation mechanisms associated with the inhomogeneities at melt pool boundaries can enable AM-specific considerations for improved process and alloy design, particularly for eutectic alloys.