The objective of this research program is to study mixed-mode fracture of aluminum alloys containing two types of precipitates. Deformation behavior is examined in tension and compression, using plane strain and bend tests. The topography and extent of shear localization, void nucleation and growth, and fractography are followed for specimens with different particle sizes and particle spacings. Surface roughness is determined and related to surface plastic instability. Theoretical calculations are carried out for dislocation-crack tip configurations near a two-phase interface.