The stress and yield behavior of Al alloys, Al(Cu) and Al(SiCu), have been investigated using bending beam and x-ray diffraction techniques, and the effect of passivation on the stress-temperature behavior of alloys is examined. A stress analysis of trilayer (SiO2/Al alloy film/Si) structure was formulated in order to deduce the stress of the confined metal films from bending beam measurements. The stress-temperature behavior of Al alloy films obtained from bending beam techniques was in agreement with that determined directly by x-ray diffraction techniques. The grain structure and precipitate morphology of these alloy films were studied using transmission electron microscopes. Presence of passivation leads to a change in microstructure of Al alloys, resulting in hardening for the Al(SiCu) films and softening for the Al(Cu) films when compared with the unpassivated films at room temperature. Our results reveal that oxide thickness, Al thickness, and microstructure play an important sole in determining the plastic deformation behavior of the metal films, and can satisfactorily explain the contrasting behavior observed for Al(SiCu) and Al(Cu) films.