The effect of second-phase particle clustering on the formability of four model aluminum-silicon (Al-Si) alloy sheets is evaluated using quantitative stereology and mechanical testing methods. Results indicate that the size, aspect ratio, orientation, and spatial distribution of first-order clusters in the Al-Si alloys under study have a significant impact on forming limits through their intrinsic promotion of void nucleation and growth.

An image analysis software package, developed during the course of this work, is employed to acquire and process large-scale high-resolution digital images of the Al-Si microstructures. Explicit measures of second-phase particle clustering at several orders of magnitude are extracted from digitized particle fields with the aid of spatial tessellation and dilational counting techniques. Distinct second-phase particle clustering characteristics are evident in each Al-Si alloy sheet, pertaining to the overall degree of clustering as well as the preferential orientation for high aspect ratio first-order clusters.

Strain localization behaviour in the Al-Si alloys is investigated on the basis of stress-strain data and forming limit diagrams (FLD's), obtained from uniaxial tensile and hemispherical punch tests, respectively. A general divergence in forming limits with increasing tensile minor strains is observed, indicating the predominant role of void damage in the onset of strain localization. Void damage rates are known to increase directly with stress triaxiality. The FLD data also reveals varying levels of forming limit anisotropy between the four Al-Si alloy sheets, reflecting the noted trends for preferential orientation of first-order clusters.

Void damage within undeformed and deformed Al-Si microstructures is detected and associated with adjacent second-phase features to facilitate correlational studies. These analyses confirm that voids are primarily concentrated within first-order clusters in the Al-Si microstructures.

The impact of first-order cluster orientation on forming limit anisotropy is validated through numerical simulation. A simulation of voids evolving within first-order cluster fields of the Al-Si alloy sheets produces anisotropic in-plane behaviour that is consistent with experimental trends.