Influence of 3D connectivity of rigid phases on damage evolution during tensile deformation of an AlSi12Cu4Ni2 piston alloy

The microstructural evolution during solution treatment at 500°C of a cast AlSi12Cu4Ni2 piston alloy is evaluated by two dimensional and three dimensional imaging methods aiming at identifying the microstructural features affecting the processes of damage formation and accumulation under tensile deformation. Highly interconnected networks of aluminides and Si undergo a local loss of connecting branches within these networks owing to the partial dissolution of Cu-rich aluminides and a slight Si spheroidisation. The damage by tensile deformation is studied using synchrotron tomography during in situ tensile tests. In both studied heat treatment conditions (0h and 4h solution treated) damage initiates in the form of micro-cracks in clusters of primary Si particles and debonding at the interface between Si and the matrix. These micro-cracks grow through intermetallic phases in the last stages of deformation. Final failure occurs by coalescence of these cracks mainly through the rigid phases. The loss of connectedness of the Si-intermetallics network during solution treatment allows the alloy to accommodate more damage and plastic strain resulting in an increase of ductility with respect to the as cast condition.