Conditions for the early onset of blisters during heat treatments of Al-Si-Cu CAST PART

The evolution of subsurface pressurized pores, originating blisters during heat treatment cycles, on High Pressure Die Cast components made of Al-Si-Cu alloys was studied using a Finite Element Model in order to understand under which conditions blister form even below 400°C. The initial defect geometry, depth, inner pressure and the maximum temperature of the thermal cycle were varied in limited ranges, while the material was modelled as elastoplastic, considering creep effects negligible. Results suggested that blisters develop as a result of high plastic strain accumulation in localized regions lying between the pore and the outer surface and that blisters can form even at temperatures of 350-370°C. The simulations were experimentally validated by two sets of experiments carried out on cast parts, monitoring the surface and volume evolution of subsurface defects coupled by optical microscopy and microtomography analyses.