The surface quality of a heat treatable Al-Si-Mg alloy by means compression tests at 450°C was evaluated. Samples were obtained from an ingot with unidirectional solidification in order to obtain a microstructural gradient influenced by the cooling and solidification rate. The samples were heat treated by homogenization at 520°C for 4 hours prior to deformation by compression. Inverted optical and scanning electron microscopes were used to assess the surface damage of deformed samples.
Analysis of deformed surface indicates a greater influence of microstructural refinement on hardening rate. It was found that the samples solidified at high cooling rates showed no defects, but at low cooling rates produced growth of grain size and intermetallic phases and thereby the high incidence of cracks in the surface.