Effect of Inclusions on the Tensile Properties Inside a LPPM A356 Casting

Abstract

Contrary to metallurgical properties such as dendrite fineness or microporosity, the level of inclusions in a casting is difficult if not impossible to assess accurately. Consequently, it is not easy to quantify the detrimental effect of inclusions on tensile properties. In the present work, this has been attempted on an aluminum A356 step casting, the geometry of which offers a wide range of solidifying conditions. It was poured in low pressure permanent mold, a process which minimizes the variability of mold filling. The interaction between the melt gas content and inclusions in producing microporosity was highlighted by analyzing reduced pressure test samples. Radiographic analyses and die penetrant checks were performed to detect microshrinkage and inclusions in the castings. The effect of inclusions on tensile properties was assessed by separating tensile samples in which inclusions were observed in the fracture surface from those with a flawless fracture surface. It was thus possible to compare tensile properties with and without inclusions in the same casting. This procedure eliminated the variability introduced by the numerous additional factors bearing on the tensile properties such as the chemical composition, melt preparation and heat treatment. This distinguishes the present study from those previously carried out on the influence of inclusions on tensile properties.