Effect of a degassing treatment on the quality of Al-7Si and A356 melts - Degassing diffusers

A degassing treatment is necessary to assure the quality of aluminum alloy castings. Its effect on the mechanical properties of the A356 alloys has been well studied and documented. This study assessed the effect of different degassing diffusers, a lance and a porous bar, on the areas of the foggy marks and the pore counts as revealed in the chilled Al-7Si and the A356 alloy sample sections. The degassing bubbles rose in the melt floating with induced convection loops during degassing. The porous diffuser generated a strong and wide convection loop in the melt. There are two bubble explosion sites when a porous diffuser was used: one in the area close to the wall of the crucible and another near the diffuser. Using a lance diffuser generated a coarse-bubble cloud near the diffuser during degassing. For Al-7Si alloy, different diffusers produced a close ratio of foggy marked area and a close pore count but the quality of A356 alloy melt was affected by diffusers and/or Sr addition. During rotating bending tests, the fatigue life of the specimens was affected by the pore count and the relative porosity, but was irrelevant to the foggy marks.