Influence of solidification variables on the microporosity formation on Al–Cu (4.5 wt%) alloy with axial heat processing

The effects of solidification rate, hydrogen concentration, and level of convection on porosity formation in Al–Cu (4.5 wt%) alloys were investigated using Axial Heat Processing (AHP). This processing technique is similar to the conventional directional solidification (DS) technique, except that it utilizes a graphite baffle immersed near the solidification interface to control the shape of the interface and impart an axial temperature gradient. It was found that the samples produced by AHP contained 20–40% less microporosity than similar samples produced by conventional DS. The reduction was also more pronounced with decreasing a cooling rate and increasing an initial hydrogen concentration in the melt. These differences are attributed to the solute accumulation that is due to the confinement of the liquid below the baffle and the concomitant reduction in the convection level near the interface.