The effects of melt quality and the placement of a filter in the filling system on Weibull distributions of tensile strength and elongation of Al–7%Si–Mg alloy castings were investigated. Three different combinations of melt quality and filtering were used: (a) unstirred, with filter in the filling system, (b) stirred to produce and entrain surface oxide films with no filter in the filling system to emulate poor initial melt preparation and melt handling, and (c) stirred and with a filter placed in the filling system. The results showed that the highest elongation and tensile strength values were obtained from the unstirred, filtered condition and lowest values were from stirred and unfiltered castings. Statistical analysis of tensile data showed that (i) producing and entraining new surface oxides resulted in a significant reduction in tensile strength and elongation, (ii) the distribution of tensile properties was Weibull for unstirred, filtered and stirred, unfiltered castings, and (iii) tensile strength and elongation of stirred and filtered specimens followed bi-Weibull distributions. By introducing a filter into the filling system, the damage caused by stirring can be only partially remedied. The filter is 72% effective in preventing very large old oxide bifilms from entering the mold cavity but overall the filter was found to be incapable of eliminating the damage given to the metal by stirring.
