Assessment of melt cleanliness and analysis of inclusions in Al-Si alloys using the Prefil pressure filtration technique

The aluminium casting alloys A356.2 and A390.1 are two of the most popular AI-Si alloys used in automotive and die casting applications. To obtain pre mium quality castings, their alloy melts must possess optimum melt cleanlin ess, i.e., the inclusions present therein, particularly those harmful to th e alloy properties, must be minimised. In recent years, melt cleanliness of aluminium alloys has been assessed by means of various filtration techniqu es, In the present work, the measurement of inclusions was carried out usin g the recently introduced pressure filtration 'Prefil' technique which has the advantage of providing irt situ results in the form of flow rate charts , These minimise the need for time-consuming metallographic examinations fo r inclusion analysis demanded by other pressure filtration techniques such as PoDFA, Experiments carried out using the 'Prefil' technique indicate tha t for obtaining appropriate results, the pressure chamber and filtration cr ucible of the 'Prefil' appratus should be heated to similar to 300-350 degr ees C, to reduce heat loss during transfer of the liquid metal from the mel t crucible to the filtration crucible. Also, the filtration temperature sho uld be high enough to avoid possible sedimentation of inclusions in the lad le during the transfer. It was found that the main inclusions in A356.2 all oy are Al4C3, dispersed oxides, MgO and MgAl2O4, while those in A390.1 allo y are bone ash and alkaline compounds. Generation of oxide films (associate d with the use of mechanical stirring to dissolve grain refiner/modifier ad ditions to the melt) can be avoided by employing degassing instead.