Effect of Mg on the microstructure and indentation hardness of as-cast Al-4.5Cu-3.4Fe in-situ composite

The effect of Mg addition on the change in microstructure and indentation hardness of as-cast Al-4.5 mass% Cu-3.4 mass% Fe in-situ composite was investigated. Test specimens were produced by keeping the percentage of iron, copper and aluminium constant and varying the mass% of Mg (1.5%, 2.5%, 3.5% and 4.0%). The composite was produced by solidification processing by means of which Al₃Fe intermetallic formed in-situ in Al-Cu matrix. The microstructure of the original composite revealed needle shaped Al₃Fe intermetallic phase/precipitates. These needle shaped precipitates changed to irregular shaped precipitates as Mg additions were increased from 1.5 mass% to 4.0 mass%. As the microstructure evolved from needle shaped precipitates to irregular shaped precipitates, the microhardness of the in-situ composite increased. This increase in hardness can be attributed to the change in microstructure of the composites from needle shaped precipitates to widely dispersed irregular shaped precipitates.