Effect of delta-Al2O3 fibres on the precipitation behaviour of 2014A1 composites

Composites of 2014Al alloy reinforced with 20 and 26 vol% of delta-Al2O3 fibres made by a squeeze casting technique were subjected to controlled and systematic ageing treatment. For comparison, the precipitation characteristics of the 2014Al control alloy made by identical processing as that of composites were also examined. The investigated materials were aged at either ambient or 185 degrees C and the ageing processes were monitored with both hardness and dilation measurements for various ageing times. The composites were found to be harder than the control alloy. It is noticed that the time required to reach the peak hardness of composites was almost the same as that of the control alloy. Similar to conventional alloys, dilation measurements of composites of samples cut normal to the fibre array can be used to identify the precipitation phases. Precipitation sequences of the control alloy and composites were almost the same, except in case of artificially aged samples at 185 degrees C, where no theta stable phase was precipitated in the composite samples. Tensile testing of composites showed higher yield and ultimate strengths than those of the control alloy, however, the ductility revealed a drastic reduction.