Interfacial reactions between the aluminium alloy matrix and intermetallicreinforcement particles in novel P/M 5056/Ni3AlP composites

Interfacial reactions were investigated for a novel P/M (powder metallurgy) 5056 aluminium alloy metal matrix composite reinforced with particulate in termetallic Ni3Al Composites were fabricated by extrusion of a blend of mat rix alloy powder and intermetallic particles produced by self-propagating h igh temperature synthesis. Extrusion of 5056/15 vol.% Ni3Al at 400 degreesC produced bars of excellent quality, whereas extrusion of 5056/15 vol.% Ni3 Al at 420 degreesC and of 5056/25 vol.% Ni3Al at 380 degreesC resulted in s evere interfacial reactions and volume expansion during extrusion. The same reactions occurred in the good quality composite during subsequent heat tr eatment at 500 and 520 degreesC. The 5056 Al alloy with its high (similar t o5%) Mg content exhibited a higher reactivity with Ni3Al than Al alloys wit h low Mg content. The interfacial reaction products were identified to be A l3Ni and Al3Ni2. The interfacial reactions consumed Al so raising the Mg co ntent of the residual matrix. This gave the possibility for the matrix to b ecome partially molten at lower temperatures than expected from its nominal composition. Segregation of Mg near the reinforcement particles is acceler ated by the presence of a high dislocation density in the matrix generated during extrusion.