Microstructural changes to AlCu6Ni1 alloy after prolonged annealing at elevated temperature

Abstract

This work presents results of microstructure examination of AlCu 6Ni1 aluminium alloy. The commercial AlCu 4Ni2Mg2 (M-309) alloy is widely used for elements of aircraft and automotive engines. Modification its chemical composition was aimed at improving the stability of mechanical properties of the alloy subjected to long-term exposure to high temperature. The alloy after standard T6 heat treatment (solution heat treated at 818 K/10 h/water quenched followed by ageing at 498 K/8 h/air cooled) was annealed for 150 h at elevated temperature of 573 K corresponding to the maximum value at which structural elements of jet piston engines made of aluminium alloys operate. It was found that applied heat treatment caused an increasing in the particles of hardening phase (θ′-Al2Cu) size. The significant growth of the length of θ′-Al2Cu precipitations was observed in particularly. Nevertheless, it did not strongly result in change of its shape - the 'crystallites' and 'rods' were still characteristic of hardening phase morphology. The phenomena of the growth of θ′-Al2Cu precipitates caused decreasing the mechanical properties of the alloy, what is the subject of further investigations by the authors. © 2010 The Royal Microscopical Society.