CHANGES IN MICROSTRUCTURE AND TENSILE PROPERTIES OF HOT ROLLED 1420 AL-LI ALLOY SUBJECTED TO THERMOCYCLING

摘要

The thermal cycling tests, which simulate the cyclic temperature events in space, between 77 and 393K with a period of 480s by a constraint thermal cycling apparatus were performed to hot rolled 1420 Al-Li alloy. The tensile properties before and after thermal cycling were evaluated. The microstructure of the alloy was studied by means of TEM. Experimental results show that the strength and ductility of the alloy decrease obviously after 1000 or 3000 thermal cycles. Thermal stress induces changes in microstructure are characterized by emitting dislocations from boundaries to matrix, forming dislocation pile-ups against grain boundaries and an increase of dislocation density. The accumulation of changes in microstructure may lead to stress concentration at grain boundaries, and result in an obvious degradation in tensile properties.