Creep and microstructure stability of different purity aluminium and its alloy processed by ECAP method

Abstract

Severe plastic deformation (SPD) is a perspective method for preparation of ultrafine-grained materials. A coarse-grained aluminium with different purity and Al-0.2Sc alloy were processed by equal-channel angular pressing (ECAP) to evaluate the effect of severe plastic deformation on the thermal stability of resulting ultrafine-grained (UFG) microstructure and on creep behaviour of the SPD processed samples. These materials were subjected to ECAP up to 8 passes by route BC at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The microstructural investigations were performed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with an electron back-scatter diffraction (EBSD) unit. Tension creep tests in constant load regime were conducted at temperature of 473 K on a both coarse-grained and UFG states of materials. It was found that creep behaviour of aluminium and its alloy is influences by their grain size, stability during creep test, material purity, solid solution and precipitate strengthening and fraction of high-angle grain boundaries development during ECAP process. While creep resistance of pure aluminium at elevated temperatures is improved already after 1 ECAP pass, further ECAP passes lead to degradation of creep life in case of low purity Al and Al-0.2Sc alloy.