Effect of microstructure and microtexture evolution on creep behavior of hot-rolled and mushy-state rolled Al-4.5Cu-5TiB2 in-situ composite

Abstract

Tensile creep behavior of the Al-4.5 wt.%Cu-5wt.%TiB2 in-situ composite, subjected to hot rolling, and mushy state rolling with or without prior cold rolling has been examined at two different temperatures (275°C and 300°C) under 25 MPa stress in order to study the effects of the microstructural and microtextural evolutions introduced by the thermo-mechanical treatments. The creep behavior of the investigated samples has been analyzed in terms of minimum or steady-state creep rate, time to rupture, and strain fractions in primary, secondary or tertiary stages of creep along with a thorough assessment of microstructural evolution and related damage examined using scanning electron microscopy, transmission electron microscopy, and electron back-scattered diffraction technique. The creep resistance of the pre-cold rolled mushy state rolled composite (PCMRC) at both the test temperatures has been found to be superior to that of the hot rolled composite or mushy state rolled composite. When tested at 275°C, the PCMRC composite has exhibited the lowest steady-state creep rate (∼1.36 × 10−10 s−1) and the highest time to rupture (∼903 h). The homogeneity of elemental Cu in the solid solution, a uniform distribution of CuAl2 and TiB2 particles in the matrix, and the highest low angle boundary density achieved due to mushy state rolling with prior cold rolling have imparted higher creep resistance through restricting dislocation glide. The formation of fine CuAl2 precipitates at the pre-existing dislocations and sub-grain boundaries within grains in course of the creep test has further improved the creep resistance through Orowan strengthening. The fracture surfaces have revealed the presence of dimples containing fine CuAl2 precipitates confirming partial ductile failure, along with intergranular cracking due to de-cohesion of CuAl2 and TiB2 particles at the α-Al grain boundaries.