Bulk Al materials from back pressure equal channel angular consolidation of mechanically milled particles

Mechanically milled pure aluminium powders were fabricated into bulk materials using back pressure equal channel angular consolidation (BP-ECAC) for four or eight passes at 373K. The bulk materials consolidated from 0 h and 4 h mechanically milled powders were characterised by Vickers hardness tests and density measurements. Thermal stability of the consolidated bulk materials was evaluated by isothermal heat treatments at 673K. The as-consolidated bulk material from the 0 h milled (i.e. unmilled) powder showed nearly full density. However, full density was not obtained with the 4 h milled powder even after eight passes. The HV values for the as-consolidated materials fabricated from the 0 h and 4 h milled powders after four passes and from the 4 h milled powder after eight passes were 57, 121 and 136, respectively. Softening was observed in the bulk material consolidated from the 0 h milled powder during the isothermal heat treatment. However, the hardness of the bulk materials consolidated from the 4 h milled powders after four and eight passes increased to maximum values of 137 and 141 after heat treatment for 28 h and 8 h at 673K, respectively. The maximum hardness was maintained for up to 100 h at 673K in both materials. The hardening and thermal stability in the bulk materials from the milled powders are attributable to dispersion strengthening of Al4C3 particles formed by solid-state reaction during the isothermal heat treatment.