Microstructural evolution and thermal stability of ultra-fine grained Al-4Mg alloy by equal channel angular pressing

Experiments were conducted to evaluate the grain refinement and the thermal stability of ultra-fine grained Al-4Mg alloy introduced by equal-channel angular pressing (ECAP) at 473 K. The results show that the intensities of X-ray (111/222) and (200/400) peaks for the alloy processed by ECAP decrease significantly and the peak widths of half height become broadening compared with the corresponding values in the annealed alloy. The microstructure of 2 passes ECAPed alloy consists of both elongated subgrain and equiaxed subgrain. The residual strain in the alloy increases with the increase of passes numbers, that appears as increasing the dislocation density and lattice constant of matrix. An equiaxed ultra-fine grained structure of -0.2 μm is obtained in the present alloy after 8 passes. The ultra-fine grains in the Al-4Mg alloy are stable below 523 K, because the alloy retains extremely fine grain size of -1 μm after static annealing at 523 K for 1 h.