The microstructural evolution of A1-Cu alloy after ECAP was investigated by transmission electron microscope, giving especial attention to the variation of θ＇ precipitates from the aspect of the morphology and chemical composition. With increasing passes of ECAP, grain refinement of A1 matrix and local decomposition of θ＇ precipitates occur. Dislocations nucleate at the interface between θ＇ precipitates and A1 matrix and move to neighboring the θ＇/A1 matrix interface after 1 pass of ECAP. Dislocation piling up at the θ＇/ A1 matrix interface induces high density of dislocation in A1 matrix. With increasing plastic strain after 2 pass of ECAP, heavily tangled dislocations are evolved into subgrain-boundary along the shear direction. High stress concentration is developed at the θ＇/A1 matrix interface and dislocation slip is activated inside θ＇ precipitates, inducing curving and fragmentation of plate-shape θ＇ precipitates. After 3 and 4 passes of ECAP, subgrain-boundaries are evolved into equiaxed grain boundaries. Plenty of θ＇ precipitates arrange in a disorder. Dislocations inside θ＇ precipitates shear θ＇ into fragmentations, with local decomposition occurring around slip plane inside θ＇ precipitates.
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