Abstract
	Accumulative rolling bonding (ARB) is a kind of severe plastic deformation process which can produce high strength metals with ultra fine (sub-micron) grained microstructure. Microstructure and mechanical properties of AZ91 alloy sheets manufactured by accumulative roll bonding (ARB) at temperature 360?C were investigated. Microstructure of rolled materials indicates formation of sub-grains inside the original grains, which show traces of deformation, which elongated them in direction of rolling. In the AZ91 sheet, the grain size was locally reduced down to 1 ?m by the ARB process and the strength increased up to 392 MPa, The strength of the AZ 91 alloy increased from 168 MPa (without deformation  and after heat treatment) to 334 MPa after the 4 cycles, but during subsequent ARB processing it rose only very slightly. Experimentally was proved that the mean grain size after 5 cycles decreased from initial 120 ?m to 3,6 ?m. Typical twins, which were formed at plastic deformation in case of forging and conventional longitudinal rolling did not occur when ARB technology was used, which is probably caused by amount of deformation, which was the decisive factor already at the first pass, where it exceeded the value of 60%, while on the other hand at forging or rolling this amount of deformation was not higher than 30%.