Institute I: General Materials Properties
Hardness profile of an AA6014/AA5754 laminate with alternating material layers after 6 ARB cycles.
Production and characterisation of ultrafine-grained laminate materials by Accumulative Roll Bonding
As a method of severe plastic deformation the accumulative roll bonding process allows the production of ultrafine-grained sheet metals. Two sheets are cleaned and wire brushed before roll bonding them using a thickness reduction of 50 %. Thus the initial geometry is kept wherefore the process can be repeated cyclically. By the repeated roll bonding a high degree of deformation is reached causing an ultrafine-grained microstructure with grain sizes between 100 nm and 1 µm. The grain refinement causes extraordinary mechanical properties. The strength increases by a factor of 2 to 3 in comparison to the conventional grained counterpart. Nevertheless ductility is kept or even increases with increasing number of ARB cycles when comparing to the cold formed reference.
By the use of two sheets the ARB process allows to join different materials to laminates. After N ARB cycles the roll bonded sheet consists of 2N layers allowing a high variety of stacking orders. Hence, sheet materials with tailored properties can be produced. Beside the combination of different metals laminate or sandwich materials consisting of different alloys of the same metal are also of great interest. For example, joining aluminium alloys of the 5xxx series and the 6xxx series leads to a unique combination of the beneficial properties of the materials involved. Furthermore these laminates show high strength and adequate ductility due to the ultrafine-grained microstructure. Regarding the cyclic behaviour the properties are also improved which is related to the material interfaces.