Texture, microstructure, and tensile behavior of technically pure aluminum AA1050 and of the age-hardening alloy AA6016 produced by accumulative roll bonding (ARB) were studied for different numbers of ARB cycles. After eight cycles an ultrafine grained microstructure with grain sizes of the order of 0.5 mu m is reached. The grain size decreases with increasing alloying content. The texture consists of a major copper component and a minor brass component. The latter strengthens with alloying. Due to shear deformation in the surface region also a rotated cube component is found. It is stronger in the pure material and is partly added up in the bulk during ARB. Due to dislocation and grain boundary hardening the tensile strength increases with increasing ARB cycles following the Hall-Petch behavior while a moderate ductility is kept. Within the sheet plane no significant influence of the tensile direction on the observed mechanical properties was found.

In order to quantify the plastic anisotropy of the ultrafine grained aluminium alloy AA6016 produced by accumulative roll-bonding (ARB) the Lankford parameter is measured by tensile testing as a function of the number of ARB cycles. The experimental results are compared with those from texture-based Taylor simulations. Increasing differences between experiment and theory at higher number of ARB cycles may be attributed to highly oriented microstructural features.

Ultrafine-grained sheets of the commercial-purity aluminium AA1050 and the aluminium alloy AA6016 were processed by accumulative roll bonding. As-received, conventionally grained and ultrafine-grained aluminium sheets with an average grain size ranging from 20μm to 30μm and 200nm, respectively, were successfully joined by friction stir welding, and the microstructure and the mechanical properties of the welded zone were investigated. Ultrafine-grained materials showed softening in the nugget, although the hardness remained comparable to the as-received, conventionally grained aluminium sheets.

Commercial purity aluminium AA1050 and aluminium alloy AA6016 were accumulative roll bonded and subsequently friction stir welded. The microstructure of the conventional and ultrafine-grained materials produced by accumulative roll bonding is strongly affected by friction stir welding. The elongated ultrafine-grained microstructure of roll bonded sheets becomes coarser and equiaxed in the nugget region. Hydraulic bulge tests showed that higher burst pressure can be achieved for samples without friction stir welding than for the ones with friction stir welding. Localised deformation, crack initiation and propagation, as well as the final fracture occurred within the nugget. Friction stir welded AA1050 sheet showed similar achievable burst pressures and von Mises equivalent strains compared to the as-received conventionally grained sheets. On the other hand, significantly higher burst pressures and at the same time higher von Mises equivalent strains were observed for the friction stir welded ultrafine-grained material than for the friction stir welded conventionally grained material.

The texture of ultrafine-grained Al alloy AA6016 produced by accumulative roll bonding (ARB) has been measured by neutron diffraction. The starting texture consists of a strong cube component. During ARB, this texture breaks down and a texture typical for rolling of face-centered cubic metals with high stacking fault energy develops. The texture after 8 ARB cycles is characterised by the β-fiber with the Cu component dominating. Moreover, the rotated cube component is formed. This component is typical for simple shear, which takes place during rolling on the surfaces of the sheets. Based on the Taylor factor and calculated Lankford parameter, the mechanical anisotropy of the advanced metal sheets is discussed.

Commercial purity aluminium AA 1050 and aluminium alloy AA6016 were accumulative roll bonded and subsequently friction stir welded. The microstructure of the conventional and ultrafine-grained materials produced by accumulative roll bonding is strongly affected by friction stir,welding. The elongated ultrafine-grained microstructure of roll bonded sheets becomes coarser and equiaxed in the nugget region. Hydraulic bulge tests showed that higher burst pressure can be achieved for samples without friction stir welding than for the ones with friction stir welding. Localised deformation, crack initiation and propagation, as well as the final fracture occurred within the nugget. Friction stir welded AA1050 sheet showed similar achievable burst pressures and von Mises equivalent strains compared to the as-received conventionally grained sheets. On the other hand, significantly higher burst pressures and at the same time higher von Mises equivalent strains were observed for the friction stir welded ultrafine-grained material than for the friction stir welded conventionally grained material.

The paper reports one of the very first attempts to investigate the formability of ultrafine-grained aluminum sheets produced by a severe plastic deformation process known as accumulative roll bonding. During hydraulic bulge testing the samples showed a tendency to higher achievable burst pressures and/or von Mises equivalent strains with increasing number of accumulative roll bonding cycles, indicating promising deformation behaviour and good formability.

Sheets from commercial purity aluminium AA1050 and aluminium alloy AA6016 were processed by accumulative roll bonding to obtain an ultrafine-grained microstructure. The accumulative roll bonded samples showed a significant increase in specific strength paired with high ductility. Despite a strongly elongated grain structure, tensile testing of samples oriented 45° to the rolling direction revealed considerable improvement in elongation to failure compared to the samples oriented parallel to the rolling direction. From hydraulic bulge tests, it was observed that the accumulative roll bonded samples reached higher burst pressures and slightly lower equivalent strains in comparison to the as-received conventionally grain-sized samples. This behaviour reflects the extraordinary mechanical properties of the ultrafine-grained materials and indicates promising metal sheet formability.

The technologically relevant aluminium alloy AA6016 was successfully processed using accumulative roll bonding to 8 cycles (epsilon(von Mises) = 6.4) in order to obtain an ultrafine-grained microstructure with an average grain size of approximately 200 nm. With the aim of optimising the accumulative roll bonding process detailed investigations on the robustness, the type of rolling mill, the influence of temperature, the microstructural evolution and the mechanical properties have been carried out. Processing at 230 degrees C provided a good compromise between thermal stability and interlamellar bonding. Samples strained up to 6 cycles (epsilon(von mises) = 4.8) showed an increase in the yield strength by a factor of 3 in comparison to the as-received material. The ductility of the roll bonded samples was slightly sacrificed, although an increase in ductility can be achieved by increasing the number of accumulative roll bonding cycles. The mechanical properties depend on the strain rate, as has also been found for many other ultrafine-grained materials. Annealing of ultrafine-grained samples revealed a stability limit of approximately 200 degrees C.

The magnetic properties of conventional and ultrafine-grained WC/Co hardmetals have been measured and related to the microstructure. The microstructure was characterised using scanning electron and atomic force microscopy. The WC grain size was found to vary between 1.0–2.5 and 0.1–0.3μm for conventional and ultrafine-grained hardmetals, respectively. In conventional WC/Co hardmetals the coercivity increases as the WC grain size decreases. In the ultrafine-grained hardmetals with the WC grain size below 0.5μm, the coercivity was found to increase strongly and be one order of magnitude higher than in the conventional hardmetals. The relationship between magnetic properties and microstructure in this work can be extended to smaller grain sizes and ties in well with literature results. The developed relationship can be used as a quick method to estimate the WC grain size by measuring the magnetic coercivity. Furthermore, it was confirmed that the coercivity is not only a function of grain size, but also of cobalt content. All results lead to the conclusion that an increase in WC–Co interface area increases the coercivity values.