Formability of Accumulative Roll Bonded Aluminum AA1050 and AA6016 Investigated Using Bulge Tests

Abstract

The importance of ultrafine-grained (UFG) materials, with an average grain size below 1 lm, produced by severe plastic deformation (SPD) techniques, has been recognised by many researchers. [1] Ultrafine-grained materials show especially interesting mechanical properties, namely higher specific strength and/or ductility in comparison to conventionally grained materials with an average grain size between 10 lm and 50 lm. Valiev showed that some nanocrystalline materials like copper and titanium exhibit outstanding strength and at the same time high ductility. [2] As such, the nanocrystalline or UFG materials have a strong potential for prospective engineering applications for structural, high durability components in automobile, aerospace and medical industry. The biggest contemporary limitation of most SPD techniques like equal channel angular pressing (ECAP) and high pressure torsion (HPT) is the upscaling of the process to mass production for commercial applications.Accumulative roll bonding (ARB) is an adequate method for practical applications since it can be easily scaled up and adapted to a conventional rolling process to produce large scale UFG metal sheets. Accumulative roll bonding of various materials, especially aluminum has already been investigated by a number of authors. [3,4,10] This work focuses primarily on the ARB processed commercial purity aluminum AA1050 and the technically relevant aluminum alloy AA6016. The ultrafine-grained aluminum metal sheets have especially aroused attention as potential candidates for modern light weight materials in the automotive industry. In order to qualify the accumulative roll bonding process for these purposes detailed investigations on microstructural evolution, mechanical properties and ability of sheet metal forming using hydraulic bulge tests have been carried out and investigated. The sheet forming capability of the ARB processed materials is very crucial for a successful use of these modern classes of materials in technical applications. One test that can be used for the evaluation of the sheet forming capability is the so-called hydraulic bulge test, [5,6] where a metal sheet is clamped under a circular die and deformed by a pressurised liquid medium into a dome shape until fracture. The advantages of the bulge test include the avoidance of friction and plastic instability like necking. Due to the biaxial stress state higher achievable strains to failure can be achieved compared to the uniaxial tensile experiments. From a metal sheet forming point of view, it is an important method since the loads acting on the sheet during forming are similar to many technological processes like hydroforming, deep drawing, etc. [7,8] Up to now, very limited amount of data is available in the literature on the sheet forming capability of UFG materials. [9] Experiments Material The materials used for the investigation were commercial purity aluminum AA1050 and aluminum alloy AA6016. Their chemical compositions are listed in Table 1. Prior to roll bonding both materials we...

Mechanical properties of aluminium laminates produced by accumulative roll bonding

“…Similar trends of increasing ductility during ARB processing have been reported previously . This seems to be related to grain refinement, which leads to a higher strain rate sensitivity and grain boundary mediated plasticity.…”

Microstructure, Texture, and Mechanical Properties of Laminar Metal Composites Produced by Accumulative Roll Bonding

“…In the Al2N/Al2N ARB sheets, ϵ f drops by more than an order of magnitude after the application of ARB but then increases with higher number of ARB cycles. Such trends of increasing ductility with additional ARB cycles numbers were reported previously and may be explained by grain boundary mediated plasticity caused by the grain refinement. ϵ f in the Al2N/Al5N ARB laminates behaves similarly up to 6 ARB cycles, but then the ductility starts to decrease.…”

Strengthening mechanisms and Hall-Petch stress of ultrafine grained Al-0.3%Cu

“…The as-deformed sample has a flow stress (0.2% offset) of 198 MPa, a UTS of 224 MPa and a total elongation of ~ 5%. The strength is close to that seen in nanostructured AA1050 and AA1100 with 0.5 ~ 1.0 percent of impurities produced by accumulative roll bonding (ARB) [9,29]. The elongation is slightly lower than the reported value for these alloys (~ 7%).…”