A comprehensive study on size-effect, plastic anisotropy and microformability of aluminum with varied alloy chemistry, crystallographic texture, and microstructure

Fabrication of microparts with large aspect-ratio and complex shapes remains a huge challenge for industries and microforming is a potential solution to manufacture such microparts. However, similarity in specimendeformation and microstructural length scales during microforming results in size effect, leading to unpredictable plastic behavior and increased process scatter. One approach to counter size effect is by engineering suitable microstructure in the material. In the present work, three grades of Al (AA1070, AA5083, AA2014) with unique alloy chemistry and microstructural profile are processed by cryorolling (CR) to 95% thickness reduction. By imparting controlled postprocess annealing on the CR materials, three distinctive microstructures - (i) ultrafine grained (UFG) with average grain size around 1 & mu;m, (ii) fine grained (FG) with average grain size near to 5 & mu;m, and (iii) coarse grained (CG) with approximate average grain size of 20 & mu;m are engineered. The influence of alloy chemistry, grain boundary engineering and crystallographic texture on microformability are studied. For pure Al (AA1070), the UFG and FG microstructures show superior microformability than the CG counterparts. The equiaxed UFG grains present in these microstructures mitigate the size effect abnormalities by increasing the number of grains in the deformation volume and uniformly distributing the complex microforming strain via grain boundary mediated plasticity. Their corresponding texture containing strong Copper mixed with scattered Cube elements promotes in-plane strain condition and high resistance to localized thinning. Also, the material shows near-zero planar anisotropy that leads to a homogenous in-plane strain distribution. Unlike pure Al, the UFG and FG Al alloys suffer from increased strain localization due to presence of solute clouds and nanoprecipitates. They influence strain-aging (Portevin-Le Chatelier effect), strain gradient hardening phenomenon, and shear propensity during failure of the Al alloys. A composite texture consisting of a combination of Brass, Dillamore, S, and & beta;-fiber elements in the Al alloys is found to be detrimental to their microformability. The Dillamore texture is contributed by formation of adiabatic shear bands during deformation of Al alloys.

Automated summary

Fabricating large aspect-ratio and complex-shaped microparts is challenging due to size effect caused by similar deformation and microstructural length scales during microforming. This study investigates the influence of alloy chemistry, grain boundary engineering, and crystallographic texture on microformability by processing three grades of Al with distinctive microstructures. Ultrafine grained (UFG) and fine grained (FG) microstructures show superior microformability compared to coarse grained (CG) microstructure in pure Al. However, UFG and FG Al alloys suffer from increased strain localization due to solute clouds and nanoprecipitates, while a composite texture is detrimental to their microformability.