Superplasticity of coarse grained aluminum alloys

PhD ceremony: Mr. Zhenguo Chen, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Superplasticity of coarse grained aluminum alloys

Promotor(s): prof. J.T.M de Hosson

Faculty: Mathematics and Natural Sciences

Aluminum alloys may fulfill the increasing demands in automotive industry to reduce weight so as to enhance performance and to reduce fuel consumption. A coarse-grained aluminum alloy is a promising candidate for the so-called Quick Plastic Forming (QPF®) technique to produce aluminum parts at relatively high volumes and extremely complex shapes. Uniaxial tensile tests of aluminum alloy AA5182 sheet material were conducted over a wide range of experimental conditions. The AA5182 with grain size of 21 µm and 37 µm exhibited optimum deformation conditions at equal to 10-2 s-1 and at T equal to 425°C and above 475°C, respectively, with maximum elongations to failure between 300 and 400% along, and at 45° to the Rolling Direction and approximately equal to 300% perpendicularly to the Rolling Direction. Strain-rate-change tests were employed to characterize the deformation behavior of AA5182 specimens. At very low flow stress region, the activation energy Qc of 110 kJ/mol suggests a grain-boundary sliding deformation. At an intermediate flow stress region the Qc increases to 136 kJ/mole pointing at a solute drag creep deformation mechanism corresponding to the diffusion of Mg solute in the Al matrix. While at the highest region, Qc increases to more than 180 kJ/mol. This phenomenon is attributed to the dislocation glide creep mechanism, which can be explained by the dislocation-dislocation interactions or by dislocation glide limited by dispersion particles. As proved in this thesis work, our AA5182 aluminum alloy is demonstrated to be the perfect candidate to the new technique known as Quick Plastic Forming (QPF®).