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In this work, the effect of the laser-material interaction on the formability of a superplastic aluminum alloy was investigated. In applications such as Tailor-Welded Blanks and in the manufacturing of very large components with a complex shape, laser welding combined with superplastic forming may be a very fitting industrial tool. Bead on plate tests were carried out in order to simulate the laser-welding process and then, free inflation tests were performed to evaluate the compatibility of these two processing techniques. The Al-Mg alloy used in this work has a very small grain size which ensures the superplastic behavior. With the aim of preserving this peculiarity, the following aspects on the formability were investigated: (i) the surface condition of the bead before the forming test (with and without the removal of the excess of metal); (ii) the effect of the travel speed of the laser source on the mean grain size; (iii) the introduction of a refiner, commonly used in aluminum casts, in the molten pool in order to further reduce the mean grain size. [ABSTRACT FROM AUTHOR]

Abstract: The research activity reported in the present paper aims to evaluate the Forming Limit Curves (FLC) of the Mg alloy AZ31 in warm conditions (200°C) while keeping the equivalent strain rate constant. Specific tools to carry out such a formability test were designed and created: a flat punch (in line with Marciniak’s test) embedding a heating system was adopted in order to heat the central part of the specimen both rapidly and uniformly, where ruptures were forced due to the presence of a driving sheet between the specimen and the punch. A Digital Image Correlation system was also embedded in the formability equipment in order to acquire major and minor strains continuously and evaluate the moment and location of failures. Finite Element simulations were run in order to define punch speed profiles (which differ according to the geometry of the specimen) that were able to keep a constant equivalent strain rate in the region where ruptures were forced. Experimental tests implementing the punch speed profiles were carried out in order to obtain temperature, load and strain data. FLCs at two different strain rate levels (0.02s−1 and 0.002s−1) both confirmed and allowed us to quantify the noticeable strain rate effect of such an alloy on the FLC at a temperature of 200°C. The proposed approach for FLC evaluation is effective for materials whose properties are strongly influenced by the strain rate. Such FLC data can be usefully implemented in numerical simulations of sheet metal forming processes: while tensile tests can be used to determine variations in mechanical behaviour according to the strain rate, the FLCs evaluated in this work allow us to determine the occurrence of strain path-dependent critical conditions according to the strain rate. [Copyright &y& Elsevier]

Abstract: Warm forming of magnesium alloys has attracted much attention due to the very poor formability of Mg alloys at room temperature. In the present paper, the warm deep drawing of magnesium alloy AZ31 (3wt.% Al, 1wt.% Zn) sheets was studied by both the experimental approach and the finite element analysis. The results indicated that the formability of the AZ31 sheets could be improved significantly at elevated temperatures. Sound cups could be formed at 150°C with the highest punch speed of 6mm/min, while when the forming temperature was increased up to 250°C, sound cups could be drawn with the highest punch speed of 120mm/min. Finite element analyses were performed to investigate the effects of the process parameters on the drawability of rectangular cups and to predict the formation of the process defects. The reasonable agreement between the numerical simulation results and experimental data validated the accuracy of the finite element analysis. [Copyright &y& Elsevier]