Pressure Profile Designing in Superplastic Forming Based on the Strain Rate and on Post-forming Properties

In this work, the feasibility of reducing the cycle time in superplastic forming through a selective approach in the algorithm that calculates the forming pressure profile was investigated. First, a 3D numerical model of the blow forming process is created. Then, the blank was partitioned in different characteristic areas according to their strain and strain rate histories. Thus, different pressure profiles were numerically calculated choosing different combinations of those partitions of the blank. Experimental trials were finally carried out in order to explore the potential reduction of the forming time that can be achieved through the described approach without affecting the post-forming properties of the formed specimens. Post-forming properties were measured in terms of thickness distribution, mean grain size, and cavitation effects along the formed sheet. In particular, experiments were performed both with the conventional approach (with the whole sheet being monitored) and considering only the area of the sheet that experiences the highest strain values at the end of the forming process. Results highlighted that this latter approach can efficiently reduce the cycle time

PROPERTIES, MICROSTRUCTURE AND HOT DEFORMATIONBEHAVIOUR OF DIFFERENT Al-Zn-Mg (Zr) ALLOYS.

Two alloys based on Al-Zn-Mg (Zr), were characterized from microstructural and mechanical points of view. Hot tensile tests and torsion test on as-cast samples were performed. Deformed samples exhibit some static recrystallization (SRX) more evident in the alloy without Zr. As-cast alloys hot deformed by tension exhibits considerable cavitation that increases with temperature (T) . The analysis of this phenomena on 7000 as cast alloy has shown that cavity growth is mainly controlled by plastic strain both at 250°C and 400°C even if grain boundary sliding (GBS) contributes to enhance the fraction of cavities at the highest T . Cavitation is reduced if the alloy is solutionized before deformation

Correlation between microstructure and phosphorus segregation in a hypereutectoid Wootz steel

The influence of bands rich in phosphorus on the microstructure of hypereutectoid Wootz steel implement is described. Electron probe micro-analysis is combined with optical microscopy. Phosphorus-rich bands are seen to correspond to regions of internal cracking, carbon depletion, and enhanced frequency of spheroidized cementite in place of pearlite. A rationale for the findings is presented in terms of the influence of phosphorus on the Fe&ndash;C phase diagram and on the rate of the eutectoid reaction.<br /