Cast AZ31 magnesium alloy was deformed in tension and compression at temperatures between 25 -350°C and at a constant strain rate of 10 -3 s -1 . Measurements of the acoustic emission (AE) during testing are presented and related to the microstructure of the sample material. The AE count rates increase with increasing temperature from room temperature to a maximum at 230°C. At higher temperatures they decrease. This behaviour is discussed with a view to the role of twinning during deformation at elevated temperature.
In the present work, the influence of the additions of zinc, zirconium and cerium-rich mischmetal on the microstructural recrystallization development of magnesium were investigated. Grain size and chemical composition were the principal variables of the billets used for indirect extrusion experiments. Significant changes in the evolution of the dynamic recrystallization (DRX) process as a function of the alloying element contents and the process variables were observed. Microstructures and preferred orientation of crystallites were correlated in order to discuss the role of alloy composition on the DRX. This discussion was based on the macro-texture measurements and some EBSD measurements of selected samples.
In this study, the influence of thermal treatments on the properties of the martensitic stainless steel X30Cr13 (EN 10088-3: 1.4028) were investigated. These steels are characterized by a high hardness as well as corrosion resistance and can be specifically adjusted by heat treatment. In particular, the austenitizing temperature ϑA and cooling rate T˙ affect the hardness and corrosion properties of martensitic stainless steels. In order to investigate these influences, the Jominy end quench tests were performed at varying austenitizing temperatures. The aim is to determine the hardness and corrosion properties as a function of the austenitizing temperature and the cooling rate. The austenitizing temperature strongly influences the solubility of alloying elements within the austenitic lattice as well as the grain size, and thus affects both precipitation and phase transformation kinetics. In consequence, different austenitizing temperatures lead to different macroscopic material properties, like hardness and pitting corrosion potential. The heat treatment was simulated using finite element (FE) method and compared with time-temperature sequences measured at different locations of the Jominy end quench sample using thermocouples. That allows determining the cooling rate T˙ between 800∘C and 500∘C and to assign it to each location of the Jominy end quench sample. The numerical estimations were in close conformity with the experimental values. By assigning the hardness and pitting corrosion potentials to the respective cooling rates as a function of the austenitizing temperature, it is possible to determine optimum process windows for the required properties.
Hot formed sheet components made of Martensitic Stainless Steels (MSS) can achieve ultra-high strengths in combination with very high corrosion resistance. This enables to manufacture complex lightweight sheet components with longer lifespan. Nevertheless, the hot formability of MSS sheets has not been accurately evaluated considering high temperatures and complex stress and strain states. In this work, the hot sheet formability of three MSS alloys under thermomechanical process conditions was investigated. Initially, mechanical properties of this sheet material were determined by uniaxial tensile test. Finite Element Method (FEM) simulation of a hot deep drawing process was performed under consideration of thermo physical calculated material models using the software JMatPro® and Simufact Forming® 15.0. The resulting strains and cooling rates developed locally in the work piece during the forming process were estimated. The numerical results were validated experimentally. Round cups were manufactured by hot deep drawing process. The resulting maximum drawing depth and hardness were measured. In general, all three alloys developed very good formability at forming temperatures between 700 and 900 °C and increased hardness values. However, they are highly susceptible to chemical composition, austenitization temperature, dwell time, and flange gap. A statistic approach is given to explain the correlation between hardness and its influencing factors.
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