Papers by Author: Volker Wesling

Abstract: The grain refinement after thermo-mechanical treatment (TMT) was investigated in AZ91, AE42, und QE22 magnesium alloys. The optimal over-aging temperature was determined to be 300 °C in the case of AZ91 and AE42 alloys and 350 °C for QE22 alloy. After optimized TMT, the average grain sizes were 13.5 µm (AE42), 11.1 µm (AZ91) and 1.9 µm (QE22). The QE22 alloy exhibited the superior superplastic properties, with maximum elongation to failure 750 % and strain rate sensitivity parameter m=0.73. The Friction Stir Welding showed that the original base material grain structure of the alloys AZ31 and AZ91 replaced by ultrafine grains in the stir zone. The purpose of the present paper is to present the results of the grain refinement in magnesium alloys by thermo mechanical treatment and stir welding.

Abstract: The superplastic deformation characteristics of the AZ91, the mostly used magnesium alloy, were investigated at various strain rates in the interval from 3x10-5 to 1x10-2 s-1 and temperature of 420 °C. To prepare superplastic alloys thermo-mechanical treatment was used. Cast materials were heat-treated in two stages, after homogenization at 415 °C for 10 h were submitted to the precipitation annealing at temperature in the range of 200-380 °C for 10 h, and deformed by hot extrusion. Microstructure of samples was observed by the light microscope Olympus. Strain rate sensitivity parameter m has been estimated by the abrupt strain rate changes method. The strong strain rate dependence of the m-parameter was found. The highest elongation to failure, 584%, was found for the samples aged at 380 °C. Possible physical mechanisms of the superplastic flow are discussed.

Abstract: New interdisciplinary material and manufacturing technologies make local configuration of material properties possible. The availability of material property information in the early construction process and adequate welding technologies are essential needs to realize a maximum utilization of material. The research objective of two cooperating institutes at the Technical University of Clausthal is to develop a design strategy with related design rules in order to engineer high strength coupling elements of requirement optimized composite materials. Special attention is paid to the usage of future welding technologies and their influence on material properties of locally altered materials. Further objective is an early survey of the consequences caused by the usage of locally altered materials in mixed architecture design projects to the whole production process.

Abstract: The advantages of low heat joining techniques, such as low distortion and little influence on the local material properties due to the low introduced amount of heat, shall be made usable for the manufacture of high strength structures by increasing the process reliability. The dependency between the parameters of the joining process, the seam geometry, the type of solder, the load type und the fatigue life especially of soldered structure with local strengthening shall be examined to allow a calculative estimation of the part’s life.

Abstract: The subproject B5 examines the welding technological processing of locally hardened materials to produce structures and knots by means of high-freqency welding (HFW). The aim of B5 is a defined intervention in process and plant technology to control current voltage, temperature and compressive stress distribution of the entire weld seam. Particularly the effects on locally hardened areas have to be measured and optimized. Also the process specific advantages of HFW (e.g. plastic deformations and the application of an in situ heat treatment) have to be examined and optimized to improve structural strength.