Livarski vestnik 58 / 2011 Nr. 2
P. Schumacher, S.Borzorgi, Th. Pabel, K. Haberl
DEVELOPMENT OF HIGH PERFORMANCE AL ALLOYS – INFLUENCE OF HOT TEARING
Adam Kowalski, Józef Turzyński, Mieczysław Kuder
COMPUTER – AIDED ANALYSIS OF THE STRUCTURE OF SPHEROIDAL GRAPHITE CAST IRON AND ADI
Franc Zupanič
QUANTITATIVE ANALYSIS OF BACKSCATTERED ELECTRON IMAGES AS AN AID FOR PHASE IDENTIFICATION IN CAST ALLOYS
P. Schumacher, S.Borzorgi, Th. Pabel, K. Haberl
Development of high performance Al alloys – Influence of hot tearing
Abstract
Current Al alloys have reached in some applications their limits in light weight automotive structures. However, metallurgical design of new alloys is not only driven by mechanical properties but also by castability. Alloys other than Al-Si show a strong tendency to form hot tears due the lack of Si expansion in the later stages of solidification. The present paper addresses the hot tearing tendency of Al alloys and the use of thermodynamic phase diagram calculations to evaluate the hot tearing tendency.
Adam Kowalski, Józef Turzyński, Mieczysław Kuder
Computer – Aided Analysis of the Structure of Spheroidal Graphite Cast Iron and ADI
Abstract
The structure of spheroidal graphite cast iron and ADI was evaluated on a LUCIA (Laboratory Universal Computer Image Analysis) computer programme. The aim of the study was to develop algorithms for quick determination of graphite parameters and deriving mathematical relationships (empirical equations) between austenite content in ADI and mechanical properties (Rm, A5, HB) of this material. The structure of graphite in spheroidal graphite cast iron was evaluated using cast ingots of different wall cross-sections, i.e. 3, 6, 10, 20, 25, 40, 50, 60, 75, 100 and 150 mm. The following parameters were determined in the investigations: surface area occupied by graphite, diameter of graphite spheroids, the number of spheroids falling to a surface unit, and the nodularity (circularity) index. In ADI, the austenite content was measured after special coloured etching of the specimens, and mean length and thickness of the ferrite „needles” was determined. Studies were carried out on specimens austempered in the temperature range from 280 to 390 oC, with temperature increase of every 10 K. The results of the investigations were disclosed in the form of numbers, plotted graphs and photographs of microstructure. Microstructure was examined under the optical microscope and scanning microscope. Empirical equations allowing for relationships between the austenite content and austempering temperature, and between the values of Rm, A5 and HB and austenite content in the matrix were derived. The results of investigations enable quick evaluation of graphite and mechanical properties of ADI basing on the measured structure parameters. This enables corrections to be introduced to the technological process as early as at the production stage.
Key words: spheroidal graphite cast iron, ADI, austempering, metallography,
Key words: spheroidal graphite cast iron, ADI, austempering, metallography,
Franc Zupanič
Quantitative Analysis of Backscattered Electron Images as an Aid for Phase Identification in Cast Alloys
Abstract
By microstructural characterization of cast alloys the combination of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) is predominantly used, in addition to light microscopy. By using up-to-date EDS detectors, it is possible to perform qualitative analysis of elements from Be to U, and quantitative analysis of all elements from B to U. Nevertheless, the accuracy of EDS-analysis may not be appropriate in some cases, such as when inadequate accelerating voltage, and primary beam current are used, as well as due to the small sizes of analysed phases. SEM can provide backscattered electron micrographs (BSE), carrying information regarding the chemical compositions of phases. Recently, a method was developed enabling the extraction of electron backscattering coefficients, η, of phases present in the microstructure. Electron backscattering coefficients can also be calculated from the results of EDS-analysis using empirical equations or Monte-Carlo simulations. Comparison of backscattering coefficients obtained by two completely independent methods enables verification of EDS-results, and prevents their false interpretation. In some specific cases it is also possible to obtain the contents of the elements that cannot even be detected using EDS.