Morphological analysis of SSM Al-4.5wt.% Cu measured by the rheocast quality index
Abstract There is a direct relationship between grain size obtained from macrostructure characterisation and the globule size and shape factor, obtained from microstructure characterisation: the smaller the grain size, the smaller the globule size and shape factor. Due to this a rheocast quality index ( RQI = globule size /( grain size × shape factor) ) was used to evaluate the Al–4.5 wt.% Cu alloy produced by strain induced melting activation (SIMA). The structure that presents the smallest grain size, the smallest shape factor, and the most homogeneous and globular size of the primary phase, has the best RQI and consequently the best behaviour in the semi-solid forming. Four different as-cast structures were cold rolled to obtain 20 and 40% deformation and were partially melted at 635 °C at holding times of 5 min. Both, macro- and microstructure were characterised.
Microstructural evolution during partial remelting of AlSi7Mg alloys
Forming of alloys and composites in the semi-solid state, i.e. within the solidification range, is recognized as a technology offering several potential advantages over casting and forging, such as reduction of macrosegregations, reduction of porosity and low forming efforts. The typical non-dendritic microstructure needed is constituted of solid phase globules suspended in the liquid phase. This paper describes the influence of the thermomechanical history on the obtaining of such a globular microstructure during partial remelting and subsequent isothermal holding of Al-Si7Mg thixocasting feedstock alloys. A shape factor capable of a realistic description of the microstructural evolution is introduced. This shape factor is used to describe the influence of initial solidification conditions (like electromagnetic stirring, solidification time, modification of the eutectic and grain refinement) and thermomechanical treatments prior to partial remelting (like solutionizing and cold rolling) on the microstructural evolution during partial remelting of Al-Si7Mg thixocasting feedstock alloys.
Methods of determining the desired frequency characteristics of the automatic control systems
Considered the methods of determining the desired frequency characteristics of the automatic control systems while the synthesis of their corrective devices.