Deformační chování hořčíkové slitiny AZ31 za tepla

Abstract

Magnesium alloys, for which low specific weight and good strength properties after heat treatment are characteristic, are currently demanded mainly in aeronautical and automotive industry. Most magnesium alloys are processed in high temperatures due to unfavourable formability at the room temperature. It is caused above all by magnesium itself, which crystallises in the hexagonal system with tight arrangement. By this magnesium differs from most technical metals that crystallise in the cubic system. Formability of magnesium alloys depends significantly on temperature and strain rate and on grain size. Influence of softening processes on final mechanical properties is important. Present dissertation concerns therefore deals with the most complete possible description of the deformation behavior of selected magnesium alloy AZ31 with the designation, which ranks among one of the most commonly used magnesium alloys for forming. For this purpose have also been several selected experiments, whether it is a hot-rolled or pressure tests on Gleeble simulator plastometric 3800, or other, to obtain as much as possible the output data and their subsequent treatment, respectively comparing. An experiment leading to obtain the mathematical model of the mean equivalent stress (ps) of magnesium alloy with 2.8 wt. % Al was realized in laboratory rolling mill Tandem. It was based on the measurement of rolling forces during hot rolling of the flat samples with varying thickness. The measured rolling force values were converted to the ps values. Compression tests of magnesium alloy Mg-3Al-1Zn (AZ31) at different temperatures and strain rate were made on plastometer Gleeble 3800. Deformation behaviour and particularly shape of stress-strain curves of the alloy AZ31 differ significantly at low and high values of Zener-Hollomon parameter Z. Regression and statistical analysis of experimental data have confirmed unequivocally, that it was impossible to describe by a uniform equation the whole set of data (i.e. traditional stress-strain curves, as well as those with atypical initial stage, given by the massive twinning). That’s why two mathematical models were developed enabling prediction of the flow stress of investigated magnesium alloy in dependence on temperature, strain and strain rate, with inclusion of the influence of dynamic recrystallisation. Basic advantage of the developed original models consists in their relative simplicity and suitability for a rapid application in an extensive range of deformation conditions.