| Magnesium alloys,as the lightest structural metals,have drawn considerable attention from aerospace and automobile industries.However,the wide application of magnesium alloys in industry is hindered because of the limited formability at room temperature.Twinning is an important deformation mechanism for magnesium alloys,due to the insufficient slip systems during plastic deformation at room temperature.As we all known,annealing treatment has great influence on the evolution of twins in magnesium alloys.But whether the other heat treatments will affect the evolution of twins remains to be studied.In this paper,the ZK21 extruded Mg alloy(Mg-1.5wt.%Zn-0.6wt.%Zr)was selected.To generate different size of {10-12} twins,pre-compressions were carried out to 2.0%,3.5% and 5.0%.Then,a part of the specimens were quenched at 150℃,200℃ and 250℃ respectively.After quenching,re-compressive or reverse tensile tests were carried out at room temperature.The purpose of this study is to explore the influence of the induction heating quenching on tensile and compression mechanical properties of Mg alloys.At the same time,the electron back-scattered diffraction(EBSD)analyses was carried out to explore the effect of induction heating and pre-strain levels on twinning and detwinning before and after recompression or reverse tension.The results show that induction heating quenching has different effects on yield strengths between recompression and reverse tension.The recompressive yield strength after quenching is lower than that without quenching for all the samples and the yield strength is also dependent on pre-strain levels.The yield strengths increase when the temperature rises from 150℃ to 200℃,while decrease when the temperature rises from 200℃ to 250℃ for the samples pre-compressed by 2% and 3.5%.But the yield strength almost linearly decrease with the increase of temperature for the sample pre-compressed by 5%.However,the reverse tensile yield strength after quenching is higher than that without quenching and the yield strength increases gradually with the increase of temperature for all the samples.Moreover,the yield strengths increase rapidly when the temperature rises from 150℃ to 200℃,but slightly from 200℃ to 250℃ for all the samples during reverse tension.The volume fraction of twins before and after recompression or reverse tension are calculated via in-situ electron back-scattered diffraction.It is found that the growth and shrinkage of the previous twin generated by pre-compression are impeded for all the samples after quenching and the extent of twin growth or shrinkage is closely related to pre-strain levels.At the same quenching temperature,the extent of twin growth during recompression for PR3.5% sample is lowest.And the extent of shrinkage during reverse tension for PR2% sample is lowest.Finally,the twin incidence and Schmidt factor of new nucleated twins are calculated after recompression.It is found that induction quenching has little influence on twin nucleation during recompression,while with the increase of pre-strain levels,the twin incidence of new twins decreases dramatically.With the increase of pre-deformation from 2% to 5%,the incidence of new nucleated twins reduces rapidly during the recompression.At the same time,the Schmidt factor of the new nucleated twins during recompression for the sample pre-compressed by 2.0% is statistically analyzed.The results show that the Schmidt factor(SF)for all the activated twins are greatest during recompression.And the distribution of SF for the twinning variant is similar,that is to say,induction heating quenching has little effect on the activation of twin variants during recompression. |
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