Effect of Ca addition on the room-temperature formability of AZ31 magnesium alloy
Introduction
For reducing the oil consumption and avoiding the related environmental problems, scientists are always looking for lightweight structural materials that show high performance during both processing and application. Among the various candidates, magnesium (Mg) seems to be the most promising to achieve this target, where it is ∼33, 60, and 75% lighter than aluminium (Al), titanium (Ti) and steel, respectively [1]. However, the poor formability of Mg limits its potentiality in several fields [2]. The poor formability is mainly related to the high mechanical anisotropy and limited number independent slip systems of Mg. In this regard, a lot of works have been carried out to overcome these limitations and to reach the full potential of Mg [3], [4], [5]. Most of the works reported on the formability and ductility of Mg alloys concluded that the weakening of the basal texture and/or reducing the critical resolved shear stresses (CRSS) of the non-basal slip systems (prismatic and pyramidal) are the key points to enhance the performance of Mg. Several methods like reducing the grain size during primary processing or alloying with different elements were used to modify the texture and CRSS to improve the formability of Mg alloys [6], [7].
In this work, we suggest an alloy combination with improved formability which can be achieved even at high rate. The newly designed AZ31-0.5Ca alloy demonstrates good performance with high mechanical properties at the same time. We will also figure out the mechanism that is responsible for the improved performance of the Ca-modified AZ31 Mg alloy. AZ31 Mg alloy was selected in the present study due to its good cast-ability and low cost.
Section snippets
Experiments
The sheets used in the present work (AZ31-0.5Ca and AZ31 with similar grain size) were received from POSCO (South Korea). These were fabricated using a twin-roll strip casting process. The casted strips were then subjected to a multi-pass warm rolling process followed by heat treatment and water quenching until ∼1 mm sheets with homogeneous microstructure were obtained. For microstructure and texture evolution, samples cut from TD–RD plane of the sheets were mechanically grinded and polished
Results and discussion
Fig. 1a shows the cups left after the room-temperature Erichsen tests carried out on the AZ31 and AZ31-0.5Ca sheets at a punch speed of 0.33 mm/s. It is clearly seen that the addition of 0.5 wt% Ca significantly enhanced the formability of the AZ31 alloy, where Erichsen values of ∼2.2 and 6 mm were recorded for the AZ31 and AZ31-0.5Ca sheets tested at punch speed of 0.33 mm/s, respectively. More importantly, the value recorded for this alloy (AZ31-0.5Ca) was reached at a high punch speed
Conclusions
In summary, the present work showed that the modification of the well-known Mg alloy, AZ31, by 0.5 wt% Ca can lead to a highly formable Mg based material capable of withstanding high punch speed at room temperature. The IGMA analysis revealed that the AZ31-0.5Ca alloy exhibited a higher activity of non-basal slip (prismatic slip) during the deformation as compared to the Ca-free alloy (AZ31). This was attributed to the formation of the (Mg,Al)2Ca particles which can contribute to the activity
Acknowledgments
This research was supported by National Research Foundation (NRF) of South Korea (2017R1C1B5017204).
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