Novel Mg-Al-Sn-Ca with enhanced mechanical properties and high corrosion rate via sub-rapid solidification for degradable magnesium alloy

Coarse eutectic phases generally exist in cast alloys and have dramatic effects on mechanical properties and corrosion behaviors. Therefore, it would be convenient and feasible to modify the mechanical properties and corrosion behaviors via tuning the eutectic phases. Herein, sub-rapid solidification (SRS) is employed to modify the microstructure, especially the eutectic phase of Mg-4.5Al-1.5Sn-0.5Ca alloy. Our results reveal that SRS followed by homogenization treatment not only reduces the grain size of alpha-Mg matrix, but also spheroidizes and refines the large stick-like CaMgSn phase to ~1 mu m. The pronounced structure modification leads to a superior strength-ductility synergy of SRS alloy, i.e., an ultimate tensile strength (UTS) of ~236 MPa and an elongation to failure (sigma f) of ~24%, in comparison to the alloy prepared via conventional solidification, with an UTS of ~220 MPa and an sigma f of ~21%. Moreover, the homogenized SRS alloy exhibits homogeneous corrosion with increased corrosion rates of ~145 and ~2739 mm y-1 at 25 and 93 degrees C, respectively. It is mainly owing to the large contact area and short distance between CaMgSn and alpha-Mg matrix derived from the refined CaMgSn particles in SRS alloy. Our work proposes a novel degradable magnesium alloy and a processing method to prepare degradable magnesium alloy by structure modification, which is different from conventional addition of Cu, Fe, Ni elements. The novel degradable magnesium alloy shows great advantage in avoiding the residue of large amount of insoluble coarse eutectic phases, which would block the horizontal wells.

Automated summary

This study utilizes sub-rapid solidification (SRS) to modify the microstructure, particularly the eutectic phase, of Mg-4.5Al-1.5Sn-0.5Ca alloy. The SRS alloy exhibits superior strength-ductility synergy and increased corrosion rates compared to the conventional solidification alloy. This work proposes a novel degradable magnesium alloy and a processing method for its preparation.