Abstract
Recently it was reported that icosahedral phase (I-phase) with quasicrystalline structure is formed in some lightweight Mg alloys. It was found that Mg alloys containing I-phase exhibit improved mechanical properties which make them attractive for industrial applications.
This work presents microstructure investigations and defect studies of squeeze cast Mg-Y-Nd-Zr (WE43) alloy with addition of 14 wt.% and 26 wt.% Zn. For comparison WE43 alloy without any Zn was investigated as well.
Presence of the quasicrystalline I-phase was detected by electron diffraction and X-ray diffraction in both WE43 alloys modified by Zn addition. On the other hand, WE43 without Zn does not contain any I-phase.
Mechanical properties of as-cast alloys were examined by Vickers microhardness (HV) testing. It was found that presence of I-phase leads to a significant hardening.
Defects in as-cast alloys were investigated by positron lifetime (LT) spectroscopy combined with coincidence Doppler broadening (CDB). Reference sample WE43 alloy without Zn exhibits a single-component LT spectrum with lifetime of ~ 224 ps which is close to the Mg bulk lifetime.
On the other hand, vacancy-like defects characterized by positron lifetime of ~ 300 ps were found in WE43 alloys modified by Zn addition. CDB investigations revealed that chemical environment of these defects is enriched with Zn and Y.
Hence, our results indicate the existence of vacancy-like defects connected with the I-phase. We suggest that these defects are located at the interfaces between the I-phase and the Mg-matrix.