Effect of stacking faults and long period stacking order on mechanical properties for rare-earth magnesium alloy: As-cast versus as-solutioned

In this paper, the microstructure and tensile mechanical properties of Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr rare-earth (RE) magnesium alloy in the as -cast state and its solid solution state were investigated by means of microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), backscatter diffraction (EBSD), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and principles simulation. The results show that the mechanical properties were improved after solution ment. The CS520-12 alloy, treated at 520 degrees C for 12 h, exhibited excellent mechanical properties, possessing ultimate tensile strength (UTS) of 343 +/- 5 MPa and an elongation of 18.9 +/- 0.8 %. These main reasons improving of mechanical properties was attributed the formation of I1 stacking faults (SFs) and accumulated dislocations. The Y element, originating from the melt of the eutectic phase during solution treatment, ted in a reduction in stacking faults energy (SFE) and facilitated the formation of I1 faults. The presence numerous SFs hindered dislocation slip. The other key factors for elongation improving were that the weaken texture, and geometrically necessary dislocation (GND) density decreased from 1.52 x 1013m-2 to 1013m-2. 14H-LPSO phase played an important role in the improving mechanical properties for CS480-12, CS480-24 and CS520-24 alloys. The higher elastic modulus of LPSO compared to Mg matrix, according first -principles calculated results, enabled its function as a short -fiber, thus strengthened the mechanical erties. Block -shaped 14H-LPSO in CS480-12 alloys, distributed at the grain boundaries (GBs), suppressed grow of cracks. The lamellar 14H-LPSO within the grains of CS480-24 and CS520-24 alloys were parallel dislocations, which compared with SFs of CS520-12 alloy, can't effectively inhibit the movement dislocations.