Search

The influence of primary and secondary extrusion on the microstructure and mechanical properties of the Mg-12Gd-2Er-0.4Zr alloy was investigated. After the primary extrusion, incomplete dynamic recrystallization (DRX) had led to the formation of non-homogenous grain structure with fine equiaxed grain and coarse grains, while the secondary extrusion refined the microstructure remarkably and further improved the mechanical properties. Moreover, the secondary phases were broken into small particles and distributed along the extrusion direction (ED). The secondary extruded (EX2) alloy had the smallest grain size ~3.0 µm and exhibited the best balance of strength and elongation (ultimate tensile strength (UTS) of 305 ± 5.7 MPa, tensile yield strength (TYS) of 258 ± 10 MPa, and elongation (EL) of 31 ± 2.4%). The excellent EL was mainly ascribed to the fully refined dynamic recrystallized (DRXed) grains after the secondary extrusion. Furthermore, the aged EX2 alloy (AEX2) exhibited an excellent balance of strength and elongation (TYS of 382 ± 11 MPa, UTS of 423 ± 6.2 MPa, and EL of 7.6 ± 0.9%). The alloy strengthening was mainly attributed to the refined grains and strong precipitation strengthening.

In this study, the Mg–4Y–1Gd–1Nd–xCa–1Zn–0.3Zr (x = 0 and 0.4 wt%) cast alloys with low rare earth concentration were prepared in different routes of heat treatments, and their microstructures and mechanical properties were investigated. The Mg–4Y–1Gd–1Nd–1Zn–0.4Ca–0.3Zr cast alloy with ultimate tensile strength (UTS) of 264 ± 7.8 MPa, tensile yield strength (TYS) of 153 ± 1.2 MPa and elongation to failure (EL) of 17.2 ± 1.2% was successfully developed by appropriate heat treatment. The improved mechanical performance was attributed to the combined strengthening effects of fine grains, Mg24RE5, $$\beta ^{\prime}$$ , $$\beta _{1}$$ , $$\gamma ^{\prime}$$ and LPSO phases. In the heat treatment process, cooling method of T4 treatment affected the microstructure, which consequently determined the mechanical properties air cooling, rather than water cooling, gave rise to the formation of $$\gamma ^{\prime}$$ phase in the alloy without Ca addition. However, Ca addition facilitated the formation of $$\gamma ^{\prime}$$ phase, and the $$\gamma ^{\prime}$$ phase precipitated in the alloy after T4 treatment either by water cooling or by air cooling, but the air cooling increased the number density of $$\gamma ^{\prime}$$ phase in comparison to the water cooling. Although the $$\gamma ^{\prime}$$ phase strengthened the studied alloys, the formation of $$\gamma ^{\prime}$$ phase inhibited the precipitatition of $$\beta ^{\prime}$$ and $$\beta _{1}$$ phases in the following T6 treatment, and consequently reduced the strengthening effect of $$\beta ^{\prime}$$ and $$\beta _{1}$$ phases. The results showed that the mechanical performance of the studied alloys was largely determined by the precipitation of $$\gamma ^{\prime}$$ phase, which was regulated by the Ca addition and the cooling method of T4 treatment.

The magnesium alloy has a unique advantage in 3C fields due to its high specific strength and excellent electromagnetic shielding characteristic. However, it is difficult to deform homogeneously because of hexagonal close-packed structure. In the present work, the microstructure, mechanical properties and stretch formability of magnesium alloy sheets with different alloying elements were investigated. It was indicated that a trace addition of Zn or/and Er made a key role in modifying texture, activating shear bands formation and precipitating nanoscale second phases, respectively, which resulted in an obvious improvement in both stretch formability and mechanical properties. The results suggested that the Mg–0.5Zn–0.5Er alloy sheet exhibited higher tensile strength along the rolling direction, i.e., yield strength of 180 MPa and ultimate tensile strength of 201 MPa, accompanying with superior Erichsen value of 7.0 mm at room temperature. The good performances of the sheet were ascribed to weakening basal texture intensity, formation of shear bands and precipitation of nanoscale W-phase (Mg3Zn3Er2). The microstructure, mechanical properties and stretch formability of magnesium alloy sheets with different alloying elements were investigated in the present investigation. It was indicated that a trace addition of Zn or/and Er made a key role in modifying texture (Fig. 1), activating shear bands formation and precipitating nanoscale secondary phases (Fig. 2), respectively, which resulted in an obvious improvement in both stretch formability and mechanical properties (Fig. 3).