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Grain refinement is of very important significance for improving the microstructure and mechanical properties of Mg alloys. This work investigated how the addition of various amounts of Y element affected the microstructure and mechanical properties of Mg-9Al-1Zn alloy. It was found that the grain size of Mg-9Al-1Zn alloy decreases as Y element content increases. When 1.2 wt.% Y element content was added, the grain size of Mg-9Al-1Zn alloy could be reduced from 334.2 μm to 134.6 μm, and grain refinement efficiency of 60% was achieved. HRTEM analysis demonstrated a good orientation relationship between the Al2Y phase and the Mg interface, and therefore, it was determined that the Al2Y phase can be used as a heterogeneous nucleation site for α-Mg grains, which promotes the grain refinement of α-Mg grain. Furthermore, the addition of Y element can also significantly refine the eutectic Mg17Al12 phase of the Mg-9Al-1Zn alloy. In this way, the mechanical properties of the Mg-9Al-1Zn alloy are significantly enhanced. It was found that the YS and UTS of the Mg-9Al-1Zn alloy reached 87 MPa and 154 MPa with the addition of 0.9 wt.% of Y element—24% and 43% higher than the Mg-9Al-1Zn alloy. [ABSTRACT FROM AUTHOR]

Master alloys containing Zirconium (Zr) serve as effective grain refiners in most commercial cast magnesium (Mg) alloys. However, their efficacy is diminished in Mg–Al series alloys due to the formation of Al–Zr compounds. In this work, a novel Mg-GNP@MgO master alloy was prepared utilizing the in-situ reaction between CO 2 and Mg. The grain refinement efficiency of this composite inoculation on Mg–9Al alloys was systematically investigated using SEM-EBSD, HRTEM observations, Density Functional Theory (DFT), and Sharp Interface Model (SIM) calculations. The findings suggest that the composite grain refiner (GNP@MgO) exerted a notable refining influence on Mg–9Al alloy. Through the conventional casting process, the average grain size was refined to approximately 13 μm upon the addition of 3 vol% GNP@MgO, achieving a grain refinement efficiency of 90 %. The enhanced refining efficiency arises from the synergistic control over the nucleation and growth processes of α-Mg grains, facilitated by GNP@MgO particles. This process includes improved heterogeneous nucleation, triggered by the newly formed Al 4 C 3 phases through the interaction between GNPs and Al element, followed by the limited expansion of α-Mg grains induced by the nano-sized MgO particles. The MgO particles predominantly gather around grain boundaries to establish stable nano-coating layers, thereby exerting a substantial Zener pinning effect. The pinning role played by the MgO nanoparticles was also verified by a sharp interface model. The findings in this work not only carve out a new avenue for the grain refinement of cast Mg–Al alloys but also inspire fresh perspectives for the development of novel grain refiners. [ABSTRACT FROM AUTHOR]

The hybrid addition of CNTs was used to improve both the strengths and ductility of SiCp reinforced Mg matrix composites. A novel method was developed to simultaneously disperse SiCp and CNTs in Mg melt. Firstly, new CNTs@SiCp hybrid reinforcements were synthesized by CVD. Thus, CNTs were well pre-dispersed on the SiCp surfaces before they were added to Mg melt. Therefore, the following semisolid stirring and ultrasonic vibration dispersed the new hybrid reinforcements well in Mg-6Zn melt. The hybrid composite exhibits some unique features in microstructures. Although the distribution of SiCp was very uniform in the Mg-6Zn matrix, most CNTs distributed along the strips in the state of micro-clusters, in which CNTs were bonded very well with Mg matrix. Most of the CNTs kept their structure integrity during fabrication process. All these factors ensure that the hybrid composite have much higher strength and elongation than the mono SiC/Mg-6Zn composites. The dominant strengthening mechanism is the load transfer effect of CNTs. Apart from grain refinement, the CNTs toughen the composites by impeding the microcrack propagation inside the material. Thus, the hybrid CNTs@SiCp successfully realizes the reinforcing advantage of "1 + 1> 2". [ABSTRACT FROM AUTHOR]

In this work, AZ31 magnesium alloy was successfully manufactured by the electron beam additive manufacturing (EBAM) technique. The microstructure and mechanical properties of the EBAM samples under different energy densities and deposition passes were analyzed. The results show that the energy density has a decisive effect on the manufacturability of the sample, wherein the sample prepared at an energy density of 1.432 × 1010 J·m-3 possesses the best manufacturability. The thermal cycling of the EBAM technique resulted in apparent grain size variation and layered arrangement along the deposition height. The fine grains with an average size of approximately 20 µm account for 30% of the sample while the remaining coarse grains possess an average size of approximately 40 µm. Moreover, a large number of fine Al 8 Mn 5 and Mg 17 Al 12 phases precipitated due to the high cooling rate of the molten pool. The microhardness of the sample first decreased and then increased slightly with increasing deposition height. Under the combined effects of dispersion strengthening and grain refinement, the EBAM specimens demonstrated excellent tensile strength and elongation of 230 MPa and 13.5%, respectively, which are superior to those of the die-cast AZ31 alloy. • AZ31 magnesium alloy was first successfully manufactured by the electron beam additive manufacturing. • The rapid cooling can refine the grain, reduce the composition segregation, and change the distribution of Al elements. • Compared with die-cast AZ31, the yield strength is increased by 50% and the tensile strength is increased by 40% [ABSTRACT FROM AUTHOR]

The effect of 0–1.0 at.% Al additions on grain refinement and phase transformation of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy containing a long period stacking ordered (LPSO) phase was investigated in this work. The addition of Al promoted the formation of the Al2RE phase in the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy, and the dominant secondary phases in the as-cast Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn-1.0Al (at.%) alloy were the Mg3RE phase, LPSO phase, and Al2RE phase. With increased Al addition, the area fraction of the Al2RE phase increased monotonously, while the area fraction of LPSO phase and Mg3RE phase decreased gradually. The orientation relationship between the Al2RE phase and the α-Mg matrix was determined to be <112>Al2RE//<11 2 ¯ 0>α-Mg, {101}Al2RE//{10 1 ¯ 0}α-Mg, which was not affected by Zn and Mn concentrations in the Al2RE phase. Since the Al2RE particles with a size more than 6 μm located at the center of grains could act as nucleants for α-Mg grains, the average grain size of the as-cast alloys decreased from 276 μm to 49 μm after 1.0% Al addition. The effect of the Al addition on the grain refinement of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn alloy was comparable to that of the Zr refined counterpart. [ABSTRACT FROM AUTHOR]

Grain refinement by inoculation treatment is one of the simplest and most efficient ways to improve the mechanical properties of Mg Al alloys. In this study, a novel GNP@MgO grain refiner was designed by an in-situ reaction of CO 2 gas and Mg melt. It can significantly reduce the average grain sizes of Mg 9Al alloys from 126.9 μm to 12.7 μm. The mechanical properties of Mg 9Al alloys were significantly enhanced, and its ultimate compressive strength was increased from 370 MPa to 436 MPa. HRTEM characterization and atomic interface analyses have shown that the Al 4 C 3 phase has an orientation relationship with α-Mg as (009) Al4C3 //(002) Mg , and [11−20] Al4C3 //[11–20] Mg , which has a low degree of lattice mismatch of 5.79%. Besides, these MgO nanoparticles can adsorb on the surface of α-Mg grains and play a role in hindering growth and solute diffusion. The ultra-high grain refinement efficiency of 90% is achieved through the synergistic effects of GNP promoting heterogeneous nucleation and MgO nanoparticles inhibiting grain growth. This work sheds new light on designing innovative and effective grain refiners for Mg alloys. [Display omitted] • A novel GNP@MgO grain refiner was designed by utilizing the in-situ reaction of CO 2 with Mg melts. • Through the coordinated regulation of nucleation and growth stages during crystal growth achieves ultra-high refinement efficiency in Mg 9Al alloys. • The simultaneous refinement of α-Mg grains and the eutectic β-Mg 17 Al 12 phase was achieved. • The mechanical properties of Mg 9Al alloys were significantly enhanced, and the UCS was increased from 370 MPa to 436 MPa. [ABSTRACT FROM AUTHOR]