Microstructure, texture evolution and mechanical properties of a large-scale multidirectionally forged Mg-Gd-Y-Zn-Zr-Ag alloy

A large-scale Mg-6.2Gd-3.7Y-0.9Zn-0.3Zr-0.3Ag (wt.%) magnesium component with the dimension of 480 × 250 × 160 mm3 was fabricated via direct-chill (DC) casting, homogenization and multidirectional forging (MDF). The evolution of the microstructure, texture and uniaxial tensile properties during MDF process were comprehensively investigated. 2.5%, 5.6% and 10.9% anisotropy were obtained in the MDF alloy subjected to 9, 18 and 27 passes, respectively. The MDF alloy subjected to 27 passes tensile along FD exhibits superior comprehensive mechanical properties, with a yield strength (TYS) of 292 MPa, ultimate tensile strength (UTS) of 384 MPa and elongation of 9.0%. Interdendritic Mg5(Gd, Y, Zn) phases dissolved after homogenization, with the precipitation of intragranular lamellar 14H long period stacking ordered (LPSO) phases from α-Mg matrix. During the MDF process, intragranular lamellar LPSO phases were initially kinked, suppressing dynamic recrystallization (DRX) behavior in the first 9 passes, and subsequently partially dissolved. Dynamic precipitation of Mg5(Gd, Y) and ultrafine LPSO phase were also induced by MDF. With the cumulative deformation of MDF, increased volume fraction of Mg5(Gd, Y) phases, enhanced texture and refined α-Mg grains are likely responsible for the improved mechanical properties via MDF. We also found that prismatic slip is activated in the deformed grains with the c-axis around FD and multiple slip is activated in the other deformed grains during the MDF process. This paper provides a superior MDF processing route to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production

Influence of Long-Period Stacked Ordered Phases on Inductive Impedance of Mg-Gd-Y-Zn-Zr-Ag Alloys

In this paper, the influence of long-period stacked ordered (LPSO) phases on the electrochemical impedance spectroscopy (EIS) of a Mg-Gd-Y-Zn-Zr-Ag alloy in 0.9 wt.% NaCl was investigated. The Mg-6Gd-3Y-1Zn-0.5Zr-0.3Ag (wt.%) alloy samples with and without LPSO phases in the grain interior (HOMO and LPSO, respectively) were prepared using different heat treatments. The EIS results showed that both the HOMO and LPSO samples’ Nyquist diagrams contained two inductive loops. However, in the Nyquist plots of the LPSO samples, the inductive loops at 1.71–0.67 Hz appeared in the first quadrant rather than the fourth quadrant. Analysis of the fitting parameters illustrated that the abnormal shape of the inductive loops is related to greater values of the surface film capacitance Cf and double layer capacitance Cdl in the LPSO samples. Further investigations through corrosion morphology observation indicated that the greater values of Cf and Cdl in the LPSO samples resulted from the existence of intragranular LPSO phases that created more film-free areas. The above results show that a better understanding of the relationship between the inductive impedance and corrosion morphology of a Mg-6Gd-3Y-1Zn-0.5Zr-0.3Ag alloy in 0.9 wt.% NaCl solution was attained

Achieving high strength-ductility synergy in a dilute Mg-Gd-Zn-Zr alloy with heterogeneous structure via hot extrusion

The common problem of low tensile yield strength (TYS) prevails in high ductility dilute-alloying Mg-RE alloys prepared by traditional hot extrusion. The design strategy of heterostructures in the microstructure of Mg alloys can effectively improve the strength-ductility synergy in mechanical properties, which is expected to break the trade-off dilemma between strength and ductility. In this work, we successfully prepared a series of high ductility as-extruded Mg-Gd-Zn-Zr alloys with all elongations (ELs) greater than 26.0% at room temperature. By controlling the extrusion process and thus introducing heterogeneous fiberous structure, we finally obtained a superior Mg-1.5Gd-0.5Zn-0.5Zr (wt.%) alloy with strength-ductility synergy, which exhibits a TYS of 246 MPa, ultimate tensile strength (UTS) of 274 MPa and an EL of 29.0%. The microstructure examination for the alloy with the heterostructure reveals that the structure consists of alternating filamentous deformed-grain and fine-grain layers. The overall fine grains in the microstructure, a large amount of nanoprecipitates and the relatively high density of residual dislocations contribute to the high TYS of the alloy. The alloy maintaining high ductility is attributed to the activation of multiple slip systems, especially the active and mobile dislocations, the inhibition of the P-type dislocation to B-type dislocation transition, {10 1¯ 2} tensile twinning generated early during tensile testing, and full intergranular slip transfers caused by high geometric compatibility. The present work can further promote the development of dilute-alloying Mg-RE alloys with high strength-ductility synergy

Non-linear energy harvesting from coupled impacting beams

AbstractEnergy harvesting has many potential applications for structures with broadband excitation, such as aircraft noise and low frequency vibrations from human motion. The advantage with a vibro-impacting system is the capability of converting low frequency response to high frequencies. A coupled beam system is base excited and the influence of different system parameters are studied. Exciting the system at a single resonant frequency highlights the influence of clearance and base excitation amplitude on the beam responses. The frequency sweep study shows the sensitivity of the power generated to the contact stiffness, damping and clearance between the beams. The power generated by the coupled system from the non-linear impact is sensitive to the thickness ratio of the beams and the clearance. The variation in thickness ratio alters the spacing of the natural frequencies of the system which causes modes to interact. This study shows that higher power is produced than the linear system, depending on the dissimilarity in the mode shapes of the interacting close modes