Effect of heat treatment on the microstructure and mechanical properties of a multidirectionally forged Mg-Gd-Y-Zn-Zr-Ag alloy

Multidirectional forging(MDF)was successfully applied to fabricate large-size Mg-Gd-Y-Zn-Zr-Ag alloy in this work and effects of T4,T5 and T6 treatments on the microstructure and mechanical properties of the as-forged alloy were analyzed.Results show that dynamic recrystallization(DRX)occurs and second phase particles precipitate along the grain boundary during the MDF process.After annealing treatment(T4),the volume fraction and size of dynamic precipitates slightly increase at a lower temperature(430℃)compared with those of MDFed sample,while they are dissolved into theα-Mg matrix at a higher temperature(450℃).At the meantime,short plate-shaped long-period stacking ordered(LPSO)phases are observed in the DRX grains of the MDFed sample and then dissolved into theα-Mg matrix during annealing at both temperatures.Typical basal texture is identified in the MDFed sample,but the basal pole tilts away from final forging direction and rare-earth texture component with<1121>orientation parallel to penultimate forging direction becomes visible after annealing.The T6 sample annealing at 430℃for 4 h and ageing at 200℃for 34 h exhibits the superior strength and ductility in this study.The ultimate tensile strength,tensile yield strength and elongation to failure,which is 455 MPa,308 MPa and 7.7%,respectively,are overall improved compared with the directly-aged(T5)sample.This paper provides a superior heat treatment schedule to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.

Formation of nanocrystalline AZ31B Mg alloys via cryogenic rotary swaging

A bulk nanocrystalline AZ31B Mg alloy with extraordinarily high strength was prepared via cryogenic rotary swaging in this study.The obtained alloy shows finer grains,higher strength,and a negligible tension-compression yield asymmetry,compared with that prepared via room-temperature rotary swaging.Transmission electron microscopy investigations showed that at the initial stage,multiple twins,mostly tension twins,were activated and intersected with each other,thereby refining the coarse grains into a fine lamellar structure.Then,two types of nanoscale subgrains were generated with increasing swaging strain.The first type of nanoscale subgrain contained twin boundaries and low-angle grain boundaries.This type of subgrain appeared at the twin-twin intersections and was mainly driven by high local stress.The second type of nanoscale subgrain was formed within the twin lamellae.The boundaries of this type of subgrain did not contain twin boundaries and were transformed from massive dislocation arrays.Finally,randomly oriented nanograins were obtained via dynamic recrystallization,under the combined function of deformation heat and increased stored energy.Compared with room-temperature rotary swaging,cryogenic rotary swaging exhibits a slower grain refinement process but a remarkably enhanced grain refinement effect after the same five-pass swaging.

Dislocations-induced precipitates and their effect on mechanical properties of Mg-Gd-Y-Zr alloy

Optical microscope(OM),scanning electron microscope(SEM),transmission electron microscope(TEM)and tensile machine were used to characterize the microstructures and mechanical properties of as-forged and aged Mg-9.5Gd-3.8Y-0.6Zr alloys.The results show that a novel kind of dislocation arrays,comprising parallel arranged dislocations,were obtained in the forged alloy.The arrays tend to extend parallel and are heterogeneously distributed with adjacent distances varying from 0.3μm to 1.4μm.After aging the alloy at 265°C,a large number of preferential-oriented phases were precipitated on the dislocation arrays,forming a structure of"precipitation chains"(PCs),which results in simultaneous increments of strength and ductility.

UDP-glucose epimerase 1,moonlighting as a transcriptional activator,is essential for tapetum degradation and male fertility in rice

Multiple enzymes perform moonlighting functions distinct from their main roles.UDP-glucose epimerases(UGEs),a subclass of isomerases,catalyze the interconversion of UDP-glucose(UDP-Glc)and UDP-galactose(UDP-Gal).We identified a rice male-sterile mutant,osuge1,with delayed tapetum degradation and abortive pollen.The mutant osuge1 protein lacked UDP-glucose epimerase activity,resulting in higher UDP-Gal content and lower UDP-Glc levels in the osuge1 mutant compared with the wild type.Interestingly,we discovered that OsUGE1 participates in the TIP2/bHLH142–TDR–EAT1/DTD transcriptional regulatory cascade involved in tapetum degradation,in which TIP2 and TDR regulate the expression of OsUGE1 while OsUGE1 regulates the expression of EAT1.In addition,we found that OsUGE1 regulates the expression of its own gene by directly binding to an E-box element in the OsUGE1 promoter.Collectively,our results indicate that OsUGE1 not only functions as a UDP-glucose epimerase but also moonlights as a transcriptional activator to promote tapetum degradation,revealing a novel regulatory mechanism of rice reproductive development.