查看更多>>摘要：In this study,the phase transformations,crystallization kinetics and dissolution mechanism of β phase(Mg17Al12)in magnesium alloy AZ91 were investigated by optical microscopy,X-ray diffraction,differential scanning calorimetry and differential dilatometry.The results indicate that this AZ91 alloy undergoes a phase transformation during aging,a discontinuous precipitation of the β phase(Mg17Al12)at 150 ℃ at the grain boundaries and another continuous at 350 ℃ within the grains.The activation energy of the dissolution reaction of the β phase(Mg17Al12)under non-isothermal conditions is 116.781 kJ·mol-1,while it is 129.7383 kJ·mol-1 under isothermal conditions.The Avrami coefficient,n,relevant for the dissolution kinetics of the β phase(Mg17Al12)is 1.152 and 1.211 in the non-isothermal and isothermal conditions respectively.The nu-merical coefficients m and Avrami n are 0.993 and 1.152.
查看更多>>摘要：Mg-based hydrides are too stable and the kinetics of hydrogen absorption and desorption is not satisfactory.An efficient way to improve these shortcomings is to employ reactive ball milling to synthesize the nanocomposite materials of Mg and additives.In this experiment,TiF3 was se-lected as an additive,and the mechanical milling method was employed to prepare the experimental alloys.The alloys used in this experiment were the as-cast Ce5Mg85Ni10,as-milled Ce5Mg85Ni10 and Ce5Mg85Ni10+3％(mass fraction)TiF3.The phase transformation,structural evolu-tion,isothermal and non-isothermal hydrogenation and dehydrogenation performances of the alloys were inspected by XRD,SEM,TEM,Sievert apparatus,DSC and TGA.It revealed that nanocrystalline appeared in the as-milled samples.Compared with the as-cast alloy,ball milling made the particle dimension and grain size decrease dramatically and the defect density increase significantly.The addition of TiF3 made the surface of ball milling alloy particles markedly coarser and more irregular.Ball milling and adding TiF3 distinctly improved the activation and kinetics of the alloys.Moreover,ball milling along with TiF3 can decrease the onset dehydrogenation temperature of Mg-based hydrides and slightly amel-iorate their thermodynamics.
查看更多>>摘要：Magnesium alloys have many advantages as lightweight materials for engineering applications,especially in the fields of automotive and aero-space.They undergo extensive cutting or machining while making products out of them.Dry cutting,a sustainable machining method,causes more friction and adhesion at the tool-chip interface.One of the promising solutions to this problem is cutting tool surface texturing,which can reduce tool wear and friction in dry cutting and improve machining performance.This paper aims to investigate the impact of dimple textures(made on the flank face of cutting inserts)on tool wear and chip morphology in the dry machining of AZ31B magnesium alloy.The results show that the cutting speed was the most significant factor affecting tool flank wear,followed by feed rate and cutting depth.The tool wear mechanism was examined using scanning electron microscope(SEM)images and energy dispersive X-ray spectroscopy(EDS)analysis reports,which showed that at low cutting speed,the main wear mechanism was abrasion,while at high speed,it was adhesion.The chips are discontinu-ous at low cutting speeds,while continuous at high cutting speeds.The dimple textured flank face cutting tools facilitate the dry machining of AZ31B magnesium alloy and contribute to ecological benefits.
查看更多>>摘要：Hot torsion tests for AZ80 magnesium alloy were carried out in the temperature range of 380-260 ℃,with a constant decreasing temperature rate of 10 ℃·s-1 in order to weaken the basal texture and refine the grains.The results indicated that the average grain sizes were refined form-ing gradient structure with increasing specimen radial position from center(12.2-5.4 μm),and that the initial basal texture intensity of the extru-ded magnesium alloy was weakened from 46.2 to 8.3.Furthermore,the extension twins(ETs)could be disintegrated from the twins forming sep-arated twins with smaller sizes.Interestingly,ETs with the same twin variant intersecting with each other could be coalesced forming grains with similar orientation,while ETs with different twin variants were separated by twins boundaries contributing to grain refinement.Moreover,in ad-dition to the conventional continuous dynamic recrystallized(CDRX)grains with 30° orientation rotated around c-axis of the parent grains,CDRXed grains with 30° rotation around a-axis and random rotation axis were also discerned.Besides,the CDRX evolution induced twins were also elaborated,exhibiting the complex competition between CDRX and twining.Hot torsion deformation with constant decreasing temperatures rate is an effective way of grain refinement and texture modification.
查看更多>>摘要：Cold metal transfer-based wire arc directed energy deposition(CMT-WA-DED)presents a promising avenue for the rapid fabrication of com-ponents crucial to automotive,shipbuilding,and aerospace industries.However,the susceptibility to fatigue of CMT-WA-DED-produced AZ31 Mg alloy components has impeded their widespread adoption for critical load-bearing applications.In this study,a comprehensive investigation into the fatigue behaviour of WA-DED-fabricated AZ31 Mg alloy has been carried out and compared to commercially available wrought AZ31 alloy.Our findings indicate that the as-deposited parts exhibit a lower fatigue life than wrought Mg alloy,primarily due to poor surface finish,tensile residual stress,porosity,and coarse grain microstructure inherent in the WA-DED process.Low Plasticity Burnishing(LPB)treatment is applied to mitigate these issues,which induce significant plastic deformation on the surface.This treatment resulted in a remarkable improve-ment of fatigue life by 42％,accompanied by a reduction in surface roughness,grain refinement and enhancement of compressive residual stress levels.Furthermore,during cyclic deformation,WA-DED specimens exhibited higher plasticity and dislocation density compared to both wrought and WA-DED+LPB specimens.A higher fraction of low angle grain boundaries(LAGBs)in WA-DED specimens contributed to mul-tiple crack initiation sites and convoluted crack paths,ultimately leading to premature failure.In contrast,wrought and WA-DED+LPB speci-mens displayed a higher percentage of high angle grain boundaries(HAGBs),which hindered dislocation movement and resulted in fewer crack initiation sites and less complex crack paths,thereby extending fatigue life.These findings underscore the effectiveness of LPB as a post-pro-cessing technique to enhance the fatigue performance of WA-DED-fabricated AZ31 Mg alloy components.Our study highlights the importance of LPB surface treatment on AZ31 Mg components produced by CMT-WA-DED to remove surface defects,enabling their widespread use in load-bearing applications.
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维普