Chief EditorScientific ReportsThe Macmillan Building4 Crinan StreetLondon N19XW, UKDear Editor:Please find attached our manuscript entitled “A new insight into ductile fracture of ultrafine-grained Al-Mg alloys” which we wish to submit for possible publication in Scientific Reports. This manuscript, or any part of it, has not been published and will not be submitted elsewhere for publication while being considered by Scientific Reports. The manuscript has not been discussed with a Scientific Reports Editor prior to submission. The authors declare that there are no competing financial interests.The authors have a collective research background unifying nanoscale materials, metals and alloys, composite materials, fracture and damage mechanics, applied physics, and mechanical properties. In the current study, we have discovered a relationship between the ductile fracture mechanism and grain refinement of ultrafine-grained/nanostructured metals. We found that the mean grain size at fracture end approaches the theoretical minimum achievable mean grain size value that directly determines the fracture behavior of metals post necking. This finding will be a milestone in fracture mechanics and nanostructured materials. Thus this work will be of great interest to readers of various scientific disciplines, in particular materials scientists and physicists working on nanostructured materials as well as micromechanics.In the past 50 years, many ductile fracture criteria have been proposed. The basic principles upon which ductile fracture criteria are based can be generally divided into four categories: (a) energy dissipation; (b) void growth: material modeling; (c) void growth: growth mechanisms; and (d) void growth: void geometry. It is assumed that the fracture evolution directly depends on the strength, strain hardening capability and strain rate sensitivity of the matrix surrounding the voids. None of these criteria are related to the microstructure change in ductile fracture processing. In the current study, it is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that grains are refined to nanoscale approaching the theoretical minimum achievable value and become brittle in the shear band zone. As explained in the paper, the observation suggested the innovative five-step ductile fracture mechanism: uniform elongation, void nucleation and growth, local necking, grain refinement until the mean grain size approaches the minimum achievable mean grain size, and finally damage.The corresponding author is Dr. Hailiang Yu, School of Mechanical, Materials and Mechatronics Engineering, University of Wollongong, Wollongong, Australia, contactable by email address ****************.au or **********************. The primary work telephone number is +61 (04) 2505 5006 and fax number is +61 (02) 4221 5474.Thank you for your kind consideration.近年笔者发表的主要论文1.Yu H.L.*, Tieu K., Lu C., Liu X., Liu M., Godbole A., Kong C., Qin Q.H. A new insightinto ductile fracture of ultrafine-grained Al-Mg alloys. Scientific Reports, 2015, 5: 9568.Free access available from: /10.1038/srep095682.Yu H.L.*, Tieu K., Hadi S., Lu C., Godbole A., Kong C. High strength and ductility ofultrathin laminate foils using accumulative roll bonding and asymmetric rolling.Metallurgical and Materials Transactions A, 2015, 46: 869-879.Available from: /10.1007/s11661-014-2640-33.Yu H.L.*, Tieu K., Lu C., Kong C. Abnormally high residual dislocation density in purealuminum after Al/Ti/Al laminate annealing for seven days. Philosophical Magazine Letters, 2014, 94: 732-740.Free access available from: /10.1080/09500839.2014.9719024.Yu H.L.*, Tieu K., Lu C., Lou Y.S., Liu X.H., Godbole A., Kong C. Tensile fracture ofultrafine Al 6061 sheets by asymmetric cryorolling for microforming. International Journal of Damage Mechanics, 2014, 23: 1077-1095.Available from: /10.1177/10567895145380835.Yu H.L.*, Tieu K., Lu C., Liu X., Godbole A., Li H.J., Kong C., Qin Q.H. A deformationmechanism of hard metal surrounded by soft metal during roll forming. Scientific Reports, 2014, 4: 5017.Free access available from: /10.1038/srep050176.Yu H.L.*, Tieu K., Lu C., Godbole A. An investigation of interface bonding of bimetallicfoils by combined accumulative roll bonding and asymmetric rolling techniques.Metallurgical and Materials Transactions A, 2014, 45: 4038-4045.Available from: /10.1007/s11661-014-2311-47.Yu H.L.*, Liu X.H., Li X.W., Godbole A. Crack healing in a low-carbon steel under hotplastic deformation. Metallurgical and Materials Transactions A, 2014, 45, 1001-1009.Available from: /10.1007/s11661-013-2049-48.Yu H.L.*, Lu C., Tieu K., Godbole A., Sun Y., Liu M., Su L.H., Tang D.L., Kong C.Fabrication of ultrathin nanostructured bimetal foils by accumulative roll bonding and asymmetric rolling.Scientific Reports, 2013, 3: 2373.Free access available from: /10.1038/srep023739.Yu H.L.*, Tieu K. Lu C., Liu X.H., Godbole A., Kong C. Mechanical properties ofAl-Mg-Si alloy sheets produced using asymmetric cryorolling and ageing treatment.Materials Science Engineering A, 2013, 568: 212-218.Available from: /10.1016/j.msea.2013.01.04810.Y u H.L.*, Lu C., Tieu K., Liu X.H., Sun Y., Yu Q.B., Kong C. Asymmetric cryorollingfor fabrication of nanostructural aluminum sheets,Scientific Reports, 2012, 2: 772.Free access available from: DOI: /10.1038/srep00772*******如果您不能下载全文，请通过****************.au联系*******。