Microstructures and impact toughness behavior of Al 5083 alloy processed by cryorolling and afterwards annealing

The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvements in strength and hardness. The ultimate tensile strength increases up to 340 MPa and 390 MPa for the 30% and 50% cryorolled samples, respectively. The cryorolled samples, with 30% and 50% reduction, were subjected to Charpy impact testing at various temperatures from 190℃ to 100℃. It is observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility. Annealing of samples after cryorolling shows remarkable increment in impact toughness through recovery and recrystallization. The average grain size of the 50% cryorolled sample （14 μm） after annealing at 350℃ for 1 h is found to be finer than that of the 30% cryorolled sample （25 μm）. The scanning electron microscopy （SEM） analysis of fractured surfaces shows a large-size dimpled morphology, resembling the ductile fracture mechanism in the starting material and fibrous structure with very fine dimples in cryorolled samples corresponding to the brittle fracture mechanism.

Corrosion behavior of ultrafine-grained AA2024 aluminum alloy produced by cryorolling

The objectives of this study were to produce ultrafine-grained(UFG) AA2024 aluminum alloy by cryorolling followed by aging and to evaluate its corrosion behavior. Solutionized samples were cryorolled to ~85% reduction in thickness. Subsequent aging resulted in a UFG structure with finer precipitates of Al_2CuMg in the cryorolled alloy. The(1) solutionized and(2) solutionized and cryorolled samples were uniformly aged at 160°C/24 h and were designated as CGPA and CRPA, respectively; these samples were subsequently subjected to corrosion studies. Potentiodynamic polarization studies in 3.5 wt% NaCl solution indicated an increase in corrosion potential and a decrease in corrosion current density for CRPA compared to CGPA. In the case of CRPA, electrochemical impedance spectroscopic studies indicated the presence of two complex passive oxide layers with a higher charge transfer resistance and lower mass loss during intergranular corrosion tests. The improved corrosion resistance of CRPA was mainly attributed to its UFG structure, uniform distribution of fine precipitates, and absence of coarse grain-boundary precipitation and associated precipitate-free zones as compared with the CGPA alloy.

Achieving High Strength and Tensile Ductility in Pure Nickel by Cryorolling with Subsequent Low-Temperature Short-Time Annealing

Ultra fine-grained pure metals and their alloys have high strength and low ductility.In this study,cryorolling under different strains followed by low-temperature short-time annealing was used to fabricate pure nickel sheets combining high strength with good ductility.The results show that,for different cryorolling strains,the uniform elongation was greatly increased without sacrificing the strength after annealing.A yield strength of 607 MPa and a uniform elongation of 11.7%were obtained after annealing at a small cryorolling strain(ε=0.22),while annealing at a large cryorolling strain(ε=1.6)resulted in a yield strength of 990 MPa and a uniform elongation of 6.4%.X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),and electron backscattered diffraction(EBSD)were used to characterize the microstructure of the specimens and showed that the high strength could be attributed to strain hardening during cryorolling,with an additional contribution from grain refinement and the formation of dislocation walls.The high ductility could be attributed to annealing twins and micro-shear bands during stretching,which improved the strain hardening capacity.The results show that the synergistic effect of strength and ductility can be regulated through low-temperature short-time annealing with different cryorolling strains,which provides a new reference for the design of future thermo-mechanical processes.

Effect of Post Cryorolling Treatments on Microstructural and Mechanical Behaviour of Ultrafine Grained Al-Mg-Si Alloy

To investigate the effect of post cryorolling treatments on simultaneous enhancement in strength and ductility of ultrafine grained material （UFG）, AI 6061 alloy was subjected to cryorolling followed by warm rolling （CR ＋ WR） and compared with cryorolling followed by short annealing （CR ＋ SA） at the same temperature. Transmission electron microscopy （TEM） was used to characterize the microstructural features of the processed material. The mechanical properties were investigated through Vickers hardness testing and tensile testing at room temperature. TEM, X-ray diffraction （XRD） and differential scanning calorimetry （DSC） were used to investigate the precipitation evolution in UFG material. Results indicated that the alloy subjected to CR ＋ WR has shown improved mechanical properties （114 HV, ultimate tensile strength （UTS）： 350 MPa） as compared to that in the case of CR ＋ SA （105 HV, UTS： 285 MPa）. The size of the precipitates observed in CR ＋ WR sample after peak ageing treatment is finer than that of peak aged CR ＋ SA sample. The UTS of peak aged CR ＋ WR sample （UTS： 390 MPa） was found to be higher than that of peak aged CR ＋ SA sample （UTS： 355 MPa）, without decrease in ductility.

Fabrication and Characterization of High-Bonding-Strength Al/Ti/Al-Laminated Composites via Cryorolling

Sandwich-like Al/Ti/Al-laminated composites have many advantages such as low density and high specific strength with value in mechanical manufacturing and aerospace engineering. Here, Al/Ti/Al-laminated composites were fabricated by hot roll bonding and subsequent processes: cryorolling(-190 ℃ and-100 ℃), cold rolling(25 ℃), and hot rolling(300 ℃). Their bonding strength and mechanical properties were then studied by an Autograph AGS-X universal electronic testing machine. The results show that cryorolling can improve the interface bonding strength and tensile strength of Al/Ti/Allaminated composites. For the Al/Ti/Al-laminated composites subjected to cryorolling at-100 ℃, they have the highest strength near 260 MPa—this is 48 MPa and 41 MPa higher than the laminated composites subjected to cold and hot rolling, respectively. These results also show the strongest peeling strength. Finally, the mechanisms of the enhancement of bonding strength and mechanical properties of Al/Ti/Al-laminated composites subjected to cryorolling were mainly discussed.

Enhanced Mechanical Properties of AA5083 Matrix Composite via Introducing Al_(0.5)CoCrFeNi Particles and Cryorolling

High-entropy alloy particles(HEAPs)can markedly enhance the mechanical properties of metal matrix composites(MMCs).In this study,AA5083/Al_(0.5) CoCrFeNi HEAPs MMCs with diff erent HEAPs contents(0,1,and 3 wt%)were prepared via a stir-casting,and then these MMCs sheets were hot rolled(573 K)and cryorolled(77 K),respectively.The mechanical properties of the MMCs sheets were measured by tensile testing and microhardness test.Additionally,their microstructures were analyzed by scanning electron microscopy and transmission electron microscopy.Results revealed that the ultimate tensile strength(UTS)of the as-cast AA5083/Al_(0.5) CoC rF eN i HEAPs MMCs were improved from 203 to 257 MPa by adding 3 wt%HEAPs.And the mechanical properties of the MMCs sheets were improved after cryorolling.After cryorolling with 50%rolling reduction ratio,the MMCs with 1 wt%HEAPs had an UTS of 382 MPa,which was 1.9 times that of the MMCs before rolling.Finally,the strengthening mechanisms of HEAPs and cryorolling on the AA5083/HEAPs MMCs were discussed.

Microstructure and mechanical properties of cryorolled AZ31 magnesium alloy sheets with different initial textures

AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.

Effect of annealing time on microstructure and mechanical properties of cryorolled AISI 310S stainless steel

AISI 310S stable austenitic stainless steel was subjected to 90%cryorolling and then annealed at 800 ℃ for 2-60 min.The effect of annealing time on the microstructure and mechanical properties was studied by optical microscopy,scanning electron microscopy,transmission electron microscopy,microhardness and tensile test.The results show that the grain size of AISI 310S stainless steel is refined to the nanometer level after 90%cryorolling,and the grain size is approximately 20 nm.With the increase in annealing time,the degree of grain recrystallization occurs more fully and completely,as the grain begins to grow and then tends to stabilize.The strength and hardness of the annealed specimens decrease with increasing annealing time,while elongation tends to increase.When the annealing time is 10 min,the yield strength increases by about 2 times compared to that of the original austenite(unrolled),and the elongation is also above 20%,which is the best preparation process for ultra-fine grain austenitic stainless steel under this experimental condition.As the annealing time treatment increases,the fracture morphology changes from mixed quasi-cleavage and ductile fracture(after cryorolling)to ductile fracture(after annealing).

Low-temperature superplasticity of cryorolled Ti-6Al-4V titanium alloy sheets

To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760℃and 830℃with different strain rate.The evolution of grain and micro structure has been studied using transmission electron microscopy and electron backscatter diffraction.When the tensile temperature was 760℃(<0.5T_(m),T_(m)is absolute melting point of alloy.)and the strain rate was 5×10^(-4)s^(-1),the fracture elongation of the sample reached 385%,showing good low-temperature superplasticity.Compared with the tensile temperature of 760℃,the fracture elongation of the s ample at 830℃was lower due to grain coarsening and oxidation.The strain rate sensitivity value m of all samples was larger than0.3,which confirmed that the cryorolled Ti-6A1-4V titanium alloy with a non-equiaxed grains structure can achieve high superplasticity at a temperature lower than 0.5T_(m),and indicated that the main deformation mechanisms in the tensile test at760-830℃were grain rotation and grain boundary sliding.After the tensile test,the average grain size of all samples was less than 5μm,in which significant dynamic recrystallization and recovery occurred.