Development of ultrafine grained Al–Mg–Si alloy with enhanced strength and ductility

The microstructure and mechanical properties of a precipitation hardenable Al–Mg–Si alloy subjected to cryorolling (CR), short annealing and ageing treatments are reported in this present work. The pre-cryorolled solid solution treatment combined with post-CR short annealing (155 °C for 5 min) and then ageing treatment (125 °C for 12 h) has been found to be the optimum processing condition to obtain the ultrafine grained microstructure with substantial improvement of tensile strength (286 MPa) and good tensile ductility (14%) in the Al–Mg–Si alloy. The significant improvement of the mechanical properties of the cryorolled and peak aged 6063 Al alloys have been observed as compared to its bulk alloys in the peak-aged condition (T6).     

Microstructure evolution and mechanical properties of Al−3.6Cu−1Li alloy via cryorolling and aging

An Al−3.6Cu−1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties. The microstructure and aging characteristics of the room temperature-rolled and the cryorolled alloys with 70% and 90% of thickness reductions were studied by microstructure analysis and mechanical tests. The samples subjected to cryorolling with 90% of thickness reduction have high strength and good toughness. This is mainly due to the inhibition of dynamic recovery and the accumulation of high-density dislocations in cryorolled samples. In addition, the artificial aging reveals that the temperature at which peak hardness is attained is inversely proportional to the deformation amount and directly proportional to the rolling temperature. Moreover, bright field images of cryorolled samples after aging indicate the existence of T1 (Al2CuLi) precipitates. This suggests that the high stored strain energy enhances the aging kinetics of the alloy, which further promotes the nucleation of T1 phases.     

Development of ultrafine grained high strength Al–Cu alloy by cryorolling

In the present paper, the microstructure and mechanical properties of a precipitation hardening Al–Cu (2219) alloy subjected to cryorolling, low temperature annealing and ageing treatments are reported. Under optimal processing conditions, ultrafine grained microstructure with improved tensile strength (540 MPa) and good ductility (11% tensile elongation) was obtained.     

Mechanical Properties and Microstructural Evolution of Bulk UFG Al 2014 Alloy Processed Through Cryorolling and Warm Rolling

Tensile properties,microstructural evolution and fracture toughness of A1 2014 alloy subjected to cryorolling followed by warm rolling(CR + WR)have been investigated in the present study.The solution-treated(ST)A1 2014 alloy is cryorolled followed by warm rolling process at different temperatures(110,170 and 210 ℃).The mechanical properties and microstructural features of deformed and undeformed A1 2014 alloys were characterised by optical microscopy,transmission electron microscopy(TEM)and scanning electron microscopy(SEM).The CR + WR samples at 170 ℃ showed an improved hardness(179 HV),tensile(UTS 499 MPa,YS 457 MPa)and fracture toughness(K_Q= 37.49 MPa m~(1/2),K_(ee) = 37.39 MPa m~(1/2) and J integral= 33.25 kJ/mm~2)with respect to ST alloy as measured from the tensile and fracture toughness test.The improved mechanical properties of CR + WR alloy are attributed to grain boundary strengthening,combined recovery and recrystallisation,precipitation hardening and dynamic ageing effect during the deformation.The precipitation of metastable spherical phase Al_2Cu was responsible for the improved tensile and fracture properties of finegrained A1 2014 alloy observed in the present work.     

Double-peak age strengthening of cold-worked 2024 aluminum alloy

The microstructure and mechanical properties of a 2024 Al alloy subjected to different levels of cold-rolling at room temperature and their evolution upon ageing at 453 K were investigated by means of microhardness measurements, tensile tests and transmission electron microscopy. The cold-worked 2024 Al alloy showed double-peak age strengthening behavior. After ageing for 120 min, the samples reached the first peak strength with quite low ductility. However, simultaneous high strength and ductility were achieved by prolonged ageing of 720 min. The first strengthening peak is due to the precipitation of fine S′ precipitates. The optimized mechanical properties of high strength and suitable ductility are attributed mainly to the precipitation of Ω-phase particles at the expense of S′ precipitates after ageing for 720 min. The Ω precipitates are effective in dislocation pinning and accumulation, and they can undergo plastic deformation to some extent, leading to simultaneously improved tensile strength, work-hardening ability and ductility. The present finding sheds light on the development of processing techniques to optimize the mechanical properties of 2024 Al alloy.     

In situ thermomechanical processing to avoid grain boundary precipitation and strength-ductility loss of age hardening alloys

To avoid grain boundary (GB) precipitation during aging, a new strategy of in situ thermomechanical processing for age hardening alloys was proposed. Specifically, high-density nanoscale precipitates were introduced into ultrafine grain (UFG) interiors of 7075Al alloy by equal-channel-angular (ECAP) processing at 250 °C for 8 passes, thus avoiding GB precipitation. Tensile test results indicated that the UFG 7075Al alloy exhibits superior mechanical properties (yield strength of 350 MPa, ultimate tensile strength of 500 MPa, uniform elongation of 18% and tensile ductility of 19%) compared with the UFG 1050Al counterpart (yield strength of 170 MPa, ultimate tensile strength of 180 MPa, uniform elongation of 2.5% and tensile ductility of 7%). Fracture surface morphology studies revealed numerous homogeneous micro shear bands in necking shrinkage areas of both UFG 7075Al and 1050Al alloys, which are controlled by cooperative GB sliding. Moreover, the introduction of nanoscale precipitates in UFG 7075Al matrix weakened the tendency of shear fracture, resulting in a higher tensile ductility and more homogeneous deformation. Different from the GB precipitation during postmortem aging, in situ thermomechanical treatment dynamically formed GBs after precipitation, thus avoiding precipitation on GBs.     

Microstructure and mechanical properties of a basal textured AZ31 magnesium alloy cryorolled at liquid-nitrogen temperature

A strongly basal textured AZ31 magnesium alloy were cryorolled at liquid-nitrogen temperature at various strains. The microstructure and texture of the rolled sheets have been investigated using electron backscatter diffraction (EBSD) and X-ray diffraction. The microstructural and textural evolutions of the AZ31 magnesium alloy during cryorolling have been discussed. A lot of twins were observed in the rolled sheets. The influence of strain on the twin types and variant selection during cryorolling for the magnesium alloy has been discussed quantitatively based on the orientation data collected using EBSD. The influence of the twins on the microstructural and textural evolutions for the AZ31 magnesium alloy during cryorolling has also been discussed. The mechanical properties of the cryorolled sheets were tested by uniaxial tensile tests at the ambient temperature with a strain rate 10^-3s^-1 in the tensile direction respectively along the rolling and transverse directions of the rolled sheets. The relationships between the mechanical properties and microstructure of the cryorolled sheets have been discussed in the present work. The active twinning during rolling at that cryogenic temperature has been found to play an important role in influencing the microstructure, texture, as well as the mechanical properties of the AZ31 magnesium alloy.     

Tensile Behavior of Ultrafine-Grained Al-4Zn-2Mg Alloy Produced by Cryorolling

An Al-4Zn-2Mg alloy was subjected to cryorolling (CR) followed by short annealing. An average grain size of ~100 nm was achieved. Cryorolled samples showed large reduction in grain size due to suppression of dynamic recovery and absence of annihilation of dislocations, as compared to room temperature rolled samples. Further, the ultrafine-grained (UFG) Al-4Zn-2Mg alloy when subjected to natural aging showed an improved strength of ~413 MPa with ductility of ~25%, as compared to ~360 MPa and 22% ductility in peak aged condition of coarse-grained alloy. However, UFG alloy in peak aging condition, exhibited a relatively strength (~375 MPa) and 24% ductility combinations than the natural aging condition. The latter is attributed to dynamic precipitation and stored energy. In the present study, it is demonstrated that simultaneous improvement in strength as well as ductility can be achieved for the Al-4Zn-2Mg alloy through CR and controlled heat treatment combinations.     

Mechanical properties at room temperature of an Al-Zn-Mg-Cu alloy processed by equal channel angular pressing

Tensile tests were conducted to evaluate the influence of equal-channel angular pressing (ECAP) on the mechanical properties at room temperature of overaged Al 7075-O alloy. ECAP processing was performed using route B_C at different temperatures and number of passes, i.e. different processing severity conditions. The maximum load (F_max) recorded during the last pass of each ECAP path considered in this study is a very good estimation of the processing severity. The mechanical properties were studied in terms of the balance between tensile strength and ductility. In the processed Al 7075-O alloy, the grain size was reduced down to ∼150 nm. Consequently, tensile testing at room temperature revealed a significant increase in the maximum tensile strength after ECAP with respect to the as start material. In the present study, as the processing severity increases with the number of ECAP passes or with the decrease in processing temperature, there is a consistent trend of increment in ultimate tensile strength with minor decrease in uniform plastic elongation respect to the first ECAP pass at room temperature. This is in contrast to the behaviour after more severe plastic deformation conditions, where an increase in strength together with a strong decrease in elongation would be expected.     

Improved Fracture Toughness of Cryorolled and Room Temperature Rolled 6082 Al Alloys

In the present work,6082 Al alloy has been rolled to 40% and 70% thickness reductions at the cryogenic and room temperatures for the improvement in mechanical and fracture toughness properties.All cryorolled samples are subjected to aging at different temperatures,i.e.,140,160,and 190 °C to improve the strength,ductility,and fracture toughness.The microstructures of the cryorolled(CR) and room temperature rolled(RTR) alloy after 40% and 70%thickness reductions are characterized by FE-SEM to reveal the modes of failure.The results show that the starting bulk Al alloy specimen is fractured in total ductile manner,consisting of well-developed dimples over the entire surface.The mechanical properties and fracture toughness of the 70% CR alloy are found better than 70% RTR alloy due to higher dislocations density and formation of sub-grain structures in the CR alloy.     

Effect of post equal-channel-angular-pressing aging on the modified 7075 Al alloy containing Sc

The effect of post-ECAP low-temperature aging on mechanical properties of the 7075 Al aluminum alloy containing Sc (7 × 51) after a single pressing was examined. The best aging effect on strengthening was achieved at 373 K after 20–30 h. After the post-ECAP aging treatment, the yield stress and UTS of the 7 × 51 alloy have increased to 680 MPa and 730 MPa, respectively. This achievement is remarkable when compared with the 7075 Al alloy conventionally ECAP processed for three passes exhibiting the YS of 667 MPa and UTS of 677 MPa. The post-ECAP aging was also effective in improving the tensile ductility of the ECAPed alloy. The unECAPed and ECAPed 7 × 51 Al alloys before or after aging at 373 K showed a big difference in strain hardening ability. According to the model assessing the extent to which the hardening and softening mechanisms are active during the plastic deformation of the materials, the low strain hardening rate of the ECAPed alloy could be attributed to a significant contribution to softening by cross slip and a small contribution of precipitation to hardening.     

Microstructure and mechanical properties of Mg-Gd-Dy-Zn alloy with long period stacking ordered structure or stacking faults

The Mg-6.5Gd-2.5Dy-1.8Zn (wt.%) alloy with high strength and ductility was prepared by conventional casting method. At room temperature, the as-cast alloy with 14H long period stacking ordered (LPSO) structure exhibits an ultimate tensile strength of 276 MPa and elongation to failure of 10.8%, while they are 392 MPa and 6.1% for the peak-aged alloy with basal plane stacking faults (SF). The results indicate that the kinking of LPSO structure is beneficial for both work hardening and plasticity, and 14H LPSO structure contributes more to the improvement of ductility while SF is more effective in increasing strength.     

Cryorolling-Induced Texture,Mechanical Properties and Fracture Behavior of Al-Mg-Si Alloys During Cold Deformation

This study investigated the texture, mechanical properties, and fracture behavior during cold working of cryorolled (CR) Al-Mg-Si alloys. An x-ray texture goniometer was used to examine the crystallographic texture, and tensile tests were performed to understand the deformation behavior in more detail. SEM/EBSD/TEM was used to observe the microstructures and fracture morphology of the alloy during cryorolling. The microstructures indicated that a large number of ultrafine grains and dislocations formed after cryorolled. The recrystallization was prohibited due to low temperature during deformation. The ultrafine grains and dislocation strength improved the tensile strength from 279.38 MPa for the room-rolled alloy to 313.98 MPa for the cryorolled alloy; better plasticity (4.6%) was observed in the CR sheet. Ductile and intergranular fractures were observed in the CR sheet deformation from 20 to 90%.     

Characterization of Microstructure,Mechanical Properties and Formability of Cryorolled AA5083 Alloy Sheets

In this work, microstructure, mechanical properties and formability of cryorolled and annealed AA5083 alloy sheets have been characterized and a comparison has been made with cold rolled and annealed sheets. Five-millimeter-thick sheets of this alloy were cryorolled in multiple passes to a final thickness of 1 mm (80% reduction with a true strain of 1.6). Effect of annealing time and temperature on hardness has been studied, and it has been found that a short annealing at 275 °C for 15 min after cryorolling would yield a good combination of strength and ductility. Microstructural investigations showed that the cryorolled and short annealed samples possess bimodal grain structure which is responsible for better mechanical properties than cold rolled sheets. From the experimentally determined forming limit diagrams, the limit strains of cryorolled sheets have been found to be almost equal to conventional cold rolled and annealed sheets in all modes of deformation. No major differences have been found in strain distribution also. This work clearly demonstrates that cryorolling of AA5083 alloy sheets followed by a short annealing with bimodal grain structure can be used for sheet metal forming applications with higher strength and toughness than conventional sheets without any reduction in formability.     

Enhanced Mechanical Properties of AA5083 Matrix Composite via Introducing Al0.5CoCrFeNi Particles and Cryorolling

High-entropy alloy particles (HEAPs) can markedly enhance the mechanical properties of metal matrix composites (MMCs). In this study, AA5083/Al_0.5CoCrFeNi HEAPs MMCs with different 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_0.5CoCrFeNi 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.     

低温轧制超高强度Al-4％Cu-3％TiB2原位复合材料的强化机理

为了开发超高强度铝合金和评估各种强化机制对合金屈服强度的影响,将Al-4%Cu-3%TiB2进行低温轧制,然后再在175℃下快速退火、在125℃下时效。在总伸长率为9%的情况下,Al-4%Cu-3%TiB2原位复合材料得到800 MPa的高强度。使用标准方程来评估固溶强化、晶粒细化、位错强化、弥散强化和析出硬化等各种强化机制的贡献。其中贡献最大的是低温轧制引起的晶粒细化,其次是析出硬化、弥散强化。     

Fabrication of ultrafine-grained AA1060 sheets via accumulative roll bonding with subsequent cryorolling

Ultrafine-grained (UFG) AA1060 sheets were fabricated via five-cycle accumulative roll bonding (ARB) and subsequent three-pass cold rolling (298 K), or cryorolling (83 K and 173 K). Microstructures of the aluminum samples were examined via transmission electron microscopy, and their mechanical properties were measured via tensile and microhardness testing. Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling, and the grain size became finer with reducing rolling temperature. The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm, respectively, via subsequent cold rolling or cryorolling (83 K). Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.     

Influence of yttrium on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy

The influence of Y on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy was investigated. The results show that the phase compositions of Mg-5Li-3Al-2Zn consist of α-Mg and AlLi phases. Adding Y to the alloy results in the formation of Al₂Y compound and facilitates grain refinement. The addition of 0.8 wt.% Y produces the smallest grain size. The tensile tests performed at room temperature show that the additions of Y can improve the mechanical properties of the alloy; the tensile strength and ductility reach peak values when the Y additions are 0.8 wt.% and 1.2 wt.%, respectively. The mechanisms of improvement are related to grain refinement and compound strengthening effects.     

Restoring the tensile properties of PVD-TiN coated Al 7075-T6 using a post heat treatment

In this work, a post heat treatment cycle is proposed with the aim to recover the lost tensile properties of aluminium alloy 7075-T6 coated with a 3 μm thick titanium nitride (TiN) film by using a physical vapour deposition (PVD) process. First, it was found that the application of the PVD hot process with a high operating temperature of 450 °C significantly decreased the tensile properties of the coating-substrate system compared to those of Al 7075-T6. The yield and ultimate strength decreased by 78% and 54%, respectively. However, as a result of re-applying the T6 cycle (as the post heat treatment), substantial improvements of 243% and 77% were achieved in the yield and ultimate strength of the coated material, respectively. Fractography of the failed specimens indicated the TiN coating layer to be satisfactorily adhered to the substrate under tensile loading.     

不完全再结晶Fe40Mn10Cr25Ni25高熵合金的室温及低温力学性能

采用冷轧和退火热处理工艺制备了不完全再结晶结构的Fe₄₀Mn₁₀Cr₂₅Ni₂₅高熵合金,分析了合金的室温(298 K)及低温(77 K)拉伸时的力学性能。结果表明,合金具有优良的室温及低温力学性能,合金在低温拉伸时强度和塑性均得到了提高,其室温强度和断后伸长率分别为880 MPa和18%,低温强度和断后伸长率分别为1360 MPa和36%。合金在室温变形以位错滑移为主,低温变形以位错滑移和孪生为主。室温拉伸时,粗晶晶粒先于细晶晶粒变形,导致试样内部产生了应变梯度,提高了合金的加工硬化率,使合金在室温下具有良好的强塑性。低温拉伸时,粗晶晶粒中形成了大量的变形孪晶,从而提高了合金的低温力学性能。