秦川牛宰后成熟过程中线粒体Tu翻译延长因子对牛肉持水性的影响

探究秦川牛宰后成熟过程中线粒体Tu翻译延长因子(mitochondrial Tu translation elongation factor,TUFM)表达对肉的持水性影响。以秦川牛背最长肌为研究对象,测定4℃不同成熟时间下的pH值、贮藏损失、离心损失、蒸煮损失、水分分布、肌原纤维蛋白等指标变化情况,测定不同成熟时间(0、96、192 h)下TUFM表达量及其含量、Beclin1蛋白表达量。结果显示:在秦川牛宰后成熟期间,肌原纤维蛋白发生降解,TUFM的表达量与Beclin1蛋白表达量和牛肉的持水性存在密切关系,其中蛋白质组学测定的TUFM表达量变化与TUFM含量变化趋势一致,Beclin1蛋白表达量、贮藏损失、离心损失、蒸煮损失整体均呈先上升后下降趋势,pH值呈先下降后上升趋势;Pearson相关性分析表明,牛背最长肌中TUFM表达量与低场核磁共振峰面积比P_(2b)、Beclin1蛋白表达量呈极显著正相关(P<0.01),与贮藏损失、离心损失、蒸煮损失呈显著正相关(P<0.05),与P_(21)呈极显著负相关(P<0.01),与P_(22)呈显著负相关(P<0.05),与pH值无显著相关性(P>0.05)。通过蛋白质组学鉴定出23种与TUFM相关的差异蛋白,通过基因本体论、京都基因与基因组百科全书通路分析发现,差异蛋白可通过多种途径参与能量代谢,进而介导细胞自噬;对差异蛋白和持水性指标进行Pearson相关性分析发现,有5种差异蛋白(ATP5F1D、EEF1A2、GSPT1、NDUFB5、SUCLG1)与持水性指标具有显著相关性(P<0.05、P<0.01)。分析可知,包括TUFM在内,共6种蛋白主要通过能量代谢和氧转运等途径正向或负向影响细胞自噬,从而影响肉的持水性。

Ultra-large aluminum shape casting:Opportunities and challenges

Ultra-large aluminum shape castings have been increasingly used in automotive vehicles,particularly in electric vehicles for light-weighting and vehicle manufacturing cost reduction.As most of them are structural components subject to both quasi-static,dynamic and cyclic loading,the quality and quantifiable performance of the ultra-large aluminum shape castings is critical to their success in both design and manufacturing.This paper briefly reviews some application examples of ultra-large aluminum castings in automotive industry and outlines their advantages and benefits.Factors affecting quality,microstructure and mechanical properties of ultra-large aluminum castings are evaluated and discussed as aluminum shape casting processing is very complex and often involves many competing mechanisms,multi-physics phenomena,and potentially large uncertainties that significantly influence the casting quality and performance.Metallurgical analysis and mechanical property assessment of an ultra-large aluminum shape casting are presented.Challenges are highlighted and suggestions are made for robust design and manufacturing of ultra-large aluminum castings.

Improvement of Microstructure and Mechanical Properties of Rapid Cooling Friction Stir-welded A1050 Pure Aluminum

Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding(FSW), respectively. The microstructure and mechanical properties of the welded joints were investigated by electron backscatter diffraction characterization, Vickers hardness measurements, and tensile testing. The results showed that liquid CO_(2) coolant significantly reduced the peak temperature and increased the cooling rate, so the rapidly cooled FSW joint exhibited fine grains with a large number of dislocations. The grain refinement mechanism of the FSW A1050 pure aluminum joint was primarily attributed to the combined effects of continuous dynamic recrystallization, grain subdivision, and geometric dynamic recrystallization. Compared with conventional FSW, the yield strength, ultimate tensile strength, and fracture elongation of rapidly cooled FSW joint were significantly enhanced, and the welding efficiency was increased from 80% to 93%. The enhanced mechanical properties and improved synergy of strength and ductility were obtained due to the increased dislocation density and remarkable grain refinement. The wear of the tool can produce several WC particles retained in the joint, and the contribution of second phase strengthening to the enhanced strength should not be ignored.

Structure and dynamical properties during solidification of liquid aluminum induced by cooling and compression

The structural transformation from a liquid into a crystalline solid is an important subject in condensed matter physics and materials science. In the present study, first-principles molecular dynamics calculations are performed to investigate the structure and properties of aluminum during the solidification which is induced by cooling and compression. In the cooling process and compression process, it is found that the icosahedral short-range order is initially enhanced and then begin to decay, the face-centered cubic short-range order eventually becomes dominant before it transforms into a crystalline solid.

Effect of quenching cooling rate on residual stress and microstructure evolution of 6061 aluminum alloy

In this study,the cooling rate was manipulated by quenching with water of different temperatures(30,60 and 100℃).Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods,respectively.Then,the processability of the quenched samples was evaluated at cryogenic temperatures.The mechanical properties of the as-aged samples were assessed,and microstructure evolution was analyzed.The surface residual stresses of samples W30℃,W60℃and W100℃is−178.7,−161.7 and−117.2 MPa,respectively along x-direction,respectively;and−191.2,−172.1 and−126.2 MPa,respectively along y-direction.The sample quenched in boiling water displaying the lowest residual stress(~34%and~60%reduction in the surface and core).The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient.Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures.The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30℃to 100℃.Fine and homogeneous β"phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones(GP zones)premature precipitated during quenching process.

Effect of Heat Treatment on Microstructure and Mechanical Properties of Multiscale SiC_p Hybrid Reinforced 6061 Aluminum Matrix Composites

The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp), submicron silicon carbide particles(1 μm Si Cp) and Ti particles were studied. The Al/Si Cp composite powder was prepared by high-energy ball milling, and then cold-pressed, sintered, hotextruded, and then heat-treated with different solution temperatures and aging times for the extruded composites. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy(EDS), X-ray diffractometer(XRD) and extrusion testing were used to analyze and test the microstructure and mechanical properties of aluminum matrix composites. The results show that after the multi-stage solid solution at 530 ℃×2 h+535 ℃×2 h+540 ℃×2 h, the particles are mainly equiaxed grains and uniformly distributed. There is no reinforcement agglomeration, and the surface is dense and the insoluble phase is basically dissolved. In the matrix, the strengthening effect is good, and the hardness and compressive strength are 179.43 HV and 680.42 MPa, respectively. Under this solution process, when the aluminum matrix composites are aged at 170 ℃ for 10 h, the hardness and compressive strength can reach their peaks and increase to 195.82 HV and 721.48 MPa, respectively.

Microstructure and properties of 35 kg large aluminum alloy flywheel housing components formed by squeeze casting with local pressure compensation

The squeeze casting method with local pressure compensation was proposed to form a flywheel housing component with a weight of 35 kg.The numerical simulation,microstructure observation and phase characterization were performed,and the influence of local pressure compensation on feeding of thick-wall position,microstructure and mechanical properties of the formed components were discussed.Results show that the molten metal keeps a good fluidity and the filling is complete during the filling process.Although the solidification at thick-wall positions of the mounting ports is slow,the local pressure compensation effectively realizes the local forced feeding,significantly eliminating the shrinkage cavity defects.In the microstructure of AlSi9Mg alloy,α-Al primarily consists of fragmented dendrites and rosette grains,while eutectic Si predominantly comprises needles and short rods.The impact of local pressure compensation on strength is relatively minimal,yet its influence on elongation is considerable.Following local pressure compensation,the average elongation at the compensated areas is 9.18%,which represents a 44.90%higher than that before compensation.The average tensile strength is 209.1 MPa,and the average yield strength is 100.6 MPa.The local pressure compensation can significantly reduce or even eliminate the internal defects in the 35 kg large-weight components formed by squeeze casting.

Influence of Non-Natural Ageing Temperature on the Microstructural Characteristics and Mechanical Properties of Cast Aluminum 6063 Alloy

This research considered the effect of non-natural aging on the microstructural characteristics and mechanical properties of as-cast aluminum 6063 alloys. The samples were developed through a sand casting process and machined into tensile and impact test samples before carrying out solution heat treatment at 550?C (0.83 Tm) on two parts of the samples while retaining one part as the control. The two parts were further divided into sets denoted A and B and were aged at 180?C (0.27 Tm) and 160?C (0.24 Tm), respectively, for 12 hours. The results showed that sample A has the optimal yield strength and ultimate tensile strength of 192 and 206 MPa, respectively. Likewise, the sample gave the highest impact strength value of about 9.63 J/mm2. The observed results were supported by the optical micrograph, which revealed that the sample has evenly dispersed precipitates in its microstructure. This is deemed responsible for the observed increase in strength of the sample.

Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

Force analysis and experimental study of pure aluminum and Al-5%Ti-1%B alloy continuous expansion extrusion forming process

The deformation zone of CONFORM extrusion was divided into primary gripping zone,gripping zone,conical expansion chamber zone,cylindrical zone and sizing zone of die,and corresponding force equilibrium equations were established using the Slab method.The deformation force formulae of CONFORM machine at any wrapping angle with an expansion chamber were obtained.Experiment on pure aluminum and Al-5%Ti-1%B alloy was conducted on the CONFORM machine self-designed.The resistance to deformation of Al-5%Ti-1%B alloy at the deformation temperature of 400℃ and the strain rate of 3.07 s-1 was measured to be 50 MPa using Gleeble-1500 thermal simulation machine.The calculation results of deformation forces for CONFORM process with an expansion chamber for pure aluminum and Al-5%Ti-1%B alloy were given.The experimental CONFORM radial force is in agreement with the radial force obtained by theoretical formula.

Effect of ultrasonic melt treatment on structure refinement of solidified high purity aluminum

Effect of ultrasonic melt treatment on the macrostructure of solidified high purity aluminum was studied experimentally using metallographic method and complementary numerical calculations of acoustic pressure and velocity distribution in the melt. The results reveal that the macrostructure is effectively refined within a cone-shaped zone ahead of the irradiating face. Inner crystals along with wall crystals multiply particularly within the effectively refined zone and they contribute equally to structure refining. Isothermal holding after ultrasonic melt treatment results in loss of nucleation potency for nearly a half of nuclei, indicating that ultrasound activated heterogeneous nucleation may be as equal important as homogeneous nucleation for ultrasonic induced structure refining.

Homogenization on microstructure and mechanical properties of 2A50 aluminum alloy prepared by liquid forging

The homogenization on microstructure and mechanical properties of 2A50 aluminum alloy prepared by liquid forging was investigated.Wheel hubs were produced using direct and compound loading.The results show that the microstructure and mechanical properties are inhomogeneous in direct forged samples.The microstructure of the wall is coarser than that of the base,and the mechanical properties are lower and some defects are detected at the wheel corner.Using compound loading,the microstructure and mechanical properties of the wall are improved evidently.With increasing feeding amount,the microstructure and mechanical properties become more homogeneous.The defects disappear when the feeding amount is 4 mm.The forged wheel hubs could obtain fine and homogeneous microstructure with grain size of 20-30 μm,tensile strength of 355 MPa and elongation of 10% when the feeding amount is 10 mm.The microstructure and mechanical properties of liquid forged workpieces could be controlled and homogenized using compound loading.

Effect of heat treatment on stress corrosion cracking, fracture toughness and strength of 7085 aluminum alloy

The influences of heat treatment on stress corrosion cracking （SCC）, fracture toughness and strength of 7085 aluminum alloy were investigated by slow strain rate testing, Kahn tear testing combined with scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that the fracture toughness of T74 overaging is increased by 22.9% at the expense of 13.6% strength, and retrogression and reaging （RRA） enhances fracture toughness 14.2% without reducing the strength compared with T6 temper. The fracture toughness of dual-retrogression and reaging （DRRA） is equivalent to that of T74 with an increased strength of 14.6%. The SCC resistance increases in the order： T6〈RRA〈DRRA≈T74. The differences of fracture toughness and SCC were explained on the basis of the role of matrix precipitates and grain boundary orecioitates.

Effects of cold rolling and heat treatment on microstructure and mechanical properties of AA 5052 aluminum alloy

The microstructures and mechanical properties of homogenized-rolled AA5052 aluminum alloys with different rolling reductions and following annealing treatments were investigated by optical microscope, scanning electron microscope, X-ray diffractometer, micro-hardness and tensile tests. The results show that with increasing rolling reduction, the equiaxed grains are elongated along the rolling direction obviously, and accumulation of rolling reduction increases the work hardening effect, which results in the enhanced strength and degraded plasticity. When rolling reduction is 87%, the ultimate tensile strength reaches 325 MPa but elongation is only 2.5%. There are much more secondary phase precipitates after annealing treatment. With an increase of annealing temperature, the amount of precipitates increases and work hardening diminishes continuously. The elongation is improved to ~23% but the tensile strength is decreased to 212 MPa after annealing at 300 °C for 4 h, which are comparable to those of as-homogenized alloy.

Effects of silicon content on microstructure and stress corrosion cracking resistance of 7050 aluminum alloy

Evolution of microstructure and stress corrosion cracking （SCC） susceptibility of 7050 aluminum alloy with 0.094%, 0.134% and 0.261% Si （mass fraction） in T7651 condition have been investigated. The results show that the area fraction of Mg2Si increases from 0.16% to 1,48% and the size becomes coarser, while the area fraction of the other coarse phases including Al2CuMg, Mg（Al,Cu,Zn）2 and A17Cu2Fe decreases from 2.42% to 0.78% with Si content increasing from 0.094% to 0.261%. The tensile strength and elongation of 7050-T7651 alloys is decreased with the increase of Si content by slow strain rate test （SSRT） in ambient air. However, electrical conductivity is improved and SCC susceptibility is reduced with the increase of Si content by SSRT in corrosion environment with 3.5% NaCl solution.

Effects of boric acid on microstructure and corrosion resistance of boric/sulfuric acid anodic film on 7050 aluminum alloy

The microstructure and corrosion resistance of different boric/sulfuric acid anodic（BSAA） films on 7050 aluminum alloy were studied by atomic force microscopy（AFM）,electrochemical impedance spectroscopy（EIS） and scanning Kelvin probe（SKP）.The results show that boric acid does not change the structure of barrier layer of anodic film,but will significantly affect the structure of porous layer,consequently affect the corrosion resistance of anodic film.As the content of boric acid in electrolyte increases from 0 to 8 g/L,the resistance of porous layer（Rp） of BSAA film increases,the capacitance of porous layer（CPEp） decreases,the surface potential moves positively,the pore size lessens,and the corrosion resistance improves.However,the Rp,CPEp and surface potential will change towards opposite direction when the content of boric acid is over 8 g/L.

Flow softening behavior and microstructure evolution of Al-5Zn-2Mg aluminum alloy during dynamic recovery

The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50 s-1. The deformed structures of the samples were observed by optical microscopy （OM）, transmission electron microscopy （TEM） and electron backscattering diffraction （EBSD） analysis. The calculated activation energy is 147 kJ/mol, which is very close to the activation energy for lattice self-diffusion in aluminum （142 kJ/mol）. Dynamic recovery is the dominant restoration mechanism during the deformation. At high strain rate of 50 s-1, temperature rise due to deformation heating leads to a significant flow softening. Microstructure observations indicated that the remaining softening after deformation heating correction at high strain rate and the softening observed at high temperature are associated with grain coarsening induced by grain boundary migration during dynamic recovery process.

Microstructure and mechanical properties of A356 aluminum alloy wheels prepared by thixo-forging combined with a low superheat casting process

The A356 aluminum alloy wheels were prepared by thixo-forging combined with a low superheat casting process. The as-cast microstructure, microstructure evolution during reheating and the mechanical properties of the thixo-forged A356 aluminum alloy wheels were investigated. The results show that the A356 aluminum alloy billet with fine, uniform and non-dendritic grains can be obtained when the melt is cast at 635 ℃. When the billet is reheated at 600 ℃ for 60 min, the non-dendritic grains are changed into spherical ones and the billet can be easily thixo-forged into wheels. The tensile strength and elongation of thixo-forged wheels with T6 heat treatment are 327.6 MPa and 7.8%, respectively, which are higher than those of a cast wheel. It is suggested that the thixo-forging combined with the low superheat casting process is an effective technique to produce aluminum alloy wheels with high mechanical properties.

Hot deformation behavior of Al-Zn-Mg-Cu-Zr aluminum alloys during compression at elevated temperature

The hot compression tests of Al-Zn-Mg-Cu-Zr aluminum alloys （7056 alloy and 7150 alloy） were performed in a temperature range from 300 to 450 °C and at strain rate range from 0.01 to 10 s-1. The results show that the true stress-true strain curves exhibit a peak stress at a critical strain, then the flow stresses decrease monotonically until high strains, showing a dynamic flow softening. The peak stresses depend on the temperature compensated strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic-sine equation with hot deformation activation energy of 244.64 kJ/mol for 7056 alloy and 229.75 kJ/mol for 7150 alloy, respectively, while the peak stresses for the former are lower than those for the latter under the similar compression condition. The deformed microstructures consist of a great amount of precipitates within subgrains in the elongated grains at high Z value and exhibit well formed subgrains in the recrystallized grains at low Z value. The smaller subgrains and greater density of fine precipitates in 7150 alloy are responsible for the high peak stresses because of the substructural strengthening and precipitating hardening compared with 7056 alloy.

Microstructural evolution of 2026 aluminum alloy during hot compression and subsequent heat treatment

2026 aluminum alloy was compressed in a temperature range of 300-450 ℃ and strain rate range of 0.01-10 s^-1. The correlation between compression conditions and microstructural evolution after solution and aging heat treatment was investigated. It is found that the recrystallization and precipitation behavior after heat treatment are associated with the temperature compensated strain rate Z value during hot deformation. Under low Z parameter condition, a small quantity of free recrystallized grains are formed, and the well formed subgrains with clean high-angle boundaries and coarse precipitates seem to be remained during heat treatment. Under high Z parameter condition, a large number of fine equiaxed recrystallized grains are produced, and a high dislocation density with poorly developed cellularity and considerable fine dynamic precipitates are replaced by the well formed subgrains and relatively coarse precipitates after heat treatment. The average recrystallized grain size after heat treatment decreases with increasing Z value and a quantitative relation between the average grain size and the Z value is obtained.