Microstructural evolution during reheating of A356 machining chips at semisolid state

The microstructural evolution of A356 machining chips in the semisolid state was studied at different temperatures and holding times. The results showed that the elongated α-Al grains first recrystallized in the semisolid state and then became globular with a high shape factor(SF). Both the temperature and the holding time clearly affected the grain size and SF. When the heating temperature or holding time was increased, the grain size and SF gradually increased and finally became stable. Moreover, the Vickers hardness of primary α-Al grains gradually decreased with increasing heating temperature. The optimal slurry for semisolid processing, with a good combination of grain size and SF, was obtained when the chips were held at 600℃ for 15 min. The semisolid slurry of A356 chips exhibited a lower coarsening rate of α-Al grains than those produced by most of the conventional semisolid processes. The coarsening coefficient was determined to be 436 μm^3·s^(-1) on the basis of the linear Lifshitz–Slyozov–Wagner(LSW) relationship.

Effect of Spark Plasma Sintering on Microstructures and Properties of Al-Fe Alloy

2024 Aluminum alloy powder( 60wt%) and Fe-based amorphous powder( 40 wt%) were adopted. They were mechanical machined for 48hours after being mixed. Bulk material was gained after Spark Plasma Sintering. The sintering parameters included sintering temperature,heating or cooling rates,pressure and holding time. 300 ℃- 800 ℃ were adopted while the heating or cooling rate was 100 ℃ / min and with the pressure of 50 MPa in the experiments. The holding time was 10 min or 20 min at different temperatures, respectively. Bulk materials after sintering were examined by Scanning Electron Microscopy and X-Ray Diffraction. The micro-hardness and relative density also were tested. The sintering temperature had the most significant influence on the microstructure and property of the bulk material. The influence of holding time came second while the heating or cooling rates and pressure were fixed. The density became larger with the increase of the temperature. The compactness was best at 500℃. The pressure and generation of high-temperature phases were the factors which affected the density and the compactness.

Hot Deformation Behavior of Aluminum Alloy 5083 for Automotive and Aviation Applications

This article concentrates on the investigation of hot deformation behavior of conventionally rolled commercial grade AA5083 alloy （A1-4. 5Mg）, for automotive and aviation applications. The superplastic response of the alloy was investigated at high strain rates （ 1〉10-3 s-I） , and a temperature range of 400℃to 550 ℃. An elongation to failure of 201% was achieved at low temperature （425 ℃ ） and high strain rate （ 10-2s-1 ）, which indicates sufficient ductility under hot deformation for manufacturing of extremely complex shapes using superplastic forming technology. Furthermore, the alloy exhibited a maximum elongation of about 470% at strain rate of 10-3s-1 and a temperature of 525℃. The deformation and failure mechanisms at both the critical conditions were studied as a function of strain rate and temperature. The contributions of strain-rate sensitivity and strain hardening were analyzed in relation to the observed tensile ductilities. Deformation mechanism of the alloy was also investigated with reference to Strain rate sensitivity index （m） and Activation energy （Q） for the given test condition. Empirical calculations reveal that dominant deformation mechanism responsible for hot deformation of the alloy is grain boundary sliding （ GBS）, which is further supported by deformed surface examination using scanning electron microscopy （SEM）. Fracture surfaces of the samples deformed to failure, at relatively higher and lower strain rates, was examined to investigate the micro- mechanisms governing failure. Phenomenon of cavity nucleation, growth and coalescence was observed to be the failure mechanism in the investigated alloy.

Comparative TEM investigation on the precipitation behaviors in Cu-15wt% Sn alloy

The decomposition and precipitation behaviors of a quenched Cu-15wt%Sn alloy as a function of aging temperature were investigated using transmission electron microscopy （TEM）. Focused ion beam （FIB） was employed to assist TEM specimen preparation. At 300 ℃, the decomposition of the supersaturated phase occurred at grain boundaries, displaying a cellular morphology. The lamellae were found with and phases, rather than with the equilibrium e and phases. The and phases exhibit a welldefined orientation relationship （OR） as On the other hand, at 320 ℃, only incipient lamellar structures of several micron meters were observed, which were composed of the 6 and phases. At the same time, abundant intragranular precipitation of the e phase in the form of platelets was observed, and OR as （lil）J/ （001）, [110] J/[100] exists between e phase and the ct phase. These contrasting precipitation behaviors are discussed from the viewpoint of crystallographic coherency of these phases.

Fabrication and Mechanical Properties of 2024 Aluminum Alloy Reinforced by FeNiCrCoAl_3 High Entropy Particles

This article mainly discussed bulk material lHvl^ared by powder metallurgy, and the commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy powder （both produced by argon gas atomization process） were ball-milled for different hours. The prepared powder was consolidated by hot extrusion method. The microstruetures of the milled powder and bulk alloy were examined by X - Ray Diffraction （XRD）, Scanning Electron Microscopy （SEM） and Transmission Electron Microscopy （TEM）. The thermal stability was tested by differential scanning calorimetry （DSC）. Mechanical properties of the extruded alloy were examined by Vickers hardness tester and mechanical testing machine. The results show that after milling, the mixed particle sizes and microstructures of the alloy powder change obviously. The compressive strength of the extruded alloy has reached 580 MPa under certain conditions of milling time and composition.

Mechanical and Microstructural Characteristics of Superplastic Al-4. 42Mg Aluminum Alloy

Abstract： The superplastic response of commercial 5083 alloy （Al-4. 42Mg） under uniaxial tension at strain rates ranging from 5 × 10-5 to 10-2s -1 in the temperature interval 400 -550℃ was systematically studied in this paper. The tension test was conducted on samples of rolling direction. The maximum elongation-to-failure of 486% was found at 500 % and strain rate of 10-4s-1. To identify the main characteristics of superplastic deformation and to determine the mechanism of superplastic deformation of the alloy, the microstructure and fracture of the alloy were analyzed as a function of strain, strain rate and temperature using optical microscopy （OM） and scanning electron microscopy （SEM）, the apparent strain rate sensitivity exponent ma and the apparent activation energy Qa were also studied. Based on the fracture analysis and the calculated data of m and Qa, it is suggested that the dominant deformation mechanism in the present alloy is grain boundary sliding （GBS） during the best deformation condition.

Microstructures and grain refinement performance of Al-Ti-B-C grain refiner via powder metallurgy

The Al-5Ti-0.5B-0.5C grain refiner was pre-pared by powder metallurgy(PM).Microstructures of the grain refiner and its grain refinement performance in commercially pure aluminum(Al)were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),and differential scanning calorimetry(DSC).It is found that the average grain size of commercially pure Al can be reduced from~15,000 to~180μm by the addition of Al-5Ti-0.5B-0.5C grain refiner prepared by PM,based on 0.01 wt%Ti addition.The grain refinement efficiency begins to decrease slightly when the grain refiner is kept in the melt for 60 min.The grain refinement is attributed to high stability,proper size,and high density of Al3Ti,TiB2,and TiC particles.

Effect of oxygen addition and annealing time on microstructure and mechanical properties of Ti-34Nb alloy

The effect of oxygen addition and annealing time on microstructure and mechanical properties of Ti-34Nb and Ti-34Nb-0.2O alloys was investigated.The addition of O suppresses the martensitic transformation.The phase composition changes from singleα''phase toα''+βphases with oxygen addition.The addition of oxygen increases strength significantly at as-received,cold-rolled,and annealed alloys through solid solution strengthening.The accumulation of abundance of defects and grain refinement introduced by cold rolling have a significant strengthening effect but also damage plasticity.The addition of oxygen increasesα/βtransformation temperature and promotes the precipitation ofαphase during annealing in Ti-34Nb-0.2O alloy.αprecipitates can inhibit grain growth during annealing.The strength decreases with annealing time increased due to the increase in grain size in Ti-34Nb alloy,while the strength increases in Ti-34Nb-0.2O alloy mainly due to the precipitation ofαphase.The cold rolling followed by annealing and addition of oxygen can improve the properties of alloys.