Al-4 Wt Pct Research Articles

Microstructural development in complex nickel-aluminum bronzes

The development of microstructure in complex nickel-aluminum bronzes of nominal composition Cu-10 wt pet Al-5 wt pct Ni-5 wt pct Fe, during continuous cooling from temperatures approaching the solidus, has been investigated using optical and electron microscopic techniques. At high temperatures the alloy consists of bccβ phase, and as the temperature is lowered the fcc copper-rich α phase is precipitated with a Widmanstatten morphology. As the temperature continues to decrease, Fe3Al precipitates form in theβ phase and this is followed by the formation of Fe3Al precipitates in the a phase. On further cooling theβ phase decomposes eutectoidally into ga+ NiAl; the eutectoid reaction initiates at thea/β interface and grows into theβ regions. Under normal cooling conditions the decomposition ofβ into α+ NiAl does not reach completion and the remnantβ phase transforms to martensite.

Deformation processing of an aluminum alloy containing particles: Studies on AI-5 pct Si alloy 4043

Al-5 wt pct Si alloy is processed by upset forging in the temperature range 300 K to 800 K and in the strain rate range 0.02 to 200 s−1. The hardness and tensile properties of the product have been studied. A “safe” window in the strain rate-temperature field has been identified for processing of this alloy to obtain maximum tensile ductility in the product. For the above strain rate range, the temperature range of processing is 550 K to 700 K for obtaining high ductility in the product. On the basis of microstructure and the ductility of the product, the temperature-strain rate regimes of damage due to cavity formation at particles and wedge cracking have been isolated for this alloy. The tensile fracture features recorded on the product specimens are in conformity with the above damage mechanisms. A high temperature treatment above ≈600 K followed by fairly fast cooling gives solid solution strengthening in the alloy at room temperature.

The early stages of GP zone formation in naturally aged Ai-4 wt pct cu alloys

The early stages of the room temperature decomposition of supersaturated solid solutions of Al-4 wt pct Cu alloys have been investigated. Diffuse satellites have been found to flank fundamental reflections in electron diffraction patterns prior to the formation of the platelike GP zones. These are herein interpreted as evidence for the occurrence of spinodal decomposition at room temperature. The development of GP zones from the modulated microstructure is documented by the bright field and weak beam dark field techniques. This continuous formation of GP zones is then interpreted in terms of Cahn’s later stage spinodal theory.

The anisotropy of Al-4 wt pct Cu single crystals tested in plane-strain compression

The anisotropy of Al-4 wt pct Cu single crystals tested in plane-strain compression

A transmission electron microscopy investigation of the early stages of precipitation in an Al-Zn-Mg alloy

The growth of spherical precipitates in an Al-5 wt pct Zn-2 wt pct Mg alloy was monitored by hardness measurements and transmission electron microscopy. The growth of precipitates from 15 to 80A in diameter was followed for various aging times at temperatures of 30, 70, 100, and 150°C. For short times at low aging temperatures precipitate growth followed at 1/9 law, whereas growth at longer times, or higher temperatures, followed at 1’3 law. Various contrast experiments lead to the conclusion that the precipitates produced at all but the shortest aging times at the lowest aging temperatures have a hexagonal structure and are spherical precursors of the η′ phase. The advantages and disadvantages associated with the various imaging techniques for small precipitates utilized in this study are discussed.

Discussion of “effect of stress during aging on the precipitation of ø’ in Al-4 Wt pct Cu”

Discussion of “effect of stress during aging on the precipitation of ø’ in Al-4 Wt pct Cu”

Discussion of “effect of stress during aging on the precipitation of θ′ in Al-4 wt pct Cu”

Discussion of “effect of stress during aging on the precipitation of θ′ in Al-4 wt pct Cu”

Effect of stress during aging on the precipitation of θ′ in Al-4 Wt pct Cu

Experiments have been made on Al-4 wt pct Cu single crystals to determine the influence of stress, applied during aging, on precipitation. Without stress, θ platelets precipitate on all (100) planes. Transmission electron microscopy showed a marked effect of aging stress on the microstructure. A compressive stress of approximately 48 MPa (∼ 7,000 psi) parallel to [001] favored precipitation on (010) and (100) and inhibited precipitation on (001). When a tensile stress of similar magnitude was applied parallel to [001], precipitation was favored on (001) and inhibited on (010) and (100).

A structural investigation of multiple aging of Al-7 wt pct Zn-2.3 wt pct Mg

A transmission electron microscopy study of the structural changes which attend aging at 180°C with and without pre-aging at 100°C was conducted on a high purity aluminum alloy containing 6.8 pct Zn and 2.3 pct Mg. The refinement in precipitate dispersion accompanying multiple aging is caused by the operation of aging sequences which differ from those occurring in material given the single age at 180°C only. The high nucleation rate which occurs during the low temperature pre-aging treatment is responsible for the observed precipitate refinement. The results of this investigation appear to agree favorably with the Pashleyet al. model of multiple aging.

Substructure and dispersion hardening in aged, cold worked, and annealed Al-4 wt pct Cu alloy

Electron microscopy and X-ray line profile analyses have been employed to define the microstructures and substructures of pure aluminum and an overaged Al-4 wt pct Cu alloy after various thermomechanical treatments. Tensile tests were performed on the same materials, and the results have been interpreted in terms of structure. A given cold rolling reduction of the aged Al-4 wt pct Cu alloy produced a much higher dislocation density and a less cellular substructure than the same treatment produced in pure aluminum of comparable initial grain size. Annealing after cold work produced similar responses in both the pure metal and the alloy. For the aged alloy in the as-rolled, or rolled-and-annealed condition, dispersion strengthening and substructure strengthening were found to be linearly additive, and they accounted for virtually all the observed tensile yield strength. Substructure strengthening has been discussed in terms of the relation between dislocation density and the spacing and nature of the substructure boundaries.

Intergranular fracture in an Al-15 Wt Pct Zn alloy

Crack propagation rates for the intergranular fracture of an Al-15 wt pct Zn alloy tested in air, distilled H2O, and 0.5M NaCl have been studied using a double cantilever beam specimen. This technique has been applied to two different types of specimens: polycrystals with large equiaxed grains and bicrystals. The susceptibility to intergranular fracture in air and 0.5M NaCl increases as the volume fraction of G.P. zones in the matrix increases. The microstructure which is most susceptible to fracture exhibits intense planar slip traces while the more resistant microstructures have a more diffuse surface slip pattern. The dependence of cracking rates on the microstructure is explained in terms of the blocking of inhomogeneous plastic flow in the matrix by grain boundaries, resulting in locally severe stress concentrations at the boundaries. Bicrystal tests substantiate these results and show that orientations favoring partial continuity of slip bands across grain boundaries are less susceptible to stress corrosion cracking than arbitrarily oriented boundaries with no slip continuity.

Macrosegregation in castings rotated and oscillated during solidification

The macrosegregation present in stationary, rotated, and oscillated castings of Al-3 wt pct Ag was determined by measuring the distribution of radioactive silver added to the melt. Considerable scatter was observed in the measurements, the scatter being dependent on the sampling technique used. It was found that no significant macrosegregation was present in the stationary and rotated castings. Extensive macrosegregation was detected in the oscillated casting. For the oscillating case the macrosegregation can be accounted for on the basis of the long range movement of dendrite fragments which break and/or melt off in the solid-liquid interface region. This movement is a direct result of turbulent waves associated with the oscillation. The maximum silver concentration is shown to be related to the columnar-to-equiaxed transition.

Solution kinetics of CuAl2 in an Al-4Cu alloy

The results of a recently-developed, spherical, finite geometry, mathematical model using numerical methods are compared to existing closed-form models. The geometry and boundary conditions imposed by the closed-form models are shown to be restrictive in the application of these models to the solution kinetics of second phases. A quantitative metallography study of the solution kinetics of CuAl2 in an Al-4 wt pct Cu alloy was undertaken to provide data on the changes in second-phase particle size distributions as a function of solution treatment time. The size distributions were shown to vary according to the proposed spherical, finite model formulated using numerical methods.

The nucleation of aluminum grains in alloys of aluminum with titanium and boron

The microstructure of a ternary alloy, Al-5 wt pct Ti, 1 wt pct B, has been examined by optical and electron transmission microscopy, by selected area diffraction, and electron probe microscopy, by selected area diffraction, and electron probe microanalysis. Particles of Al3Ti are found at the center of grains and there exist preferred epitaxial orientations between this compound and the surrounding aluminum. Particles containing titanium and boron occur at aluminum grain boundaries and have no preferred configurations with respect to the aluminum or to one another. It is concluded that the active heterogeneous nuclei are therefore Al3Ti and that particles of TiB2, AlB2, or a ternary compound are not active in this alloy. Grain size measurements in binary Al-Ti alloys suggest that particles of a nucleating phase must be present at concentrations as low as 0.01 wt pct Ti, and it is suggested that these could be Al3Ti if the existing binary phase diagram Al-Ti is in error.