Advanced Materials Research Vol. 409

Abstract: Ti has high strength, good corrosion resistance, is lightweight and shows good biocompatibility. It has thus been used extensively for mechanical and medical structural components. On the other hand, the disadvantages of Ti include a high melting point, ease of oxidization at high temperatures, low specific heat and low thermal conductivity. There are three specific problems associated with Ti metallurgy. The first is that powder metallurgical processing requires high temperatures and a high vacuum, the second is that samples produced by existing powder metallurgy techniques have a low density, and the third is the occurrence of burning because of a local temperature rise during the cutting process. Therefore, in the present work, a new high-speed, room-temperature molding process involving compression rotation shearing was developed. This method can be used for solidification of metal powders by enforced plastic flow and breaking of oxide films. Therefore, no external heat is required and the molding time is short. The proposed method represents an easy approach to consolidating high melting point metallic materials.

Abstract: An integrally stiffened panel (ISP) made from extruded 2099-T83 Al-Li alloy was subjected to fatigue loadings to investigate the influence of both the local texture and grain structure on fatigue crack propagation (FCP) behavior. The microstructure was mainly unrecrystallized. Grains were mostly layered in the web and fibrous in the other locations. Fiber texture components were present in the stiffener locations, and a rolling-type texture in the web. Resistance to FCP decreases as the local aspect ratio increases. Changes in FCP rates in the web, stiffener base and stiffener web were consistent with the microstructural features and texture. The stiffener cap with a strong fiber texture similar to that of the stiffener base exhibited a lower resistance to FCP, suggesting that the influence of the texture is convoluted in the stiffener cap by the markedly different grain structure. Therefore, FCP behavior in this alloy appears to be governed by both texture and grain structure.

Abstract: The current study investigates the effects of mixing parameters on the quality of anode paste and green anode used in aluminum electrolysis. Four mixing times and four mixing temperatures were applied to prepare anode pastes using calcined petroleum coke and coal tar pitch, as raw materials. The volume of the pores in the paste was used as the indicator for mixing effectiveness. A compression test was applied to the pastes to study the compactability of these pastes and to investigate the effect of mixing parameters on density of the green samples. It was shown that mixing parameters influence the size, volume and surface area of paste porosity and also its compaction behaviour.

Abstract: This study examines the recovery behaviour of the inter-alloy region between a core AA6XXX clad with AA3003 after 72% rolling reduction. Sample coupons were heated isochronally or isothermally, at different temperatures or times, respectively, to probe the recovery kinetics of x-ray peak broadening, x-ray macro-texture, and micro-hardness from the cold rolled state. The inter-alloy region had a strong β-fibre typical of rolled Al. The recovery of the {220} and {311} x-ray line profiles were observed between anneals. The full width half maximum was determined from a pseudo-Voigt fit of the profiles to obtain the defect-related information. Distinct changes in the peak shape and microhardness were observed above 80°C (start of recovery), which goes on all the way to 300°C due to recovery, and beyond 300°C both hardness and peak width drop rapidly (recrystallization start), the latter behaviour being closer to AA3004. Modified Williamson-Hall analysis confirms that recovery is due to dislocation annihilation.

Abstract: Utilization of aluminium-lithium alloys in aerospace applications requires an understanding of how processing and product geometry impact their microstructure, crystallographic texture and mechanical properties. In this paper, the effect of various microstructural features as well as deformation textures on the static mechanical properties of Al-Li extruded components has been investigated. These relationships are discussed with regard to two 2099-T83 extruded sections, i.e. a cylindrical extrusion and an integrally stiffened panel (ISP). The ISP typically shows an unrecrystallized microstructure with varying texture depending on the location along its cross section while the cylindrical extrusions present a strong fibre texture. The anisotropy is noticeable in tensile and compressive tests for both types of extrusions.

Abstract: Aluminum-copper alloy B206 has an excellent potential for use in automobiles as suspension knuckles and control arms. The main shortfall of this alloy however, is its high susceptibility to hot tearing. Grain refinement has been shown to reduce hot tearing severity in Al alloys. In the present study, Ti-B grain refiner was added at two levels (0.02 and 0.05 wt% Ti) to B206 to investigate the effect on hot tearing. Residual lattice strain was measured for each condition using neutron diffraction. Equiaxed fine grains significantly reduced hot tears in the alloy, and this resulted in a lower magnitude of residual strain along the casting.

Abstract: A novel Al-Cu-Mg-Ag alloy with small additions of zirconium and scandium was subjected to equal channel angular pressing (ECAP) by using route B_C at 300°C to strains ranging from ~1 to ~12. Initially, the alloy was subjected to solution treatment followed by water quenching; subsequent overageing was carried out at 380°C for 3 h. It was shown that continuous dynamic recrystallization (CDRX) occurs during ECAP resulting in partially recrystallized structure; at a total strain of ~12, the portion of high-angle boundaries (HAB) attains 50 pct., average misorientation is ~25°. Crystallites having elongated shape and an average size of ~1 μm are evolved after a total strain of ~12.

Abstract: An increasing interest has been being taken in hydrogen as a clean energy for solving the global environmental problems. In order to use the hydrogen in safety, investigation on the hydrogen behavior is required. Although hydrogen microprint technique (HMPT) has been known to be effective to investigate the hydrogen behavior, the low detection efficiency for hydrogen was reported. Ion-plating (IP) was reported to increase the detection efficiency in HMPT emitted from the specimen by plastic deformation. On the other hand, no such increase was found for hydrogen permeating through the specimen ion-plated with substrate heating in the previous study by the authors. In the present study, the sheet samples of pure aluminum with 99.99% purity were dehydrogenated and subjected to (a) holding in the IP chamber, (b) bombardment with Ar ions, (c) substrate heating after the bombardment and (d) holding in air. Hydrogen behavior in these samples has been investigated by means of thermal desorption spectroscopy (TDS). The amount of desorbed hydrogen was evidently larger in the conditions of (a) and (b) than in (d). However, the amount of desorbed hydrogen was decreased by the substrate heating (c) to the same level as in (d).

Abstract: In this work, the partial isothermal section of the Al-Ca-Zn system in the region between 33.3 and 100 at.% Ca has been investigated at 350°C using key alloys. The actual composition of the alloys is measured by inductively coupled plasma technique. Phase relations and solubility limits of the binary and ternary compounds have been determined by means of electron probe microanalysis and X-ray diffraction. In the current work, a new ternary compound has been identified in this region with the Al₉Ca₃₁Zn₁₀ (IM1) composition. Binary compound Al₁₄Ca₁₃ (IM2) has an extended solid solubility into the ternary system. The homogeneity ranges of the Al₂Ca, the MgNi₂-type C36 phase Al_2-xCaZn_x (0.28≤x≤0.70) (IM3) at 350°C and CaZn₂ compounds in the pseudobinary Al₂Ca-CaZn₂ section have been determined at 350°C and the results are combined with the literature to construct the partial vertical Al₂Ca-CaZn₂ section and partial isothermal Al-Ca-Zn section at 350°C.