Mg , Si and die geometry effects on the formability and the machinability of recycled aluminium alloys
Mg, Si and die geometry effects on the formability and machinability were experimentally reported, concerning AA6xxx aluminium alloys which were produced by recycling raw material. The aluminium alloys formability characteristics were evaluated during extrusion and open die forging tests estimating the needed load; the machinability characteristics of the same aluminium alloys were conducted via cutting force measurements during simple turning process. Key-Words: formability, machinability, Mg ratio, Si ratio, extrusion test, cutting, recycling
Hot torsion tests to model the deformation behavior of aluminium alloys at hot working temperatures
Abstract Knowledge of the deformation behavior of aluminium alloys at hot working temperatures is very important for high temperature manufacturing processes such as hot extrusion. Hot torsion tests were adopted to model this property in this paper. Constitutive equations for stress and strain were developed based on the functional relationship between torque and twist, which enables the material constants to be identified directly from the hot torsion test data. Hot torsion tests were conducted with the material AA5252 over a range of twist rate from 0.015 to 14.9 rev s −1 and for each twist rate at an initial temperature range of 350–550°C, respectively, which produced data to validate the constitutive equations with the proposed linear regression and the non-linear iteration formats to identify the material constants. A good agreement between the experimental data and the predicted results has been achieved, which demonstrates that the proposed constitutive equations and the methods of determination of the material constants are suitable to model the high temperature deformation behavior of aluminium alloys, which also demonstrates that hot torsion tests can not only produce data to identify material constants but also serve as a basis for the development of constitutive equations.
Transmission electron microscopy of lattice planes in human alveolar bone apatite crystals
SummaryPeriodic fringes corresponding to six different lattice planes have been observed in apatite crystals of human normal alveolar bone by transmission electron microscopy. Three of these sets of fringes have spacings less than 3.5 Å corresponding to the Scherzer resolution of the microscope used. The (0002) lattice plane of hydroxyapatite of 3.4 Å d-spacings, the
$$\left( {21\bar 11} \right)$$
 lattice plane with a d-spacing of 2.81 Å, and the
$$\left( {30\bar 30} \right)$$
 lattice plane with a d-spacing of 2.72 Å have been identified. The (0002) and
$$\left( {21\bar 21} \right)$$
 lattice planes have been observed for the first time in bone microcrystals. Some of the crystals studied were characterized by a mean width/thickness ratio of 6.91, typical of platelike habit, whereas observations of crystals aligned along the
$$\left\langle {1\bar 210} \right\rangle $$
 and
$$\left\langle {1\bar 211} \right\rangle $$
 directions showed a needlelike habit. The mean length of the bone apatite crystals was 470 Å. A dark line similar to the one observed in enamel and dentine crystals was also seen. The bone microcrystals observed have shown a high sensitivity to beam damage.