The solidification sequence of an AlMg4.7Si8 alloy is imaged in situ by synchrotron microtomography. Tomograms with (1.4 μm)3/voxel have been recorded every minute while cooling the melt from 600 °C at a cooling rate of 5 K min−1 to 540 °C in the solid state. The solidification process starts with the three-dimensional evolution of the α-Al dendritic structure at 590 °C. The growth of the α-Al dendrites is described by curvature parameters that represent the coarsening quantitatively, and ends in droplet-like shapes of the secondary dendrite arms at 577 °C. There, the eutectic valley of α-Al/Mg2Si is reached, forming initially octahedral Mg2Si particles preferentially at the bases of the secondary dendrite arms. The eutectic grows with seaweed-like Mg2Si structures, with increasing connectivity. During this solidification stage Fe-aluminides form and expand as thin objects within the interdendritic liquid. Finally, the remaining liquid freezes as ternary α-Al/Mg2Si/Si eutectic at 558 °C, increasing further the connectivity of the intermetallic phases. The frozen alloy consists of four phases exhibiting morphologies characteristic of their mode of solidification: α-Al dendrites, eutectic α-Al/Mg2Si “Chinese script” with Fe-aluminides, and interpenetrating α-Al/Mg2Si/Si ternary eutectic.

all operation. Compensation for these changes is available on a control lever which provides adjustments to the normal release speed settings.Manual control levers with four positions are provided, as shown in Fig. 6. One position selects automatic opera tion and the others select retarder pressures which override automatic control. Associated with the group retarders are supervisory controls for selecting the zones of pene tration. Controls are also available for each power switch so that the operator can select routes for reverse moves from the classification yard to the hump. AUTOMATIC OPERATIONUNDER NORMAL CONDITIONS the string of cars being classified moves to the crest at constant speed and the retarder controls are in the automatic position. The retarder operator, located in a tower near the group retarders, watches the cars for unusual rolling conditions and for errors which may be made in the route selection.He does not touch the controls except to make occasional adjustments to the zone selector. In case of unusual conditions, such as a car with dragging brakes, failure of cars to uncouple at the crest, or too fast a humping speed, manual control may be used until normal operations are restored. CONCLUSIONS THIS SYSTEM for automatically controlling the movement of cars into classification tracks is now operating in several classification yards and produces the following benefits:(1) More consistent and accurate control than can be obtained by manual control; (2) reduction in damage to lading by minimizing unsafe couplings; (3) maintenance of high humping speeds at all times ; (4) reduction in work strain on operator, which enables him to spend more time supervising the over-all operation; and (5) operations can be maintained during heavy fog conditions when cars are invisible to the operator.Electronic equipments and components sub jected to conditions of high humidity, rough handling, and thermal shock require the use of encapsulating materials for protection. As each of these materials has its own special qualities, any one of them should be considered for a given application in accordance with the various characteristics, as described.