A vertical-type tandem twin-roll caster is able to produce three-layer clad strips from molten metal directly. Three Al-Si alloys (10%Si, 12.6%Si, 14%Si) were used as the overlay alloy to clad the A3003 base alloy. The effects of Si composition on the solidification manner of the overlay and bonding conditions of the base/overlay interface were investigated to examine whether high Si composition brazing sheets can be fabricated by subsequent cold rolling. Regardless of the Si composition, the microstructure of the overlay consisted of an α-Al phase and eutectic phase from the surface to the mid-central region in the thickness direction. This is due to the high cooling rates, which promotes the shift of the coupled zone. On the other hand, the microstructure of the overlay close to the interface of the base strip was not uniform along the casting direction. An α-Al rich region and eutectic-rich region was observed intermittently. The local difference in α-Al ratio was due to the compressive and shear forces generated by the roll rotation. At the base/overlay interface, no un-bonded area was observed in 10%Si, but local un-bonded areas were observed for 12.6%Si and 14%Si. From the EBSD analysis, the orientations of the base and overlay crystal were equivalent at the bonded area. This indicates that heterogeneous nucleation of the overlay alloy took place on the base alloy strip surface. Thus, solidification of the overlay on the base strip surface is the one of the important factors promoting strong base/overlay bonding. A local un-bonded area at the base/overlay interface and dispersion of fine primary Si particles were observed for 12.6 and 14%Si. Regardless of this, cold rolling of these clad strips was successful without any fracture. This implies that the Si composition range applicable for the overlay of the brazing sheet can be expanded by vertical-type tandem twin-roll casting.
When toughness or corrosion resistance as high as that in AC4CH alloy cannot be obtained for aluminum alloy casting, inexpensive alloys such as AC2A or AC2B may be used in some cases. Modification treatment is applied to these alloys, and this is expected to prevend interior shrinkage rather than improve toughness. However, there are few reports on the effects of modification treatment on shrinkage characteristics. Therefore, in the present study, Na, which is considered to have a high modification effect, was varied at 0, 30, and 60 ppm for AC2B alloy. on the other hand, the P content ranged from 7 to 27ppm. Interior and exterior shrinkage rates were measured by the Tatur mold method. Shrinkage formed on the longitudinal section of the specimens and microstructures were observed.
The results revealed that the threshold of P content for shrinkage transition from external shrinkage to interior shrinkage was 10ppm. Porosity was observed in all specimens. Shrinkage porosity formed in almost all specimens, but in comparison with 8ppm, P content was small, Na content was not observed in 33ppm specimens, which are indicated to have the appropriate quantity. The modification / un-modification threshold of the eutectic structure was Na/P = 2.2.
Spheroidal graphite cast iron tends to have shrinkage cavities at the final solidification portion during cooling in casting. These cavities can significantly deteriorate the fatigue strength depending on the size and distribution. However, there are very few quantitative studies on this issue. In this study, ferritic-pearlitic spheroidal graphite cast iron cylindrical specimens, in which internal shrinkage cavities were intentionally developed, were prepared by utilizing a solidification simulation software. High cycle axial loading fatigue tests were then performed at an R of 0.1 to quantitatively investigate the influence of internal shrinkage cavities on the fatigue strength. Non-destructive measurement of size and distribution of internal shrinkage cavities was carried using an X-ray CT device. The S-N data showed a large scatter because of the different influences of shrinkage cavities in respective specimens on the fatigue crack initiation and propagation characteristics. The cluster of shrinkage cavities was approximated to an equivalent penny-shaped crack by projecting it in the loading direction. The mode I stress intensity factor (SIF) range, ΔK, estimated based on both the crack size and applied stress amplitude, described reasonably the experimental results. The fatigue limit could successfully be evaluated using the threshold SIF range, ΔKth, for a long fatigue crack obtained from compact tension specimens.
In our previous research, a mathematical model of a rod-tank system for liquid transfer with an overhead crane was built using a double-pendulum model taking viscosity into consideration. However, since the frequency analysis of the proposed model behavior with respect to the natural frequency was insufficient, the vibration control design of the transport control system was not taken into account. In this paper, the frequency response of the derived model was analyzed, and the design of shape and size of the rod-tank system was discussed based on natural frequency. A feedforward control system using a notch-filter was also designed for reducing sloshing during liquid transfer by the overhead crane. It usefulness was clarified by simulations and experiments.