Casting-chill interface heat transfer during solidification of an aluminum alloy

Abstract

Unidirectional solidification tests on an aluminum alloy were conducted with a computer-controlled instrumented rig. The alloys employed in this study were poured into isolated ingot molds (made of recrystallized alumina and covered with ceramic fiber) placed on top of a steel plate, coated either with a graphite-or ceramic-based paint in order to avoid sticking of the material. Thermal evolution during the test was captured by type-K thermocouples placed at different positions in both the ingot and the plate. The bottom surface of the plate was either cooled with water or left to cool in air. The heat-transfer coefficients across the aluminum-steel interface were evaluated by means of a finitedifference model. It was concluded that the heat-transfer rate depends on the conditions at the interface, such as the type of coating used to protect the plate, and the solidification reactions occurring on the aluminum during its solidification.

Application of cast Al–Si alloys in internal combustion engine components

“…6,22 Therefore, to prevent crack initiation, the alloy must have either high yield strength to accommodate stress elastically, or high ductility to delay crack formation. 23,26,27 The former is required to prevent gas leakage, and the latter is required to prevent cracking in the valve bridge area of a cylinder head. Another factor that must be taken into account is the degradation of strength owing to overaging, which makes plastic deformation easier.…”

“…Another factor that must be taken into account is the degradation of strength owing to overaging, which makes plastic deformation easier. 22,26,28 Moreover, there are some other parameters that improve TMF resistance such as: narrow thermal stress hysteresis loop, 26,29 high thermal conductivity, low thermal expansion coefficient, [30][31][32] microstructural stability, 26,28 small secondary dendrite arm spacing (SDAS), 23,33 low porosity level [34][35][36] and low content of coarse intermetallic phases. 26,37…”

Effect of Solidification Rate and Heat Treating on the Microstructure and Tensile Behavior of an Aluminum-Copper Alloy

“…The reactions that take place during solidification and cooling are detected by the inflections that occur in any of the three curves, because second degree reactions (solidification and precipitation in this case) cannot proceed until the latent heat of transformation has evolved, [16,17] and this affects the cooling rate and modifies the shape of the curves. [4,6,10,11] The reactions that were detected are identified and indicated in the three curves by surrounding them by ellipses. The change of different microstructural parameters as a function of distance from the chilled end is shown in Figure 5.…”

“…The time-derivative (dT/dt) was obtained by fitting a second-degree polynomial through an odd number of points from the cooling curves; dT/dt was evaluated at the midpoint of the odd points. [2,10,11] The specimens used for microstructural evaluation were sectioned from different heights and prepared for light optical microscopy observation using standard techniques. Analysis of porosity was conducted on as-polished samples; measurements of the dendrite arm spacing and grain size were carried out on samples etched with a solution of 1 pct NaOH, 4 pct KMnO 4 , and 95 pct H 2 O.…”

Visioplastic analysis of experimental rolling of steel

“…The small dots in Fig. 3 indicate the width along the rolled specimen that resulted from tting third-degree polynomial splines [25] to the width measurements (indicated by the symbol "). The change in width (spreading) was used to compensate the equivalent strain, •°c, following the procedure described elsewhere [24]:…”