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The present study was carried out on ultra-pure aluminum, 1050, and 356 alloys. The results revealed that when Al-4%B is added to ultra-pure aluminum, it forms AlB12 and AlB2 which have no grain refining effect in pure aluminum. When no grain refiner is added to pure aluminum, the microstructure is a mixture of columnar and equiaxed grains. The addition of 30 ppm Ti to pure aluminum is sufficient to promote equiaxed grains when the metal is solidified at high rate ~ 10°C/s but requires an addition of 1000 ppm B at 0.8°C. Increasing the Si content to 7% reduces the initial grain size of pure aluminum from 2800 μm to 1200 μm. In commercial aluminum, B reacts with traces of Ti to form TiB2 phases which are active grain refining agents. However, in Al-7%Si, Ti reacts with Si forming (Al,Si)2Ti phase which is a poor refining agent. [ABSTRACT FROM AUTHOR]

A study on the effect of different grain refiners and addition technique in Al-7%Si alloys was carried out. The results show that the Al3Ti phase reacts with silicon (Si) in the molten alloy forming a new compound (Al,Si)3Ti. This reaction is independent of the grain refiner addition technique. The temperature of the liquid metal causes a significant change in the Al3Ti phase morphology, which precipitates in the form of platelets at 750°C and in a dendritic form at 950°C. It has also been observed that while (Al,Si)3Ti phase platelets precipitate within the α-aluminum dendrites, the TiB2 or AlB2 particles are rejected into the surrounding interdendritic regions. The results also reveal that addition of 100ppm B will reduce the initial grain size by ~ 85%, which is more than the reduction obtained with the addition of 0.2%Ti in the form of Al-10%Ti (about 65%). [ABSTRACT FROM AUTHOR]

The present work was performed on A413.1 alloy containing 0.2–1.5 wt% rare earth metals (lanthanum or cerium), 0.05–0.15% Ti, and 0–0.02 wt% Sr. These elements were either added individually or combined. Thermal analysis, image analysis, and electron probe microanalysis were the main techniques employed in the present study. The results show that the use of the depression in the eutectic temperature as a function of alloy modification cannot be applied in the case when the alloy is treated with rare earth metals. Increasing the concentration of RE increases the solidification zone especially in Sr-modified alloys leading to poor feeding ability. This observation is more prominent in the case of Ce addition. Depending upon the amount of added Ti, two RE based intermetallics can be formed: (i) a white phase, mainly platelet-like (approximately 2.5 μm thick), that is rich in RE, Si, Cu, and Al and (ii) a second phase made up of mainly grey sludge particles (star-like) branching in different directions. The grey phase is rich in Ti with some RE (almost 20% of that in the white phase) with traces of Si and Cu. There is a strong interaction between RE and Sr leading to a reduction in the efficiency of Sr as a eutectic Si modifier causing particle demodification. [ABSTRACT FROM AUTHOR]

Two V-8 engine blocks with cast-in grey iron liners were cast from a heat-treatable aluminium alloy. These blocks were instrumented by the insertion of 24 type K thermocouples placed at different points in the casting to record the thermal evolution during solidification. One of the blocks was cast after heating up the liners by induction, whereas the second was cast without the use of induction heating. The temperature–time readings from the thermocouples were obtained for thermal analysis. The solidification reactions detected were the formation of primary pre-eutectic aluminium dendrites, and two different eutectics that corresponded to Al–Si and complex Al–Si–Mg–Cu aggregates. It was found that the different solidification reactions were affected by the use of induction to heat up the liners, and by the chilling effect caused by a grey iron inset located at the bottom of the engine block moulds. The results indicate that solidification starts either at the window (bottom) or deck (top) positions in the interliners depending on whether the block was cast with or without the use of induction heating. [ABSTRACT FROM AUTHOR]

Abstract: DTA analysis was used to investigate the solidification reactions of alloy A319 with either 12 or 136ppm of Sr added. Strontium does not affect primary solidification of (Al) dendrites but modifies the kinetics of the (Al)–Si eutectic. The effects of Sr level and of cooling rate on the characteristic temperatures for the (Al)–Si and other eutectic reactions are described. [Copyright &y& Elsevier]

Abstract: Solidification of a series of aluminium alloys was studied by means of thermal analysis; the study was centred on the effect that silicon and iron exert on the temperatures for the onset of different microstructural characteristics. The alloys were prepared in a gas fired furnace and were poured into graphite moulds instrumented with a type K thermocouple. The cooling curve was registered with the aid of a computer-driven data logging system and was derived to determine the temperatures for the onset of the formation of pre-eutectic aluminium dendrites, and those for the Al–Si eutectic and for a complex Al–Si–Cu–Mg eutectic. It was found that silicon exerts a strong influence on the two former temperatures, whereas the third one is independent of the content of silicon or iron. [ABSTRACT FROM AUTHOR]