Some control mechanisms of spatial solidification in light alloys

Abstract

Some control mechanisms of spatial solidification in light alloysTwo unconventional approaches of controlling the size and distribution of primary particles in aluminium and magnesium alloys are suggested. The first approach uses the ultrasonic cavitation treatment for multiplication of solidification sites for primary crystals by activating catalytic impurities that are present in the melt. The second way, on the contrary, involves elimination of active solidification nuclei by melt overheating with subsequent nucleation of primary particles at a higher undercooling. Both approaches result in refinement of primary crystals.

Solidification Analysis of an Al-19 Pct Si Alloy Using In-Situ Neutron Diffraction

“…The molten hypereutectic Al-Si alloys are recognized to have a heterogeneous distribution of Si atoms (clusters) with a short range atomic order [3,7,8] at nearliquidus temperatures. Most of these heterogeneities act as solidification sites and facilitate primary Si nucleation [7].…”

“…Most of these heterogeneities act as solidification sites and facilitate primary Si nucleation [7]. Most likely they exist in the liquid state well above the liquidus temperature.…”

“…Moreover, the industrial practice shows heterogeneous primary Si (#1 -dark) distribution within casting's sections containing primary α-Al dendrites (#2 -gray) most likely prematurely nucleated above Al-Si eutectic temperature ( Figure 2) [1,5,7].…”

Solidification Analysis of Al‐Si Alloys Modified with Addition of Cu Using In‐Situ Neutron Diffraction

“…It is understood that as-cast microstructure of the material is much dependent on melt processing in casting operations. Molten metal pouring temperature and cooling rate (hence, solidification rate), for example, determines size and distribution of primary Si particles, as well as crystallographic characteristics of the Al-Si eutectic [7][8][9]. All these in many ways determine in-service properties of the cast components.…”

In Situ Study of Microstructure Evolution in Solidification of Hypereutectic Al-Si Alloys with Application of Thermal Analysis and Neutron Diffraction

“…As temperature is further reduced, the peaks become narrower and taller as the Si clusters grow and form micrometre-sized crystals floating in the melt. [21][22][23][24]31,32] From the diffraction pattern, it appears likely that the Si crystallites are present in the melt at higher temperatures [most likely exceeding 950 K (677°C)], but much longer counting time is required to acquire the statistically valid data to support this claim. Verification of this hypothesis may become crucial for proper selection of melt processing and casting parameters, since it affects the size and distribution of Si in the cast component.…”