Effect of Conditions of Unidirectional Solidification on Microstructure and Pore Morphology of Al-Mg-Si Alloys

Abstract

Aluminum and Al-Mg-Si alloy ingots with pores were fabricated by unidirectional solidification through thermal decomposition of Ca(OH) 2 powders. The porosity of aluminum and Al-Mg-Si alloy were 10-17% and 0.1-2%, respectively. While the pores with 250-400 mm diameter were observed in a grain or across several grains in the aluminum ingots, smaller pores with 50-300 mm were observed in an eutectic region between primary dendrites in the Al-Mg-Si ingots. In the alloys with Mg(0.25-0.5 mass%) and Si(0.2-0.4 mass%), the unidirectional pores were aligned between columnar dendrites grown in the unidirectional solidification. With higher Mg and Si contents, the equiaxed dendrite zones with spherical pores were observed in a region with low temperature gradient. The results of thermal analysis showed that constitutional supercooling, which causes equiaxed dendrites, tends to occur with increase in Mg and Si contents and with low temperature gradient at the solid-liquid interface. Under this condition, spherical pores were evolved, because the surrounding -dendrites solidified isotropically. Therefore, it is concluded that the pore growth direction is affected by morphology of dendrites.

Quantification and characterisation of porosity in selectively laser melted Al–Si10–Mg using X-ray computed tomography

“…This is the interpretation previously suggested by Spierings et al [36] for a similar observation in SLM stainless steel 316L. Conversely, other work on Al-Mg-Si alloys by Kim et al [58] and Al-Mg alloy by Fang et al [59] has shown that larger pores result from lower cooling rates.…”

Fatigue life of ablation-cast 6061-T6 components

“…The liquidus and solidus temperatures for [6]. Castings for a military application, as shown in Fig.…”

Pore Morphology of Porous Al-Ti Alloy Fabricated by Continuous Casting in Hydrogen Atmosphere

“…The peritectic microstructure is the finest among the three transfer velocities, which is consistent with a gereral relationship between the microstructure and solidification velocity. 15,16) The precipitates indicated by the arrow are also finest and distributed homogeneously in the matrix. 17) EPMA and XRD measurements were performed to identify the precipitates.…”

“…Importantly, the primary crystals are more easily formed at high transfer velocity. 15,16) The formed primary crystals possibly suppresses the decrease in the porosity at high transfer velocity, because the crystals would suppress the escape of hydrogen from the solid/liquid interface. As a result, in porous Al-Ti alloy, the porosity possibly does not decrease at high transfer velocity.…”