Assessment of Mechanism of Pore Formation in Directionally Solidified A356 Alloy

Abstract

It is well-known that the better the control of the liquid aluminium allows obtaining of better properties. One of the most important defects that is held responsible for lower properties has been the presence of porosity. Porosity has always been associated with the amount of dissolved hydrogen in the liquid. However, it was shown that hydrogen was not the major source but only a contributor the porosity. The most important defect that causes porosity is the presence of bifilms. These defects are surface entrained mainly due to turbulence and uncontrolled melt transfer. In this work, a cylindrical mould was designed (Ø30 x 300 mm) both from sand and die. Moulds were produced both from sand and die. Water cooled copper chill was placed at the bottom of the mould in order to generate a directional solidification. After the melt was prepared, prior to casting of the DC cast samples, reduced pressure test sample was taken to measure the melt quality (i.e. bifilm index). The cast parts were then sectioned into regions and longitudinal and transverse areas were investigated metallographically. Pore size, shape and distribution was measured by image analysis. The formation of porosity was evaluated by means of bifilm content, size and distribution in A356 alloy.

Influence of Al-B grain refiner on porosity formation of directionally solidified Al-Si alloys

“…Furthermore, AlB 2 has a great effect on porosity formation [12] . A previous study by Uludağ et al [13] shows that titanium-free grain refiner addition yields lower porosity in Al alloys while titanium addition reveals higher volumetric porosity formation. Therefore, the characterization of grain refiners and their effect on porosity formation has been a great debate among researchers.…”

ETİAL 221 Alaşımında Katılaşma Hızı ve Su Verme Ortamlarının Mekanik Özelliklere Etkisinin İstatistiksel Analizi

“…On the other hand, one of the biggest problems which adversely affects the mechanical properties of aluminum alloys is the amount of porosity (Emadi et al, 1993;Uludağ and DiĢpinar, 2017;. Although the reason of porosity formation is associated with hydrogen and solidification shrinkage (Laslaz and Laty, 1991;Lee and Gokhale, 2006;Sigworth and Wang, 1993), it is claimed that the main reason is the oxide layer formed on the surface of the liquid alloy which is broken down and submerged in the liquid during mold filling and thus forms porosity during solidification (Dispinar et al, 2010;Dispinar and Campbell, 2004;Dispinar and Campbell, 2006;Dispinar and Campbell, 2011).…”

Effect of Ti addition holding time on casting quality and mechanical properties of A356 alloy

“…On the other hand, Tondel [30] first show the improved equiaxed globular structure by Al-B grain refinement. Later, Dispinar [31] and Uludağ [32] studied Al-B additions and showed that feed ability was improved significantly and pore formation was localized in A356 alloy. Additionally, the effect of rare earth elements (La and Ce) on the mechanical and microstructural properties of A357 was described by Jiang et al [33].…”