Modeling of Microporosity Size Distribution in Aluminum Alloy A356

Abstract

Porosity is one of the most common defects to degrade the mechanical properties of aluminum alloys. Prediction of pore size, therefore, is critical to optimize the quality of castings. Moreover, to the design engineer, knowledge of the inherent pore population in a casting is essential to avoid potential fatigue failure of the component. In this work, the size distribution of the porosity was modeled based on the assumptions that the hydrogen pores are nucleated heterogeneously and that the nucleation site distribution is a Gaussian function of hydrogen supersaturation in the melt. The pore growth is simulated as a hydrogen-diffusion-controlled process, which is driven by the hydrogen concentration gradient at the pore liquid interface. Directionally solidified A356 (Al-7Si-0.3Mg) alloy castings were used to evaluate the predictive capability of the proposed model. The cast pore volume fraction and size distributions were measured using X-ray microtomography (XMT). Comparison of the experimental and simulation results showed that good agreement could be obtained in terms of both porosity fraction and size distribution. The model can effectively evaluate the effect of hydrogen content, heterogeneous pore nucleation population, cooling conditions, and degassing time on microporosity formation.

Cellular Automaton Modeling of Microporosity Formation during Solidification of Aluminum Alloys

“…(15) will give rise to the solute and hydrogen partitions around the S/L interface according Eq. (18). The rejected amount of solute Si and hydrogen, ΔC(X) = is added to the remaining liquid in the same interface cell and its surrounding neighbor cells.…”

“…2,3) Because of the fundamental and practical importance, extensive efforts have been devoted to develop models for predicting the occurrence of porosity in castings. As reviewed by Lee et al 2) and Stefanescu,3) most models, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] such as analytical solutions, criteria functions, Darcy's law coupled with the conservation and continuity equations, and gas diffusion-controlled pore growth models, focus on predicting the amount of porosity in a solidified casting, but without graphical morphology output.…”

Effect of (Pr+Ce) Additions on Microstructure and Mechanical Properties of AlSi5Cu1Mg Alloy

“…However, there are many factors affecting eutectic solidification that need further study. Furthermore, some scholars believe that the addition of RE (≥3%) will increase the pore size [35], the increase of pore size will deteriorate the mechanical properties of the alloy [36]. From Table. 2 we can see that the appropriate amount of RE additions will not increase the porosity.…”

Influence of Atomic and Molecular Hydrogen in Silumins Melts on Their Mechanical Properties

“…As compared with the other gases present in aluminum alloys, hydrogen has the highest solubility in liquid aluminum [13]. Under certain conditions, hydrogen dissolved in the alloy promotes the formation of gas and gasshrinkage porosity that becomes more intense as the hydrogen content increases [14]. In particular, this kind of porosity is formed in the course of crystallization of an aluminum alloy containing dissolved hydrogen due to the difference between the solubilities of hydrogen in solid and liquid phases.…”