A Model for Gas Microporosity in Aluminum and Magnesium Alloys

Abstract

A quantitative prediction of the amount of gas microporosity in aluminum and magnesiumalloy castings is performed with a continuum model of dendritic solidification. The distribution of the pore volume fraction and pore size is calculated from a set of conservation equations that solves the transport phenomena during solidification at the macroscale and the hydrogen diffusion into the pores at the microscale. A technique based on a pseudo-alloy solute that is transported by the melt is used to determine the potential sites of pore growth, subject to considerations of mechanical and thermodynamic equilibrium. The modeling results for aluminum alloy A356 are found to agree well with published studies. In view of the limited availability of experimental data for Mg-alloy gravity-poured castings, the formation of porosity in AZ91 is studied qualitatively, assuming that casting conditions are similar to A356. In particular, the minimum initial hydrogen content that leads to the formation of gas porosity was compared for both alloys. It is found that the initial hydrogen content necessary for forming porosity is much higher in AZ91 than in A356. This is attributed to significant differences in the solubility of the hydrogen in both alloys.

Effect of weld travel speed on solidification cracking behavior. Part 3: modeling

“…Stress based models applied solid-state fracture mechanics to liquid film rupture, taking into account surface energy effects and a modified Griffith criterion [65]. A pressure based model assumed a microscopic gas pore to grow as a pore [69,70] or a crack [51] [71][72][73] if the sum of pressures contributing to its growth (liquid pressure drop and dissolved gas pressure) exceeds the pressures contributing to its shrinkage (metallostatic pressure, capillary pressure, atmospheric pressure). Simplified mass balance approaches [36,67,68] consider the crack opening due to transverse deformation to be compensated by advancement of the crack and feeding of liquid.…”

Printed and Hybrid Electronics Enabled by Digital Additive Manufacturing Technologies

“…The growth of the solid phases, with dendritic, cellular, lamellar, or other structures, is significantly affected by the transport phenomena in the molten pool. [46][47][48][49][50][51][52][53][54] Thermal history determines the microstructure, which in turn determines the mechanical properties. Many experimental studies have been performed to analyze the morphology of the microstructures.…”

Physics of microporosity formation in casting alloys – sensitivity analysis for Al–Si alloys

“…Other researchers worked with significantly smaller numbers, such as 3 mm (Ref. 14) or even 1 mm. 18 It appears that SDAS/2 is too large an initial radius, as experimental measurements show that the final radius is on the order of SDAS/2.…”