Modeling studies on divorced eutectic formation of high pressure die cast magnesium alloy

Abstract

A s the lightest known structural metals, magnesium alloys have attracted much attention due to their superior properties such as low density, high specific strength, excellent castability, good machinability and recyclability [1,2] . Magnesium alloys have been widely used in automotive, aerospace and 3C (computer, communication and consumer electronics) industries to replace steel, cast iron and even aluminum alloy [3] . The high pressure die casting (HPDC) process is a netshape or near net-shape process with the advantages of high efficiency, considerable economic benefit and high precision of the product size. These remarkable advantages make the HPDC process particularly suitable for various complex productions with magnesium alloys, and generally, magnesium alloy parts are mainly formed by the HPDC process [4] .The performance of magnesium alloy die castings Abstract:The morphology and content of the divorced eutectic in the microstructure of high pressure die casting (HPDC) magnesium alloy have a great influence on the final performance of castings. Based on the previous work concerning simulation of the nucleation and dendritic growth of primary α-Mg during the solidification of magnesium alloy under HPDC process, an extension was made to the formerly established CA (Cellular Automaton) model with the purpose of modeling the nucleation and growth of Mg-Al eutectic. With a temperature field and solute field obtained during simulation of the primary α-Mg dendrites as the initial condition of the modified CA model, modeling of the Mg-Al eutectic with a divorced morphology was achieved. Moreover, the simulated results were in accordance with the experimental ones regarding the distribution and content of the divorced eutectic. Taking a "cover-plate" die casting with AM60 magnesium alloy as an example, the rapid solidification with a high cooling rate at the surface layer of the casting led to a fine and uniform grain size of primary α-Mg, while the divorced eutectic at the grain boundary revealed a more dispersed and granular morphology. Islands of divorced eutectic were observed at the central region of the casting, due to the existence of ESCs (Externally Solidified Crystals) which contributed to a coarse and non-uniform grain size of primary α-Mg. The volume percentage of the eutectic β-Mg 17 Al 12 phase is about 2%-6% in the die casting as a whole. The numerical model established in this study is of great significance to the study of the divorced eutectic in the microstructure of die cast magnesium alloy.

Direct‐Chill Casting of Large‐Scale Al–Cu Alloy Ingot Under Ultrasound: Distribution of Physical Fields and Analysis of Microstructure

“…Consequently, the other phase, the θ-Al 2 Cu phase, will nucleate and grow separately on the grain boundaries of α-Al, forming a coarsening divorced eutectic structure. [36] During UADC, the natural convection is transformed to forced convection, and the intensity of convection is increased, causing the changes in the size of the α-Al phase, eutectic structure, and distribution of Cu element. First, the dendritic α-Al grains can be effectively fragmented under the synergistic effect of cavitation bubbles and acoustic streaming.…”

“…Consequently, the other phase, the θ‐Al 2 Cu phase, will nucleate and grow separately on the grain boundaries of α‐Al, forming a coarsening divorced eutectic structure. [ 36 ]…”

Effect of Gd on the Microstructure and Mechanical Properties of High-Pressure Die-Cast Mg-La-Ce Alloys at Ambient and Elevated Temperatures

“…However, the calculated Mg 5 RE phase was not observed by the previous microstructure analysis. It may be due to the rapid solidification of HPDC, where the variation of the composition of the liquid and solid phases during the solidification of the alloy has deviated far from the equilibrium solidification [41,42]. Instead, the Mg 2 Gd and Mg 3 Gd phases with a higher solidification point formed in the liquid phase in the Gd-rich region at the beginning of solidification was retained at room temperature [28].…”

Physical Simulation of Medium and Low Temperature Rolling of Mg-Li Alloy Sheet

“…It has excellent mechanical properties, strong penetration resistance to high-energy particles, electromagnetic shielding performance and other advantages [1]. In the field of communication electronics, biomedical materials, especially in the field of aerospace, it has a very large application prospect [2]. Although the specific stiffness of magnesium-lithium alloy is high, the absolute strength of magnesium-lithium alloy is low.…”