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Investigation on Precipitation and Valence Electron Structure of Phases in Mg3AllCelSb Alloy

Author: HuZhongHua
Tutor: LiuShengXin
School: Zhengzhou University
Course: Materials Processing Engineering
Keywords: Mg-Al -based alloys Ce Sb Liquid quenching Microstructure Valence electron structure
CLC: TG111.1
Type: Master's thesis
Year: 2010
Downloads: 27
Quote: 1
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Abstract

AZ31 magnesium alloy is one of the most widely used wrought magnesium alloy, magnesium alloy has a the typical hexagonal close packed structure, plastic degeneration less capable, production efficiency is generally not high, restricting the widely used high processing costs. The rare earth alloy is an effective method to improve the comprehensive performance of the magnesium alloy, but severely affected by the plasticity and toughness of the alloy containing aluminum-magnesium alloy in the rare phase acicular morphology. How to control the rare-earth-phase morphology, and to improve the deformation of the deformation ability of the magnesium alloy, is the current problems to be solved. In this thesis, optical microscopy (OM), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis testing means to add RE and Sb Mg3Al based alloys, cast alloy display microstructure; analysis of the different temperature liquid the quenched alloy composition phase morphology evolution. Experience of valence electrons (EET) of solids and molecules of theoretical research phase and the ball of the needle-like rare earth phase in the alloy strengthening mechanisms and phase structure formation factor analysis of the alloy phase precipitates in the melt law, magnesium alloys for high-performance component design, preparation, and its further application of experimental data and theoretical basis. The study added Mg3Al based alloys? After, the original coarse divorced eutectic Mg17Al12 phase quantity decreased at the same time to generate a large number along grain boundaries the acicular Al4Ce phase; 1% Sb the Mg3Al1Ce alloys, the needle-like phase of rare earth The number of disappeared to generate the granular CeSb phase and a small amount of irregular lumps of β-Mg17Al12 phase at grain boundaries. The liquid quenching experimental studies have shown that the Mg-Ce added to the Mg3Al alloys intermediate alloy and high-temperature standing, Al, Ce atom in the melt first spontaneous diffusion formation of atomic groups then began to form small, rare earth phase particles were dispersed aluminum cooling during solidification, Al, Ce atoms to the solidification interface forefront of enrichment, the occurrence of the Al-Ce atomic Group to the Al4Ce phase of the transition gradually grew up into a the independent long needle-like structure along the grain boundaries. With a further reduction of the temperature, the eutectic reaction occurs to form a β-Mg17Al12 phase. Added Mg3Al alloy Ce, Sb element, first formed in the melt similar needle-like Al-Ce atomic Group, the Sb atoms then gradually spread to the Al-Ce atomic Group, needle-like aluminum rare earth atoms Group gradually transformed into The granular CeSb atomic Group. Continuous cooling process, the supercooled liquid Ce-Sb atom clusters will begin nucleation and gradually grow. When the eutectic reaction temperature is reached, the eutectic reaction occurs to form a co-crystal of α-Mg β-Mg17Al12. EET theoretical calculation of the valence electron structure of pure magnesium and α-Mg solid solution, Zn, Mn solid solution to the α-Mg matrix elements, the strongest bond valence electron number increases, the ability to change the bonding between atoms within a matrix structure unit , the strength of the alloy increases, and thus play the role of solid-solution strengthening. Calculated valence electron structure Al4Ce phase and CeSb phase space, both the strongest bond total number of valence electrons is much larger than the number of covalent electrons on the strongest bond in the a-Mg bonding capacity than the matrix a-Mg stronger impediment of dislocation slip and grain boundary migration during deformation is stronger than the a-Mg matrix. Al-Ce bond Al4Ce phase strongest covalent electron number of electrons is much smaller than the strongest bond in its structural unit, its the weak link the Al4Ce structure, is apt to cause stress concentration in the alloy deformation process, destruction of its phase structure, thereby causing the alloy to VALID. CeSb phase mainly by nearest neighbor Ce atoms and Sb atoms are connected to each other from the uniform structure, the structure of valence electrons in the covalent bond distribution uniform, no weak link. Therefore CeSb relatively Mg-Al-based alloy strengthening effect of the reinforcing effect than Al4Ce phase better. Is formed with the phase structure factor S, the total valence electron number of Na in the strongest bond between atoms of the phase structure of the alloy phase of solidification Priority: In the case of the presence of Sb atoms, Al4Ce phase impossible precipitated valence electron number na Ce element in the alloy is only exist in the form of CeSb phase. Composite consider the β-Mg17Al12 phase and α-Mg the structure factor S and the strongest bond is formed nA value that the the β of Mg17Al12 phase α-Mg (α-Mg β-Mg17Al12) co-crystal is formed by the eutectic reaction precipitation.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Physics of metals > The electron theory of metals
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