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La AZ91 magnesium alloy refining and modification effect of its

Author: ZhangJinLing
Tutor: XuBingShe;WangSheBin
School: Taiyuan University of Technology
Course: Materials Science
Keywords: AZ91 magnesium alloy Refining Evaporation Rate La Absorption rate Modification Mechanism
CLC: TF822
Type: Master's thesis
Year: 2007
Downloads: 205
Quote: 4
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Abstract


Magnesium alloys have specific strength and specific stiffness, damping, and easy casting, easy recovery, etc., and limited mechanical strength but limited its promotion and application. With magnesium alloys in electronics, aerospace, automotive and other industries more widely, magnesium alloys, the application has attracted national attention manufacturers. For now widely AZ91 magnesium alloy, this study used a vacuum resistance furnace refining was carried out and got the La content of different rare earth alloys. Use spark atomic emission spectroscopy, inductively coupled plasma spectrometry, X-ray diffraction, optical microscopy, scanning electron microscopy with energy dispersive, tensile testing machine tools, analysis and research of the refining process, the evaporation rate of Mg element, the apparent mass coefficient of Rare Earth La solid solubility in the alloy, the formation of a compound shape, the absorption rate and La on Modification of AZ91 Magnesium Alloy; identified obtain excellent magnesium alloy of La optimal dosage and process parameters, a kind of trial and σ b ≥ 190MPa, δ ≥ 11% of high-strength and high-toughness magnesium alloys and their manufacturing process. Through experiment and analysis, the following conclusions: (1) under an argon atmosphere in a vacuum refining magnesium alloys AZ91, since the vapor pressure of Mg alloys is much greater than the vapor pressure of the other elements, therefore, an alloy ratio before the test, the need Taking into account the amount of Mg element loss. Mg element restrictive aspects of the evaporation process of magnesium atoms are diffused into the liquid through the liquid boundary layer alloy liquid / vapor interface. Through calculation and analysis of test results and found that Mg element mass transfer coefficient and the apparent size of evaporation interface, refining temperature; the experimental conditions and its value at 2 × 10 -5 ~ 24 × 10 -5 cm / s range; evaporation rate and temperature refining, refining time-related, the experimental conditions and its value at 8.6 × 10 -3 ~ 13.5 × 10 < sup> -3 g / cm 2 · s range. (2) by measuring the test samples before and after the magnesium content in the rare earth element La, and found that the absorption of La element with added amount of Al content in the alloy, refining temperature, and the number of inclusions, and La in AZ91 magnesium alloys by Al 11 La 3 compound exists in the form. Adding the La content of <0.2%, La absorption rate with increasing of the amount added; the La added content> 0.2%, La absorption rate of 75% ± 5%; due to the formation Al 11 La 3 compound solubility with La added amount soared. When the Al content is <9% of the, La absorption rate with the increase of Al content increased; when the Al content> 9% while, La absorption rate remained stable at 75% ± 5% level. La absorption rate with the increase of temperature;, but the higher the temperature refining, Mg greater evaporation loss element. (3) due to added rare earth elements La, AZ91 magnesium alloy can make continuous, coarse mesh Mg 17 Al 12 phase transition is small, dense discontinuous state , the grain refinement, compact. (4) due to added rare earth elements La, AZ91 magnesium alloy specimen tensile fracture appeared a large number of torn edges and tiny dimples, and also appeared in small cleavage steps, you can improve the plasticity and AZ91 magnesium alloy toughness. (5) The modification mechanism of rare earth La: In addition to micro-Mg solid solution, and the rest of La and Al to form Al 11 La 3 compounds. This aluminum - rare earth compounds, first precipitates at the grain boundaries after growing up, when the amount of rare earth continually increases, Al 11 La 3 compounds will be in the matrix needle or slug to form precipitates; continue to increase the amount of rare earth, when the Al and Mg, La compound is depleted, La will be present in the form of inclusions in the alloy. During solidification, with decreasing temperature, the solid solution of La in AZ91 due to reduced solubility precipitates at the grain boundaries, hindering the grain boundary migration, refined grains, but also played a dispersion strengthening effect, reducing The grain size of the organization; number of La to Al 11 La 3 strengthening phase morphology precedence β phases in the grain boundary precipitation of alloy played a \effect, \The La content is <0.2%, with the increase of the La content, the average grain size of the alloy decreases linearly, hardness, tensile properties with La content increases. When the La content> 0.2%, the alloy performance indicators did not change much. Therefore, by adding rare earth elements La can improve the alloy strength, toughness and high temperature performance. Considering the absorption of La, Mg and La on the evaporation rate of magnesium alloy AZ91 Modification, refining appropriate temperature should be set at 993K. (6) Through analysis and comparison, we can see an argon atmosphere in a vacuum refining, anaerobic conditions obtained excellent cast magnesium alloys, its hardness, toughness more than double than the national standard, the tensile strength increased by 73% elongation increased sevenfold. Refining magnesium alloys herein experimental basis, the experimental data in the melting of Mg element and the evaporation rate of absorption elements of La, Analysis and Discussion of Rare Earth La on Modification of AZ91 magnesium alloy, magnesium alloy to improve mechanical properties, expand the scope of application of magnesium alloy and development of magnesium alloy refining process, provided some basic experimental data.

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CLC: > Industrial Technology > Metallurgical Industry > Nonferrous metal smelting > Light metal smelting > Magnesium
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