HONGKONG GREAT WALL CO.,LTD
更新時間：2016-08-16 瀏覽次數(shù)：644
In wrought magnesium alloy, Mg-Li is a kind of special alloy, and the lowest density of the l in the structure is called super light alloy. Magnesium density 1738kg/m3, lithium density 534kg/m3. Therefore, according to the composition of different, the density of Mg Li alloy 970kg /m3~1350kg/m3, the light can be floating in the water, become "floating" alloy, used in the manufacture of aerospace structure parts having a significant effect on weight loss. September 2015 25 Chinese shot "Pujiang No. 1" satellite of some parts is China Xi'an Sifang super light material Co., Ltd. offers it in 2010 built China's first mg Li alloy production line, and now production capacity of 100 tons / year. In the satellite launched by China, the density of the Mg-Li alloy is lighter than that of the conventional magnesium alloy 20%~30%, lighter than that of the aluminum alloy 40%~50%. It is the first time for the Chinese satellite to use Mg-Li alloy parts.
Phase structure and composition
001
002
The phase diagram of the Mg-Li two alloy (Fig. 1, Fig. 2) is the relationship between the two element phase diagram, the composition of the alloy phase, the plasticity of the cold rolling and the lithium content, and the relationship between the mechanical properties of the alloy and the lithium content and phase composition of the alloy 3. According to the content of lithium and the phase composition of Mg-Li alloy can be divided into three categories.
Classification of Mg-Li alloys
Alloy with lithium content less than 5.7%
The structure of this kind of alloy is composed of Li single phase alpha solid solution in Mg, dense six party structure, low plasticity, and the strength properties decrease with the increase of Li content, and there is no commercial value.
The lithium content > 5.7% and < 10.2% alloy
003
This kind of alloy phase structure for alpha + beta, beta phase is formed in the Li mg solid solution solid solution, body centered cubic (BCC), multiple slip systems, high plasticity, so that the alloy with large cold deformation capacity, but with the increase of Li content, the strength of the alloy decreased (Figure 3). In the alpha + beta cast tissue distributed in the alpha beta phase basic piece of Widmanstatten structure morphology. By the phase diagram of visible, (alpha + beta and beta phase field on solid solubility line is inclined in that some of the alloy formed with a certain amount of time to strengthen the ability.
Alloy with lithium content > 10.3%
The organization of this kind of alloy are magnesium in lithium single solid solution of beta phase, the body centered cubic lattice, cold and heat, good plastic workability and formability, processing rate of up to 50% ~ 60%, but industrial application of the lithium content of the alloy should not be less than 13%. With further decline the tensile strength of magnesium alloy 15%Li about to approximately 100N/mm2. To increase the strength of Li content will not increase, elongation began to decline, processing deteriorates the formability, indicating that have commercial value of Mg Li alloy of Li content should be less than or equal to 16%.
Magnesium density is 1738kg/m3, the density of lithium is only 534kg/m3, is a rare light l, it is added to the magnesium melt, you can make the world's lightest l structure. In addition, it also has the following characteristics: high specific stiffness, high specific strength, high damping, high radiation resistance, high anti electromagnetic interference and high shock resistance, etc..
Mg Li alloy is present the lightest structure alloy, with high specific strength and stiffness, is the best material for lightweight parts manufacturing, but their high chemical activity, the corrosion resistance of low, of some impurities, especially sodium is very sensitive, when the sodium content is greater than 0.06%, gold plastic worsened. Therefore, Mg Li alloy gained only limited applications, only in the quality of parts and components Zi Zhubi study of industry, such as aerospace industry is meaningful.
Usually, Mg Li alloy to add a small amount of Al, Zn or Si, to improve certain properties, for example, the addition of Al can improve the performance of the alloy creep resistance and stable alloy; adding Si can be the formation of Mg2Si, also have certain strengthening effect; you can add a small amount of Zr, Pb, Ag or re to Mg Li alloy and have a positive impact on some performance, but not significant. Mg-Li-Zn alloy aging hardening effect and low Li content, the alloy for single alpha phase microstructure, aging by alpha matrix stable precipitation phase theta MgLiZn generated hardening, increasing the Li content alloy structure for alpha + beta and aging by beta phase precipitation of stable theta 'phase (MgLi2Zn); Li content to increase, the alloy is composed of a single beta phase, the aging precipitation of stable theta' phase and hardening.
Mg-Li-Al alloy after solid solution treatment (350 /1h) and quenching at 50 C after the aging has a certain degree of hardening, but will soon soften. Zr is a commonly used micro alloying element, can refine the casting microstructure, improve the plastic deformation ability of the alloy, the cold deformation of alpha + beta alloy can reach 90%, which is equivalent to the cold working rate of pure beta phase alloy. At the same time, Zr can also increase the recrystallization temperature of the alloy, and inhibit the recrystallization of the material.
The rare earth element has a great effect on the magnesium alloy, and it is beneficial to the thermal stability of the precipitated phase, so the high temperature mechanical properties of the alloy can be improved.
The corrosion resistance of Mg-Li alloy is low, it is the main deficiency, Mn, Zn, Cd to its corrosion resistance, especially the effect of Mn is the most outstanding. When the content of Cd is less than 4%, the corrosion resistance of the alloy can be increased, and the corrosion resistance is decreased by more than 4%. The corrosion resistance of Mg-Li alloy was significantly reduced by Si and Sb. The influence of Al and Sn on the corrosion resistance of Mg-Li alloy is determined by the content, content is 0.6%~1.0%, the corrosion resistance of the alloy decreases with the increase of the content, more than 1%, the corrosion resistance increases with the increase of the content. Adding a small amount of Al or Ca to the Mg-Li alloy can form a high stability Mg (OH) 2 compound, which has a certain protective effect, which is not only beneficial to the corrosion resistance, but also can improve the plasticity and creep resistance of the alloy. Mg-Li alloys have strong stress corrosion sensitivity in moist atmosphere.
mechanical property
Trace Na can cause Mg
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