Pure magnesium has poor mechanical properties and cannot be used as a structural material. However, after the alloying and heat treatment of magnesium, its strength has been greatly improved and it has been widely used in aviation, aerospace, automotive, machinery and construction industries.
The main alloying elements in magnesium alloys are Al, Zn, Mn, and RE, which all have a solubility change in magnesium, which makes it possible to use a heat treatment method (solid solution + Shi Qingqing magnesium alloying. Table 11-1 for our country's Cast magnesium alloy chemical composition.
The main impurity in magnesium is Ni. Fe, Cu "Si and Sn' Ni are the most dangerous, and dramatically reduce the corrosion resistance of magnesium. Ni's melting point and density far exceed Mg, but it is easily dissolved in magnesium. Therefore, The iron site of smelting magnesium alloys must not contain Ni-Fe and its solubility in magnesium is very low, so the manure and tools for smelting magnesium alloys can be made of steels that do not contain Ni, but Fe also has adverse effects on the corrosion resistance of magnesium. When the content of Fe is increased from 0.03% to 0.26%, the corrosion resistance is reduced to 1/5 of the former. The commonly used alloying elements in magnesium alloys are Al, Zn "Mn" Si "RE, Ag, Cu and so on. The role of Al and RE is to improve the mechanical properties and casting properties of magnesium alloys. Mn forms A1FeMn compounds, reduces the mass fraction of Fe, improves the corrosion resistance of magnesium alloys, and Zn improves the corrosion resistance and strength of magnesium alloys. In the formation of a hard silicon point, to increase the creep strength of magnesium alloys, Ag can increase the heat resistance of magnesium alloys.
Cast magnesium alloys can be divided into the following three categories:
1Mg-Al, 'Alloy: ZMgA18Zn (ZM5), ZMgAl10Zn (ZM 10), AZ91 A, AM60A, AS41 A, etc.
2 Mg-Zn-Zr-based alloys: ZMgZn5Zr (ZMD, ZMgZn4RE1ZrZM2Z, ZM-ping n8AgZr (ZM1).
(3) Mg-RE-Zr-based alloys: ZMgRE3ZnZr (ZM3), ZMgRE3Zn2Zr (ZM4), ZMgRE2ZnZr (ZM6).
The latter two types of alloys all contain grain refinement elements that are often called boling-magnesium alloys, and the first category is called aluminum-magnesium alloys.
The development of cast magnesium alloys can be roughly divided into three stages. The first stage of the study is mainly to add aluminum and zinc to magnesium, ie Mg-Al-Zn alloys. Such alloys can be obtained similar to cast aluminum alloys. tensile strength. ZM5 in our country, L121 in the United Kingdom, and AM80A in the United States belong to this type of alloy. The main additive element is Al, and the content of Zn is relatively low. As the content of Zn is increased, microscopic porosity easily occurs. The main disadvantage of this type of alloy is that the crystallization temperature interval is relatively wide, about 1570C, and it is easy to produce micro-sulfur loose in casting production; the mechanical properties are affected by the wall thickness of the casting, and the mechanical properties tend to decrease as the wall thickness of the casting increases. Low yield strength and so on.
The second phase is an improvement phase. In order to improve the yield strength of Mg-AI-Zn magnesium alloys, ZM1 was developed in China, ZK51 A was developed in the United States, and 2970 MAG4P was used in the United Kingdom. With the addition of Zr, the grain size is significantly refined, the yield strength is increased by a factor of two, and it has good fatigue resistance and low notch sensitivity. The disadvantage is still that the crystallization temperature is widely spaced and microporosity and hot cracking tend to occur. In order to improve performance, some magnesium alloys have been added with rare earth elements such as ZM2 in China, 2970MAG5P in the United Kingdom, and ZE41A in the United States. In order to improve the creep resistance at high temperature, the third phase of ZM3, ZM6 with rare earth elements as the main constituent of the alloy, DTD5051 from the United Kingdom, and HK31Ao from the United States is the perfect stage. For example, silver is added to a magnesium alloy to form an Mg-Zr-Ag-RE-Zr alloy. After silver alloying, the yield strength and creep resistance of magnesium alloys reach the best level. There are also magnesium alloys to which niobium is added, and these alloys have a high specific strength. Only the high price of these alloys limits their industrial application.
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