Low Temperature Performance Of Aluminum Alloy

The high-speed rail carriages are welded with aluminum, and some high-speed rail lines pass through the cold zone of minus 30-40 degrees Celsius; some of the instruments, equipment and daily necessities on the Antarctic scientific research ship are made of aluminum, which need to withstand temperatures of minus sixty to seventy degrees Celsius. Test; some equipment on the merchant ships from China to Europe via the Arctic are also made of aluminum, part of which is exposed, and the ambient temperature is also minus 50 or 60 degrees Celsius; can they operate normally in such a cold environment? No problem, aluminum alloys and aluminum materials are least afraid of cold and heat.

Aluminum and aluminum alloys are the best low-temperature materials. They have no low-temperature brittleness. Unlike ordinary steel and nickel alloys, they have obvious low-temperature brittleness. Although their strength properties increase with the decrease of temperature, their plasticity and toughness increase. As the temperature drops, it decreases, that is, there is obvious low-temperature brittleness.

However, aluminum and aluminum alloys are quite different. There is no trace of low-temperature brittleness. All their mechanical properties increase significantly as the temperature decreases, regardless of the composition of the material, whether it is cast aluminum alloy or deformed aluminum alloy, regardless of whether it is cast aluminum alloy or deformed aluminum alloy. It is a powder metallurgy alloy or a composite material; it has nothing to do with the state of the material, whether it is processed or heat-treated; it has nothing to do with the preparation process of the ingot, whether it is rolled by ingot or continuously cast by melt Rolled or continuous rolling; has nothing to do with the extraction process of aluminum, electrolytic, carbothermal reduction, chemical extraction, all have no low temperature brittleness; it has nothing to do with purity, whether it is 99.50%~99.79% process pure aluminum , It is still 99.80%~99.949% high purity aluminum, 99.950%~99.9959% super pure aluminum (Super Purity), 99.9960%~99.9990% extremely pure aluminum (extreme purity), >99.9990% ultra high purity aluminum, etc. There is no low temperature brittleness. Interestingly, the other two light metals—magnesium and titanium, like aluminum, have no low-temperature brittleness.
The relationship between the mechanical properties and temperature of several commonly used high-speed rail car body extruded aluminum alloy profiles is shown in the following table.

High-speed rail car aluminum materials include Al-Mg series of 5005 alloy plates, 5052 alloy plates, 5083 alloy plates and profiles, Al-Mg-Si series 6061 alloy plates and profiles, 6N01 alloy profiles, 6063 alloy profiles, Al-Zn-Mg It is 7N01 alloy plate and profile, 7003 alloy profile. The standard states are O, H14, H18, H112, T4, T5, T6.

No matter what kind of aluminum alloy, its mechanical properties increase with the decrease of temperature, so aluminum is a kind of exquisite low-temperature structural material, the low-temperature fuel (liquid hydrogen, liquid oxygen) storage tanks of rockets, and liquefied natural gas (LNG) Aluminium can be used on transport ships and shore-based storage tanks, containers for low-temperature chemical products, cold storage, and refrigerated trucks.

The structural parts of the carriages and the front of the high-speed trains running on the earth can be made of the current corresponding aluminum alloys. All parts that can be made of aluminum alloy can be made of the current corresponding aluminum alloys, and there is no need to find another way to study a kind of aluminum alloy and its car body structure that operates in high-cold areas Of course, if we can develop a 6XXX alloy with various properties about 10% greater than that of 6061 alloy, or 7XXX alloy that is about 8% greater than 7N01 alloy, of course, it will be of great credit.

In fact, the high-speed rail running in Heilongjiang Province of China, and later in Inner Mongolia Autonomous Region, Xinjiang Uygur Autonomous Region, Tibet Autonomous Region, and Qinghai Province cannot be regarded as "high cold" for aluminum alloy structures, and does not require special treatment of alloy components, nor Need to make special adjustments to the material production process parameters.

As long as the performance of aluminum materials produced for the high-speed high-speed rail or later for high-speed rail vehicles operating in other cold regions meets the requirements of Chinese GB, European EN, Japanese JIS, American ASTM and other standards, it is a qualified product and no special measures are required. So as not to increase costs.

The development trend of aluminum alloy in carriages

The sheet alloys used in the manufacturing and maintenance of rail vehicle bodies include 5052, 5083, 5454, 6061 and other alloys, and the extruded profiles used are 5083, 6061, 7N01, etc., in addition to some new alloys such as 5059, 5383, 6082, etc. It has also been applied. They all have good weldability. The welding wire is 5356 or 5556 alloy. Of course, it is best to use friction stir welding (FSW), which not only has high welding quality, but also does not require welding wire. Later, the 7N01 alloy (Mn0.20~0.7, Mg1.0~2.0, Zn4.0~5.0, unit%) developed by Japan was widely used in the manufacturing of rail vehicles; Germany used 5005 alloy plate in the manufacture of high-speed rail Trans Rapid carriages Make wall panels and extrude the used profiles with 6061, 6063, and 6005 alloys. In short, these alloys are basically still used in high-speed rail vehicles manufactured in China or other countries until now.
200km/h~350km/h train body aluminum alloy

According to the operating speed of trains, we can divide the aluminum alloy of the carriage body into: the first-generation alloys used for vehicles with speeds less than 200km/h. They are conventional alloys and are mostly used to manufacture the carriage bodies of urban rail vehicles, such as 6063 and 6061. , 5083 alloys, etc.; second-generation aluminum alloys such as 6N01, 5005, 6005A, 7003, 7005 alloys, etc. are used to manufacture high-speed rail vehicles with speeds of 200km/h to 350km/h; the third-generation alloy is 6082, containing scandium Aluminum alloy, etc.

In addition to 6N01 and 7N01 alloys (they are Japanese alloys, and N stands for Nippon), there is also 7003 alloy. Its Mg content is lower than that of 7N01 alloy. It is a low Mg Al-Zn-Mg alloy. Its solderability And the strength is equivalent to that of 7N01 alloy, and it has higher extrudability. Tohoku, Joetsu Shinkansen, and Sapporo Subway use a large number of 7003 and 7N01 alloys to produce wide profiles with a wall thickness of 3mm.

The 6005A alloy (Si0.50~0.9, Mg0.40~0.7, Mn and Cr 0.12~0.50,%) is registered in France. Compared with the US 6005 alloy, the content of Mg and Si is equal, but an increase of 0.12%~0.50 % Mn of Cr, not only has extrudability comparable to 6063 alloy, but also has improved strength properties. The same is true for 6N01 alloy. The side panels (507mm width, 2.5mm wall thickness) of the Japanese Sanyo Electric Railway's 3050 vehicle body, the floor of 558mm width, and the large and wide hollow profiles for the manufacture of side plate hooks and eaves beams are all used 6N01 alloy extruded.
350ktm/h~450km/h train car body aluminum alloy, this is a new generation of aluminum alloy used in the car body, the train speed is up to 450m/h, the vehicle has to withstand greater external force and the vibration is more intense, so it should be developed new A generation of lightweight high-speed aluminum alloy.

Aluminum alloy containing scandium. Scandium is the most effective grain refiner for aluminum and aluminum alloys, and it is also one of the effective elements for optimizing the properties of aluminum alloys. The content of scandium is less than 0.5%. All alloys containing scandium, regardless of the content, are collectively referred to as aluminum-scandium alloys. Al-Sc alloy has the advantages of high strength, good plasticity, excellent weldability, and strong corrosion resistance. It is one of the new generation aluminum alloys used in the fields of ships, aerospace vehicles, reactors, national defense and military equipment, and of course. Used in the manufacture of railway vehicle structures.

However, how the addition of scandium to the current aluminum alloy can improve the structure and performance remains to be systematically studied. Scandium is a rare-earth element. China is the world's largest producer of scandium and ranks among the world's forefront of Al-Sc alloy research. Overall, it is not as good as Russia, which is the leader in the research and application of Al-Sc alloys. Northeast Light Alloy Co., Ltd., Central South University, and Institute of Aerospace Materials and Technology have done a lot of work on the research and development of Al-Sc alloy. The "large size 5B70 aluminum-magnesium-scandium alloy sheet" they studied won the 2017 China Nonferrous Metal Industry The first prize for science and technology, and the second prize for the “weldable high-strength Al-Zn-Mg-Sc alloy for aerospace”.

6082 alloy following the popularization of 6N01 alloy, 6082 alloy formed in 1972 has attracted the attention of railway equipment manufacturing department. The strength of this alloy is between the strength of 7N01 alloy and 6N01 alloy. The tensile strength Rm of 6082-T5 square tube (spray on-line quenching) meets the corresponding requirements of the underframe beam. Basic experiments show that this alloy can be applied in the corresponding field. However, if it is to be widely promoted in the railway equipment department, a lot of work still needs to be done. Regarding the fatigue strength of the assembly nodes of aluminum trains that were regarded as foolproof 30 years ago, due to the changes in the weight of the trains and the lighter structure, it is no longer suitable for the current new high-speed trains, but this has nothing to do with the temperature in the high-cold area, because Minus tens of degrees Celsius is really a "small test" for aluminum alloys. It is not a low temperature. At the same time, the lower the temperature, the stronger the aluminum structure.

Foamed aluminum: High-speed trains have the characteristics of light axle load, frequent acceleration and deceleration, and overload operation. The car body structure is required to be as light as possible under the premise of meeting strength, rigidity, safety and comfort. Obviously, the high specific strength, high specific modulus, high damping and other properties of ultra-light aluminum foam are very consistent with these requirements. Foreign countries have conducted detailed research and evaluation on the application of foamed aluminum on high-speed trains. It is found that the energy absorption capacity of steel pipes filled with foamed aluminum is 35%-40% higher than that of empty pipes, and the bending strength is increased by 40%-50%. Make the carriage pillars and partitions stronger and not easy to collapse; filling the locomotive head buffer with foam aluminum can improve the ability to absorb impact energy; the sandwich panel made of 10mm thick foam aluminum and thin aluminum plates is 50% lighter than the original steel plate. The stiffness has been increased by 8 times.

Currently, relevant units of China's high-speed rail are studying the feasibility of using foamed aluminum sandwich panels to prepare high-speed rail compartment floors and doors. In order to expedite the resolution of a series of major scientific and technological problems facing the next generation of high-speed rail, the railway department and the Chinese Academy of Sciences jointly established the Advanced Rail Transit Mechanics Research Center to conduct research on high-speed train material and structural reliability, noise reduction theory and technology, etc. A considerable part of the content is related to ultra-light foamed aluminum.

With the continuous increase in the speed of high-speed trains, the impact of noise on passenger comfort and the surrounding environment has become one of the key constraints on the development of high-speed trains. Compared with the noise inside the car, the noise outside the car has a more serious impact on the environment, and the reverberant noise and the resulting vibration generated when a high-speed train passes through a tunnel or two high-speed rails intersect in a tunnel have quite strong destructive power, such as Without effective control, it may become a major obstacle to the development of high-speed rail. In order to reduce the noise pollution of high-speed trains, barriers must be installed on both sides of the railway passing through densely populated areas and in tunnels. One of the main functions of ultra-light open-cell aluminum foam is sound absorption, and this performance can be adjusted by changing the cell type or acoustic structure. In addition, foamed aluminum also has good anti-corrosion, weather resistance and processing properties, so it is a good sound-absorbing material for outdoor sound barriers.

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