One of the most common metals on Earth is aluminum. It is also called "flying metal." Despite the fact that in nature it does not occur in its pure form, it can be found in many minerals. And the most common alloy that is used to produce many parts and structures is duralumin (duralumin).
It was invented by the German scientist Alfred Wilm, who worked at the plant Dürener Metallwerke AG (city of Duren). He determined that the alloy of aluminum with copper has much better characteristics than the metal itself in its pure form.
High Strength Alloys Group
In fact, duralumin is a whole group of alloys in which aluminum is the main component, and its alloying elements are copper, zinc, manganese, and magnesium. But in general, their characteristics are determined not only by the composition, but also by the heat treatment method. In 1903, it was first discovered that during aging, the alloy of aluminum with copper becomes even stronger and harder.
As it turned out later, this is because when the metal is quenched for several days at room temperature, its supersaturated solid solution decomposes, and this, in turn, is accompanied by hardening of the material.
The aging process and a return to a previous state
As mentioned earlier, metal aging is an important process, which is caused by structural transformations that cause changes in physical and mechanical properties. It can be natural and artificial. In the first case, the alloy is kept for several days at room temperature.
With artificial aging, the processing time is reduced, but the temperature rises. In order to return the alloy to its previous state, it is necessary for several seconds to heat up to 270 degrees and then quickly cool.
Aluminum production
In order to make an alloy of aluminum with copper, you need high-tech equipment and, of course, the metal itself. It is extracted from bauxites. This is a rock that needs to be crushed, added to it and treated with steam under high pressure. Thus, silicon is separated from alumina. Then the thick mass is placed in a special bath with expanded cryolite. The contents are heated to 950 ° C and an electric current of 400 kA is passed through it.
This allows you to break the bond between the atoms of oxygen and aluminum. As a result, the latter settles to the bottom as a liquid metal. So castings are made of liquid aluminum. Now the metal is completely ready for machining. However, in order to increase its strength, it is necessary to add alloying elements to it and thus obtain a high-quality alloy of aluminum with copper.
Dural production
In total, all aluminum alloys are divided into two groups: cast and deformed. The process of their production depends on what kind should ultimately be obtained. In addition, the manufacturing method also depends on the required characteristics.
For the production of duralumin, aluminum ingots are melted in an electric furnace. Interestingly, this is one of the few metals that can be converted from solid to liquid and vice versa many times. This will not affect its performance. Copper and other alloying elements, such as manganese, iron, and magnesium, are added to the molten aluminum in turn. It is very important to observe the percentage ratio: 93% aluminum, 5% copper, the remaining 2% falls on other alloying elements.
Hardening and annealing of duralumin
Mandatory for such an alloy is the hardening process. The exposure time for small parts is only a few minutes, and the temperature is about 500 ° C. Immediately after the procedure, duralumin is soft and viscous. It is easy to deform and process. After some time, the alloy hardens and its mechanical properties increase. If the temperature threshold is exceeded, oxidation occurs and the material loses its characteristics. After quenching, it must be slowly cooled in cool water.
So, you already know the name of the alloy of aluminum with copper. It is often amenable to deformation: cold rolling, drawing, forging. This creates the so-called fretting. This is a process during which dislocations move and multiply in the metal structure. As a result, the alloy itself changes its structure, becomes harder and stronger. This reduces its ductility and toughness. In order for the deformations to pass more easily and the fretting does not destroy the metal, annealing is used. For this, the alloy is heated to 350 ° C and then cooled in air.
Alloy state diagram (aluminum and copper)
In order to most clearly describe the interaction of the components of duralumin in the solid and liquid state, as well as to explain the nature of the change in the properties of the alloy, use the state diagram.
It is seen from it that the highest solubility of Cu in the alloy with aluminum is observed at a temperature of 548 ° C and at the same time it is 5.7%. With an increase in temperature, it will increase, and with a decrease, it will decrease. Minimum solubility (0.5%) will be observed at room temperature. If the duralumin is quenched above 400 ° C, it will become a solid homogeneous solution - α.
During this process, the decomposition of the solid solution will occur. An alloy of aluminum and copper behaves very unusual, the formula of which is CuAl 2. The process is accompanied by the release of an excess A1 phase. This decay takes place over a long time. This is the natural aging that we mentioned earlier.
Alloy properties
Alloying metal with one or another element can improve its characteristics. Do you remember the name of the alloy of aluminum with copper? What properties does he possess?
Aluminum itself is very light, soft and completely unstable. It is soluble in weakly concentrated alkalis and acids. By adding copper and magnesium to aluminum, an already sufficiently strong alloy can be obtained. Its operational parameters are quite easy to improve - you just need to leave it to lie down at room temperature. So, the aging effect increases the strength of duralumin, as we discussed above.
Aluminum itself is light enough. A small percentage of copper does not weight the alloy. Another positive feature is the ability to repeatedly re-melt the alloy. However, he will not lose his properties. The only thing necessary is to give it a “rest” after a casting for a couple of days.
The disadvantage of duralumin is its low corrosion resistance. Therefore, most often such a material is coated with a clean layer of aluminum or painted with varnishes and paints.
Aluminum alloys and their application
For the first time, duralumin was used to make airships. The lightness and strength of this material made it possible to create an excellent aircraft. For this, the D16t brand was used. Currently, alloys with aluminum, zinc, copper and other alloying elements are widely used in astronautics, aviation and other fields of engineering.
So, for example, the use of duralumin in the manufacture of cars can significantly reduce its weight and cost, but it will be quite durable.
In general, it can be noted that the range of this alloy is quite wide: pipes, wires, sheets, tapes, rods and cast parts of various shapes. One of the most popular and widespread brands is still considered D16t. The small letter “t” at the end of the marking means that the alloy is hardened and naturally aged. It is used:
- In the construction of spacecraft, ships and aircraft.
- For the manufacture of various parts for machine tools and machines.
- For the manufacture of street signs, road signs.
Everyone should know the name of the alloy of aluminum and copper. Duralumin is also used in the oil industry. So, special pipes made of it can ensure the operation of the well for 6-7 years.
The name of the alloy of aluminum and copper is easy to remember. So, we talked about what properties it has and where it is applied. It can easily replace rolled steel, especially if it is necessary to make the structure lightweight.