One of the most common materials used in industry and construction is metal. Even against the backdrop of the emergence of technological fiberglass and composites, its unique combinations of performance properties do not lose their relevance. However, factors such as metal aging, fatigue effects, corrosion and other degradation processes limit its application, forcing technologists to look for ways to improve the durability of the structure.
The aging process
The aging of metal alloys and pure elements is understood as a change in their performance. Over time, designs and parts change in their structure, which is reflected in performance. It is believed that the process of metal aging has negative consequences, although it also causes an increase in certain useful technical and physical properties. For example, the hardness of the material increases, although the brittleness also increases in parallel. In any case, the change in structure deviates from the performance that is expected, for example, when developing a building or engineering project.
Time is the main cause of aging, but not the only one. External conditions can play a significant role in this process.especially chemical aggressive environments with which the material comes into contact. Under normal operating conditions, a slow mechanical aging of the metal occurs, against which the atoms of the product undergo diffusion.
Artificial aging
Since this process does not always lead to a complete loss of the operational value of the material, and also contributes to the growth of some qualities, artificial aging is often used. For example, this technique is applied to aluminum and titanium alloys in order to increase their strength. This effect is achieved through heat treatment. If the natural aging of the metal can occur very slowly even at normal room temperature, then the artificial process requires special hardening. But it is important to take into account the fundamental difference between this method and metal tempering technology. Aging under artificially created conditions causes an increase in hardness and strength, but also contributes to a decrease in ductility.
Measures to prevent aging
In principle, this process cannot be stopped. But it is quite possible to slow it down or eliminate the factors that stimulate aging, with varying degrees of success. For example, in some industries, metals of individual structures are periodically treated with protective solutions and polishes, which minimize the impact of negative operating factors - chemical, temperature, mechanical, etc. As for slowing down the effect of metal aging under normal operating conditions, inDepending on the type of structure or part, the same heat treatment may be applied. Welders, for example, expose seams to high temperatures at 600-650 °C. This technique is more similar to metal tempering, but it also reduces the intensity of aging.
Chemical corrosion
The process of rusting is more dangerous for metals in terms of changes in technical and physical qualities. Corrosion can occur under the influence of chemical or electrochemical influence on the structure. And if the aging of the metal is slow, then the rate of rust propagation can be very high depending on the external conditions.
Chemical corrosion processes usually occur when the metal is in direct contact with acid solutions, gases, s alts and alkalis. These are the most active corrosion promoters that are always found in the environment, but in different forms. Ultimately, a brittle and loose layer forms on the affected area, the presence of which reduces the durability of the material.
Electrical corrosion
In this case, there is a process of spontaneous interaction of metal products with the electrolytic medium. Against its background, the part undergoes oxidation, and the liquid active component is restored. Such processes can occur at the points of contact between alloys that have different electrode charges. If in such areas there are s alt oracid solutions, then a galvanic couple is formed, in which the anode function is performed by an element with a low electrode charge. Accordingly, a high potential makes the metal a cathode.
It is important to note that both aging and corrosion of metal can occur even without strong stimulants. For electrochemical rusting, minimal exposure to an acidic environment is sufficient, which can also be present in enclosed spaces. But most often such processes are subjected to the element base of cars. The cause of electrochemical corrosion in such situations can be clogging of carburetor jets, fuel valves, violations in the wiring of electrical equipment pairs, etc.
Corrosion control measures
Most protective equipment is an external coating, from which the destruction of the structure begins. For this, special coatings, paints, powders, enamels and varnish compositions can be used. An effective barrier against corrosion damage is also formed by pre-galvanizing methods before putting a structure or part into operation.
More serious preparation also involves alloying. Such a modification of the structure, in particular, can change the rate of aging of the metal, both upward and downward. There are also special high-tech methods used in production and industry. These include phaoliting, deaeration and gas thermal treatment.
Conclusion
The listed processes of destruction and changes in the structure of metals are only a part of those phenomena that can affect the characteristics of the material. A special place among them is occupied by the effect of fatigue. This is a process in which gradually accumulated damage causes an increase in stress in the structure, which subsequently leads to a loss of operational properties. But unlike the aging of metal, its fatigue is almost always caused by external physical influences.
To ensure that none of the considered processes has a negative impact on the structural stability of the product, it is necessary to initially assess its susceptibility to the influence of certain factors. For this, technologists develop special methods for monitoring workpieces, indicating their weak and strong technical and physical qualities for design materials.
