Pure aluminum has a low mechanical function and is not suitable for manufacturing structural parts that accept large loads. In order to improve the mechanical function of aluminum, some alloying elements are made into alloys in pure aluminum. The alloying elements commonly used are copper, magnesium, chromium, zinc, silicon, manganese, nickel, cobalt, titanium and niobium. Participate in some alloys. These alloying elements are strengthened after they are joined by the following aspects.
1.Solid solution strengthening
Alloying elements participate in pure aluminum to form an infinite solid solution or a limited solid solution, which not only achieves high strength, but also achieves excellent plasticity and outstanding pressure processing. The most commonly used alloying elements for solid solution strengthening in aluminum alloys are elements such as copper, magnesium, manganese, zinc, silicon, and nickel. Generally, the alloying of aluminum constitutes a limited solid solution, and binary alloys such as Al-Cu, Al-Mg, Al-Zn, Al-Si, and Al-Mn all constitute a finite solid solution, and both have a large limit solubility. Large solid solution strengthening.
2. Time strengthening
After the aluminum alloy is heat treated, a supersaturated aluminum-based solid solution can be obtained. When the supersaturated aluminum-based solid solution is heated to a certain temperature at room temperature, its strength and hardness increase with time and elongation, but the plasticity decreases. This process is called timeliness. The appearance of increasing the strength and hardness of the alloy during the aging process is called age strengthening or age hardening.
3. Excessive phase strengthening
When the water content of the alloying elements participating in aluminum exceeds its ultimate solubility, a part of the second phase which cannot be dissolved into the solid solution during quenching heating is called a surplus phase. The excess phase in the aluminum alloy is mostly a hard and brittle intermetallic compound. They act to prevent slip and dislocation motion in the alloy, which leads to an increase in strength and hardness, and a decrease in plasticity and resistance. The more the excess phase in the alloy, the better the strengthening effect, but when the excess phase is too much, the strength and plasticity decrease due to the brittleness of the alloy.
4. Refinement arrangements
Adding trace element refinement arrangements to aluminum alloys is another important way to improve the mechanical properties of aluminum alloys.
A large amount of titanium, zirconium, hafnium, yttrium and rare earth elements are added to the deformed aluminum alloy, which can form a refractory compound. When the alloy crystallizes, it acts as a non-conscious crystal nucleus to refine the grain and improve the strength and plasticity of the alloy.
Forged aluminum alloys often participate in the transformation of trace elements for micro-elements to refine the alloy arrangement and improve strength and plasticity. The enthalpy treatment has an extraordinarily important meaning for the forged aluminum alloy and the deformed aluminum alloy which cannot be heat-treated or strengthened. For example, in aluminum-silicon forged aluminum alloys, a small amount of sodium or sodium salt or bismuth is used as a mutator to carry out the enthalpy treatment, and the refinement arrangement can significantly improve the plasticity and strength. Also in the forged aluminum alloy, a small amount of elements such as manganese, chromium, cobalt, etc. can refine the plate-like or acicular compound AlFeSi composed of the impurity iron, and improve the plasticity. Participation in the trace amount of germanium can eliminate or reduce the primary silicon and make the eutectic silicon. Refinement; particle garden progress.
5. Cold deformation strengthening
Cold deformation strengthening is also called cold work hardening, that is, the metal data is cold-deformed below the recrystallization temperature. When cold deformation, the internal dislocation density of the metal increases, and entangles with each other to form a cell structure, preventing dislocation motion. The greater the degree of deformation, the more serious the dislocation entanglement, the greater the deformation resistance and the higher the strength. The degree of strengthening after cold deformation varies with the degree of deformation, the temperature of deformation, and the nature of the material itself. When the same data is cold-deformed at the same temperature, the greater the degree of deformation, the higher the strength. The plasticity decreases as the degree of deformation increases.