Aluminum profiles are a type of aluminum alloy material primarily composed of aluminum, with the addition of other metal elements such as magnesium, copper, manganese, and silicon. They are formed through a series of processes including heating, extrusion, and surface treatment. Depending on the composition of alloy elements, aluminum profiles are categorized into various models, each suitable for different industries, primarily the automotive and aerospace industries.
The main alloying elements in aluminum profiles are copper, silicon, magnesium, zinc, and manganese; minor alloying elements include nickel, iron, titanium, chromium, and lithium; and there are also a small amount of impurity elements such as vanadium, calcium, lead, tin, bismuth, antimony, beryllium, and sodium. Although these impurity elements are present in small quantities, they still have a certain impact on the quality of aluminum profiles.
First, let's talk about the metal element vanadium. Vanadium forms a compound called VAL11 in aluminum alloys, which can refine grain size during the melting and casting process. It can also refine the recrystallized structure and increase its crystallization temperature. However, it is very difficult to melt and its refining effect is not as good as titanium and zirconium. Adding a small amount of vanadium can make the surface of aluminum profiles smoother.
Next is calcium. Calcium can form CaSi with silicon, which can improve the conductivity of pure aluminum to some extent. Calcium forms a calcium tetra-aluminide compound with aluminum, which is insoluble in aluminum and can change the cutting performance of aluminum alloys. The generated calcium disilicide cannot strengthen aluminum profiles through heat treatment. A small amount of calcium can remove hydrogen from aluminum liquid, and calcium can reduce the mechanical properties of aluminum profiles.
Next is sodium. Sodium has a very low melting point and is almost insoluble in aluminum. When aluminum profiles containing sodium are heated during melting and casting, the sodium solidified on the grain boundaries can form a liquid adsorption layer, leading to brittle cracking and the formation of NaClSi. At this point, there is no free sodium in the compound. When the magnesium content is greater than 2%, free sodium will precipitate, causing sodium embrittlement. Therefore, sodium salt solvents are not allowed in high-magnesium aluminum alloy profiles. However, bismuth can be added to prevent sodium embrittlement, and chlorination can also be used to prevent sodium embrittlement by generating sodium chloride for discharge. Adding bismuth to aluminum-magnesium alloys can form disodium bismuthide, which enters the metal's substrate layer. Sodium can reduce the load-bearing capacity of aluminum profiles and decrease their performance.
Next is the element antimony. Antimony is primarily used as a modifier in casting aluminum alloys, but is rarely used in wrought aluminum alloys. It is only used in aluminum-magnesium wrought alloys to replace bismuth in order to prevent sodium embrittlement cracking. Adding antimony to certain aluminum-magnesium-zinc-copper alloys can improve the process performance of hot pressing and cold pressing, and enhance the mechanical properties of aluminum profiles.
Beryllium is also a toxic element that can cause allergic poisoning. Therefore, it is essential to ensure that aluminum profiles used in the production of food and beverages do not contain beryllium, which is beneficial for ensuring food safety and personal safety. Adding beryllium to wrought aluminum alloys can effectively improve the structure of the oxide film layer, reduce burning loss and inclusions during melting and casting. For aluminum profiles used as welding substrates, the beryllium content should be controlled below 8μm/ml.
Lastly, let's talk about lead, tin, and bismuth. These elements have low melting points and exhibit low solid solubility in aluminum, which can reduce the strength and machinability of aluminum profiles. They have a certain impact on the mechanical properties and load-bearing capacity of aluminum profiles. Bismuth undergoes expansion during solidification, which has a certain shrinkage-compensating effect on the forming of aluminum profiles. The addition of bismuth to aluminum-magnesium alloys can also prevent sodium-induced brittle cracking, making it suitable for use in wrought aluminum alloys.