There are many reasons why aluminum is the most commonly used non-ferrous metal. It is very malleable and malleable, so it is suitable for a wide range of applications. Its ductility allows it to be made into aluminum foil, and its ductility allows aluminum to be drawn into rods and wires.
Aluminum also has high corrosion resistance because when the material is exposed to air, a protective oxide layer will naturally form. This oxidation can also be artificially induced to provide stronger protection. The natural protective layer of aluminum makes it more resistant to corrosion than carbon steel. In addition, aluminum is a good heat conductor and conductor, better than carbon steel and stainless steel.
(aluminum foil)
It is faster and easier to process than steel, and its strength to weight ratio makes it a good choice for many applications that require strong, hard materials. Finally, compared with other metals, aluminum can be recovered well, so more chip materials can be saved, melted and reused. Compared with the energy required to produce pure aluminum, recycled aluminum can save up to 95% of energy.
Of course, using aluminum has some disadvantages, especially compared with steel. It is not as hard as steel, which makes it a bad choice for parts with higher impact force or extremely high bearing capacity. The melting point of aluminum is also significantly lower (660 ℃, and the melting point of steel is about 1400 ℃), so it cannot withstand extreme high temperature applications. It also has a very high coefficient of thermal expansion. Therefore, if the temperature is too high during processing, it will deform and it is difficult to maintain strict tolerance. Finally, aluminum may be more expensive than steel due to the higher power demand in the consumption process.
aluminium alloy
By slightly adjusting the amount of aluminum alloy elements, countless kinds of aluminum alloys can be manufactured. However, some compositions have proven to be more useful than others. These common aluminum alloys are grouped according to the major alloying elements. Each series has some common attributes. For example, 3000, 4000 and 5000 Series Aluminum Alloys cannot be heat treated, so cold working, also known as work hardening, is adopted.
Main aluminum alloy types
1000 series
Aluminum 1xxx alloy contains the purest aluminum, with an aluminum content of at least 99% by weight. There are no specific alloying elements, most of which are almost pure aluminum. For example, aluminum 1199 contains 99.99% aluminum by weight and is used to manufacture aluminum foil. These are the softest grades, but they can be work hardened, which means they become stronger when repeatedly deformed.
2000 series
The main alloying element of 2000 series aluminum is copper. These grades of aluminum can be precipitation hardened, which makes them almost as strong as steel. Precipitation hardening involves heating the metal to a certain temperature to precipitate other metals from the metal solution (while the metal remains solid), and helps to improve the yield strength. However, due to the addition of copper, the corrosion resistance of 2XXX aluminum grade is low. Aluminum 2024 also contains manganese and magnesium for aerospace parts.
3000 Series
Manganese is the most important additive element in aluminum 3000 series. These aluminum alloys can also be work hardened (which is necessary to achieve a sufficient hardness level because these grades of aluminum cannot be heat treated). Aluminum 3004 also contains magnesium, which is an alloy used in aluminum beverage cans, and a hardening variant thereof.
4000 series
The 4000 series aluminum includes silicon as the main alloying element. Silicon reduces the melting point of 4xxx grade aluminum. Aluminum 4043 is used as a filler rod material for welding 6000 series aluminum alloy, and aluminum 4047 is used as a thin plate and a coating.
5000 Series
Magnesium is the main alloying element of the 5000 series. These grades have some of the best corrosion resistance, so they are usually used in marine applications or other situations facing extreme environments. Aluminum 5083 is an alloy commonly used for marine parts.
6000 Series
Magnesium and silicon are used to make some of the most common aluminum alloys. The combination of these elements is used to create the 6000 series, which is generally easy to process and can be precipitation hardened. 6061 is one of the most common aluminum alloys and has high corrosion resistance. It is commonly used in structural and aerospace applications.
7000 series
These aluminum alloys are made of zinc and sometimes contain copper, chromium and magnesium. They can be the strongest of all aluminum alloys by precipitation hardening. 7000 is commonly used in aerospace applications because of its high strength. 7075 is a common brand. Although its corrosion resistance is higher than that of 2000 series materials, its corrosion resistance is lower than that of other alloys. This alloy is widely used, but is particularly suitable for aerospace applications.
These aluminum alloys are made of zinc and sometimes copper, chromium and magnesium, and can be the strongest of all aluminum alloys by precipitation hardening. Class 7000 is usually used in aerospace applications due to its high strength. 7075 is a common grade with lower corrosion resistance than other alloys.
8000 Series
8000 Series is a general term that is not applicable to any other type of aluminum alloy. These alloys may include many other elements, including iron and lithium. For example, 8176 aluminum contains 0.6% iron and 0.1% silicon by weight and is used to make electric wires.
Aluminum quenching and tempering treatment and surface treatment
Heat treatment is a common conditioning process, which means that it changes the material properties of many metals at the chemical level. Especially for aluminum, it is necessary to increase hardness and strength. Untreated aluminum is a soft metal, so in order to withstand certain applications, it needs to undergo some adjustment process. For aluminum, the process is indicated by the letter designation at the end of the grade number.
heat treatment
2XXX, 6xxx and 7xxx series aluminum can be heat treated. This helps to improve the strength and hardness of the metal and is beneficial for some applications. Other alloys 3xxx, 4xxx and 5xxx can only be cold worked to increase strength and hardness. Alloys can be given different letter names (called tempering names) to determine which treatment is used. These names are:
F indicates that it is in the manufacturing state or the material has not undergone any heat treatment.
H means that the material has undergone some work hardening, whether or not it is carried out simultaneously with the heat treatment. The numbers after "H" indicate the type of heat treatment and hardness.
O indicates that aluminum is annealed, which reduces strength and hardness. This seems like a strange choice - who wants softer materials? However, annealing produces a material that is easier to process, possibly stronger and more ductile, which is advantageous for some manufacturing methods.
T indicates that the aluminum has been heat treated, and the number after "t" indicates the details of the heat treatment process. For example, Al 6061-T6 is solution heat treated (maintained at 980 ° F, then quenched in water for rapid cooling) and then aged between 325 and 400 ° F.
surface treatment
There are many surface treatments that can be applied to aluminum, and each surface treatment has the appearance and protection characteristics suitable for different applications.
There is no effect on the material after polishing. This surface treatment requires less time and effort, but is usually not sufficient for decorative parts and is best suited for prototypes that only test function and suitability.
Grinding is the next step up from the machined surface. Pay more attention to the use of sharp tools and finishing passes to produce a smoother surface finish. This is also a more accurate machining method, usually used to test parts. However, this process still leaves machine marks and is not usually used in the final product.
Sandblasting creates a matte surface by spraying tiny glass beads on aluminum parts. This will remove most (but not all) of the machining marks and give it a smooth but granular appearance. The iconic appearance and feel of some popular laptops come from sandblasting before anodizing.
Anodic oxidation is a common surface treatment method. It is a protective oxide layer that will naturally form on the aluminum surface when exposed to air. In the process of manual machining, the aluminum parts are suspended on the conductive support, immersed in the electrolytic solution, and direct current is introduced into the electrolytic solution. When the acidic solution dissolves the naturally formed oxide layer, the current releases oxygen on its surface, thereby forming a new protective layer of alumina.
By balancing the dissolution rate and the deposition rate, the oxide layer forms nanopores, allowing the coating to continue to grow beyond the range of natural possibilities. After that, for the sake of aesthetics, the nanopores are sometimes filled with other corrosion inhibitors or colored dyes, and then sealed to complete the protective coating.
Aluminum processing skills
1. If the workpiece is overheated during processing, the high thermal expansion coefficient of aluminum will affect the tolerance, especially for thin parts. To prevent any negative effects, heat concentration can be avoided by creating tool paths that do not concentrate on one area for too long. This method can dissipate heat, and the tool path can be viewed and modified in the cam software that generates the CNC machining program.
2. If the force is too large, the softness of some aluminum alloys will promote the deformation during processing. Therefore, a specific grade of aluminum is processed according to the recommended feed rate and speed to generate an appropriate force during processing. Another rule of thumb for preventing deformation is to keep the part thickness greater than 0.020 inch in all areas.
3. Another effect of the ductility of aluminum is that it can form composite edges of material on the tool. This will mask the sharp cutting surface of the tool, blunt the tool and reduce its cutting efficiency. This accumulated edge can also cause poor surface finish on the part. In order to avoid accumulated edges, the tool material is used for the test; Try to replace HSS (high speed steel) with cemented carbide inserts, and vice versa, and adjust the cutting speed. You can also try to adjust the amount and type of cutting fluid.
