There are many reasons why aluminum is the most commonly used non-ferrous metal. It is highly malleable and malleable, making it suitable for a wide range of applications. Its ductility allows it to be made into aluminum foil, while its ductility allows aluminum to be drawn into bars and wires.
Aluminum also has high corrosion resistance because when the material is exposed to air, it naturally forms a protective oxide layer. This oxidation can also be artificially induced to provide stronger protection. The natural protective layer of aluminum makes it more corrosion-resistant than carbon steel. In addition, aluminum is a good thermal and conductive material, which is better than both carbon steel and stainless steel.
It is faster and easier to machine than steel, and its strength to weight ratio makes it a good choice for many applications that require sturdy and hard materials. Finally, compared to other metals, aluminum can be recycled well, so more chip materials can be preserved, melted, and reused. Compared to the energy required to produce pure aluminum, recycling aluminum can save up to 95% of energy.
Of course, using aluminum also has some drawbacks, especially compared to steel. It is not as hard as steel, which makes it a bad choice for parts that withstand greater impact or extremely high load-bearing capacity. The melting point of aluminum is also significantly lower (660 ℃, while the melting point of steel is about 1400 ℃), making it unable to withstand extreme high temperature applications. It also has a high coefficient of thermal expansion, so if the temperature is too high during processing, it will deform and it is difficult to maintain strict tolerances. Finally, due to the higher electricity demand during the consumption process, aluminum may be more expensive than steel.
aluminium alloy
By slightly adjusting the number of aluminum alloy elements, countless types of aluminum alloys can be produced. However, some compositions have been proven to be more useful than others. These common aluminum alloys are grouped according to the main alloying elements. Each series has some common attributes. For example, aluminum alloys of the 3000, 4000, and 5000 series cannot undergo heat treatment, so cold working, also known as work hardening, is used.
Main types of aluminum alloys
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, which is used to manufacture aluminum foil. These are the softest grades, but they can work hard, which means they become stronger during repeated deformation.
2000 series
The main alloying element of the 2000 series aluminum is copper. These grades of aluminum can precipitate and harden, making them almost as sturdy as steel. Precipitation hardening involves heating the metal to a certain temperature, causing other metal precipitates to precipitate from the metal solution (while the metal remains solid), and helping to improve yield strength. However, due to the addition of copper, the corrosion resistance of 2xxx aluminum grade is relatively low. Aluminum 2024 also contains manganese and magnesium, which are used in aerospace parts.
3000 series
Manganese is the most important additive element in the aluminum 3000 series. These aluminum alloys can also undergo work hardening (which is necessary to achieve sufficient hardness levels as these grades of aluminum cannot undergo heat treatment). Aluminum 3004 also contains magnesium, which is an alloy used in aluminum beverage cans and its hardening variant.
4000 series
The 4000 series of aluminum includes silicon as the main alloying element. Silicon reduces the melting point of 4xxx grade aluminum. Aluminum 4043 is used as a filler material for welding 6000 series aluminum alloys, while aluminum 4047 is used for thin plates and cladding.
5000 series
Magnesium is the main alloying element of the 5000 series. These grades have some of the best corrosion resistance, so they are typically used for marine applications or other situations facing extreme environments. Aluminum 5083 is an alloy commonly used in marine parts.
6000 series
Magnesium and silicon are both used to manufacture some of the most common aluminum alloys. The combination of these elements is used to create the 6000 series, which is usually easy to machine and can be precipitation hardened. 6061 is particularly one of the most common aluminum alloys and has high corrosion resistance. It is typically used for structural and aerospace applications.
7000 series
These aluminum alloys are made of zinc and sometimes contain copper, chromium, and magnesium, which can become the strongest of all aluminum alloys through precipitation hardening. The 7000 grade is commonly used in aerospace applications due to its high strength. 7075 is a common grade, although its corrosion resistance is higher than that of the 2000 series materials, its corrosion resistance is lower than other alloys. This alloy is widely used, but particularly suitable for aerospace applications.
These aluminum alloys are made of zinc, sometimes copper, chromium, and magnesium, and can become the strongest of all aluminum alloys through precipitation hardening. The 7000 level is typically used for aerospace applications due to its high strength. 7075 is a common grade with lower corrosion resistance than other alloys.
8000 series
The 8000 series is a general term for aluminum alloys that are not applicable to any other category. These alloys can include many other elements, including iron and lithium. For example, 8176 aluminum contains 0.6% iron and 0.1% silicon by weight, used in the manufacturing of wires.
Aluminum material quenching and surface treatment
Heat treatment is a common regulatory process, which means that it changes the material properties of many metals at the chemical level. Especially for aluminum, it is necessary to increase its hardness and strength. Untreated aluminum is a soft metal, so in order to withstand certain applications, it needs to undergo a certain adjustment process. For aluminum, this process is represented by the letter name at the end of the grade number.
heat treatment
2xxx, 6xxx, and 7xxx series aluminum can all undergo heat treatment. This helps to improve the strength and hardness of the metal and is beneficial for certain applications. Other alloys 3xxx, 4xxx, and 5xxx can only be cold worked to increase strength and hardness. Alloys can be named with different letters (called tempering names) to determine which treatment is used. These names are:
F indicates that it is in the manufacturing state or that the material has not undergone any heat treatment.
H means that the material has undergone some type of work hardening, regardless of whether it is carried out simultaneously with heat treatment. The number after "H" indicates the type of heat treatment and hardness.
O indicates that aluminum has undergone annealing treatment, which reduces strength and hardness. This seems like a strange choice - who would want a softer material? However, annealing produces a material that is easier to machine, possibly more tough, and more ductile, which is beneficial for certain 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 undergoes solution heat treatment (maintained at 980 degrees Fahrenheit and then quenched in water for rapid cooling), followed by aging treatment between 325 and 400 degrees Fahrenheit.
surface treatment
There are many surface treatments that can be applied to aluminum, each with appearance and protective properties suitable for different applications.
Polishing has no effect on the material. This surface treatment requires less time and effort, but is usually not sufficient for decorative parts and is most suitable for prototypes that only test functionality and suitability.
Grinding is the next step up from the machined surface. Pay more attention to using sharp tools and finishing passes to produce a smoother surface finish. This is also a more accurate machining method, commonly used for testing parts. However, this process still leaves machine marks, so it is usually not used in the final product.
Sandblasting produces a matte surface by spraying tiny glass beads onto 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.
Anodizing is a common surface treatment method, which is a protective oxide layer that forms naturally on the aluminum surface when exposed to air. During manual processing, aluminum components are suspended on conductive supports, immersed in an electrolytic solution, and direct current is introduced into the electrolytic solution. When the acidic solution dissolves into the naturally formed oxide layer, the current releases oxygen on its surface, forming a new protective layer of alumina.
By balancing the dissolution rate and stacking rate, the oxide layer forms nanopores, allowing the coating to continue to grow beyond the range of natural possibilities. Afterwards, 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 techniques
If the workpiece overheats 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 are not concentrated in one area for too long. This method can dissipate heat and view and modify tool paths in CAM software that generates CNC machining programs.
If the force is too high, the softness of certain aluminum alloys can promote deformation during the processing. Therefore, process a specific grade of aluminum according to the recommended feed rate and speed to generate appropriate force during the processing. Another rule of thumb for preventing deformation is to maintain a part thickness greater than 0.020 inches in all areas.
Another impact of aluminum's ductility is that it can form composite edges of the material on the cutting tool. This will mask the sharp cutting surface of the tool, making it blunt and reducing its cutting efficiency. The stacked edges can also cause poor surface finish on the parts. To avoid accumulated edges, use tool materials for testing; Try using a hard alloy blade instead of HSS (high-speed steel), and vice versa, and adjust the cutting speed. You can also try adjusting the quantity and type of cutting fluid.
