1. I have a question
In mechanical projects, we often use aluminum alloys. For example, 6061-T6 and 7075-T651 are the two most commonly used aluminum alloys.
Because they have a good strength-to-weight ratio, meaning they are light but also strong, they are popularly used in weight-sensitive areas such as high-speed platforms, aircraft structures and bicycle frames.
So the question is: What is the difference between 6061-T6 and 7075-T651? What do the designations “6xxx” and “7xxx” mean? And what do “T6” and “T651” indicate?
Speaking of which, we must mention the method of classification and nomenclature of aluminum alloys.
2. Classification of aluminum alloys
(1) Forged and cast aluminum alloys:
We know that aluminum alloys are based on aluminum and added with one or two main alloying elements that have metallic characteristics.
In most aluminum alloys, the aluminum content is between 90% to 96%, and other alloying elements include copper, zinc, manganese, magnesium, silicon, etc.
According to the type of production process, aluminum alloys can be classified into wrought aluminum alloys and cast aluminum alloys.
Forged aluminum alloys are produced in the form of ingots or billets and then processed through various processes such as rolling, extrusion, deformation, drawing, etc., to produce alloys that can be machined into parts by end users.
Cast aluminum alloys are made by casting methods to produce ingot alloys.
| Forged aluminum alloys of different grades | ||||||
| Note | Main alloying elements | Strengthening method | Strength | Corrosion resistance | Processability/formability | Connection/welding performance |
| 1xxx | Not connected (99% AI) | strain hardening | 5 | 1 | 1 | 3 |
| 2xxx | copper | heat treatment | 1 | 4 | 4 | 5 |
| manganese | strain hardening | 3 | two | 1 | 1 | |
| 4xxx | silicon | Strain hardened magnesium containing heat treatable | 3 | 4 | 1 | 1 |
| 5xXx | magnesium | strain hardening | two | 1 | 1 | 1 |
| 6xxx | Magnesium, silicon | heat treatment | two | 3 | two | two |
| 7xxx | zinc | heat treatment | 1 | 1 | 4 | 3 |
| 8xxx | Lithium, tin | heat treatment | ||||
| Cast aluminum alloys of different grades | ||||||
| Note | Main alloying elements | Strengthening method | Breakage sensitivity | Corrosion resistance | Final performance | Welding performance |
| 1xx.x | Not connected (99% A) | strain hardening | – | 1 | 1 | 1 |
| 2xx.x | copper | heat treatment | 4 | 4 | 1-3 | 2-4 |
| 3xx.x | Silicon, magnesium, copper | heat treatment | 1-2 | 2-3 | 3-4 | 1-3 |
| 4xx.x | silicon | strain hardening | 1 | 2-3 | 4-5 | 1 |
| 5xx.x | magnesium | strain hardening | 4 | two | 1-2 | 3 |
| 6xx.x | anything | anything | – | – | ||
| 7xx.x | zinc | heat treatment | 4 | 4 | 1-2 | 4 |
| 8xx.x | Tin, copper, nickel | heat treatment | 5 | 5 | 3 | 5 |
| Note: Cells without numbers are often unspecified or difficult to summarize. Level 1 indicates a very good rating, while level 5 indicates a poor rating, and levels 2 to 4 fall into the intermediate range. | ||||||
Forged aluminum alloys and cast aluminum alloys.
Forged aluminum alloys contain no more than 4% alloying elements, while cast aluminum alloys have an alloy composition of more than 10%.
This is because the higher content of alloying elements leads to lower ductility, which can make subsequent processing difficult.
Therefore, in practical engineering, most cases use forged aluminum alloys, such as the commonly used 6061, 7075, 5083, 1100 and even AL-Li8090-T8771.
(2) Heat treatable aluminum alloys and non-heat treatable aluminum alloys.
Aluminum alloys can also be classified into heat treatable and non-heat treatable categories based on whether they can be subjected to heat treatment. Heat-treatable aluminum alloys rely on major (and some minor) alloying elements to provide significant solid solution and precipitation hardening during the aging process, thus improving the strength and hardness of the alloy.
This involves several concepts such as solid solution heat treatment and aging. Later, we will cover other concepts related to alloy strengthening, such as cold working and strain hardening.
Cold working refers to the plastic deformation that occurs in metals at a certain temperature and rate, which achieves strain hardening – for example, through rolling or drawing – to increase strength.
The principle behind cold working is that it creates dislocations and gaps in the microstructure, which suppress relative motion between atoms and ultimately increase the strength of the alloy.
Strain hardening is a way of modifying metal structure by cold working, which increases strength and hardness but decreases ductility. See Figure 4 in this article for a better understanding of strain hardening.
Solid solution heat treatment is a method of heating a product to an appropriate temperature and holding it there for a period of time sufficient to allow the solutes to enter solid solutions, followed by rapid cooling to keep the solute elements in solution solid.
For aluminum alloys, solid solution heat treatment involves heating the alloy to a high temperature of 440°C-530°C (the specific temperature depends on the alloying elements), which aims to dissolve the alloying elements in the aluminum to soften it. it.
The material is normally then quenched in water to maintain the distribution of solute elements within the alloy.
Aging refers to the precipitation of solute atoms from a supersaturated solid solution after heat treatment of solid solution. This can occur naturally at room temperature or artificially in a low temperature furnace, resulting in finer atomic precipitation and thus improving the strength of the alloy.
For aluminum alloys, aging is the process of precipitation of a portion of the alloying elements or compounds from the supersaturated solid solution to produce the desired mechanical properties.
After heat treatment and solid solution quenching, the material is relatively soft, making it suitable for stretching to strengthen the material.
If the material is aged naturally in the air after quenching, it will gradually become harder. However, this change occurs very slowly and some alloys may take several years to reach their maximum hardness.
Alternatively, if the material is immediately subjected to artificial aging, whereby it is heated again to 100-200°C and held for a certain period of time, it will harden due to the precipitation of hardening compounds and its strength will be greatly increased.
In the aging process, it is essential to properly control temperature and time. A high temperature with a long aging time can result in the formation of larger precipitation elements and greatly reduce the precipitation hardening effect.
On the other hand, too low an aging temperature will consume too much precipitation time to produce good strengthening effects. A longer time means lower efficiency and higher cost.
Annealing: heating and slow cooling to eliminate internal stresses and improve toughness.
Quenching: reheating after quenching. The English word “temper” also means to be angry. When someone is calm, their temper is small, but when they become angry, their temper increases. It can be understood that when someone gets angry, their temper returns, hence the term “temper” (just to make it easier to remember).
Now that we've explained several concepts, let's continue.
Non-heat treatable aluminum alloys cannot provide significant solid solution and precipitation hardening effects with their primary alloying elements during solution heat treatment and aging processes. Therefore, its strength can only be improved through strain hardening methods such as cold rolling or drawing.
For example, forging aluminum alloys of classes 1, 3 and 5 are not heat treatable, while classes 2, 6 and 7 can be heat treated.
For cast aluminum alloys, types 1, 4 and 5 are not heat treatable, while types 2, 3, 7 and 8 can be heat treated.
Non-heat treatable aluminum alloys can only have their strength increased through hardening processes such as rolling and drawing, which create dislocations and gaps in the structure, inhibiting relative atomic movement and thus increasing the strength of the alloy.
Heat-treatable aluminum alloys can have their strength increased through both heat treatment and work hardening.
In other words, whether or not an aluminum alloy can be heat treated determines its strengthening method.
| Strength of forged aluminum alloys | ||||
| Note | Main element content (%) |
Strengthening method | Tensile strength (MPa) |
Yield Strength (MPa) 0.2% |
| 1xxx | Aluminum: 99.00-99.99 | Cold work | 75-175 | 28-152 |
| 2xxx | Copper: 2.2-6.8 | heat treatment | 170-520 | 76-345 |
| 3xxx | Manganese: 0.3-1.5 | Cold work | 140-280 | 41-248 |
| 4xxx | Silicon: 3.6-13.5 Copper: 0.1-4.7 Magnesium: 0.05-1.3 |
Cold working, some can be heat treated | 105-350 | 45-180 |
| 5xxx | Magnesium: 0.5-5.5 | Cold work | 140-380 | 41-345 |
| 6xXx | Silicon: 0.2-1.8 Magnesium: 0.35-1.5 |
heat treatment | 150-380 | 55.2-276 |
| 7xXx | Zinc: 0.8-8.2 Magnesium: 0.1-3.4 Copper: 0.05-2.6 |
heat treatment | 380-620 | 103-503 |
| Note: Tensile strength and yield strength in the table are average values | ||||
| Strength of cast aluminum alloys | ||||
| Note | Main element content (%) |
Strengthening method | Tensile strength (MPa) |
Yield strength (MPa) 0.2% |
| 1xx.x | Aluminum: 99-99.99 | Cold work | 131-448 | 28-152 |
| 2xx.x | Copper: 4-4.6 | heat treatment | 131-276 | 90-345 |
| 3xx.x | Silicon: 5-17 | heat treatment | 117-172 | 66-172 |
| 4xx.X | Silicon: 5-12 | Cold work | 117-172 | 41-48 |
| 5xx.x | Magnesium: 5-12 | Cold work | 131-448 | 62-152 |
| 6xx.x | / | |||
| 7xx.x | Zinc: 6.2-7.5 | heat treatment | 207-379 | 117-310 |
| Note: Tensile strength and yield strength in the table are average values | ||||
3. Representation of Aluminum Alloys
Aluminum alloys are represented by four digits followed by some symbols, such as 5083-H112, 7075-T73, etc.
The representation method also clearly distinguishes between forged aluminum alloys and cast aluminum alloys.
There is a decimal point in the first 4 digits of cast aluminum alloys, while there is no decimal point in forged aluminum alloys.
For example, 1xxx, 3xxx, 5xxx, 7xxx represent wrought aluminum alloys, while 1xx.x, 3xx.x, 5xx.x, 7xx.x represent cast aluminum alloys.
Since forged aluminum alloys are more commonly used in real engineering, I will mainly focus on forged aluminum alloys below.
The first digit represents the type of aluminum alloy, consisting of the digits 1 to 9, with different digits representing different alloy compositions.
The second digit represents the modification of the alloy composition, where 0 represents the original composition, 1 represents the first modification, 2 represents the second modification, and so on, indicating the differences in the content of different elements in the alloy. For example, 7075 represents the original aluminum-zinc alloy, while 7175 and 7475 represent modified aluminum-zinc alloys. 7175 and 7475 are modified grades of 7075.
The third and fourth digits represent specific leagues in the league series. The values of these digits have no special meaning.
Series 1xxx
The 1xxx series of aluminum alloys are not actually a true aluminum alloy as their aluminum content is 99%, making them commercially pure aluminum.
From a mechanical point of view, this type of alloy has good ductility. For example, 1100 is commonly used for sheet metal forming and for common pharmaceutical and food aluminum foil packaging, which are also made from 1xxx series alloys.
In addition, 1xxx series alloys have good corrosion resistance, processability and can be hardened by processing to increase their strength.
Due to their excellent conductivity and thermal conductivity, these alloys are widely used in the field of power transmission.
Series 2xxx
The main alloying element in the 2xxx series is copper, with a small amount of magnesium.
Because copper can dissolve in aluminum at high temperatures, this type of alloy reacts to solid solution strengthening and is called heat treatable aluminum alloy.
After heat treatment, it can have excellent strength, comparable to low-carbon steel.
Naturally, due to the presence of copper, it is also more susceptible to corrosion.
2024 is a typical and widely used 2xxx series aluminum alloy.
Series 3xxx
The main alloying element of class 3 aluminum alloys is manganese.
These alloys have moderate strength and excellent workability.
For example, 3003 aluminum alloy of this class is commonly used for heat dissipation devices because of its good formability.
Another example is aluminum alloy 3004, which has good ductility and workability and is often used in the manufacture of beverage cans.
4xxx series
The main alloying element of class 4 aluminum alloys is silicon.
Adding silicon can lower the melting point without affecting ductility. Therefore, these alloys are generally used as welding wires to connect other aluminum materials.
Additionally, the oxide layer of Class 4 alloys is aesthetically pleasing, making them popular in construction applications. The most representative alloy in this class is 4047, which has good thermal and electrical conductivity, as well as resistance to corrosion.
These alloys are generally not heat treatable, but depending on the content of silicon and other alloying elements, some can be subjected to a certain degree of heat treatment.
5xxx series
The main element of class 5 aluminum alloys is magnesium, with a small amount of manganese in specific alloys.
These alloys can be strengthened by strain hardening, are easy to weld and have excellent corrosion resistance, making them suitable for marine environments such as ship hulls, walkways and other marine equipment.
For example, alloy 5052 has good seawater corrosion resistance and excellent formability, making it commonly used in marine vessels. Alloy 5083 is suitable for tanks and fighter planes, while alloy 5005 is often used in building structures.
The 6xxx series
The main alloying elements of 6xxx series aluminum alloy are magnesium and silicon, which will form Mg2Si during solid solution heat treatment.
This type of alloy can improve its strength through heat treatment. Although it does not have the high strength of 2xxx and 7xxx series aluminum alloys, it combines good strength, workability, weldability, formability and corrosion resistance.
The 6xxx series alloy produced by extrusion is the first choice in the fields of mechanical and structural engineering.
For example, 6061 aluminum alloy is the most flexible heat-treatable aluminum alloy, which maintains most of the excellent characteristics of aluminum. Therefore, it is also the most used aluminum alloy in our projects. This grade has a wide range of mechanical properties and corrosion resistance, excellent workability under annealed conditions, can be processed using conventional methods and can also be welded.
7xxx series aluminum alloys
The main alloying element of 7xxx series aluminum alloys is zinc, generally with a certain amount of copper and magnesium.
Due to the use of zinc, this type of alloy is the strongest of all forging alloys and its strength can even exceed that of some steels.
For this reason, 7xxx alloys are commonly used in the aircraft industry. Although the addition of zinc reduces its workability, its excellent resistance compensates for these deficiencies.
For example, 7075 aluminum alloy, having an excellent strength-to-weight ratio, is the ideal choice for high-stress parts. It can be formed and processed according to need, as well as heat treated and other operations.
8xxx series aluminum alloys
8xxx series aluminum alloys use unusual elements as alloying elements, such as lithium, tin, or iron.
This type of alloy is generally used in specific applications such as high temperature performance, lower density, higher rigidity and other requirements.
For example, 8090-T8771 aluminum-lithium alloy is used for high-speed rotation, low moment of inertia and large high-rigidity turntable.
8xxx alloys are also commonly used in helicopter components and other aerospace applications.
4. Quenching treatment of aluminum alloys
Aluminum alloys are grouped and represented by four-digit numbers, with different digits representing different alloy compositions.
For example, the main alloying element of 2xxx alloys is copper, while the main alloying elements of 6xxx aluminum alloys are magnesium and silicon, and the main alloying element of 7xxx aluminum alloys is zinc.
The heat treatment of aluminum alloy is represented by capital letters and numbers.
Capital letters such as F, O, H, W, T, etc. represent different types of heat treatments.
For example, 6061-T6: This aluminum alloy belongs to the 6xxx series aluminum alloy, which is an aluminum-magnesium-silicon alloy, has undergone solid solution heat treatment and then artificial aging: T6.
Another example is 7075-T651, which is basically tempered like T6. This means that it has undergone solid solution heat treatment, quenching and then artificial aging. The number 5 represents stress relief and the number 1 indicates that the elongation after stress relief is between 0.5-2%.
| Quenching and strengthening methods for aluminum alloys | ||||
| F | – | F=As Fabricated, indicating a product made through a molding process. For example, wrought or cast alloy products are manufactured by processes such as rolling, extrusion, forging, drawing or casting, which have no special control over thermal conditions during processing or strain hardening. For example, 2014-F represents the processed product form of aluminum alloy 2014, which can represent any process or product form, such as products produced using rolling, extrusion, forging processes, or combinations of these processes. | ||
| O | – | Annealed. This symbol indicates wrought or cast alloy products made by certain forming processes, such as rolling, extrusion, forging, drawing, or casting. Used to achieve the minimum strength state of the relevant alloy, improve subsequent machinability, or improve ductility and toughness. | ||
| H | – | Stress hardened by cold working. For non-heat treatable aluminum alloys, strength is generally improved by strain hardening at room temperature. H is usually followed by two or three symbols to indicate the amount of cold working and subsequent heat treatment. | ||
| H1 | Stress hardening. Applied to products that do not undergo heat treatment, but only obtain the necessary resistance through strain hardening. The number after H1 indicates the amount of strain hardening. | |||
| H2 | Strain hardening and partial annealing. When using this type of tempering, the alloy is intentionally overstressed and then partially annealed to reduce its strength to the required value. The number after H2 indicates the amount of strain hardening remaining after partial annealing. | |||
| H3 | Strain hardening followed by thermal stabilization treatment. It is applied to products that undergo strain hardening and then stabilize the fabric by the heat generated by low temperature heat treatment or processing. Stabilization treatment can often improve ductility. H3 tempering is only used for alloys that naturally age at room temperature and therefore soften, such as magnesium-containing alloys. The number after H3 indicates the remaining amount of strain hardening after stabilization. | |||
| H4 | Hardening by deformation and painting. Apply to painted products after strain hardening. During the painting process, some heat is introduced, which can reduce the amount of residual hardening in the alloy and improve the stability of the alloy. | |||
| The number after H4 indicates the amount of strain hardening remaining after painting. | ||||
| HX2 | 2/8 = 1/4 times the strengthening, with an increase in tensile strength of 25% of the total amount of hardening compared to annealing | |||
| HX4 | 4/8 = 1/2 times the strengthening, with an increase in tensile strength of 50% of the total amount of hardening compared to annealing | |||
| HX6 | 6/8 = 3/4 times strengthening, tensile strength increased by 75% of the total amount of hardening compared to annealing | |||
| HX8 | Fully hardened. Use 8 for basic reinforcement. | |||
| HX9 | Extremely reinforced, generally 14 Mpa larger than HX8, or more | |||
| H111 | Indicates that after annealing, slight strain hardening is performed during stretching and is typically applied to extruded profiles that must be straightened after annealing to obtain a straightness tolerance. | |||
| H112 | Used for products that have achieved a small amount of tempering through a high-temperature molding process and have no special control over strain hardening and heat treatment, but have certain requirements for mechanical properties or mechanical testing. | |||
| HX11 | Suitable for products that can produce sufficient strain hardening after final annealing. | |||
| T | Heat treatment | |||
| T1 | After high-temperature molding (lamination or extrusion) and cooling, it ages naturally to a stable state. | |||
| T2 | High temperature molding and cooling, followed by cold processing and natural aging to steady state. | |||
| T3 | Solution heat treatment followed by cold processing followed by natural aging to a stable state. Widely used in 2 series aluminum alloys such as 2024. | |||
| T4 | After heat treatment of the solution, it ages naturally to a stable state. It is mainly used for 2 series leagues. | |||
| T5 | After molding and cooling at high temperature, artificial aging is carried out. | |||
| TX51 | Stress is released by stretching, typically between 1% and 3%. Suitable for rolled plate and rod extruded products, occasionally used for mold or forged rings. | |||
| TX510 | ||||
| TX511 | ||||
| TX52 | “Stress relief through compression is commonly used for hand and die forgings.”. | |||
| TX54 | Relieve stress by stretching and compressing. | |||
| T6 | After solution heat treatment, artificial aging is carried out to achieve precipitation hardening. | |||
| T651 | After T6 treatment, internal stress is eliminated by stretching 0.5% – 2%. | |||
| T7 | Solution heat treatment followed by aging in a furnace to an overaged state (or steady state). | |||
| T8 | Solution heat treatment, cold work hardening and then artificial aging treatment. | |||
| T9 | Solution heat treatment, artificial age hardening and cold working increase strength. | |||
| T10 | After high temperature molding and cooling, cold processing is carried out, and then artificial aging is carried out to achieve precipitation hardening | |||
| W | – | Heat Treated Solution | ||
Quenching and strengthening methods for aluminum alloys
The specific meanings of different letters are as follows:
F = As Fabricated, representing products manufactured through forming processes.
These alloys do not have special requirements for strain hardening and heat treatment, and may receive some tempering during the forming process. There are no limitations on mechanical properties.
For example, 2014-F represents a product formed from 2014 aluminum alloy, which can be formed by rolling, extrusion, forging, drawing or casting, and these processes have no special control over thermal conditions.
O: annealed
The main purpose of annealing is to improve workability, ductility and elongation, and to bring aluminum alloys to their lowest strength state.
For example, 5083-O represents any form of 5083 product whose most recent treatment was heating to a high temperature of 345°C and then naturally cooling to room temperature.
H: Strain Hardened
For non-heat treatable aluminum alloys, strength is generally increased by strain hardening at room temperature. H usually has 2 or 3 symbols, indicating the amount of cold working and subsequent heat treatment.
For example, the first number after H, H1 represents strain hardening only, H2 represents strain hardening and partial annealing, H3 represents strain hardening followed by low temperature stabilization, and H4 represents strain hardening and painting.
The specific meanings of H1-H4 are as follows:
H1: No heat treatment process, just strain hardening to increase strength. The numerical value after this code represents the degree of hardening.
H2: Strain hardening and partial annealing. Used for products that have undergone excessive strain hardening and then partially annealed to reduce strength to the required level. The number after H2 represents the strain hardening remaining after annealing.
H3: Strain hardening and low temperature stabilization. Used for products that have undergone strain hardening and then stabilized at low temperature to reduce strength and increase ductility. The number after this symbol represents the hardening remaining after strain hardening and low temperature stabilization.
The second number after H, like X in H1X, represents the actual strain hardening level of the alloy.
For example, X in H2X represents the effective amount of cold work remaining after exceeding the required amount of cold work and partial annealing.
X in H3X represents the effective amount of cold work remaining after cold work and temperature stabilization treatment.
X in H4X represents the effective amount of cold working remaining after cold working, subsequent forming and painting processes involving exposure to heat.
As mentioned above, the second digit after H represents the degree of strain hardening. If a number follows HX (X = 1, 2, 3, 4), the specific meaning is as follows:
2: 1/4 of the hardening amount.
4: 1/2 amount of hardening.
6: 3/4 of the hardening amount.
8: Total amount of hardening.
9: Excessive amount of hardening.
In summary, the second digit after H represents the remaining amount of cold work.
The third digit after H, such as HXX1, is a variation of the two-digit tempering, which is used to control mechanical properties or precision machining, but the differences are usually not significant.
For example, H111 represents annealing followed by slight strain hardening during stretching, which is typically used for extruded profiles that must be straightened after annealing to obtain straightness tolerance.
H112 is used for products that have undergone light tempering through high-temperature forming processes and have no special control over strain hardening and heat treatment amounts, but have certain requirements for mechanical properties.
H111, H311 and H321 are used for alloys with less hardening than H11, H31 and H32.
W: Heat treated solution
This is an unstable quench and is only applied to alloys that have undergone solution heat treatment and then natural aging at room temperature. This symbol is only used when a specified period of natural aging is required.
T: Heat Treated, Heat Treated
T represents heat treatment, which produces a stable tempering other than F, O or H after heat treatment.
T is the most widely used symbol in heat treatable alloys and can be used for any heat treatable alloy.
After solution heat treatment, heat treatable alloys are generally quenched quickly and aged naturally or artificially.
There are always one or more numbers after T to define the different subsequent treatments.
T1: After forming and cooling at high temperature, natural aging to the stabilized basic state.
Used for products that undergo high-temperature forming processes (such as casting or extrusion) and then room temperature aging treatment according to a cooling rate sufficient to increase strength.
Applicable to products that have not been cold worked after high temperature forming and cooling, or products whose effect on mechanical properties such as flattening or stretching is not significant.
T2: After high temperature forming and cooling, cold working and natural aging to stabilized state.
T3: Solution heat treated, then cold worked and finally aged naturally to a stable state. Used for products that can be strengthened by cold working, such as straightening or stretching.
T4: Solution heat treated and then aged naturally until stabilized state. Used for products that have not been cold worked after solution heat treatment or products whose cold working cannot increase the strength.
T5: After high temperature forming and cooling, artificially aged. Used for products that undergo high-temperature forming (such as casting or extrusion) and cooling, and then artificially aged to improve mechanical strength and dimensional stability.
T6: Solution heat treated and then artificially aged. Used for products that have not been cold worked after solution heat treatment or for products whose cold working cannot increase strength.
T7: Solution heat treated and then aged in the oven for stabilization. The purpose of stabilization is to increase its tensile strength.
T8: Solution heat treated, then cold worked to harden and finally artificially aged. Used for products that can be strengthened by cold working, such as straightening or stretching.
T9: Solution heat treated, then artificially aged to harden, and finally cold worked to increase strength.
T10: After high temperature forming and cooling, cold worked and then artificially aged to achieve precipitation hardening.
5. The difference between 6061-T6 and 7075-T651.
Okay, at this point we have a global understanding of aluminum alloy systems.
So now let's talk about 6061 and 7075, which should be relatively easy to understand.
Let's first present the results and then delve into the details.
| Comparison of Material Properties Between Aluminum Alloys 60617075 | ||
| 6061-T6/6061-T651 | 7075-T6/7075-T651 | |
| Yield strength (Mpa) 0.2% | 276 | 503 |
| Tensile strength (Mpa) | 310 | 572 |
| Shear strength (Mpa) | 207 | 330 |
| Modulus of elasticity (Gpa) | 68.9 | 71.7 |
| Brinell Hardness (HB) | 95 | 150 |
| Elongation (%) at 24℃ | 17 | 11 |
| Density (g/cm3) | 2.7 | 2.81 |
| Processability | good | A little poor (more difficult) |
| Weldability | Weldable | Not weldable |
| Heat treatment performance | Heat treatable | Heat treatable |
| Corrosion resistance | High corrosion resistance, resistant to stress corrosion cracking | A little lower. Prone to stress corrosion and cracking. |
| application | Sports platform, bicycle frame, building and other structures. | Aviation gears, rods and other high stress applications. |
| Coefficient of thermal expansion (um/m/C) @ 20-100 ℃ | 23.6 | 23.4 |
| Thermal conductivity (W/m/K) | 167 | 130 |
| Melting point (C) | 582-652 | 477-635 |
| Resistivity (ohmcm) | three point nine nine × 10-6 | 515×10-6 |
Performance comparison between 6061 and 7075 aluminum alloy.
6061-T6: This aluminum alloy belongs to the sixth category of aluminum-magnesium-silicon alloys and has undergone solution heat treatment and artificial aging treatment: T6.
T6″ indicates that the aluminum alloy has undergone quenching heat treatment.
This heat treatment is divided into two stages. In the first step, the alloy is heated to a constant temperature of about 527°C and held for about 1 hour to dissolve the alloy elements in the aluminum and distribute them evenly in the aluminum.
Then the alloy is removed and quickly quenched in cold water to retain the alloy elements, such as magnesium and silicon, in a fixed position. If the part is cooled slowly, precipitation of the alloying element often occurs.
The second step, aging treatment, is to reheat the part to 177°C and keep it warm for 1 to 18 hours (the specific retention time is determined according to factors such as the size, shape and application of the part). The purpose of this step is to precipitate and strengthen the Mg2Si hardening element in the aluminum alloy.
7075-T651: This is a typical 7 series alloy, which is an aluminum alloy with zinc as the main alloying element.
Its heat treatment type is similar to 6061-T6, and the basic tempering is T6, indicating solution heat treatment, followed by quenching and finally artificial aging. The aging strengthening elements are Mg and ZnAlCu2.
One difference is that “5” indicates that it was stretched to release stress, and “1” indicates that the amount of stress released by stretching is 0.5-2%.
