Which is better, aluminum alloy or high carbon steel? Do you know anything? Please let me know. Thank you.

Iron (Fe)-carbon (C) alloy without any alloying elements is carbon steel, and carbon can improve the strength in steel.

The higher the carbon content, the better the strength, but when the carbon content is higher than 0.8%, the higher the carbon content, the more brittle the steel, so in the frame and

The front fork is made of medium-low carbon steel with moderate strength, good plasticity and easy processing, and its carbon content is about 0.25%-0.35%.

Carbon fiber (CERP)

The scientific name of carbon fiber is "polypropylene acrylic carbon fiber". The composite material made of carbon fiber and related matrix resin (such as epoxy resin) can be comparable to metal in many physical properties, such as specific strength and specific elastic modulus, but its specific gravity is much lighter than metal. Carbon fiber frame is characterized by "light weight, no bending and good impact absorption". However, it is not so easy to give full play to the excellent performance of carbon fiber, and the quality of carbon fiber manufacturers is also very different. Considering the cost, bicycle manufacturers are unlikely to use advanced carbon fiber to make the frame. Despite the above practical problems, carbon fiber frame still has advantages that other materials do not have, and it can make lightweight bicycles of about 8 kg and 9kg. This kind of carbon fiber lightweight bicycle can best reflect its advantages when climbing, and the slope is flat and refreshing. Unlike some lightweight aluminum alloy frames, there is a pulling force when climbing.

Carbon fiber is what solidifies carbon fiber with resin. It is very light, but it belongs to directional material (strong tensile strength but easy to break), so the method of stacking thin layers of materials is adopted to solve the shortcomings.

Usually, each bundle of carbon fiber is called 3K braided carbon fiber cloth, which can be divided into 5 bundles, 6 bundles, 7 bundles, 8 bundles and so on. According to the knitting density per square centimeter. The thickness of its single layer is about 0.25——0.29mm, and the greater the density, the thicker the thickness. Each bundle containing 1 0,000 thousand pieces is called 1K, and its knitting density is much higher than that of 3K carbon fiber cloth, but its thickness is only about 0.65,438+05-0.2 mm. Because of the complicated process, the price of 1K carbon fiber cloth is almost three times that of 3K carbon fiber cloth. Perhaps because of the cost performance, most manufacturers use 3K carbon fiber cloth.

● Advantages of carbon fiber frame

(1). A light frame can be made.

The carbon fiber frame is obtained by laminating carbon fibers along the stress direction. Carbon fiber frame is very light, which is composed of its density and strong tensile strength.

Giant's carbon fiber frame is very light, and the model in 2000 was1.2kg.

(2) Good impact absorption

Carbon fiber is used to make artificial legs for disabled people, or special springs are used in various fields. With its excellent performance of absorbing impact, we can make bicycles without shock absorbers. For example, the elevated Scott factory is famous. However, the quality of different manufacturers varies greatly, and some of them are very hard. You will know whether this kind of frame is good or not after riding it.

(3). It can make various shapes of car frames.

The basic molding method of carbon fiber is to spread the fiber sheet on the mold, then flow the resin and burn it. Can be made into frames of various shapes. For example, TREK's Y box is very famous.

● Disadvantages of carbon fiber frame

(1). Complex stress calculation

The carbon fiber frame is made of carbon fiber, which is characterized by strong tensile strength and weak shear strength. In the process of machining, complex stress calculation (longitudinal stiffness and transverse stiffness) is needed, and carbon fiber sheets are superimposed and formed according to the calculation. The processing technology of each manufacturer is different, so it is very important to choose the products of experienced and reliable manufacturers.

(2) It is difficult to change the size.

It is difficult to change the size because of the molding after the mold is finished. Cannot correspond to orders of multiple sizes and styles.

(3). Aging?

Will the resin used age? This is an existing subject, which will gradually turn white when placed in the sun. Of course, this phenomenon is related to the technology of the manufacturer. It is best not to put it in the sun.

chrome-molybdenum steel

Cr-Mo steel (Fe-Cr-Mo)

In the history of bicycle 100 years, iron material is an ideal material for rigidity and weight balance. The biggest feature of the iron frame is that it can arbitrarily choose the required iron pipes with various compositions and thicknesses to accelerate. So you can choose the frame with the most suitable size, rigidity and riding feeling, which is very beneficial to the old drivers who are also sensitive to the difference of several millimeters. Its biggest disadvantage is that it is heavier than other materials. However, the recent iron frame has been heat-treated to make thin tubes into thick tubes, and the weight will not be lost to light alloys.

Chromium-molybdenum steel is an alloy of chromium and molybdenum. Its performance is as follows:

○ Good quenching performance.

○ High tempering resistance.

○ Tempering brittleness tendency is less.

○ Good processability at high temperature and beautiful appearance after processing.

○ Good solderability.

● Advantages of Cr-Mo steel frame

(1). Good processability.

The frame of Cr-Mo steel is the oldest frame, so it has been studied for the longest time. Very thin pipes can now reach the required strength of the frame.

(2) Good shock absorption performance.

Excellent riding feeling, such as "riding feeling like a spring". The Cr-Mo steel pipeline that constitutes the frame has excellent impact absorption performance.

(3) easy to weld

Chromium-molybdenum steel is easier to weld than titanium and aluminum. Can be designed into famous shapes. In addition, there is no need for heat treatment after welding, so there is no need for large-scale heat treatment equipment and the cost is low.

(4) the price is cheap

Although some high-grade chromium-molybdenum steel frames are expensive, they are generally very cheap. In other words, you can buy a high-gear frame at a cheap price.

● Disadvantages of Cr-Mo steel frame

(1). Easy to rust.

Cr-Mo steel used for car frame contains Cr, but the addition amount is small (stainless steel contains 12% Cr). Without surface treatment, it is easy to rust when there is a wound. However, anti-rust treatment is generally carried out. When riding, the meat in the pipeline is pressed very thin, and the influence of rust will be very great. Rust → lower meat pressure → lower strength (stress concentration).

(2) Metal fatigue is significant (metal fatigue caused by stress concentration).

If you use a very thin chrome-molybdenum steel frame, you should pay attention! Of course, any metal will produce metal fatigue, including aluminum. Simply put, metal fatigue phenomenon refers to the fact that although metal has a small force to prevent plastic deformation, it may be destroyed when repeated stress is applied (called fine stress concentration). When an airplane accident happens, it is sometimes caused by metal fatigue of a certain part. For bicycles, strength may not be maintained due to metal fatigue. For example, the impact force generated during DH shortens the life of bicycles. If it doesn't feel so smooth when you step on it, it is likely that the metal is tired.

The characteristics of crystallization will change significantly at the welding position, such as from the pipe side (parent body) to the melting position (fusion joint). In order to homogenize these tissues, they should have been crystallized again (details will be discussed later). But this kind of large furnace is not necessarily available in the frame processing factory. On the other hand, this treatment makes the cooled pipeline harden again, which reduces the strength of the reinforced pipeline.

For the above reasons, various methods are used for welding. Such as using low temperature welding and other methods to manufacture the frame. No matter any excellent welding, the temperature difference between the welding site (above 1000℃) and the other pipeline side (room temperature) will shrink when cooling, resulting in residual stress. Cracks may occur when the component is subjected to stress concentration. In this way, riding for a long time may cause metal fatigue, and micro-hardening also makes the absorption of impact worse.

Aluminum alloy (aluminum-magnesium-silicon, aluminum-zinc-magnesium-(copper))

The aluminum alloy frame has been used for a long time. Light weight and low price are its advantages. But in terms of "light", there is not much difference between the current and iron materials. The old driver's response to it is "light but easy to bend". Although it has been improved many times, it still can't overcome the shortcoming of low Young's modulus of elasticity. Recently, in order to improve Young's modulus of elasticity and increase the outer diameter of pipes, flat pipes or aluminum pipes are used to make light rigid frames. This latest aluminum alloy frame is light and strong enough for drivers.

Aluminum alloy is an alloy in which magnesium, zinc, silicon, copper and other metals are added to pure aluminum. Aluminum itself has the advantages of light weight, good plasticity and corrosion resistance, and its mechanical properties are significantly improved after adding other metals. Most aluminum alloys used for bicycles are 6000 series (Al-Mg-Si) and 7000 series (Al-Zn-Mg-Cu), which can be made into various materials after heat treatment (aluminum can resist high temperature, and its properties will change at high temperature).

6000 series is considered as a kind of material with corrosion resistance, good strength and good weldability. The following table shows the mechanical strength of the most widely used 606 1 alloy.

7000 series is the strongest material in aluminum alloy. In particular, 7075 is superhard aluminum (the material for making airplanes), but it is difficult to weld and has poor corrosion resistance (it will turn white). The following table shows the mechanical properties of the most commonly used 7005 and 7075 alloys. The heat treatment in the table is represented by the following figure:

-0: complete annealing

-T5: Artificial aging (no solution treatment)

-[T6]: Artificial aging after solution treatment.

-T7: Stabilization after solution treatment.

-T8: solid solution, hardening and artificial aging.

● Advantages of aluminum alloy frame

(1). A light frame can be made.

Aluminum has a light specific gravity, but it is not hard enough. In order to improve its strength, it is alloyed and heat treated. [Heat treatment process] The aging precipitation strengthening method is adopted. In short, substances that hinder metal deformation are formed in the metal. Heat treatment at a certain high temperature will cause aging precipitation, and without the framework of this program, it will also cause aging at room temperature. In other words, placing a picture frame in the room will gradually become stronger.

Many aluminum alloy frames are made of 606 1T6 material. T6 marks indicate heat treatment and aging. Without heat treatment, the strength can only reach 1/2 or 1/5.

Bicycle parts marked with 7075 (such as XTR crank, etc. ) has not undergone strict heat treatment. That is to say, because there is no aging, it is aging at room temperature. It is necessary to heat treat 7075 alloy, and its strength can be improved by 5 times through heat treatment.

In addition, 7005 alloy is also commonly used to make automobile frames. Its strength is not as good as 7075, but it can be fully aged at room temperature. This material can also be made into a thin material by padding. However, the strength and Young's modulus of the material itself are low, so the diameter of the pipeline is enlarged to improve the rigidity. This type is usually called aluminum thick pipe.

(2) The appearance changes little after long-term use.

Aluminum itself is a metal that is easily corroded. There is almost no unoxidized aluminum in the air, and it will be oxidized immediately when placed in the air, forming a thin oxide film. Why not rust? The reason is that after the oxide film reaches a certain level, it prevents further rust. The oxide film is almost colorless, so it is not easy to find the change of appearance (sometimes it turns white).

On the other hand, the more times you ride a bicycle made of this material, the more times you are stressed, and the strength also changes obviously. Recently, in order to seek lightweight, many frames are made of thin materials (extremely thin). These are all aluminum alloys, and there is no fatigue limit. What will happen to the strength after long-term use? SC6 1- 10A produced by Dedacciai Company is a kind of pipeline with surface shot peening (KET treatment). The purpose of this treatment is to prolong the fatigue life. According to the published data, 140% can be increased. KET treatment is fatigue damage caused by cracks on the metal surface, so hardening technology is used to improve the hardness of the metal surface.

● Disadvantages of aluminum alloy frame

1). Aluminum is a material with low elasticity and rigidity. So use thick pipes or change shapes, such as cross pipes and padded pipes.

(2) heat treatment is required.

Heat treatment is necessary, otherwise the strength is not enough. Therefore, ordinary small-scale factories are unable to buy heat treatment equipment. Especially for 6000 series aluminum alloy pipes, in most cases, the heat treatment conditions are stipulated by the pipe manufacturer.

● Classification of aluminum alloy: aluminum alloy has a 4-digit specification number in industry, indicating its material, characteristics and main uses as follows:

1000 series pure aluminum (Al content (mass fraction) is not less than 99.00%);

1050, 1070

High purity aluminum, electrical conductivity, thermal conductivity and corrosion resistance

Pipes for heat conducting materials, heat exchange equipment and chemical equipment.

-

2000 series aluminum alloy with copper as the main alloying element;

20 1 1,20 14,20 17,2 1 17,2024

Excellent machinability, high strength and weak corrosion resistance.

Dura aluminum, cutting materials, structural materials such as parts and screws, aircraft materials, forging materials, hydraulic components of automobiles and locomotives, and sporting goods.

-

3000 series aluminum alloy with manganese as the main alloying element;

3003,3203

Better heat resistance, higher strength and better corrosion resistance than pure aluminum.

Chemical equipment pipeline, heat exchanger, copier photosensitive drum.

-

4000 series aluminum alloy with silicon as the main alloying element;

4032

Good heat resistance and wear resistance

Video recorder head, piston parts, forgings.

-

5000 series aluminum alloy with magnesium as the main alloying element;

5052,5056

Medium strength alloy, good corrosion resistance and weldability.

Chemical pipeline, mechanical parts, camera lens barrel.

-

6000 series aluminum alloy with magnesium and silicon as main alloying elements and Mg2Si as strengthening phase;

606 1

Medium strength structural alloy with excellent corrosion resistance, weldability and good machinability.

Road vehicles, ships, marine materials, road building materials, sporting goods, etc.

6063

Good corrosion resistance, good surface treatment and excellent extrudability.

Building materials, building materials, decorative materials, household appliances and other general products that account for most of the extruded materials.

-

7000 series aluminum alloy with zinc as the main alloying element

7005

Medium strength

Structural alloy for welding, parts of vehicles, automobiles and locomotives.

7075

Known as superhard aluminum, it is the highest strength alloy with poor corrosion resistance and weldability.

High strength materials: aircraft and other mechanical parts, sporting goods, etc.

-

8000 series aluminum alloys with other alloying elements as the main elements.

8090,809 1

Few practical alloys.

-

9000 series spare alloy group

9000 series aluminum alloy materials are protected by American defense industry. At present, only Klein and Trick are used in the bicycle industry. 9000 series aluminum alloy materials have ultra-light, ultra-high strength and excellent weldability, and most of them are used in aerospace industry.

● Application of aluminum alloy in bicycle industry

There are many aluminum alloy parts used in bicycle industry, and nearly 95% of visible metal parts can be made of aluminum alloy. Such as rims, spokes, flower drums, cranks, purlins, flywheels, drivers, brake clamps, faucets, seat pipes, seat bows, front fork bowls and so on.

The materials are mostly 2000, 5000, 6000 and 7000 series, and the 7000 series is the most used frame and front fork.

In addition, it is also widely used in 2000 and 6000 series, such as drivers, calipers, cranks, faucets, seat pipes and so on. The wide use of aluminum alloy materials in bicycle industry is only in the past 20 years. Although aluminum alloy materials have been used in bicycle industry for a long time, the progress and popularization of processing level is the driving force for the wide use of aluminum alloy materials.

Take Taiwan Province Province as an example: the aluminum alloy bicycle frame appeared in about 1986. At that time, the heat treatment and welding technology were not mature, and people didn't know much about the characteristics of aluminum alloy. However, after 4-5 years of exploration, people have been able to master the tricks of production and start mass production, especially in pipe and processing.

But you will definitely ask: How can such a soft material as aluminum alloy be used to make bicycle frames and other parts?

The answer is simple, just harden the aluminum alloy. That is to say, aluminum alloy materials can be hardened by the process of [heat treatment technology], so as to meet the safety standards of bicycle frames and other parts.

Scandium aluminum alloy

The most effective modifier of Al-Mg-based alloy-Sc-Al master alloy: the production of special alloys for missiles and spacecraft, automobiles and ships. Scandium has a magical alloying effect on aluminum alloys. As long as a few thousandths of scandium is added to aluminum, a new phase of Al3Sc will be formed, and the aluminum alloy will be modified, so that the microstructure and properties of the alloy will change obviously. Addition of 0.2%~0.4%Sc can increase the recrystallization temperature of the alloy 150~200OC, obviously improve the high-temperature strength, microstructure stability, weldability and corrosion resistance, and avoid the embrittlement phenomenon that is easy to occur when working at high temperature for a long time.

By adding trace scandium, it is expected to develop a series of new generation aluminum alloy materials on the basis of existing aluminum alloys, such as ultra-high strength and toughness aluminum alloy, new high strength and corrosion resistance weldable aluminum alloy, new high temperature aluminum alloy, high strength and neutron radiation resistance aluminum alloy and so on. It has very attractive development prospects in aerospace, aviation, ships, nuclear reactors, light vehicles and high-speed trains. It is reported that Russia, the earliest and most in-depth research in this field, has developed a series of aluminum alloys with excellent properties, and is moving towards popularization and industrial production. 1420 alloy has been widely used as structural parts of MIG -29, MIG -26, Tu -204 and Jacques -36 VTOL aircraft. 142 1 alloy is also used as the longitudinal beam of Antonov conveyor in the form of extruded profile. In addition, the United States, Japan, Germany and Canada, as well as China and South Korea have also begun to study scandium alloys. In recent years, scandium aluminum alloy has been used to manufacture welding wires and sports equipment (such as baseball and softball sticks, hockey sticks, bicycle beams, etc.). ) In America. Baseball and softball bats made of scandium aluminum alloy have been used in many world competitions and summer Olympic Games.

Because the melting point of scandium (1540℃) is much higher than that of aluminum (660℃), and the density of scandium (3.0g/cm2) is close to that of aluminum (2.7g/cm3), scandium has always been considered as a substitute for aluminum as some structural materials for rockets and spacecraft. When studying the structural materials of spacecraft in the United States, it is required that the materials should also have high strength, corrosion resistance and stability at 920℃ and low specific gravity. It is considered that scandium titanium alloy and scandium magnesium alloy are one of the ideal materials with high melting point, low specific gravity and high strength. Scandium is also an excellent modifier for iron, and a small amount of scandium can significantly improve the strength and hardness of cast iron. Scandium can also be used as an additive for high temperature tungsten and chromium alloys.

magnesium alloy

Magnesium is a very flammable metal. In early photography, magnesium lamps, that is, the strong light produced by the burning of magnesium powder, were relatively heavy.

Its weight and strength are about 2/3 of that of aluminum alloy. Although light, it is not easy to process and fragile. It is rarely used in general frameworks.

Magnesium is the lightest metal structural material in engineering application, and its density is only 1.8g/cm? 3, namely 1/4 steel and 2/3 aluminum. Magnesium alloy has the advantages of light weight, high specific strength and stiffness, good damping and shock absorption performance, good machinability and so on, and has a very broad application prospect in aviation, aerospace, automobile, rail transit and electronic industry. Although the discovery time of magnesium is close to that of aluminum, compared with the annual consumption of 27 million tons of aluminum in the world, the consumption of magnesium is still very small, so there is great opportunity and potential for developing magnesium industry. In the research of magnesium science and technology, the research and development of magnesium in the world, including western developed countries, is still very limited, and the gap between China and developed countries is far smaller than that of aluminum and steel. As long as we seize the opportunity and carry out original research and development, it is entirely possible to realize the leap-forward development of magnesium industry and form a complete industrial chain of innovation, design and manufacturing.