Bicycle aluminium alloys: 6061 and 7005
Bike frame materials
Most bicycle frames made of
- steel
- aluminum alloys.
Less commonly and more expensively, bicycle frames are made from
- carbon fiber
- titanium alloys.
Steel
- Steel frames are mainly chrome molybdenum steel frames of the type 4130. Good frame made of chrome-nickel steel has the necessary strength, durability and relatively little weight.
- Reynolds 525 and 725 use the same base alloy (very similar, if not the same as 4130), but 725 has improved properties due to heat treatment.
- Some steel frames, mainly children's bicycles, made from a cheaper carbon steel - they are also strong and durable, but heavier than chromoly, because thicker.
Aluminium alloys
- Most Velor aluminum alloys have about the same strength and weight, as close to them in the frame price of chrome-molybdenum steel.
- Their increased stiffness is good for a ride in the mountains or in the sprint, but not to overcome the pits and bumps.
- In contrast to the steel frames, aluminum does not rust. On the other hand, frames made of aluminum alloys are more prone to fatigue failure and less maintainable, than steel.
- However, a well-made aluminum frame will serve faithfully for many years.
Frame - the main part of the bicycle and a base for mounting the rest of its parts. Rama's modern bicycles are usually made of pipes, which connect to form the so-called "double triangle". This form is also called «diamond» – someone, it resembles a diamond and even, may be, diamond. The shape of the frame in more than one hundred years remained almost unchanged, although with the development of modern technologies and materials, and there are many innovations. In the last couple of decades, especially actively looking for new materials for frames, including among aluminum alloys.
quality factors
The quality of a bicycle frame as a structure is determined by four main factors:
- rigidity,
- strength,
- fatigue strength
- weight.
The stiffness of the bike frames
Rigidity determines the ability of a structure to elastically deform: the greater the rigidity, the less elastic displacement of structural elements relative to each other. Elastic frame soften the blows of the pits and bumps, whereas the more rigid frame will transmit the rider strikes from each pit and bumps. On the other hand, a flexible frame longer flex under load, absorbing part of the energy, which is designed to move forward. Therefore cyclists, who want to win in the sprint and time trial prefer rigid frame.
Strength of material the bicycle frame
strength characteristics frame material - tensile strength and yield strength - under normal conditions does not directly affect the ride quality or the thrill of it, but it is essential for resistance to a strong frame, "Emergency" shock. Robust frame withstand such impact, and less strong - weak – can not survive.
Fatigue strength of the bike frames
In normal driving each turn of the pedals, hole or bump in the frame cause small cyclic stresses. Although these voltage and a much lower yield strength material, several hundreds of thousands of cycles they can cause so-called fatigue cracks and, in the end, endurance failure. Resist material call this type of destruction fatigue strength. If you want to ride my bike a few decades, your weight is above average and you rarely peel from the saddle, something for you fatigue strength – important factor.
The weight of the bike frames
Weight, or rather the frame weight, It depends on the density of the material and, of course, frame structure, in particular, its thickness pipes. Typical frame weighs from 1,5 to 3,0 kg, which is about a quarter of the weight of the bicycle. However, the full weight of the bike is often ten times less, than the cyclist in full "battle" attire. So most cyclists will not notice a small difference in weight frames, if, of course, they will not have long to climb the mountains on a bike or below.
Aluminum alloys for bicycle frames
6061 or 7005
Aluminum bike frames are mainly made from aluminum alloys:
Some other aluminum alloys, for example, 7075 и 2014, stronger, than both alloys 6061 и 7005, but they are not enough suitable for the manufacture of bicycle frames, because they are almost impossible to weld, at least, usually argon-arc welding.
often considered, that the aluminum alloy 6061 more suitable for bicycle frames, than an alloy 7005, although the alloy 7005 and somewhat more durable. The tensile strength of the alloy is 7005-T6 350 MP, and alloy 6061-T6 - 310 MPa, yield strength 290 и 275 MPa, respectively.
When it comes to the strength of the frame as a whole, the large differences in strength arise from the quality of welds, selecting the shape and thickness of the pipe, as well as the overall design of the frame. In fact, under the load, which is generally subjected bicycle frame, differences between aluminum alloys 6061 и 7005 Hardly ever, because the voltage, that arise in the frame, sufficiently far from these limit values.
Aluminium alloy 6061
Chemical composition
Aluminium alloy 6061 belongs to the 6xxx series of aluminum alloys (Al-Mg-Si). The main alloying elements are:
- magnesium (0.8-1.2 %) and
- silicon (0.40-0.6 %),
- as well as copper (0.15-0.40 %) and
- iron (up to 0,7 %).
Heat treatment after welding
Alloy 6061 It has a relatively high strength, easily welded and is widely used not only for making bicycle frames, but also in construction, aircraft, shipbuilding.
Like all 6xxx series alloys Alloy 6061 It is thermally hardenable alloy. Heat treatment, which is applied to the already welded frames, includes:
- heating up 530 ° C
- intensive water cooling
- artificial aging at about 180 ° C. 8 hours.
Aluminium alloy 6061 after such treatment designate 6061-T6.
Figure – Chemical composition of 6061 aluminium alloy according to EN 575-3.
A fragment of the table 6 from the EN 753-3 standard
Mechanical properties
Figure – Mecanical properties for 6061 alloy extruded tubes in T6 temper.
A fragment of the table 41 from the EN 755-2 standard
Aluminium alloy 7005
Chemical composition
Aluminium alloy 7005 belongs to a series of 7xxx aluminum alloys without copper alloying (Al-Zn-Mg). Main alloying elements:
- zinc (approx 4,5 %) and
- magnesium (about 1,4 %).
Aluminium alloy 7005, as Alloy 6061, It is thermally hardenable. However, Unlike alloy 6061:
- for alloy hardening 7005 enough air cooling.
Figure – Chemical composition of 7005 aluminium alloy according to EN 575-3.
A fragment of the table 7 from the EN 753-3 standard
Figure – Mecanical properties for 7005 alloy extruded tubes.
A fragment of the table 54 from the EN 755-2 standard
Heat treatment after welding
Alloy 7005 have ability to age-harden in the heat-affected zone up to about 80 % of the parent metal by natural aging and can be recover 100 % of strength if artifically aged after welding
Brand aluminum alloys
Aluxx, Aluxx SL and Aluxx SLR
The well-known bicycle company Giant apply their, branded aluminum alloy "Aluxx". At the same time, the usual "Aluxx" – it's just an aluminum alloy 6061, but with special designs "butted", hydroforming technology, and heat treatment.
- Butting - thickening of pipes in critical sections, often at the ends of pipes.
- Hydroforming - forming pipes by placing them in special dies and pumping water or special oil under high pressure into them.
More advanced brands Aluxx SL and Aluxx SLR use aluminum alloy 6011, which is different from the alloy 6061 a slightly larger copper.
Figure – Chemical composition of 6011 aluminium alloy according to EN 575-3.
A fragment of the table 6 from the EN 753-3 standard
Alpha White, Black and Red
Trek uses brands:
- Alpha White Aluminum и Alpha Black Aluminum – this is the usual alloy 6061,
- Alpha Red Aluminum - aluminum alloy is thermally hardened 7075.
Figure – Chemical composition of 7075 aluminium alloy according to EN 575-3.
A fragment of the table 7 from the EN 753-3 standard
Figure – Mecanical properties for 7005 alloy extruded tubes.
A fragment of the table 61 from the EN 755-2 standard
Sources:
https://off.road.cc/content/feature/the-ultimate-guide-to-frame-materials-whats-best-for-bikes-664
https://www.bikeradar.com/advice/buyers-guides/bike-frame-materials/
https://www.giant-bicycles.com/global/aluxx-slr
https://www.bikeexchange.com.au/blog/bike-frame-materials-explained
