You may have noticed that there are two types of aluminum listed in the specs for aluminum bikes; 7005 or 6061. Which is the stronger material? Your first answer may be 6061 because you see it on the more expensive bikes. 7005 aluminum is actually the stronger aluminum alloy. This begs the next question, which is the better material? 6061 is of course, or at least that is the opinion of most bike manufacturers. Why is it better? To see the differences one must take a look at the two materials and their properties. In the table below several different aluminum alloys are listed for comparison; 2014, 6061, and 7005.
Alloy
Trace Metals
Tensile Strength
Yield Strength
Percent Elongation
HB
Notes
2014
4.5% Copper
0.8% Silicon
0.8% Manganese
0.5% Magnesium 27,000 psi
14,000 psi
18%
45
2XXX series aluminum is primarily alloyed with copper.
2014-T6
4.5% Copper
0.8% Silicon
0.8% Manganese
0.5% Magnesium 70,000 psi
60,000 psi
13%
135
2XXX series aluminum is primarily alloyed with copper.
6061
1% Magnesium
0.6% Silicon
0.2% Chromium
0.3% Copper 18,000 psi
8,000 psi
25%
30
6XXX series aluminum is primarily alloyed with magnesium and silicon.
6061-T6
1% Magnesium
0.6% Silicon
0.2% Chromium
0.3% Copper 45,000 psi
40,000 psi
12%
95
6XXX series aluminum is primarily alloyed with magnesium and silicon.
7005-T6
4.5% Zinc
1.4% Magnesium
0.45% Manganese
0.13% Chromium 51,000 psi
42,000 psi
13%
NA
7XXX series aluminum is primarily alloyed with zinc.
The tensile strength of the material is the amount of stress that it can take before complete failure, and the yield strength is the amount of stress before the material is permanently deformed (try jumping on an old frame until you bend it and you have exceeded the yield strength of the material). Percent elongation is the amount of deformation that the material undergoes before it breaks and the HB is a measure of the hardness. It should be noted that the ‘T6’ listed after the alloy is the heat treatment of the alloy. T6 refers to a solution treatment and artificial aging of the metal. All bike frames are heat treated even if the manufacturer does not list the T6 behind the grade of aluminum.
From the chart you can see that 7005-T6 is slightly stronger than 6061-T6, but stronger than both of them is 2014-T6 and in fact there is another 7XXX series aluminum (7075) that is stronger as well. Why choose 7005 and 6061 then? Bike frames are not made out of solid aluminum, which is how the test samples for comparing material strengths are constructed. A bike frame is made up of tubing that is welded together: welding 7005 and 2014 are almost impossible feats that eliminate them as viable choices for making a bike. That leaves 7005 (a zinc alloy) and 6061 (a magnesium/silicon alloy). The difference between the two is that 7005, because of its high alloy content (over 6%), is harder to manipulate the material and to weld it. This means that with 6061 it is much easier to add strength adding tubing features like triple butting, ovalized tubing, and tapered walls that reduce the weight and improve the strength of the tubing.
A final note to put this into perspective is to compare aluminum to the other frame materials. Aluminum is far weaker than both titanium and cro-mo steel, so why use it? Aluminum’s greatest advantage is that it is so light when compared to cro-mo steel and cheap when compared to titanium. This combination of features makes it the choice of material for making light, high-performance frames for a reasonable price.''
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