6061 or 7075?
Firearms are debated as much as politics. Everyone has an opinion on what’s best, worst, and everything in-between. For example, what do we need to know the types of aluminum used to make AR15/10s? Which aluminum is better for ARs; 6061 or 7075? I thought I’d share some facts and throw my opinion into the mix.
Aluminum and AR15s/AR10s
Aluminum has always been the prime building material for AR 15/10s. It’s a manufacturer favorite because of its strength, corrosion resistance, and ease of manufacturing. Aluminum is not used in a pure form, however. It is usually mixed with different alloys, to give it different properties and then assigned a number, hence 6061 or 7075. The alloy content is important because it helps establish its strength and performance. Don’t get too wrapped up in the numbers as they only represent the mix of alloys used in the aluminum’s preparation and to differentiate between properties.
6061 and 7075 Properties
6061 and 7075 Aluminum have different properties that make them attractive to manufacturers. Both are better suited for certain types of application than the other. I have listed their properties give you an overall sense between the two:
- Ultimate Tensile Strength 45000 psi
- Tensile Yield Strength 40000 psi
- Fatigue Strength 14000 psi
- Shear Strength 30000 psi
- Hardness, Rockwell 40
- Machinability 50%
- Ultimate Tensile Strength 83000 psi
- Tensile Yield Strength 73000 psi
- Fatigue Strength 23000 psi
- Shear Strength 48000 psi
- Hardness, Rockwell 53.5
- Machinability 70%
On face value, you might say that 7075 is better because it appears stronger. Take tensile strength; 6061 is 45,000 psi (pounds per square inch) and 7075 is 83,000 psi. You might equate the higher number as being better, but there is more to the story that numbers. As with anything, you have to determine the best use. One question you can ask is all that extra strength necessary in order to make a safe and reliable AR?
The fact is there is nothing wrong with 6061 Aluminum in an AR application. 6061 was the original aluminum used for M16s up until 1968 when the military changed over to 7075. They changed over for added corrosion protection because of all the issues they were having in the jungles of Vietnam. The corrosion was due to high temperatures, high humidity, and the interaction with human sweat when handling the rifle.
The technical term for this is intergranular exfoliation. In layman’s terms, since the microstructure of metals is made up of grains, and separated by grain boundaries, the corrosion attacks the boundaries. This causes the grains to separate. In other words, the change from 6061 to 7075 had nothing to do with poor 6061 strength issues. It was a specific set of circumstances that the average person who uses an AR for recreation or hunting would not encounter.
So why the fuss?
Manufacturers sell what people want to buy. If someone read an article that stated ABC was the next best thing and people started asking for it, manufacturers would scramble to sell it. Unfortunately, people sometimes think that sales equal quality. Sales benchmarks don’t mean a product is better; it just means that it’s purchased more.
Since I’m former military, I tend to stay with what the military uses. If they went to 7075 for whatever reason, I’m in (but that’s just my opinion).
I’m lucky to work for Live Free Armory. In addition to writing for them, I’m still a qualified an armorer/builder. I have built myself several ARs in 5.56 and .308 using 7075 aluminum. Live Free Armory likes the added benefits that 7075 Aluminum has. In the end, I think it’s a matter of personal preference versus which one is better. They both will get the job done.
If you’d like more information or have any questions, feel free to email me at Murgado.firstname.lastname@example.org. Please remember that Live Free Armory is here to help you whether you choose to buy from us or not. We believe that obtaining the right information should always be your first step.