7075 Aluminum

The most widely available aluminum alloy for home craftsmen is 6061. I have been using 6061 for many of my reel components. But when I decided that I should make (vs. buy) aluminum screws, I chose alloy 7075 to get higher strength. While making screws, I found that 7075 machines as easily as 6061, despite its greater strength and hardness.

Later, I notice a small problem with a reel that I had made. I had it mounted on a bamboo rod with “Leonard style” hardware, wherein a nickel silver ring slides back over the front part of the foot. The ring made a small scar on the softer 6061 aluminum foot. This would not have happened with a locking style of hardware, which I prefer in any case. But I decided to try 7075 for the feet of my next batch of reels.

IMG_3239
And the machining is going quite well. I would say that it is definitely better than using 6061. When I mill 6061, small chips get welded back on to the finish surface of the part. This is not happening with 7075.

Comparison of the two alloys (data from On-Line Metals):
6061: 40 ksi yield, 45 ksi ultimate, 60 HRB
7075: 73 ksi yield, 83 ksi ultimate, 87 HRB

The aluminum guide of McMaster-Carr rates 6061 machinability as “fair” and 7075 as “good”.

Like 6061, 7075 can be anodized without “smutting” problems.

The disadvantages are
1. Higher cost – not a big factor for the small cross sections needed for screws and feet.
2. Lesser selection of bar size. To make a foot of 6061, I can buy 3/8 by 5/8 rectangle and mill to 0.550 width. When using 7075, I have to buy 1/2 by 3/4 and mill to 0.37 by 0.550.

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