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Thread: Keeping turned aluminum shiny

  1. #11
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    One of the other problem I find is how soft a turned part is. It takes one fumbled drop or clank and the surface gets nicked. Is all aluminum this way and I just haven't noticed, or is there a typical hardening process 'professional' parts typically get?
    Aluminum is available in a very wide range of alloys, just like steel. The properties vary just as much too. If you want real scratch resistance then for parts like that use 7075-T6 alloy. It is harder than mild steel and stronger too. It also costs more. Another alloy with similar properties is 2024-T4. Also as hard and as strong as steel. To resist weathering it does need protection of some sort.

    I will warn you that if you don't know what alloy you are using you run the risk of using something that is not strong enough for the job. Pure aluminum takes a very high finish when polished. The only element with higher reflectivity is silver. Unfortunately, pure aluminum has only about 1/10 the strength of mild steel and if used for something like those standoffs could be easily bent.

    I go along with the objection to clear coat. Once it becomes cracked or scratched it looks like garbage. Instead use regular car wax and polish as required.

    Aluminum alloys come in two main varieties, those that can be hardened by heat treatment and those that can be hardened only by cold working. As for "professional" parts, many are made from regular 6061-T561 alloy and then anodized. Anodizing is a very thin coating of transparent aluminum oxide that may or may not be dyed different colours. It is a very hard surface and is very resistant to scratches. I use it to protect parts that will see heavy use. Example:

    Last edited by Evan; 01-10-2011 at 11:39 AM.
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  2. #12

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    Quote Originally Posted by jep24601
    BMW doesn't polish or coat it's aluminum motorcycle engine parts.
    Yeah, but most of that is rough cast, right?

  3. #13

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    Quote Originally Posted by firbikrhd1
    My suggestion, and what I do to solve the problem is use an aluminum alloy with high corrosion resistance and polish it when it begins to look the least bit dull. I have made several parts for my bike and they still look as good as when I made them. Trust me, I am not a frequent polisher of my bike as I really don't enjoy polishing as much as I enjoy riding. One additional benefit is that uncoated parts seem to have a higher luster than coated parts.
    The problem comes from my choice in aluminum stock. Occasionally I'll find a mother chunk at the salvage yard with a '7075' in grease paint on it, but a lot of times it's...well, it sure IS aluminum! But the vintage is unknown.

    Does Harbor Freight sell a Rockwell Hardness tester?

  4. #14
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    Bmw must use some sort of superia aluminium ..it does not corrode much ..ive noticed that a lot .

    all the best.markj

  5. #15
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    Unfortunately, the stronger the aluminum alloy the lower the corrosion resistance. Pure aluminum is nearly corrosion proof but is soft as butter. You don't get both in the same alloy. 7075 that has been laying around outside for a while is pretty easy to identify. It turns a medium shade of gray.
    L&S Industries sells grinding wheels Made In USA, all types and sizes. Also Superabrasive diamond and CBN wheels, no extra cost for custom wheels, Made in Canada. 10% discount for HSM members. Call Janet 250-392-3393 08:00-12:00, 13:00-15:00 M-F Pacific Paid Ad, updated Apr 01 2013
    update 2013/3/31 . Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  6. #16
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    Quote:
    Originally Posted by jep24601
    BMW doesn't polish or coat it's aluminum motorcycle engine parts.

    Quote Originally Posted by rocketsled
    Yeah, but most of that is rough cast, right?
    It sure is. Looks just as good 40 years later.

  7. #17
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    Quote Originally Posted by Evan
    If you want real scratch resistance then for parts like that use 7075-T6 alloy. It is harder than mild steel and stronger too.
    Evan, what is your definition of "scratch resistance"?


  8. #18
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    Evan, what is your definition of "scratch resistance"?
    Not the same as "scratch proof" just like "water resistant" isn't the same as "water proof".

    Incidentally, the piece of bar stock doesn't look like 7075 to me.
    Last edited by Evan; 01-11-2011 at 08:22 AM.
    L&S Industries sells grinding wheels Made In USA, all types and sizes. Also Superabrasive diamond and CBN wheels, no extra cost for custom wheels, Made in Canada. 10% discount for HSM members. Call Janet 250-392-3393 08:00-12:00, 13:00-15:00 M-F Pacific Paid Ad, updated Apr 01 2013
    update 2013/3/31 . Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  9. #19
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    You are correct. The bar stock is 6061. The forgings are 7075. I'm just trying to understand why 7075-T6 scratches more easily (seems that way, anyway) than mild steel if it is harder and stronger?
    Keep in mind, I don't have any scientific test equipment. Just my usual ham-fisted clumsiness as experience.
    Last edited by Highpower; 01-11-2011 at 08:57 AM.

  10. #20

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    Quote Originally Posted by Highpower
    Evan, what is your definition of "scratch resistance"?
    ...and my definition is even less scientific. I make a nifty part (e.g. a really cool knurled knob that would look great on a stereo), polish it up all shiny, then drop it on the floor at the office, now my part has a ding in it that ruins the true beauty of my shop-class level project.

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