Mystery Aluminum Sheet?

[canuck750]

I bought two pieces of 1/4" sheet aluminum to make extended carrier racks for KLR650s, the scrap yard told me one was more expansive than the other (identical size) but he would sell me both pieces for the lesser price, I didn't ask what the difference was.

The racks need a slot cut out of the middle and some trimming. 1st one cut easy enough with a hack saw blade in a skill saw. The second one went through 5 blades before I got half of the cuts done. I ended up drilling 1/8" diameter holes very close together and then cut through the holes.

The sheets weigh about the same, what the heck could the harder of the two alloys be? I have never come across any aluminum that was so difficult to cut. It's like the stuff is stainless steel, but it's an aluminum alloy of some type.

[injundave]

Hmmmmm, sounds suspiciously like unobtainium.

[Kentktk]

I have sheet like yours of 6061 T6. It`s kind of a bear to cut. More so than others I have cut.

[Kiwi_Roy]

Slightly off topic but if you need to cut regular aluminium especially curves a regular hand coping saw is the way to go,
it cut's much faster than a hacksaw and you can cut any curve you like.

[Triple Jim]

From what you're describing, the hard to cut one could be titanium, although you should be able to see a weight difference if it is.  I've seen titanium in the aluminum section at scrap yards.

[Chuck in Indiana]

6061 is free machining. 7075, not so much.  That would be my guess. No, it's not titanium, that stuff is a bear.

[dsrdave]

I suspect 7075 or 2024.  In either case don't plan on welding it.  Also, you MUST not leave any rough edges.  Even a relatively small scratch from the saw will result in crack propagation.  Make sure all the edges are nice and smooth !!!

[twhitaker]

6061 is free machining. 7075, not so much.  That would be my guess. No, it's not titanium, that stuff is a bear.

That's the stuff bears avoid. 

[Triple Jim]

2024 machines nicer than 6061!  I doubt if that's the problem alloy.  Are there any identifying marks on the pieces?

No, it's not titanium, that stuff is a bear.

Well, canuck750 said "The second one went through 5 blades before I got half of the cuts done."  That sounds like a bear to me.  I supposed it could be 7075 or 7078 (etc) if the blades that broke were really poor quality.

[Daniel Kalal]

it's all those letters after the first number (2024, 7075, 6061) that you'll also want to know.  -T6 has strength (but, comes with other problems associated with that temper).  Plenty of aluminum alloys can have the strength of mild steel.  Trouble is, they'll corrode and crack soon enough if you don't pay attention.

[Bill Havins]

Some of this stuff is really difficult to "saw," but "turns" very nicely on a lathe:  https://en.wikipedia.org/wiki/7075_aluminium_alloy#Basic_properties

I have a block of "Fortal" sitting in the garage.  In the right light it has a bit of a copper-to-red hue to it.  When I use my power bandsaw to cut pieces from it the cut takes forever - I have to use a very coarse-tooth blade.  It turns very nicely.  It is really, really tough.

[Testarossa]

I have experience with ski poles and ski construction. 70** is harder but not as ductile as 60**.  If overloaded to failure it will snap, not bend, and leave a wicked sharp end.

[boatdetective]

I live for this sort of stuff     

differentiating aluminum alloys in the field could be a bit tough. The sailboat masts an spreaders I work with are all extruded 6061 T6. The T6 mens it is age hardened. However, I've never had a problem sawing or drilling it.  Titanium definitely has a different color- more "gunmetal" than silver. What is being described seems to be such a significant difference that I'd suspect a different material altogether. I did not think that diferent Al alloys would vary this much (RE breaking blades)

[Daniel Kalal]

It occurs to me that there might very well be some aluminum-lithium alloy out there in the scrap yards by now (enough time has gone by since its introduction).  If it is, and depending on the alloy you've got, it can be pretty tricky stuff to work with.  It's strong, I'll give it that.

[canuck750]

Wow, I had no idea there was such a vast array of aluminum alloys available. The two pieces looked the same except the harder one was stamped ASME, no other marks such as a 4 digit code or T6 or anything else for that matter.

The pieces I am making are 13" x 16" and are secured over the original KLR 650 rear rack using the stock 6mm mounting bolts at the four corners and two across the centre. I am fitting a vertical 'L' bracket to affix a RotoPax 1 gallon gas can behind my back and the same bracket will carry a padded backrest on the opposite side of the 'L' bracket. The flat area of the deck remaining (about equal to the original rack surface area and location) will carry a soft top bag. I think the 1/4" aluminum will adequately support the 5" wide X 10" tall upright leg of the 'L' bracket carrying the gas tank and the backrest. Six - 6mm bolts support the base of the 'L' bracket (5" x 5") to the aluminum deck.

I had a similar set up for years with a heavy steel rack, two 1 gallon gas tanks mounted at the very far end of the rack hanging out over the rear fender and a Honda Line adjustable backrest, very, very heavy. By scrapping the steel deck and the Honda Line kit I should save at least 7 lbs.

[kevdog3019]

Call them back and ask??
Report back with aswer. 

[Sasquatch Jim]

 Unobtainium?  If it is titanium it will ring if rapped with a steel rod.

[charlie b]

Were the blade breaking because the metal was 'hard' or were the teeth packing up?

I've had the latter problem on some Al alloys before.  Even had some pack up the milling machine tools.  Even good cutting fluid doesn't help.  I don't remember the alloys.  Some were cheap and some very expensive.

6061 (including the T6) cuts nicely with hand tools.  I love that stuff and will keep it around for various odd jobs.

[Chuck in Indiana]

Were the blade breaking because the metal was 'hard' or were the teeth packing up?

I've had the latter problem on some Al alloys before.  Even had some pack up the milling machine tools.  Even good cutting fluid doesn't help.  I don't remember the alloys.  Some were cheap and some very expensive.

6061 (including the T6) cuts nicely with hand tools.  I love that stuff and will keep it around for various odd jobs.

Yeah, about the only way to cut that soft gummy crap is to flood it with kerosene. Paraffin to you limeys.. 

[Robert]

Wow, I had no idea there was such a vast array of aluminum alloys available. The two pieces looked the same except the harder one was stamped ASME, no other marks such as a 4 digit code or T6 or anything else for that matter.

Some of the alloys have 'grain' due to the direction they were rolled when formed.  The markings on the sheet are parallel to the grain.  Bending parallel to the grain is more likely to crack. [As I recall from school, many moons ago.]

[Chuck in Indiana]

parallel to the grain

Uh, yeah. Don't do that unless absolutely necessary.