Had a go at the search function, and didn't find anything, so that probably means this is a dumb question - but here goes anyway.

 

I want to make a mount frame for my electric motor on my kayak, part of doing this means shaping aluminium to both the hull form, as well as to curve it to grip the shaft of the motor.

My question is that given aluminiums propensity to crack when bent / folded, can you use heat to help shape the metal to get away from that risk?

IE can you work aluminium like you can steel? I know it does change colour as it heats, but I am not looking to approach forging (if possible with aluminium) or indeed melting temp, just to make it easier to shape.

Yes, aluminum works easily.

Do you have any specific questions? Details of what you need to do? You know the kind of stuff you need to provide if you want meaningful answers.

Frosty The Lucky.

Aloys ment for extrusion can indeed be forged, almost all bar stock is  infact "forged" by a rolling mill.

When forging aluminum bar for shoes, generally one heats it till the tip of your fire rake feels like it is being drug across something sticky. 

as most aloys work harden, annealing will help with cracking, as will proper design (no cold shunts and healthy fellets) and proper choice of filler material when welding.  

Very dependent on alloy as mentioned.  Also you have to be quite careful about temps as the distance between just right and oops! is not that large.

What common alloy is going to need special heat treatment? I mean sure I've been out of working al for quite some time, have they started using special needs alloys for common stuff? I mean really what's a motor mount on a kayak need, a little plate maybe some angle? Something wood working tools and a sharpie or scrap of paper aren't more than up to the task?

Frosty The Lucky.

Na, Jerry, but when you go whacking on it with a hammer it dose work harden, and I have seen many horse and stock trailers with weld cracks do to the wrong filler. Heck for the allocation he is talking about forged and riveted parts are good

Al's work hardening cues are strong enough a person has to ignore them to miss them. Wrong filler MIGHT make a bad weld? NOOO!

I don't know what Jackdawg wants to do so I can't suggest how to do it.

Frosty The Lucky.

You can double check, but I think the extruded, forgeable aluminum you would order is numbered 6001 or 6003. Jim Keith, the tool maker from Tucumcari, NM, likens extrusion to how a mule processes grain. When heated, the aluminum does not change color. Some smiths keep some small pine splinters handy and when sprinkled on the heated aluminum, it smokes, and you're ready to forge. A coal fire might make the metal surface ugly. You could heat, say, a 1/4" plate on the forge and lay the aluminum on top, heating by conduction, thereby keeping the work cleaner.

Thanks Fella's not quite sure what I want to do design wise as yet, but wanted to know if aluminium is an option, obviously weight is a serious consideration.

Idea will be to form something along the top/sides of the kayak (polyethylene sit on top) to be a mount and take the weight of the small electric motor, attached to some sort of a quick release bracket to hold the shaft of the motor. Obviously will need to have the material flush with the hull, and will want to make some sort of clamping arrangement for quick release of the motor shaft for ease of assembly / disassembly. That would be the points I might want to work the materials shape.

Knowing you can work aluminium with heat means I can have a scrounge around and see what I can find that might be adaptable, maybe have a play. All just ideas at the moment.

 

I forge lots of Al and you can do pretty much anything with it that you can with steel; draw, upset, punch, ... except forge weld of course. The most common structural alloys in the US are 6061 and 6063. 6063 is slightly easier to forge than 6061 but is special order in the area where I live. Sheet in my area is predominantly 3003 which is quite soft, and can be annealed and forged much like copper.

Forging (and annealing) temperature is 850-900F and is usually measured by periodically rubbing the heating metal with a pine stick (paint stirrer works) until the stick leaves a black mark on the surface. If the metal turns a slightly yellowish color on the surface, gently set it aside to cool and it *may* be OK. 

The forging temp requirements are the same for most common alloys so scrap is worth a try. Some 7000 series aircraft alloys are quite hard and more difficult to forge, but the few that I have tried are all easier than forging steel.

If this is for a salt water environment, you might consider knowing your alloy since copper containing alloys are much more subject to corrosion.

Good luck,

Doug

cheers Doug.

mostly fresh, but probably the odd salt water use, so will keep that in mind.

Making a quick release for the motor is easy. Making the motor mount to the boat attachment is a little more complicated not knowing what surface features we're talking about.

Making it form fit is easy enough if it's s simple curve, compound curves are harder. If it's a simple arc you can do it cold with a hydraulic jack. The farther you can move it in the first bend the farther you can take it, it will work harden progressively with each movement.

You can use the soft flame of a weed burner and stir stick to gauge annealing. Don't get carried away with the heat.

Shop around the marine boat guys with a little Beeah and see about picking up some drops. Get some to play with before you start on the real mount. Be sure to use dielectric fasteners and connections, electrolysis is an ugly thing.

PIcs, don't forget to take pics.

Frosty The Lucky.

 

Ta Frosty. Will do.

Hot forging is fine, works like butter compared to steel. I use the same sticky-then-charring stick method IronAlchemy described.

You can do a lot of work cold. If you anneal it first. I was able to make hinge eyes around a Ø1" pintle from 1 ¹/₂"x ¹/₄" . The process was to wipe a bar of soap along the bar in a wiggly line, heat with a propane torch until the soap mark turned dark brown/black then cut to length, bend into a U and then squeeze the straight ends down onto a ¹/₈" spacer plate. Just the one heat treatment required.

Aluminium age hardens as well as work hardens which is worth bearing in mind. Old stock / recycled material might need an anneal before working.

As Frosty says you have to deliberately ignore the cues of its resilience to carry on working it once it gets hard. It is that obvious.

Alan

note that age hardening is alloy dependent (and temperature as well as time dependent)

My concern with work hardening is that a work hardened peice put in to service may fail much sooner than one that has been annealed after manufacture. 

Again if you plan to weld it, the wrong fill (easy to do) will lead to cracks along the side of the weld. Make dang sure you know what aloy you are using and that the fill material you buy is appropriate to it (big issue around here with aluminum trailers) Normalizing after welding won't hurt either. 

Doug pretty much said it all but I'll add a few things. 

When annealing use a stick of wood or a wire brush handle works well. Rub the wood across the hot metal when it leaves a black (starts slick turns brown then solid black) mark the metal is annealed. Annealing can be done with a propane burner in open air. (One of those leaf burners from harbor frieght or a roofing torch works well) I like to anneal in a oven set at a thousand degrees for uniformity. If you stick it in the forge watch out you can easily turn it into a puddle in short order. I have found it makes little diference if I quench or air cool. I understand the science and ideally it is a slower cool but for forging quenching does not do any discernible change or hardening of the metal. 

I would do all your forging cold on annealed metal. When forging aluminum hot it becomes very easy to over heat and very easy to strike hard enough to do damage. Annealed aluminum moves like hot steel. Working hot just isn't needed and rarely gives good results. The only exception would be large billets. 

Do not anneal finished work unless you want it to continue to move. Structural aluminum is hardened and the only way to harden aluminum is by working it. This can be done by bead blasting, tumbling or just forging with a hammer. 

It is very easy to tell when aluminum becomes to hard to work it talks to you as you forge it. Strike hard the more strikes with the hammer the harder it gets until it feels like cold steel. At that point it will crack.  

6061 is an excellent marine grade aluminum and 4043 filler works well with little chance of cracking. 

I use a lot of aluminum in my work I've discovered some neat tricks. I mig and tig copper to aluminum for artistic applications. Blacking aluminum to look like steel. Patinas for aluminum to make them look just like aging copper. I compare forging annealed aluminum very much to hot steel. The power hammer goes a long ways in aluminum forging like I said hit it hard you only have so many hits before it hardens. 

Cheers fellas, the motor is only very light, maybe 3kg, only 18lb thrust, so wont be a lot of vibration / strain on what ever I make.

It will definately be a suck it and see show when I get around to it, and if the aluminum doesn't work out my fall back is stainless steel.

A suggestion towards mounting. If you can, use rubber/plastic spacers between the aluminum mount,and the boat. This will allow air to circulate and keep the aluminum from corroding. I have seen items that were sealed with silicone when mounted that were very corroded when removed. The water ends up getting in between the surfaces due to flexing, and deterioration over time. 

One method I have used to determine temp when heating aluminum was to smoke it with an acetylene torch first. When the carbon burns off it is ready to work.  

I still don't know what the boat looks like, what kind of attachments are available, etc. so this is all speculation. I say a pair of plastic sit in the little seat spot kayaks on a SUV a couple hours ago. Were I making a motor mount to go one of the ones I caught a glimpse of, I'd just heat a piece of poly plastic in the oven and lay it on the deck where I wanted the motor mount and let gravity form it. Then weld what ever attachment points the motor needs and just tie it to the boat deck. It had nicely laced lines.

Making it out of aluminum or stainless wouldn't enter my thinking for a drive with only 18lbs of thrust. Heck I might just mount it on a long selfy stick and glue a shark fin on it. Tell stories about walking my shark.

Frosty The Lucky.