How to bend thickish alloy bar?

[stinkwheel]

This might be a bit too much of an ask of the material but worth a try.

I want to make a rear rack for a bike. I'm too tight to blow £150 on a quick-rust rentec. The plan is for it to be really basic, two bars about 300mm long sticking out the back from the grab rail mounts with a fenestrated plate mounted on top.

I've got some 10x30mm 6082 flat bar for the job (overkill?).

Each bar will need a slight dog-leg in the middle of about 10 degrees. This will need to be in the vertical aixs. So if you're looking straight at the 30mm face of the bar, that's where you'd see the dog-leg.

I planned to heat it up in the oven for an hour or so (my fan oven will go to 250C) then clamp it firmly just before the bend, slide a long bit of pipe over and slowly-slowly apply a bending force (or just the weight of the pipe) while heating the metal on the outside of the bend radius. Then leave it to sit somewhere cool for a few days to re-harden before doing anything else with it.

Option 2 would be to half cut through it, apply the bend in a similar way to above then lumiweld the slot (any weight would be acting to close rather than open the slot).

The other option would be to cut the angles and see if I can find someone to TIG it up.

However, a bend would be nice if it's achievable.

Sketch attached, although I intend the finished article to have a more radiused finish.

Main thing is, I'm not sure if this kind of bend is possible without cracking the material, or if the heat treating to achieve one without cracking will rob so much strength it wont recover enough to be useable.
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[MCN]

I think aluminium melting point 600-700ºC.

We used to use bar soap rubbed on the piece before heating as an indicator. It will go black or dark brown at annealing temp.

I think I seen an aluminium slab being rolled into sheet on youtube. They pre-heated the slab and then rolled in a hot mill before continuing in a cold mill.

You will be messing with any post production properties of the material if you heat an bend.

This is aircraft related. Not the same alloy but there are some temperatures in there. (In American )

They say 650F 343C So at least your bar won't melt.


https://www.tinmantech.com/education/articles/aluminum-alloys-annealing.php

You can only try.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[ThatDippyTwat]

As said, any heat treatment of the alloy is going to be nullified. Chances are it will be soft as shit. Alu both age and work hardens. The more you manipulate it, the more likely it is to "snap".

You'll have better results with steel tubing, filling it with sand (must be dry), heating and bending. It's be softer than it started unless you get it *really* hot, but it will still be harder than Alu that's had a similar process. Chuck on a primer and paint of your choice.

Source - I work in a foundry, part of my job involves manipulation of metals, and heat treatment of metals, some of which are Alu alloys.
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[Riejufixing]

It's a long time ago, but ISTR you need rather more than 250C to anneal it, more like 400 and slow cooling (don't quote me).

Might another technique be to thin the edge of the bar by beating it, flat side on an anvil or RSJ offcut or whatever, with annealing?

I might be tempted to get it welded...

[Pete.]

You're bending it the hard way by the looks of your drawing. Bending that 30mm width in T6 harness I would say you'll need a good 150mm radius bend or it'll start cracking on the outside edge.

No scientific data was harmed during this guesstimation.
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[Robby]

Round pipe is easier and will look better. I would braze the joins, this looks like the right application and it needs a lot less cocking around to make it look nice afterwards compared to mig.

[MarJay]

Cut pie slice out, reweld.
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[Riejufixing]

[Pete.]

[MCN]

Lumiweld (Fucking phone) is not welding. It uses a similar material but it is a brazing technique like soldering.
Aluminium is notoriously difficult to weld without the proper materials and preparation.

It will probably hold if lumiweld is applied but any structural strength will also rely on excess material applied during the process.
Removing this extra material will reduce the properties of the joint.

Aluminium can be welded using coated filler rods and arc or oxy-acetylene. Or MIG for this thickness of material. Not everyone has access to the equipment.

I would just heat that bar in the oven (when she is at work) then bend (until resistance is too much to overcome) then heat in the oven till max temp. Switch off the oven and allow the workpiece to cool slowly with the oven.
The inside radius of the bend will puff up as that material will have been pushed out by the mechanical force applied in forming the bend.
Sand that bit down.
Sanding aluminium has some issues too. It clogs the abrasive used so frequent changes are required and aluminium grows a protective oxide layer (rust) immediately it's exposed to the atmosphere so needs a was or something to protect any shine. Aluminium polishes have a was incorporated in their compounds and the grit particle size is bigger than that used for Brass. But you already know this. 😂
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Grubscrew]

You could modify a pipe bender to accept , or hire one which uses a hydraulic ram.
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FJR1300/CBR1000F

[ART-ADS]

you can get handheld torch off ebay for cheap i use a MAP bottle.
cut out a semicircle of wood and screw it to the bench
drill holes in a strip of metal and screw that to the wood.
heat up the metal and pull it around the shape you made
this method was used a lot when building chop frames
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[ThatDippyTwat]

[kramdra]

Aluminium is not suited to home made bending when it will be holding a 10kg+ dynamic load off the back of a bike. Id also be going for 12-15mm wide in the vertical.

Cut and bolt two lengths to create the angle. Add a side plate as reinforcement.

Aluminium is cheap. Cut the side rails out of 100mm x 15mm plate.

While rentec's are expensive new, and they do rust, mine has been reliable and has had a lot of abuse, with a full heavy box mounted on it for most of 7 years.

[ART-ADS]

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[ART-ADS]

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[P.]

[ThatDippyTwat]