Hardening Aluminum

[lxskllr]

I was looking at my toy biner this morning, and thinking about the time I bent it lifting a manhole cover. I had to bend it back afterward. I would like to harden the aluminum so it doesn't bend as easily. Wikipedia gave me precipitation hardening, but no specifics...

https://en.wikipedia.org/wiki/Precipitation_hardening

Is this something I could do in a woodstove without giving it much attention? I'm thinking I could stuff it in the coal bed for awhile(a couple hours?), and maybe get something a little more usable?

I have real carabiners, but they're bulkier, and a waste of good product for my purposes. I need something I can beat up, and inexpensive enough to abandon if necessary. The HarborFreight biner matches that requirement, but is a little too soft.

 

[Fenixgoon]

first, you need to know what type of aluminum you have. if you have some friends with equipment, you can check composition, hardness, and conductivity. these 3 pieces will tell you everything you need to know about what alloy and what heat treatment.

1xxx, 3xxx, 4xxx, and 5xxx are work-hardenable alloys - you need to deform them to strengthen them (rolling reduction, forging, etc.). if you have one of these, you're more or less SOL.

2xxx, 6xxx, and 7xxx are the precipitation hardening (heat treatable) alloys. 6061 is probably the most commonly used alloy for consumer structural stuff.

your biner may already have been heat treated, in which case there is nothing you can do (6061 is commonly used in the t6 condition, which is the highest strength..unlike 2024 or 7xxx alloys where there are more significant tradeoffs between strength, toughness, and stress-corrosion resistance).

but if you want to try and heat treat it, you'd need your oven and a quench tank. temperature control is pretty important as well, so a kitchen oven might not actually do it properly (a high-quality heat treating oven is +- 3C over the entire volume). but it would be fun to try either way.

the process will go 1) solution heat treat (heat at high temp), 2) quench in water. don't let the part sit out between the oven and the quench tank - getting into the quench quickly is essential! 3) artificially age - heat to a lower temperature to cause the precipitation reaction
i don't know the heat treating temperatures off the top of my head, but it should be google-able.

 

[OILFIELDTRASH]

We use to hear treat aluminum in the 900f range about 2 to 3 hours. Quench in water. Water could not go over 100f when quenching. Then precipitation harden at around 350 for 8 or 9 hours.
Worked at a heat treat facility once.

 

[OILFIELDTRASH]

Also when you heat the aluminum back up you will put it back in the anneal state. Which basically means it loses all its hardness. If you don't quench it right and precipitation harden right your aluminum will be softer than before. Going from solution to quench should almost be instantaneous. We had a elevator that would drop from furnace to directly into water. Furnaces were calibrated within a few degrees uniformly throughout the furnace. It was definitely way out of the kind of thing youd be able to do at home. You might be able to get it to work.

 

[lxskllr]

Maybe I'll try a water quench. HarborFreight biners are 80¢. Not a big deal if I screw it up, and it'll be interesting to try. I have no idea what kind of aluminum they are. Probably recycled beer cans :^D

 

[BoomerD]

Or...bear with me here...you COULD just buy a decent quality steel carabiner that will do the job without all this fuss.

Never send a boy to do a man's job...

 

[lxskllr]

Or...bear with me here...you COULD just buy a decent quality steel carabiner that will do the job without all this fuss.

Never send a boy to do a man's job...

I could. I also have real biners that far outclass the cord I have it attached to, but it then adds bulk and/or weight. The cheap aluminum biner is perfect except for the malleability. It's also an interesting question, at least to me. I'm familiar with working steel, but had little idea before this thread on how it all works with aluminum.

 

[Fenixgoon]

I could. I also have real biners that far outclass the cord I have it attached to, but it then adds bulk and/or weight. The cheap aluminum biner is perfect except for the malleability. It's also an interesting question, at least to me. I'm familiar with working steel, but had little idea before this thread on how it all works with aluminum.

some steels operate on the same principles as hardening aluminum alloys (17-4, 15-5, 13-8, Custom450/455/465/475, etc.).

your classic carbon steel, however, is quench to harden (strengthen), temper to restore ductility/toughness.

 

[John Connor]

I took up welding and we used a spray or powder that hardened steel. I don't know about aluminum though.

 

[BrainEater]

Fenixgoon is bang on .

The really good aluminum grades are hardened by compression . That's basically "aircraft grade" . It actually changes the crystalline structure of the aluminum.

John , you are describing 'shot peening' ....It's where the term 'Ball-peen hammer' came from.You use a sandblaster with tiny little hardened ball bearings.
https://en.wikipedia.org/wiki/Peening

Peening increases metal strength through both 'work-hardening' and 'dimpling' .
-----

Honestly , I'd be afraid to harden aluminum. Tempermental .
It's not allowed for any lifting grade equipment anywhere I know of.

 

[deadlyapp]

Fenixgoon is bang on .

The really good aluminum grades are hardened by compression . That's basically "aircraft grade" . It actually changes the crystalline structure of the aluminum.

John , you are describing 'shot peening' ....It's where the term 'Ball-peen hammer' came from.You use a sandblaster with tiny little hardened ball bearings.
https://en.wikipedia.org/wiki/Peening

Peening increases metal strength through both 'work-hardening' and 'dimpling' .
-----

Honestly , I'd be afraid to harden aluminum. Tempermental .
It's not allowed for any lifting grade equipment anywhere I know of.

I think john is actually talking about a coating, either high velocity oxy fuel (HVOF) or something like Direct laser deposition (DLD). Those would both harden the surface, but would do nothing about the tensile strength of the carabiner.

 

[Newbian]

You are better off going for transparent aluminum.

 

[Red Squirrel]

I imagine pop can aluminium is lower grade than what is used in actual products, but my experience is that hot fire coals will pretty much vaporize it. I always throw pop cans in the camp fire if I'm too lazy to bring it to the recycling or don't want to shake up the mosquitoes in the grass. It will be gone within an hour.

One thing that has crossed my mind that would be neat is to use a camp fire as a forge, if you can get it to liquid state without it vaporizing it could be used to cast stuff. Need a good way to actually measure/regulate temperature though when working with stuff like that. Too hot and it starts to evaporate, too cold and you get lot of slag.

 

[Rubycon]

I imagine pop can aluminium is lower grade than what is used in actual products, but my experience is that hot fire coals will pretty much vaporize it. I always throw pop cans in the camp fire if I'm too lazy to bring it to the recycling or don't want to shake up the mosquitoes in the grass. It will be gone within an hour.

One thing that has crossed my mind that would be neat is to use a camp fire as a forge, if you can get it to liquid state without it vaporizing it could be used to cast stuff. Need a good way to actually measure/regulate temperature though when working with stuff like that. Too hot and it starts to evaporate, too cold and you get lot of slag.

Building a fire inside of a tub made from an old front load washer (stainless steel) drum works well. Force air induction from a decent power leaf blower (200MPH - 600CFM) will produce intense heat. In just a few minutes providing there's a decent ember base from burning hardwood for a few hours, the temperature will soar to over 2,000F and get things glowing lemon yellow. A standard steel barrel would be sparking nice at this point and won't last very long.

 

[John Connor]

I imagine pop can aluminium is lower grade than what is used in actual products, but my experience is that hot fire coals will pretty much vaporize it. I always throw pop cans in the camp fire if I'm too lazy to bring it to the recycling or don't want to shake up the mosquitoes in the grass. It will be gone within an hour.

One thing that has crossed my mind that would be neat is to use a camp fire as a forge, if you can get it to liquid state without it vaporizing it could be used to cast stuff. Need a good way to actually measure/regulate temperature though when working with stuff like that. Too hot and it starts to evaporate, too cold and you get lot of slag.

On YouTube they have instructions on building your own forge. But you have to be EXTRA careful.

 

[Red Squirrel]

Building a fire inside of a tub made from an old front load washer (stainless steel) drum works well. Force air induction from a decent power leaf blower (200MPH - 600CFM) will produce intense heat. In just a few minutes providing there's a decent ember base from burning hardwood for a few hours, the temperature will soar to over 2,000F and get things glowing lemon yellow. A standard steel barrel would be sparking nice at this point and won't last very long.

Haha brings back childhood memories of this one camp site I use to camp at with my grandma all the time. Those bins were pretty much standard issue fire pits. Some would use angle iron legs to lift it off the ground. With the small holes you definitely get a good combustion out of those.

 

[Fenixgoon]

Fenixgoon is bang on .

The really good aluminum grades are hardened by compression . That's basically "aircraft grade" . It actually changes the crystalline structure of the aluminum.

John , you are describing 'shot peening' ....It's where the term 'Ball-peen hammer' came from.You use a sandblaster with tiny little hardened ball bearings.
https://en.wikipedia.org/wiki/Peening

Peening increases metal strength through both 'work-hardening' and 'dimpling' .
-----

Honestly , I'd be afraid to harden aluminum. Tempermental .
It's not allowed for any lifting grade equipment anywhere I know of.

peening imparts a compressive residual stress on the surface, which is useful in enhancing the fatigue life of parts since you 1) reduce the mean stress 2) create plastic zones that blunt cracks

i wouldn't say "good" aluminum is work hardened. it's merely different. also, there are going to be practical strength limitations with work hardening vs. other strengthening mechanisms, with precipitation hardening being more effective than work hardening, as far as i know. also, heat treatable alloys are generally going to be able to be made in much larger section sizes than work hardening ones (uniformity of work goes down as section size goes up).

the majority of aircraft parts i've worked with are precipitation hardening, not work hardening. for example, large aircraft forgings, say a bulkhead or wing spar, might be 7050 (or more recently, 7085) which are both precipitation hardening, but they're overaged and given a small bit of compression after the fact for stress relief (T7452). wing skins, on the other hand, might be a 2xxx alloy in the T8 condition (i think?) for high strength and thermal stability.

there is nothing wrong with hardened aluminum (work hardening or precipitation hardened). it's merely all about balancing properties and proper design. do you want super high strength while sacrificing other properties (toughness, SCC resistance)? 7075-T6, have fun. just don't let it get anywhere near salt. on the other hand, maybe you're making something that needs reasonable structural properties but also good formability and machinability, in which case 6061 or 6063 (used in scuba tanks) might suffice. the strength is lower, but the corrosion properties will be better than 7075-T6, and they can be made in a number of shapes/sizes relatively easily.

i would say there are relatively few "bad" materials. but there are bad material selection choices and designs.

anyway, i'll get off my soapbox now

 

[MrSquished]

Can you take some of your excess hardened aluminum and make a tv stand? I know someone in need.

 

[John Connor]

LOL