There is an old Blackburn lowrider sitting in my pile of stuff that is going to be repurposed for another project. Blackburn used a press of some sort to flatten an end on the lowrider, but I'm betting it was a single press and not multiple pressings to get the desired effect.

If I use a hammer to flatten an end and put a hole thru it for mounting purposes, will the processes of flattening with a hammer work harden that area and cause problems with crack failure in time?

If it's going to crack, it will probably do it right away. This depends on the alloy.

Thank you for the quick reply. Taking your cue, I went to the garage and hammered away at the rod end. Did not crack, but was surprised that there was a lot of heat created. Not sure what the alloy mix is in this old lowrider, but it seems to be very malleable. Also straightened out a 90 degree bend and only the paint cracked, the aluminum was fine.

Story time! In the '70s I worked at Alpenlite, a shop that made high-end backpacks, including frames made of welded 6061 tubes that were heat-treated to T6 after welding. Welded frames were sent out for the HT, so I wasn't aware of what-all that entailed. But there was this little hoop that wasn't really structural, just held the open end of the pack open for convenience, so it didn't need a HT. The last inch or so of each end of the tube was squished flat, then a hole punched that a clevis went through in use. Similar to the Blackburn shape.

That was one of my jobs. Before squishing and punching, the end was put into a small electric furnace with a "glory hole" just big enough to let the tube in. I don't remember how long it was left in the furnace or how hot it got (this was ~50 years ago) but I think it was a few seconds. Did I quench them after the heating? Don't remember, but probably. The point of this story is that some industrial engineer designed the process and those parts had a high reliability in the field. They felt it was necessary or at least worthwhile to do that heating step.

It's my understanding that 6061 softened this way will naturally age to T4 condition, not as strong as T6 but often strong enough. I'll bet that's what Blackburn racks are, anyone know? I assume heat treating each rack after welding would be too expensive for such a commodity part, plus they'd yell it from the rooftops if they were heat-treated. I don't remember them claiming that.

If you're flattening it somewhere away from any welds, then the rod is probably T6 there. If I had to do that job, I would look up how hot to get it and the other details of how to soften it before hammering, and how long aging is going to take to get it back to an acceptable strength. Maybe someone here knows off the top of their head. I'm not an aluminum guy, never studied that stuff.

I suppose you could just do it without softening, and find out "the hard way" if it's going to crack. I could see it failing later, some miles down the road though, maybe at the worst possible time and place if the gods are not smiling on you.

Do you feel lucky?

You could always heat it afterward with a torch to stress relieve the hammered area.

I used the original Blackburn FL-1 Lowriders extensively in the 80’s, 90’s and ‘00’s when I used to do cycle camping.

Story: 1996 my wife and I did a two month loaded tour of New Zealand. Partway through the trip, one of the lowrider points that had a hole in it which was bolted to the front eyelet, broke. I happened to be in a small town with a service station. I got a piece of small diameter steel tube from them, used their service bay to (a) flatten out the end, (b) drill a hole through it to align with the original now broken hole and (c) slotted the steel tube, slipped it over the original and clamped it down with a couple of small diameter hose clamps. It held for another month of loaded touring.

Upon return to my store, I registered a warranty claim with Blackburn and received a new set of lowriders. Lo and behold, the new ones were made with an additional piece of aluminum tubing slipped over the bit with the hole and stamped/bonded in place. Obviously I wasn‘t the first to have this failure. Huh.

Mark Beaver, that is the rack that I am using. The ends are simply stamped and no reinforcements. The package had it marked as FL-1. Fairly soft aluminum for sure. Getting close to finishing the project now. If I take the torch to the flattened ends, how hot do I get them and quench or no quench? Oil quench or water?

I wrote something about heat treatments back in the days....
Aluminium and heat treatment

Wiel, after reading through the article it occurs to me that without knowing the material, what it actually is, there is no way to get a reliable heat treatment. To me it is aluminum, but to the scientist it is much more than that.

You are right , I don't know any easy trick to show what kind of alloy is used.