The definitive no marketing BS thread about aluminum

[zank]

Maybe if this thread catches on, we can have similar threads about other materials used in bicycle frames.

The goal here is to dispel some of the myths and misunderstandings about a given material; in this case we'll discuss aluminum. As you all know, I'm early in my fabrication experience with aluminum, so I'm hoping that others here with more experience will jump in too. But I've been studying the material for a long time, and some of the most in-depth and interesting reading I've done has been in welding and heat treating texts. So I am happy to help with some of the science and metallurgy. Take notes. There might be a test at Ballers next spring.

I have my own topics I'd like to cover. But please, post questions and be interactive.

[zank]

The first topic I'd like to hit is bead appearance. Aluminum weld beads look different than other materials. They are larger and generally have a more defined ripple pattern ("stack of dimes" look). There are a number of reasons for this, but there are two primary drivers. But first, we need to take a step back. There are families of aluminum that are heat treatable and those that are not. 6000 and 7000 series alloys are among the heat-treatable alloys. You probably know two specific alloys if you know bikes, and those are 6061 and 7005. That's all you really need to know is that both of these grades are heat-treatable.

One characteristic of some heat-treatable aluminum alloys is that if you weld them using the same alloy as the filler material, the welds tend to crack. For this reason, a different alloy is chosen as the filler. When welding 7005 and 6061, a 5000 series alloy is generally used used, namely 5356 (always in the case of 7005). 5000 series alloys are not heat treatable. One reason why an aluminum weld bead is as big as it is is because you need enough 5356 filler in the weld puddle to dilute the 6061 or 7005 parent metal to prevent short-cracking of the weld.

The second reason that aluminum weld beads are generally larger is the physical properties of the filler wire (say 5356) are lower than either 6061 or 7005. And since the filler metal will not benefit from heat treating (remember that 5000 series are not heat treatable), you need more of it to carry a given load compared to 6061 or 7005.

I know that the look of an aluminum weld bead doesn't appeal to some. But at least now you know that it isn't fabricator doing it by choice. The material dictates the need.

[Saab2000]

Question: the different aluminum designations become confusing to the average fan like myself. I have no idea about them. What are the various properties that make one more or less desirable than another for a bicycle application. Different alloys? Or is it different tube wall thicknesses and diameter?

[Roman]

Merry Christmas, Zank!

That's all I got.

Play Santa to the zanklet.

R

[spopepro]

Since we're on the topic of beads, what did cannondale and DeRosa (on the merak) *actually* do to make the welds look like big fillets, and does it matter for anything other than aesthetics? I've heard stories, but none from anyone I'd call "no marketing BS".

[dhoff]

the physical properties of the filler wire (say 5356) are lower than either 6061 or 7005.

What does it mean that the physical properties are "lower". I know little about metallurgy so english translation is greatly appreciated.

[zank]

What does it mean that the physical properties are "lower". I know little about metallurgy so english translation is greatly appreciated.

Strength and stiffness.

[nahtnoj]

Since we're on the topic of beads, what did cannondale and DeRosa (on the merak) *actually* do to make the welds look like big fillets, and does it matter for anything other than aesthetics? I've heard stories, but none from anyone I'd call "no marketing BS".

DeRosa - El Chaba?

Cannondale - sand them.

[zank]

Since we're on the topic of beads, what did cannondale and DeRosa (on the merak) *actually* do to make the welds look like big fillets, and does it matter for anything other than aesthetics? I've heard stories, but none from anyone I'd call "no marketing BS".

They ground them smooth. Grinding weld beads is generally frowned upon. In fact, many welding codes do not permit it. But there are plenty of those bikes that aren't falling apart.

[zank]

Question: the different aluminum designations become confusing to the average fan like myself. I have no idea about them. What are the various properties that make one more or less desirable than another for a bicycle application. Different alloys? Or is it different tube wall thicknesses and diameter?

I'm working on a lengthy post about 6061 vs 7005.

[edoz]

4043 is a common filler used with 6061. 4043 is heat treatable, so when you weld 6061 T-6 material with 4043, you can stick the finished product back in the oven and get a complete heat treated part. The down side is that 4043 turns crappy dark grey or black when it's anodized, so 5356 is used for those applications. 5356 is also the filler to use on anything that's going to get machined, like if you're filling a bolt hole and redrilling/threading it or building up something that will get milled back down.

[edoz]

Since we're on the topic of beads, what did cannondale and DeRosa (on the merak) *actually* do to make the welds look like big fillets, and does it matter for anything other than aesthetics? I've heard stories, but none from anyone I'd call "no marketing BS".

Not really. Maybe on paper the more rippled beads could be said to have stress risers at the transitions, but in practice it really doesn't matter.

[edoz]

They ground them smooth.

You can also make them smooth without grinding, you just have to run a nice hot, wide puddle and feed the rod in continuously. Thin bicycle tubing makes that hard, but it's doable.

[zank]

You can also make them smooth without grinding, you just have to run a nice hot, wide puddle and feed the rod in continuously. Thin bicycle tubing makes that hard, but it's doable.

Sure, but that's not what the bike guys were doing.

[EddieBirdsell]

They ground them smooth. Grinding weld beads is generally frowned upon. In fact, many welding codes do not permit it. But there are plenty of those bikes that aren't falling apart.

My daily driver is an early 90's Klein with (I've been told) ground triple pass welds. It looks like it's been fillet brazed, the transitions are super sexy. I beat the shit out of it hoping I can eventually break it. No luck.

[edoz]

Sure, but that's not what the bike guys were doing.

I remember seeing a Cannondale factory tour video and they were pretty flat before they ground them. They did grind them, but they didn't look like your typical aluminum bike weld you'd see on something like a Ventana or Yeti when they were laid down. They also weren't feeding wire by hand, they are using handheld wire feeders.

[zank]

I remember seeing a Cannondale factory tour video and they were pretty flat before they ground them. They did grind them, but they didn't look like your typical aluminum bike weld you'd see on something like a Ventana or Yeti when they were laid down. They also weren't feeding wire by hand, they are using handheld wire feeders.

Cool. It would have been fun seeing that shop at its peak.

[edoz]

Yeah, it would. Sorry for the hijack, btw.

[Justin Spinelli]

why are there not more polished aluminum frames on the market? in my opinion, that is a very nice look.

thank you,
justin

[einreb]

My daily driver is an early 90's Klein with (I've been told) ground triple pass welds. It looks like it's been fillet brazed, the transitions are super sexy. I beat the shit out of it hoping I can eventually break it. No luck.

What do you mean by 'triple pass'? (i.e. the definitive no marketing BS thread about aluminum!) Three welds with filler added each time (usually used to weld thick plates?) or a single pass with filler and then 2 smoothing passes? Then ground?

There is a method to go back over the weld again to smooth it out, is that what you are referring to? I was always under the assumption that doing that second pass was good for aesthetics, but not for strength. However, I recall reading this post by FTW a while pack and it poked me in the eye...

new frame for me. | Frank The Welder

Lets keep this rolling!

-Bernie