That Cracked Aluminium frame

[Omicrom]

So a few months ago my brother noticed a crack on his frame, at first he thought it was a paint crack but as he rode it more it grew in size and after a few rides he could see the inside of the crack bending the chain-stay slightly inward.

 

Long story short he scraped the frame ,because he bought it secondhand. And I decided to have a shot at repairing the bike.

I also thought about writing a long term review as how the repairs hold up and the whole repair process from start to finish.

I will do all the repairs myself so I will also share some of the lessons learnt through the process.

The bike will become my commuter bike later on ,but more about that later.

 

 

[King_Crispy]

Not worth it.

Bin it

[Omicrom]

Not worth it.

Bin it

That is the primary reason for attempting this repair, too may people have said it is not possible and I would like to share the experience if it does hold up at all.

[Vetseun]

I can have it repaired here in Bloem at Weidemans. I think. Would need an opinion first.

[Omicrom]

I can have it repaired here in Bloem at Weidemans. I think. Would need an opinion first.

Hi Vetseun , 

Fortunately I have the necessary skills and equipment to do it myself. 

Thank you

[bikebloke]

Not worth it.

Bin it

 

this ^^^^^^^^^^^^^^^^^

 

if you don't use jigs the frame will never be true ...

[big_mtn]

I'm very curious to see he it turns out. Please do tell us how you get on, it's an interesting experiment. If it's a 6061 alloy, it's heat treated after welding. You'll have to avoid creating a stress riser I think.

[Fox3]

Give it a go bud. I hope it is a success!

[Omicrom]

I'm very curious to see he it turns out. Please do tell us how you get on, it's an interesting experiment. If it's a 6061 alloy, it's heat treated after welding. You'll have to avoid creating a stress riser I think.

Yes it is 6061-T6 aluminium , which is basically a Aluminium alloy with magnesium ,silicon ,and chromium as main alloying materials that is artificially aged to improve hardness.

Yes I will only relieve the stresses caused by welding , called recovery, I don't want any recrystallization or grain growth to occur because that would make the frame to soft and thus decrease stiffness. So the heat treatment is at a relatively low temperature for a short time and then air cooled.

 

Yes as the welding goes you don't want to hang in there with the torch longer than necessary otherwise grain growth will occur. Regarding filler material you want enough to prevent hot-cold cracking on the weld but not to much otherwise it will cause a stress concentration next to the weld.

[lechatnoir]

Yes it is 6061-T6 aluminium , which is basically a Aluminium alloy with magnesium ,silicon ,and chromium as main alloying materials that is artificially aged to improve hardness.

Yes I will only relieve the stresses caused by welding , called recovery, I don't want any recrystallization or grain growth to occur because that would make the frame to soft and thus decrease stiffness. So the heat treatment is at a relatively low temperature for a short time and then air cooled.

 

Yes as the welding goes you don't want to hang in there with the torch longer than necessary otherwise grain growth will occur. Regarding filler material you want enough to prevent hot-cold cracking on the weld but not to much otherwise it will cause a stress concentration next to the weld.

 

seems like you know what's up with this process, so good luck. Who knows? Perhaps there's a new frame repairer on the horizon? Nothing ventured, nothing gained.

[Omicrom]

Step 1

Cleaning the frame with a mild detergent and removing any grease from the paint to have a clean surface for the paint stripper to work on.

 

Step 2

Apply the paint stripper and let it do it's thing. I used Built it branded paint stripper and 500ml proved to be more than enough for 3 coats.

 

Step 3 

Wash the frame again with a mild detergent, to remove excess paint stripper and lose bits of paint.

 

The clean frame actually looked quite nice and I am thinking of keeping it that way for a brushed aluminium look.

Upon closer inspection 3 cracks was found on the frame , as well as 3 lose bottle cage nuts.

The welding on the frame did look good accept for 2 or 3 spots and I suspect that more than one person welded on the frame (it was probably a production line setup).

 

Step 4

Clean all the cracks with acetone, and drill the tips of the cracks to stop the crack from spreading.

 

Step 5

 File down the crack to form a "v" all along the crack. This helps to stay on course during the weld because it is quite difficult to see such a small crack next to the arc and it will give the weld bead a slightly flatter appearance.

 

Step 6

Clean all the cracks again with acetone, On the inside as well as the outside, to remove any possible weld contaminants.

 

The frame is now ready for welding and tomorrow is the big day.

 

 

[BaGearA]

If it doesn't work : oh well

 

If it does work : bloody good on ya    and it will make A killer conversation piece

 

Excited to see what happens

[Sepia]

Yip, keep us posted?

[V12man]

I ensure the welding will be fine - curious as to how you intend to do the post welding head treatment.

 

Also what alloy are you going to use as filler?

 

I also have the kit but still need a bit more practice before trying a frame - at least I finished painting my new welder cart today - still need to make up all the cable management bits but it's usable now - going to give the paint a day or two still before bolting them all down.

[Omicrom]

I ensure the welding will be fine - curious as to how you intend to do the post welding head treatment.

 

Also what alloy are you going to use as filler?

 

I also have the kit but still need a bit more practice before trying a frame - at least I finished painting my new welder cart today - still need to make up all the cable management bits but it's usable now - going to give the paint a day or two still before bolting them all down.

I am going to heat that part of the frame ,wrapped in aluminium foil ,with a blowtorch to about 200'C. This is only to relieve the stresses caused by the welding.

I have done my calculations and a simulation has shown that the max stress in that region will be around 40MPa with the riding I intend to do. Which will give me a fatigue live of around 5*10E7 stress cycles considered that the alloy will not be aged again as it's supposed to.

 

Regarding filler rod I intend on using 4043 in 3.2mm thickness.

[Omicrom]

I ensure the welding will be fine - curious as to how you intend to do the post welding head treatment.

 

Also what alloy are you going to use as filler?

 

I also have the kit but still need a bit more practice before trying a frame - at least I finished painting my new welder cart today - still need to make up all the cable management bits but it's usable now - going to give the paint a day or two still before bolting them all down.

I am going to heat that part of the frame ,wrapped in aluminium foil ,with a blowtorch to about 200'C. This is only to relieve the stresses caused by the welding.

I have done my calculations and a simulation has shown that the max stress in that region will be around 40MPa with the riding I intend to do. Which will give me a fatigue live of around 5*10E6 stress cycles considered that the alloy will not be aged again as it's supposed to.

 

Regarding filler rod I intend on using 4043 in 3.2mm thickness.