Now going custom with alloy bodywork!!

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hobot said:
Oh 7075 s'not that bad a hillbilly welding shop can't handle. Here's Ms Peels
7075 welded to hold caliper on fork slider that matches factory finish perfectly.
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7075 is generally considered unweldable for structural applications. The problem with welding 7075 is the potential for failure of the weld. This answer from ESAB gives a nice summary of the issue.

How Do I Weld 2024 and 7075?

Q - I come into contact with two aluminum alloys of which I have found difficulty in obtaining information about arc welding. These alloys are 2024 and 7075. Can you provide me with information on how to weld these alloys with either the GMAW or GTAW process?
A –The reason you are having difficulty finding information on welding 2024 and 7075 is that both of these materials belong to a small group of aluminum alloys that are generally considered as being unweldable by the arc welding process. These materials are often found on aircraft, sporting equipment and other types of high-performance, safety-critical equipment and are not usually arc welded on the original component. Probably, the two most commonly found aluminum alloys within this category are 2024, which is an aluminum, copper, magnesium alloy, and 7075, which is an aluminum, zinc, copper, magnesium alloy. Both of these materials can become susceptible to stress corrosion cracking after welding. This phenomenon is particularly dangerous because it is not detectable immediately after welding, and usually develops at a later date when the component is in service. The completed weld joint can appear to be of excellent quality immediately after welding. However, changes which occur within the base material adjacent to the weld during the welding process, can produce a metallurgical condition within these materials which can result in intergranular micro cracking, which may be susceptible to propagation and eventual failure of the welded component. The probability of failure can be high, and the time to failure is generally unpredictable and dependent on variables such as tensile stress applied to the joint, environmental conditions, and the period of time which the component is subjected to these variables.

It is strongly recommended that great care be taken when considering the repair of components made from these materials. It must be stressed that if there is any possibility of a weld failure becoming the cause of damage or injury to person or property, do not perform repair work by arc welding on these alloys and then return them to service.
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The problems seem to be limited to arc welding (MIG, TIG, or stick). Makes me wonder if you would have the same problem if you gas welded it, either oxy-acetylene or oxy-hydrogen. There are other ways to weld 7075 successfully, but they are beyond the reach of most of us. Before I retired, I spent a lot of time at various aerospace companies, and most had large laser welding chambers where they sometimes welded heavy sections of 7075 together.

Ken
 
Ugh Ken,a serious warning. IIRC Peel caliper adapter was gas shield arc melted with hand stick flowed in. Where does this leave me now? Main force is straight into the seam not much side loading if that matters, ugh, down the road.
 
I once built a very highly stressed rear brake lever out of 2024 aluminum. It had some complicated bends because it was on a Honda CR500 frame where a 4 stroke engine had been mounted so it had to go around the frame on the outside rather that up through where the orriginal went. We couldn't find any welding rod for 2024 so we just sheered little thin strips off of a sheet of 1/16 2024. The whole thing was tig welded and had several pieces between the pivot point and the other end. Never broke in 15 years and still counting. I think the ESAB article makes a good point, which is that; where human life would be at risk in the event of a failure then choose another option.
The fact that your caliper mount is putting force directly toward the joint is another plus. I would say that one of the main welding problems is that welding stores generally sell just one type of rod for welding all aluminum alloys. Make sure that if you are welding 2024 that your rod is 2024 and if you are welding 7075 your rod is 7075. The right gas and tungsten is also important.
 
Why not use one of the weldable aluminum alloys instead? There are lots of them to choose from. Not referring to hobots fork here, Im thinking about Brads bike, where he still could make the change.


Glen
 
Thanks for the example to calm me mortorson. The rod filler used wasn't plan Al but some alloy compatable as could be. Al makes the best mirror surface of any metal.
 
Worntorn, the main reason to choose 7075 or 2024 is strength. Both are stronger than 6061 T6 with 2024 matching the strength of mild steel size for size.
 
I purchased a 17" rim for a project bike it was made of 7075 , before I even laced it up , it rolled of my bench on to the floor about 3 feet and it cracked at the buttweld.
All the flanged rims I have manufactured are 6061
the 7075 rim is as hard as , my opinion is great stuff as long as you dont wish to weld it.
No doubt successful welding can be achieved.
 
Finished up the cradle and got a start on the swingarm. Easier than I expected. Should have it done this week and be able to get the bike back together. It will be nice to get it rolling again.
Now going custom with alloy bodywork!!

Now going custom with alloy bodywork!!

Now going custom with alloy bodywork!!

Now going custom with alloy bodywork!!
 
Gosh Brent its looks like your own UFO wonder! Might consider gussets on the swing arm joints keeping in mind it ain't steel rigid tube back there no more.

7075 definitely wieghs a good bit more than lessor strength alloys.
 
motorson said:
Worntorn, the main reason to choose 7075 or 2024 is strength. Both are stronger than 6061 T6 with 2024 matching the strength of mild steel size for size.
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Until it is welded that is..... They will over age and become very brittle, the elongation at break will be down to 1% or 2% as well as being more susceptible to fatigue and stress corrosion cracking due to the larger copper based precipitates. Also the steel is almost three times stiffer than aluminium (205GPa cf 70GPa)
 
Worked on swingarm and new rearset hangers. Hopefully friday morning I can finish up the swingarm.

Now going custom with alloy bodywork!!

Now going custom with alloy bodywork!!

Now going custom with alloy bodywork!!



I got my spokes from Central Wheel Compoonents, and after telling them several times that I was using the dual disk hub from RGM, they assumed wrong and sent me a std disk set. Now I have to deal with returning these and waiting another week for the correct set, ugh....
 
Brent its delight to watch your work progress form my rocking chair. I've got some Al welding comming up for crash cage frame back up, what is your method?
 
I will try and be a little bit non negative about your swing arm. Firstly the steel original that you are copying form is probably on the marginal side (in terms of torsional stiffness not strength). I will be the first to admit that quick and dirty CAD FEA is a dangerous thing but I did compare the deflection of the swing arm due to a moment from the wheel with some arbitrary values, in the axle slot I applied 100N up on one side and 100N down on the other, not a large load. The steel version deflected 2.5mm and the aluminium over 8mm, this is pretty much as expected since steel is close to three times stiffer, the actual deflections seem reasonable as well (from the experience of straightening my swing arm on the mill table).

Now if I was going to do an aluminium swing arm I would be lazy and start with a dirt bike swing arm and modify to suit. It saves buying all of the stock length material and it will be over kill in terms of strength (it will probably weigh more than the steel original as well). Very very generally speaking when you replace a steel component with an aluminium one (in an application like this or a push bike frame for example) you may be able to get an increase in stiffness but no significant reduction in weight, the increase in stiffness comes from the ability to use larger section sizes and still have enough wall thickness to allow successful welding (and prevent localised buckling)
 
Cheesy said:
I will try and be a little bit non negative about your swing arm. Firstly the steel original that you are copying form is probably on the marginal side (in terms of torsional stiffness not strength). I will be the first to admit that quick and dirty CAD FEA is a dangerous thing but I did compare the deflection of the swing arm due to a moment from the wheel with some arbitrary values, in the axle slot I applied 100N up on one side and 100N down on the other, not a large load. The steel version deflected 2.5mm and the aluminium over 8mm, this is pretty much as expected since steel is close to three times stiffer, the actual deflections seem reasonable as well (from the experience of straightening my swing arm on the mill table).

Now if I was going to do an aluminium swing arm I would be lazy and start with a dirt bike swing arm and modify to suit. It saves buying all of the stock length material and it will be over kill in terms of strength (it will probably weigh more than the steel original as well). Very very generally speaking when you replace a steel component with an aluminium one (in an application like this or a push bike frame for example) you may be able to get an increase in stiffness but no significant reduction in weight, the increase in stiffness comes from the ability to use larger section sizes and still have enough wall thickness to allow successful welding (and prevent localised buckling)
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Like, I'm guessing, that using oval tube may have been a slightly better choice?
 
Boxed slabbed sided with half again larger OD cross brace, like RGM sells or gruder triangualted like the mono shock swing arms.
 
Wow, I am going to move the swingarm to a new thread by itself. That should explode this forum. :twisted:

Seriously, I know it might not work, but it's worth a shot. I don't have any fancy CAD software, well that's not true I have it, I just don't know how to use it.

I'll do some real world testing of it when I get it installed. I'm not planning any trips to Bonneville.

I can always throw the steel one back on, or build version 2.0.

I did copy the latest and best version, so that should be worth something.

We'll see.

I did decide to ditch the stock instruments and install my acewell gauge. And I ordered a Moto-gadget M-Unit today.

So I will have simple trouble free feature packed wiring That solves a few issues I created.
 
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