I've lined up a guy to weld a small bit onto a bike frame right at the 1/4 inch plate where the rear wheel attaches to the frame tubing. (This plate is called the "dropout".)
Once welded, does this weaken the frame at this point?
If the answer is "yes", what are the common practices, if any, to restore strength to the 6061?
Is welding a bike at this location without permanent damage possible? Recommended?
Secondly, when prepping the weld area, any grinding wheels or stainless wire wheels the welder uses should be either new or if used, only used on aluminum previously, yes?
I'm not experienced enough (even after reading that great web page!) to make the decision whether or not it's recommended to have this weld done or to instead look into bolting the piece to the frame rather than welding it.
This is the location and a template of the part:
The aluminum "hump" on the frame is not important and can probably be leveled and the fabricated part made without a notch. (Note: holes are 7/32, not 7/16 as shown.)
Note the proximity of other welds in the area where the tube meets the plate aluminum.
Opinions & suggestions about whether this is recommended (as well as how best to minimize any risk) or whether it's too risky are welcome.
In article , snipped-for-privacy@invalid.net says...
In short, Yes- the 6061-T6 is much weaker in the as-welded condition. Typically, you'll lose about half the strength of the base material.
Also, Yes- You need to use either new stainless steel brushes or brushes that have only been used on Al, because Al is very susceptible to impurities.
Here is an AWS article that may help your understanding- I hope I'm not violating a copyright by posting it.
ALUMINUM Q&A
BY TONY ANDERSON Q: I have been experiencing problems when attempting to qualify my welding procedure specification in accordance with AWS D1.2, Structural Welding Code ? Aluminum. I have been trying to qualify a groove weld procedure with 1/2 -in. 6061-T6 base metal, using the gas metal arc welding (GMAW) process. The problem is that I am not able to obtain the minimum tensile strength as required by the welding code. The welded test samples underwent radiographic testing before destructive testing and there was no sign of any significant discontinuities in the weld. My guided bend tests taken from the same welded test samples are passing the bending requirements and appear to be free of any significant weld discontinuities. The transverse tension test specimens are failing in the heat-affected zone providing a calculated tensile strength lower than that required by the AWS specification. How is it possible for a perfectly sound weld with no significant welding discontinuities to not meet the strength requirements of the code?
A: Unfortunately, I receive variations of this type of question frequently. They always concern a heat treatable base alloy, usually one of the 6xxx series base metals, weld of otherwise good integrity, unable to meet the minimum tensile strength requirements of the code.
The most common reason for a weld made in this type of base metal, which is free from major discontinuities, not to meet the minimum tensile requirement, is overheating of the base metal during the welding process. To understand why this problem can occur, we must first understand the characteristics of the heat treatable aluminum alloys and, in this case, the 6xxx series base metals. This series of aluminum alloys is one of the heat treatable series, which acquire their strength through a process of thermal treatments. They are often used in the -T6 condition, which indicates that they have been solution heat treated and artificially aged. The -T6 condition is achieved by heating the base metal to a temperature of around 990°F. This step in the operation is necessary in order to dissolve the major alloying elements into solution. Quenching, usually in water, follows the heating process in order to trap the alloying elements and produce a supersaturated solution. In the case of the 6xxx series alloys, the major alloying elements are magnesium and silicon, which combine during the thermal treatment to form the compound magnesium silicide. After solution heat treatment, the metal is reheated to a lower temperature (around 320°F) and held at temperature for a predetermined time. This second thermal treatment ? termed artificial aging ? is conducted in order to precipitate a portion of the elements or compounds back out of the supersaturated solution to enhance the mechanical properties of the metal.
When we consider the controlled heat treatment that has been conducted on these alloys prior to welding, in order to obtain the -T6 condition, we can appreciate their response to the arc welding process, which heats the material to the same temperatures used for heat treatment in an uncontrolled manner. The 6061-T6 base metals, as purchased, have a typical tensile strength of 45 ksi before welding. The AWS D1.2 Structural Code recognizes the metallurgical changes that occur to this base metal from the exposure to heat during arc welding, and consequently, requires a minimum tensile strength of 24 ksi. The minimum tensile strength specified by the code is based on historical testing using a variety of welding procedures. If we consider the fully annealed typical tensile strength of 6061 as being around 18 ksi, we can appreciate the importance of controlling the overall heat input during the arc welding process. There is a direct association between the total welding heat input and mechanical properties of the base metal adjacent to the weld (the heat-affected zone) after welding. The higher the total heat input, the lower the tensile strength will fall. Figure 1 provides us with an appreciation of the differences in strengths between the as- welded and postweld heat-treated condition of some of the heat treatable aluminum alloys. Figure 2 provides a relationship between heat input in joules per centimeter and hardness profiles, which relate to tensile strength. We are able to see quite clearly in Fig. 2 that the higher the heat input, the more substantial the reduction in strength of the base metal adjacent to the weld.
(Pictures of graphs here)
Fig. 1 ? There can be significant differences in the as-welded and postweld heat treated strength of the heat treatable aluminum alloys. Fig. 2 ? The higher the heat input during the welding operation, the more pronounced the reduction in strength in the heat-affected zone.
In order to meet the minimum tensile strength requirements of the code, we need to closely control our welding procedure to prevent overheating of the base metal. First, we must consider the size of the test samples for welding. The code provides minimum dimensions for groove weld test plate size. You must comply with this requirement; in fact, if practical, use a larger test sample than specified. This will provide a superior heat sink and lower the possibility of excessive overheating and prolonged time at temperature within the heat-affected zone. Secondly, comply with the preheating and interpass temperature requirements of the code, which for this type of metal specifies 250°F as the maximum preheat and interpass temperature. Also, observe the holding time at temperature requirement, which is not to exceed 15 minutes. If possible, conduct the certification testing without preheating, or at lower preheating temperatures, and allow the base metal to cool to well below the maximum interpass temperature before welding resumes.
A major contributor to the overall heat input of a weld is the travel speed during the welding process. For this reason, it is preferable to select a welding sequence and technique that makes use of faster stringer-type weld beads as opposed to slower weaving techniques. The above recommendations apply to welding the 6061-T6 base metals with either a 4xxx series or a 5xxx series filler metal, and regardless of shielding gas type or mixture used.
-------- TONY ANDERSON is Director of Technical Training for ESAB North America. He is a Senior Member of the TWI and a Registered Chartered Engineer. He is Chairman of the Aluminum Association Technical Advisory Committee for Welding and Joining and holds numerous positions including Chairman, Vice Chairman, and Member of various AWS technical committees. Questions may be sent to Mr. Anderson c/o Welding Journal, 550 NW LeJeune Rd., Miami, FL 33126 or via e-mail at snipped-for-privacy@esab.com.
No, copyright doesn't work that way. You can read/download anything that's publicly accessible, but you can't republish it on your own website or via a Usenet posting.
I am an AWS member, and I auto-logon to their site. I wasn't sure posting a link to the page would allow access to someone without a username/password.
I was hoping that by stating it was an AWS article and keeping all of the original article's authorship info in my posting that I would not violate a copyright. I know plagiarism is bad... but I don't know the law as it relates to posting information on Usenet.
Disregarding the above very good information I would suggest that you look into how your frame was manufactured as obviously the drop-outs were welded to the tubes and it seems possible that after this welding was accomplished that the entire frame was not re-heatreated. If this is the case then welding an additional bracket onto the already welded drop-out should not significantly decrease strength.
Another point that might be looked into is whether there is a need for T-6 strength in the drop-outs. A steel frame frequently uses expensive double butted chrome-moly tubes brazed onto mild steel lugs and drop-outs.
Re. post-weld treating, GT is not very helpful in this regard (in their defense, the parent company is not the original and such knowledge usually goes with the founding GT employees). This model was a long time ago (mid
90's).
Re. the plate metal not needing to be as strong as the tubes, I also thought this to be so. But welding the brake adapter to the dropout plate will heat at least one seat tube (it's just a half inch away, at the closest), possibly overheating it.
I'm thinking that the simplest solution may be to just bolt a machined 6061 adapter to the dropout. This will be a bit heavier, as it'll have to have a heavy flange for support and attachment.
Heavier? I am assuming this IS NOT a skinny wheel road bike or you wouldn't be adding all this junk. With big heavy shocks on the front end and (I assume) a great disk on the rear, you are worrying about weight ;-?
Another thought - it is possible to determine approximate strengths of heat treated aluminum by hardness testing. See the URL below for additional details (note that is all one long URL)
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You might be able to determine, very closely, what you have by hardness testing.
Another thought - Sail boats often use 6061-T6 for spars and I doubt that a 50 ft. mast is re-heat treated after welding.
A final thought - Why go it alone? All of the bike magazines have question and answer columns. Why not write and see whether they have any idea about the feasibility of welding on a T6 frame? After all; guys here are into welding. Guys at the bike magazine are into bicycles...
Are you sure your bike is 6061? Most aluminum bikes are made from 7005 aluminum. \It has identical tensile strength to 6016-T6, but it's strength is derived from it's chemistry, not from heat treat, so you can weld it all you like and lose no strength.
7005 was created to get around the necessity of re-heat-treating a bike frame after welding.
BTW if you weld 6061-T6, immediately post-weld the aluminum will have dropped to a T1 or T2 hardness. However, over the next few weeks the hardness will creep back up to about a T5. This is called Age hardening or Precipitation hardening and is the normal mechanism of hardening aluminum. Unfortunately to get back to a T6 condition you would have to have the frame re-heat-treated by a professional shop.
There is mention of aging of the tubes 4 - 5 days after welding..
In addition they list quite a number of frame builders. You might try e-mailing some of those guys asking whether they heat-treat after welding (I have heard that TREK does).
In most cases the people doing professional fab work will have a process they follow to meet code requirements. In this case, they probably have some type of clamp-on resistance heater they put around the weld, crank up the temp, hold it for a set time, quench it, crank up the temp again (lower this time), hold it for another set time, then shut off the heaters, allowing it to cool to ambient and reach its final temper.
In the case of the spar, they are probably happy with a T4 temper due to its greater flexibility. T6 is much stonger, but also more brittle.
Lincoln Electric has a nice, free, no-registration-needed web-page:
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Go to the section titled, "Heat Treatable Alloys."
Of course the copyright holder can grant additional rights. I'm talking about what you can do with published material to which you don't have additional rights.
I can't see any problem with posting a URL where the owner has already put the material. After all, if they've got it on a website, don't they _want_ people to see it?
But downloading the stuff, and claiming it as your own is a clear violation, of course.
There's also this thing called "fair use", but I think that's intended for quoting stuff in, like, technical journals, for putting together some kind of term paper or so.
("Isaac Asimov said, 'They've broken the First Law! They've broken the First Law!' Clarke replied, 'Well, Isaac, strike them down with a bolt of lightning!'")
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