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Corrosion at Aluminum/Steel Junction
I need to build a dozen outdoor canopies for an office building.
I want to use structural aluminum channel, bolted with steel bolts. Where might expect corrosion to arise over the years, and would it be mainly in the aluminum or in the steel bolts? Thanks for any help. Please post here or email me at grayscale[AT]verizon.net Ralph |
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Corrosion at Aluminum/Steel Junction
Front Office wrote: I need to build a dozen outdoor canopies for an office building. I want to use structural aluminum channel, bolted with steel bolts. Where might expect corrosion to arise over the years, and would it be mainly in the aluminum or in the steel bolts? Thanks for any help. Please post here or email me at grayscale[AT]verizon.net Ralph I would think stainless steel bolts or some form of fiber or plastic (lucite) washer would provide the rigidity and separation. Not that that view is universal: http://www.eng-tips.com/viewthread.c...=154321&page=1 mattmlm (Structural) 9 May 06 10:21 I've got a project where Aluminum columns (and base plates) are being anchored to a concrete pier/footing. The contractor used your everyday common steel threaded anchor rods. In less than two weeks they are completely rusted over. The contract documents called for hot-dipped galvanized anchor bolts. (before judging, we did not provide the design or specifications, simply consulting on a separate portion of the larger project) I'm thinking of having the contractor cut off and drill-in epoxy grout anchors. Will the galvanized anchor bolts react to the aluminum? Should I use aluminum anchor bolts? If alum, what affect would the anchors have in steel reinforced concrete? Thank you, MLM Start your own Eng-Tips Group! Click Here! Goahead (Aerospace) 9 May 06 11:10 Galvanized steel anchor bolts should be OK with aluminum. As an extra precaution the contact areas could be painted with insulating paint. http://www.welding-advisers.com/ TVP (Materials) 9 May 06 11:30 Al bolts are unlikely to be strong enough if they were not specifically incorporated into the design. Zinc is the most compatible coating for steel bolts that is also relatively cost effective. Heckler (Mechanical) 9 May 06 12:09 Aluminum and Zinc are really close together on my Galvanic Corrosion Potential Chart. mattmlm (Structural) 9 May 06 12:24 Is that good thing or a bad thing? MLM theonlynamenottaken (Structural) 9 May 06 13:17 Its a good thing... the farther apart two metals are on the galvanic series the greater potential between them, hence more aggressive attack. Aluminum embedded in and in direct contact with concrete is not acceptable. A chemical reaction occurs and the concrete literally self destructs from the expansion (product of the reaction, just like rust on carbon steel that is allowed to corrode in concrete). I don't know about epoxy grouted aluminum in concrete but I've seen slabs with aluminum cast into it break themselves apart. UcfSE (Structural) 9 May 06 13:23 I have a question to go along with this. I have noticed in the past with aluminum panels that the manufacturer of the panels has recommended stainless steel screws with some kind of special washer between the steel and the aluminum. Does that line of thinking work also in this case, say with using stainless steel anchor bolts or epoxy bolts with an aluminum base plate? mattmlm (Structural) 9 May 06 13:40 How good is stainless in direct contact with Aluminum? When this issue first came up, the only thing that I thought of was stainless. Then came the comments about the specs calling for hot-dipped galvanized. I've always assumed that stainless was preferred, if not required. Is that assumption correct? MLM Also, thanks for the input. Heckler (Mechanical) 9 May 06 14:35 ASTM A-153 or ISO 1461 covers hot-dip galvanizing. I think it's more of a cost factor when considering Stainless verses galvanized steel. Goahead (Aerospace) 10 May 06 12:04 Stainless should not be in contact with aluminum. Stainless fasteners should be Cadmium or Zinc plated before being inserted in aluminum bodies. Usual anodizing or conversion coating are not protective enough at the contact place. http://www.welding-advisers.com/ IFRs (Petroleum) 26 May 06 16:21 In my experience (27 years in the petrochemical industry), aluminum and stainless fasteners are acceptable in most environments. Althought they are far apart on the galvanic scale, the typically much larger area of the aluminum part compared to the fastener reduces to nearly nil the tendency of the aluminum to corrode. However, in this case, I'd definitly use galvanized anchors - they were specified, are compatible, are probably more available not to mention less costly. Note that the environment is a critical issue - If this is on the seashore, or exposed to wet atmosphere, or under water, or vibrating from machinery, etc then corrosion needs to be re-evaluated. |
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Corrosion at Aluminum/Steel Junction
"Front Office" wrote in message . .. I need to build a dozen outdoor canopies for an office building. I want to use structural aluminum channel, bolted with steel bolts. Where might expect corrosion to arise over the years, and would it be mainly in the aluminum or in the steel bolts? Thanks for any help. Please post here or email me at grayscale[AT]verizon.net Ralph Ralph, I'm 'going through' my 11 year old aluminum boat trailer right now which was bolted together with galvanized bolts. I don't see the aluminum pitting I would have expected around the bolt holes. I do have a few rusty bolts which are easily replaced. I recommend you use this method. If you go with S/S bolts you WILL have pitting around the aluminum holes (as the least noble metal gets the damage) and it will not be easily repaired in the future. Larry My turbine powered boat project; http://www.turbinefun.com |
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Corrosion at Aluminum/Steel Junction
"Front Office" wrote in message . .. Where might expect corrosion to arise over the years, and would it be mainly in the aluminum or in the steel bolts? I suggest you take this question to rec.crafts.metalworking. Vaughn |
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Corrosion at Aluminum/Steel Junction
Front Office wrote:
I need to build a dozen outdoor canopies for an office building. I want to use structural aluminum channel, bolted with steel bolts. Where might expect corrosion to arise over the years, and would it be mainly in the aluminum or in the steel bolts? Thanks for any help. Please post here or email me at grayscale[AT]verizon.net Ralph In a marine environment, the aluminum will go more quickly. The ADAMS-class DDG and the FFs made during the 1960s had aluminum---or should I say, al-loo-min-ee-um?-- bolted to a steel plate with a special sort of bolt called a Huck bolt. They all experienced corrosion of the aluminum. (black electrical tape separated the two metals.) The TICONDROGA and SPRUANCE class ships had aluminum superstructures which were welded to a "fusion bar" which consisted of a piece of very clean and smoothly-machined piece of aluminum FLAT BAR joined to a very clean piece and smoothly machined piece of steel flat bar via explosive charges. M.S. |
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Corrosion at Aluminum/Steel Junction
On Mon, 19 Jun 2006 18:34:46 +0000, Front Office
wrote: I need to build a dozen outdoor canopies for an office building. I want to use structural aluminum channel, bolted with steel bolts. Where might expect corrosion to arise over the years, and would it be mainly in the aluminum or in the steel bolts? Thanks for any help. Please post here or email me at grayscale[AT]verizon.net Ralph a product called Duralac is designed to prevent the electrolytic corrosion between dissimilar metals. it is an aviation product made in england. comes in a white and yellow tube. it is a toothpaste consistency yellow fluid containing zinc chromate. it dries slowly to a rubber consistency. the stuff is used for pop rivets with great benefit in corrosion control. you just dip them in it prior to setting the pop in a wing skin. it is good stuff. two tubes in my aviation tool box. Stealth Pilot |
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Corrosion at Aluminum/Steel Junction
On Tue, 20 Jun 2006 22:05:55 +0800, Stealth Pilot
wrote: a product called Duralac is designed to prevent the electrolytic corrosion between dissimilar metals. it is an aviation product made in england. comes in a white and yellow tube. it is a toothpaste consistency yellow fluid containing zinc chromate. it dries slowly to a rubber consistency. Minor point, it only contains Barium Chromate and White Spirit. You can also buy bigger tins of it, It's used in a lot of marine applications as well as aviation. -- |
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Corrosion at Aluminum/Steel Junction
On Wed, 21 Jun 2006 00:41:07 +0100, Martin Evans
wrote: On Tue, 20 Jun 2006 22:05:55 +0800, Stealth Pilot wrote: a product called Duralac is designed to prevent the electrolytic corrosion between dissimilar metals. it is an aviation product made in england. comes in a white and yellow tube. it is a toothpaste consistency yellow fluid containing zinc chromate. it dries slowly to a rubber consistency. Minor point, it only contains Barium Chromate and White Spirit. You can also buy bigger tins of it, It's used in a lot of marine applications as well as aviation. had to drag out my tube. that's true. Stealth Pilot |
#9
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Corrosion at Aluminum/Steel Junction
Stealth Pilot wrote: On Wed, 21 Jun 2006 00:41:07 +0100, Martin Evans wrote: On Tue, 20 Jun 2006 22:05:55 +0800, Stealth Pilot wrote: a product called Duralac is designed to prevent the electrolytic corrosion between dissimilar metals. it is an aviation product made in england. comes in a white and yellow tube. it is a toothpaste consistency yellow fluid containing zinc chromate. it dries slowly to a rubber consistency. Minor point, it only contains Barium Chromate and White Spirit. You can also buy bigger tins of it, It's used in a lot of marine applications as well as aviation. had to drag out my tube. that's true. Stealth Pilot Hard to get zinc chromate in the average consumer product anymore. It's been linked to cancer. Zinc *oxide* is often seen in those green aerosol primers now. I can still get Endura epoxy zinc chromate, clearly labelled "for industrial use only." Dan |
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