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Okay so um, here are again a number of aluminum alloys with their compositions. It doesn't go to the 1100s because they're basically nearly pure aluminum. So they have these aluminum copper alloys in the 2000 series which are fairly highly alloyed. This is, I don't remember, this is like five percent or so out here at the eutectic. So these are way out towards the eutectic, on the, in most cases, or if they have smaller amounts they have larger amounts of something else, in this case manganese or magnesium or whatever.

Then you get to the, they've got some of the 6000 series. These must be the heat treatable, heat, these must be the heat treatable aluminum alloys. 6061 is the workhorse, and it says structural alloy, automotive, railway, marine applications, pipe and pipe fittings, good formability, weldability, corrosion resistance and strength. And I told you that's probably the most commonly used aluminum alloy. Available as extrusions, sheet, plate. Go to a supply center, it has everything. We have the 7075, high strength aircraft and other applications. But we really don't weld the 7000 series much most of the time, and I'll show you that in a little bit.

They like to rank, the aluminum companies rank the aluminum alloys in terms of their weldability. So this is sort of an aluminum association table. Most aluminum association tables came out of either Alcoa or Alcan, developed them. And here's your 2000 series. And A is good welding, actually show it to you down here. A is readily weldable, B is weldable in most applications, may require special technique or preliminary trials, which means it's not that weldable folks. And C is limited weldability, which don't bother, okay. Um, I wouldn't say you couldn't do it but you're gonna have to have all kinds of problems.

So if you look at the 2000 series, the best any of them do, except 2219 or 2218 or something, anyway, is like arc welding with an A, but everything else is B and C. If you go here at 6061, whether you're talking about oxy-acetylene or arc with flux or arc with inert gas, it's good for everything. It's got a B for pressure welding and B for soldering. But aluminum is extremely difficult to solder, okay. That's a rule we could, I'd probably go through that on the, I'd probably go through that on the soldering part of the course that you get a watch by video. But anyway, that's why 6061 you won't find. Here's 6101 which is A's everywhere but, and here's a 60, 101 as something, remember, is fairly lightly alloyed. 6951. But 6061 is good strength and readily weldable.

Now, let's talk a little bit about design of aluminum. And one of the problems you have is, this happens to be an example of the strength variation. Let's close these things a little bit. The strength variation both within a lot and among many lots. So this high peak here is, was it say, 180 specimens from a single sheet of aluminum. Let me turn that off. Stopped it. So this is a bunch of specimens taken from one sheet. Has a fairly narrow distribution of heat treated properties. This is for 4300 samples from many sheets just coming out of the mill, and a wider distribution of properties. And it has a little A line here and a little B line here. This is in strength in megapascals. This is yield strength, and now this is 7075. So this is getting up towards 70 or 75 ksi yield strength. Not necessarily readily weldable.

But what does it mean, A and B? Anybody know what A and B in aluminum is? It has to do with the, how tight your mechanical properties are going to be. And I will now tell you a secret. If you like to have scientific data or engineering data on your computer, there's nothing cheaper than buying technical literature from the U.S. government. Because they have to sell it at cost, and if you download it the cost is zero, okay. So Mil Handbook, what used to be Mil Handbook Five for about forty years, is a, like fifteen volume set of these things of the mechanical properties to be used for design of aircraft, okay.

So if I want to know about aluminum, this is one of the places to go. In fact, if you read about the introduction of this, the scope of the handbook, and it says, it used to be Mil Handbook Five, it's now called Metallic Materials Properties Development and Standardization, MMPDS-05, okay, but it used to be Mil Handbook Five. Was prepared by Patel [Battelle] Memorial Institute under contract to the FAA, Federal Aviation Administration. And somewhere in here it basically says that if you're going to build an aircraft for the defense, for any part of the U.S. government, FAA, Defense Department, anybody else, you must use this handbook for your mechanical properties of your material.

And I'll show you a little bit where you design it. You can get the fifteen volume set in hard copy like this for a hundred and five dollars. You can download it for free, just go to the internet and look up MMPDS-05 and download it, and so you can have all fifteen volumes. Now I told you how important steel is. Here's, chapter two is steels, okay. This is not too old, this is April 2010. Chapters, chapter three comes in volume A, which is aluminum alloys 2000 and thousand series, and volume B which is six thousand and seven thousand series. Compare the thickness of steel versus the thickness of aluminum, okay. Here's one case where there's a lot more data on aluminum than zero on steel. Why? Because this is aircraft. We don't build less steel aircraft, we do build some frames and there's landing gears and other things that go in here.

But there's a lot of good technical information in here, particularly if you're trying to go to sleep at night. For example, if I want to look up, I mean there are tables after tables of, you know, stress intensity factors and fatigue curves and things like that. And this is what you have to design things to. If I look at one of the tables in here, it will tell me that here's my A and B. By the way this is 7075 aluminum alloy extrusions. There's going to be a different table for aluminum alloy plate and there's going to be a different one for aluminum alloy sheet, okay. So they, you have slightly different properties depending on the form of the material. Here the mechanical properties: ultimate tensile strength, longitudinal, transverse direction of the extrusion, okay. So there's tensile strength and yield strength. I have A values and B values. B, strength, I have A values and B values. A are, if you're just building some commercial airliner or some military jet. A are very tight values such as you're building a spacecraft, okay.

And so if I went back to the thing I put up before and said what's the difference between A and B values, well, this particular book told you, I'm sorry, B has to be tighter spec than A. So yeah, okay, that's right. B has got a tighter spec than A, because there's a lot more testing that goes on. You verify each sheet, not each alloy, okay. And you're going to have traceability if you're going into a spacecraft or something like that, and so B has tighter tolerances than A. Um, see if that's true. B is going to give you, uh, and, a strength level that you can consider your minimum, whereas you'll have a wider range for A. So A is going into common aircraft, uh, aerospace applications. B is going into very critical applications.

They also give you the properties as a function of thickness of the material, okay. And you can see it doesn't change a lot. But if you're trying to be really weight critical, particularly on spacecraft or something, another one ksi, you know, one or two percent could make a difference, okay. They're really designing these things fairly tightly. But, so that's the design standard for aircraft and has a lot of material on aluminum.

If I'm just building some sewage treatment plant out of aluminum, I'm going to use the structural welding code for aluminum which is AWS D1.1, steel code is, I mean the steel code is D1.1 and the structural aluminum code is D1.2. And I think I showed you the stainless steel code yesterday, I had with me. I don't think I still have it with me but it's 1.6. And there's structural welding codes for rotating machinery, there's structural welding codes for large cast steel castings. There's about twenty different structural welding codes. There's structural welding codes for reinforcing bar for concrete. There's structural welding codes I think for cast iron now. But anyway, they make money by coming up with more codes, as far as that goes.

If, but if I look in here, structural welding codes will give me design values. All the codes, structural welding codes will have, either chapter one or, either chapter two or three depending on the code. So it says number one is always general requirements of the code, design of welded connections, and it will give you in qualification of the welders, and then you go on to other things like inspection and welding and stuff. But design of welded connections, well, there's only three pages on design of welding connections. Why is that?

So if we go to that, it should show me, um, here's the scope of design of welded connections and it's going to tell me somewhere in here to go to, I'm not seeing it right now. Basically, without, I'm not finding it right now, but it's going to tell me to go to the aluminum design manual which is a little thicker than three pages, okay. This is going to tell me for aluminum, it's called out by the structural welding code. Maybe it was on, maybe it's on the introduction chapter one. Anyway it does call it out. Um, oh here it is, in chapter two it says, well shall be sized for strength requirement using the effective areas defined in section 2 and conform with the aluminum design manual and specifications for aluminum structures unless otherwise cut. So they shorten this code by calling out a standard written by the aluminum association. So this is Alcan, Alcoa, Pechiney [Pechinet], Kaiser, Reynolds, all getting together in collusion to tell you how to weld aluminum.

And like we could go through here, but they're going to give you, in fatigue, guess what you're going to see something very similar to these types of tables we saw in the steel welding code, where you have A, B, C, D, E, and F types of joints, and you're going to have these pictures of different bars and what the fatigue strength is, uh, in different conditions, welded conditions. Almost identical but not exactly identical, because you use slightly different connections in aluminum than you do in steel in many cases. It will give you all kinds of, well, other design criteria.

Um, the big thing in the steel business now is what they call allowable stress design, okay. Which is a different philosophy. The old time they just said this is your safety factor. Now after the Northridge earthquake in night [nineteen] early 90s, like '91 or '92, in Los Angeles, the steel construction folks went back and said let's get the design out of the 1920s and bring it into the 1980s. And they did, and it's called the allowable stress design. And so you probably didn't catch it because I didn't emphasize it, but I brought in the aluminum steel, the steel construction manual. I said this used to be the bible, okay. It was, before the allowable stress design bible came out in the late 90s. And that was really as a result of a lot of the problems they had with buildings in the Northridge earthquake in Los Angeles.

So the steel guys got together and said, we need to do a more modern design, that's not as weak in some areas and too strong in other areas. And now it's the allowable stress design, and I have no idea what they're talking about when I go look at it. You have to be trained as a civil engineer. But they got sections on material properties, they'll have sections on weld properties. You'd be surprised, in aluminum, in steel you usually can say the fatigue life or the allowable stress and steel might be one-third. In fact it is, it's um, I take that back. For the base metal the allowable stress for design is typically uh 0.6 of the ultimate tensile strength. Is that right? No, 0.6 of the yield strength. And the weld is 0.3, so they upped the safety factor for the weld by a factor of two, okay.

So if I've got a, no, the 0.3 is on ultimate tensile strength. So if I got a 60 ksi weld metal in steel, I can design it to 20 ksi. It's a factor of three or 3.3 or something. If I look at the code for the base metal, it's half of that. I can actually have the base metal stressed to 35 ksi or something like that. In any case, in aluminum I might have 25 ksi but as a yield, not an ultimate. And I may only be allowed seven ksi as my design strength. Because aluminum is less forgiving. Why is aluminum less forgiving? It's not as tough as steel. If I went back to that plot I showed you in the very beginning, A, steel is the toughest material, has the greatest combination of strength and toughness and cost of any material. And that's why we use one and a half billion tons. Well, aluminum we use 45 million tons a year. But aluminum doesn't have the same type of toughness. So aluminum is not as tolerant of large defects. I told you the critical flaw size for ripping a sheet of paper, if it was in a steel, an HY-100 steel, it'd be two feet in most cases. But in aluminum it might be two inches, okay.

The toughest aluminum alloy, and it's ten times tougher than any other aluminum alloy, is one that was developed in the mid twenties. And they use it for propellers, aluminum propellers. Will bend 180 degrees before they'll break, okay. But we don't use that for aluminum structures because we need more strength. Aluminum, if you actually look at it, it's actually 2025 alloy. If you look in here for 2025 alloy there's all kinds of data on 2025 alloy in the old Mil Handbook for aluminum alloys. I could look up 2025. Its toughness is five to ten times greater than 2024, but its strength is probably about two-thirds as much. But it can bend like steel. But it's the only aluminum alloy that comes anywhere close to that. Because we're usually trying to push the aluminums, just like baseball bats, to higher and higher strength, which means more, most, more and more corrosion problems, of stress corrosion cracking and other things. Because we're using aluminum because we need the performance of the lightweight for whatever reason for our structure.

And now the Navy has changed in the last ten to fifteen years where you'd like to emphasize, well, you still build ships out of steel but you sort of learned to do that over the years. But now you, uh, are building your newer ships, the littoral ships, out of aluminum, because you have to have speed capability. In fact, when I first went to a littoral, first time I ever heard the word littoral was probably, I don't know, late 90s, early 2000s. I went to a conference down this mountain resort in Virginia, and snowing as January as I remember. Um, and they, they're, I walked in a little late and they were talking about the littoral battlefield. I had to ask someone at the break, what's the littoral? I thought that was a latrine. No, uh, they explained that it's close in, uh, near the coast. Um, and they were talking at the time of, um, fifty knots minimum or something on the ships. Is that still kind of what they're trying to do on these?

Yeah, I'm sure they had to drop it because whatever they were saying at that time, I thought, I mean the only way you're going to do it was with hydrofoils, okay. And you can't put everything on a hydrofoil. You can't afford that much fuel, okay. Even the Navy can't, even the government can't afford that much fuel.

Anyway, one of the things about aluminum alloys which I've already alluded to is you have to avoid mixing the alloys with the wrong thing. This comes out of the welding handbook but it's on any book on welding aluminum. And there's lots of notes on this table, this goes for two pages in the welding handbook. But what it is, a table of how to select a welding filler metal, okay. Um, if I'm going to weld, uh, was this 1060 aluminum which is 99.4 aluminum, to a casting of aluminum 201 which is aluminum copper casting, I've got to use 4145. ER just means electrode, okay. If I'm going to weld it to 356 a very common, or 357, two very common aluminum castings used on motorcycles, all kinds of things, you're going to use a 4043 filler metal. That's the workhorse filler metal. If I'm going to use 6061 and weld it to 5083, something the Navy might do, a lot of other people too, but they're going to use a 5356 filler metal. If you're going to weld 6061 to itself, use a 4043.

If you try to use some of these other welding electrodes and you don't follow this table you're going to get cracking. Because you're going to be, you're liable to be not in this range or this range where you want to be lightly alloyed when you mix the weld metal with the base metal, or highly alloyed. You'll be in the wide freezing range and you're going to have cracking. So when people come to me, when I told you, when people come to me and say I want to weld a piece of steel, I say give me the composition, give me the thickness, and I need to know hardness and hardenability of that steel. On aluminum I need to know composition so that I can pick a proper filler metal, okay. And I need to know composition on both sides if it's dissimilar alloys.

And anyway, so if you're doing 5083 to 5083, you should use a 5183 filler metal. You're not going to buy 5183 plate. 5183 is an electrode, okay. Alloy designed for 5083. And so they change it, make it 5183. It's not like steels where it tells you the carbon content and things. These are just thousand series alloys, and you have some new alloy and you apply to the aluminum association and get it. And I'll give you a little case study on how to select aluminum alloys in a little bit. Anybody have any questions? I want to talk about design of aluminum welds first.

So if I was welding steel, this actually happens to be an example of welding two plates of different thickness, and they show how you would taper one down in aluminum. Because you can't, steel has more toughness which means it can tolerate sharp corners a lot more than aluminum. It has lots of ductility. Aluminum doesn't have as much ductility, okay. The director of research at U.S. Steel, admittedly not the most unbiased person when it comes to aluminum, this is John Groves who helped develop HY-80s back in the 50s and 60s, when I was a young engineer I heard him say he called aluminum the near-metal, okay. Steel was the metal and aluminum was nearly a metal. Might have a little ductility but it wasn't quite, he wasn't anything close to steel, according to John. Which there's some truth to that, but it's also a little bit unfair.

Um, because you might be welding heat-treatable alloys but in some cases when you have the, even in the non-heat-treatable alloys when you have the luxury, you don't necessarily just weld a groove weld between two plates. You might put two cover plates on and put fillet welds on. Why? It's easier to make fillet welds than it is to make groove welds. It takes more skill for the welder.

Student: Tom, were you the one saying you had to have qualified aluminum welders, did you mention that?

Okay, it's harder to find qualified aluminum welders. I was doing something for MIT Lincoln Lab. They wanted to, the Air Force wanted to take the old MIT Millstone radon, not a radio, well it is a radon, but MIT has this little peak out here in Millis, Massachusetts. I can't remember where the town is, just north of Boston here. And they had built this radar antenna back in the 50s, and it was for research purposes for the MIT physics department. And that type of physics went away or got exhausted or whatever. So they had this big steel bearing that could hold this thing, and they were trying to find some application for it.

They decided they would sell the Air Force on a three, I think is a 300 gigahertz radar system, okay. And they were gonna officially, what they told me, they were gonna look for space junk. I mean there's tens of thousands of things orbiting the earth, a lot of it's just little shreds of things that, you know, when something blew up there or whatever. And it's floating around. And if you're on a manned spacecraft or the International Space Shuttle [Station], Space Station, and you run into one of these things you could be running into it at 17,000 miles an hour I guess in some cases, and something the size of a pea could go right through, you know, a one inch thick piece of aluminum like a laser beam, okay. So there are hazards to this, plus they'd like to know if some of that space junk is not really junk but might have antennas on it or things like that.

And so if they had higher frequencies they could get better imaging from earth. And so they wanted to build on top of the steel pedestal and bearing that was probably worth a hundred million dollars if you had to build it today, had been built for physics research back in the 50s or whatever, they wanted to put this big aluminum structure, which was basically just a big radar dish. Only at 300 gigahertz you start thinking of the wavelength of the frequency, and you're down to one or two millimeters or something as the wavelength of this 300 gigahertz. You know, most of your, what's the frequency of most of your radar is ten or twenty gigahertz. I mean this is way up there in frequency compared to what you might be using with a phased array radar on a ship or something. Not that I'm an expert on radar frequencies. But anyway, this was a much higher frequency and therefore required a dish that was much more precise.

This had to be sort of a spherical or nearly spherical piece of aluminum sheet metal, and it was about, if I remember correctly, about 150 feet across. And the tolerance was like an eighth of an inch end to end. Well, you can't even, first of all it's inside a radome and so the sun doesn't shine on it to get thermal expansion problems. But you now got to start worrying about the temperature that this thing's at, because it can distort. And it had all kinds of active things they do, things for, uh, microscopes and optical telescopes now that will change the shape of things actively, active shape change. They do this on aircraft, military aircraft. They change the shape of the wings in real time. About ten times a second some computer's changing the shape of the wing, because of instabilities and stuff.

So they wanted to build this thing, and so they went out for bid and no one would bid on it, okay. Because you had to do, like, you had to build structures that would be across the size of this room and you had to have a tolerance, without doing any active, be a half an inch side to side. So you're going to build a truss structure from here to there, welded, and you're going to have that thing meet in x, y, z coordinates within a half an inch, plus minus half an inch, or actually plus or minus a quarter of an inch I think it was, a half an inch total in all three dimensions. So if you're fixed over here, you know, fifty feet away, that's not fifty feet but it was like fifty feet away. It was just a tremendous tolerance.

And no one was willing to bid on it. So they called in a team of us to figure out what to do. And they did find a company. It was a guy who used to work Electric Boat and started a very fancy welding company. He was doing a lot of Electric Boat work. In fact when we went through they were redoing some of the boomers. Have been turned into uh, yeah so they don't have nuclear anymore. They basically take the tubes and they put a bunch of non-nuclear warheads in there or something, okay. So SSGNs or something. They were doing the retrofits for some of these boomers to take, this was all part of SALT I guess, you know, getting, cutting down on the number of nuclear warheads. And, but they were putting like 19 of these tubes inside of one of the big old uh, Poseidon, right? Was Tried Mission Tridents, Trident tubes.

So they were building the inserts for this, and there was a lot of precision to that. We went to this place, it was really pretty incredible welding shop, one of the best ones I've ever seen. And they finally took the contract and they successfully built it. They did have some cracks that, I, so I got to go up to Millis and look at the cracks. But it wasn't, in my opinion it wasn't a big deal. All the physicists were worried because they saw a crack, it's a big deal. We have cracks in everything, but they didn't understand. That just like the Air Force general I told you about.

In any case, in aluminum you like to have lots of fillet welds because you can find welder, oh there's the reason I got on that story. No, they couldn't find enough qualified aluminum welders in all of New England to build this structure the time frame they wanted. So they had to train some new ones or they had to import them, okay. When you're only making 45 million tons a year as opposed to one and a half billion tons a year, there's not as many people who can weld aluminum. And that's what you would mention, and sometimes you can't even find them in that region, okay.

That's also true in some types of welding of steel for example, but it's more political in that case. All the pipeline welding in the world is done by a union out of Tulsa, Oklahoma, okay. And we still manually weld pipelines, you know, gas pipelines in the field, because if you try to weld them automated you will never build that pipeline. According to the union. Doesn't go in any written contract. It goes sort of like, it's sort of like a deal, you know, you watch The Godfather, and they make a deal they can't refuse. So the union in Tulsa will make sure everybody knows. They had the technology to do automated welding in 1976 on the Alaskan pipeline. Probably could have come up with better quality than manual welders. Built it manually, and they still do, forty years later, because the Tulsa union is a very powerful union. You will not build a pipeline anywhere in the world, unless you have to be the former Soviet Union where that union doesn't have so much power, okay, or China or something. But in general you go to a Iraq or somewhere you want to build a pipeline, the Tulsa union's got the job, okay. Just so you know there's a little corruption in this country too.

So anyway, they have different designs. This is actually sort of a lousy design, to put intermittent welds in this double lap design, rather than a straight butt weld. You know, you'd like to have nice clean straight butt welds than you do in steel. But in aluminum a lot of times you can do a straight butt weld in aluminum, but a lot of times we do other things.

Here are some designs out of an aluminum design manual. One of them is, you're going to make a U-shaped, um, uh, joint. And you could do two fillet welds on the outside, or you could do four fillet welds, or you could actually, since aluminum is relatively easily formed at low temperatures, you can basically just get a simple lap joint and you don't put anything at the corners. We really like to avoid welds at the corners in aluminum. Steel has lots of toughness and so we don't mind corners in steel. We put the welds in the corners and usually do pretty well. But aluminum, you don't like to put welds at corners. They will tend to crack, either crack or fatigue.

Here's a little lap joint where they actually machine the edge of the aluminum. Aluminum is easy to machine, relatively easy to machine compared to steel. And you actually put two partial penetration welds in to make a lap joint. You can do this if it's not a fatigue-loaded situation. So it depends on the stress in your application, depends on what room you have available. Uh, here's a design down here where they're making a T-joint, they actually use an extrusion, and then they, and to a plate, and that, you put a fillet weld here and groove weld here to try to get rid of some of the corner welds.

Gets to be pretty extreme. You're going to say well, I've seen lots of aluminum structures that are welded just like steel structures. Yes, but I took about a two-thirds hit in my safety factor or my allowable stress in order to build it that way. If you really want to make aluminum and get the same type of stress level, percentage of yield stress that you get in steel, you've got to start worrying a lot about your design of your joints. This one's probably not that useful.

Here's one that, sort of, a little bit shocking. Um, ordinarily you take a butt joint and then steel you just make a pipe weld. In aluminum you might put a sleeve over it, and you might even put a weld in here, but you don't trust that weld particularly if it's heat treatable alloy and you can't get full joint efficiency. You put another sleeve around, make a bunch of fillet welds. It doesn't take a lot of high qualification for a welder to be able to make that joint.

Other types of improvements in aluminum joints that we don't usually worry about in steel so much: in steel you might make a joint like this, or you might make a full weld all the way around. And aluminum you'll start to taper the edges. This structure that, oh actually the other thing they do, and they used a lot on this thing at Millstone for Lincoln Lab, a lot of gussets. So in steel you'd bring a pipe into the side of a web of a steel flange, and you just bevel the pipe and weld a circle around it, right. Not in aluminum, you weld on a gusset, and then you'll put a little slit, and you'll slip that over and you'll do a bunch of fillet welds. So now you have lots of weld area for the gusset up against the web. You also have lots of fillet weld area. Again, a fillet weld very easy to weld.

And needle in aluminum where you get, you need the extra strength of lots of weld metal, you'll taper down to get more area. And you don't want to have the stress concentrations that you have from abrupt right angles, that you can tolerate in steel. Let's not say you can't tolerate in aluminum, but you're going to have to take a hit on your safety factor or your allowable stress in order to do so. Any questions on that? Okay.

So there are lots of design considerations, most of which, if you think of a Navy ship made out of aluminum, they don't do right. So, and now you wonder why you got cracking. So they take a chance.

I put, I've given you this slide before about different materials. I think I gave you this one, I think I handed it out to you even. Different materials, steels, aluminum, and different gases in welding. Aluminum does form porosity. It's not like hydrogen cracking in steels and it's not delayed cracking in aluminum. You have a problem with both oxide films with oxygen, or inclusions, but with hydrogen you end up with gas porosity. And it looks like it's the same physical principle in terms of solubility of the hydrogen in the metal, but it looks like lots of porosity.

This is, I think this one may have even told you how much hydrogen was around. The last one, the bottom one, is one percent hydrogen in the shielding gas. This is a quarter percent hydrogen in the shielding gas. And here's argon gas with no hydrogen, in theory. There's always a little moisture around unless you take special precautions. But the problem is you have about a fifty...