5052 H32...Yay or Nay.

I'm considering building a 18ft mod V boat. Roughly 7 ft chine to chine, 5052 H32 bottom plates (3/16) and 1/8 sides. I know a good number of manufacturers use 5052, but it seems they mostly use H34, H36, variants of 5052. I understand they are somewhat stiffer, but also not as readily available, and for the thickness im considering, im wondering if they are even necessary? Most of my fishing/boating will be inland lakes, Detroit River for spring walleye, and maybe Fairweather days on the Great lakes bays. No saltwater. I'd love to use some of the more exotic alloys (5083, 5086, etc) but they are sell your soul expensive, and very hard to source. My question then becomes, is the common H32 hardness of 5052 an acceptable, and reputable choice for hull bottoms?

 

""5052
All 5000 alloys use magnesium as the principal alloying element. This makes the aluminum easier to weld, which is important for construction. It’s generally the “softest” of the four, and because of this it’s also considered the most workable. This aluminum alloy is not as susceptible to cracking during the forming process and is also the least expensive of the common marine alloys. 5052 is generally used for interior parts of the boat such as cabins, decks, and gunwales.

5083
Aluminum alloy 5083 is commonly used by the US Navy. It’s stronger than 5052, yet it’s still formable and easily welded. This aluminum alloy is widely used in chemical and marine environments where corrosion resistance is crucial and can also withstand extremely cold temperatures without becoming brittle. But, all these great properties come at a higher cost than 5052, and although 5083 is stiffer than 5052, it’s also more prone to cracking. 5083’s corrosion resistance and toughness make it a great choice for hull bottoms and side sheets.

5086
Considered the superior alloy for marine environments, 5086 has similar characteristics of 5083, but with added strength. This alloy is so close to its 5083 brother that the two are arguably interchangeable. In fact, 5086’s strength increases when it is cold worked. The main benefit of this aluminum alloy is its increased corrosion resistance properties, especially in salt water. It is the most popular choice for hull bottoms and side sheets. ""
The above pirated from the internet

Our alloys of choice, and most of the boat builders in the northwest, is 5086H112 for the hull and 5052 H32 for the deck, cabin etc as 5052 is more formable.
As our boats were meant for running rivers and expecting confrontations with the odd rock at 30mph, we used 1/4 inch bottoms with 1/8inch sides.

Extrusions for stringers etc. As we had a brake and a shear. we formed these but you may have to use 60 series extrusions.

Link to Metalboat kits, re alloys. A Guide to Marine Grade Aluminum - MetalBoatKits https://metalboatkits.com/a-guide-to-marine-grade-aluminum/ For some reason they do not list the H112 treatment but only the H32.

If 5086 is "sell your soul expensive" you may be looking to the wrong supplier. There seems to many companies who sell aluminum in small amounts to retail and price their products
accordingly. It is unlikely for you to be able to purchase from a manufacturer ( make it a few manufacturer's and distributors) but a quick call to the sales staff to find
1) out who their distributor is in your area would be worth the effort.
2) what treatment that they sell most to for the boat industry, ie H32 or H112


If you can determine exactly what your needs are, a larger purchase, ie for the whole boat may attract a lower price.

We found that the 5086 might be a buck a pound more. I am trying to remember what our 18 foot boats weighed but I believe that they were around a 1000 pounds
Of course if you are installing an aluminum deck with storage compartments you will add more weight. BUT 5052H32 is acceptable. Just not my choice.

For the amount of labor and other costs to build the boat I would go with the higher priced alloy. This is not a place to try to save a thousand bucks.

If you have not built one before, I would recommend purchasing
1) a complete kit including aluminum (which might be cheaper than trying to build everything yourself as these type of companies purchase tons of aluminum at
high discounted costs) OR
2) a set of cut files, and have someone precut the main hull pieces.

On 1) above, you may find that purchasing a complete kit may not be far apart from the cost of building your own jig, (with limited experience), paying a much higher price for the aluminum,
obtaining a proven design, (a shape that has developable surfaces) and I believe that you will obtain a HIN.

One advantage of either of the above is that you do not have to build an elaborate male jig to build the hull. Ie the, jig if you have the precut parts, the build proces will be much less labor intensive and save money on the jig.

Who is doing the welding?
Depending on what alloy you use, ensure that you use the correct welding wire
Are you using Tig or Mig?


Another option, and one that I pursued recently, was to buy a boat hull and finished it to my liking. There may be a boat manufacturer in your area that would sell you a completed bottom and sides and internal stiffners and you can finish the rest. This might get you a HIN, Hull Identification Number, which will help you get insurance without a costly survey.

As we had a jig for an 18 foot hull and patterns to cut the hull pieces, it would take about 60 ish manhours to build the side, bottom and internal stringers, and strakes. (the deck etc would be extra)

 

Thank you for that well thought out response and advice. This would be my first boat build, and I'd be doing the welding (pulsed mig). I'm a certified welder for all metals, a Journeyman in machine building/repair, and 20+ years of experience in fabrication. So I've welded a ton of aluminum, both structural and sheet metal....That said, I'm approaching this build with much studying, and caution...I'm from the West Michigan area, so leads on potential suppliers or ways to find connections are going to be valuable. The big name metal suppliers largely want to only deal with corporations, and understandably so. Just sucks to be a hobbyist in a corporate world.

 

Simple answer is that 5052 has less strength - when welded - than 5083, which is the go-to alloy.

If you wish to form or bend the ally, then using a highly strain hardened temper, such as H32, will make it more difficult for you. You also have the issue of most likely over straining the alloy when forming and therefore reducing its capacity for additional deformation prior to failure/cracking.

 

Can't add any to what Barry said, it's a very good summation of the prevailing though of the west coast builders I'm familiar with.

A few asides on price.

I've done a couple of small projects and recently bought a couple hundred pounds of plate both 5086 h112 a sheet or two of 5052 price differences were a bit over a dollar a pound. Granted we've had a commercial account with them for decades and done some big orders over the years so it may or may not be prices to take to the bank.

It really pays to shop around, between covid disruption, rolling lock downs, supply chain interruptions, sanctions on heavy source mineral countries, heavy variation in dod consumption... markets been all over. Seems to be leveling off a bit but it made for some sporadic pricing. We did a big railing project before Christmas and the variation in 6061 pipe from two outfits was greater than 30%. In bygone days it was so close in price it depended on who was closer to the job.

My second advice is, if you have an established design usually they have a materials list. If not it's worth getting a solid materials list and add on your wastage for nesting and cutting. Then shop that number of pounds of aluminum, volume does make a difference. My price per pound for 500 pounds was more than 2500.

Seems like there should be some decent outfits up there, but it wouldn't shock me that their is heavy regional availability.

 

Great Link. Thanks. I've added it to my links page.

 

5052 H32 (S basis MIL-HDBK-5, now MMPDS) has a yield strength of 23 ksi (131MPa), elongation of 7% and bend radius for H32, [mm,t] .8mm, 0t; 1.6mm, 1t; 3.2mm, 1.5t; 4.8mm, 1.5t; 6.35mm, 1.5t; 9.5mm, 1.5t. ASM Handbook Vol 2. ("13mm, 2t" 2t means that the minimum bend radius without cracking for a 13mm thick plate is twice the thickness, or 26mm.) H34 will give you 26,000 psi yield strength, 6% elongation and the same bend radii. As welded strength, can't find it, but it should be lower than the base metal by a similar amount as 5083, probably around 17 ksi. It is always safe to assume a weld is dead soft (O-temper is 9.5 ksi yield) but not quite accurate as it is affected by the weld filler chemistry.

5083 is stronger. H321 ys 31, 12% elongation. H131 37 ys, 8% elongation. As welded strength is 23 ksi ys with 11% elongation. The minimum bend radii are slightly larger for 5083, so it does not bend as well as 5052. Be careful to get only marine grade per ASTM B 928. https://www.boatdesign.net/attachments/5083-alloy-pdf.7541/ I think that the reason H112 was not listed in Barry's link is that that temper is susceptible to intergranular corrosion and not suitable for marine use, see the ASTM B 928 link. The problem is with the higher magnesium content which can cause corrosion problems if the heat treatment isn't just right. The marine grade has a corrosion test requirement in the spec to avoid the problem.The problems were with heat (~150F? in the sun) and stress around welds, as I recall. So H112 might work in AK, but not AL. I read the article in the link 20 years ago, and the link is here, so it is not hard to check.

Stiffness is not affected by hardness, but is to some extent by alloying elements. For all aluminum alloys the tensile modulus is about 10,000,000 psi. The difference between 5052 at 10,100,000 psi and 5083 at 10,200,000 psi is pretty insignificant.

Overall, I would say that where a design is stiffness driven, any of these alloys is OK, but if it is strength driven, then the 5052 needs to be a little thicker, which will make it a lot stiffer.

 

Why would you assume that?

Any alloy is susceptible.
But it depends upon how the strain hardening was conducted (non heat-treatable), in terms of hot or cold rolled and for how long, as well as if the Si/Mg ratio is exceeded for the Mg2Si compound (heat treatable).

Intergranular corrosion requires 3 conditions to exist simultaneously:
1. Presence of a corrosive aqueous solution
2. Difference in an electrical potential of at least 100mV (between the intermetallics and solid solution)
3. Continuous precipitation of intermetallics at the grain boundaries.

There is a significant difference in the as-welded strength.

 

It is safe to assume that the material was overheated during welding to the extent that the heat affected zone was fully annealed. Safe meaning the worst case scenario where you take the dead soft temper, which is what O temper means, as the condition of the HAZ. Designing around the minimum possible strength condition in that area is safe, if inefficient. It is better to have the welding done by certified welders using a protocol that has been established to produce welds of a known strength. The as welded strength for 5083 that I gave was fairly typical of the results of good welding practices around 2000. Without going back and reviewing records that are no longer available to me, I can't say exactly what filler metal, plate thickness, process, etc were used, other than to say that there was nothing unusual about them. This is a forum, you should not trust any information given freely to strangers by strangers. I am confident that you could confirm the numbers that I gave, but no one in his right mind should use them without independently confirming them. All that I am saying is that you can take the numbers as a decent indication that the material is worthy of consideration if the numbers meet your needs.

Yes, the 5000 series are all strain hardened, not precipitation heat treated, but there is some heat treating involved at times during the process. In the link to the write up about ASTM B928, on page 7 there was some diccussion of grain boundary precipitates and thermal processing to alter them. The thermomechanical processing has to be carefully controlled in the high Mg members of the 5000 series. Page 8 from the link to the ASTM story:

The heat treatment is not considered as part of the strengthening process. At least not to the casual observer. The information is largely proprietary as to the times and temperatures in some alloys, and if a rolling mill hasn't worked it out for for themselves, they can't meet the specification. When the guys who can make your orphan alloy won't talk less than a million pounds per year, you have a problem.

1. {EDIT--oops -- Incorrect, it can be non-aqueous, such as anhydrous methanol causing cracking of titanium.} ( delete this: Correct, although it can be mostly non-aqueous, such as a trace of moisture in methanol causing cracking in titanium.)
2. Intemetallics are not necessary. SCC is common enough in precipitation hardened stainless steels at the highest strength tempers.
3. Grain boundary precipitates are not necessary for SCC. There is both TGSCC and IGSCC.

I was talking about the modulus of elasticity, not weld strength there. I did say "5083 is stronger. H321 ys 31, 12% elongation. H131 37 ys, 8% elongation. As welded strength is 23 ksi ys with 11% elongation." Sounds significant to me. I did not give separate weld strengths for the two tempers because the difference, if any wasn't significant.

 

Then all you are stating that what is an inexperienced person what would say. Since one ALWAYS designs to the minimum possible value.
It is called fit-for-purpose.

Coded welder cannot change the physical and material properties of an alloy. Thus unsure what you're attempting to say here.
They may produce rubbish welds, but good quality coded welders cannot make the materials any stronger than it already is, once welded.

Indeed.
Once assumes all that you also are part of that…

This is a very well document story, often with misinformation.
One needs to understand what is actually going on in this process, that caused these issues.
There is a classical dividing line (temperature) between “hot work” and “cold work”, and is said to be about one half the melting point of the metal in °Kelvin.
So, the typical operating temperatures for the hot and cold mills are:
– Hot mills: 250°C - 550°C range
– Cold mills: 25°C - 200°C range

In hot rolled marine grade alloy, the magnesium is distributed evenly throughout the metal in very small quantities. The magnesium reacts with the salt water oxidizing and forming a white hazy coating, which acts to protect the aluminium plate. A cold rolled process adopted by some mills, prevents this process from occurring, this is what occurred in those plates noted in that paper. A simple process error that caused major problems.

I'm unsure what does that mean??

Then you do not understand the difference between class approved 3.1 and 3.2 certified alloys.

That is incorrect.
An aqueous solution means – with water forming part of the electrolyte

It is 100% necessary.
Without the intermetallics, there is no intermetallic corrosion.

SCC is attributed to an appearance of atomic hydrogen as a result of chemical reaction between Al and water, or of cathodic charging, followed by hydrogen diffusion into the crack tip.
Hydrogen present in the lattice is known to cause failure by decohesion of the lattice, decrease of flow stress in near - boundary area or by formation of brittle unstable hydrides.
Thus unsure what you’re attempting to say here…

There is a significant difference between the two as-welded strengths:
5052 when welded has only 45% the strength compared to 5083....I call that significant.
Once ALWAYS designs to the weld strength, as THAT is the weakest link.

 

OK, fine, don't ask a NA for advice on metallurgy, and don't ask a M&P guy about hydrodynamics.

You took a portion of a sentence out of context. I clearly stated that I was describing different tempers of the same alloy.

Perhaps the professor will allow me to rephrase the statement:
According to MIL-HDBK-5, Alloy 5083 H321 has an S basis yield strength of 31 ksi and 12% elongation, and 5083 H131 has a yield strength of 37 ksi with 8% elongation. The measured values of as welded 5083 plate where I worked was 23 ksi ys with 11% elongation. The as welded strength is that of the heat affected zone, which will be almost the same for any of the work hardened tempers.

Yes, that is what I said. I also said that the weld strength is variable and depends on the skill of the welder and the protocol followed.

I thought that it was necessary to speak to the less experienced among us who need to be reminded of these things, not you.

That is why there has to be a specific procedure followed. The welder can not improve the properties, but he can screw them up. And as I indicated before, the actual yield strength, as welded and tested by several major corporations and places like TWI. The yield strength will vary with the process and is normally higher than the O-temper for both precipitation hardened and strain hardened alloys.

If you are qualified to critique the paper perhaps you should elaborate on the errors with respect to metallurgy. Have you ever been through a rolling mill? Do you think that a continuous cast 50-60 cm thick ingot lacks any segregation? Do you know what homogenization heat treatment is? Do you know why they have to anneal the plate after several passes through the rolls? The final pass is cold. I don't remember off hand what thermal processing was involved to break up, avoid or spheroidize the intermetallic grain boundary precipitates, but the simple process error was some combination of time temperature and reduction. The corrosion resistant patina is not a white hazy non-adherent material. Unless you can show me high-resolution X-ray photoelectron spectroscopy (XPS) spectra of passive films formed in seawater, I will contend that the MgO is largely dissolved away leaving mostly Al2O3 and that the Mg addition degrades the corrosion resistance slightly. I don't see a lot of Mg in the surface film on 5083 (b) here, but they were formed in a citric acid solution:

Figure 5. XPS depth profile for passive films on 1060 (a), 2024 (b) and 5083 (c) Al alloys after 60 min of potentiostatic polarization.


Ad Hoc again: "An aqueous solution means – with water forming part of the electrolyte"
Water as in immersion? What about the water present in the corrosive films covering every surface in humid air. I was wrong about the water in the methanol above. The trace of water prevented SCC in Ti when it was exposed to anhydrous MeOH. So that was non-aqueous, and I did make a mistake there. I was going to ask when a few ppm of water made it an aqueous solution, but that is what prevented SCC. It was late and I was sloppy, and still haven't found my copy of Vol 13 of the ASM handbook to check the facts. That is where I read how much water in the methanol will prevent SCC.

 

Hmmmm....

What you should be saying is that no matter what the level of strain hardening the alloy receives, with it associated “H” temper designation, the HAZ – i.e. its as-welded strength, remains the same.

Well, what you said was this:

It is not the case of “better” to have coded welders – one always uses coded welders, for that very reason.
The way you have written it suggests that coded welders can change the proprieties of the as-welded strength, simply because they follow a procedure.
Coded welders are coded because they have been through a process to ensure their welds are consistent and always produce the same level/quality of weld, which have been independently verified by testing and witnessed/approved by Class.

Again, this is where either you have misunderstood, or just worded it incorrectly.
The as-welded yields strength is not higher with a different temper alloy, only the filler wire can influence this value.

To what errors are you referring to?

Water is water, no matter its source – thus unsure what you’re alluding to here?