Aluminium plate sheet orientation question

Ad Hoc · Jun 18, 2024

jehardiman said: ↑

.... As far as heat treating after fabrication, it is common in certain deep submergence PV applications. ...
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I only deal with surface vessels,....all these use 5000 and 6000 series alloys.
One never uses heat or heat treats post fabrication.

Thus I cannot comment on what occurs below surface applications...as I am unaware of which alloys and tempers may be selected when using aluminium in this application.

RSD · Jun 18, 2024

Barry said: ↑

I suspect that Tansl is referring to steel wrt to a blasting machine. (I have never ran across a "blasting machine for aluminum)
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Ah OK - that explains it!

The large aluminum distributors will received the aluminum (plate) up to at least 3/16 in coils. The coil is unwound and ran through several sets of rolls to straighten the plate.
This permits a client to order long sheets as long as can be transported to the build site.
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OK that fits with what I have read that 3/16's is fairly easy to end whereas 1/4 inch is not.

Certainly, smaller aluminum distributors carry the standard sizes: 4x8 or 10 or 12, 5 x 8 or 10 or 12, etc For out 21 foot boats, we would order 22 foot sheets, 23 foot 24 etc.
The issue though can be freight as putting a 24 foot sheet on a 44 foot high boy, uses up quite a bit of trailer deck space. Normally, a manufacturer will provide quite expensive
crating to ensure that the sheets get to where they are going without damage.
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I'm very fortunate that a distributor here does every thickness up to 1/2 inch in sheets up to 27 x 6'4" - they carry a wide variety of sizes.

For a nominal amount, and if you are not going to paint the hull, you can order sheets with plastic on one side or the other to reduce surface scratches, to a point.
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To be honest I'm not that worried about surface scratches as its a dive boat - they get banged around alot.

In order to reduce distortion, as other have said but it extremely important especially with thinner sheets, keep the sheets as long as possible with as few butt welds
as you can design to. Heat distortion can be significant. Usually, but not always using maximum length sheets, the joint between sheet may occur on an
inflection interface, ie change of direction at the weld joint. This "kink" (discontinuity) will provide a higher resistance to distortion and "follow" the lines of the boat.
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I'm going to be using the new handheld laser welding to do the welding, from everything that I have read and seen that massively reduces the heat that is put in when welding and so there is much less distortion.

RSD · Jun 18, 2024

jehardiman said: ↑

As an aside, these two comments bring up two seemingly trivial things about thin aluminum plate...until they unexpectedly bite you.

In manufacture, aluminum billets are hot formed by continuous casting. To get to a specific thickness, the billets are then rolled (either hot or cold) and below a certain thickness, coiled. This does two things, primarily it elongates the grain in the rolled direction and secondly it stresses the grain structure. These changes in the metal grain structure have two effects...it changes the material properties of the alloy in both the rolled and cross rolled directions, and it changes the weldability of the base alloy. That said, these changes can be mitigated by post forming heat treatment, but you had better know what you are ordering because these post forming treatments add to the cost of the plate...sometimes significantly. In the naval yards we did our own receipt inspection for every lot and also sent a sample to the weld shop for process testing (i.e. to verify final properties after welding). I think a lot of the issues small fabricators sometimes have is the lack of deep pockets to ensure 1) they got what they needed, and 2) they used the right process for the material they have.

Temper Designations for Aluminum | Metal Supermarkets https://www.metalsupermarkets.com/temper-designations-for-aluminum/

Edit to add: I forgot to add that the above comments about changes to material and welding also apply to forming after the plate is in the yard. A lot of either hot or cold forming to get it on the hull can significantly change the final post welded strength of the heat affected zone.
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More good information for me to work through - thanks!

RSD · Jun 18, 2024

Ad Hoc said: ↑

The hot rolling or cold rolling depends upon the alloy and temper being obtained....
The grain direction, on a sheet of plate, can be identified by an experienced plater. They can "see" the rolling direction on the plate and will ensure the bending is done with the rolling direction, not against it.
The coil is not stressed after being correctly rolled and the correct temper is applied. The last 'minor' rolling process will be used as a final dimensional thickness tolerance check.

That's not strictly correct and is misleading..
The "change" in alloy structure is the process of tempering during the production of the alloy and is the reason for whether the temper and the grade of ally is hot rolled or cold rolled.
But the final result, is stable and is exactly as ordered.

One never heat-treats ally once it is finished fabrication...and if one is having to apply excessive work to the plate to "fit-it-in" then it is poor fabrication and poor QA procedures.
The ally plate must always be offered up stress-free...and never apply force or heat.
To do so, is poor steel work methodology being applied to aluminium fabrication.

Exactly.
One always uses the as-welded properties of the alloy.
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I'm learning heaps from you guys - thanks!

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