welded and unwelded strength of Aluminum?

what are the welded and unwelded characteristics of aluminum as defined in ABS rule? How do I identify welded and unwelded strength of the aluminum that I'm going to use? It's aluminum 5083 H111.
Thanks,

 

The strength is dependent upon both the material composition (5083) and the heat treatment (H111).

Welded joints loose the benefit of the known heat treatment process, so the weld joint material has to be considered un-heatreaded or 0000 callout.
Just look up the strength for that heat treat.

Its a lot lower, which is the problem with welding aluminum.

 

Min Ultimate strength of 5083-O = 270 Mpa
Min Ultimate strength of 5083-H116 = 300 Mpa
Min Yield strength of 5083-O = 115 Mpa
Min Yield strength of 5083-H116 = 215 Mpa

So, I take minimum yield strength of unwelded aluminum=215 Mpa and minimum ultimate strength of welded aluminum= 270 Mpa. Am I right?

One question more, please. If welding reduces the strength of aluminum, what is the point of using Heat-treated aluminum alloys (for eg-H111), in shipbuilding, rather than un-heat treated -O alloys?

 

{One question more, please. If welding reduces the strength of aluminum, what is the point of using Heat-treated aluminum alloys (for eg-H111), in shipbuilding, rather than un-heat treated -O alloys?[/QUOTE]}

The strength of the aluminum goes to untreated alloy levels only in the HAZ, Heat Affected Zone

So you still get benefit of the additional strength in areas outside of HAZ

Ad Hoc will probably add input here as a couple of years ago there was a thread and I believe that he mentioned that he
always/sometimes specs non heat treated and non hardened alloys

 

5xxx series aluminum are strengthened by strain hardening not heat treatment

So H111 is strain hardened while say 6xxx series are heat treatable T-4 T-xxx etc

But both strength treatments are impacted by welding

 

http://www.aluminiumindustry.org/en/aluminum-strengthening-mechanisms.html

Here is a quick over view of strengthening methods for aluminum

 

Nope.

the UTS is very very different from yield and very different from as-welded strength. One never ever designs to UTS always to yield. And when designing welded joints, one must always use the as-welded strength , such as below:



As for why use any other temper...easy. The joint is at the weld. But mid-panel, no welding. Thus if the panel is subjected to high loads and the designer does not wish to increase the thickness to prevent buckling, for example, the simple solution is the increase the temper. Thus one must be selective and also understand what grades what temper and why.

 

Ditto what Barry said re: strain hardening v heat treatment.

 

Thank you, I can now clearly see that I should consider carefully about these two characteristics, UTS and yield. However, I'm about to calculate an equation in the ABS rule, and one factor it's asking for is minimum yield strength of unwelded aluminum and another factor is minimum ultimate strength of welded aluminum , so , according to your table, minimum ultimate strength of welded aluminum is 270 MPa, Ok, and for minimum yield strength of unwelded aluminum, should I take, 150 MPa (as said in the attached photo for 5083 H111) .

 

Thank you all, but ,I'm a little confused about their behaviors. I know they both have different mechanical properties in the unwelded condition. (tempered grades are higher in UTS and yield strength relative to -O(annealed grade) ) But, I have somewhat heard that, after welding has been processed on tempered grades, their mechanical properties fall back to annealed grade. Is that knowledge correct? Or, their mechanical properties for welded and unwelded states are individually stated in manufacturers' booklets?

 

No incorrect.

You need to understand the difference between yeild(proof) stress and Ultimate Tensile stress. And then what these means in the welded condition too. and how it relates to tempers.

No, not necessarily.
Look at O-temper..its UTS ranges from 275-350MPa.
Whereas highly strain hardened H321 from 305-385MPa.

Thus there is a significant overlap in the 305-350MPa range. depending upon the mills quality control etc.

Correct. Look at the as-weld yield strength of O and H321 temper, it is the same. Heat anneals the strain hardening process. In simple language the locked in dislocations that are caused by strain hardening become loosened by the heat and go back to its original condition, that of O-temper. There is a good article about all this in professional boat builder magazine Feb-March 2014 called Altered Properties.

 

Thanks Ad-Hoc. I can now quite imagine how these aluminum grades are different. Thanks.

 

It is also possible to weld material in one condition (in this case a 6X alloy) say T4 temper and then re heat treat the entire part back to T6. On smallish parts which would include masts, this is done. Obviously you need the oven to do this....

 

Solution treating is typically performed in the 450 to 575°C (842 to 1067°F) range in air, followed by rapid quenching into cold water, hot water, boiling water (-T61 temper), water-polymer (glycol) solution, water spray or forced air. Natural ageing to the T4 temper will occur at ambient temperature for 2XXX, 6XXX, 2XX and 3XX alloys, with most reaching a stable temper after 96 hours. Artificial ageing in the 93 to 245°C (199 to 473°F) range is utilised to meet the T6 and T7X tempers.

Immediately after quenching from solution treating, all alloys are relatively soft and can be moderately formed or straightened if performed within a couple of hours. These alloys will naturally age harden at ambient temperature, with their hardness gradually increasing with time following quenching. This can be suppressed by refrigeration below about 0°C (32°F) if it is desired to form or straighten the material more than a couple of hours after quench. Cooling to below about minus 23°C (minus 10°F) or colder is required to retain the As-Quenched (AQ) temper for prolonged storage times beyond a few days.


The above taken from another site

The problem is also one of distortion. With different thickness of some items, when heated and quenched the cooling rate of various thickness is difficult to control and you might need to re-straighten the items. Perhaps on other items the distortion is within design limits.

 

Thanks Barry and SukiSolo. I'm doing a final year project at my university and, my country is very under-developed, and, aluminum material is still of quite uncommon usage in shipbuilding industry. So, I don't think we can perform any retreatment processes here. But, thanks for your information and your attention.
However, I have a question, if you don't mind. I don't know if this is too basic question. Can aluminum sections be formed by welding plates, as they are done with steel sections? I have known that factory-manufactured extruded sections are available with the least defects, but, as far as I have found, these sections are made of tempered materials, like T6, and I assume they would be quite expensive. I want to design an aluminum craft for use in my country, thus, procurement for raw material should not be difficult and I think on using 5083-H111 plates for shell plating. So, I want to know if I could find extruded profiles of 5083-H111 material or, if I could consider these sections can be formed by welding plates (for example- two plates welded to form T-section).